Iron(II) Sulfate1


[7720-78-7]  · FeO4S  · Iron(II) Sulfate  · (MW 278.06)

(reductive cleavage of N-O bonds;2-14 Skraup synthesis;15 carboxylation of aromatic bases17)

Alternate Name: ferrous sulfate.

Physical Data: mp 300 °C (-7H2O); bp dec 671 °C; d 1.89 g cm-3; refractive index 1.471.

Solubility: sol water (48 g/100 mL); slightly sol ethanol; sol methanol.

Form Supplied in: light blue or light green crystals; many commercial sources.

Handling, Storage, and Precautions: air and moisture sensitive; keep in a tightly closed container. Incompatible with strong oxidizing agents; irritant; ingestion may be lethal.18

Reductive Cleavage of N-O Bonds.2-14

Basic iron(II) sulfate is the reducing agent of choice for the conversion of o-nitrobenzaldehydes to o-aminobenzaldehydes.2 FeSO4.7H2O has been used in combination with ammonia;3 however, ammonium hydroxide is the most synthetically useful base.2 Detailed syntheses of o-aminobenzaldehyde have been reported using FeSO4/NH4OH (eq 1).2,4 The o-aminobenzaldehydes should be prepared immediately prior to use as they are prone to polymerize extensively on standing and when treated with acid. o-Aminobenzaldehyde is stable for up to 2 months at 5 °C.5 Several alternate strategies are available for synthesis of o-amino aldehydes;1 more recently, dihydrolipoamide-iron(II) under weakly alkaline conditions has been reported as a general nitrobenzene reducing agent.6

Reductive cyclization utilizing FeSO4.7H2O has been used to synthesize thieno[c]-fused 1,5-naphthyridine 5-oxides (eq 2) (30-86%).7 Reduction of the N-O bond in 1,2,4-oxadiazolines and amidoximes and hydrolysis of the intermediate iron complexes to amidines (eq 3)8 provides an alternative to the reducing agents P/Hydrogen Iodide9 or Pentacarbonyliron.10 Iron(II) sulfate has been used to cleave various C-substituted oxiridines.11 Bicyclic oxaziridines have been cleaved to amides,12 and tricyclic oxaziridines yield seven-,13 eight- and nine-membered oxolactams (eqs 4 and 5).14

Skraup Synthesis.

The Skraup synthesis of quinolines from a nitrobenzene, glycerol, and H2SO4 proceeds with extreme violence unless FeSO4.7H2O is included. A detailed synthetic procedure for quinoline has been reported,15 which is amenable to synthesis of derivatives (eq 6).16

Carboxylation of Aromatic Bases.

Heteroaromatic bases can be carboxylated via reaction with the carboxyl radical generated with H2O2, keto ester, and FeSO4.7H2O (eq 7).17

Related Reagents.

Copper(II) Acetate-Iron(II) Sulfate; Hydrogen Peroxide-Iron(II) Sulfate; Iron(II) Sulfate-Oxygen.

1. Caluwe, P. T 1980, 36, 2539.
2. Smith, L. I.; Opie, J. W. OSC 1955, 3, 56.
3. Foy, B. D.; Smudde, R. A.; Wood, W. F. J. Chem. Educ. 1993, 70, 322.
4. Mann, F. G.; Wilkinson, A. J. JCS 1957, 79, 3346.
5. Yamamoto, H.; Albert, A. JCS(B) 1966, 956.
6. Kijima, M.; Nambu, Y.; Endo, T.; Okawara, M. JOC 1984, 49, 1434.
7. Malm, J.; Hornfeldt, A.-B.; Gronowitz, S. H 1993, 35, 245.
8. Kurasawa, Y.; Okamoto, Y.; Takada, A. H 1984, 22, 1391.
9. Behr, C. Chem. Heterocycl. Compd. 1962, 17, 256.
10. Dondoni, A. CC 1975, 761.
11. Black, D. St. C.; Johnstone, L. M. AJC 1984, 37, 109 and references therein.
12. Black, D. St. C.; Johnstone, L. M. AG(E) 1981, 20, 669.
13. (a) Bischoff, C. JPR 1976, 318, 848. (b) Bischoff, C., Herma, H.; Schroder, E. JPR 1976, 318, 895.
14. Black, D. St. C.; Johnstone, L. M. AG(E) 1981, 20, 670.
15. Clarke, H. T.; Davis, A. W. OSC 1941, 1, 478.
16. Adolfsson, L.; Olsson. K. ACS 1983, 37B, 157.
17. Bernardi, R.; Caronna, T.; Galli, R.; Minisci, F.; Perchinunno, M. TL 1973, 645.
18. Sigma-Aldrich Library of Chemical Safety Data; 2nd ed.; Lenga, R. E., Ed.; Sigma-Aldrich: Milwaukee, 1988; p 2014D.

Andrew D. White

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

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