Oxidation of organic compounds with cerium(IV). XVIII. Oxidative decarboxylation of substituted phenylacetic acids

Abstract

Substituted phenylacetic acids are readily decarboxylated when treated with ceric ammonium nitrate in aqueous acetonitrile solutions containing nitric acid to give carbon dioxide and the corresponding benzyl alcohol, benzaldehyde, and benzyl nitrate. Oxygen-trapping experiments indicate that benzyl radicals are formed as intermediates. A Hammett plot of the relative rates of oxidation of meta-and para-substituted phenylacetic acids vs. + values gave a p of -2.91 ± 0.29. The oxidative decarboxylation is proposed to be a one-electron process with the rate-determining step being the decomposition of a carboxylic acid-cerium(IV) complex to a benzyl radical and carbon dioxide through a very polar transition state.The oxidative decarboxylation of carboxylic acids has been studied extensively. Many of the oxidants used for this reaction are metallic ones such as lead(IV),2 cobalt(III),3 silver(II),4 manganese(III),5 thallium(III),6 and chromic acid,7 but nonmetallic oxidants8 have also been used. In addition, oxidative decarboxylations have been effected electrolytically.9

Copper‐Mediated Deoxygenative Trifluoromethylation of Benzylic Xanthates: Generation of a CCF3 Bond from an O‐Based Electrophile

“…Based on the above results and previous reports,5c, 14–16, 19–23 we propose a plausible mechanism for Cu 0 ‐mediated deoxygenative trifluoromethylation of benzylic xanthates using Umemoto’s reagent 2 a (Scheme ). Reduction of 2 a by Cu 0 in situ provides CuCF 3 in addition to CuOTf 5c.…”

“…This could be attributed to the weak Lewis acidic nature of CuOTf, which generates weak positive charge at benzylic position in the transition state 15a. b, 22 Alternatively, the small negative value for ρ + could be attributed to a pathway involving a benzylic radical cation intermediate 23. The reaction of 1 a with a pregenerated combination of CuCF 3 /CuOTf was inhibited in the presence of several radical scavengers, including 1,4‐dinitrobenzene, hydroquinone, and 2,2,6,6‐tetramethyl‐1‐piperidinyloxy [TEMPO, Eq.…”

Substituent effects on the kinetics of the cerium(IV) oxidation of mandelic acids in sulfate media. Anomalous kinetic behavior of the methoxy derivative

“…2) range of 1.00-2.00 mol/dm3: at 25.0°C, k; = 18 dm3/mol s and k; = 37 mol/dm3 s. Moreover, if we consider the experimental condition at 2.00 mol/dm" sulfuric acid, we evaluate that k ; = 6.8 dm6/mo12 s, k i = 14 s-l, and k ; + ki/[H2S04]2 = 10.3 dm6/moI2 s. The latter value is in good agreement with that [see eq. (3)] obtained in H2S04-LiHS04 mixtures and gives a further support to the validity of the final rate equation (6) for the cerium(1V) oxidation of p-methoxymandelic acid.…”

“…Anomalously high rates were also observed previously [6,7,15] in the oxidation of methoxy derivatives of several organic substrates containing a benzene ring and were generally ascribed to a change in the reaction mechanism. It was suggested that the methoxy group facilitates [IS] attack on the aromatic nucleus with the probable formation of an intermediate radical cation [6,7,15]. The same explanation can reasonably apply to the p-methoxy derivative of the present study.…”

Effect of CoOOH loading on the photoelectrocatalytic performance of WO3 nanorod array film

“…9. When WO 3 is illuminated, the photoelectrons would be excited from the valance band to conduction band and then transfer from the vertical-aligned WO 3 the organic enclosing the cobalt ion valency circle [29,30] and meantime the organic would be degraded. The CoOOH serving as hole trap could promote photogenerated carriers separation and improve photoelectrocatalytic degradation of MB over the WO 3 -CoOOH composite (Fig.…”