Mechanisms of Oxidation of Benzaldehyde

Oxidation of Liquid Aldehydes by Molecular Oxygen.

“…The oxidation of decanal ivas found to be of the 3/2 order for the thermal rate and of the first order for the photo rate (82) when the reaction was carried out in decane solution. The oxidation of benzaldehyde in benzene solution (36) with benzoyl peroxide as initiator was found to be of the first order in aldehyde, while the order of the thermal reaction was observed to be between 2 and 2.5. Later work (38) indicated that the thermal reaction was of the second order in aldehyde at high pressures of oxygen.…”

“…Wittig and Pieper (36) tried to analyze for the complex between perbenzoic acid and benzaldehyde which their kinetic data indicated was formed rapidly and decomposed slowly at room temperature, but n-ere not successful. They suggested two possible structures (46).…”

“…Pure reactants give a half-order reaction, while added inhibitors give a reaction of the first order. Examples of half-order kinetics are found for initiation by photolysis (11,21,23,26,33), radical sources (36,37,38, 44), ozone (16), and metal catalysts (7,8). The data in reference 16 had to be plotted by the authors to obtain the order.…”

The benzaldehyde oxidation paradox explained by the interception of peroxy radical by benzyl alcohol

“…The presence of catalysts, such as transition-metal ions, or free radical initiators, such as benzoyl peroxide or azo-bis-isobutyronitrile, increases the rate of this oxidation 20,21 . Photochemical excitation also facilitates this transformation and the consensus is that this reaction is a radical chain process [22][23][24] . It is therefore logical to ask how benzyl alcohol can be partially oxidized to give benzaldehyde in very high yield even in the presence of oxidation catalysts that are active in promoting conversion of benzaldehyde into benzoic acid, in some cases at temperatures as high as 433 K in the presence of 10 bar O 2 pressure.…”

Reaction Kinetics

“…Mulcahy & Watt(112) have investigated the peroxide-induced autoxidation of benzaldehyde. Cooper & Melville (113) have used the intermittent-light technique to obtain the chain length for the autoxidation of n-decanal.…”