Phosphorous tricloride on 2 phenol
Answers
Phosphorus trichloride is the precursor to organophosphorus compounds that contain one or more P(III) atoms, most notably phosphites and phosphonates. These compounds do not usually contain the chlorine atoms found in PCl3.
PCl3 reacts vigorously with water to form phosphorous acid, H3PO3 and HCl:
PCl3 + 3 H2O → H3PO3 + 3 HCl
A large number of similar substitution reactions are known, the most important of which is the formation of phosphites by reaction with alcohols or phenols. For example, with phenol, triphenyl phosphite is formed:
3 PhOH + PCl3 → P(OPh)3 + 3 HCl
where "Ph" stands for phenyl group, -C6H5. Alcohols such as ethanol react similarly in the presence of a base such as a tertiary amine:[3]
PCl3 + 3 EtOH + 3 R3N → P(OEt)3 + 3 R3NH+Cl−
In the absence of base, however, the reaction proceeds with the following stoichiometry to give diethylphosphite:[4][5]
PCl3 + 3 EtOH → (EtO)2P(O)H + 2 HCl + EtCl
Secondary amines (R2NH) form aminophosphines, e.g., tris(dimethylamino)phosphine. Thiols (RSH) form P(SR)3. An industrially relevant reaction of PCl3 with amines is phosphonomethylation, which employs formaldehyde:
R2NH + PCl3 + CH2O → (HO)2P(O)CH2NR2 + 3 HCl
Aminophosphonates are widely used as sequestring and antiscale agents in water treatment. The large volume herbicide glyphosate is also produced this way. The reaction of PCl3 with Grignard reagents and organolithium reagents is a useful method for the preparation of organic phosphines with the formula R3P (sometimes called phosphanes) such as triphenylphosphine, Ph3P.
3 PhMgBr + PCl3 → Ph3P + 3 MgBrCl
Under controlled conditions or especially with bulky organic groups, similar reactions afford less substituted derivatives such as chlorodiisopropylphosphine.