Phosphinous acid chlorides

B. By Hydrolysis Reactions.—Details have appeared of the synthesis of dibenzophosphorin oxides (15) from 5-alkyldibenzophospholes, by reaction with methyl propiolate in the presence of water, and of confirmatory syntheses from phosphinic acid chlorides, as shown below. Evidence for the suggested mechanism of the ring-expansion reaction is presented. The hydrolysis of enamine phosphine oxides is an efficient, although somewhat indirect, method for the preparation of j8-ketoalkylphosphine oxides (16) [see Section 3(iii), for the preparation of enamine oxides]. Reasonable yields (48—66%) of trialkylphosphine oxides (17) have been obtained by the alkaline hydrolysis of the products from the pyrolysis at 220 °C of red phosphorus with alkyl halides, in the presence of iodine. 

Mach isolated a crystalline stericaUy uniform substance, m.p. 77-78,5 °C, identified as 4-chloro-phosphinic acid chloride 94. 1.1.1.4-Tetra-chloro-2.4.6-tri-tert-butyl-X -phosphorin 93 is assumed to be the primary chlorination product. 

Thus phosphaallenes react with HC1 or methanolate, respectively, adding to the PC double bond and forming the phosphinous acid chloride or the corresponding methyl ester. In these cases the phosphorus atom acts as an electrophilic center. During the turnover of la,c together with H202/H20 the phosphorus atom again is attacked in a nucleophilic way and is oxidized to phosphinic acid 4a,c (Scheme 15). 

Phosphinic add esters from chlorophosphines via phosphinic acid chlorides... 

Sym. diphosphine oxides from 2 phosphinous acid chloride molecules >P(0)P(0)<... 

Thionyl chloride Phosphinic acid chlorides from diphosphine disulfides... 

Phosphine oxides from phosphinous acid chlorides > PCI... 

Phosphinic acid anhydrides from phosphinic acid chlorides s. 17, 178 ... 

Without additional reagents Thiophosphinic acid bromides from diphosphine disulfides s. 19, 590 Thionyl chloride Phosphinic acid chlorides from diphosphine disulfides s. 19, 591... 

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