Iron(II) Perchlorate


[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 Hydroxylation (Fenton Oxidation).1

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.

Aliphatic Hydroxylation.

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.

Reductive Decarboxylation of Peracids.

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.

Dehydration and Monooxygenation of Organic Compounds.

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.

1. (a) Walling, C. ACR 1975, 8, 125. (b) Walling, C.; Johnson, R. A. JACS 1975, 97, 363.
2. Kurata, T.; Watanabe, Y.; Katoh, M.; Sawaki, Y. JACS 1988, 110, 7472.
3. (a) Muetterties, E. L. Science 1977, 196, 839. (b) Parshall, G. W. ACC 1975, 8, 113.
4. Patin, H.; Mignani, G. CC 1979, 685.
5. Groves, J. T.; Van Der Puy, M. JACS 1975, 97, 7118.
6. (a) Sugimoto, H.; Sawyer, D. T. JACS 1985, 107, 5712. (b) Sugimoto, H.; Sawyer, D. T. JACS 1984, 106, 4283.
7. Gilbert, B. C.; Norman, R. O. C.; Sealy, R. C. JCS(P2) 1975, 303.

Mark W. Zettler

The Dow Chemical Company, Midland, MI, USA

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