Phosphorus has a very high affinity for oxygen, and compounds of the type R₄P⁺ react readily with hydroxide (or alkoxide) ions to give phosphine oxides (R₃PO) and hydrocarbons. The order of ease of replacement of R groups; C₆H₅CH₂ > C₆H₅ > CH₃, and ρ-NO₂C₆H₄ > C₆H₅ > ρ-CH₃C₆H₄, indicates that the R group may be leaving as R-. The reaction with hydroxide ions of a series of substituted phenyltriphenylphosphonium salts ArP⁺(Ph) ₃X- (X = halogen) in an aqueous 1,2-dimethoxyethane solvent system has been studied, and this thesis presents the results of this study.