Physical and Chemical Characteristics

CAS #:


Chemical name:

N-(phosphonomethyl) glycine

Chemical class/use:

Phosphanoglycine herbicide

Solubility in water:

900,000 mg/l

Solubility in other solvents:

insoluble in common organics

Melting Point:

200 degrees C

Vapor Pressure:

negligible (Monsanto)

Dissociation values:

2.27 (pKa)

Partition Coefficient:

0.17 x 10 to the minus 2 power at 20 ppm; 0.6 x 10 to the minus 3 power at 100 ppm

Glyphosate is a white crystalline solid with an empirical formula of C3H8NO5P which exists as a zwitterion in the solid state as follows:

Glyphosate has relatively low soluibility in water (1.2-8% at 25-100oC) and is insoluble in organic solvents.This is thought to be a result of the strong and very extensive system of hydrogen bonding within the glyphosate crystal lattice. The pKa values for glyphosate in aqueous solution correspond to the proton dissociation reactions shown below. The values for pK1,pK2 and pK3 are 2.27, 5.58 and 10.25 respectively.

The fluids within plants, generally, operates inside very narrow pH ranges. Phloem sap has a pH of 8-8.5; and xylem and apoplastic solutions a pH of 5-6. This means that glyphosate exists in the apoplast mainly in its monoanionic form and it is translocated about the plant mainly in its dianionic form.

It can be seen that glyphosate is quite a strong acid which means that it can be converted in to just about any salt via its reaction with the appropriate base. For example metal salts can be obtained by reaction of glyphosate with aqeuous bicarbonate, carbonate and hydroxide solution whereas onium salts are generally prepared reaction with the hydroxides in alcoholic or aqueous media. Glyphosate is amphoteric in nature and so will dissolve in strong acids to produce salts with negative pKa values and crystalline hemisalts have, also, been isolated. Glyphosate has pKa values which means that it dissociates in three stages and, hence, it is capable of forming mono-, di- and tri- salts. The stability constants of the Cu, Zn, Ca and Mg complexes of glyphosate have been reported and it has been found that, in general, the complexing properties of glyphosate are similar to those of iminodiacetic acid and that it has no known utility as a chelating agent.

When glyphosate is heated at 200-230oC it softens and then resolidifies. N,N'-diphosphonomethyl-2,5-piperazinedione is formed as a result. This occurs via a dehydration reaction. This 2,5-piperazinedione is very water soluble and is thermally stable to 316oC. Glyphosate can be regenerated by refluxing the 2,5-piperazinediones with strong mineral acids such as hydrobromic acid.

Glyphosate has the reactivity typical of many secondary alpha-amino acids, but its low solubility in aqueous solutions and organic solvents makes some transformations quite difficult. The most important reactions glyphosate undergoes are esterification amination, dehydration, N-alkylation, N-acylation, N-sulfonylation and the formation of acyl and phosphonyl halides. I will not go into detail about these reactions, as there is little point, because they all involve standard reagents and mechanisms. In fact i can see little poinrt in me going through a whole list of possible reaction and reagents as there is likely to be thousands upon thousands.