KINETICS AND MECHANISM OF ACETALDEHYDE CHLORINATION IN A NONPOLAR SOLVENT - 1 - BASIC FEATURES OF THE PROCESS

Kinetics of the liquid-phase acetaldehyde chlorination to monochloroac etaldehyde was studied in the medium of water-free carbon tetrachlorid e containing a catalyst, trichloroacetic acid or hydrogen chloride, Th e apparent activation energy and reaction orders for all components of the reacting mixture were determined. A mechanistic scheme for the re action in a nonpolar medium was proposed: A + catalyst <----> I-1 --> I-2(+Cl-2,) --> CH2ClCHO + HCl + catalyst, The mechanism involves thre e steps: (1) the reaction of acetaldehyde with the catalyst, which yie lds an intermediate species I-1; (2) the isomerization of I-1 into ano ther intermediate I-2; and (3) the reaction of I-2 with chlorine disso lved in the mixture. Isomerization is a rate-limiting step of the proc ess, and the rate is independent of the chlorine concentration. The ki netic description is presented for the pseudo-steady-state chlorinatio n in the nonpolar medium in the presence of Bronsted acids. The effect of association of catalyst molecules on the apparent rate order (n) w ith respect to the catalyst (HCl) in homogeneous reactions was analyze d. The value of II varies depending on the dominating catalyst structu re and activities of various structures: lip < rt < p, where p is the maximum number of associated monomer molecules. The fractional reactio n order with respect to the catalyst in acetaldehyde chlorination resu lts from specific features of equilibria in the steps preceding the li miting step, rather than HCl association.