Studies of diethylenetriaminepentaacetic acid degradation in pulp mill process liquors

The general focus of this study was to synthesise 1-(carboxymethyl)-4-[2- [bis(carboxymethyl)amino]ethyl]-2-oxopiperazine (1a), a cyclic degradation product of diethylenetriaminepentaacetic acid (DTPA) present in pulping liquors, and then determine its complexing ability with metal ions of relevance to the paper industry. Three independent but related methods were developed for the preparation of 1a, although ultimately it was necessary to fully develop only one. In this method, 2- chloroethyliminodiacetonitrile was prepared by Mannich's reaction of 2- chloroethylamine, formaldehyde and potassium cyanide and converted to dimethyl 2-chloroethyliminodiacetate by treatment with gaseous HC1 in methanol. Alkylation of 1-methoxycarbonylmethyl-2-oxopiperazine with dimethyl 2- chloroethyliminodiacetate produced 1-(methoxycarbonylmethyl)-4-[2- [bis(methoxycarbonylmethyl)amino]ethyl]-2-oxopiperazine, which when hydrolysed in acidic solution gave the trihydrochloride salt of 1a. The overall yield of 1a trihydrochloride (via 1-methoxycarbonylmethyl-2-oxopiperazine) was 20%. Using this new method, sufficient quantities of 1a were synthesised for both characterisation and complexing studies.