Aldehydes Sommelet synthesis

SOMMELET Aldehyde synthesis Aldehyde synthesis from primary alkyl halides with hexamethylene tetramine. 

SOMMELET Aldehyde synthesis Aldehyde synthesis (rom primaiy alkyl haUdes with hexamethylene tetranilna. 

The Sommelet reaction, also known as the Sommelet oxidation, is the oxidation of benzyl halides (1) to the corresponding aldehydes (3) using hexamethylenetetramine (HMTA) followed by hydrolysis of the hexaminium salt 2.1-3 This reaction is closely related to the Delepine amine synthesis, the Duff aldehyde synthesis, and the Krtihnke reaction (see Section 7.10.3). 

Oxidation of the aldehyde was not used earlier because of the difficulty of obtaining the aldehyde, which is now readily available by the Sommelet synthesis from 3-thenyl bromide. Campaigne and LeSuer 7 also used alkaline permanganate as the oxidizing agent, but the yields decreased to 40-60%. The present procedure gives an over-all yield from 3-methylthiophene of about 45%. 

Cf. Gabriel synthesis, where the product is also amine and Sommelet reaction, where the product is aldehyde. The Delepine works well for active halides such as benzyl, allyl halides, and a-halo-ketones. 

Formylbenzenesulfonamide has been prepared by chromic acid oxidation of -toluenesulfonamide, the Sommelet reaction on p-chloromethylbenzenesulfonamide, and by the Stephen reduction of j -cyanobenzenesulfonamide. The present method provides a general procedure for the synthesis of substituted aromatic aldehydes as illustrated in Table I. 

The synthesis of aldehydes by the Sommelet reaction, the Rosenmund reduction and the Stephens reaction all involve the conversion of a group already present in the molecule. The Rosenmund reduction (Scheme 6.7) is the catalytic hydrogenation of a benzoyl chloride in the presence of a catalyst poison, quinoline/sulfur, which prevents over-reduction to the alcohol. In the Stephens reaction (Scheme 6.7), a nitrile group is reduced by tin(II) chloride and hydrochloric acid to an imine salt, which is then hydrolysed. 

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