Kinetics of reduction of cinnamaldehyde by means of hydrido‐ and deuteridocobalt tetracarbonyl

Abstract

The reaction of HCo(CO)4 (HT) or DCo(CO)4 (DT) with excess cinnamaldehyde (CA) in methylcyclohexane (RH) at 22.2° and under 1 atm of CO follows pseudo-first-order kinetics in HT or DT with an inverse isotopic effect of 0.54. Identified products of the reaction are hydrocinnamaldehyde (HCA) and styrene (STY). The STY is believed to be an artifact of the thermal decomposition of the true product PhCH2CH2C( (DOUBLE BOND) O)Co(CO)4 (X) or its isomer. Reduction of the carbon-carbon double bond in CA is effected by hydrogen from both the cobalt compound and RH. It is proposed that the reaction involves a free-radical chain mechanism in which the rate of the slow step is proportional to [CA], the initial molar concentration of CA raised to a power of 1.5− 1.8. Additionally the rate of conversion of CA to HCA and X meets the criteria of a homocompetitive reaction with [CA], [HCA], and [STY] simple functions of t0.5 (where t is reaction time) for use of DT or (in a single case) a function of (t0.5 + t) for use of HT. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 473–481, 1997.