Perbenzoic acid, decomposition

The enthalpy of activation for the decomposition of perlauric acid is given in Table 128 the Arrhenius activation energy, determined with the use of diphenyl-picrylhydrazyl, was found to be 19 + 2 kcal.mole . In the aromatic series, the activation energy for perbenzoic acid decomposition is reported to be 30 kcal. mole in benzene solvent . The measurements were made by following the rate of disappearance of the free radical scavenger, diphenylpicrylhydrazyl. The activation energies appear to be low and the difficulty may be due to induced decomposition. Additional rate data are given in Table 129 for various aliphatic peracids. 

Rate of thermal decomposition reported in ref (11) for perbenzoic acid. A number of other peracids give approximately the same rates. 

Cornellissen PJ, Beijersbergen van Henegouwen G, Gerritsma KW. Photochemical decomposition of 1,4-benzodiazepines. Chlordiazepoxide. Int J Pharm 1979 3 205-220. Vargas F, Rivas C, Canudas N. Formation of a perbenzoic acid derivative in the photodegradation of fenofibrate phototoxicity studies on etrythrocytes. J Pharm Sci 1993 87(6) 590-591. 

After the perbenzoic acid is liberated with sulfuric add, it may be extracted from the aqueous solution with any appropriate organic solvent (e.g. ether or ethyl acetate). Even if concentrated solutions of perbenzoic acid are requirdl, it is better to apply the amount of solvent specified (or more) and then to concentrate the solution under reduced pressure at a temperature not above 30-35°. The solution may, but need not, be dried before concentration. Anhydrous sodium sulfate is the only satisfactory drying agent. Calcium chloride sometimes causes a sudden decomposition of the peracid. 

Boeseken et a/. first studied the kinetics of such reactions the first report dealt with the reaction of perbenzoic acid with derivatives of styrene in chloroform solution and despite the ease of decomposition of the reagent, styrene was proved to react less rapidly than /3-methyl- or /3-ethyl-styrene. In the second paper, the rates of reaction of a number of olefins with peracetic acid in acetic acid were shown to increase with substitution of the olefinic bond, viz. 

Chimerical decomposition with the cleavage of one bond and formation of another bon is close to concerted decomposition. ortho-Substituted esters of perbenzoic acid decompose very rapidly if the substituent X is the iodine atom, RS radical or a substituent with the double bond. The accelerating eifect of these ortho-substituents is explained by the fact that the cleavage of the O—O bonds in the transition state is compensated in part by O—X bond formation, for example. 

Colorless composites with good mechanical properties can be obtained with either -butyl perbenzoate, cumene- or -butyl hydroperoxide and ascorbic acid or ascorbyl palmitate systems (50). Mechanisms for the free radical formation are given in Fig. 4. Addition of trace amounts of transition metals in their higher oxidation state (Cu", Fe" ) to the perester component further speeds up the polymerization. On admixture with the ascorbic acid derivative the metal cation is reduced to its lower oxidation state which, because it is a potent one electron reductant and will rapidly activate the free radical decomposition of the perester, which it in turn is reoxidized to its higher oxidation state. Means for prevention of oxidation of ascorbic acid or its derivatives on prolonged storage must be developed for these formulations to be suitable for dental application. 

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