Sommelet reaction quaternary

SOMMELET REACTION. Preparation of aldehydes from aralkyl or alkyl halides by reaction with hexamethylenetetramine followed by mild hydrolysis of the formed quaternary salt,... 

Aromatic and heteroaromatic aldehydes can alternatively be prepared from the corresponding methyl compound by subjecting the chloromethyl or bromomethyl derivative to the Sommelet reaction. This procedure involves an initial reaction between the halomethyl compound and hexamethylenetetramine (hexamine), and hydrolysing the resulting quaternary hexamine salt (4) with hot aqueous acetic acid. 

The net outcome of the Sommelet reaction is the oxidation of the benzyl methylene position into the corresponding carbonyl, and in that sense, the Krbhnke reaction may be considered a close variant. The KrOhnke reaction transforms benzyl halides to benzaldehydes using pyridine and an aromatic nitroso compound 16.16,17 As shown below, quaternary pyridinium salt (15) is formed from addition of pyridine to benzyl halide 1. Oxidation of 15 with p-nitrosodimethylaniline (16) affords nitrone 17, which is then hydrolyzed to benzaldehyde 3 and hydroxylamine 18. 

Aryl-4-chloromethylthiazoles (64) undergo the Sommelet reaction with hexamethylenetetramine, affording the aldehydes (66) by way of intermediate quaternary salts (65). ... 

The Sommelet-Hauser rearrangement has rarely been used as a tool in organic synthesis and then only for very special systems [54], The reason is undoubtedly that the Hofmann elimination and the dealkylation reaction of quaternary nitrogen atoms are in direct competition with the ring expansion reactions of these substrates. 

Sommelet-Hauser rearrangement The rearrangement of a benzyl quaternary ammonium salt, C6H5CH2N+R3X-, when treated with an alkali metal amide to give the orthomethylbenzyl tertiary amine, o-CH3C6H4CH2NR2. The tertiary amine may subsequently be alkylated, and the reaction... 

In a Sommelet preparation of a-naphthaldehyde which is noteworthy because of the high yield, the entire reaction is carried out in refluxing 50% acetic acid and the quaternary salt is not isolated. At the end of the reflux period (2 hrs.), hydro-... 

In the presence of NaNH2 benzylic quaternary ammonium salts generally lead to the Sommelet-Hauser rearrangement (refs. 90, 92-104). An ortho alkylation takes place via an exomethylene intermediate. If the two ortho and ortho positions are methylated, the methylene compounds can be isolated (refs. 92, 93). The first anion formed in this reaction can be trapped at a very low temperature (-80 °C) in an aldol reaction for example (ref. 103). At -30°C the isomerization and the rearrangement occur (Fig. 16). 

The transformation of quaternary ammonium salts 1 and sulfonium salts 3 to the corresponding amines 2 and sulfides 4 in the presence of a strong base is known as Stevens rearrangement. The salts are usually obtained by the alkylation of the corresponding amines and sulfides. The competing reaction is the Sommelet-Hauser rearrangement. 

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