Ionic–molecular isomerism in chlorophenylphosphoranes Ph_nPCl_{5 –n}(1 ⩽n⩽ 3)

A convenient and mild chromatography-free method for the purification of the products of Wittig and Appel reactions

“…From Table 1, it can be seen that this procedure was successful for the removal of triphenylphosphine oxide, isobutyldiphenylphosphine oxide, and methyldiphenylphosphine 35 oxide from Wittig reaction crude products, and is applicable to the crude products of the reactions of all phosphonium ylide types (non-stabilised, semi-stabilised and stabilised) with both aromatic and aliphatic aldehydes, and with ketones. In all cases, comparison of the Z/E ratio of the crude alkene product with that 40 of the product after treatment with oxalyl chloride showed it to be unaffected by the procedure.…”

“…30 We now report a convenient work-up procedure for both Wittig and Appel reactions that allows such a rapid separation of the reaction product from phosphine oxide, and facilitates the reduction of the latter by -product to phosphine. In the case of the Wittig reaction, the method is also successful in removing the 35 aldehyde starting material and the conjugate acid of the ylidegenerating base from the alkene and phosphine products of the process.…”

“…Regeneration of phosphine is achieved by reaction of oxide with phosgene to give triphenylphosphine dichloride (vide infra), which is then treated with elemental phosphorus to give 30 triphenylphosphine and phosphorus trichloride, the latter being also a starting material for the former. Triphenylphosphine dichloride can also be converted to triphenylphosphine by mixing with finely divided aluminium metal in chlorobenzene, which forms a triphenylphosphine-aluminium trichloride complex that 35 can be decomposed hydrolytically. Phase separation allows isolation of triphenylphosphine from the water-soluble aluminium-containing product, Al(OH)Cl 2 .…”

“…30 We were already interested in such salts because of their involvement in other chemistry in our laboratory . 31,32 They can also be generated by the reactions of phosphine with chlorine (in various solvents), 33,34,35,36 and phosphine oxide with sulfuryl 45 chloride, methanesulfonyl chloride, thionyl chloride or trichloromethyl chloroformate. 30,32 The structure of the entity produced seems to depend heavily on the solvent.…”

“…This crude product contains pentachloroacetone (by-product from chlorinating agent). 35 With a method for isolation of the alkene in hand, we turned our attention to the possibility of reduction of the CPS to phosphine. We were encouraged in this because we had recently discovered that both chlorophosphonium salts and alkoxyphosphonium salts 40 could be subjected to reduction and in-situ boranation using NaBH 4 , thus providing facile conversion from phosphine oxide to phosphine-borane.…”