Iron(III) Sulfate


[10028-22-5]  · Fe2O12S3  · Iron(III) Sulfate  · (MW 399.91) (Fe2(SO4)3.5H2O)

[-]  · Fe2O12S3  · Iron(III) Sulfate  · (MW 490.01)

(catalyst for the dehydration of alcohols to give alkenes; serves as a useful oxidant during the alkoxylation of quinones; catalyzes the ring opening of 2-oxazolines with amines)

Alternate Names: ferric sulfate; ferric sesquisulfate; ferric tersulfate; diiron trisulfate.

Physical Data: hygroscopic.

Solubility: slowly sol H2O; sparingly sol alcohol.

Form Supplied in: grayish white powder.

Handling, Storage, and Precautions: moisture sensitive; harmful dust; irritant.

Preparation of Alkenes: Dehydration of Alcohols.1

Silica gel supported iron(III) sulfate efficiently catalyzes the dehydration of secondary and tertiary alcohols under moderate conditions to give the corresponding alkenes. Iron(III) sulfate-SiO2 was found to be more active than all other silica gel supported sulfates tested (CuSO4, NaHSO4, Al2(SO4)3, SnSO4, ZnSO4, etc.), but promoted undesirable side reactions in some cases (Table 1).

Primary alcohols generally give complex mixtures of products. The order of reactivity, tertiary > secondary > primary, implies that the generation of a cationic intermediate is a key step in the reaction. Conventional methods for dehydration utilize simple reagents such as HBr, H2SO4, and NaHSO4, as well as non-silica gel complexed NaHSO4 and CuSO4.

Preparation of Alkoxyquinones: Addition of Alcohols to 1,4-Benzoquinones.2

Iron(III) sulfate oxidizes the initial adduct formed by the reaction of an alcohol with a dimethoxynaphthoquinone derivative under acidic conditions to give the desired alkoxyquinone in good to excellent yield (eq 1) (Table 2). In the absence of an added oxidant the starting material oxidizes the initial adduct, alkoxyhydroquinone, which greatly reduces the potential yield of the reaction. Other oxidants, such as DDQ and air/light, were found to be less effective than iron(III) sulfate.

Preparation of Substituted Ethylenediamines.

The catalyzed, nucleophilic ring opening of 2-oxazolines with amines provides a convenient method for preparing unsymmetrically substituted ethylenediamines (eq 2).3 Coordination of the oxazoline with Fe2(SO4)3 and other Lewis acids increases the electrophilic character of the oxazoline and increases its susceptibility for nucleophilic attack at the 2 (reversible) and 5 (irreversible) positions. Better yields were obtained with alternative catalysts, including Zn(OAc)2, p-Toluenesulfonic Acid, and Boron Trifluoride Etherate. This method serves as an alternative to the reported synthesis of ethylenediamines from aziridines, phthalimides, nitriles, and 2-aminopropionamides.

Stereoselective 1,4-Addition of Alcohols to Phenylazostilbene to give Alkoxyphenylhydrazones.

The addition of alcohols to phenylazostilbenes in the presence of 2 equiv of iron(III) sulfate gives predominantly, or exclusively, the anti isomer of the resulting alkoxyphenylhydrazone.4 No reaction took place in the absence of the iron ion (or copper ion) (eq 3).

Miscellaneous Reactions.

Alcohols react with 3-aroylpropionic acids in the presence of hydrated iron(III) sulfate to produce 3-aroylpropionic esters.5 The condensation of cyclohexanone under the catalysis of hydrated iron(III) sulfate in the presence of cyclohexane, benzene, or toluene produces the desired aldol products in 49-52% yield.6 The alkylation of p-cresol with mixed 2,3-dimethyl-1- and 2-butene in 1.5:1 cresol:alkene ratio in the presence of iron(III) sulfate gives 4,2-Me(Me2CHCMe2)C6H3OH in ~75% yield.7

1. Nishiguchi, T.; Kamio, C. JCS(P1) 1989, 707.
2. (a) Farina, F.; Martinez-Utrilla, R.; Paredes, M. C. S 1981, 300. (b) Finley, K. T. In The Chemistry of the Quinonoid Compounds; S. Patai, Ed.; Wiley: London, 1974; p 941.
3. Fazio, M. J. JOC 1984, 49, 4889.
4. Attanasi, O. SC 1979, 9, 465.
5. Li, Y.; Wang, Z.; Huang, H.; Zhang, S. CA 1993, 118, 254 494z.
6. Li, Y.; Huang, H.; Hin, H.; Xu, Y. CA 1990, 112, 198 234b.
7. Kheifits, L. A.; Podberezina, A. S.; Klimakhina, S. T.; Grigor'eva, L. T. CA 1976, 85, 176 915w.

Mark W. Zettler

The Dow Chemical Company, Midland, MI, USA

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