BENZYL PHOSPHINES AND THEIR DERIVATIVES. 613 



the mixture of phosphorus and its iodide is moistened with the benzyl alcohol a violent 

 reaction occurs — violet vapours of iodine appearing and a dense white smoke. It is 

 advisable, as soon as the reaction has commenced, to run in the benzyl alcohol in fairly 

 large portions, waiting, however, each time until it moderates. By this means constant 

 ebullition is kept up until the end of the reaction. Towards the close of the operation 

 (that is to say when all or most of the alcohol has been added) the flask is well shaken 

 from time to time, so as to mix its contents thoroughly. This generally starts the reaction 

 afresh, and ebullition becomes energetic. 



When all action is over, the product is allowed to cool, water is added until the flask 

 is half full, and the mixture thoroughly shaken, when it becomes warm. Then a current 

 of steam is blown through it and the vapours condensed, as they contain toluol, &c, the 

 steaming being continued so long as volatile matters pass over. The aqueous solution is 

 next decanted through a linen filter from the brown resinous mass which remains, and the 

 latter is again mixed with water and steamed as before, the operation being repeated a 

 third time. All the aqueous extracts are united and allowed to cool, when a considerable 

 quantity of dibenzyl phosphinic acid separates out. This is filtered off through a linen 

 filter and well squeezed, so as to avoid loss of liquid. The solution is next evaporated 

 until fumes of hydriodic acid appear, and then allowed to stand for some hours, when the 

 crude benzyl phosphinic acid separates out. It is thoroughly squeezed in a linen filter, 

 and the mother-liquors again concentrated, &c, when a fresh quantity of the acid usually 

 separates. 



The yield of crude acid from the quantities mentioned should be about 60 grms. The 

 acid thus obtained is very impure, and contains considerable quantities of hydriodic and 

 phosphoric acids. It may be recrystallised from water, but cannot be readily purified by 

 that means, as the impurities cling most tenaciously to it. By far the best method of 

 purification consists in converting it into its barium salt, and decomposing the latter with 

 sulphuric acid. The barium salt is easily obtained pure by neutralising a dilute solution 

 of the acid with caustic baryta, filtering from the precipitate of phosphate of barium and 

 boiling the solution, when it separates in the crystalline state. 



Properties. — Monobenzyl phosphinic acid is a colourless body which crystallises from 

 a hot and concentrated aqueous solution. It is readily soluble in water and alcohol. 

 Its melting point was found to be 169°- 169° "5 (corr.). It is a dibasic acid, and forms a 

 number of salts, most of which crystallise easily from water. 



For analysis a quantity of the acid was prepared from the barium salt, and was dried 

 first in a desiccator then for a short time at 110° C. 



Analysis. 



( 01842 H 2 = -020466 H= 5-63 per cent. 

 Odbdl gave j . 6485 C02 = . l76863 c =48 . 70 n 



* 0-2559 gave 0-1608 Mg 2 P 2 7 = -044908 P. = 17-54 



* By the oxide of copper method. 



