2,2-Dichloropropionate ester

In a typical example (Figure 2), the 2,2-dichloropropionate ester of chitin was prepared by reacting 1.0 g of chitin dissolved in 100 ml of a 5% LiCl/N,N-dimethylacetamide solution with 0.006 moles of 2,2-dichloropropionyl chloride at 140°C for three hours. The product was isolated by precipitation into methanol. 

Dichloropropionic acid is a cheap reagent that can be linked to insoluble polymers either as an ester or an amide (1, Fig. 2). Although both chlorine atoms of this substrate were expected to show a slightly different reactivity toward nucleophiles, all attempts to displace these two leaving groups by two different nucleophiles failed. Regardless of the reaction conditions and the type of nucleophile used, both chlorine atoms were displaced by the first nucleophile. 

The elimination/addition reaction already proceeded at room temperature when the dichloropropionic acid had been linked as an ester to the support, but required heating when an amide linkage had been chosen. When amines with low nucleophilicity were used, such as aniline or a-amino acid esters, higher reaction temperatures were also beneficial. Occasional by-products for this reaction sequence were acrylic acid derivatives or the corresponding hydrogenated products (2-thiopropionic acid derivatives). These by-products were usually formed when a very small excess of amine was used in the elimination/addition step. Both the thiols and the amines used in this reaction sequence could be polyfunctional, as illustrated by the examples sketched in Fig. 3. 

Abramov, V.S., and ITina, N.A., Mechanism of the Arbuzov rearrangement. Part 3. Reaction of the nitrile and methyl ester of a,P-dibromo- and a,P-dichloropropionic acids with phosphites, Zh. Obshch. Khim., 26, 2014, 1956 Chem. Abstr., 51, 1822c, 1957. 

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