BENZYL PHOSPHINES AND THEIR DERIVATIVES. 60& 



PART III.— THE PRODUCTS OF THE OXIDATION OF BENZYL 



PHOSPHINES. 



The substances which we describe in this part of our paper are four in number, viz., 

 benzyl phosphinous acid and beDzyl phosphinic acid, derived from the primary phosphine ; 

 dibenzyl phosphinic acid, from the secondary phosphine ; and oxide of tribenzyl phosphine, 

 from the tertiary base. # Benzyl phosphinous acid we obtained for the first time by the 

 oxidation of the primary phosphine, while we discovered benzyl phosphinic acid during our 

 investigations on the action of benzyl alcohol on a mixture of phosphorus and its iodide. 

 One of us and W. Wheeler were the first to obtain dibenzyl phosphinic acid, which we 

 isolated from the products of Hofmann's sealed tube reaction. In this part of our com- 

 munication we describe the properties and compounds of the three acids, as well as those 

 of the tertiary phosphine oxide, which we have so frequently, and at times unexpectedly, 

 encountered in the course of our investigations. 



(1) Benzyl Phosphinous Acid, (C 7 H 7 )H 2 P0 2 . 



We have obtained this acid in three different ways — (1) By the oxidation of mono- 

 benzyl phosphine ; (2) Among the products of Hofmann's sealed tube reaction ; (3) 

 Among the products of the action of benzyl alcohol on a mixture of phosphorus and its 

 iodide. We have already described the steps which we employed for isolating it in each 

 of these three cases, but it may not be unadvisable to describe the best method of 

 obtaining it. 



The primary phosphine is allowed to oxidise in the air, care being taken to prevent 

 the temperature from rising too high. The final product is a thick syrupy liquid, which 

 contains phosphoric acid and benzyl phosphinic acid, in addition to the phosphinous 

 acid. Either of the two following methods may be employed for isolating the latter : — 



(1) The viscous mass is dissolved in water and the solution just neutralised with 

 baryta. It is then filtered from the precipitated phosphate of barium and evaporated to 

 a small volume, when practically the whole of the phosphinate of barium separates out. 

 The phosphinous acid is then obtained by decomposing the filtered solution with the 

 proper quantity of sulphuric acid. 



(2) The aqueous solution of the product of oxidation is dissolved in water and 

 precipitated with acetate of lead, filtered from the phosphate and phosphinate of lead, 

 which separates, precipitated with sulphuretted hydrogen, and the filtered solution 

 evaporated until the whole of the acetic acid has passed off. 



Properties. — Benzyl phosphinous acid is a syrupy liquid which refuses to crystallise. 

 It is fairly soluble in water, but separates from a strong solution in oily drops. It dis- 



* As we have mentioned on p. 585, it is possible that other oxidised derivatives exist, but the above are the most 

 important. 



