Stephen reaction

What is Stephen reaction?

The initial report of the reaction described herein was made by Stephen in 1925. The Stephen reaction involves the synthesis of aldehydes through treatment of nitriles with anhydrous stannous chloride SnCl2 saturated with dry hydrogen chloride HCl gas, forming crystalline “aldimine stannichloride“, which is then hydrolyzed with water. This reaction is commonly referred to as the Stephen reaction or Stephen reduction.

Stephen reaction - general reaction scheme - Stephen reduction
Stephen reaction

R = alkyl, aryl (see list of acronyms)

Initially, the success of the reaction depended on the precipitation of the ether-insoluble crystalline “aldimine stannichloride” (i.e., (RCH=NH·HCl)2SnCl4), which was isolated, washed with ether Et2O, and then hydrolyzed to yield the aldehyde. Nitriles that could not form precipitates were deemed unsuitable for the reaction.

However, it has since been discovered that whether the precipitate forms or not depends on the method of reaction, and it is not necessary to isolate the precipitate before hydrolysis. Although Stephen reaction can yield aldehydes in “almost quantitative yields,” it is generally more effective for aromatic nitriles than aliphatic ones.

Certain aldehydes, such as trifluoroacetaldehyde and β-hydroxypropionaldehyde, cannot be synthesized via the Stephen reaction from their corresponding nitriles. In addition, Stephen reaction does not provide satisfactory yields for some aromatic nitriles, including 2-carbethoxybenzaldehyde (11%), o-tolualdehyde, α-naphthaldehyde, and p-acetylbenzaldehyde.

References

Stephen, H. (1925). CCLII.—A new synthesis of aldehydes. J. Chem. Soc. Trans., 127(0), 1874-1877
DOI: 10.1039/CT9252701874

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