Preparation of l-Phenyl-2-propanone

The arylnitroalkenes may be produced by the condensation of aromatic aldehydes and nitroparaffins (Knoevenagel and Walter, Ber. vol. 37, p. 4502 (1904) Worrall, Jour. Am. Chem. Soc vol. 56, p. 1556 (1934) Alles, Jour. Am. Chem Soc. vol. 54, p. 271 (1932)). Compounds of this type are desirably reduced to form amino compounds and more or less successful reductions have been obtained in the case of compounds such as ome a-nitrostyrene, obtained by the condensation of nitromethane with an aromatic aldehyde. However, in the case of nitroalkenes of the type it has been found to be extremely difficult to effect satisfactory reduction. For example, Benzedrine (l-phenyl-2-aminopropane) may theoretically be obtained by the reduction of l-phenyl-2-nitropropene, but in practice it has been found to be almost impossible to effect the desired reaction. Relatively low yields of Benzedrine have been secured by electrolytic reduction of the nitropropene but catalytic hydrogenation appears to yield only high molecular weight polymerization products. 

The initial reduction of our process is effected in aqueous solution in the presence of sufficient finely divided iron to effect the reduction of all of the nitroalkene. An acid need not be employed in conjunction with the iron, but if employed, the concentration of the acid will affect the nature of the reduction process. With no acid or only low concentrations of acid, the re-action product is predominantly the oxime, whereas in the presence of relatively high concentrations of acid the reaction product is predominantly the ketone. 

An amount of iron equal to at least 1.5 mol per mol of nitroalkene is required, and the amount required by one of the equations is 3 mols 

It may also be seen from the above equations that at least 1 mol of water is required per mol of nitroalkene in order to secure reduction to the oxime. We prefer, however, to utilize a considerable excess of water in order to obtain a mixture which can be satisfactorily handled, and agitated during the reaction. Other solvents can be employed in conjunction with water if desired, but these should preferably be miscible with water in order to maintain a single liquid phase and thus facilitate the reduction. The use of an organic solvent in conjunction with water may be an advantage in controlling the type of reduction product secured. Thus, if it is desired to obtain the oxime rather than the ketone, the use of an aliphatic alcohol in conjunction with water will tend to increase the ratio of oxime to ketone in the products. 

The reduction of nitroalkenes to ketones and oximes may be further illustrated by the following specific example  

---