Arsonoacetic acid, decarboxylation

This is easily done if R is propyl, because the azeotrope of water and propan-l-ol boils at a temperature well below the boiling point of the propanol, so one can distill off this azeotrope up a fractionating column until the temperature of the vapor reaches the boiling point of propanol. When this is done with an arsonoacetic acid, decarboxylation results. It may be that that hydron is involved, as shown in Fig. 13, since the reaction does not proceed if one starts with a monoanion of the arsonoacetic acid. 

Fig. 13. Conceivable mechanism for the decarboxylation of arsonoacetic acids. When an arsonoacetic acid is boiled in propan-l-ol, and the propanol-water azeotrope is distilled off, the acid will be esterified completely on the arsono group but not on the carboxy group. Decarboxylation is observed.

---