Quaternary ammonium salts dealkylation

Dealkylation of quaternary ammonium salts using ethanol-amine is more convenient than the use of aqueous ammonia in sealed tubes at high temperatures. Ethanolamine may be replaced by other ethanolamines. The reaction leads to preferential removal of methyl groups. 

Sodium hydrogen telluride efficiently dealkylates quaternary ammonium salts to the corresponding tertiary amines in high yields. ... 

Higher homologs of PEI can be obtained by cationic ring-opening polymerization of azetidine monomers21). Polymers of this kind can also be N-methylated as previously described in the case of PEI. The cationic polymerization of N-substituted azetidines may give rise to poly(tertiary amine)s. Linear poly(tertiary amine)s have been obtained by selective dealkylation of poly(quaternary ammonium salt)s22). 

Hagi, H., Ooishi, O., Tanaka, R. Synthesis of linear poly(tertiary amine)s by selective dealkylation of poly(quaternary ammonium salt)s, in Polymeric amines and ammonium salts (ed.) Goethals, E. J., p. 31, New York, Pergamon Press 1980, and references therein... 

Dealkylalitm of quaternary ammonium salts. Treatment of a quaternary ammonium salt (1 mmole) with DABCO (2 mmole) in refluxing ethanol or DMF effects dealkylation to the tertiary amine in yields of SO-90%. 

The reductive cleavage of quaternary ammonium salts to give a tertiary amine and a hydrocarbon by reaction with sodium amalgam in hydroxylic solvents is called the Emde degradation. However, saturated hydrocarbons are not cleaved under these conditions. Grovenstein suggested that the reason for this unreactivity is due to the fact that the sodium reacts with the alcohol much faster than with the ammonium salts. However, by operating in dioxane or dioxane-alcohol mixtures, the dealkylation reaction could be accomplished. The products of the decomposition of either tetramethylammonium chloride or bromide are methane, ethylene, trimethylamine, and dimethylethylamine. 

The reaction of thiophenoxide with simple quaternary ammonium salts was reported by Shamma, Deno, and Remar 134> in 1966. They reported that the dealkylation of triethylmethylammonium thiophenoxide could be achieved in 95% yield by heating the salt to 80 °C for 19 hours in solvents such as 2-butanone or acetonitrile or by heating the dry salt for 2 hours. Demethylation was far more prevalent than deethylation by a factor of 3 and no ethylene was produced. 

Lithium n-propylmercaptide in hexamethylphosphoramide provides a mild system for the rapid dealkylation of quaternary ammonium salts, with high propensity for methyl group removaL. Substituted amidines have been prepared under very mild conditions from nitriles, halides, and amines with the help of a Lewis acid such as ferric chloride . a,a-Dichloro-/ -ketoesters undergo a rapid fragmentation with nucleophiles, even with relatively weak ones such as diethylamine, and can thus serve as acylating agents... 

The dealkylation of quaternary ammonium salts by 1,4-diazabicyclo [2,2,23-octane has been described. Electrochemically generated cobalt(i) species catal3rtically cleav carbon-nitrogen bonds in quaternary ammonium salts. 

N-Demethylation. Li- -propylmercaptide in hexamethylphosphoramide provides a mild, rapid, and convenient system for dealkylation of quaternary ammonium salts in excellent yield with high propensity for methyl group removal. - E A soln. of phenyldimethylethylammonium iodide in hexamethylphosphoramide treated at 0-5° with LiH followed by n-propylmercaptan, and stirred 0.5 hr. at 0° under N2 phenylmethylethylamine. Y 97% 94% after 5 min. at 85°. F. e. s. R. O. Hutchins and F. J. Dux, J. Org. Chem. 38, 1961 (1973). 

Elguero and Espada29S have used this dealkylation reaction with quaternary salts of heterocyclic compounds. Another application is the preparation of tertiary amines functionalized in the <5 position.296 In these reactions, the ammonium salt 196 is both the catalyst and the reagent. 

Dealkylation. Quaternary ammonium ions containing benzyl, allyl and methyl groups are decomposed by NaTeH. Accordingly, such salts should not be used in phase-transfer reactions involving NaTeH. 

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