Peresters peroxide value

I. 463 A) is close to the value for fert-butyl hydroperoxide (1) (95° and 104°, two crystallo-graphically independent molecules), which points to a comparatively small steric demand of the acyl group in peresters. Due to its structural similarity to diaUsyl peroxides, it is reasonable that the ortho ester 56 P2, 0—0 = 1.481 A, C—O—O—C = 145.1°) exhibits a significantly larger peroxide dihedral angle than 54 . 

In this section we discuss the thermochemistry of some species with the general formulas, RC(=0)00H, RC(=0)00R and RC(=0)00C(=0)R. These species have the generic names peracids (peroxycarboxyUc acids), peresters (percarboxylate esters) and acyl peroxides. The enthalpy of formation values are in Table 3. Three formal reactions that are discussed here are conceptually the same as in the earlier sections. Because now there is a carbonyl group present, we rewrite equations 5, 6 and 9 as equations 14, 15 and 16. 

The three saturated long-chain tert-butyl peresters are members of a homologons series, and as such, the weighted least-squares regression analysis of the enthalpies of formation V5. number of carbons yields a methylene increment of —26.7 kJmol , a typical valne for liquids. The methylene increment for the terf-butyl esters of the Cg, Cjo, Cn and C14 acids is —28.0 kJmol. The closeness of these two values ensures that the enthalpies of formal reaction 16 will be nearly constant. For the three pairs from Table 3, the value is —70.3 8.1 kJmol. The standard deviation from the mean is quite large because the arithmetic difference for the C12 ester and perester, —79.5 kJmol, is quite a bit more negative than the differences for the Cio and C14 pairs, —64.4 and —66.9 kJmol, respectively. Unfortunately, the acids and esters are in different phases and so we are reluctant to attempt any comparison between them, such as a formal hydrolysis reaction or disproportionation with hydrogen peroxide. 

The enthalpies of reaction 16 for solid and gaseous dibenzoyl peroxide are —45.8 and —47.3 kJmoU, respectively. These values are much smaller than those calculated for the liquid dialkyl peroxides ca —56 kJmoU ), the acyl peresters ca —70 kJmoU ) or the non-aromatic diacyl peroxides (—89 or —59 kJmol ). However, we have no reason not to accept the result. It would be futile to use this result for further calculations concerning the solid phase enthalpies of formation of bis(o-toluyl) peroxide, bis(p-toluyl) peroxide and dicinnamoyl peroxide because all the peroxide and the anhydride product enthalpy of formation data are from the same suspect source . 

The values of k and ki at 119.4 °C were calculated to be 9.36 x 10 sec and 3.89 X 10 l. mole. sec, respectively. Induced decomposition of /-butyl perbenzoate is less important relative to unimolecular decomposition than it is in the benzoyl peroxide reaction. The values of the first-order (kj) and induced decomposition (kj) rate coefficients for the latter peroxide in toluene at 80 °C are 3.28 x 10 sec and 4.28x10 I. mole". sec , respectively . Some caution should be used in assuming that rate law (1) will be obeyed for all peresters in all solvents. It was stated previously in the diaroyl peroxide section (13.2.1), that the order in peroxide was dependent upon the mode of termination. It is then conceivable that the first-order rate coefficient could contain contributions from both unimolecular and induced decomposition reactions. The effect of concentration variation on the... 

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