This appears to bee a nifty way to reduce o-nitrotoluene to o-toluidine!
Selective reduction of aromatic nitro compounds with stannous chloride in non acidic and non aqueous mediumTetrahedron Letters, Volume 25, Issue 8, 1984, Pages 839-842
F. D. Bellamy, and K. Ou
Abstract
Aromatic nitro compounds are readily reduced by SnCl2*2H2O in alcohol or ethyl acetate or by anhydrous SnCl2 in alcohol where other reducible or acid sensitive groups such as aldehyde, ketone, ester, cyano, halogen and O-benzyl remain unaffected.
In our search for a mild, selective, inexpensive and general method for this transformation, we found that either SnCl2*2H20 in alcohol or ethyl acetate, or anhydrous SnCl2 in alcohol work very efficiently (5). A wide variety of substituted nitrobenzenes had been selectively reduced in almost quantitative yields using this simple procedure (see table). Under the conditions used, other reducible or acid sensitive groups are recovered unchanged. The table also shows that the yields of substituted anilines are not affected by the nature or the position of the aromatic substituents on the corresponding nitrobenzenes. The yields obtained in the presence of groups such as aldehyde, O-acetate and 0-benzyl are particularly noteworthy.
Table: Reduction Results for various Nitrobenzene's
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Substituents on nitrobenzene; Yield(%)
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p-Cl; 96%
p-Cl,m-CN; 98%
p-COOEt; 97%
p-OCH3; 97%
p-Cl,m-COOEt; 95%
p-CHO; 96%
p-COOH; 94%
p-OH; 91%
p-OCOCH3; 92%
p-OCH3,o-CN; 99%
m-CH3,o-COOH; 99%
p-PhCH2O; 91%
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ProcedureA typical experimental procedure is illustrated below for the reduction of p-nitrobenzoic acid: a mixture (6) of 1.67 g (0.01 mole) of p-nitrobenzoic acid and 11.275 g (0.05 mole) of SnCl2*2H20 (7) in 20 ml of absolute ethanol is heated at 70°C under nitrogen. After 30 mn the starting material has disappeared and the solution is allowed
to cool down and then poured into ice. The pH is made slightly basic (pH 7-8) by addition of 5 % aqueous sodium bicarbonate (
before being extracted with ethyl acetate. The organic phase is thorougly washed with brine, treated with charcoal and dried over sodium sulphate. Evaporation of the solvent leaves 1.5 g (94,5 %) of p-aminobenzoic acid, which gives one spot on tlc and melts over 300C.
We feel that the mildness and the selectivity of this method which works in nonaqueous conditions together with the ease of the treatment and the purity of the products obtained should largely extend the scope of the use of stannous chloride which is a safe and inexpensive reagent.
6. SnCl2*2H20 and anhydrous SnCl2 are both insoluble either in ethanol or in ethyl acetate as already noted by J.R. Sampey, J. Am. Chem. Sot., 2, 88 (1930).
7. SnCl2*2H20 or anhydrous SnCl2 can be used indifferently. When SnCl2*2H20 may be utilized in ethanol (absolute or not) or in ethyl acetate or in a mixture of these solvents, the presence of ethanol is necessary for the reduction with anhydrous SnCl2 to work.
8. 5 % aqueous sodium bicarbonate may be replaced by solid sodium bicarbonate, or aqueous or solid NaOH Without affecting the yield noticeably.
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