Preparation of alkyl- and acylphosphonic acids

For the hydrolysis of dialkyl alkylphosphonates to alkylphos-phonic acids KosolapofiF used hot concentrated hydrochloric acid, and for more stubborn cases, 48 per cent hydrobromic 

Dry hydrogen halide was passed into the ester. The ethyl halide was trapped at — 78°, and the weight of it served to indicate the progress of dealkylation. Dealkylation being completed, volatile matter was removed from the residue at low pressure. Crude acids were thus obtained in absence of water. Similar results to those obtained at 100° were obtained at 25°, but of course longer reaction time was required. 

The Arbusov reaction is of course a method par excellence for producing C—P links (p. 95). Among other methods, the following also may be mentioned  

X can be COOR or C N, and the reaction takes place against Markownikov s rule. 

The first method is quicker, but the filtration entailed in this reaction presents a hazard because of the danger of inhalation. If it is desired to employ volatile radioactive materials, e.g. to introduce P into the molecule, the second method is recommended. Further, the first method involves some danger because of the pressure developed in an enclosed reaction vessel containing ethyl chloride. It is considered essential that operations with the more volatile radioactive compounds (up to b.p. 150°/760 mm.) should be carried out in a completely enclosed system. This is possible with the second method, and the extra time of operation involves a decrease in the radioactivity of only 15 per cent compared with the first method.  

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