Some reactions of phosphorus compounds as studied by 31p nmr techniques

Abstract

The solution chemistry of some simple phosphorus halides has been investigated in sulphuric acid, oleums, and halo-substituted sulphuric acids by (^31) p n.m.r. spectroscopy. Solution of phosphorus (III) compounds was accompanied by oxidation to the phosphorus (V) state. The phosphorus (V) species so formed as well as those derived directly from phosphorus (V) halides and oxyhalides were stable over measurable periods of time. Solvolysis of phosphorus (V) – halogen bonds occurred in all the solvents, with some complications arising in the halo-substituted acids where halogen exchange was observed. Oxidation of some phosphorus (III) halides by halogens produced phosphorus (V) - halo species which were stabilized by solution in these highly acidic solvents. The (^31) p n.m.r. solution spectrum of various phosphorus (V) - iodine species have been recorded for the first time with the help of a pulsed Fourier Transform instrument capable of studying reacting systems. The solution chemistry of a series of phenyl organophosphoryl compounds in these acid solvents has also been investigated by (^31) P n.m.r. Protonation of the phosphoryl group takes place in all of the solvents, as well as sulphonation of the phenyl ring in 25% and 65% oleum, and to a lesser extent in ClHSO (_3). Mixed halo and organohalo phosphorus (V) compounds such as [PCl (_N) Br (_4-n)] (^+) A (^-), R (_N) PX (_5-n), [R (_n) PX (_4-n)] (^+) A (^-), where X = Cl or Br and A (^-) is an anion, dissolve in 25% oleum with the formation of stable phosphonium cations. An investigation of the solution chemistry of phenoxyhalophosphoranes indicates that the stable species in the system are the non halo containing (PhO) (_4) p (^+) cation and (PhO) (_5) P, neither of which show acceptor properties towards pyridine or chloride ions. A limited investigation of the Lewis acid properties of PI (_3) towards pyridines and the Lewis base properties of PI (_3) towards BBr (_3) and BIr (_3) suggests that coordination complexes are formed in both systems. Oxidation of PI (_3) has been attempted by means of halogens and other halogen-containing oxidizing agents. No direct evidence for the formation of phosphorus (V)-iodine species was obtained, although reactions with SbCl (_5) and PCl (_5) produced unstable compounds which decomposed at low temperature liberating iodine.