BENZYL PHOSPHINES AND THEIR DERIVATIVES. 603 



weighed, when dried as far as possible by pressure, 30 grms. The residual mother- 

 liquors left on evaporation 3 to 4 grms. of a viscous mass, which was not further 

 examined. 



Experiment 4. — We had as yet not proved the production of benzyl phosphinous 

 acid, though we had reason for suspecting its presence, as well as that of either 

 phosphorous or hypophosphorous acids. For, on heating the mother-liquors from the 

 crude phosphinic acid, we had noticed the production of the primary phosphine (or rather 

 its hydriodate) and phosphonium iodide, and their formation seemed to be most readily 

 explained on the hypothesis that the acids we have named were present originally, 

 but were decomposed by heat. 



To decide this question we performed a new experiment.* 



Three quantities of benzyl alcohol, amounting in all to 145 grms., and three quantities 

 of the phosphorus mixture, amounting to 200 grms., were worked up as described in 

 Experiment 3, with this difference, that the benzyl alcohol was run in rather more slowly, 

 so that the action was not quite so violent. The treatment of the crude product was at 

 first substantially the same as in the previous experiment. 



The tribenzyl phosphine oxide, however, at once showed itself to be impure, for 

 when dried it became brown. It would not dissolve completely in cold acetic acid, 

 whereas the pure oxide dissolves with the greatest ease. On boiling with acetic acid 

 it entirely dissolved, but as the solution cooled, a substance separated in feathery crystals 

 like sal-ammoniac, quite unlike the oxide of tribenzyl phosphine, which crystallises in 

 needles. From the appearance of these crystals we were led to suspect that they were 

 iodide of tetrabenzyl phosphonium, — a suspicion which was verified both by their analysis 

 (after recrystallisation from alcohol) and by their properties. 



Analysis. 



0-7732 gave 03390 AgI=0\L83204 1=23-69 per cent. 



Obtained. Calculated for (C 7 H 7 ) 4 PI 



Iodine, 23-69 24-32 



When boiled with alcoholic soda solution they were decomposed, and on washing with 

 water and recrystallising from alcohol, needles were obtained, melting at 216° C. (corr.). 

 (The pure oxide melting at 215°-5.)t Some of the crystals were dissolved in alcohol, 

 decomposed with oxide of silver, the product boiled with hydrochloric acid, and extracted 

 with boiling water. The solution gave on cooling the characteristic needles of chloride 

 of tetrabenzyl phosphonium, a further proof that the original substance was the iodide. 



The main object of this experiment was, as we have said, to ascertain whether benzyl 

 phosphinous acid was formed in the reaction. As it is a very soluble substance, we 

 expected to find it, if it was produced at all, in the mother-liquors from the phosphinic 



* In the meantime we had obtained benzyl phosphinous acid from other sources, and had become acquainted with 

 some of its properties. Among them, we had ascertained that it yields the primary phosphine when heated. 



t One of us and N. Collie have shown that the haloid salts of tetrabenzyl phosphonium are decomposed when 

 treated with an alkali, and yield the tertiary phosphine oxide (see p. 575). 



