618 PROF. LETTS AND MR R. F. BLAKE ON 



A was slightly evaporated, and on cooling gave a crop of colourless crystals, unlike 

 the original acid, and probably the pyro acid. 



B was evaporated to a small bulk, and was completely converted into the original 

 acid, as was proved by the production of the characteristic barium salt. 



C was neutralised with caustic baryta, and gave the long needles of the pyro- 

 phosphate exactly similar to those obtained in the first experiment. 



We may conclude, then, that at a temperature of 200°-230° C, benzyl phosphinic acid 

 is converted into the pyro acid, (C 7 H 7 ) 2 H 2 P 2 5 (which gives a characteristic barium salt, 

 and is less soluble than the original acid). The pyro acid, on boiling for a long time with 

 water, is rehydrated, and gives the original benzyl phosphinic acid.* 



Action of a Rapid Heat on Benzyl Phosphinic Acid. — 5 grms. of the acid were cau- 

 tiously heated in a small retort over the naked flame of a Bunsen burner. At first a few 

 drops of water passed over, then a yellowish oil distilled, and presently a sudden 

 decomposition occurred, the mass charring. The lamp was instantly removed, but the 

 decomposition went on spontaneously. 



The receiver contained 1 to 2 c.c. of a yellowish oil, smelling very slightly of the 

 primary phosphine, and partly solidifying on cooling. The black tarry matter in the 

 retort contained a little free phosphorus. It was boiled with water and the solution 

 filtered. The filtrate was neutralised with caustic baryta, and gave a white amorphous 

 precipitate, which, when filtered off and dissolved in nitric acid, gave a strong phosphoric 

 acid reaction with molybdate of ammonium. 



The filtrate from the amorphous precipitate, when boiled, gave characteristic crystals 

 of barium benzyl phosphinate, showing that some of the acid had escaped decomposition. 

 According to Michaelis and Matthias (loc. cit.), phenyl phosphinic acid decomposes at 

 250° C. into benzol and meta-phosphoric acid, with charring — 



C c H 5 H 2 P0 3 = C 6 H 6 +HP0 3 . 



They do not mention how the benzol was identified. 



We had not sufficient of the oily distillate to determine its boiling point or to 

 identify it as toluol, but as the production of phosphoric acid was proved, it is probable 

 that benzyl-phosphinic acid decomposes like the phenylated acid thus — 



C 7 H 7 H 2 P0 3 =C 7 H 8 +HP0 3 . 



Action of Phosjihorous Acid on Benzyl Phosphinic Acid. — Having obtained the 

 benzyl phosphinic acid in large quantities, and with ease, we were anxious to discover some 

 method by which it could be reduced to the phosphine, and as we had proved that the 

 action of heat alone did not lead to the desired result, we decided to try the effect of 



* Michaelis and Matthias (Ikr., vii. 1070) and Michaelis (Annalen, 181, p. 323) found that the corresponding 

 phenyl phosphinic acid, when heated to 200° C, loses sufficient water to give the pyro acid analogous to the one we 

 oMained, viz., (C G H 5 ) 2 H 2 P 2 6 ; while at 210° C. three molecules of the acid lose two molecules of water, giving, they 

 suppose, (C 6 H s ) 3 H 2 P 3 O r . They did not succeed in isolating either of the pyro acids or in obtaining their salts, as they 

 re-hydrate when treated with water. 



