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Metalloporphyrin catalyzed oxidation of chlorophenols Sveinson, Kelly P. 1992

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METALLOPORPHYRIN CATALYZED OXIDATION OF CHLOROPHENOLSbyKELLY P. SVEINSONB.Sc., University of Waterloo, 1989A Thesis Submitted in Partial Fulfilment ofthe Requirements for the Degree ofMaster of ScienceinThe Faculty of Graduate StudiesDepartment of ChemistryWe Accept This Thesis As Conformingto the Required StandardTHE UNIVERSITY OF BRITISH COLUMBIAMarch 1992© Kelly Paul Sveinson, 1992In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature) Department of C.AMAAA (---)(ThrThe University of British ColumbiaVancouver, CanadaDate ^DE-6 (2/88)ABSTRACTThe use of water soluble, non-aggregating metalloporphyrins (meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrin (TDCSPP) and meso-tetra(2,6-dichloro-3-sulfonatopheny1)-0-octachloroporphyrin (TDCS-(3-C1 8P) coordinated with iron or manganese) as catalysts for theperoxide oxidation of chlorophenols were investigated. The relative rates of chlorophenoloxidation with respect to several variables (catalyst, pH, oxidant, and chlorophenol structure)were determined. The rate was found to be pseudo-first order in the catalyst. The oxidationwas most efficient using the iron porphyrins, at pH < 4. The oxidation rate was dependenton the oxidant. In order of decreasing rate, meta-chloroperoxybenzoic acid > potassiummonoperoxysulfate > hydrogen peroxide > t-butylhydroperoxide. The oxidation rate wasstrongly dependent on both the number and the position of chlorine substitution on thephenol. In order of decreasing rate, 2,4-dichlorophenol > 2,4,5-trichlorophenol > 2-chlorophenol 4-chlorophenol > 3,4-dichlorophenol 2,4,6-trichlorophenol > 2,3,4,6-tetrachlorophenol^2,3,5,6-tetrachlorophenol > 3-chlorophenol > 3,5-dichlorophenol2,3,4,5-tetrachlorophenol. The structures of some of the catalyzed reactions were elucidated.Products of phenoxy radical coupling, and quinones are typical. The results are discussed inthe context of the possible use of these metalloporphyrins for pollution remediation.iiTABLE OF CONTENTSAbstract^ iiTable of Contents^ iiiList of Tables, Figures and Schemes^ viList of Abbreviations^ viiiAcknowledgements x1 Introduction^ 11.1 General Introduction^ 11.2 Chlorophenols^ 31.2.1 Sources and Scope of Environmental Contamination^31.2.2 Toxicity 51.2.3 Remediation of Chlorophenol Pollution^ Microbial Techniques^ Enzymatic Techniques Chemical and Physical Techniques^131.3 Chemistry of Phenol Oxidation^ 151.4 Porphyrins^ 181.4.1 Structural Considerations^ 18iii1.4.2 Catalytic Mechanisms^ 241.4.3 Reactions of Chlorinated Metalloporphyrins^262 Results^ 292.1 Analysis of Products from Chlorophenol Oxidation^292.1.1 Products from Monochlorophenol Oxidation 292.1.2 Products from 2,4-Dichlorophenol Oxidation^302.1.3 Products from 2,4,6-Trichlorophenol Oxidation 342.1.4 Products from 2,4,5-Trichlorophenol Oxidation^372.1.5 Products from Tetrachlorophenol Oxidation 382.1.6 Products from Pentachlorophenol Oxidation^382.2 Kinetic Studies^ 422.2.1 Effect of the Catalyst^ 422.2.2 Relative Chlorophenol Oxidation Rates^ 472.2.3 Effect of the Type of Oxidant 532.2.4 Effect of Catalyst Type^ 532.2.5 Effect of pH^ 572.2.6 Effect of Generating a Quinone 572.3 Effect of Catalyst on Product Distribution^ 622.4 Experimental^ 642.4.1 Chemicals and Instrumentation^ 642.4.2 Oxidation of Monochlorophenols 662.4.3 Oxidation of 2,4-Dichlorophenol 682.4.4 Oxidation of 2,4,5-Trichlorophenol^ 752.4.5 Oxidation of 2,4,6-Trichlorophenol 79iv2.4.6 Oxidation of 2,3,5,6-Tetrachlorophenol^ 823 Discussion^ 863.1 Discussion of Results of Oxidation Product Analysis^863.2 Discussion of Kinetic Results^ 883.2.1 Effect of pH 883.2.2 Effect of the Coordinated Metal^ 893.2.3 Effect of the Oxidant Type 903.2.4 Effect of Chlorophenol Structure 913.3 Conclusions and Suggestions for Further Studies^ 93References^ 95vLIST OF FIGURES, TABLES AND SCHEMESFigure 1.1Figure 1.2Figure 1.3Figure 1.4Figure 1.5Figure 1.6Figure 2.1Figure 2.2Figure 2.3Figure 2.4Figure 2.5Figure 2.6Figure 2.7Figure 2.8Figure 2.9Figure 2.10Figure 2.11Figure 2.12Figure 2.13Figure 2.14Figure 2.15Figure 2.16Figure 2.17Resonance Forms of the Phenoxy RadicalProducts of Phenol DimerizationStructure of PorphineStructure of Iron Protoporphyrin IXStructure of Meso-tetraphenylporphyrinStructure of Chlorinated Water Soluble MetalloporphyrinsMass Spectrum of 2-Chlorophenol Oxidation ProductTwo Possible Products of 2-Chlorophenol OxidationProducts of Oxidation of 2,4-DichlorophenolProducts of 2,4,5- and 2 ,4,6-Trichlorophenol OxidationProducts of 2 ,3,5 ,6-Tetrachlorophenol OxidationHPLC Traces Taken During Reaction of Pentachlorophenol.Relationship of HPLC Integrator Response (at 270 nm) and2-Chlorophenol Concentration.Effect of Catalyst Concentration on Oxidation of 4-ChlorophenolRelationship Between Initial 4-Chlorophenol Oxidation Rate andCatalyst Concentration.Kinetics of Oxidation of MonochlorophenolsKinetics of Oxidation of DichlorophenolsKinetics of Oxidation of TrichlorophenolsKinetics of Oxidation of TetrachlorophenolsComparison of Oxidation Rates of Several ChlorophenolsChange in UV Spectrum During Oxidation of 2,4,6-Trichlorophenol to2,6-DichlorobenzoquinoneOxidation of 2,4,6-Trichlorophenol to Quinane with Different OxidantsEffect of Catalyst Type on Oxidation of 2-ChlorophenolviFigure 2.18Figure 2.19Figure 2.20Figure 2.21Figure 2.22Figure 2.23Figure 2.24Figure 2.25Figure 2.26Effect of pH on the Oxidation of 2-ChlorophenolEffect of pH on the Oxidation of 2-ChlorophenolEffect of pH on Oxidation of 2,4 ,6-TrichlorophenolEffect of Added Quinone on Oxidation of 2,4 ,6-TrichlorophenolHPLC of Reaction Products of 2,4,6-Trichlorophenol with mCPBAHPLC Traces of 2-Chlorophenol Oxidation ProductsHPLC Traces of 2,4-Dichlorophenol Oxidation ProductsHPLC Traces of 2,4,5-Trichlorophenol Oxidation ProductsHPLC Traces of 2,3,5,6-Tetrachlorophenol Oxidation ProductsScheme 1.1^Phenol Oxidation to Form a QuinoneScheme 1.2^Formation of Porphyrin 11.-oxo DimersScheme 1.3^Proposed Catalytic Cycle of Metalloporphyrin Oxidation withHydrogen Peroxide and Reduction by SubstrateScheme 2.1^Reaction Pathways of 2,4-Dichlorophenol OxidationTable 2.1^Oxidation Rates of 4-ChlorophenolTable 2.2^Relative Chlorophenol Oxidation RatesviiLIST OF ABBREVIATIONSgmol^ micromoleabs absorbanceCP chlorophenolDCP^ dichlorophenolDNA deoxyribonucleic acidFeTDCS-13-C18PC1^[iron(Ill)(meso-tetra(2,6-dichloro-3-sulfanatopheny1)-(3-octachloroporphyrinato)] chlorideFeTDCSPPC1^[iron(III)(meso-tetra(2,6-dichloro-3-sulphonatophenyl)porphyrinato)] chlorideHRP^ horseradish peroxidaseHPLC high performance liquid chromatographyHRMS high resolution mass spectrometryLRMS^ low resolution mass spectrometrymCBA meta-chlorobenzoic acidmCPBA meta-chloroperoxybenzoic acidmmol^ millimoleMnTDCSPPC1^[manganese(III)(meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrinato)] chloridemol^ molenm nanometrePCB polychlorinated biphenylPPM^ parts per millionrel. int. intensity relative to base peak (100%)T temperaturet^ timet-BuOH t-butyl alcoholt-BuOOH^ t-butylhydroperoxideviiiTCP^ trichlorophenolTDCS-13-C1 8P^meso-tetra(2,6-dichloro-3-sulfanatopheny1) -13-octachloroporphyrinTDCSPP meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrinTeCP^ tetrachlorophenolTFA trifluoroacetic acidTLC thin layer chromatographyTPP^ meso-tetraphenyl porphyrintr retention time (chromatography)TSPP meso-tetra(4-sulphonatophenyl) porphyrinUV^ ultravioletVis visibleixACKNOWLEDGEMENTSSincere thanks are due to Dr. David Dolphin for his advice at all stages of this project. Iwould also like to thank all members of the group for their essential and expert help,especially Tilak Wijesekera. The continuous support and encouragement of my friends andfamily is most gratefully acknowledged. Finally, and most importantly, thanks for everythingSue.This research was funded by the Institute for Chemical Science and Technology (ICST).x11. INTRODUCTION1.1 General IntroductionIn 1988 ancient Inuit tissue, frozen for over 400 years, was analyzed for the presence ofchlorinated dioxins. None of these toxic chemicals were detected. In contrast, modernhuman tissue samples have an average of 1 ppb dioxinsm.Another study, focusing on the measurement of chlorinated dioxins in core samples from lakesediments, illustrated that only sediments deposited after about 1938 contained anymeasurable quantities of these compounds [21 .The implication of these data is that some aspects of recent human activities have led to theformation of these compounds. It has been suggested [2 '31 that the production and use ofindustrial quantities of chlorinated organic chemicals, which began around 1940, was the keytransformation. These chlorinated materials subsequently entered the environment, boththrough use and through waste streams, in large quantities. Burning the contaminated wastescreated dangerous and persistent chlorinated organic compounds (in particular, dioxins) anddispersed them widely. Within a very short period of time, the global environment hasbecome contaminated with measurable quantities of potentially damaging chemicals.2This realization underscores the importance of acquiring a general understanding of thesources, the behaviour and the control of anthropogenic inputs into the environment.Following this theme, this thesis studies the use of water soluble metalloporphyrin catalystsfor the oxidation of chlorophenols in aqueous wastes. Products of the oxidation reactions aredescribed, and the relative rates of chlorophenol removal are reported. The technique isevaluated in terms of its viability as a new method for remediation of chlorophenol-containingaqueous wastes.31.2 Chlorophenols1.2.1 Sources and Scope of Environmental ContaminationThe world wide production of chlorophenols exceeded an estimated 200 million kilogramsin 1975'43 , of which approximately half was pentachlorophenol. In Canada, during 1981, 5.3million kilograms of chlorophenols was consumed. It was reported that 1.4 million kilograms(26%) were eventually released into the environment 151 . The general biocidal nature ofchlorophenols led to the extensive use of technical mixtures of chlorophenols, in particularpentachlorophenol, as a wood preservatives 141 .The soil and water around many sawmille•• and wood preserving facilitiest iv il is heavilycontaminated with chlorophenols. A study (1987) of sawmills and lumber export terminalsusing chlorophenol treated wood in the lower mainland of British Columbia, found that stormwater run-off from these facilities contained in excess of 100 gg/L total chlorophenols,concentrations which affect the growth and reproduction of fish'''.Vast quantities of 2,4-dichlorophenol and 2,4,5-trichlorophenol have been made, as thesecompounds are the starting materials for the preparation of the important herbicides2,4-dichlorophenoxyacetate (2,4-D) and 2,4,5-trichlorophenoxyacetate (2,4,5-T), widely usedin agriculture. Since the initial biodegradation products of 2,4-D and 2,4,5-T are42,4-dichlorophenol and 2,4,5-trichlorophenol, respectively, these two chlorophenols areparticularly widespread environmental contaminants [131 .Chlorination of drinking water supplies leads to the formation of chlorophenols. Chlorinetreatment of water containing two naturally occurring benzoic acids (p-hydroxybenzoic acidand vanillic acid) yielded 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenolf 141 .Chlorophenols are also generated as side products during many industrial processes. Theyhave been detected in the waste of at least twelve industrial categories, including textiles,polymer manufacturing, metal refining, and coal conversion [151 .The presence of chlorophenols in the waste waters of pulp and paper bleach plants isparticularly well documented 116.17 . 18 . 191 . Treatment of pulp with chlorine to solubilise lignin(an intricate polymer containing phenylpropane moieties) naturally yields a complex mixtureof chlorinated organic compounds including many chlorophenols [161 . In a review of chemicalspresent in pulp mill effluent, researchers list 14 chlorophenol congeners. They reported avalue of 2 g/tonne of effluent for 2,4-dichlorophenol.A natural solution to the problem of generating chlorinated wastes is to use alternativebleaching agents. Although new chlorine free bleaching techniques are becoming industriallyimplemented, the majority of Canadian mills were built before 1975, and due to the high costof retrofitting, these older mills will likely be dedicated to chlorine processes for some time.5Some chlorophenols are known to occur naturally. For example, 2,6-dichlorophenol is a sexpheromone for several species of tick' 41. Compared to anthropogenic inputs, naturallyoccurring sources are negligible.In general it can be said that chlorophenols are ubiquitous in the environment, having beendetected in municipal sludgest20I, waste-waters [211 , soils [6,7,10] , groundwater1223 , surface waterr231 ,food141 , animals 1241 and humanst4 .251 .1.2.2 ToxicityIn many early chlorophenol toxicity studies the effect of the presence of chlorinated dioxins,now known to be a common chlorophenol contaminant, was not evaluated. Due to the hightoxicity of the dioxins the results of this early work is questionable. However, recentevaluations, using pure chlorophenol samples, have determined chlorophenols to be acutelytoxic to a variety of organisms.Increased acute toxicity with increased chlorine substitution was demonstrated for severalspecies of fish. For example, two LC 50 (24 hr) values (the concentration at which 50% ofthe sample population dies) for trout are 1.7 ppm for 2,4-dichlorophenol to 0.2 ppm forpentachlorophenol [27] . Similar results were obtained for fathead minnows1281.6Inhibition of bacterial growth also follows the general trend of increased toxicity withincreased chlorine substitution 129.301 . Values expressed as IC50 (effective concentration causing50% growth inhibition) were determined for 19 chlorophenols and varied from 700 ppm for2-chlorophenol to 4 ppm for 2,3,4,5-tetrachlorophenol.The toxicity investigations also found a dependency of the toxicity on the position of chlorinesubstitution. Chlorophenols with chlorine in the 3 and 5 positions are often more toxic thanexpected solely on the basis of their degree of substitution. No rationalization was forwardedfor this observation. However, based on the work in this thesis, there is some correlationbetween oxidative stability and toxicity. This will be discussed further in a subsequentsection.Toxicity to phytoplankton, zooplankton, and invertebrates has been studiedr 43 . The IC50 valuesare similar and in the region of 0.5 to 15 mg/L.The mammalian carcinogenicity of 2,4,6- and 2,4,5-trichlorophenol has been evaluated by theInternational Agency for Research on Cancert 261 . It was concluded that 2,4,6-trichlorophenolis an animal carcinogen, and that there were inadequate data for the assessment of thecarcinogenicity of 2,4,5-trichlorophenol.As well as being inherently toxic, the generation of highly toxic dioxins from the lowtemperature incineration of chlorophenols and from photolysis of chlorophenols in the7presence of chlorobenzenes is well documented131 '321 .The toxicity, and the widespread nature of the contamination, has led to the inclusion of fourchlorophenols on the U.S. Environmental Protection Agency's list of 129 Priority Pollutants [41 .It is known however, that partial oxidation of chlorophenols significantly decreases theirtoxicitf ] .1.2.3 Remediation of Chlorophenol PollutionMuch effort has been focused on methods of degradation or removal of chlorophenols forremediation of contaminated soils and waste water. Due to the complexity and variety of thewaste, no single system has been developed which removes or degrades chlorophenols underall conditions. Several abatement techniques are discussed here. Microbial TechniquesBiorestoration of contaminated sites is a promising technique [34 '35.3637 '381 . Biodegradation offersdistinct advantages over other treatments, primarily the potential for complete mineralizationof contaminants to carbon dioxide and inorganics, a most desirable result. The 'ecologically8sound' nature of the technique, and the ability to treat soils in situ are other advantages oftenquoted.Biodegradation of chlorophenols has been extensively studied, using both individual strainsand mixed cultures of aerobicr 391 and anaerobic [40,41,42,43,44] microorganisms. Sincechlorophenols are used specifically as antimicrobial and antifungal agents, it was not asurprising discovery to find that biodegradation by native microorganisms is slow.In a recent study, biodegradation of pentachlorophenol by native microorganisms incontaminated soil from a wood preserving facility was monitored [451 . The soil was tilled andfertilized with appropriate nutrients. Over 90 days pentachlorophenol concentration decreasedfrom 90 mg/kg soil to 25 mg/kg soil. The researchers considered this rate of degradation tooslow for a full scale remediation strategy.More efficient biodegradation was observed when pentachlorophenol was present in lowconcentrations. In soil amended with sewage sludge, '4C labelled pentachlorophenol (0.75mg PCP/kg soil) was observed to be degraded to ' 4CO2, with a half life of ten to fifteendays [2°3 .Soil heavily contaminated with a chlorophenol based fungicide (mostly2,3,4,6-tetrachlorophenol) was isolated and monitored for chlorophenol degradation 1461 . Aftertwo years the total chlorophenol concentration decreased from 212 mg/kg to 15 mg/kg.9Genetic selection in vivo and genetic manipulations in vitro have allowed construction ofbacteria strains which have wider biodegradation potentials than their natural counterparts.Several isolated cultures have been shown to utilize, under laboratory conditions, somechlorophenols as their carbon or energy source.A Flavobacterium species has been shown to effectively degrade pentachlorophenol, utilizingthis substrate as its sole source of carbon and energy [47,481. A solution of pentachlorophenol(50 mg/L) was completely mineralized within 48 hours. However, inoculation ofcontaminated soils with this species enhanced pentachlorophenol degradation, but the efficacywas not total and repeated culture applications were necessary for 80% removal after 100days [5°1 .As with most metabolic processes, the biochemical mechanism for bacterial metabolism ofchlorophenols is highly specific. For example, the above mentioned Flavobacterium specieswas specific to pentachlorophenol and did not metabolize other chlorinated phenols; of thefifteen di- tri- and tetra- chlorophenols, only 2,4,6-trichlorophenol and 2,3,5,6-tetrachlorophenol were significantly degraded [491 .In contrast to the substrate specificity of bacteria, the basidiomycetes fungus Phanerochaetechrysosporium has the ability to degrade a wide variety of organic pollutants 1511 . Theextractable pentachlorophenol in soils inoculated with P. chrysosporium decreased by 98%over two months [52) . It was determined that the major degradative pathway was not to CO2,10but rather irreversible binding to soil organic matter was likely. Other researchers have foundthat basidiomycetes fungi methylate chlorophenol hydroxyl groups, producingchloroanisoles ]53] . Chloroanisoles would be strongly bound to the soil organic matter, andthus less available for attack by fungal enzymes. The biotransformation of xenobioticsubstrates into new, sometimes more recalcitrant, compounds is an important consideration.As with basidiomycetes fungi, the bacterium Rhodococcus chlorophenolicus generateschlorinated methoxyphenols as well as completely degrading chlorophenolsI 50 '54] .The use of microbes as a technology for remediation of contaminated sites or wastes facesother limitations. It has been suggestedfss] that environmental conditions such as extremesof pH and temperature, toxins, predators, competition from indigenous populations, nutrientlimitations and, high concentrations of pollutants and their by-products, may inhibit growth,or kill microbial cells and prevent biodegradation. Practical difficulties such as maintainingactive cells during transportation to polluted sites and limited mobility of the cells within thesoil are other restricting factors. Enzymatic TechniquesEnzymes have been reported to be less sensitive than bacteria to variations in pH, pollutantconcentration, toxins, and temperature s] . The use of enzymes could circumvent some of thedrawbacks encountered by microorganisms. The function of enzymes in vivo is to perform11only one of many steps in the metabolism of a substrate. Thus, enzymatic treatments do nothave the potential for complete mineralization of pollutants.Enzymes which catalyze phenol oxidation (phenol oxidases, laccases, peroxidases) have beenused to detoxify phenol solutions and industrial waste waters [551 . Oxidation andpolymerization of the phenols yields less soluble high molecular weight compounds whichcan be removed by filtration or sedimentation. The precipitates formed during thepolymerization of 2,4-dichlorophenol were oligomers with average molecular weights of 800.As well, inorganic chloride was released during the reaction. Up to 20% of the chlorineinitially associated with the phenol was released.Extracellular laccases from the fungi Rhizoctonia practicola and Tramates versicolor as wellas horseradish peroxidase and tyrosinase have been used as oxidation catalysts to detoxifyaqueous chlorophenol solutionsP 6."'581 .2,4-dichlorophenol is completely removed from solution within 5 hours by horseradishperoxidase with hydrogen peroxide, but only 83% of 4-chlorophenol is removed after 15hours. After 15 hours, the laccase from T. versicolor removed 90% of 2,4-dichlorophenolfrom solution, but under the same conditions, only 38% of the 2,4,5-trichlorophenol wasremoved. As with microorganisms, the enzymes appear to exhibit significant substratespecificity.12The activity of the enzymes is dependent on the pH of the solutions. The laccase enzymefrom R. practicola was inactive towards oxidation of 2,4-dichlorophenol above pH 9 andbelow pH 4. Horseradish peroxidase must be between pH 5.5 and 8.5 to retain 90% or moreof it's activity.Although the laccases are less effective than horseradish peroxidase, for potential large scaleapplications, the laccases have the advantage of utilizing molecular oxygen as the oxidant,whereas peroxidase requires more costly hydrogen peroxide.Efficient dechlorination of 2,4,6-trichlorophenol by extracellular lignin peroxidases (ligninase)from Phanerochaete chrysosporium has been observed 1"'6°J. The researchers identified2,6-dichlorobenzoquinone as the product of quantitative 4-dechlorination. 2,4-dichlorophenolwas oxidized to 2-chloro-1,4-benzoquinone 1611 .Although enzymes are potentially more robust than microbes, enzymatic detoxificationprocesses also show disadvantages. Thermal denaturation of enzymes is well known and canoccur at temperatures as low as 40°C. Many inorganic and organic substances act asinhibitors of enzymes and can render them inactive. Phenol polymers, like those generatedin some of the enzymatic reactions, are known to be generated by plants in response to cutwounds as a mechanism of protection, their purpose being to inhibit foreign enzymes. Thismay work against an enzymatic technique for detoxification of phenolic wastes. Technicalconfines such as enzyme extraction and purification, and practical obstacles like susceptibility13to degradation by microbial proteases inherent in the waste, may be limitations. Formationof minute amounts of dibenzo-p-dioxins and dibenzofurans during the peroxidase catalysedoxidation of chlorophenols has been tentatively determinee 2 . Generation of these highlytoxic products may preclude the use of these techniques for waste clean-up. Chemical and Physical TechniquesAqueous solutions of iron (II) sulfate and hydrogen peroxide (Fenton's reagent) have beenused to oxidize mono- and di-chlorophenols.Researchers recovered stoichiometric quantities of chloride when using excess hydrogenperoxide, and with ferrous ion present in concentrations similar to that of the initialchlorophenol concentration [371 . The half life of five of the lower chlorinated phenols rangedfrom six to twelve minutes. The ultimate fate of the aromatic ring was not elucidated.Using a similar system, a 2,4-dichlorophenol solution and two phenolic industrialwaste-waters were partially oxidized as a pretreatment step prior to biological treatment [331 .The residual products of hydrogen peroxide oxidation were evaluated based on microorganismtoxicity and biodegradability. It was found that the products were an order of magnitude lesstoxic than the initial solutions. Also, the oxidized material was much more readily consumedby municipal sludge.14Although formation of dioxins from low temperature burning of chlorophenols is knownf",high temperature rotary kiln incineration has been demonstrated to be effective forchlorophenol destructionr641 . However many complex wastes contain material such as volatilemetals, which are dangerous to incinerate.Other, less widely applicable, techniques for chlorophenol destruction have been reported.Polymerization and dechlorination of pentachlorophenol by oxidation with copper (II)immobilized on smectite clay, was evaluated as a detoxication technology [651 . Extendedreaction in refluxing hexane was required, and oxidation was incomplete. Partialdechlorination of chloroaromatics using a semiconductor photoreactor has been reportedf 661 .Using boiling nitric acid or permanganate does destroy chlorophenols but these conditions areconsidered too severe for general use 1671 . Many other degradation technologies have beenreported. Microwave discharge, ozonation, photodecomposition, and physical adsorption areinteresting techniques which hold some promise for future developmentr67'681.151.3 Chemistry of Phenol OxidationThe oxidation of phenols has been extensively studied [69 .70 '713 . Biosynthetic pathways to awide range of natural products including tannins, lignins, pigments, alkaloids and antibioticsinvolve oxidation and coupling of phenols as key reactions. This same mechanism isimplicated in other important biological processes such as the browning of damaged fruitsurfaces, and the formation of complex soil humic materials.Many oxidants have been used to effect phenol oxidationt721 . The most widely used methodsinvolve the use of a variety of inorganic salts and oxides (e.g., of lead, silver, manganese,copper, iron, cobalt, vanadium, thallium, cerium, iridium, and others), particularly leaddioxide, potassium ferricyanide, and ferric chloride. Organic reagents such as nitrites,quinones, peroxides and hydroperoxides have been used. Some other techniques include useof molecular oxygen, enzymes, photolysis, electrolysis, radiolysis and pyrolysis.The removal of a single electron and a proton generates a phenoxy radical (Figure 1.1).OH e-,H+Figure 1.1 Resonance Forms of the Phenoxy RadicalHO kOHhOHOH HO OH0 — 0aCf16ESR measurernentsf 731 demonstrate that the highest spin density is found on oxygen and onthe para carbon (aHp=10.1 Gauss). The spin density is next highest at the ortho carbons(aH0=6.6 Gauss), and the density is much smaller at the 1, 3, and 5 positions.Two radicals can combine (Figure 1.2), and the dimers a to f may result. The dimerstautomerize rapidly in protic solvents to the stable aromatic compounds g to k.Oligomerization or polymerization is effected by oxidation of the dimers and further couplingwith other phenoxy radicals.Figure 1.2 Products of Phenol Dimerization17An alternative fate of the phenoxy radical is possiblet 59,741 (Scheme 1.1). A second oneelectron oxidation, generating a cation, is followed by nucleophilic attack by solvent (water).Loss of the para substituent and a proton yields the benzoquinone. The use ofoxygen-transferring oxidants, such as potassium nitrosodisulfonate (Fremy's salt) or thalliumtrifluoroacetate also generate quinones in high yields [74 •75] . Quinone formation is mostcommon in aqueous reactions with para-substituted phenols. Oxidation of 2,6-disubstitutedphenols leads to the formation of the pars Para coupled dimer which can be further oxidizedto an extended quinone. o.e-, WCICl -, 2WScheme 1.1 Phenol Oxidation to Form a Quinone3 517 15 1318Figure 1.3 Structure of Porphine1210181.4 Porphyrins1.4.1 Structural ConsiderationsAll porphyrins are derivatives of the parent methylene bridged tetrapyrrolic macrocycle,porphine (Figure 1.3). The numbering system for IUPAC nomenclature is shown, howevernon-IUPAC nomenclature is often used. The methylene bridge carbons (5,10,15,20) are alsoknown as the meso - positions, and the peripheral pyrrolic carbons (2,3,7,8,12,13,17,18) aretermed the 13- positions.The ring is a conjugated 7r-system and a number of pathways through the ring involve 18 7C-electrons which satisfies the Hiickel '4n + 2' rule for aromaticity. The ring is planar, rigid19and has 1 1-I NMR chemical shifts typical of aromatic compoundst 761 . The ring is also a goodtetradentate ligand, readily coordinating metals through the four pyrrole nitrogens, to formmetalloporphyrins. Most metals take up axial ligands to complete their coordination sphere.An important and interesting property of metalloporphyrins is that they can be reversiblyoxidized; electrons can abstracted from the porphyrin ring, the chelated metal, or frombothf7"81 .Metalloporphyrins occur widely in nature and are at the core of the essential processes of life,playing key roles in both plant photosynthesis and animal respiration. A particularmetalloporphyrin, iron protoporphyrin IX (Figure 1.4), is the prosthetic group in manyenzyme and metalloprotein systems (cytochrome P-450, peroxidases, catalases, haemoglobin,and others), and acts in mediation of a variety of redox reactions, oxygen transportation, andoxygen activationt 721 .CO2HFigure 1.4 Structure of Iron Protoporphyrin IXCO2H20An approach to studying the fundamental chemistry of these important biological processeshas been the use of synthetic metalloporphyrins as models [80,8182,83]. Use of protein free ironprotoporphyrin IX for in vitro studies has not been successful as the porphyrin moiety isreactive, particularly at the meso-positions and the vinyl groups. Meso-tetraphenylporphyrin,TPP (Figure 1.5; R I =R2=H) is more stable than protoporphyrin IX, and, importantly, is readilyprepared by simple synthetic sequences. Thus, TPP and derivatives, with a wide variety ofcoordinated metals, have been extensively studied.R NH^HNR1   RiR 2Figure 1.5^Structure of Meso-tetraphenylporphyrin (R1=R2=H)21Beyond their biological relevance, the catalytic redox activity of metalloporphyrins may leadto their use as catalysts for synthesis or industry. The potential to perform importantreactions which are catalyzed by enzymes, while avoiding the difficulties associated withcomplicated biological systems, is very exciting and promising.Although capable of oxidizing unactivated alkanes and alkenes, oxidation reactions usingmetallated TPP are characterized by low tumovere' 851 . In the presence of molecular oxygen,iron (III) TPP dimerizes through a bridging oxygen atom, as shown in scheme 1.2 [861 . Thedimer is not catalytically active. This, coupled with oxidative destruction of theporphyrin, are the likely causes of the observed low turnovers. 020II 2P2 P 1dimerP—C1—) PorPhYtinScheme 1.2 Formation of Porphyrin woxo Dimers22Through structural modification of the porphyrin periphery the chemical properties of themolecule can be substantially altered. Researchers in our laboratories and elsewhere haveprepared modified porphyrins which are more robust and efficient oxidation catalysts thanTpp[84,87,88] .Since the phenyl and porphyrin rings are sterically constrained to be essentially perpendicularto each other, the use of bulky substituents on the ortho-phenyl position (Figure 1.5, R 2)sterically prevents formation of the p-oxo dimert 89 . 90 .911 . This non-aggregating behaviourincreases catalytic activityl m 'n.") .Additional stabilization of the porphyrin ring towards oxidation can be accomplished viamodification of the porphyrin ring (particularly at the pyrrolic 3-position (Figure 1.5, R 1 ) withelectron withdrawing groups. Chlorination of the eight 13-positions (Figure 1.5, R 1 =C1,R2=H), produces a positive shift of 0.41 V of the measured E112 for the first reduction,compared to TPP. The effect of chlorination at the ortho-phenyl positions on the E112 is muchsmaller, because electronic effects can only be inductively transmitted to the porphyrin ring [941Water solubility can be imparted by substitution with an ionic group. Examples includemeso-carboxyphenyl, -sulfonatophenyl, -methylpyridinium, and -trimethylaniliniumsubstituents.Thus, by using bulky ortho - substituents and electron-withdrawing 13-substituents, porphyrinssty.'sogiCl^aCI^a2a: M=FeC12b: M=MnC123Figure 1.6 Structure of Chlorinated Water Soluble Metalloporphyrins.la=firon(111)(meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrinato)]chloride; 2a= firon(11.0(meso-tetra(2,6-dichloro-3-sulfanatopheny1)-13-octachloroporphyrinatoE chloride 2b=[manganese(III)(meso-tetra(2,6-dichloro-3-sulfanatopheny1)-13-octachloroporphyrinato)] chloride.24which have greatly increased stability towards oxidative degradation can be prepared.Following this rational, meso-tetra(2,6-dichloro-3-sulfanatophenyl)porphyrin, 1, (TDCSPP),and meso-tetra(2,6-dichloro-3-sulfanatopheny1)-0-octachloroporphyrin, 2, (TDCSP-(3-C1 8P),have been synthesized (Figure 1.6) (951 . The chloride complexes of three metallated derivatives(iron la, and 2a; manganese 2b) are the catalysts used for this study.1.4.2 Catalytic MechanismsAs mentioned earlier, metalloporphyrins can be reversibly oxidized. In solution, high valent,reactive species are generated by transfer of an oxygen atom to the metal center, forming anoxometal complex.For example, for iron(III) porphyrins, both the product oxidized by one electron at the metal(oxoiron(IV) porphyrin), and the two electron oxidation product, one electron from the metal,and one electron from the ic-cloud of the porphyrin moiety (oxoiron(IV) porphyrin it-radicalcation) are known. These compounds have been obtained in their crystalline state andcharacterized by their chemical reactions, resonance Raman, EPR, EXAF, 1H NMR, andUV/Vis spectroscopy, and with electrochemical and magnetic techniquest 96 '97981 .Recently, an oxoiron(IV) porphyrin it-radical cation which is stable at a relatively hightemperature was described.^meso-tetra(2,6-dichloropheny1)-13-octaphenylporphyrin'25oxoiron(IV) was obtained and characterized spectroscopically at 8 °C 1961 . An example of arecently characterized oxoiron(IV) species is that of porphyrin la. The one electron oxidizedspecies was stable for several hours in water at ambient temperaturee71 .Whereas there is consensus of opinion with respect to the mechanism of oxygen transfer fromacyl hydroperoxides to iron(III) porphyrins, there is considerable debate as to the oxygentransfer mechanism with alkyl peroxides or hydrogen peroxide.When the oxidant is an acyl hydroperoxide or peroxyacid, heterolytic cleavage of the 0-0bond occurs, and the metalloporphyrin is oxidized by two electrons (equation 1).Porph Fem + YOOH ---> Porph' Fe"O + YOH^(1)For alkyl hydroperoxides a similar heterolytic cleavage has been proposed [99 ' l00l, howeverstrong evidence (kinetic and product distribution studies) for homolytic 0-0 bond scissionhas been presentedf 101,102,103,104). Porphyrin la in water, and the non-sulfonated TDCPP Fe(III)in organic solvents, have typically been used for these studies. The porphyrin oxidationwould thus proceed in two distinct steps (equations 2 and 3).Porph Fern + ROOH -p Porph Fe"O + RO .^(2)Porph Fe"O + RO' --> Porph" Fe1v0 + RO -^(3)26For hydrogen peroxide or alkyl hydroperoxides, the catalytic cycle of porphyrin oxidation andreduction can be summarized as in scheme 1.3. Initial one electron oxidation generates theoxoferryl porphyrin species. A second one electron oxidation produces the oxoferrylporphyrin it-radical cation. Two subsequent one electron transfers to a substrate regeneratesthe starting iron(III) porphyrin.1.4.3 Reactions of Chlorinated MetalloporphyrinsThe stability of the halogenated metalloporphyrins to oxidative degradation has led tosubstantial interest in their use as catalysts.These catalysts have been used to effect alkene epoxidation. Norbornene was epoxidized in85% yields with 10,000 turnovers using TDCPP FeC1 [84.921 . Using hydrogen peroxide, styrenewas epoxidized (93% yield) with TDCPP Mnelf l 'i. Also using this catalyst, epoxidation ofseveral alkenes including cyclooctene and limonene, was studied under a variety ofconditions"6] .Low temperature hydroxylation of alkanes by molecular oxygen is catalyzed by halogenatedmetalloporphyrinst i°7 '1°81 . The catalyst was shown to be long lived, effecting over 12 000turnovers in this industrially important reaction. Other oxidations such as hydroxylation ofaromatic compounds [933°91 , and aldehyde conversion to carboxylic acids [1101 , have been0'IHO'H2020IISub0IISub= Porphyrin Sub = Substrate= Porphyrin it-radical cation Subox = Oxidized by le'27Scheme 1.3 Proposed Catalytic Cycle of Metalloporphyrin Oxidation with HydrogenPeroxide and Reduction by Substrate.28catalysed by these catalysts in organic solvents.Catalyst la was used as a new route to quinones from methoxyarenes [1113 . Catalyst la andlb were used as a biomimetic analogue of ligninase, catalyzing oxidation reactions of ligninmodel compoundsf 123131 . These catalysts were shown to be effective in alkyl peroxide pulpbleachin g[114J.292. RESULTS2.1 Analysis of Products from the Oxidation of ChlorophenolsThe reaction products of the oxidation of several chlorophenols were identified.Chlorophenols were dissolved in water, catalyst and oxidant (usually hydrogen peroxide) wereadded, and the mixture stirred. The reactions were monitored by HPLC or by UV/Visspectrophotometry. The reaction mixtures were extracted with organic solvent, separated bychromatography, and identified by NMR spectroscopy, and mass spectrometry. The detailsare discussed in the experimental section.2.1.1 Products from the Oxidation of MonochlorophenolThe reaction products of 2-chlorophenol, 3-chlorophenol and 4-chlorophenol were similarThe product was typically a brown colloidal material which was insoluble in water. With asmall excess of oxidant the yield of the precipitate was quantitative for 2- and 4-chlorophenol,by gravimetric analysis. HPLC demonstrated that no chlorophenol remained in solution(Figure 2.23). The yield of precipitate for 3-chlorophenol, under similar conditions, wasapproximately 20%. Individual compounds could not be isolated as chromatography was notsuccessful.30HPLC of the colloidal precipitate demonstrated that it was a mixture of several components.The infrared spectra of the crude has absorbances assignable to alcohol 0-H stretch (3300 cm -br) and aryl ether C-0 stretch (1223 cm'). Mass spectrometry of the crude materialdemonstrated strong m/e peaks at 508, 380, 254 (Figure 2.1). These can be tentativelyassigned to the tetramer, trimer and dimer, respectively. Although characterization is notcomplete, experimental evidence suggests that the product of monochlorophenol oxidation isa mixture of phenolic oligomers. Figure 2.2 demonstrates two possible structures.2.1.2 Products from the Oxidation of 2,4-DichlorophenolThe formation of at least eight products by the oxidation of 2,4-dichlorophenol was observedby HPLC (Figure 2.24) and TLC. Several of these products were isolated and identified(Figure 2.3). All of the products were obtained in low yield ( < 15%).The most abundant of the isolated products (15% yield) was 2-chloro-1,4-benzoquinone, 3.The mechanism of a two electron oxidation and nucleophilic attack by water at the 4-chloroposition, as mentioned in the introduction, is probable.Dimer coupling products and products arising from the oxidation of the dimers were isolated.Due to the presence of the chlorine at the 2- and 4- positions, coupling can only occur at theoxygen and the C6- position. Two electron oxidation of the phenol group of the•5OS614221472416^36518II^  31422^443^461^480^511^522^541^561^581^611381254312ISO4222111,236h ?ill I'll222^241574 3361274^292^I^11111 1 1 1263 281^30171362p 46L'1 1 1 1 I I I II)^III! e321^342^362^38113148/60 155635IS211 717i 1F 1111,1111 91i11111.11111111111 1 411101^121128iltliirli111.11111111^i r . 1 .111[1 111 141,1 .111 i yi t il141^162^IBSII200 220Figure 2.1 Mass Spectrum of 2-Chlorophenol Oxidation ProductCl32CIClClCIFigure 2.2 Two Possible Products of 2-Chlorophenol Oxidation33CI(3)^(4)(5)^(6)Figure 2.3 Products of Oxidation of 2,4-Dichlorophenol34phenoxyphenol dimer (2-(2,4-dichlorophenoxy)-4,6-dichlorophenol), and subsequentnucleophilic attack by water is the proposed mechanism for the formation of 2-(2,4-dichlorophenoxy)-1,4-benzoquinone, 4. A similar mechanism to account for the formationof 2-(3-chloro-cyclohexa-3,6-diene-2,5-dione)-4,6-dichlorophenol, 5, is proposed.The C-C bonded quinone dimer (2-(3-chlorocyclohexa-3,6-diene-2,5-dione)-6-chloro-1,4-benzoquinone, 6) was also a product of the oxidation. As before, oxidation of the phenolgroup of 5 to form the quinone moiety is the suggested mechanism.Scheme 2.1 summarizes a possible reaction pathway of the oxidation of 2,4-dichlorophenolbased on these products and previously suggested mechanismsr 59 . 691 .A product was isolated in insufficient quantities for complete characterization, but wastentatively identified as a trimer of the phenol, based on mass spectrometry. Other minorproducts (<5%) were formed as observed by HPLC, but were not isolated and identified.Products such as tetramers and other oligomers are likely.2.1.3 Products from the Oxidation of 2,4,6-TrichlorophenolThe product from the oxidation of 2,4,6-trichlorophenol was 2,6-dichloro-1,4-benzoquinone,7 (Figure 2.4). This product was obtained in 94% yield.CI HO ClH2O2e-,C1-VCl^OHHO CIC1ii20-- \N 2e-,CIV4.4ouplinOH35 CIScheme 2.1 Reaction Pathways of 2,4-Dichlorophenol OxidationCI ClCI36(7)^(8)CICl(9)^(10)Figure 2.4 Products of 2,4,5- and 2,4,6-Trichlorophenol Oxidation37When the reaction is done under conditions of high substrate concentration, a second productwas detected by HPLC. This product was minor and could not be isolated in sufficient yieldfor complete characterization. Based on mass spectroscopy a possible structure is thediphenoquinone (8).2.1.4 Products from the Oxidation of 2,4,5-TrichlorophenolThe formation of at least seven products from the oxidation of 2,4,5-trichlorophenol can beobserved by HPLC (Figure 2.25) and TLC.Two of the products were isolated and identified (Figure 2.4). The two electron oxidationproduct, 2,5-dichloro-1,4-benzoquinone, 9, was isolated in 10% yield. 2-(2,4,5-trichlorophenoxy)-3,6-dichloro-1,4-benzoquinone, 10, was also identified. This productpresumably arises from the oxidation of the phenoxyphenol dimer as illustrated in the caseof 2,4-dichlorophenol.Other products were not isolated but likely structures (analogous to the products of 2,4-dichlorophenol oxidation) include: the phenoxyphenol dimer, the C-C bonded biphenyl dimer,the oxidized biphenyl products; the quinone and diquinone dimers, as well as trimers andoligomers.382.1S Products from the Oxidation of TetrachlorophenolsOxidation of 2,3,5,6-tetrachlorophenol results in two main products as detected by HPLC(Figure 2.26). Because the ortho positions are blocked by the chlorine substituents, couplingcan occur only at the oxygen and the para positions. As might be expected from themechanism, 4-(2,3,5,6-tetrachlorophenoxy)-2,3,5,6-tetrachlorophenol, 11, and 4,4'-dihydroxytetrachlorobiphenyl, 12, were obtained (Figure 2.5). By comparison of HPLCretention times and UV spectra at the HPLC detector of the reaction mixture and standardsample, a minor amount of tetrachloroquinone, 13 was detected.As judged by HPLC, there is primarily one product from the oxidation of 2,3,4,6-tetrachlorophenol. It was produced in low yield (<15%) and this product was not completelycharacterized, but the UV spectrum of the peak at the HPLC detector has a strong absorbanceat 270 nm, characteristic of the quinones. The product is likely 2,3,6-trichloro-1,4-benzoquinone.2.1.6 Oxidation of PentachlorophenolThe oxidation of pentachlorophenol is an unusual case.Figure 2.6 demonstrates the HPLC traces taken during the reaction. Initially, the peakH 0Cl(13)H 0 OHCl Cl^CIClCl^Cl^Cl(12)Cl39Cl^ClFigure 2.5 Products of 2,3,5,6-Tetrachlorophenol Oxidation4010^ 201 01B; t=2 hrs 210 10 2020 0 10 20Figure 2.6 HPLC Traces Taken During Reaction of Pentachlorophenol.A, t=0; B, t=2 hrs; C, t=12 hrs; D, t=22 hrs.41corresponding to pentachiorophenol (t r=5.2 min) decreases and a new peak (4=15.6 min)appears, and begins to increase in intensity. After approximately 3 hours thepentachiorophenol peak intensity stops decreasing and slowly begins increasing, andcorrespondingly, the new peak starts to decrease in intensity. After 24 hours, thepentachiorophenol peak returns to near it's original intensity, and the new peak diminishesto the baseline. Similar observations, or no oxidation of pentachlorophenol is seen with thethree catalysts (la, 2a, 2b), used with several oxidants (t-butylhydroperoxide, meta-chloroperoxybenzoic acid, and hydrogen peroxide), over a range of pH values andtemperatures. In all cases, only pentachlorophenol was recovered upon attempted isolationof the new product. When the above oxidants are used without catalyst, the HPLC trace doesnot change over 24 hours.A possible explanation for this observation is as follows. Oxidation generates the phenoxyradical intermediate. Since both the ortho and the para positions are occupied by chlorinesubstituents, only the 0-0 coupling takes place. This peroxide is unstable and, throughreaction with residual hydrogen peroxide or water, the phenol is regenerated. That is, theformation and decomposition of the aryl peroxide is an equilibrium process. When thehydrogen peroxide concentration is high, the phenol is oxidized. When the hydrogenperoxide concentration decreases, decomposition of the dimer to the phenol is favoured.422.2 Kinetic StudiesThe rate of oxidation of 11 chlorophenols was examined by monitoring HPLC peakintegration of the substrate with time (Figure 2.7 demonstrates the linearity of the HPLCdetector response to chlorophenol concentration). The effect of pH, oxidant type, and catalysttype was evaluated. The HPLC conditions are detailed in the experimental section.2.2.1 Effect of the CatalystThe effect of adding the metalloporphyrin catalyst la on the oxidation of 4-chlorophenol isclearly demonstrated in figure 2.8.From this graph the initial rate of disappearance (V 0) of 4-chlorophenol was obtained bycalculating, via computer, the slope of the line at t=0. Table 2.1 summarizes these initialrates.A plot of catalyst concentration against initial rate (absolute value) generates a straight line(Figure 2.9, r2 = 0.996, slope = 182). The reaction is pseudo-first order in the catalyst.Z 0.145.1^0.12ac 0.100-.7.a 0.08o,a)c 0.0643 Concentration (MMOL/L)Figure 2.7 Relationship of HPLC Integrator Response (at 270 nm) and 2-ChlorophenolConcentration.TABLE 2.1 Oxidation Rates of 4-ChiorophenolCatalyst Concentration(mmol/L)Initial Rate(d[%consumed]/d(min))0 0.0490.00292 0.730.00586 1.330.0293 5.980.0586 10.7044catalyst:substrate10 20 30 40 50 60 70 80 9010080604020no cat A1:2000 01:1000 01:200 V1:100 ^45Time in MinutesFigure 2.8 Effect of Catalyst Concentration on Oxidation of 4-Chlorophenol.Conditions: catalyst la; initial chlorophenol concentration 5.8 mmollL;hydrogen peroxide 28.4 mrnolfL; pH=2.1,T=23°C; detection by HPLC 270nm.460.01^0.02^0.03^0.04^0.05^0.06Catalyst Conc. (mmol/L)Figure 2.9 Relationship Between Initial 4-Chlorophenol Oxidation Rate and CatalystConcentration.Conditions: catalyst la; initial chlorophenol concentration 5.8 mmoll L;hydrogen peroxide 28.4 mmol1L; pH=2 .1 , T=23° C; detection by HPLC 270nm.472.2.2 Relative Chlorophenol Oxidation RatesBy measuring chlorophenol disappearance, graphs 2.10 to 2.14 were generated. The pH, theinitial chlorophenol concentration, oxidant, and catalyst concentration were constant. Fromthese graphs, the initial rate of disappearance (V0) was obtained by calculating, via computer,the slope of the line at t=0. Table 2.2 summarizes these initial rates.TABLE 2.2 Chlorophenol Oxidation RatesChlorophenol Initial Rate(d[%consumed]/d(min)2-Chlorophenol 6.203-Chlorophenol 2.664-Chlorophenol 5.982,4-Dichlorophenol 11.963,4-Dichlorophenol 4.783,5-Dichlorophenol 0.792,4,5-Trichlorophenol 8.482,4,6-Trichlorophenol 5.162,3,4,5-Tetrachlorophenol 0.982,3,4,6-Tetrachlorophenol 3.572,3,5,6-Tetrachlorophenol 3.341008060402002—CP ^4—CP3—CP 0480^10^20^30^40^50^60Time in MinutesFigure 2.10 Kinetics of Oxidation of Monochlorophenols.Conditions: catalyst la (FeTDCSPPCI), 0.026 mmol/L; initial chlorophenolconcentration 5.2 mmol/L; hydrogen peroxide 10.9 mmol/L; pH=2 .1, T=23°C ;detection by HPLC 270nm.100806040203,5—DCP 03,4—DCP ^2,4—DCP V4910^20^30^40^50^60^70Time in MinutesFigure 2.11 Kinetics of Oxidation of Dichlorophenols.Conditions: catalyst la (FeTDCSPPCI), 0.026 mmol1L; initial chlorophenolconcentration 5.2 mmollL; hydrogen peroxide 10.9 mmollL; pH=2.1, T=23°C;detection by HPLC 270nm.1 008060402 02,4,6 —TCP ^2,4,5—TCPsubstrate501 0^20^30Time in MinutesFigure 2.12 Kinetics of Oxidation of Trichlorophenols.Conditions: catalyst la (FeTDCSPPCI), 0.026 mmol/L; initial chlorophenolconcentration 5.2 mmollL; hydrogen peroxide 10.9 mmollL; pH=2.1, T=23°C;detection by HPLC 270nm.806040200substrate2,3,4,5—TeCP 02,3,5,6—TeCP A2,3,4,6—TeCP At■511 00 ^0^10^20^30^40^50Time in MinutesFigure 2.13 Kinetics of Oxidation of Tetrachlorophenols.Conditions: catalyst la (FeTDCSPPCI), 0.026 mmollL; initial chlorophenolconcentration 5.2 mmollL; hydrogen peroxide 10.9 mmol/L; pH=2.1, T=23°C;detection by HPLC 270nm.521 00802010^20^30^40^50^60^70Time in MinutesChlorophenol2—CP 03—CP •2,4—DCP 03,5—DCP A2,4,5—TCP ■2,3,4,5—TeCP V2,3,5,6—TeCP ^6040Figure 2.14 Comparison of Oxidation Rates of Several Chlorophenols.Conditions: mole ratio catalystIchlorophenollhydrogen peroxide II 112001210;catalyst la (FeTDCSPPC1); initial chlorophenol concentration 5.2 mmol/L;pH=2.1, T=23°C; detection by HPLC 270nm.53Oxidation rate depends on the number and position of chlorine substituents.Meso-substitution deactivates the phenol to oxidation. Meso-substituted mono- anddi-chlorophenols are much more slowly oxidized than those not meso-substituted. Reactivityto oxidation in order of decreasing rate is: 2,4-dichlorophenol > 2,4,5-trichlorophenol >2-chlorophenol -= 4-chlorophenol > 3,4-dichlorophenol 2,4,6-trichlorophenol >2,3,4,6-tetrachlorophenol .---, 2,3,5,6-tetrachlorophenol > 3-chlorophenol > 3,5-dichlorophenol--. 2,3,4 ,5 -tetrac hlorophenol.2.2.3 Effect of the Type of OxidantOxidation of 2,4,6-trichlorophenol was monitored by UV/Vis spectroscopy. The product ofthis oxidation is 2,6-dichlorobenzoquinone which has a distinct absorbance at 272 nm and caneasily be monitored during the reaction (Figure 2.15). The type of oxidant has a large effecton the oxidation rate, qualitatively, meta-chloroperoxybenzoic acid » Oxone® (potassiummonoperoxysulfate) >> hydrogen peroxide --=. t-butylhydroperoxide (Figure 2.16).2.2.4 Effect of Catalyst TypeFor the oxidation of 2-chlorophenol, with hydrogen peroxide, at pH 2.1, the iron catalysts laand 2a are more effective than the manganese catalyst 2b. Figure 2.17 compares2-chlorophenol consumption using the three catalysts.1.5Abs 10rbanc 0.5eI^I-294^304^3140234^244^254^I I^I^ I^264^274^284Wavelength nmi^54Figure 2.15 Change in UV Spectrum During Oxidation of 2,4 ,6-Trichlorophenol to2,6-Dichlorobenzoquinone. Catalyst la (FeTDCSPPC1), oxidant hydrogenperoxide, pH=2.1. Measurement interval of 2.0 minutes.55 OxidantmCPBA VOXONEhydrogen peroxide At—butyl hydroperoxide ^50^100^150Time in SecondsFigure 2.16 Oxidation of 2,4,6-7'richlorophenol to Quinone with Different Oxidants.Conditions: catalyst la (FeTDCSPPCI), 5 ilmol1L; initial trichlorophenolconcentration 2.5 rnmollL; oxidant 122 mmollL; pH=4.5; T=22°C; detectionby UV 272nm.catalystMn C18 C1 8 LFe C18 C1 8 ^Fe CIa 0100802006040\t••••560^10^20^30^40Time in MinutesFigure 2.17 Effect of Catalyst Type on Oxidation of 2 -Chlorophenol.Conditions: catalyst, 30 gmol1L; initial chlorophenol concentration 5.9mmol/L; hydrogen peroxide 29.3 mmollL; T=22°C ; detection by HPLC,270nm.572.2.5 Effect of pHFor the hydrogen peroxide oxidation of 2-chlorophenol, with la and 2a as catalysts, the rateof reaction is strongly dependent on solution pH, as can be seen in figures 2.18, and 2.19.In both cases, oxidation is fastest at pH 2.1. Rate decreases at higher pH, although no simpletrend is evident. The mCPBA oxidation of 2,4,6-trichlorophenol with 2b as the catalyst isfastest at pH 4.5, and slower at the other investigated pH values (Figure 2.20). Again, notrend is obvious. Solution pH was adjusted using phosphate buffers.2.2.6 Effect of Generating a QuinoneQuinones are known to be oxidants. Dicyanodichloroquinone (DDQ) is a common mildoxidant in organic chemistry 11241 . To determine if the quinones generated in the reactionthemselves can oxidize the phenol substrates, 2,6-dichloroquinone was added to a solutionof 2,4,6-trichlorophenol and meta-chloroperoxybenzoic acid. As can be seen in figure 2.21,the quinone with the oxidant does not oxidize the trichlorophenol. Upon addition of catalyst(t=8 min), the phenol is quickly oxidized.pH = 9.1 0pH = 6.4 0pH = 4.5 VpH = 2.1 01 00802006040580^10^20^30^40Time in MinutesFigure 2.18 Effect of pH on the Oxidation of 2-Chlorophenol.Conditions: catalyst la (FeTDCSPPC1), 30 gmollL; initial chlorophenolconcentration 5.9 mmol/L; hydrogen peroxide 29.3 mmol/L; T=22°C ; detectionby HPLC 270nm.■•••7■a^pH =pH =pH =pH =4.5 09.1 ^6.4 V2.1 01 00806040200590^10^20^30^40^50Time in MinutesFigure 2.19 Effect of pH on the Oxidation of 2-Chlorophenol.Conditions: catalyst 2a (FeTDCSP-13-Cl8PC1), 30 gmollL; initial chlorophenolconcentration 5.9 mmol/L; hydrogen peroxide 29.3 mmollL; T=22°C; detectionby HPLC, 270nm.Seconds120pH = 2.1pH = 4.5pH = 6.5pH = 9.0pH = 12.560Figure 2.20 Effect of pH on the Oxidation of 2,4,6-Trichlorophenol.Conditions: catalyst 2b (MnTDCSP-(3-C18PCI), 2.5 gmollL; initialchlorophenol concentration 13 mmollL; mCPBA 23 mmollL; T=22°C;detection by UV, 272nm.612. ^0 3^6^9^12Time in MinutesFigure 2.21 Effect of Added Quinone to Oxidation of 2,4,6-Trichlorophenol.Conditions: initial chlorophenol concentration 1.3 mmol1L; mCPBA 2.5mmollL; 2,6-dichlorobenzoquinone (0.1 mmol1L). At t=8 min, catalyst la wasadded (3.0 Wnol/L), and rapid oxidation of trichlorophenol to quinone wasevidenced by increase in UV absorbance. pH=2.1; T=23°C.622.3 Effect of Catalyst on Product DistributionTo determine if the catalyst affects the type of product formed in the oxidation of 2,4,6-trichlorophenol by meta-chloroperoxybenzoic acid, four similar reactions were run, in whichthe catalyst was varied. The four reactions contained; no catalyst (A), iron(III) meso-tetra(3-sulfonatophenyl)porphyrin chloride (B), catalyst la (C), and catalyst 2a (D).The reaction products were analyzed by I-IPLC after 24 hours. Figure 2.22 shows theconversion of 2,4,6-trichlorophenol, 4 = 12.2 min, to 2,6-dichlorobenzoquinone, t = 7.1 min(meta-chloroperoxybenzoic acid and meta-chlorobenzoic acid co-elute at 4 = 6.0 min). In thereactions catalyzed by la and 2a, the conversion to the quinone was 100%. These catalystsgreatly increased the reaction rate; in the un-catalyzed reaction 96% of the 2,4,6-trichlorophenol remained after 24 hours. Although not as effective as the chlorinatedporphyrins la and 2a, sulfonated TPP also increased the reaction rate. 60% of the 2,4,6-trichlorophenol remained after 24 hours.In all cases, oxidation of 2,4,6-trichlorophenol produced only 2,6-dichlorobenzoquinone.1 11.12AM163B 1 UC DFigure 2.22 HPLC of Reaction Mixture of 2,4,6-Trichlorophenol with mCPBA After 24 h.Top trace 220 nm, bottom trace 270 nm. A: no catalyst; B: FeTSPP; C: la(FeTDCSPPC1); D: 2a (FeTDCSP-(3-C18PC1). Conditions: initial phenolconcentration 5.0 mmol/L; mole ratio catalyst/phenol/oxidant II 1150011500;pH=2.1.642.4 Experimental2.4.1 Chemicals and InstrumentationReagent grade chlorophenols and quinones were obtained from Aldrich or Pfalz and Bauerand purified by chromatography when necessary. Metalloporphyrins 1 and 2 were kindlysupplied by T. Wijesekera and D. Dupre. Phosphate buffers were used to control pH.All high performance liquid chromatography was performed using a Waters Gradientcontroller, Waters Model 994 diode array UV detector, with a Waters C-18 microBondapakreverse phase column (30cm x 0.39cm). All chromatography was done at ambienttemperature with a flow rate of 1.0 mL/min. Detection was typically set to 220 nm and 270nm. HPLC solvent conditions: Monochlorophenols; 50% water / 50% acetonitrile / 0.1%TFA. Di- and Trichlorophenols; 45% water / 55% acetonitrile / 0.1% TFA.Tetrachlorophenols; 35% water / 65% acetonitrile/ 0.1% TFA. Pentachlorophenol; 20% water/ 80% acetonitrile / 0.1% TFA.A Hewlett Packard Model 8459 diode array spectrophotometer was used for UV/Visspectrometric studies. Mass spectrometry (electron impact ionization, 150-220°C) wasperformed by Dr. G. Eigendorf and coworkers using a Kratos MS50 (high resolution) or aAEI MS9 (low resolution) spectrometer. NMR spectra were recorded at room temperature,65with TMS internal standard, on a Varian XL 300 spectrometer. Melting points (uncorrected)were determined using a Thomas Model 40 micro hot stage.Preparative TLC was preformed using a Harrison Model 7924T Chromatotron® (rotatingplate) with Merck PF254 silica gel adsorbent.662.42 Oxidation of MonochlorophenolsTypical reaction conditions:A 250 mL round bottom flask was charged with 75 mg (5.8 x 10 -4 mol) 2-chlorophenol, 200mL pH 2.1 phosphate buffer (0.05 M), 1.51 mg la (1.03 x 10 -6 mol), (mole ratiocatalyst/substrate: 1/500).As the mixture was stirred, 120 IA. 30% hydrogen peroxide solution (1.44 x 10 -3 mol) wasadded (mole ratio oxidant/substrate: 2.5/1).The mixture was stirred and monitored by HPLC (Figure 2.23). A brown precipitate wasproduced, which was removed by filtration on a fine glass frit (yield 74 mg, 99%). Reverseand normal phase TLC of the material produced streaks; no individual products could beisolated.Characterization of products:LRMS m/z (rel. int.):^510 (4.8), 508 (8.8), 506 (6.9), 384 (27.4), 382 (83.8), 380(85.6), 256 (43.6), 254 (69.3)67I^ IINItrt-I01.4wI4-41-L1I44Figure 2.23 HPLC Traces of 2-Chlorophenol (4=6.1 min) Oxidation Products.A: t=0, B: t=2 hrs. Reaction conditions described in section Oxidation of 2,4-DichlorophenolTypical reaction conditions:A 500 mL round bottom flask was charged with 94 mg (5.7 x 10' mol) 2,4-dichlorophenol,200 mL pH 2.1 phosphate buffer (0.05 M), 1.34 mg la (1.03 x 10 -6 mol), (mole ratiocatalyst/substrate: 1/550).As the mixture was stirred, 120 .tL 30% hydrogen peroxide solution (1.44 x 10' mol) wasadded (mole ratio oxidant/substrate: 2.5/1).The reaction was monitored by UV. When the absorbance at 260 nm no longer increased(about two hours), the reaction mixture was extracted four times with dichloromethane. Theorganic phase was dried over anhydrous magnesium sulfate, filtered, and evaporated todryness to yield 86 mg (91%) of a yellow viscous oil. Analysis by TLC and HPLC (Figure2.24) showed that the product was a mixture of at least eight compounds. The mixture wasseparated by Chromatotron® chromatography.69Characterization of products:2-chloro-1,4-benzoquinone:'H-NMR (acetone-d6) 5:^6.82 (dd, 1H, Jab = 10.2 Hz, J., = 2.4, H.); 6.93 (d, 1H, J b. =10.2 Hz, Hb); 7.02 (d, 1H, J,. = 2.4 Hz, H e)LRMS m/z (rel. int.):^144 (35.6), 142 (100.0), (Mt); 116 (27.6), 114 (66.2), (M+ -CO)HRMS:^Calculated for C6H335C1: 141.9822. Found: 141.9831.Melting point:^Found: 55-6°C, reportedi 1251 : 57°C.Yield:^15%702-(2,4-dichlorophenoxy)-6-chloro-1,4-benzoquinone 1591 :'H-NMR (acetone-d6) 8:^5.83 (d, 1H, Jab = 1.8 Hz, Ha); 7.11 (d, 1H, Jbe = 1.8 Hz HO;7.44 (d, 1H, Jed = 9.0 Hz, He); 7.54 (dd, 1H, Jcic = 9.0 Hz, Jae =2.4 Hz, Hd), 7.72 (d, 1H, Jed = 2.4 Hz, He)LRMS m/z (rel. int.): 308 (3.7), 306 (16.6), 304 (32.3), 302 (23.4), (Mt); 271 (1.7),269 (65.8), 267 (100), (M+ - Cl); 243 (3.8), 241 (23.0), 239(35.6), (M+ - Cl - CO)HRMS: Calculated for C12H535C1303 : 301.9304. Found: 301.9280.Yield: 10%712-(3-chloro-cyclohexa-3,6-diene-2,5-dione)-4,6-dichlorophenoln 261 :Cl^O He 11.• 0Cl^ Cl1H-NMR (acetone-d6) 8:^7.00 (d, 1H, J ab = 2.4 Hz, H.); 7.23 (d, 1H, Jb, = 2.4 Hz, Hb);7.28 (d, 1H, 44 = 2.4 Hz, lib); 7.55 (d, 1H, J cic = 2.4 Hz, Ha);8.9 (br, s, 1H, He)LRMS m/z (rel. int.):^308 (11.2), 306 (31.6), 304 (39.7), (Mt)HRMS:^Calculated for C12H5350303 : 301.9304. Found: 301.9297.Yield:^9%722-(3-chlorocyclohexa-3,6-diene-2,5-dione)-6-chloro-1,4-benzoquinone:(chloroquinonedimer)11271 :CI11-1-NMR (acetone -d6) 5:^7.27 (d, 1H, Jab = 2.1 Hz, Ha); 7.49 (d, 1H, Jba = 2.1 Hz, Hb)LRMS m/z (rel. int.):^286 (12.6), 284 (57.3), 282 (82.2), (Mt); 258 (1.2), 256 (6.6),254 (9.9), (W - CO)HRMS:^Calculated for C 12H435C1204 : 281.9487. Found: 281.9480.Yield:^8%732-(2,4-dichlorophenoxy)-4,6-dichlorophenol:LRMS tn/z (rel. int.):2,4-dichlorophenol trimer:LRMS m/z (rel. int.):328 (10.1), 326 (47.6), 324 (100.0),488 (3.5), 486 (7.8), 484 (9.3), 482(2.8), 446 (1.1), (W - Cl)322(4.8),(76.6), (Mt)(W); 450 (2.1), 4482U 74N2IUFigure 2.24 HPLC Traces of 2,4-Dichlorophenol (4=82 min) Oxidation Products.A: t=0, B: t=3 hrs. Reaction conditions described in section Oxidation of 2,4,5-TrichlorophenolTypical reaction conditions:A 500 mL round bottom flask was charged with 150 mg (7.6 x 10 -4 mol)2,4,5-trichlorophenol, 200 mL pH 2.1 phosphate buffer (0.05 M), 15 mL acetonitrile, 2.0 mg(1.53 x 10 -6 mol) la, (mole ratio catalyst/substrate: 1/500).As the mixture was stirred, 1.50 mL 3% hydrogen peroxide solution (1.55 x 10 -3 mol) wasadded (mole ratio oxidant/substrate: 2.1/1).After two hours, the reaction mixture was extracted four times with dichloromethane. Theorganic phase was dried over anhydrous magnesium sulfate, filtered and evaporated todryness to yield 145 mg (97%) of a yellow viscous oil. Analysis by TLC and HPLC (Figure2.25) showed that the product was a mixture of at least seven compounds. The mixture wasseparated by Chromatotron® chromatography.76Characterization of products:2,5-dickloro-1,4-benzoquinone:'H-NMR (acetone-d6) 8:^7.32 (s)LRMS m/z (rel. int.):^180 (12.5), 178 (65.7), 176 (88.6), (Mt); 152 (5.4), 150 (29.6),148 (46.8) (W - CO)HRMS:^Calculated for C6H235C12: 175.9432. Found: 175.9440.Melting point:^Found: 158-160°C, reportedU 28] : 161-2°CYield:^16%ClClHbO Cl772-(2,4,5-trichlorophenoxy)-3,6-dichloro-1,4-benzoquinone 11291 :Cl^Cl'H-NMR (acetone-d6) 8:^6.32 (s, 1H, H,); 7.69 (s, 1H, H b); 7.94 (s, 1H, He)LRMS m/z (rel. int.):^376 (3.6), 374 (9.7), 372 (14.8), 370 (9.8), (M1 ); 341 (11.2),339 (48.6), 337 (100), 335 (78.9) OW - C1); 311 (16.6), 309(33.3), 307 (27.7) (M+ - Cl - CO)HRMS:^Calculated for C12H335C1503 : 369.8525. Found: 369.8542.78I II^NIFigure 2.25 HPLC Traces of 2,4,5-Trichlorophenol (4=14.9 min) Oxidation Products.A: t=0, B: t=3 hrs. Reaction conditions described in section Oxidation of 2,4,6-trichlorophenolTypical reaction conditions:A 500 mL round bottom flask was charged with 500 mg (2.53 x 10 3 mol)2,4,6-trichlorophenol, 200 mL pH 2.1 phosphate buffer (0.05 M), 50 mL acetonitrile, 6.7 mg(5.13 x 10.6 mol) la, (mole ratio catalyst/substrate: 1/500), 650 mg (3.76 x 10 -3 mol) mCPBA(mole ratio oxidant/substrate: 1.5/1).The reaction was monitored by UV at 272 nm. When the absorbance at 272 nm no longerincreased (about two hours), the reaction mixture was extracted four times withdichloromethane. The organic phase was dried over anhydrous magnesium sulfate, filteredand evaporated to dryness to yield 420 mg (94%) of a bright yellow solid. Analysis by TLCand HPLC (Figure 2.22) showed that the product was a single compound. The material wasrecrystallized from acetone/water (3/1).Characterization of products:2,6-dichloro-1,4-benzoquinone:80CI'H-NMR (acetone-d6) 8:^7.21 (s)LRMS ink (rel. int.):^180 (6.2), 178 (28.7), 176 (41.3), (NV); 152 (0.8), 150 (6.3),148 (10.0), (M+ - CO)HRMS:^Calculated for C6H235C12 : 175.9432. Found: 175.9430.Melting point:^Found: 119-120°C, reported 11253 : 120-1°CYield:^94%81Tetrachlorodiphenoquinone:Cl^ClCl^ ClLRMS m/z (rel. int.):^324 (9.1), 322 (32.8), 320 (52.6), 318 (28.0), (W); 287 (4.3),285 (16.2), 283 (21.0), (MI - - Cl)822.4.6 Oxidation of 2,3,5,6-tetrachlorophenolTypical reaction conditions:A 250 mL flask was charged with 100 mg (4.31 x 104 mol) 2,4,5,6-tetrachlorophenol, 75 mLpH 2.1 phosphate buffer, 75 mL acetonitrile, 1.13 mg (8.62 x 10' mol) la, (molescatalyst/moles substrate: 1/500), 1.20 mL (1.06 x 10 -3 mol) 3% hydrogen peroxide solution(mole ratio oxidant/substrate: 2.5/1).After two hours, the reaction mixture was extracted four times with dichloromethane. Theorganic phase was dried over anhydrous magnesium sulfate, filtered and evaporated todryness to yield 96 mg (96%) of a yellow solid. Analysis by TLC and HPLC (Figure 2.26)showed that the product was a mixture of two main compounds. The mixture was separatedby Chromatotron® chromatography.83Characterization of products:4-(2,3,5,6-tetrachlorophenoxy)-2,3,5,6-tetrachlorophenol:H 0LRMS m/z (rel. int.):^468 (2.2), 467 (4.0), 466 (12.9), 465 (8.4), 464 (22.8), 463(10.4), 462 (45.7), 461 (9.3), 460 (38.1), 459 (3.6), 458 (13.2),(W)HRMS:^Calculated for C i2H335C1503 : 457.7562. Found: 457.7571.ClYield:^10%H 0 OHCl Cl^Cl^Cl4,4'-dihydroxyoctachlorobiphenyl:LRMS m/z (rel. int.):^466 (0.4), 464 (3.2), 462 (6.2), 460 (4.1), 458 (1.6), (W)HRMS:^Calculated for C 121-1235C1802 : 457.7562. Found: 457.7568.Melting Point:^Found: 230-235°C, reported 11301 : 235-238°CYield:^11%84tl 10,nr85Figure 2.26 HPLC Traces of 2,3,5,6-Tetrachlorophenol (t r=6.1 min) Oxidation Products.A: t=0, B: t=4 hrs. Reaction conditions described in section DISCUSSION3.1 Discussion of Results of Oxidation Product AnalysisThe products of chlorophenol oxidations are phenoxy radical coupling products or quinones.Coupling, followed by subsequent oxidation, generates phenol-quinone dimers orquinone-quinone dimers.Analyzing the products of the oxidation reactions aids in evaluating the potential use, andlimitations, of this technique for remediation of chlorophenol pollution.The efficient conversion of 2- and 4-chlorophenol to a water insoluble material which can beremoved by filtration is a potentially useful characteristic of the catalyzed oxidation reactions.Removing the chlorophenols by polymerization and filtration would isolate and concentratethis waste which could then be subsequently treated by a second technique for ultimatedestruction. Incineration may work as a secondary process as well as biological treatment,although there is some evidence which suggests that polymeric substrates are less availableto microorganisms and thus less biodegradable.Chlorophenols other than monochlorophenols are converted to dimers and oxidized dimers.Some of the products are partially water soluble which would make removal from water more87difficult than simply filtering. However, it has been shown that partially oxidizedchlorophenol mixtures are more readily biodegradable than the chlorophenols themselves 1331 .It is relevant to note that quinones are known intermediates in chlorophenol metabolism bysome bacteria and fungi. Oxidative treatment of these chlorophenols may be useful as awaste pretreatment, making biological treatment more effective.The possibility that these new products could be more environmentally damaging than thestarting chlorophenols cannot be discounted. The product from 2,4,6-trichlorophenoloxidation, 2,6-dichlorobenzoquinone, has been demonstrated to cleave DNA'''. Chlorinatedhydroxybiphenyls (one product of the coupling reactions) are thought to be one of the initialproducts of PCB metabolism, and are implicated in chick embryo toxicity' 116] .These porphyrin catalyzed oxidations cannot be considered to be an accurate mimic ofbiological metabolic processes which are complex and involve many enzyme systems.However, some of the oxidation products are the same as those of some microbialtransformations of chlorophenols. P. chrysosporium was found to produce chloroquinone and2,6-dichloroquinone as metabolites of 2,4-dichlorophenol and 2,4,6-trichlorophenol,respectively'''. Rhodococcus bacteria generate quinones as an initial step in chlorophenolmetabolism.883.2 Discussion of Kinetic Results3.2.1 Effect of pHIron porphyrins la and 2a catalyzed chlorophenol oxidation most effectively at pH 2. Thisobservation is in agreement with results obtained by other researchers examining the kineticsof water soluble iron porphyrin (tetra(2,6-dimethyl-3-sulfantophenyl)porphyrin) catalysis ofhydrogen peroxide oxidation of 2,2'-azinobis(3-ethylbenzthiazolinsulfonic acid) (ABTS) 1883 .This observation can been rationalized by considering several related factors.Hydrogen peroxide can compete with chlorophenol as a substrate for the oxidizedmetalloporphyrin. As pH increases, hydrogen peroxide oxidation ("catalase-type" reaction)(reaction 4) is favored over substrate oxidation ("peroxidase-type" reaction) (reaction 5).Other researchers found that the yield of oxidized substrate (ABTS") was 100% at pH 1 anddropped rapidly to less than 20% at pH 8, with a concomitant increase in production ofoxygen [88.117] .Porph' Felv0 + H202 —÷ Porph Fe rn + H2O + 02^(4)Porph' Fe"'O + 2 PhOH --> Porph Fe rn + 2 PhOH"^(5)89Researchers studying the formation of ferryl porphyrins (iron porphyrins oxidized by only oneelectron) found that these compounds are more readily formed at higher pH valuesf 97J . It isknown that, in contrast to the species oxidized by two electrons, the species oxidized by oneelectron is not a good substrate oxidant 11181 .Thus one may expect higher pH to disfavour phenol oxidation when considering theporphyrin behavior. However, considering the phenol substrate, one may expect higher pHto favour oxidation. The deprotonated chlorophenoxy anion, having higher electron density,would be expected to be more readily oxidized than the corresponding phenol. Withporphyrin catalyzed oxidations, higher pH does not favour chlorophenol oxidation. It isprobable that the effect of pH on metalloporphyrin chemistry (lower pH is more favourable)is the overriding factor in the overall oxidation rate.3.2.2 Effect of the Coordinated MetalAt low pH, the iron catalysts la and 2a are more effective than the manganese porphyrin 2b.Two factors may account for this observation.Manganese porphyrins are known to have a higher oxidation potential than the correspondingiron porphyrinst 1013191 . Slower conversion of the manganese porphyrin to the activatedoxidized species could explain slower substrate oxidation.90Secondly, as with iron porphyrins the manganese porphyrin can catalyze hydrogen peroxidedecomposition. The relationship between pH and the "catalase-type" versus "peroxidase-type"reactions of manganese porphyrins is opposite to that of the iron porphyrins. That ishydrogen peroxide oxidation is favoured over substrate oxidation at lower pH values [1191 . Thisalso may contribute to the observed slower chlorophenol oxidation for the manganeseporphyrin 2b compared to iron porphyrins la and 2a.3.2.3 Effect of the Oxidant TypeIn the general reaction of metalloporphyrin oxidation by a peroxide oxidant, ROOH, RO - canbe considered to be a leaving group (reaction 6).Porph Feu + ROOH —* Porph' Fe"O + RO -^(6)Reaction of metalloporphyrins with ROOH is therefore facilitated by electron withdrawingR groups. That is, the rate increases with decreasing pK a of R011 [120,121]. For the peroxidesused in this study, ROH pK„ values increase mCBA < KSO 4H < H2O < t-BuOH whichcorresponds with the observed relative oxidation rates, mCPBA > KSO 4OH (Oxone®) > H202> t-BuOOH.913.2.4 Effect of Chlorophenol StructureIn this study, the relative rates of chiorophenol oxidation were determined to be, in order ofdecreasing rate: 2,4-dichlorophenol > 2,4,5-trichlorophenol > 2-chlorophenol - ... 4-chiorophenol > 3,4-dichlorophenol ,---. 2,4,6-trichlorophenol > 2,3,4,6-tetrachlorophenol2,3,5,6-tetrachlorophenol > 3-chiorophenol > 3,5-dichlorophenol .-- 2,3,4,5-tetrachlorophenol.The most notable feature of the relative chlorophenol oxidation rates obtained in this studyis the inhibiting effect of meso-chlorines. The electron withdrawing chlorine would beexpected to deactivate the phenol to oxidation in general. ortho- and para-chlorines couldcontribute to phenoxy radical stabilization through resonance, thus moderating theirdeactivation compared to meso-chlorines.A quantitative relationship between structure and relative oxidation rate was not determined.The rates do not correlate with Hammet substituent constants.It is interesting to compare the relative chlorophenol oxidation rates obtained here, with theirrelative toxicity to bacteria. Researchers measured the effective inhibition of 19 chiorophenolconegers on the growth rate of an aerobic bacteria culture [1223 . The rate is expressed as IC 50;the effective chlorophenol concentration causing 50% growth inhibition of the bacteria. Thereare some similarities between chlorophenol oxidation by metalloporphyrin and chiorophenolinhibition of bacterial growth. For example 2,3,4,5-tetrachlorophenol (IC 50=0.030 mmol/L)inhibits bacterial growth much more than 2,3,4,6-tetrachlorophenol (IC 50=0.354 mmol/L) or922,3,5,6-tetrachlorophenol (IC50=0.319 mmol/L). Also 3,5-dichlorophenol (IC 50=0.80) mmol/L)is one of the most toxic of the tested chlorophenols. This parallels the observation that2,3,4,5-tetrachlorophenol and 3,5-dichlorophenol were the most resistant to oxidation in thestudy presented here.Developing methods for assessing potential impact on organisms and the environment of avast array of chemicals of concern is an important pursuit. The use of a simple chemicaloxidation could be a relevant part of an assay to evaluate the potential toxicity of particularsubstates to aerobic organisms. Much more research would be required to evaluate thispossibility.933.3 Conclusions and Suggestions for Further StudiesThese studies demonstrate that the use of metalloporphyrins for the catalyzed oxidation ofchlorophenols is, in principle, a useful technique for the remediation of aqueous chlorophenolwaste.To further evaluate the catalysts for industrial applications, future studies should involveoxidation of more complex chlorophenol containing wastes. Chemical characterization of thewaste and oxidation products may be too tedious, but an investigation of the effect of thistype of oxidation on the toxicity of the waste would be interesting.The products from the oxidation of chlorophenols are not necessarily more benign, but thistreatment may make the waste more treatable by other methods. The use of this techniqueas one part of a multiple step treatment of waste could be assessed. For example, oxidationfollowed by microbial treatment may be more effective than microbial treatment alone.The chlorinated metalloporphyrins have recently been immobilized onto water insoluble silicasupports11231 . Preliminary work suggests that the supported catalysts retain their catalyticactivity. The fixed catalysts may have significant advantages over homogeneous catalysts.Solid phase catalysts are easier to remove from reaction mixtures and immobilization mightextend catalyst lifetime. In terms of practical application, immobilized catalysts may facilitatedesign of a flow through bed type reactor. The uses and chemistry of these supported94catalysts should be studied.It has been suggested that dioxins are produced during horseradish peroxidase oxidation ofchlorophenolsi623 . The formation of dioxins by porphyrin oxidation was not evaluated in thisstudy but, due to the toxicity of dioxins, this possibility would be an important concern forapplication of this technique.As with all other potential methods of pollution remediation, this method has disadvantages.Of primary concern is the cost of the metalloporphyrin catalysts. Research towards cheapersynthesis of these metalloporphyrins is recommended. Use of oxygen or air as the oxidantrather than the more costly hydrogen peroxide would be a relevant investigation.95REFERENCES1) Schecter, A.; Dekin, A.; Weerasinghe, N.C.A.; Arghestani S.; Gross, M.Chemosphere, 1988, 17(4), 627-631.2) Hites, R.A. Acc. Chem. Res., 1990, 23, 194-201.3) Czuczwa, J.M.; McVeety, B.D.; Hites, R.A. Science, 1984, 226, 568-569.4) Chlorophenols other than pentachlorophenol,World Health OrganizationGeneva, 1989.5) Jones, P.A. Chlorophenols and their impurities in the Canadian environment:1983 Supplement (Environment Canada Report No. EPS-3-EP-84-3), 1984.6) Knuutinen, J.; Palm, H.; Hakala, H.; Haimi, J.; Huhta, V.; Salminen, J.Chemosphere, 1990, 20(6), 609-623.7) Kitunen, V.H.; Valo, R.A.; Salkinoja-Salonen, M.S. Environ. Sci. Technol.,1987, 21(1), 96-101.8) Humppi, T.; Knuutin, J.; Paasivirta, J. Chemosphere, 1984, 13(11), 1235-1241.9) Valo, R.A.; Kitunen, V.H.; Raisanen, S. Chemosphere, 1984, 13(8), 835-844.10) Goerlitz, D.F.; Troutman, D.E.; Godsy, E.M.; Franks, B.J. Environ. Sci.Technol., 1985, 19(10), 955-961.9611) Kitunen, V.H.; Valo, R.A.; Salkinoja-Salonen, M.S.Int. J. Environ. Anal. Chem., 1985, 20, 13-28.12) Krahn, P.K.; Shrimpton, J.A.; Glue, R.D. Environment Canada, Pacific andYukon Region, Regional Summary Report 87-15, 1987.13) Gibson, S.A.; Sulfita, J.M. Appl. Environ. Microbiol., 1986, 52(4), 681-688.14) Larson, R.A.; Rockwell, A.L. Environ. Sci. Technol., 1979, 13(3), 325-329.15) Keith, L.A.; Telliard, W.A. Env. Sci. Technol., 1979, 13(4), 416-423.16) Kringstad, K.P.; Lindstrom, K. Environ. Sci Technol., 1984, 18(8),236A-248A.17) Paasivirta, J.; Knuutinen, J.; Knuutila, M.; Maatela, P.; Pastinen, O.; Virkki,L.; Paukku, R.; Herve, S. Chemosphere, 1988, 17(1), 147-158.18) "Forest Industry Wastewaters" in Wat. Sci. Technol., 1988, 20(2), Sodergren,A.; Wartiovaara, J., Editors.19) "Forest Industry Wastewaters" in Wat. Sci. Technol., 1991, 24(3/4), Puhakka,J.; Rintala, J.; Wartiovaara, J.; Heinonen, P., Editors.20) Bellin, C.A.; O'Connor, G.A.; Jin, Y. J. Environ. Qual., 1990, 19, 603-608.21)^Wylie, G.D.; Finger, S.E.; Crawford, R.W. Environ. Pollut., 1990, 64, 43-53.9722) Valo, R.A.; Kitunen, V.H.; Salkinoja-Salonen, M.S.; Raisanen, S.Wat. Sci. Technol., 1985, 17, 1381-1384.23) Colodey, A. Environment Canada, Pacific and Yukon Region, RegionalSummary Report 86-18, 1986.24) Miyazaki, T.; Kaneko, S.; Horii, S.; Yamagishi, T. Bull. Environ. Contamin.Toxicol., 1981, 26, 577-584.25) Gilbert, F.I.; Minn, C.E; Duncan, R.C.; Wilkinson, J. Arch. Environ. Contam.Toxicol., 1990, 19, 603-609.26) Some halgenated hydrocabons: IARC Monographs on the Evaluation of theCarcinogenicity Risk of Chemicals to Humans, Vol. 20, 1979, 349-367.27) Hattula, M.L.; Wasenius, V.M.; Reunanen, H.; Artsila, A.U. Bull. Environ.Contamin. Toxicol., 1981, 26, 295-298.28) Phipps, G.L.; Holcombe, G.W.; Fiandt, J.T. Bull. Environ. Contamin. Toxicol.,1981, 26, 585-593.29) Beltrame, P.; Beltrame, P.L.; Carniti, P. Chemosphere, 1984, 13(1), 3-9.30) Lui, D.; Thompson, K.; Kaiser, K.L.E. Bull. Environ. Contamin. Toxicol.,1982, 29, 130-136.31) Ballschmiter, K.; Bruanmiller, I.; Niemczyk, R.; S werev, M. Chemosphere,1988, 17(5), 995-1005.9832) Choudhry, G.G.; Van Den Broecke, J.A.; Hutzinger, 0. Chemosphere, 1983,12(4), 487-492.33) Bowers, A.R.; Gaddipati, P.; Eckenfelder, W.W.; Monsen, R.M., Wat. Sci.Technol., 1989, 21, 477-486.34) Staps, S. Chem. Industry, 1989, 18.35) Boyle, M. Environ. Qual., 1989, 18(4), 395-402.36) Golovleva, L.A.; Aharonson, N.; Greenhalgh, R.; Sethunathan, N.; Vonk, J.W.Pure and Appl. Chem., 1990, 62(2), 351-364.37) Barbeni, M.; Minero, C.; Pelizzetti, E.; Borgarello, E.; Serpone, N.Chemosphere, 1987, 2225-2237.38) Microbial Degradation of Xenobiotics and Recalcitrant Compounds, Eds.Leisinger, T.; Hutter, R.; Cook, A.M.; Nuesch, J., Academic Press, 1980.39) Schmidt, E.; Hellwig, M.; Knackmuss, H. Appl. Environ. Microbiol., 1983,46(5), 1038 - 1044.40) Boyd, S.A.; Shelton, D.R. Appl. Environ. Microbiol., 1984, 47(2), 272-277.41) Boyd, S.A.; Shelton, D.R.; Berry, D.; Tiedje, J.M. Appl. Environ. Microbiol.,1983, 46(1), 50-54.42)^Sharak Genthner, B.R.; Price, W.A.; Pritchard, P.H. Appl. Eniron. Microbiol.,1989, 55(6), 1466-1471.9943) Kohring, G-W; Rogers, J.E.; Wiegel, J. Appl. Environ. Microbiol., 1989, 55(2),348-353.44) Gibson, S.A.; Sulfita, J.M. Appl. Environ. Microbiol., 1990, 56(6), 1825-1832.45) Mueller, J.G.; Lantz, S.E.; Blattman, B.O.; Chapman, P.J. Environ. Sci.Technol., 1991, 25, 1045-1055.46) Valo, R.A.; Salkinoja-Salonen, M.S. Appl. Microbiol. Biotechnol., 1986,25(68), 68-75.47) O'Reilly, K.T.; Crawford, R.L. Appl. Environ. Microbiol., 1989, 55(9),2113-2118.48) Topp, E.; Hanson, R.S. Appl. Environ. Microbiol., 1990, 56(2), 541-544.49) Steiert, J.G.; Pigatello, J.J.; Crawford, R.L. Appl. Environ. Microbiol., 1987,53(5), 907-910.50) Haggblom, M.M.; Apajalahti, J.H.A.; Salkinoja-Salonen, M.S. Appl. Environ.Microbiol., 1988, 54(7), 1818-1824.51) Bumpus, J.A.; Aust, S.D. BioEssays, 1987, 6(4), 166-170.52) Lamar R.T.; Glaser, J.A.; Kirk, T.K. Soil Biol. Biochem., 1990, 22(4), 433-440.53)^Guo H.; Chang, H.M.; Glaser, J.A., in Biotechnology in Pulp and PaperManufacture, Eds. Kirk, T.K.; Chang H.M., Butterworth-Heinemann, 1990.10054) Haggblom, M.M.; Noynek L.J.; Salkinoja-Salonen, M.S. Appl. Environ.Microbiol., 1988, 54(12), 3043-3052.55) Forss, K.; Johnson, K.; Savolainen, M.; Williamson, H. Paperi ja Puu - Paperand Timber, 1989, 10, 1108-1112.56) Dec, J.; Bollag, J.M. Arch. Env. Contam. Toxicol., 1990, 19, 543-550.57) Bollag, J.M.; Shuttleworth, K.L.; Anderson, D.H. Appl. Environ. Mlcrobiol.,1988, 54(12), 3086-3091.58) Ruggiero, P.; Sarkar, J.M.; Bollag, J.M. Soil Sci., 1989, 147(5), 361-370.59) Hammel, K.E.; Tardone, P.J. Biochem., 1988, 27(17), 6563-6568.60) Hammel, K.E.; Kalyanaraman, B.; Kirk, T.K. in Lignin Enzymatic andMicrobial Degradation, INRA colloquium no.40, Paris, 1987.61) Valli, K.; Gold, M.H. J. Bacteriol., 1991, 173(1), 345-352.62) Oberg, L.G.; Swanson, S.E.; Rappe, C.; Paul, K.G. Arch. Environ. Contam.Toxicol., 1990, 19, 930-938.63) Milnes, M.H. Nature, 1971, 232, 395-396.64) Daley, P.S. Environ. Sci. Technol., 1989, 23(8), 912-916.65) Boyd, S.A.; Mortland, M.M. Environ. Sci. Technol., 1986, 20, 1056-1058.10166) Xu, Y.M.; Menassa, P.E.; Langford, C.H. Chemosphere, 1988, 17(10), 1971-1976.67) Degradation of Chemical Carcinogens, Slein, M.W.; Samsone, E.B., VanNostrand Reinhold Company, 1980.68) Xu, Y.M.; Menassa, P.E.; Langford, C.H. Chemosphere, 1988, 17(10), 1971-1976.69) Oxidative Coupling of Phenols, Eds. Taylor, W.I.; Battersby, A.R., MarcelDekker, Inc, 1967.70) McDonald, P.D.; Hamilton, G.A., in Oxidation in Organic Chemistry, Ed.Trahanovsky, W.S. Academic Press, 1973, 97.71) Musso, H. Angew. Chem., 1963, 75, 965-984.72) Altwicker, E.R. Chem. Rev., 1967, 67(5), 475-531.73) Stone, T.J; Waters, W.A. J. Chem. Soc., 1964, 213.74) Ouellette, R.J., in Oxidation in Organic Chemistry, Ed. Trahanovsky, W.S.Academic Press, 1973, 135.75) Zimmer, H.; Lankin, D.C.; Horgan, S.W. Chem. Rev., 1971, 71(2), 229-237.76)^Fuhrhop, J.H. Angew. Chem. Int. Ed., 1974, 13(5), 321-355.10277) Dolphin, D.; Muljiani, Z.; Rousseau, K.; Borg, D.C.; Fajer, J.; Felton, R.H.Ann. N.Y. Acad. Sci., 1973, 206, 177-200.78) Fajer, J.; Borg, D.C.; Forman, A.; Felton, R.H.; Vegh, L.; Dolphin, D. Ann.N.Y. Acad. Sci., 1973, 206, 349-364.79) The Porphyrins, Volume 7, Ed. Dolphin, D., Academic Press, 1979.80) Scheidt, W.R.; Reed, C.A. Chem. Rev., 1981, 81, 543-555.81) Traylor, T.G. Acc. Chem. Res., 1981, 14, 102-109.82) Guengerich, F.P.; Macdonald, T.L. Acc. Chem. Res., 1984, 17, 9-16.83) Gunter, M.J.; Turner, P. Coord. Chem. Rev., 1991, 108, 115-161.84) Traylor, P.S.; Dolphin D.; Traylor, T.G. J. Chem. Soc. Chem. Comm., 1984,279-278.85) Groves, J.T.; Nemo, T.E. J. Amer. Chem. Soc., 1983, 105, 5786.86) Chin, D.H.; Lamar, G.N.; Balch, A.L. J. Amer. Chem. Soc., 1980, 102, 4344-4350.87) Tsuchiya, S. J. Chem. Soc., Chem. Commun., 1991, 716-718.88) Zipplies, M.F.; Lee, W.A.; Bruice, T.C. J. Amer. Chem. Soc., 1986, 108, 4433-4445.10389) McMurry, T.J.; Groves, J.T., in Cytochrome P-450, Ed. Ortiz de Montenallo,P.R., Plenum Press, 1986.90) Groves, J.T.; Haushalter, R.C.; Nakamura, M.; Nemo, T.E.; Evans, B.J. J.Amer. Chem. Soc., 1981, 103, 2884.91) Latos-Grazinski, L.; Cheng, R.J.; LaMar, G.N.; Balch, A.L. J. Amer. Chem.Soc., 1982, 104, 5992-6000.92) Mashiko, T.; Dolphin, D.; Nakano, T.; Traylor, T.G. J. Amer. Chem. Soc.,1985, 107, 3735-3739.93) Traylor, T.G.; Tsuchiya, S. Inorg. Chem., 1987, 26, 1338-1339.94) Wijesekera, T,; Matsumoto, A.; Dolphin, D.; Lexa, D. Angew. Chem. Int. Ed.Engl., 1990, 29(9), 1028-1030.95) Nakano, T.; Wijesekera, T.P.; Dolphin, D.; Maione, T.E.; Kirk, T.K.; Farrel,R.L. US patent 4,892,241, 1989.96) Tsuchiya, S. J. Chem. Soc., Chem. Commun., 1991, 716-718.97) Bell, S.E.J.; Cooke, P.R.; Leanord, D.R.; Lindsay Smith, J.R.; Robbins, A. J.Chem. Soc. Perkin Trans. 2, 1991, 549-559.98) Sugimoto, H.; Tung, H.C.; Sawyer, D.T. J. Amer. Chem. Soc., 1988, 110,2465.10499) Traylor, T.G.; Fann, T.C.; Bandtopadhyay, D.J. J. Amer. Chem. Soc., 1989,111, 8009.100) Traylor, T.G.; Ciccone, J.P. J. Amer. Chem. Soc., 1989, 111, 8413.101) Bruice, T.C. Acc. Chem. Res., 1991, 24, 243-249.102) Pannicucci, R.; Bruice, T.C. J. Amer. Chem. Soc., 1990, 112, 6063-6071.103) Gopinath, E.; Bruice, T.C. J. Amer. Chem. Soc., 1991, 113, 6090-6094.104) He, G.; Bruice, T.C. J. Amer. Chem. Soc., 1991, 113, 2747-2753.105) Renaud, J.P.; Battioni, P.; Bartoli, J.F.; Mansuy, D. J. Chem. Soc. Chem.Comm., 1985, 888-889.106) Rocha Gonsalves, A.M.; Johnstone, R.A.W.; Pereira, M.M.; Shaw, J. J. Chem.Soc. Perkin Trans. 1, 1991, 645-649.107) Lyons, J.E.; Ellis, P.E. Catal. Lett., 1991, 8, 45-52.108) Ellis, P.E.; Lyons, J.E. Catal. Lett., 1989, 3, 389-398.109) Carrier. M.N.; Scheer, C.; Gouvine, P.; Bartoli, J.F.; Battioni, P.; Mansuy, D.Tetrahedron Lett., 1990, 31(46), 6645-6648.110) Watanabe, Y.; Takehira, K.; Shimizu, M.; Hayakawa, T.; Orita, H. J. Chem.Soc. Chem. Comm., 1990, 927-928.105Artaud, I.; Aziza, K.B.; Chopard, C.; Mansuy, D. J. Chem. Soc. Chem. Comm.,1991, 31-33.112) Cui, F.; Dolphin, D. Holzforschung, 1991, 45(1), 31-35.113) Cui, F. PhD Thesis, University of British Columbia, 1990.114) Skerker, P.S.; Farrell, R.L.; Dolphin, D.; Cui, F.; Wijesekera, T.P., inBiotechnology in Pulp and Paper Manufacture, Eds. Kirk, T.K.; Chang H.M.,Butterworth-Heinemann, 1990.115) Juhl, U.; Blum, K.; Witte, I. Chem-Biol. Interactions, 1989, 69, 333-344.116) Wehler, E.K.; Brunstrom, B.; Rannug, U.; Bergman, A. Chem-Biol.Interactions, 1990, 73, 121-132.117) Panicucci, R.; Bruice, T.C. J. Amer. Chem. Soc., 1990, 112, 6063-6070.118) Hening, H.; Renorek, D. Pure and Appl. Chem., 1990, 62, 1489.119) Balasubramanian, P.L.; Schmidt, E.S.; Bruice, T.C. J. Amer. Chem. Soc., 1987,109, 7865-7873.120) Yuan, L.C.; Bruice, T.C. J. Amer. Chem. Soc., 1985, 107, 512-516.121) Bruice, T.C.; Balasubramanian, P.L.; Lee, R.W.; Smith, J.R.L. J. Amer. Chem.Soc., 1988, 110, 7890-7895.106122) Beltrame, P.; Beltrame, P.L.; Carniti, P.; Guardione, D.; Lanzetta, C. Biotech.Bioeng., 1988, 31, 821-828.123) BrUckner, C. Diplomarbeit, Institute of Technology, Aachen, FRG, 1991.124) March, J. Advanced Organic Chemistry, 3rd Ed., J. Wiley, 1985.125) Handbook of Chemistry and Physics, 69th Ed., Chemical Rubber Pub. Co.,1988/1989.126) Bollag, J.M. J. Agric. Food Chem., 1981, 29(2), 250-253.127) Posternak, T.; Alcalay, R. Hely. Chim. Acta., 1948, 31, 525-535.128) Kohn, M.; Gurwitsch, E. Monatsh., 1930, 56, 135-136.129) Buchan J. J. Chem. Soc. Perkin Trans. I, 1975, 21, 2185-2189.130)^Smith, D. US Pat 2,449,088, 1948.


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