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The effect of a magnetic field on chemical reactions Collins, Sonia 1950

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fir Of.i THE. EFFECT OF A MAGIETIC FIELD OU CHEMICAL REACTIONS by SOMA COLLINS A thesis submitted in parti a l fulfilment of the requirements for the degree of MASTER OF ARTS in the department of CHEMISTRY The University of British Columbia April, 1950 ABSTRACT (1) Equipment was constructed and c a l i b r a t e d for the purpose of studying the effect of a magnetic f i e l d on chemi-cal reactions. (2) The effeot of a magnetic f i e l d on the decomposition of benzoyl peroxide -was investigated, l o effeot of a mag-net i c f i e l d of 1E.000 gauss was detected. (3) The catalyzed and uncatalyzed polymerization of styrene at 80°G. was found to be unaffected by a magnetic f i e l d of 12000 gauss. The absence of an effeot i n the un-catalyzed polymerization of styrene i s i n marked disagree-^ ment with the results reported by Schmid et a l . It was con-cluded that the r e s u l t s reported by these authors are i n error. (4) A preliminary investigation of hydrogen peroxide decomposition i n a magnetic f i e l d was undertaken. Ho con-clusive evidence f o r f i e l d e f f e c t was obtained as the rate of t h i s r e a c t i o n i s very dependent on surface e f f e c t and extremely small amounts of c a t a l y t i c impurities. (5) A possible explanation for the absence of a f i e l d e f f e c t i n free r a d i c a l reactions was suggested. Schmid, Muhr and Marek, Z. Electrochem. 51, 37-8 (1945). Sincere appreciation is expressed to Dr. W. A. Bryce for suggesting and supervising this research. The assistance given by the Physics Depart-ment i n designing an electromagnet is gratefully acknowledged. TABLE; OP COIOTTS page IOTRODUCTIOH Properties of Molecules i n a Magnetio F i e l d 1 Reactions i n a Magnetic F i e l d ....... 7 Reaction Mechanisms ................. 11 Theoretical Consideration of Possible E f f e c t 16 EZPERPEKTAL Description and C a l i b r a t i o n of Equip-ment 20 Decomposition of Benzoyl Peroxide ... 31 Polymerization of Styrene ........... 39 Decomposition of Hydrogen Peroxide .. 46 DISCUSSION OF RESULTS General Discussion 50 Suggestions for Further Work ........ 56 References 57 THE EFFECT OF A MAGNETIC F I E L D ON CHEMICAL REACTIONS A p h o t o g r a p h o f t h e e x p e r i m e n t a l s e t - u p f o r t h e i n v e s t i g a t i o n o f t h e e f f e o t o f a m a g n e t i c f i e l d o n c h e m i c a l r e a c t i o n s . 1 Introduction I Properties of Molecules i n a Magnetic F i e l d The investigation of reaction k i n e t i c s i n a magnetic f i e l d requires a knowledge of the nature of magnetic forces and of molecular structure capable of responding to suoh forces. The general subject of magnetism Is adequately d i s -cussed i n several standard references (1) (2). However, i n presenting a discussion of the possible effects of a magnetic f i e l d on reaction rates, constant reference w i l l be made to diamagnetic and paramagnetic molecules and hence a b r i e f review of these two types of magnetic properties i s desirable. Induced magnetism i s the basis of the behaviour of substances placed i n a magnetic f i e l d . I f the substance i s considered to be made up of elementary dipoles (permanent or induoed by a magnetic f i e l d ) the f l u x density within the substance i s the algebraic sum of the exciting f i e l d H i n free space and the change produced i n the sample* The fl u x change can be expressed as 4 TTl where I i s the i n t e n s i t y of 2 magnetization or the magnetic moment per unit volume of the elementary dipole. The flux density within the sample is then B » 1+ 4 F I t I oan also "be expressed as kH where k is a proportionality factor called the volume susceptibility. The following re-lations are evident: Since B - H -f 4 T I and B * H (where^ is the permeability factor) then / s l f 4 7/ k The specific magnetization or susceptibility per unit mass is denoted as Y and is equal to k and therefore I where P i s the density of the sample. The magnetic properties exhibited by a substance placed i n a magnetio f i e l d depends on the electronic configu-ration of the individual atoms. Every spinning or rotating electron has a magnetio moment associated with i t . If a molecule contains an even number of eleotrons and the square of the mean of the magnetic moments of a l l the electrons vanishes, the molecule does not have a permanent magnetio moment. It also can be shown that the magnetic moment associated with a moving electron is proportional to i t s angular momentum. Therefore another criterion of a permanent magnetio moment in a molecule i s the presence of a resultant electronic angular momentum. 3 Diamagnetism If a molecule with no resultant magnetic moment is: placed i n a magnetic f i e l d , the orbits of the electron are modified and an induced angular momentum is produced. The f i e l d resulting from the induced current w i l l oppose the exciting f i e l d in accordance with Lena's law^ and hence the fi e l d within the molecule w i l l be less than the exoitlng f i e l d . This phenomenon is known as diamagnetism and can be deduoed quantitatively by the use of Larmor's precession theorem dealing with a moving charge in a magnetio f i e l d (3). The expression for the change i n magnetic moment, jlAz. , of one orbital electron in an applied f i e l d H is found to be: A ='±^JL A> where /tf is the radius of the resolved orbit whose plane is at right angles to the direction of the f i e l d (2). Por/*v elect-rons in an atom this; expression may be written as A A , = -JS« £ X* This olassical treatment w i l l only apply to atoms or ions in-dependent of eaoh other. The magnetic moment per gram-atom containing 1 atoms (Avogadro's number) is If an atom has no i n i t i a l magnetic moment the gram-atomic susoeptibllity j( for spherioally symmetrical atoms Is A/ 4 where in a spherically symmetrical atom Two oonsequences of the expression f o r a r e evi-dent. F i r s t , the diamagnetic susceptibility should not vary with temperature as thermal energy does not enter the express-ion. Secondly, diamagnetism must he a fundamental property of a l l atoms and molecules. From the negative nature of the theoretical expression, i t i s also evident that permeability must be less than unity and the f i e l d within a diamagnetio moleoule is less than the exciting f i e l d . It might be of interest to mention the quantum mechanical treatment of diamagnetism. For simple mono-nuclear systems the same results are obtained as in the classical treatment for diamagnetic atoms. Van Fleck and Pauling (4){5) arrived at similar expressions involving a screening constant which Pauling estimated for different electron groups in atoms and ions oontaining many electrons by considering a continuous distribution of space charge. Several modifications of the quantum mechanical treatment can be found in the literature. Paramagne t ism Molecules having a permanent resultant angular mo-mentum are classed as paramagnetic substances. Curie's law was stated from experimental observations and related suscep-t i b i l i t y to temperature. In a paramagnetic 5 where C is a constant and 2 is the temperature in Kelvin de-grees, Langevin proposed a theory which, i n spite of the mod-ern atomic theory, i s fundamentally important in explaining Curie's law. He assumed for paramagnetic gases that molecules with permanent magnetic moments tended to orientate themselves with their axis in the direction of the applied f i e l d . This orientation could he disturbed by thermal agitation. If mag-netic energy states are wholly dependent on the angle between the magnetic axis of the individual atoms and the direction of the applied f i e l d , at equilibrium, the susoeptibility can be calculated from s t a t i s t i c a l consideration of the distribution of atoms among these magnetic energy states. The redistribu-tion of energy on application of a f i e l d probably takes place through c o l l i s i o n or radiation. This redistribution of energy requires time so that there is a time lag between the time of application of the exciting f i e l d and the time in which e q u i l i -brium is reached. Weiss extended Langevin's theory to solids where molecules were not independent and an internal f i e l d was estab-lished. H^ , (effective field) is equal to the sum of 1/ (applied field) and H. (internal f i e l d ) . Langevin in his work on paramagnetio gases had deduced that is the gram-molecular s u s o e p t i b i l i t y , ^ is the number of molecules per gram-molecule and^/c is the molecular magnetic moment (2). The Weiss equation which takes into consideration 6 the molecular f i e l d within the sample states that YM -where O i s a c r i t i o a l temperature arising from the correction for molecular f i e l d effect. The implication of the Weiss equation is that in the presence of a molecular f i e l d the sus-c e p t i b i l i t y varies inversely with the excess of the temperature over a c r i t i c a l value O • In ferromagnetics Q corresponds to the transition point where ferromagnetism changes to paramag-netism. In other paramagnetics 6 i s usually a small positive or negative correction indicating a break in tbe linear rela-tion between J _ and T rather than a transition point. X The unit in measuring magnetic moments i s known as the Bohr magneton. In Bohr's original theory of atomic struc-ture, the angular momentum ^  of an electron was restricted to value such that . ATT where 'n is an integer. The magnetio moment associated with the angular momentum of an electron i s then expressed as The quantity — i s the natural quantum unit for magnetic d/-fT->r>C. moments and i s called the Bohr magneton. Its value is -21 9.27 x 10 electromagnetic c.g.s.. units for the unit moment per eleotron or 5,585 for the unit moment per gram-atom in which oase the symbol is usually written as ^  • The Bohr magneton is then the magnetio moment of an eleotron moving in the smallest Bohr orbit for hydrogen with an angular momentum of •„ The magnetic moment of ah electron due to spin is also equal to one Bohr magneton beoause although the angular momentum due to spin is the associated magnetic moment i s relatively twioe as large. Total magnetic susoeptibility is then the sum of the paramagnetic susceptibility and the diamagnetic suscepti-b i l i t y . Paramagnetic susceptibility is much greater than the usual diamagnetio susoeptibility being in the order of —6 1270 x 10 units for one odd electron molecule at room tem-—6 perature as compared with the negative 1-100 x 10 units for diamagnetic susoeptibility. The result is that in the pre-sence of both, paramagnetism overshadows the diamagnetism. II Reaotions in Magnetic Fields In the previous section the types of interaction which could occur between molecules and an applied f i e l d were discussed from the consideration of fundamental magnetic phenomena. Results from some of the many investigations of reaotions in magnetic fields w i l l be reviewed whenever they have a theoretical interest or deal directly with the present investigation. For a complete l i s t of references on onemioal reactions studied i n magnetic fields, the reader i s referred to an ar t i c l e by P. W. Selwood (6). In 1900 de Hemptinne (7) showed theoretically that in general the effect of a magnetic f i e l d on chemical 8 reactions would in a l l probability be too small to detect. Parker and irmes (8) reported that in the reduction of f e r r i c chloride by iron and aluminium and the reduction of permangan-ate in acid solution by metallic iron, the acceleration of the reaotion rate produced by a f i e l d was diminished by mechanical s t i r r i n g . & great many more investigators have reported negative results in both homogeneous and hetero-geneous reactions (3, 6). The most extensive and illuminating work was done . by Bhatnagar, Mathur and Zapur (9). After investigating a series of reaotions they came to the conclusion that i f the sum of the molecular susceptibilities of the i n i t i a l reactants was smaller than the sum of the molar susceptibilities of the produots, the reaction w i l l be accelerated. In the reverse oase the reaction would be inhibited and in the case of no change in the sums of molar susceptibilities the velocity of the reaction would be unaffected. In summary, the effeot of a magnetic f i e l d on the velocity of a reaction would vary as where refers to the susceptibilities of the reactants and^X M *-° susceptibilities of the products. In a l l cases investigated by Bhatnagar et a l the change in the velocity constant was i n the order of one percent when de-tected. The above results give sufficient indication that in inorganic reactions at least, some effeot of magnetic 9 fields on the velocity of a reaction can often he detected. The detection of free radioals in certain organic reactions opens up a new f i e l d of researoh i n Magnetoohemis-try. The possibility of a magnetic f i e l d affecting such re-actions arises from the fact that organic molecules are dia-magnetic but free radicals are weakly paramagnetic because of an unpaired electron. A recent investigation by Schmid et a l (10) on the unoatalyzed polymerization of styrene indicated marked inhibition of the reaction by magnetic fields'. The experiment consisted of placing a sample of purified styrene sealed i n a thoroughly cleaned glass v i a l into a f i e l d of 16000 gauss for a period of 8 hours at 80°C. A control sample done at the same time showed 4.9% of the styrene had poly-merized but the f i e l d sample showed only .56% polymerization. This, the workers explained, was the result of orientation of the molecules. Leffler and Sienko (11), while aoeepting these results, disagreed with this explanation on the grounds that a far more l i k e l y explanation, particularly at a temperature of 80°C, was not the orientation of molecules but the orienta-tion of the spin moments of the unpaired electrons. If chain propagation i s oaused by uncoupling of the 77~~*or double-bond electrons, in a magnetic f i e l d an orientation of the spin moments of these unpaired electrons i s l i k e l y . This can .be illustrated as \ \ t r ? \ ' ! i \ Ph - CH - CHg B* ^ [Ph - CH - CHg - RJ ^ P h - CH - CHg -Transition state radieal 10 in no f i e l d but in a magnetic f i e l d the radical becomes • t • .f • .* Ph - CH - GHg - R Leffler and Sienko maintain this is possible "since organic free radicals have been shown to be in *2- state in which cou-pling between spin moment, and the axis of figure of the mole-cule can be negleoted". This means that the spin moment i s chiefly responsible for the magnetio moment in many organic molecules and radicals with no contribution from angular mo-mentum. Another reaction which is of particular interest because i t leads to the formation of free radicals is the de-composition of benzoyl peroxide in a magnetic f i e l d . Only one such investigation has been reported (12). No noticeable effect of the magnetic f i e l d was detected in samples after 102 and 766 hours in a magnetio f i e l d of 7518 gauss at 35.001. .01 °C, No rate curves were reported for this investi-gation and hence possible effects of the f i e l d during the early stage of the reaction may have been overlooked. Moreover, at this temperature, the rate of decomposition was so low that i t would require a very sensitive analytioal procedure to detect the probably small effect the magnetic f i e l d might have on a reaction of this type. The investigations reported above of the polymeri-zation of styrene and of the decomposition of benzoyl peroxide in a magnetic f i e l d do not appear to have been carried out i n a satisfactory kinetic manner, and a number of important 11 details are lacking in the published results. It seemed de-sirable therefore to re-investigate these reactions using more preoise methods than those previously used in an attempt to determine whether an effect of an applied magnetic f i e l d could be detected during the course of the reaction. Interest in this investigation is further aroused by the marked effect of a high frequency electric f i e l d on the polymerization of styrene catalyzed with varying amounts of benzoyl peroxide (13). I l l Heaction Mechanisms The major part of this investigation is concerned with the study of the effeot of magnetic fields on the decom-position of benzoyl peroxide and on the polymerization of styrene. It i s , therefore, desirable to consider briefly the kinetios of these reactions tinder normal conditions as a back-ground for the discussion of the results of the present work. Decomposition of Benzoyl Peroxide Much work has been done on the kinetics of the de-composition of benzoyl peroxide i n various solvents. In general the decomposition has been treated as a unimoleoular reaction but the velocity constant of the reaction varies with concentration. Brown (14) showed that this oould be explained by a concurrent f i r s t and second order reaction. Uozaki and Bartlett (16) found that the decomposition of benzoyl peroxide can be strongly induced by the introduction of additional free 12 radicals. The free radicals present in the solution from the decomposition of the benzoyl peroxide could themselves lead to accompanying higher order reactions. They suggest a chain reaction of the following type: C^ Hg- coo-ooec f cH s > Z C t H s C 0 O - (1| 2 C tw sCoo- — > C o > + C tn sCooC f cH y U ) Cb H 5 COO- + C ^ - O o o - O o C f c r t s  C o * + C . t u s . . C o o C f c H 5 T C 6 t t s COO- (s) The benzoate radical i s often capable of attacking solvents. This causes chain transfer and the formation of new radicals which may or may not influence the over-all velocity. Experi-mentally Wozaki and Bartlett found a uni-molecular decomposi-tion of benzoyl peroxide aooompanied by reactions of three-halves order in some solvents and second order in others. These reaotions of order greater than one are believed to be chain reaotions induced by the presence of free radicals. Cass (16) supports the chain mechanism suggested by Hozaki and Bartlett in the cases where the solvent was dioxane, diethyl cellosolve or diethyl ether. The decomposition rate of benzoyl peroxide in aromatic hydrocarbons as solvents i n -dicated a f i r s t order reaction. Cass also observed inhibition by oxygen and attributed this to the formation of a peroxy radical from the combination of oxygen with a primary radical. The peroxy radical oould then combine with another primary radical to form a peroxide R-oo-R*or capture a hydrogen from 13 the solvent forming a hydroperoxide and a new radical. The latter process would increase the peroxide concentration and the result would he a marked apparent inhibition of the decom-position. The catalytic aotion of benzoyl peroxide in polymeri-zation of styrene is a consequence of the formation of free radicals whioh initiate ohain reactions. The free radicals, are able to unoouple the spins of the electrons of a double bond in the styrene molecule. This uncoupling of spins can occur only in the presence of a magnetio f i e l d such as supplied by the unpaired eleotron in a free radical (17). The tr i p l e t styrene molecule i n which tlfee unsaturation electrons have un-coupled spins is required for the formation of free radicals. The Meonanism of the Polymerization of Styrene It is now generally accepted that the addition polymerization of compounds oontaining double bonds proceeds by the formation of free radicals (18). The characteristic property of a free radioal i s an unpaired electron which i s available for the formation of a band with another free radical, atom or group on a molecule. In high polymers the fundamental reaction of a free radioal i n ohain polymerization is the reaction of the free radical with a double bond to give a larger free radical. This reaotion w i l l oontinue u n t i l the destruction of the free radical by combination of two radioals or by disproportionation. Disprpportionat ion is the favoured type of ohain termination (19) and may be illustrated as 14 follows: c r i - C h j -r K - c i + r fttH-cH^t R e H a c H 3 A number of investigations indicate that the energy of dis-proportions tion is very low or non-existant, and that the chain ends have l i t t l e trouble in colliding and reacting. The free radical mechanism of polymerization has been broken up into three stages; i n i t i a t i o n , propagation and termination, with an additional possible step, that of chain transfer (.20). These steps can be shown by the following equations (21): K, + M, —> 2M* in i t i a t i o n -at. * 4 M, —> M n + x - ~ : - propagation [2~\ + Hi — ^ + M chain transfer [s\ + — ^ + Mffi or M n + m ... termination where M is a monomer> molecule, a polymer molecule and the asterisk denotes an active center or free radical. In high polymers the rate of t33 is much greater than that of C4l as probability of col l i s i o n and recombination of two free radicals is small beoause of their low concentration. Chain transfer w i l l include transfer of active centers to and from solvent and catalyst molecules as well as transfer between monomer and polymer molecules. The main object in reviewing the mechanism of poly-merization i s to emphasize the presence of free radicals rather than to reproduce the material so thoroughly covered 15 in the references: cited. Magneto chemical evidences for the presrence of free radicals in the polymerization of styrene has been obtained through susceptibility measurements (22). Further conclusive evidence for the presence of free radicals oan be obtained from reaction kinetics (18). It has been "ob-served that compounds whioh are thought to decompose with an intermediate free radical format ion w i l l catalyze addition polymerization. The catalytic free radicals are incorporated in to the growing polymer chain as end groups by i n i t i a t i n g or terminating the chain. Catalysts w i l l produce a greater number of free radicals for a given time than the unoatalyzed monomer for chain i n i t i a t i o n . It has also been observed that the catalyzed reaction rate i s proportional to the square root of the catalyst concentration. This can be explained by a f i r s t order reaction for the appearance of free radicals from catalyst decomposition and a second order termination process whioh must Involve the destruction of a pair of free radicals* It i s hoped with this information on the two re-actions chosen for investigation* the arguments for possible effect on their rates by the application of a magnetic f i e l d can be adequately presented in the next section. 16 IV Theoretical Consideration of Possible Effeot So far i t has been shown that in both the decomposi-tion of benzoyl peroxide and the polymerization of styrene weakly paramagnetic free radicals are formed as intermediates. Also in previous studies of reaction kinetics in a magnetio f i e l d a reaction was found to be aocelerated, unchanged or inhibited as ' ' Further disoussion of magnetio f i e l d effeot on reaction rates w i l l be based to a large extent on the disoussion of the sub-ject by Bhatnagar and Kapur (3). In general for reactions in a magnetic f i e l d an effect can be expected for several reasons •—: (1) Paramagnetic molecules w i l l be concentrated in the region of the strongest f i e l d . This w i l l decrease the concen-tration of these substances in other regions. A consideration of the mass law w i l l prediet a localized shift in the direction of the reaction. This is confirmed by the observation that s t i r r i n g w i l l reduce the field effect (8). (2) On the basis of kinetic theory the probability of inelastio c o l l i s i o n governs the rate of reaction. Any agenoy affecting this probability is certain to affect the rate of reaction. In a magnetic f i e l d the discrete orientations of molecules w i l l affect the probability of such collisions i f 17 the thermal agita t i o n i s i n s u f f i c i e n t to maintain complete randomness. ( 3 ) The type of c o l l i s i o n s required f o r molecules to react must beoome important i n non spherical type of molecule. Orientation of molecules or more l i k e l y the spin moments of the unpaired electrons w i l l perhaps increase or decrease the number of e f f e c t i v e c o l l i s i o n s . (4) ' I f a molecule is diamagnetic, an applied f i e l d would tend to orientate i t so that a paramagnetic molecule i s formed. This i s understandable from the consideration of the decreased free energy i n the paramagnetic molecule on l i n i n g up. The deoreased free energy i s not a factor governing the rate of a reaction but i t does make a reaction more fe a s i b l e thermo-dynamioally. ted. This can be explained to a cert a i n extent without assuming that no e f f e c t was produced by a magnetio f i e l d . A n a l y t i c a l procedures are often too insen s i t i v e to detect very small ohanges. In reactions where the difference between the same order as the variance i n c o l l i s i o n numberZ. and the s t e r i o factor P i n the equation In many reactions negative r e s u l t s have been repor-and 2- ^Yto i e very small* the e f f e c t would be of Thermal agita t i o n might e a s i l y disturb the orientation of molecules. Negative results are also possible i n the case of 18 very fast reactions as in paramagnetic substances there is a definite relaxation time for the orientation of the molecules. This orientation might not take place i f the l i f e "of the para-magnetic molecule is too short compared with the relaxation time. The preceding general discussion can now be applied to (a) the decomposition of benzoyl peroxide and (b) the poly-merization of styrene. The thermal decomposition of benzoyl peroxide can be classed as a f a i r l y fast reaction. The l i f e time of the weakly paramagnetic free radicals are short. Unfortunately no information appeared in literature on the comparative values of the relaxation time and the length of the lifetime of a free radical. Free radicals are only an intermediate product. If their production is accelerated ^ X^ J and their disappearance inhibited 1 I L ^ . 1 ^ J( m) the two changes are probably of the same order. Furthermore at 80°0, thermal agitation should be sufficiently great to overoome the orienta-tion of weakly paramagnetic molecules. The same disoussion holds for the possible effect of a magnetic f i e l d on the catalyzed polymerization of styrene. The uncatalyzed polymerization of styrene is a much slower re-action and might be influenced by a magnetic f i e l d more readily. Such an effeot has been reported (10) as mentioned previously and the reasons for effect discussed by Leffler and Sienko (11). 19 In general i t would seem that any marked effeot of a magnetic f i e l d on the decomposition of benzoyl peroxide or the polymerization of styrene seems unlikely. A small effeot may be observed in the case of the unoatylized styrene i f the ana-l y t i c a l procedure is sufficiently sensitive to detect i t . It is f e l t , however, that not one of the reasons mentioned of why a magnetic f i e l d should influence reaction rates is s u f f i -ciently pronounced in these two reactions to enable one to make a correct prediction with regards to a possible effect. 20 EXPERLMEH TJSL I Description and Calibration of Equipment Cons true tion of Magnet The magnet used in this investigation was a D.C. electromagnet with a variable f i e l d strength. It was designed to deliver a maximum of 15000 gauss across a 1 inch gap. The magnet yoke, Fig. 1(a) was oast out of. mild steel (SAE 1010) in the form of a U . The cores for the coils and pole tips were maehined from hot r o l l stock (SAE 1010) to a diameter of 3 15/16 inches. Each core was 5 3/4 inches in length with an extension of 4 1/2 inches in length and 1 inch in diameter. This shaft was threaded on the end to enable the core to be bolted to the yoke as shown in the figure. The pole tips were conical to ensure a f i e l d of high flux density and were fastened to the core by means of a threaded 1 inch projection whioh could be sorewed into a tapped hole. The complete assembly is shown in Fig. 1(b). The ooils were wound on a brass sleeve which fi t t e d over the core. The wire used was #10 Formel. In order to dissipate heat generated in the ooils, three layers of l/'4 inch (outside diameter) copper tubing were spaced throughout the c o i l , Fig, l ( o ) . £ layer of thin copper sheeting was placed over two inside layers of copper tubing to permit smoother winding of the next seotion of the c o i l . Empire cloth 21 F i <j. 2i. C i r c u i t f o r M a j n e t . S p r i n g Swt*tfth. H O Volts D - C . a • - 4 -C o l l , 4-5A .Mftfto rtPQflo 8Mflfla 495 7 J O > ' V?fel Tu-ns. C o i l 1 43o 4»3 » v - , • •) 11M Turns. Co i l I Amme"Ur Variable vJa+er-C oo led Resistance C No*. 11.5-nJ. 23 insulation was used to minimize the danger of shorts through the oopper tubing, brass sleeve and the outside of the c o i l . The total diameter of each c o l l was approximately 15 3/4 inches and the width 5 inches. The cirouit for the magnet (Pig. 2) oonsisted of an ammeter, water-cooled resistance and the coils connected in series. The cirouit was opened and olosed by means of a heavy spring switch whioh minimized the danger of arcing at the terminals. Calibration of the Magnet The magnet was constructed so that heat produced by currents up to 12 amps, could be dissipated with ease. To calibrate the magnet, the f i e l d strengths produced by currents ranging from 4 to 12 amps, were measured by means of a flux-meter. The results of this calibration are given in Table I. At the same time the f i e l d was measured just outside the c o i l to see i f a oontrol c e l l could be placed near the ooils without being subjected to any appreciable f i e l d . It was found that when the f i e l d strength in the gap was approximately 12000 gauss, the proposed site of the control o e l l had a stray flux density of 50 gauss. This was considered to be s u f f i -ciently small to constitute a region of negligible f i e l d . 25 TABLE I Calibration of the Magnet Amperage Av. aefleotion of Fieia Strength . fluxmeter - • ., . . :  4 amperes 16.7 divisions 6770 5 20.2 8200 6 23.3 9460 7 25.5 10400 8 27.4 11100 9 28.6 11600 10 29.9 12100 11 30.9.3 12600 12 31.6 12800 12.4 32.1 13000 ¥: Approximately 409 gauss/div is ion at a f i e l d strength of 6000 gauss. In order to cut down stray flux the framework, thermostatic hath and as many of the clamps as possible were made of non-magnetio materials such as copper and brass. Thermostat ted Bath In order to f i t a bath between the pole pieces and yet have a sufficient volume of o i l to maintain a steady tem-perature, the bath was designed with a narrow top which oould slide through the 1 inch gap, between the pole pieces, S u f f i -cient volume of o i l was obtained by having a relatively large 27 base portion. A circulatory pump was used to oirculate the o i l and a baffle was placed horizontally between the narrow portion and the wider base. The pump l i f t e d the o i l from the lower portion of the bath and discharged i t along the top of the baffle through the narrow portion. In this way a rapid flow of o i l was maintained i n the narrow neck of the bath where reaction cells were to be placed. The arrangement of the components of the thermostat is shown i n Fig* 4. A flexible 500 watt heater was placed along the bottom of the bath to avoid looal heating of the reaction cells by its proximity. Control Panel The temperature of the bath was maintained at 80°C by the use of a mercury thermo-regulator and two relays. The complete oirouit (Fig. 5) was primarily designed to supply the correct ourrent and voltage to trip the relays. It had a safety feature i n that the heater could not be operated un-intentionally i f the D.C. was not switched on, but the pump was independent of the relay c i r c u i t . Two pilot lights i n -dicated the D.C. and A.C. ourrent flow i n the oirouit. A variac was placed in series with the heater to permit the re-duction of the voltage applied to the heater after the de-sired temperature had been attained. It was found that the fluctuation of the temperature was a minimum with 80 volts applied to the heater. £9 Calibration of Thermometer A Backer thermometer graduated into one-tenths of a degree was calibrated against a platinum resistance thermo-meter (Ser, l o . 169314, National Bureau of Standards C e r t i f i -cate) for the temperature range between 78,5°C, and 82.2°C. A calibration graph was drawn. A l l the temperatures quoted are the corrected values as obtained from this; graph. Beaction Cells The volume of the reaction cells was limited by the f i e l d volume of the magnet. In order to obtain the great-est possible volume, the c e l l s were in the shape of a f l a t cylinder of a diameter slightly less than that of the pole pieces. Two arms were attached to the c e l l . One of the out-lets was used for sampling and through the other nitrogen could be passed to provide an inert atmosphere for the re-action mixture. The l a t t e r outlet had a ground glass joint with a constricted long tube for the introduction of nitrogen from beneath the surface of the reaction mixture.. The c e l l is shown in Fig. 6 along with a diagram of the flow-meter used to indicate the rate at whioh nitrogen was being passed through the c e l l . 3 o Fi<|.6. Reaction Cell and Flow-meter To f l © w - m « A « r 31 II The Decomposition of the Benzoyl Peroxide Me thod 2.000 gms. of Eastman Kodak benzoyl peroxide was dissolved in 100 ml. of freshly d i s t i l l e d toluene. 15 ml. of this solution was placed in eaoh of the two reaction cells at a temperature of 80.15 t 40 °C. At the same time 6 equal portions were pipetted out for analysis to determine accurate-l y the i n i t i a l concentration. The method of analysis (23) involved the addition of 20 ml. of analytical grade acetone, 10 ml. of glacial acetic aoid and 1 gm. of analytical grade k l to eaoh aliquot of the solution. This mixture was allowed to stand for 10 minutes to ensure the complete liberation of iodine. 20 ml. of d i s t i l l e d water was added and the sample was titrated with ,G2 I. sodium theosulfate solution using a micro-burette. The disappearance of the iodine color was taken to he the end point of the reaction. The reactions involved in the analysis are the following --: R(G00)_4-2KI > 2R000K r I ^ 2 h f 2 S2°3^ — ^ 2 1 + H°6* Blanks were titrated at the same time and subtracted from the titration value of the sample. During the course of eaoh experiment samples were drawn out of the reaction cells at 1 to 2 hour intervals and analyzed by the same method. The 32 solution i n the r e a c t i o n c e l l was kept under an atmosphere of nitrogen to prevent the apparent i n h i b i t i o n of the benzoyl peroxide to which reference has been made (16), On withdraw-ing samples the atmosphere of nitrogen was repleni&hed and the c e l l s were closed with a stopper oontaining a c a p i l l a r y - s i z e d opening to allow the carbon dioxide formed to escape without introduction of a i r by convection currents. The stoppers also reduced the rate o f evaporation. The r e s u l t s of three s i m i l a r experiments were ob-tained to ensure that experimental technique was consistent. The r e s u l t s for one of the experiments are given i n Table II and the accompanying rate curve i n Pig. 7. In conjunction with this main experiment, the i n -h i b i t i o n produced by oxygen was investigated. Without apply-ing the magnetic f i e l d , portions of the s o l u t i o n of benzoyl peroxide i n toluene were placed i n eaoh of the reac t i o n c e l l s , one under an atmosphere of nitrogen and one under oxygen. The r e s u l t s of this experiment (Pig. 8) showed a normal rate ourve f o r the s o l u t i o n under nitrogen and a muoh f l a t t e r curve for the solution under oxygen. This experiment was r e a l l y only qualitative i n nature as no attempt was made to find the dependence of the i n h i b i t i o n on the amount of oxygen i n t r o -duced. An interesting observation was that a yellow color developed i n the soluti o n under oxygen afte r an hour i n the thermos tatted bath. To check the fact that the color might have been produced by aotion of oxygen on the solvent a portion 33 of toluene was kept under oxygen at 80°C. with no yellow color developing. The yellow color was apparently caused by the formation of a peroxy radical or hydroperoxy compound as suggested by Cass (16) rather than the reformation of ben^ zoyl peroxide. Results The results obtained from the decomposition of benzoyl peroxide i n toluene under nitrogen are tabulated in Table II. I n i t i a l concentration was obtained by averaging 6 titration values obtained at the beginning of the experi-ment. The amount of benzoyl peroxide present at any time is expressed in terms of ml. of .OS N«r sodium thiosulfate solu-tion and can be found in the column marked "Titer". In order to out down pipetting error, the same pipette was used for a l l the samples analyzed. 34 TABLE II Temperature - 80.2 1 .4°C Init i a l concentration (titer) -9:67 ml. of .02N Ua, Field Applied - 12000 gauss -Field Cell Control Cell Time Titer % decomposed .Time Titer % decomposed .58 hrs. 8.78mL. 9.2$ .58 hrs . 8.80 ml, 9.00$ 1.00 8.03 17.0 1.05 8.00 17,3 2.08 7.28 24,7 2.12 7.14 26.2 3.00 3.00 4.00 5.30 45.2 4.00 5.28 45°.4 5.00 4.66 51.8 5,00 4.37 54.8 5.58 4.00 58,6 6.00 3.86 60.1 6.00 3.94 59.3 7.00 3.68 61,9 7.00 3.59 . 62.9 3tr Fl J. 7. Ratfc Curves for Benzoyl 'ftroxfde I " 1 J Field Sttcn^tb flooo &o.uss Hcj t 8. The efftat of oxvcfen o r , the d e c o m p o s i t i o n o f b e n z o y l p e r o x i d e Te»«pe *-«*uve-. 9 0 It Ve. 37 For further comparison of the f i e l d and control re-aotion rates, the velocity constant k has been calculated for a f i r s t order reaction (Table III), TABLE III The Velocity Constant k for the Field and Control .Reaction; Hates k = 2.303 log a hours t a-x Field Control Time (hours) k_(hours) Time (hours) k (hours" ) .58 1.64 x lO^ 1 .58 1.63 x ID" 1 1.00 1.86 x 10"1 1.05 1.81 x 10" 1 2.00 1.41 x 10"1 2,12 1.51 x 10" 1 4.00 1.51 x 10" 1 4.00 1.51 x 10" 1 6.00 1.53 x 10 - 1 6.00 1.50 x 10" 1 The rate curves in Fig. 7 show that the f i e l d has no appreciable effect on the decomposition of benzoyl peroxide in toluene. The small variations between reaction rates in the f i e l d and in the oontrol c e l l are no greater than the scattering on points along each of the two rate curves, and in general they are smaller than the difference found between the rate curves obtained by repeating the same experiment. From the two rate curves shown in Fig. 8 i t is evident that the reproducibility of these results is greatly dependent on the 38 care taken i n maintaining the reaction mixture under an i n e r t s tmos phe re • In Table I I I , the v e l o c i t y oonstants kp and k 0 are i n close agreement •with each other at any given time. The f l u c t u a t i o n i n the v e l o c i t y oonstants f o r each reaction i s expected on the basis of the reaotlon mechanism presented e a r l i e r (14)(15). 39 III The Polymerization of Styrene Catalyzed Polymerization of Styrene Eastman Kodak styrene was d i s t i l l e d under vacuum and a constant boiling point fraction was used for this ex-periment. The benzoyl peroxide was weighed accurately and dissolved in exactly 100 ml. of d i s t i l l e d styrene. 15 ml. of this solution was measured into each of the reaction cells preheated in the thermpstatted bath at 80°C, Samples of the reaction mixture were taken for analysis at the beginning of the experiment and at 1 hour intervals. Eaoh sample was weighed and dissolved i n 10 ml. of benzene containing 0.10 gm. hydroquinine per l i t r e as an inhibitor. The polystyrene formed was precipitated through the addition of 30 ml. of methanol, i l l reagents used were of analytical grade. The solvent, methanol and residual monomer styrene were removed by vacuum d i s t i l l a t i o n at 75°C. The polymer was then dried under a vacuum to a constant weight. In this f i r s t part of the experiment rate curves were obtained for two concentrations of benzoyl peroxide. Results Obtained in the Catalyzed Polymerization of Styrene The hourly percentage of polymerized styrene for two concentrations of benzoyl peroxide are given in Table IV and the corresponding rate curves in Fig. 9. It i s evident that at both oonoentrations of benzoyl peroxide, the 40 differences between the f i e l d and control rates are within experimental error. TABLE IV Percent Conversion of Styrene in a Catalyzed Polymerization - . . Reaction . . . . . Experiment # 1 BzgOg cone. - 2.000 gm/l. of styrene I n i t i a l conversion - 0.2 fo Temperature • 80.1 .4°C Field applied - 12000 gauss Field Control Time (Hours) ' $ Conversion fo Conversion 1 11.2 11.4 2 19.9 20.0 3 28.1 28.3 4 35.7 35.9 Experiment # 2 BzgOg cone. .5000 gm/l.. of styrene I n i t i a l conversion - .05 f> Temperature - 80.Ot .3°C Field applied - 12000 gauss Field Control Time (Hours) fo Conversion fo Conversion 1 5.45 5.73 2 9.62 10.3 3 14.0 14.9 4 18.4 19.3 If I Fig. % Th« tff««A of a v n a a n e V j c field- of Itooo gauss Oh * K e CaAa\v<z.ed / 2, 3 A Titrte in Hours tl 8o.Oi3°c. X a.ooo l^/l. 42 The Unoatalyzed Polymerization of Styrene The unoatalyzed polymerization of styrene at 80°C, i s such a slow reaction that i t does not lend i t s e l f to an investigation of t h i s type. I t was, however, considered de-sirable to study the unoatalyzed reaction i n a magnetic f i e l d to check the rather remarkable r e s u l t s reported by Sohmid et a l (10). A 15 ml. portion of f r e s h l y d i s t i l l e d styrene was placed i n each of the reaction c e l l s . A f i e l d of 12000 gauss was applied and the polymerization reaotion was c a r r i e d out i n the thermos tat ted bath at 80°G. for 8 hours under an atmosphere of nitrogen. Sohmid et a l dp not specify whether their re-action took place under a vacuum or under an atmosphere of nitrogen but mpst investigations of the unoatalyzed polymeri-zation have been done i n the absence of a i r i n order to avoid the effeot of oxygen. At the end of the 8 hour period three samples from each of the reaction ©ells were analyzed f o r percentage poly-merization. Three experiments s i m i l a r to the one described above did not reproduce the r e s u l t s reported by Sohmid et a l . It was then decided to do the unoatalyzed polymerization f o r a period of 16 hours i n order to determine whether an effeot might be apparent at the end of the longer period. The o e l l s were cleaned with greater care than before i n case the d i s -agreement with Sohmid's r e s u l t s might have been due to the presence of o a t a l y t i c impurities. 15 ml, of f r e s h l y d i s t i l l e d styrene, i n which no peroxide could be detected by a 43 qualitative test, was again measured into the preheated re-action c e l l s . Samples were taken from the c e l l s at the he-ginning of the experiment, after 8 hours and at the end of 16 hours. The percentage conversion was obtained by method de-scribed above. The temperature was measured at the site of each c e l l in eaoh of the experiments on the uncatalyzed polymeri-zation of styrene to ensure that the bath did not have a marked temperature gradient. For a further oheck on the con-ditions under which the polymerization was taking place the experiment was repeated for a period of 8 hours with no f i e l d applied. The results of this last experiment showed the same variation between the percent polymerized in the f i e l d and in the control c e l l as was obtained in the presence of the f i e l d . Results for the Unoatalyzed ..Polymerization- of Styrene The results for the unoatalyzed polymerization of styrene are reported in Table 1 for two similar runs for an 8 hour period. Also i n Table V (Experiment # 3) the per-centage conversions obtained i n the two cells in the absence of a magnetic f i e l d are given for comparison. The inconsist-ency of these results support the observation made by Guthbertson, Gee and Rideal (24) on similar discrepancies ooourring in investigations carried out by other workers (25). This experimental error could be minimized by greater care in preventing atmospheric oxidation of styrene to catalytic peroxides. 44 TABLE V Unoatalyzed Polymerization of Styrene Time - 8 hours Experiment Ho. #1 #2 #3 Temperature (°C,) 80.1t.3° 80.1±.3o 79.9 ±.3° Fie l d (gauss) 12,000 12,000 No Field * I n i t i a l Conversion (fo) 0,0 0.0 0.0 * F i e l d Conversion (fo) 6,4 6.0 5.2 * Control Conversion (fo) 5.9 4,8 6.5 Average of 3 samples. Less variation between the reactions in and out of the f i e l d was observed for the 16 hour experiment. The re-sults of this experiment are shown in Table VI and the corres-ponding rate curves in Fig. 10. Too much significance cannot be attached to these rate curves as only three points were obtained. TABLE VI Unoatalyzed Polymerization of Styrene Temperature - 79.8±-5°G Field Applied - 12,000 gauss I n i t i a l Conversion - 0.0 $ Field Control Time (Hours) fo Conversion. fo Conversion 8 5.2 5.0 16 11.9 11,7 4 5 Fig. 10 The Effect of a Magnetic Field' of 12,000 Gauss on the Unoatalyzed Polymerization of Styrene. Tflfwe \v\ Hours In view of the results obtained from the unoata-lyzed polymerization of styrene i t must be oonoluaed that the effect reported by Schmid et a l cannot be reproaucea or approaohea in a f i e l d of 12,000 gauss. 46 17 The Decomposition of Hydrogen Peroxide The decomposition of hydrogen peroxide has been investigated i n great detail (26)(27). Lemoine (E6) con-cluded that the reaction was unimolecular but his velocity oonstants show a great discrepancy for the decomposition of oonoentrated solutions of hydrogen peroxide at a temperature of 100^ A period of induction was observed by Lemoine and Clayton (27). Clayton studied the thermal decomposition of l»5fo solution of hydrogen peroxide at temperatures of 50°C and 60°C under varying conditions. He found that the velo-city constants were dependent on the purity of the water and the type of reaction vessel. The only oertain conclusion reached by Clayton was that the reaction was mora consistent-l y a f i r s t order reaction rather than a seoond order. Because of the experimental d i f f i c u l t i e s , the i n -vestigation of the decomposition of hydrogen peroxide in a magnetic f i e l d might be expected to lead to results whioh could be somewhat inconclusive » However, i t was thought that a more or less qualitative set of experiments oould detect any marked effects of magnetic f i e l d s . The experimental work was not sufficient to oome to any definite conclusion on f i e l d effeot but the results may be of interest to someone intending to do a more intensive investigation of the subject. A preliminary experiment was carried out f i r s t to 47 determine the general reaotion rate to he expected. 20 ml. of Merck's assayed "Superoxol" was diluted volumetrioally to 500 ml. with d i s t i l l e d water to give a 1.2$ solution of hydrogen peroxide. The method of analysis consisted of the addition of 100 ml. of d i s t i l l e d water and 20 ml. of 1:5 H2SO4 to an aliquot portion. This mixture was then titrated to a permanent pink end point with E/lO potassium permanganate solution. Hydrogen peroxide content was expressed in terms of ml. of W/10 permanganate solution. In studying the effect of a magnetio f i e l d , 15 ml. of 1.2$ hydrogen peroxide solution was measured into eaoh re-action c e l l . The reaotion was carried out at 80°C. with a f i e l d of 12,000 gauss applied to the f i e l d sample. I n i t i a l concentration of hydrogen peroxide was determined and the course of the reaotion was followed by analysis of samples withdrawn from the cells at 1 to 2 hour intervals. A second experiment consisted of obtaining rate curves for the decomposition of 3.0$ hydrogen peroxide solu-tion using the same reaction c e l l for the f i e l d and oontrol reactions as in the f i r s t experiment. Then the cells were cleaned thoroughly, interchanged in the bath and a second portion of 3.0$ hydrogen peroxide solution was measured into each c e l l . A second rate curve for the 3.0$ solution of hydrogen peroxide was thus determined. It was hoped in this way to detect a f i e l d effect over the difference in the sur-face effects of the two reaction c e l l s . 48 Results .Obtained i n the Thermal Deoompositioii of Hydrogen  Peroxide Three sets of rate curves f o r the decomposition o f hydrogen peroxide are shown i n F i g , 11. The rate curves ob-tained for the 1,3% s o l u t i o n o f hydrogen peroxide are l a b e l l e d ^AN and the rate curves for the 3,0% solution of hydrogen peroxide are l a b e l l e d "BfT and "'C". It w i l l be r e c a l l e d that i n experiment B the same c e l l s were used for the f i e l d and the oontrol reactions as i n experiment A. In both oases the f i e l d reaction rate was slower than the rate i n the control o e l l . On interchanging the c e l l s (experiment C) the rate i n the f i e l d c e l l became twice the rate i n the control c e l l . I f there were no f i e l d effect but only a difference i n the sur-face e f f e c t s of the two reaction c e l l s , the curves f o r experi-ment 0 should be just the reverse of the curves f o r experi-ment B. Although this i s not the ease, i t s t i l l i s not pos s i -ble to say conclusively that there is an acceleration of the rate of the decomposition of hydrogen peroxide i n a magnetio f i e l d . ClaytonV(27) who exercised extreme care i n h i s i n v e s t i -gation, found that the velooity constant k for t h i s reaotion oould vary by a factor of 2 i n a r e p e t i t i o n of an experiment under i d e n t i o a l conditions. « F i o ; . I I . T k « e f f e c t of Of IIOOO ( Jau&s K^dvoefe* a m a g n e t fe. f i e l d ov\ H\e decompos i t ion "Te m pz rcA u r e - 7 9 • ?i.3 *C so Disoussion of Results Tne experimental results obtained in this investi-gation show that there is no detectable effeot of a magnetio f i e l d of 12000 gauss on the rate of the decomposition of benzoyl peroxide in toluene or on the rates of the catalyzed and uneatalyzed polymerization of styrene. Some understanding of the reasons for the absence of a f i e l d effeot can be ob-tained from a consideration of the factors which govern Jhe rate of a chemical reaction. She rate of a chemical reaotion is given by the integrated irrbenius' equation: The velocity constant k is dependent on Activation Energy E, the Absolute Temperature T, a Collision Frequency factor Z and a Probability Factor P. The probability factor P measures the probability of a reaotion taking place on the c o l l i s i o n of two activated molecules. It i s , in fact, an arbitrary quantity introduced into the rate equation to account for the discrepancies be-tween observed and calculated reaotion rates. For many simple reactions the Probability factor has a value of unity but for reactions between more complex molecules i t may range in value from unity to 10 . It is dependent on the type of orientation of molecules required for a f r u i t f u l c o l l i s i o n 51 and the state of the molecules at the time of c o l l i s i o n . The factor P w i l l he decreased s i g n i f i c a n t l y by s t e r i c hindrance including mechanical interference of bending o s c i l l a t i o n s or by r e s t r i c t e d rotations of the molecule, 'Suoh.a decrease i n the P factor w i l l decrease the v e l o c i t y constant k and therefore cause the r e a c t i o n to proceed at a reduced r a t e . f o r large non-symmetrical molecules such as benzoyl peroxide or styrene the number of eff e c t i v e c o l l i s i o n s , that i s , the number of c o l l i s i o n s leading to reaction, w i l l depend on the number of times aotive centres come into oontaot. I f the application of a magnetic f i e l d decreases the number o f effe c t i v e c o l l i s i o n s by the orientations of the molecules in such a way that the coincidence of active centres i s reduced, the value of P w i l l be reduced. The number of e f f e c t i v e c o l l i s i o n s , under some conditions, might be Increased by orientation i n a magnetic f i e l d i n which case the f i e l d would increase the P f a c t o r above i t s normal value. In order that the two molecules s h a l l react they must possess between them an amount of energy B i n excess o f the mean energy possessed by the molecules in the system at the p a r t i c u l a r temperature. This excess energy i s c a l l e d the Ac t i v a t i o n Energy for tiie r e a c t i o n . The magnitude of the a c t i v a t i o n energy required f o r a r e a c t i o n depends On the po-t e n t i a l energy b a r r i e r whioh must be surmounted by the re-acting system i n order that the reaction s h a l l take place. The potential b a r r i e r and hence the a c t i v a t i o n energy may be l o w e r e d b y p u t t i n g t n e m o l e c u l e i n i t i a l l y i n a m o r e r e a c t i v e s t a t e . S h i s m a y b e a c h i e v e d b y i n d u c i n g b o n d s t r a i n w i t h i n t h e m o l e c u l e , p o s s i b l y t h r o u g h t h e a p p l i c a t i o n o f a n e x t e r n a l p e r t u r b i n g f o r c e . H o w t h i s m i g h t b e a c c o m p l i s h e d t h r o u g h t h e a p p l i c a t i o n o f a m a g n e t i c f i e l d i s n o t a p p a r e n t . T h e p o t e n t i a l b a r r i e r m a y b e r a i s e d b y p l a c i n g a m o l e c u l e i n a l e s s r e a c t i v e s t a t e . I f , i n a m a g n e t i c f i e l d , a s L e f f l e r a n d S l e n k o (11) s u g g e s t , t h e s p i n m o m e n t s o f o d d e l e c t r o n s a r e s o o r i e n t a t e d t h a t t h e f r e e r a d i c a l s w i l l n o t r e a c t e a s i l y , t h e a c t i v a t i o n e n e r g y o f t h e s y s t e m m a y b e i n -c r e a s e d . T h i s i n c r e a s e i n t h e e n e r g y r e q u i r e d f o r a r e a c t i o n t o t a k e p l a c e w i l l l o w e r t h e v e l o c i t y o f t h e r e a c t i o n t o a m a r k e d d e g r e e s i n c e t h e a c t i v a t i o n e n e r g y a p p e a r s i n t h e e x -p o n e n t i a l o f t h e I r r h e n i u s e q u a t i o n . & s m a l l e f f e o t o n t h e a c t i v a t i o n e n e r g y o f a s y s t e m m a y h a v e a v e r y s i g n i f i c a n t e f f e c t o n t h e v e l o c i t y o f t h e r e a c t i o n . I t w o u l d s e e m t h a t t h e m o s t s i g n i f i c a n t e f f e c t o f a m a g n e t i c f i e l d o n a r e a c t i o n w o u l d b e i n f l u e n c i n g t h e o r i e n t a -t i o n o f t h e m o l e c u l e s o r r a d i c a l s t a k i n g p a r t i n t h e r e a c t i o n , i n a p p r o x i m a t e c a l c u l a t i o n c a n b e m a d e t o o b t a i n t h e f r a c t i o n o f f r e e r a d i c a l s i n t h e s y s t e m w h i o h w o u l d l i n e u p i n a n a p p l i e d m a g n e t i o f i e l d . P r o m l a n g e v i n ' s p a r a m a g n e t i c t h e o r y t h e m o l e c u l a r m a g n e t i o m o m e n t , , i n t h e d i r e c t i o n o f a m a g n e t i c f i e l d i s 53 such 'that ytZ ^ • / ' where^ i s the t o t a l magnetic moment o f the mole cole ( 3 ) , I f this expression is applied to the case of 1 molecules i n a gram mole (where I is Avogadro's number), gives the fraction of molecules which have their magnetio axes i n the direction of the f i e l d . The remaining molecules w i l l have their magnetio axes at right angles to the f i e l d . It i s realized that this would be an i d e a l i z e d case but the net result would be the same as considering the magnetic moments resolved in the d i r e c t i o n of the f i e l d . For a gram mole of a substance this f r a c t i o n of molecules ) becomes suoh that g XT In evaluating fJ/» , which i s the gram molecular magnetic moment i n organic free r a d i c a l s , the coupling between spin and o r b i t a l moments can be neglected and the molecular magnetic moment can be considerea as a r i s i n g only from the spin moments of the unpaired electrons (88). This can be written- as Bohr units or /U$ = 'J^2- e r g s p e r s a x t S S For one unpaired electron the spin quantum number S i s equal to 1/2. ' • 5 4 ^ 5 oan r e p l a c e i n tne e x p r e s s i o n f o r the f r a c t i o n of molecules or f r e e r a d i c a l s which w i l l l i n e up i n a mag-n e t i c f i e l d : 7 . / -f o r an a p p l i e d f i e l d o f 12,000 gauss and at a temperature o f 80°C. the f r a c t i o n ^ , i s of the order o f 10" 3. T h erefore, i t would seem that e f f e c t i v e l y only one f r e e r a d i c a l out of each thousand would l i n e up completely i n a f i e l d o f 1£, 000 gauss. T h i s amount of r e s t r i c t i o n on normal motion of the molecules would have v e r y l i t t l e e f f e c t on the p r o b a b i l i t y f a c t o r P. However, i n the case of r e a c t i o n h a v i ng f r e e r a d i c a l s as ohain i n i t i a t i n g c e n t r e s and as c h a i n -propagating s p e c i e s a s m a l l e f f e o t of a magnetic f i e l d on the i n i t i a l stages of the r e a c t i o n might be expected to have an a m p l i f i e d e f f e c t on the o v e r - a l l v e l o c i t y o f the prooesS. This a m p l i f i e d e f f e o t was not d e t e c t e d i n the f r e e r a d i c a l r e a o t i o n s s t u d i e d so i t can be assumed t h a t n e i t h e r the a c t i -v a t i o n energies f o r the v a r i o u s stages o f the r e a o t i o n nor the P r o b a b i l i t y F a c t o r are s i g n i f i c a n t l y a f f e c t e d by the a p p l i e d magnetic f i e l d . There i s one more p o s s i b l e e x p l a n a t i o n f o r the ab-sence of an e f f e o t by magnetic f i e l d s on r e a c t i o n s i n v o l v i n g f r e e r a d i c a l s . I n a l l paramagnetic substances, on a p p l i c a t i o n of a f i e l d , there i s a time l a g before the molecules are o r i e n t a t e d . T h i s paramagnetic r e l a x a t i o n time, i . e . , the time r e q u i r e d f o r the o r i e n t a t i o n o f molecules, i s not known f o r 55 free radicals in solution. However, i t i s probably of the same order of magnitude as the normal lifetime of a free radi-cal. It might be expected, therefore, that free radicals would disappear in reaction before appreciable orientation could take place, i n explanation of this type may account for the absence of any effect of the f i e l d on the free radical reactions investigated. A significant feature of this investigation i s the faot that i t was not possible to reproduce the results re-ported by Schmid et a l (10). Although the procedures followed were basically the same as those used by Schmid et a l , dis-tinct improvements in technique were Introduced in this pre-sent study. It can be concluded, therefore, that the results reported by the above authors are in error. This marked difference in rate between fi e l d and oontrol samples may have been a consequence of poor thermos tat ting around the restricted part of the bath in which the f i e l d c e l l was located. In this investigation particular care was exercised to ensure that the f i e l d and control c e l l s were held at the same temper-ature. A more complete discussion of the effect of a mag-netic f i e l d on reactions involving free radicals cannot be put forward u n t i l more experimental work has been done. 56 Suggesttone for Further Work; In general the investigations of the effeot of a magnetio f i e l d on chemical reactions reported in literature have heen somewhat qualitative in nature. The mechanism of a magnetio f i e l d effect might he more easily explained i f the relationship between the strength of the applied f i e l d and the magnitude of its effect on a ohemioal reaotion were investi-gated quantitatively. The following problems are suggested with this in view; (1) the dependence of the velocity constant on f i e l d strength in a reaction for which a f i e l d effeot has been observed. 1 suggested reaction is the reduction of f e r r i c chloride with metallic iron in hydrochloric acid (9). (2) the rate of change in magnetic susceptibility during the course of a reaction which i s influenced by a magnetic f i e l d . (3) the further study of hydrogen peroxide decomposition. The diamagnetic hydrogen peroxide (29) decomposes to give paramagne tic oxygen as one of i t s products. Such an effect may be determined by f i r s t establishing a normal rate curve in the absence of a f i e l d , then applying a fi e l d without changing any of the i n i t i a l conditions under which the reaotion is being carried out. A break in the rate curve may occur, thus indicating a f i e l d effeot. 57 REFERENCES (1) Joos, Georg, "Theoretical Physios'1, Blaekie and Son Ltd., London and Glasgow (1934). (2) Stoner, E. C, "Magnetism1*, Methuen and Co., Ltd., London (1948). (3) Bhatnagar and Kapur, "Physioal Principles and Applications of Magneto chemistry**, Maomillan and Co., Ltd., London (1935). (4) Pauling, L., Proc. Roy. Soc, A, 114. 181 (1927), (5) Van Fleck, wThe Theory of El e c t r i c and Magnetic Susceptibilities", Oxford University Press, Oxford (1932). (6) Selwood, P. W., Ghem. Rev., 38, 41, 1946. (7) de Hemptinne, A . , Z . physik. Chem. 34, 669 (1900). (8) Parker and Armes, Trans. Roy. Soc. Can. 18, 203 (1924) (9) Bhatnagar, Mathur and Kapur, P h i l . Mag J7 8, 457 (1929). (10) Sohmid, Muhr and Marek, £• Eleetroohem. 51, 37-8 (1945). (11) Leffler and Sienko, J.Chem.Phys. 17_, 215 (1949 ). S8 (IS) L e f f l e r , J. E., J. Chem. Phys. 17, 741 (1949). (13) Bryce, I . A., Can. J. Researoh, B. 28. (1949). (14) Brown, 33. J., J. Im. Chem. Soc. 62, 2657 (1940). (15) l o z a k i , K., and B a r t l e t t , P . D., J, im. Chem. Soo., 68, 1686-92 (1946). (16) Cass, W. E., J. Im. Chem. Soc. 68, 1976-82 (1946). (17) Eyring, H., Ann. JJ.Y.Aoad.Sei., Vol. X f l Y , A r t . 4, 371 (1942). (18) Price, G, C., ^Mechanisms of Heactions at Carbon-Garbon Double Bonds*, Interscience Publishers, Inc., lew York (1946). P r i c e , G. C., Ann. 1 . Y. Aoad. S c i . 44, 351-78 (19 43) (19) Bawn, J. Chem. Soo. 1949. 1042. (20) Staudinger, Trans. Faraday Soo. 32, 97 (1936). (21) Flory, J. Am. Cham. Soo. 59, 241 (1937). (22) Farquharson and Ady, lature 143. 1067 (1939). (23) Bar t i e t t and Altsehul, 3, Am. Chem. 67,, 816 (1945). (24) Outhbertson, Gee and Rideal, lature 140. 889 (1937). (25) Suess, P l l e h and Rudorfer, 2. physik, Ghem. A 179. 361 (1937). 5 9 M a r k a n a R a f f , Z . p h y s i k . C h e m . B 8 1 . 2 7 5 - 9 ( 1 9 3 6 ) . S o h n l z a n d H e u s s m a n , Z . p h y s i k . Ghem. B 3 6 , 1 9 4 ( 1 9 3 7 ) . ( 2 6 ) l e m o i n e , J. O h i m . P h y s . 1 2 , 1 - 5 7 ( 1 9 1 4 ) . ( 2 7 ) C l a y t o n , T r a n s . F a r a d a y S o o . 1 1 , 1 6 4 ( 1 9 1 5 ) . ( 2 8 ) M u l l e r , 3., Z , E l e k t r o e h e m . 5 1 , 2 4 ( 1 9 4 5 ) . ( 2 9 ) S a v i t h r i , K . a n d R a m a C h a n d r a R a o , S . , P r o c . I n d i a n A c a d . S o i . 1 6 J , 2 2 1 - 3 0 ( 1 9 4 2 ) . 

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