Synthesis of glyphosate from glycine using zeolites as catalysts

Abstract

Glyphosate (N-phosphonomethylglycine) is the most frequently used herbicide in the world. It is used to control a wide variety of annual and perennial weeds. Glyphosate is used worldwide in the form of an aqueous solution of isopropylamine salt and this organic phosphorous herbicide is considered as a non-toxic herbicide for mammals when used normally. At present, preparation of glyphosate in the industry comprises of two steps; (1) preparation of N-phosphonomethyliminodiacetic acid from iminodiacetic acid and (2) oxidation of N-phosphonomethyliminodiacetic to glyphosate using cobalt(II)chloride as a catalyst. In this research, we synthesized glyphosate from formaldehyde, glycine and phosphorous acid as one-pot reaction. Two optimum conditions were found: (1) The use of 2:1:1 formaldehyde:glycine: phosphorous acid mole ratio at 70 C for 2 hours giving 35% yield; (2) The use of 2:1:0.5 formaldehyde:glycine:phosphorous acid mole ratio with the catalysis of acid activated molecular sieve 3A (137 meq/100 g; 4 g per 1 mole glycine) at the same temperature and reaction time, leading to 39% yield. However, using hydrochloric acid as a catalyst gave higher yield of glyphosate than using sulfuric acid as a catalyst. The resulting product mixtures were monitored and quantitatively determined by proton nuclear magnetic resonance spectroscopy using sodium acetate as an internal standard.