Deamination of 1-Aminoalkylphosphonic Acids: Reaction Intermediates and Selectivity

Abstract

Deamination of 1-aminoalkylphosphonic acids in the reaction with HNO₂ (generated "in situ" from NaNO₂) yields a mixture of substitution products (1-hydroxyalkylphosphonic acids), elimination products (vinylphosphonic acid derivatives), rearrangement and substitution products (2-hydroxylkylphosphonic acids) as well as H₃PO₄. The variety of formed reaction products suggests that 1-phosphonoalkylium ions may be intermediates in such deamination reactions.

Keywords: 1-phosphonoalkylium ion; carbenium ion; diazotization; elimination reaction; rearrangement; substitution reaction.

Scheme 1

General presentation of deamination reaction carried out on 2-aminoalkanoic acids and their phosphorus analogs [34,35,36,37,49,50,51,52,53].

Scheme 2

Possible structures of the 1-phosphonoalkylium ions known from the literature [54,55,56,57,58].

Figure 1

Structures of 1-aminoalkylphosphonic acids used in this study.

Scheme 3

Preliminary experiments on the diazotization of alanine (2a) and valine (2b) and their corresponding phosphorus analogs 1a and 1b.

Scheme 4

Possible mechanism of the reaction of 1-aminoalkylphosphonic acids 1 with HNO₂.

Scheme 5

Deamination reaction of 3-amino-3-phosphonopropanoic acid (1e) with HNO₂.

Scheme 6

(a) Deamination of 1-amino-2-phenylethylphosphonic acid (1g) with HNO₂ and analysis of the reaction products. (b) Mechanism of phosphoric acid formation from cyclic intermediate 9″g.

Scheme 7

Mechanism of H₃PO₄ formation in rearrangement and fragmentation reaction [64,65,66].

Scheme 8

Proposed mechanisms of H₃PO₄ formation in the reactions of 1-phosphonoalkylium ion with nitrite ion.

Scheme 9

Possible transformations of 1-phosphonoalkylium ions 9 discussed in this study.