Silver(III) Oxidation of the DL-Mandelate Ion

DOI: 10.1039/P29900002123

Source and publish data:

Journal of the Chemical Society. Perkin transactions II p. 2123 - 2127 (1990)

Update date:2022-08-22

Topics:

Authors:

Kouadio, Issifou

Kirschenbaum, Louis J.

Mehrotra, Raj N.

Sun, Yunfu

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Article abstract of DOI:10.1039/P29900002123

The oxidation of DL-mandelate (MAN(1-)) by (1-) in strongly alkaline media has been investigated by stopped-flow spectrophotometry.Product analysis shows that benzaldehyde is the sole organic product when MAN(1-) is in excess.The rate law is k_obs = (a + b), where a = (6.2 +/- 0.2) dm³ mol^-1 s^-1 and b = (7.0 +/- 0.3) dm⁶ mol^-2 s^-1 at 25 deg C and l = 1.3 mol dm^-3.Oxidation of benzaldehyde (to benzoic acid) by Ag^III is more than an order of magnitude slower than the mandelate reaction.Activation parameters for both hydroxide-dependent and -independent paths are ΔH_a^<*> = (59.3 +/- 2.1) kJ mol^-1, ΔS_a^<*> = (-32.0 +/- 0.5) J mol^-1 K^-1 and ΔH_b^<*> = (48.0 +/- 2.3) kJ mol^-1, ΔS_b^<*> = (-68.5 +/- 0.6) J mol^-1 K^-1, respectively.Two different mechanistic pathways are discussed.A base-catalysed process, followed by C-C cleavage, seems to be the most probable mode of decarboxylation.The comparitive non-reactivity of phenylglyoxymate and α-methoxyphenylacetate ions underlines the importance of the α-OH group in the mandelate oxidation.