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The rearrangement of phenylacetyl chloramine to para-chloracetanilide in a magnetic field Gray, Kenneth Russel 1931

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The Condensation of Furfural and Urea. by Kenneth Rüssel Gray, B.A. A Thesis submitted for the Degree of Master of Arts in the Department of Chemistry. The University of British Columbia April - 1931 TABLE OF CONTENTS I. PREVIOUS WORK. II. EXPERIMENTAL WORK. III. DISCUSSION OF EXPERIMENTS. THE CONDENSATION OF FURFURAL AND UREA Previous Work. Although a great deal of work has been done on furfural condensations, there has been very little work done on condensations of urea and furfural. Schiff^ makes the first mention of such a condensation. He found that if a drop or two of HC1 were added to a solution of furfural and urea, a bright red colour appeared and then the solution darkened, depositing a "humus like black mass". He mentioned that the intermediate red color only appeared with old furfural. ( 2 ) Biginelli found that on heating furfural with excess urea and only so much water as was necessary for solution, "a powder was deposited". The powder was "very difficulty soluble" and melted from 168 to 189^ - a range of 21°. The composition corresponded to difurfural triureid NHgCONH(CHC^HgO)NHCONH(CHCgHgO)NHCOHNg. It is unfortunate that the Italian magazine in which this article appears is neither in the library nor abstracted in the Shemical Society Abstracts. The only description consists of a few brief lines in Beilstein. The compound, however could not have been very pure since it melted over a range of 21°. (The writer has found in this investigation that all methods in which the furfural and urea are heated give a mixture of condensation products. Probably the only reason Biginelli got a composition close to that of difurfural triureid was that higher ureids do not differ much in composition from the triureid. The formula could not of course be checked by the molecular weight due to the insolubility of the compound. Recently several patents have been taken out for furfural urea Besins. These utilize Schiff's discovery that mixtures of furfural and urea resinify on additon of hydro-chloric acid. The articles of Schiff and Biginelli and these patents constitute the entire literature on the condensation of furfural and urea. Although Schiff did not do much on the condensation of urea and furfural, he did a great deal of work on the condensation of urea with other aromatic aldehydes. Those ureids which have been prepared by the direct condensation of furfural and aromatic aldehydes are relatively few, and most of them owe their preparation to Schiff. Schiff's results show laws of condensation so general to all the aldehydes with which he worked, that it seems certain that they should extent, to some extent to furfuraldehyde. When an aromatic aldehyde and urea condense, the oxygen of the aldehyde group and a hydrogen from two different urea molecules split off as water. 0 HpNCOHHp HNCOHNp R - C ^ + ^ ^ R - C ' - H HgNCOHNg \ ENCONHg + H^O H An Aldehyde Diureid. But since urea molecules have two NHg groups, the process can go further -R - C - HNCONHg* R-C = O + HgNCONHg H ^ HNCONH^ H 2 R ) ^ R - C - HNCONH - C - HNCONHg H ^ HNCONH^ H An Aldehyde Diureid Thus the process can go on to infinity and we can have a whole series of compounds of the general formula. N Urea + (N-1) aldehyde - (m-I)HgO Schiff found that when an aldehyde acted on an urea solution a diureid was usually produced, while when the aldehyde acted on powdered urea, a tri ureid formed. In preparing the di ureids alcohol or water solution of urea were used. In some cases the diureid formed at once with evolution of heat. In other cases the solutions had to stand a number of days. In preparing the triureids, with some aldehydes, it was sufficient to merely mix aldehyde and powdered urea. With others, it was necessary to use either a very concentrated aqueous urea solution or molten urea. In all cases, the ureids had to be purified by leaching with alcohol water or ether, since they were all rather insoluble in the common solvents. Trialdehyde tetrureids were produced by warming an aldehyde diureid with an aldehyde, the quantities being two mols to one. This aldehyde could either be the same or a different aldehyde than that composing the diureid. Pentaldehyde hexaureids were prepared in the same manner from dialdehydes triureids. The diureids usually precipitated out as little white needles and were usually practically insoluble in water or ether. Some of them were somewhat soluble in alcohol, especially before they were dried. The triureids were white amorphous powders, while the tetra and hexa ureids were either yellow or white powders. All the ureids decomposed immediately on melting. Some of the aldehydes Schiff prepared were: Enanthaldiurei d Dienanthaltriureid Trienanthaltetrureid Pentenanthalhexureid Benzaldiureid Dibenzaltriureid Tri b enzalt e t rure i d Nitro-benzaldiureid Benzal-dienanthaltetraureid Benzal-tetrenanthalhexureid Anisaldiureid Dianisaltriureid Sali cylaldiureid Disalicylaltriureid Acrylaldiureid. EXPERIMENTAL PART The experiments are numbered in the order they were performed. In the paragraph headed "conclusions" the significance of the most important experiments will be explained and generalizations drawn. 1. It was found that furfural and solid urea in the presence of a few drops of concentrated or dilute hydrochloric acid in a few minutes gave a light brown solid mass resembling a hard wax. In the course of half an hour this turned to a black resin. Using more acid,the black resin would appear without the intermediate compound. The resins produced varied from porous masses resembling burnt pitch to smooth hard resins like bakelite. 2. This method is similar to that used by Beaucourt in producing acid amides. 13.6 gm. furfural and 9 gm. urea were placed in a 100 cc. flask and heated on a water bath with COg bubbling through. The quantities corresponded to, 2 mols furfural to 3 mols urea ^ a 4 gm. excess of the former to keep the mass fluid as long as possible. In twenty minutes the contents solidified and were allowed to cool. The solid mass was light brown in color and resembled the intermediate compound in the previous experiment. The mass was ground to a smooth paste with water and then more HgO added and the mixture rapidly shaken in a mechanical stirrer to leach out unches-anged products. The solid was filtered out, dried in a dessictor and later leached with alcohol. Leaching with alcohol lightened the color to a light straw color but it could not be made white. The product decomposed at 180° and the yield was 16.5 gm which is 98% of the theoretical on the basis of difurfural-triuseid. The compound could not be purified since it was not appreciably soluble in water, alcohol, ether, chloroform, carbon tetrachloride, ammonia, pyridine, 10% NagCOg, benzene or acetone. In all the experiments the products did not have true melting points but decomposed without charring to red liquids. The red liquids would solidily to red translucent solids which would later turn black. 2 3. Biginelli's method was tried. 9 gm urea was dissolved in the minimum water necessary for solution, 9.6 gm furfural added and the mixture heated on the water bath. There was a lot of decomposition and finally a dark brown powder was deposited. The powder had a very alimy feeling when wet and when dry had no definite melting poipt, melting from 170^ up. 5. 9.6 gm furfural and 9 gm urea ( 2 mols to 3) were dissolved in 100 cc of water (the minimum to dissolve the furfural, and let stand 6 days. On evaporating in a vacuum only urea and a redish resin were recovered. 6. Refluxed for 3 hours 4.8 gm furfural, 6 gm urea (1 mol to 2) and. 30 oc EtOH. By ether precipitation,recover-ed 4.4 gm of the urea. Redish resin on evaporating under vacuum the filtrate. These redish resins are formed when furfural is heated alone. 7. Refluxed for 3 hours 4.8 gm furfural, 6 gm urea, 30 cc EtOH and 3 cc of acetic acid. There was no precipitate during the boiling after precipitating as much of the urea as possible with either and evaporating by warming in a stream of air there seemed to be a little amorphous solid mixed with considerable red sticky resin. The compound could not be separated from the resin however,and on drying the whole reacted to form a hard insoluble cake. 8. Since it had been found that furfural and urea do not react on refluxing in alcohol it was decided to try heating in alcohol under pressure. 6.5 gm furfural, 4.5 gm urea and 30 oc of EtOH were heated 24 hours to a maximum of 110°. A dark brown solution was obtained which was recognized as a colloidal solution since it scattered light strongly. On adding water the contents precipitated out as a black sticky tar. 11. This is based on a method for the aldol condensation of furfural and chloreform. 8 gm of furfural and 2 gm baryta were dissolved in 85 cc of water and 5 gm urea added. 30 minutes later the baryta was precipitated by COg and the solution evaporated to dryness, first by vacuum distillation, then by blowing air over the warm solution and finally by dessication. The product (along with some resin) was extracted with alcohol from remaining barium carbonate and purified by recrystallization and precipitation by ether. From the melting point of 129° and crystalline form it was seen to be only urea. 4. 9.6 gm furfural and 9 gm urea (2 mol to 3) were boiled for 1-^- hours and gave no precipitate even on codling. The greater part of the urea should have precipitated out on cooling but it was found later that alcohol solutions, strongly supersaturated with uea, in the presence of furfural are quite stable if they are not shaken. Since no precipitate had formed on heating, the solution was allowed to stand (in a shady place) several days, ^he solution was then placed in the light of the window and a Miite amorphous precipitate soon began to come down. After several days the precipitate was filtered out on a Buchner filter, washed with alcohol and water, and then dried in a dessictor. Yield =1.5 gm. M.P. = 171-172°. The percentage nitrogen by the Gunning Method was (1) 25.45, (2) 25.53. Average - 25.49. The calculated percentage for furfural diureid is 28.28 and for difurfural triureid is 25.00. Hence the compound seemed to be difurfural triuride with some impurity such as furfural diceride. (These two compounds or higher urides are what we would expect from analogies with all recorded cases of the condensations of furfural and aromatic aldehydes. 9. Repeated with the same quantities as before but immediately after colling placed the solution in the bright light of the window* The yield in 6 days was 3.6 gm. The melting point was 169-170°. 10. The previous experiment was repeated with the same quantities this time omitting the 1-^  hours boiling, the solution only being heated long enough to dissolve the urea. The yield after standing a week on the roof was 3.5 gm. The melting point was 165-166° and analysis gave 25.68% nitrogen. The precipitate this time was not so fine as in No.4, being rather curdy this time. The composition is not quite so close to that of difurfural triuride as No.4, but there is not much difference between the two. EXPERIMENTS EMPLOYING SOLID UREA. 13. Let stand, in light 6.4 gm. furfural and. 6 gm. powdered urea (2 mol to 3). The urea persisted in sinking to the bottom. Thus at the end of five days the now solid mass consisted of two sharply separated layers. The bottom layer was a soft yellow powder. After extracting with water the yield was 2.7 gm. The melting point was 168.5-169.5°. The upper layer which had contained the larger proportion of furfural was a brownish-black hard mass evidently consisting of ureids of higher molecular weight. Melting point 185-195°(approximately) 15. 10 gm. urea and 3.8 cc. furfural were dissolved in 60 cc. of ethyl alcohol. The solution was allowed to cool and them shaken suddenly. Immediately the urea in excess of the saturation concentration came down as a fine amorphous precipitate. The flask was allowed to stand a week in the light. The precipitated urea was found to have been almost completely changed into a white compound insoluble in water. After extraction with water and alcohol the yield was 1.4 gm. Melting point was 179-179.5°. 17. Repeated the previous experiment (on a smaller scale) with crystalline instead of amorphous urea. The urea was practically unchanged after two weeks. EXPERIMENTS USING METHYL ALCOHOL AS SOLVENT. It was realized that reaction with urea in solution should give the desired diureid, unless supersaturated solution were used, ethyl alcohol did not permit large enough concentrations of urea to give any noticeable reaction in the course of two weeks. Hence it was decided to try methyl alcohol in which urea is more soluble. 14. 6 gms. urea, 2.3 cc. furfural were dissolved in 40 cc. MeOH and were allowed to stand six days in the light. The solvent was volatalized by a current of air without heating. After extracting the urea with water, there remained a powder which was soluble in methyl and ethyl alcohol but not in water and hence was not the ureids previously encountered nor urea. The compound was contaminated with considerable decomposed yellow furfural. Water would not remove it. It was found the only method of removing it was by the rather wasteful process of washing with methyl alcohol in which the compound itself was rather soluble. By the time these things had been found out there was only enough compound to take a melting point M.P. was 167-167.5. The experiment was repeated using larger quantities (No.16. ). This compound from later work is believed to be furfural diureid. Probably the reason the melting point is not much lower than No.4 which analysed as difurfural triureid is that at first it was not known that the products had to remain at least five days in a dessicator before reaching constant melting or decomposition points. 16. Repitition of No.14 with larger quantities. Used 18 gm. urea, 6 cc. furfural and 120 cc. of MeOH. Let stand one week in light. Yield was 7 gm. M.P. 165-165.5°. 19. Also a repitition of No.14. Used 17 gm. urea, 5.6 cc. furfural and 120 c.c. of MeOH. Let stand one week in light. Yield was .7 gm. M.P. was 165-169°. A nitrogen determination. EXPERIMENTS USING 50% METHYL ALCOHOL AS SOLVENT. The reaction between furfural and powdered urea is fairly rapid, but the velocity falls off very rapidly as the reactants are diluted with solvent. The solvent permitting the most concentrated solutions is methyl alcohol, but even with methyl alcohol, only a very small proportion reacts in the course of several weeks. Since urea is very soluble in water and furfural very soluble in methyl alcohol, it was realized that 50% methyl alcohol would permit much more concentrated solutions than would pure methyl alcohol. Accordingly it was decided to try 50% methyl alcohol as a solvent in the hope of speeding up the reaction. 18. 10.5 gm urea, 3.8 cc. furfural were dissolved in 22 cc. of §0% MeOH and allowed to stand in the light. In the first twenty-four hours the yield was 6 gm. with a melting point of 171-173. The yield in the next forty-eight hours was 1.9 gm. with a melting point of 175-178°. This indicates that the precipitate, on standing in solution was gradually being converted to higher ureids. It was thought this might be eliminated by changing conditions, so that the whole reaction would take place more slowly. In the next two experiments the procedure is modified to slow down the reaction. 21. Same as No. 18 except that the reaction took place in the dark. The yield after five days was 4.3 gm. with a melting point of 185.5-186.5. A nitrogen determination. 22. The reaction was again repeated. It took place in the light again but with twice as much solvent. The yield after six days was 3.2 gm. with a melting point of 168-169°. A NITROGEN DETERMINATION. 20. 23 cc. of MeOH 11.6 gm. of urea and 3.8 cc. of furfural were placed in a flask. (Only a small amount of the urea dissolved of course). A few drops of formie acid, were then added. The next day the flask was full of a white amorphous powder. Yield 3.5 gm. These were separated into a soluble portion (A) and an insoluble portion (B), yield of (A) was .6 gm. M.P. was 178-180°. Yield of (B), was .8 gm. M.P. was 182.5 to 183.5. B has the higher melting point since it polmerized in removing it from solution by vacuum distillation. DISCUSSION OF RESULTS. (It is hoped to rewrite this section in the light of further knowledge). For an understanding of the results some of the diffic-ulties should first he realized. The compounds being fairly insoluble in all the common solvents, cannot be purified by crystallization. Due to their amorphous nature, they often tend to occlude impurities. Again furfural itself has a tendency to form resinous products. In all methods in which heat or light is employed to bring about the condensation of furfural and urea, a certain amount of soluble red or yellow furfural resins is formed. If the desired product is soluble, that is, if it has to be removed by evaporation, the resin will tend to pollute it. Again, so far it has been impossible to take molecular weights. All the compounds decompose immediately on melting, so the melting point method can be used. The diureid is soluble in methyl alcohol (l/2%) but the boiling point method cannot be used since the compound decomposes in methyl alcohol. The freezing point method would be impractical with methyl alcohol, especially since the compound probably would not be soluble at the low temperature. The methods tried may be summarized thus: Methods employing heat to effect condensation. In every case mixtures of condensation products contaminated with decomposition products resulted, such methods were abandoned. Methods Using Solid Urea. a. Powdered urea and furfural react fairly completely in the course of a few days. Mixtures of products have so far resulted, the reactants evidently being too concentrated. b. Amorphous urea precipitated from a super saturated solution,in the course of a week is fairly completely changed to a white insoluble compound. It is believed that this is the triureid. Analys&s are in progress to determine the purity. c. If the previous experiment is repeated using crystallized urea, there is practically no reaction in the course of several weeks. d. Crystallize urea and a concentrated methyl alcohol Of solution furfural, in the presence of a few drops of formic acid, in a day, give a very good yield of a compound believed to be the ^riureid. Analysis are in progress to determine the purity. III. Methods employing Urea in Solution. a. An Ethyl alcohol solution of furfural and urea strongly supersaturated with the latter deposits a white insoluble amorphous precipitate. In the course of a week a 20% yield was obtained. From nitrogen determinations the compound corresponds to difurfural triureid. b. Unless the alcohol solutions were strongly supersaturated with the urea, there was very little reaction in the course of several weeks. c. A methyl alcohol solution of furfural and urea (saturated with the latter) in the course of a week, forms a small amount of a compound somewhat soluble in methyl alcohol. Nitrogen determinations have shown that it is probably for the most part furfural diureid. So far this is the only method that has been discovered for preparing the diureid. d. Using a 50% methyl alcohol solution, the reaction is much more rep id. After several hours a white compound begins to come down. Good yields were obtained in the course of five days. The melting point if the reaction has been stopped after one day is different than if it ran five days. The melting point of the product obtained if the reaction is run in the dark is different from that obtained by reaction in light. BIBLIOGRAPHY 1. Schiff, Berichte, IO, 773-776 (1877). 2. Biginelli, Gazetta Chimica Italiana 23(1), 388. Beilstein, 1, 720 (1899). 3. Chemical Abstracts, page 1729 (1929). 4. Beaucourt, Monatschefte für Chemie, page 176 (1928). 


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