Iron(III) Thiocyanate1


[4119-52-2]  · C3FeN3S3  · Iron(III) Thiocyanate  · (MW 230.12)

(reacts with trialkylboranes to give alkyl thiocyanates;2 thiocyanation of unsaturated acids and esters7)

Alternate Name: ferric thiocyanate.

Solubility: very sol water; dec in hot water; sol alcohol, ether, acetone.

Preparative Method: the reagent is prepared and used in situ, via dropwise addition of a mixture of iron(III) ammonium sulfate (6 equiv) and potassium thiocyanate (18 equiv) in water to a solution of organoborane in THF. The mixture is refluxed for 24 h. The products are obtained via extraction with petroleum ether several times and distillation.2

Handling, Storage, and Precautions: metal thiocyanates on heating to decomposition, or on contact with acid or acid fumes, emit highly toxic fumes. Organic thiocyanates have low acute toxicity, but prolonged absorption may produce skin eruptions, running nose, nausea, and vomiting. Violent reactions have occurred with strong oxidizers.8 Use in a fume hood.

Alkyl Thiocyanates.2

Trialkylboranes react with iron(III) thiocyanate to yield alkyl thiocyanates in good yield, with two alkyl groups per borane being utilized (eq 1). A small amount of the isothiocyanate is observed, easily separable on distillation of the alkyl thiocyanate. This reaction has been extended to mixed trialkylboranes which contain a useful secondary alkyl group, which is transferred preferentially to a primary alkyl group (eq 2).3 This method presents a mild alternative to the usual displacement reaction between an alkyl halide and Sodium Thiocyanate.4

Alkyl selenocyanates can be synthesized via reaction of iron(III) selenocyanate with an organoborane. Iron(III) selenocyanate is generated in situ via addition of a solution of iron(III) ammonium sulfate and potassium selenocyanate in water to the trialkylborane in THF. Alkyl selenocyanates are obtained in 40-47% yields.5 Better yields are obtained for primary alkyl groups via reaction of an alkyl halide with potassium selenocyanate.6 However, the Fe(SeCN)3 method is applicable to secondary and tertiary alkyl selenocyanates (eq 3).3

Thiocyanation of Acids and Esters.

Ethylenic carboxylic acids react with (SCN)2 to give mixtures of thiocyanate and isothiocyanates. Addition of Fe(SCN)3 affords cleanly the vicinal dithiocyanate carboxylic acids in excellent yields (84-100%).7

1. Suzuki, A. ACR 1982, 15, 178.
2. Arase, A.; Masuda, Y.; Suzuki, A. BCJ 1974, 47, 2511.
3. Arase, A.; Masuda, Y. CL 1976, 1115.
4. Wardell, J. L. The Chemistry of the Thiol Group; Wiley: New York, 1974; p 230.
5. Arase, A.; Masuda, Y. CL 1976, 785.
6. (a) Weaver, W. E.; Whaley, W. M. JACS 1946, 68, 2115. (b) Fredga, A. JPR 1929, 121, 56.
7. Maxwell, R. J.; Silbert, L. S. J. Am. Oil Chem. Soc. 1978, 55, 583.
8. Lewis, R. Hazardous Chemical Desk Reference; Van Nostrand Reinhold: New York, 1991; p 1114.

Andrew D. White

Parke-Davis Pharmaceutical Research, Ann Arbor, MI, USA

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