Phosphites, sometimes called phosphite esters, have the general structure P(OR)3 with oxidation state +3. Such species arise from the alcoholysis of phosphorus trichloride: PCl3 + 3 ROH → P(OR)3 + 3 HCl The reaction is general, thus a vast number of such species are known. Phosphites are employed in the Perkow reaction and the Michaelis–Arbuzov reaction. They also serve as ligands in organometallic chemistry. Intermediate between phosphites and phosphines are phosphonites (P(OR)2R') and phosphinite (P(OR)R'2). Such species arise via alcoholysis reactions of the corresponding phosphinous and phosphonous chlorides ((PClR'2) and PCl2R', respectively). Phosphines The parent compound of the phosphines is PH3, called phosphine in the US and British Commonwealth, but phosphane elsewhere. Replacement of one or more hydrogen centers by an organic substituents (alkyl, aryl), gives PH3−xRx, an organophosphine, generally referred to as phosphines. From the commercial perspective, the most important phosphine is triphenylphosphine, several million kilograms being produced annually. It is prepared from the reaction of chlorobenzene, PCl3, and sodium. Phosphines of a more specialized nature are usually prepared by other routes. Phosphorus halides undergo nucleophilic displacement by organometallic reagents such as Grignard reagents. Organophosphines are nucleophiles and ligands. Two major applications are as reagents in the Wittig reaction and as supporting phosphine ligands in homogeneous catalysis. Their nucleophilicity is evidenced by their reactions with alkyl halides to give phosphonium salts. Phosphines are nucleophilic catalysts in organic synthesis, e.g. the Rauhut–Currier reaction and Baylis-Hillman reaction. Phosphines are reducing agents, as illustrated in the Staudinger reduction for the conversion of organic azides to amines and in the Mitsunobu reaction for converting alcohols into esters. In these processes, the phosphine is oxidized to phosphorus(V). Phosphines have also been found to reduce activated carbonyl groups, for instance the reduction of an α-keto ester to an α-hydroxy ester. Phosphaalkenes and phosphaalkynes Compounds with carbon phosphorus(III) multiple bonds are called phosphaalkenes (R2C=PR) and phosphaalkynes (RC≡P). They are similar in structure, but not in reactivity, to imines (R2C=NR) and nitriles (RC≡N), respectively. In the compound phosphorine, one carbon atom in benzene is replaced by phosphorus. Species of this type are relatively rare but for that reason are of interest to researchers. A general method for the synthesis of phosphaalkenes is by 1,2-elimination of suitable precursors, initiated thermally or by base such as DBU, DABCO, or triethylamine: Thermolysis of Me2PH generates CH2=PMe, an unstable species in the condensed phase. Organophosphorus(0), (I), and (II) compounds Compounds where