Journal of Molecular Catalysis A: Chemical 194 (2003) 237–248 The oxidation of styrene in the presence of thiols and iron porphyrin Stefan S. Kurek ∗ , Piotr Michorczyk, Anna-Maria Balisz Institute of Chemical Engineering and Physical Chemistry, Cracow University of Technology, ul. Warszawska 24, 31-155 Kraków, Poland Received 16 May 2002; accepted 16 September 2002 Abstract Benzaldehyde and a methyl sulfide, formed from the thiol used, are two major products of the title reaction in methoxyethanol. Primary alkyl thiols were less active than secondary ones, but the most active system was obtained with an aryl thiol, ben- zenethiol. Therefore, detailed studies were carried out with it. The reaction towards benzaldehyde and the methyl sulfide proceeded only in the presence of iron porphyrins. When the catalyst degraded, only side reactions, disulfide formation and anti-Markovnikov addition occurred. Thiols do not act as sacrificial reductants in the studied system. UV-Vis spectra revealed the formation of an iron(III) porphyrin radical cation. It was present only in the active phase of the reaction. Since it was formed with some delay, it did not make an intermediate of the studied reaction but seemed to be in equilibrium with it. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Iron porphyrin; Iron porphyrin thiolate; Styrene oxidation; TOCO reactions 1. Introduction Thiols are so readily oxidised that under oxidation reaction conditions could be thought to act as sacri- ficial reductants, unless bound in a manner inhibiting their oxidation. On the other hand, they modify the iron porphyrin centre so advantageously for oxidation reactions [1,2] that their use is very tempting. There is a danger though that thiols would promote the degra- dation of the porphyrin ring [3], which is the case in plant peroxidases that degrade protoporphyrin IX in the presence of thiol containing substrates, such as glutathione and cysteine [4]. ∗ Corresponding author. E-mail address: skurek@chemia.pk.edu.pl (S.S. Kurek). Most studies on metalloporphyrin catalytic sys- tems are devoted to models of cytochrome P-450, haem-containing monooxygenases [5]. They use only one oxygen atom out of two from the O 2 molecule and require a co-reductant, which provides two elec- trons per one molecule of the product. There were also successful attempts to employ hydrogen sulfide as the reducing agent in like reactions [6,7]. Metalloporphyrins, especially electron-deficient, can act as oxygenation catalysts in abiological systems that do not require any reductants at all and use both oxygen atoms from the O 2 molecule [8–10]. Interest- ingly, ethylbenzene oxidation by dioxygen, catalysed by iron(III) tetrakis(pentafluorophenyl)porphyrin, un- der similar conditions, gave the very same products (1-phenylethyl hydroperoxide, 1-phenylethanol and acetophenone) [11] as oxidation of styrene catalysed 1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1381-1169(02)00536-8