Alkoxide-promoted decomposition of N-halo-α-amino acids in aqueous medium.

✍ Scribed by X.L. Armesto; M.Canle L; M.V. García; M. Losada; P. Rodríguez; J.A. Santaballa

• Publisher: Elsevier Science
• Year: 1994
• Tongue: French
• Weight: 580 KB
• Volume: 50
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)85084-5

✦ Synopsis

Absfmcf: B kinetic study of the alkoxide-promoted decomposition of N-halo derivatives of glyciae and earcosine in aqueous solution has been carried out. The deuterium isotope effect and the leaving group effect, together with an analysis of the date in terms of the cross interaction parameter pxu and of the More O'Fermll-Jencks diagram suggwt that the reaction takes place through e concerted non-synchronous mechanism.

Introduction.

The decomposition of N-Cl-amino acids has undoubted interest due mainly to the potential carcinogenic activity of the N-chlorinated compounds, which may be generated in any water chlorination process (a common water disinfection practise).

In neutral or slightly acidic medium N-halo-a-amino acids are not stable and decompose to yield halide ions, carbon dioxide, aldehydes or ketones, and amines or ammonia'*' depending on the structure of the Nhalo-a-amino acid. In alkaline medium the decomposition leads to the formation of cr-keto acidss*4-'*6 which in turn are precursors of undesirable products, such as trihalomethanes and other non-volatile organic compounds7*8. The study of this reaction in the presence of bases has the added interest of dealiig with an elimination reaction leading to imine formation, a process less studied than that in which olefins are generated.

Usually it has been accepted that the decomposition of N-Cl-a-amino acids in alkaline medium takes place through carbanion formation3*4' as depicted in Scheme 1.

In a previous papeld we pointed out that in the presence of hydroxide ions the process cannot take place through this mechanism, thus concluding that the only mechanistic alternatives are either a stepwise process or a concerted one, between which it is difficult to distinguish.