The mechanism of the oxidation of alcohols and aldehydes with peroxydisulphate ion

Abstract

The kinetics of the reactions of peroxydisulphate with alcohols (methanol, ethanol, propan-1 -01, propan-2-01, and butanol) and with acetaldehyde have been studied. Their radical-chain behaviour has been established. Using a radical-scavenger method it has been shown that the chain-initiating step is the monomolecular homolysis of the peroxydisulphate anion. The 'limiting' concentration of the reducing agents, the mean kinetic chain length, and the overall energy of activation have been determined. The mechanism of the autoinhibition of the reaction of primary alcohol with peroxydisulphate has been discussed.Analysis of literature data shows that there are two main and contradictory opinions on the mechanism of alcohol oxidation with peroxydisulphate ion, radical-chain and non-radical mechanisms. Bartlett and Cotman' have reported that in the presence of methanol the rate of peroxydisulphate decomposition increases 25-fold and the overall rate law is (1). Theseauthors suppose that the reaction is radical-chain, and there are two parallel reactions for the chain initiation, monomolecular and bimolecular [reactions (2) and ( 3)]. Kolthoff et d 2 have Levitt and Malinowski l 1 have investigated the propan-2-01 oxidation at temperatures 2 50 "C. They established the rate law (7) where 0 ,< n ,< 1. n depends on the alcohol R = k[P][PriOH]" (7) concentration. The overall energy of' activation was 25 kcal mol-'. anions decreased the reaction rate. They put forward the heterolytic monomolecular cleavage (8) of S 2 0 8 2 -S2OS2-SO4'-+ so4 (8) S20a2 + CH30H -HS04-+ SO4-' + e H 2 0 H (3)

Oxidation of Benzene by Persulfate in the Presence of Fe(III)- and Mn(IV)-Containing Oxides: Stoichiometric Efficiency and Transformation Products

“…In the absence of O 2 , it is possible that HCHD radical was oxidized by S 2 O 8 2− to generate phenol (Reaction 13) and the ring-cleavage product (Reaction 14) at different ratios than those observed in the presence of O 2 . 34,52 Such a process would serve as a chain propagation reaction, producing one mole of SO 4 • for every mole of S 2 O 8 2− decomposed (Reactions 13-14 in Scheme 2). In the goethite-activated persulfate system, the concentration of the unknown compound was approximately 10 times higher in the N 2 -purged solution ([O 2 ]=3 μM) than that in O 2 -supersaturated solution ([O 2 ]=410 μM) after 5 days of reaction (Figure 4B).…”

“…The N 2 -purged solutions (i.e., [O 2 ] = 3 μM) resulted in the formation of phenol at concentrations that were approximately 30% of those observed under air-saturated conditions (i.e., [O 2 ] = 250 μM) or 10% of those observed under O 2 -supersaturated conditions (i.e., [O 2 ] = 410 μM). In the absence of O 2 , it is possible that HCHD radical was oxidized by S 2 O 8 2– to generate phenol (reaction 13) and the ring-cleavage product (reaction 14) at different ratios than those observed in the presence of O 2 . , Such a process would serve as a chain propagation reaction, producing one mole of SO 4 •– for every mole of S 2 O 8 2– decomposed (reactions 13–14 in Scheme ). In the goethite-activated persulfate system, the concentration of the unknown compound was approximately 10 times higher in the N 2 -purged solution ([O 2 ] = 3 μM) than that in O 2 -supersaturated solution ([O 2 ] = 410 μM) after 5 days of reaction (Figure B).…”

“…First, S 2 O 8 2– can serve as the oxidant for the HCHD radical (reactions 13–14). Previous studies found S 2 O 8 2– reacts quickly with a variety of carbon-centered radicals, including aromatic, aliphatic, and semiquinone anion radicals, to generate oxidized products and SO 4 •– . ,,,, This would lower the stoichiometric efficiency because it only produces one mole of SO 4 •– for each mole of S 2 O 8 2– that decomposes.…”

“…The 2− to generate phenol (reaction 13) and the ring-cleavage product (reaction 14) at different ratios than those observed in the presence of O 2 . 34,52 Such a process would serve as a chain propagation reaction, producing one mole of SO 4…”

Disintegration of Waste Activated Sludge by Thermally-Activated Persulfates for Enhanced Dewaterability

“…This behavior can also be explained by the radical chain reactions initiated by the reaction of SO 4 •– . It has been suggested that the one-electron oxidation of organic substrates by SO 4 •– produces an organo radical as an intermediate, which converts another PDS molecule into SO 4 •– , propagating the chain reactions (reactions and ). , …”