351Sulfides
Phosphorus forms a wide range of sulfides, where phosphorus can be P(V), P(III) or other
oxidation states. Most famous is the three-fold symmetric P 4 S 3 used in strike-anywhere
matches. P 4 S 10 and P 4 O 10 have analogous structures.
Phosphorus (III) Compounds
Phosphine (PH 3 ) and its organic derivatives (PR 3 ) are structural analogues with ammonia
(NH 3 ) but the bond angles at phosphorus are closer to 90° for phosphine and its organic
derivatives. It is an ill-smelling, toxic compound. Phosphine is produced by hydrolysis of
calcium phosphide, Ca 3 P 2. Unlike ammonia, phosphine is oxidized by air. Phosphine is
also far less basic than ammonia.
All four symmetrical trihalides are well known: gaseous PF 3 , the yellowish liquids PCl 3 and
PBr 3 , and the solid PI 3. These materials are moisture sensitive, hydrolyzing to give
phosphorus acid.
The trichloride, a common reagent, is produced by chlorination of white phosphorus:
P 4 + 6 Cl 2 → 4 PCl 3The trifluoride is produced by from the trichloride by halide exchange. PF 3 is toxic because
it binds to hemoglobin.
Phosphorus(III) oxide, P 4 O 6 (also called tetraphosphorus hexoxide) is the anhydride of
P(OH) 3 , the minor tautomer of phosphorous acid. The structure of P 4 O 6 is like that of P 4 O 10
less the terminal oxide groups.
Mixed oxyhalides and oxyhydrides of phosphorus (III) are almost unknown.
Organophosphorus Compounds
Compounds with P-C and P-O-C bonds are often classified as organophosphorus
compounds. They are widely used commercially. The PCl 3 serves as a source of P3+ in
routes to organophosphorus (III) compounds. For example it is the precursor to
triphenylphosphine:
PCl 3 + 6 Na + 3 C 6 H 5 Cl → P(C 6 H 5 ) 3 + 6 NaClTreatment of phosphorus trihalides with alcohols and phenols gives phosphites, e.g.
triphenylphosphite:
PCl 3 + 3 C 6 H 5 OH → P(OC 6 H 5 ) 3 + 3 HClSimilar reactions occur for phosphorus oxychloride, affording triphenylphosphate:
OPCl 3 + 3 C 6 H 5 OH → OP(OC 6 H 5 ) 3 + 3 HClPhosphorus (I) and phosphorus (II) compounds
These compounds generally feature P-P bonds. Examples include catenated derivatives
of phosphine and organophosphines. The highly flammable gas diphosphine (P 2 H 4 ) is the
first of a series of derivatives of this type.