[13520-69-9] · Cl2FeO8 · Iron(II) Perchlorate · (MW 362.87)
(aromatic and aliphatic hydroxylation; reductive decarboxylation of peracids; dehydration and monooxygenation of organic compounds)
Alternate Name: ferrous perchlorate.
Physical Data: dec >100 °C.
Solubility: ~98 g/100 mL H2O at 0 °C; sol alcohol, HClO4.
Form Supplied in: light green crystalline powder.
Handling, Storage, and Precautions: eye irritant; hygroscopic; contact with combustible material may cause fire. Warning: conversion to lower hydrates by unintentional dehydration may cause explosion. Use due caution in handling, as for all perchlorates. Use in a fume hood.
Aromatic substrates are hydroxylated under mild conditions when treated with iron(II) salts, such as iron(II) perchlorate or Iron(II) Sulfate, Hydrogen Peroxide, and an appropriate oxidant (eg Fe3+, Cu2+, O2) in aqueous acetonitrile (eq 1). Yields are generally less than 50%. The rate-determining step in the reaction was shown to be the production of a hydroxyl radical which reacts directly with the aromatic substrate, generating a phenolic radical intermediate. This is ultimately converted to the corresponding phenol. An interesting rearrangement of a hydrogen atom during the oxidation (NIH shift),2 as observed during enzymatic hydroxylation, also takes place during the reaction.
C-H bond activation by metal complexes is of fundamental importance in hydrocarbon functionalization.3 The regio- and stereospecific conversion of O-cholestan-3a-yl S-methyl dithiocarbonate to cholestane-1a,3a-diyl diacetate demonstrates the coordination of iron-dioxygen complexes, formed by the reaction of iron(II) perchlorate and oxygen, with electron-rich S-alkyl xanthates to lead to the oxidation of neighboring C-H bonds (eq 2).4 In the absence of FeII, no reaction takes place.
Peroxycyclohexanecarboxylic acid is converted to cyclohexanol (25%) and cyclohexanecarboxylic acid (75%) when treated with iron(II) perchlorate at 0 °C in acetonitrile (eq 3).5 Treating cis- or trans-3-hydroxyperoxycyclohexanecarboxylic acid in a similar manner leads to nearly pure cis-1,3-cyclohexanediol (85:15 cis:trans), indicating participation by hydroxy.
Iron(II) perchlorate hexahydrate is used to prepare Fe(MeCN)4(ClO4)2, a catalyst used in combination with H2O2 to dehydrogenate and monooxygenate organic substrates in dry acetonitrile.6 No products resulting from &bdot;OH radical chemistry are observed, which suggests that classical Fenton-type chemistry1,7 does not occur under these conditions. With alcohols, aldehydes, methylstyrene, thioethers, sulfoxides, and phosphines, the active catalyst, Fe(H2O2)2+, promotes the monooxygenation to aldehydes, carboxylic acids, epoxide, sulfoxides, sulfones, and phosphine oxides, respectively.
Mark W. Zettler
The Dow Chemical Company, Midland, MI, USA