Effect of the nature of carbon catalysts on glyphosate synthesis

Aqueous solutions of PMIDA (N-phosphonomethyliminodiacetic acid) were oxidi zed, using air, to obtain glyphosate (N-(phosphonomethyl)glycine) an active herbicide. The oxidative decarboxylation reaction was catalyzed selectivel y by active carbons obtained from different precursors and modified by spec ific thermal treatments. The activities were highly dependent upon the func tional groups present on the carbon surface. Nitrogen-containing functional groups greatly enhanced the oxidation rates; these groups were either issu ed from the carbon precursors or introduced by thermal treatment under NH3 of active carbons. The highest rates of PMIDA oxidation were obtained using nonactivated carbons treated with NH3 at 900 degrees C. Activities were al so enhanced by thermal treatments at 900 degrees C under N-2 which eliminat ed the acidic sites from the carbon surface, and possibly created active ba sic sites. (C) 1999 Academic Press.