Brief Nomenclature Review:
Phosphate, phosphonate, phosphorous, phosphorus

Barbara Price

The chemical and biological literature has many archaic, even arcane, terms. The nomenclature of chemical compounds was developed to help the chemist distinguish between different classes of chemicals and to aid in anticipating the reactions in which a chemical would be likely to participate. My recent readings in nerve agent chemistry have underscored that even experienced professionals are sometimes careless in their nomenclature.

1. Tributyl phosphate, TBP, and triorthocresylphosphate, TOCP, are organophosphates. These are derivatives of phosphoric acid, P(O)(OH)₃.
2. Many of the nerve agents, and many pesticides, are derivatives of phosphonic acid, P(O)(OH)₂R, where R can be H or a side chain with a carbon covalently bonded to the P, a P-hydrocarbyl derivative. These organophosphonates have the generic formula P(O)(OR')(OR")R.

1. In soman and sarin, one of the OR groups is replaced by a fluoride.
2. In VX, an OR group is replaced with an S-R group.


3. Tabun, is actually an organophosphate because, although a carbon is bonded to the P atom, the carbon is in a cyanide group, which is chemically more similar to a halide, hydroxide or alkyloxide (OR) group and not covalently bonded to the P.

3. In both organophosphates and organophosphonates, the P atom is in the +5 oxidation state, P(V), i.e., five of the P's electrons are involved in its bonds. These are organophosphorus compounds. P(III) compounds have only three of the P's electrons involved in bonding and are called organophosphorous compounds. Phosphine, PH3, and phosphoroustrichloride, PCl3, are examples of P(III) compounds.

The nerve agents, except for Tabun, are organophosphonates, not organophosphates. TBP, TOCP, tabun, sarin, soman and VX are all organophosphorus compounds, not organophosphorous compounds.

Note: Over the years, both Jiri Matousek and Ben Garrett have made me aware of these nuances; I thank them for their help.

01-1, issue no. 82