EFFECT OF THE DISTRIBUTION OF PYRIDINE 1-OXIDE ON ITS CATALYZED TWO-PHASE REACTION OF BENZOYL CHLORIDE AND CARBOXYLATE ION

Benzoyl chloride (PhCOCl) exhibits a peculiar inhibitve effect on its reaction with some sodium carboxylates (RCOONa) catalyzed by pyridine I-oxide (PNO) in a CH₂Cl₂/H₂O medium. However, the reaction follows well the rate law -d[PhCOCl]_org/dt = K_obs[PhCOCl]_org = (k_h + k_c [PNO]_i.aq )[PhCOCl]_org. Where k_h is the uncatalyzed rate coefficient, k_c is the catalyzed rate coefficient, and [PNO]_i,aq is the initial concentration of PNO in aqueous phase. When the concentration of RCOONa is the sufficiently high, k_obs, can be expressed as k_obs, = k_h + kPNO[P-NO]_i,aq/(l + k_PNO) Where is k_PNO the intrinsic rate coefficient of the reaction between PhCOCl and PNO in CH₂Cl₂ and k_PNO is the distribution constant of PNO between H₂O/CH₂Cl₂ phases and is defined as k_PNO = [PNO]_aq/[PNO]_org. In order to account for this peculiar phenomenon, the effects of organic compounds, including CCl₄, alcohol, ester, and carboxylic acid, were investigated. The presence of organic additive affects the distribution of PNO between H₂O and CH₂Cl₂ phases, the reaction rate, and the yield of product. In general, the value of k_PNO correlated well with the effective concentration of free PNO in the CH₂Cl₂ phase. For the PNO-catalyzed reaction of PhCOCl and CH₃COONa in H₂O/CH₂Cl₂ medium, the main conclusions are:

(1)The presence of ROH additive in CH₂Cl₂ increases the distribution of PNO is CH₂Cl₂ and the value of k_PNO due to the hydrogen bonding between ROH and PNO.

(2)The presence of nonpolar CC1₄ and RCOOR' in CH₂Cl₂ decreases distribution of PNO and the values of k_PNO.

(3)The presence of RCOOH in CH₂Cl₂ enchances the distribution of PNO in CH₂Cl₂ and the value of k_PNO. However, the main product is PhCOOCOR instead of PhCOOCOCH₃ in contrast to the cases of adding ROH, CCl₄, and RCOOR'.