The heat of the photochemical addition of bromotrichloromethane to vinyl acetate has been measured using the dilatometric method described in part 1 of this series. It was found to be virtually independent of the initial concentration of the reactants, average values of 27.7 and 27.2 kcal/mole having been obtained for reactions in which initial mole ratios of bromotrichloromethane to vinyl acetate were 8 : 1 and 0-94 : 1 respectively. The specific heat and coefficient of expansion of bromotrichloromethane were found to be 0.18 cal/g and 1.062 x 10-3 deg.-1 respectively : for vinyl acetate values of 0.47 cal/g and 1.402 x 10-3 deg.-1 respectively were obtained.The photochemical addition of bromotrichloromethane to vinyl acetate is a CC13Br + CH2: C H . 0 . CO. CH3 +-CC13. CH2. CHBr. 0 . CO. CH3.
The photochemical reaction between brornotrichloromethane (TBr) and vinyl chloride (VC) has been studied over a wide range of reactant concentrations varying from 0.087 to 9.24 mole 1.-1 for TBr and from 1.26 to 14.4 mole 1.-1 for VC. The products of the reaction vary from the 1 : 1 adduct to low molecular weight polymer. Under the conditions studied, the reactions proceed by radical chain processes. When TBr is in excess, the addition of trichloromethyl radicals to VC is the rate-determining step, and the velocity coefficient for this reaction at 25°C was 990-1950
The direct photochemical addition of bromotrichloromethane (BTCM) to vinyl acetate (VA) at 25OC has been investigated. The product from initial mixtures of 10 : 1 and 1 : 1 mole ratios VA : BTCM is the 1 : 1 addition compound, and no polymer appeared to be produced. At much higher VA : BTCM ratios some low-molecular-weight polymer was found. The benzoyl-peroxide-catalyzed telomerization of these two materials was also studied at 60°C over a wide range of BTCM : VA mole ratios. The products varied from high polymer to the 1 : 1 addition compound, depending upon the mole ratio of the reactants. The change from very low to very high molecular-weight polymer, however, occurred over about a threefold change in mole ratio of the reactants. Furthermore, the rate of reaction went through a minimum in this region. The value of the ratio of the velocity coefficients for chain transfer to propagation (kt,/kp) was found to be in the region of 40 for reactions in which low-molecular-weight polymer was formed, but about 0.6 when the product of the reaction was high polymer.
Attempts have been made to measure the velocity coefficients involved in the photochemical addition of bromotrichloromethane to vinyl acetate. The system was studied using concentrations of bromotrichloromethane ranging from 0.26-9-58 mole 1.-1, and of vinyl acetate from 0.55-10.5 mole 1.-1. Conditions could not be found such that the chain-transfer reaction between a bromotrichloromethane molccule and the radical produced by the addition of a trichloromethyl radical to a vinyl acetate molecule became rate-controlling, and hence we could not measure its velocity coefficient. Rates of initiation were measured using DPPH, and the values obtained were found to be influenced to some extent by the solvent employed, and also by the technique used. These effects are reflected in the values of the velocity coefficients, which at 25°C were found to be : k2 = 795, 2410 and 1590 1. mole-1 sec-1, and k4 = 0.53 X 108, 1.61 x 108 and 1 . 0 6 ~ 108 1. mole-1 sec-1, when the rate of initiation was determined absorptiometrically in monomer, in solvent, and dilatometrically respectively. The last value in each case, is in good agreement with the results of previous workers 1 who evaluated these coefficients by substantially the same method.
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