Effect of the nature of carbon catalysts on glyphosate synthesis

Aqueous solutions of PMIDA (N-phosphonomethyliminodiacetic acid) were oxidized, using air, to obtain glyphosate (N-(phosphonomethyl)glycine) an active herbicide. The oxidative decarboxylation reaction was catalyzed selectively by active carbons obtained from different precursors and modified by specific thermal treatments. The activities were highly dependent upon the functional groups present on the carbon surface. Nitrogen-containing functional groups greatly enhanced the oxidation rates; these groups were either issued 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 also enhanced by thermal treatments at 900 degrees C under N-2 which eliminated the acidic sites from the carbon surface, and possibly created active basic sites. (C) 1999 Academic Press.