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Hypophosphorous acid as a precursor to various organophosphorus compounds

Dixon, Jay Anthony (2016) Hypophosphorous acid as a precursor to various organophosphorus compounds. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The work presented in this thesis is based on the common theme, of the use of hypophosphorous acid as a starting material for the synthesis of functionalised organophosphorus compounds. Hypophosphorous acid and its salts have gained attention as potentially greener precursors, than PCl3, to a range of organophosphorus compounds. An investigation into an alternative synthesis of perfluoroalkylphosphorus(V) compounds is presented. The reaction of hypophosphorous acid derived bis(trimethylsilyl)phosphonite [(Me3SiO)2PH] (BTSP) and bis(trimethylsilyl)- phenylphosphonite [(Me3SiO)2PPh] (BTSPP) with perfluoroalkyl iodides (RfI) is investigated. A range of reactions are discussed, including the synthesis of perfluoroalkyl H-phosphinic acids, RfPO(OH)H, perfluoroalkyl phosphonic acids, RfPO(OH)2 and perfluoroalkyl(phenyl)phosphinic acids, (Rf)PhPO(OH)H. The synthesis and catalytic testing of a new Brønsted acid catalyst is presented. 2,2’-Bis(difluoromethylene)-1,1’-binaphthyl phosphinic acid was targeted, as a stronger (more acidic) Brønsted acid catalyst compared to 1,1’-binaphthyl-2,2’-diyl hydrogen phosphate (BINOL-phosphoric acid). 2,2’-Bis(difluoromethylene)-1,1’- binaphthyl phosphinic acid was synthesised in a seven-step procedure from BINOL, including a ring closure reaction in which BTSP is used. The full synthesis of 2,2’-bis(difluoromethylene)-1,1’-binaphthyl phosphinic acid is presented with full characterisation data for four novel compounds. The X-ray crystal structures of 2,2’-bis(difluoromethylene)-1,1’-binaphthyl phosphinic acid and ethyl 2,2’- bis(difluoromethylene)-1,1’-binaphthyl phosphinate were determined. Preliminary catalytic testing of 2,2’-bis(difluoromethylene)-1,1’-binaphthyl phosphinic acid, on a Nazarov cyclisation, and comparisons to known Brønsted acid catalysts are presented. An alternative route to Aryl-dichlorophosphines (ArPCl2) is discussed. These were synthesised from stable and easily accessible aryl H-phosphinic acids (ArPO2H2). A series of aryl-dichlorophosphines are presented, on a multi-gram scale, with two novel aryl-dichlorophosphines synthesised.

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