Mechanism of oxidation of mandelic acid by Fenton's reagent

The oxidation of DL-mandeiate (MAN-) by [Ag(OH),]-in strongly alkaline media has been investigated by stopped-flow spectrophotometry. Product analysis shows that benzaldehyde is the sole organic product when MAN-is in excess. The rate law is kobs = where a = (6.2 f 0.2) dm3 mo1-l s-l and b = (7.0 f 0.3) dm6 mol-2 s-' at 25 "C and I = 1.3 mol dms. Oxidation of benzaldehyde (to benzoic acid) by Ag"' is more than an order of magnitude slower than the mandelate reaction. Activation parameters for both hydroxide-dependent and -independent paths are AH: = (59.3 f 2.1) kJ mol-', A$ = (-32.0 0.5) J mol-' K-' and AH: = (48.0 & 2.3) kJ mol-', AS: = (-68.50.6) J mol-' K-l, 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 comparative non-reactivity of phenylglyoximate and amethoxyphenylacetate ions underlines the importance of the a-OH group in the mandelate oxidation.

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“…(13H15). However, if long-RCH(OH)C02-+ ox __+ ox' + RCH(OH)C02' (13) RCH(OH)CO~* -R~H O H + H + + co, (14) (15)…”

Section: Resultsmentioning

confidence: 99%

“…Although Walling and Amarnath ' found only benzaldehyde in the reaction of Fenton's reagent (Fe2+, H202) with mandelic acid, Mahapatro et a1. 13 showed that phenylglyoxylic acid is also formed.…”

mentioning

confidence: 99%

Silver (III) oxidation of the DL-mandelate ion

Kouadio¹,

Kirschenbaum²,

Mehrotra³

et al. 1990

J. Chem. Soc., Perkin Trans. 2

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The effect of buffers and chelators on the reaction of luminol with Fenton's reagent near neutral pH

Bottu

1991

J. Biolumin. Chemilumin.

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The chemiluminescence of the system luminol +Fe2+ +H2O2 was measured in aqueous buffer at pH 7.2. In veronal (5,5-diethybarbiturate) buffer, the luminescence is strongly quenched by ethanol and mannitol, but only weakly by t-butanol, benzoate and superoxide dismutase (SOD); complexing Fe2+ with 1,20-phenanthroline or 2,2'-dipyridyl causes a decrease of light production that can be partially obviated by the simultaneous addition of SOD. In phosphate buffer, the luminescence is higher than in veronal and it is efficiently quenched by all four OH. quenchers and by SOD. In Tris buffer, no light production is observed as long as the Fe2+ is not complexed. When Fe2+ is complexed by pyrophosphate or phytate, there is a strong chemiluminescence in all three buffers, which is quenched by all four OH. quenchers and by SOD. When Fe2+ is complexed by EDTA or DTPA, very little luminescence is observed. The luminol analogue phthalhydrazide, which was suggested by Merényi and Lind as a reliable OH. detector, can replace luminol only in phosphate buffer, and thus turns out to be very specific indeed for free OH..

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