4250 [CONTRIBUTION FROM
C. G. OVERBERGER AND R. W. CUMMINS THE
VOl. 75
DEPARTMENT OF CHEMISTRY, INSTITUTE OF POLYMER RESEARCH, POLYTECHNIC INSTITUTE OF BROOKLYN]
Mechanism of the Oxidation of p,p'-Dichlorobenzyl Sulfide by Peroxybenzoic and para Substituted Peroxybenzoic Acids BY C. G. OVERBERGER AND R. W. C U M M I N S ~ RECEIVEDFEBRUARY 23, 1953 A study was made of the oxidation of p,p'-dichlorobenzyl sulfide to sulfoxide by peroxybenzoic and p-methoxyperoxybenzoic acids in toluene, and by peroxybenzoic, p-methoxy-, p-methyl-, p-chloro- and p-nitroperoxybenzoic acids in isopropyl alcohol. Activation energies, frequency factors and entropies of activation were obtained. The differences in oxidation rates between peroxyacids were found t o be influenced approximately 60% by differences in activation energy and 40% by differences in activation entropy with A S increasing approximately linearly with E. Electron attracting groups in the p-position increased the oxidation rate, while electron repelling groups decreased it. The Hammett treatment of the substituent effect gave an excellent straight line with the exception of the point for @-methoxyperoxybenzoic acid. Large differences in entropy of activation for the oxidations, by peroxybenzoic, $-methyl- and p-nitroperoxybenzoic acids in isopropyl alcohol were observed. Solvent likewise had a pronounced effect on k, E and AS*. A mechanism for peroxybenzoic acid oxidations is proposed. The four p-substituted peroxybenzoic acids employed were isolated and characterized for the first time.
*
Benzoic acid, sublimed (Baker Analyzed Reagent), 111.p. It has long been known that organic peroxyacids was used without further purification. are much stronger oxidants than hydrogen peroxide 121.5-122.0°, Isopropyl alcohol (Baker Analyzed Reagent) was dried and that of all the derivatives of hydrogen peroxide, with magnesium isopropoxide according to the general proonly the peroxyacids are strong oxidants in the cedure described previously,8 except that carbon tetracold.2 Lewin3 in 1928, commented on the ease bromide was substituted for iodine as a catalyst. The alcohol was separated from the reaction mixture by with which sulfides may be oxidized to sulfoxides dried simple distillation using a magnesium perchlorate drying by peroxybenzoic acid a t ordinary temperatures tube for protection against moisture, and the distillate fracand observed that peroxybenzoic acid will effect tionated from sodium isopropoxide using a 100- by 2-cm. some oxidations where hydrogen peroxide and column packed with '/*-inch, single-turn glass helices. A middle one-third cut was collected, b.p. 82.1-82.8" (760 other oxidants fail. Criegee2 suggested that the mm.), ?PD 1.3775 [b.p. 82.5' (760 mm.), ?PD 1.3776].9 effectiveness of peroxyacids as oxidants is the Toluene (Baker Analyzed Reagent) was extracted with result of strong polarization due to their dissym- concentrated sulfuric acid followed by distilled water, dried metry about the 0-0 bond so that a peroxyacid over sodium and fractionated from sodium using the above will dissociate more readily than symmetrical hy- described column. A middle one-half cut was taken, 110.3°(760 mm.), @D 1.4970 [b.p. 110.8" (760 mm.), drogen peroxide under the influence of a reductant. b.p. f i Z f l ~1.49551.g Medvedev and Blokh4 in 1933 reported the rates Magnesium perchlorate, C.P. anhydrous, was obtained of oxidation of cyclohexene to epoxycyclohexane in from the G. Frederick Smith Chemical Company. p,p'-Disubstituted benzoyl peroxides were prepared from benzene and xylene by several substituted peroxythe corresponding benzoyl chlorides by the method of Price benzoic acids and concluded that the oxidations and Krebs.'O p-Methoxy-, p-chloro- and p-nitrobenzoyl were bimolecular uncatalyzed by the corresponding chlorides were Eastman White Label grade; p-methylbencarboxylic acids, and that the rates were markedly zoyl chloride was prepared from p-methylbenzoic acid and influenced by solvents. More recently Szmant, thionyl chloride. All of the peroxides were of 95% purity better immediately before use as determined by the KoHarnsberger and Krahe5 found that the oxidation or katnur and Jellingll peroxide method. The peroxides had of phenyl sulfoxide to sulfone by peroxybenzoic been prepared and characterized previously: p,p'-diacid followed bimolecular reaction kinetics and that methyl-,'Z p,p'-dimethoxy-,l3 p,p'-dichloro-'4 and p,p'-dlnitrobenzoyl peroxide.l6 the oxidation was catalyzed by benzoic acid. peroxybenzoic acids were prepared from study of the kinetics of oxidation of p,p'- thep-Substituted peroxides essentially by the Kolthoff, Lee and Mairs dichlorobenzyl sulfide by peroxybenzoic and four modificationlo of the Braun pr~cedure.'~The concentration p-substituted peroxybenzoic acids was made in iso- (g./lOO ml. of solution) of the chloroform solutions of the ppropyl alcohol and toluene with the objective of substituted benzoyl peroxides employed in the peroxyacid as dictated by their solubilities, were: p-H-, obtaining an insight into the mechanism of organic preparations, 25.0; P-CHaO-, 10.0; p-CH,-, 10.0; P-Cl-, 8.0; P-S02-, peroxyacid oxidation. A similar investigation 4.0. The amounts of sodium and sulfuric acid used were with hydrogen peroxide is reported separately.6 in proportion to the peroxide concentrations. An ice-acetone-bath was found more convenient than the customary Experimental salt-ice mixture for refrigerating the reactants. The reMaterials .-p,p'-Dichlorobenzyl sulfide, m .p. 41.5-42 .0 ' uncor., was prepared as described by Overberger, Ligthelm aud Swire' (40.541.0").7 (1) A portion of a thesis by R. W.Cummins submitted t o t h e Polytechnic Institute of Brooklyn in partial fulfillment of t h e requirements for the degree of Doctor of Philosophy. ( 2 ) R. Criegee, A n n . , 560, 127 (1948). (3) L. Lewin, J . prabt. Chem., 118, 282 (1928); 119, 211 (1928); 127, 77 (1930); 128, 171 (1930). (4) S. Medvedev and 0. Blokh. J . P h y s . Chein. ( C S S R ) , 4, 721 (1933) [C. A , , 29, 6492 (1935)l. ( 3 ) 13. €1. Szmant. I T . 1'. Harnsherger and I;. Krahe, Atistracts of t h e 1 1 R f h .'.uI. Cl~ern.S i x . Rleeting, icall, 1!330, 1'. (j,jhT ~ 0 C. i . Ovrrherger awl I
