PHOSPHORUS TRICHLORIDE AND ANHYBHOUS OXALIC ACID. 151 



7.— NOTE ON THE EE ACTION BETWEEN PHOSPHORUS 

 TRICHLORIDE AND ANHYDROUS OXALIC ACID. 



By B. T. REVELL. 



Abstract. 



One of the recognised methods for the preparation of phosphorous 

 acid is that in which phosphorus trichloride is heated with anhydrous 

 oxaHc acid under a reflux condenser. (Hurtzig and Geuther, Watt's 

 Dictionary (Morley and Muir), Vol. IV., page 151.) 



A preliminary experiment showed that phosphorous acid prepared 

 in this way contained phosphoric acid, together with a j^ellow sub- 

 stance which did not dissolve in water and might have been phos- 

 phonis or a suboxide. It appeared worth while to examine the action 

 in greater detail. 



I. Excess of redistilled phosphorus trichloride was placed in a 

 flask with carefully dried oxalic acid. No perceptible reaction took 

 place in the cold, but when the temperature was raised to 60 degi'ees 

 the action became vigorous, and a white scum appeared on the surface 

 of the trichloride. When the temperature was raised to 70 degrees 

 the scum assumed a yellowish colour, and separated as a ring round 

 the flask. The heating was now continued for an hour, the tempera- 

 ture of the bath rising gradiially to 100 degrees. At the end of this 

 time no further evolution of hydrochloric acid gas was noticeable, and 

 the scum had become bright yellow in appearance. After the experi- 

 ment the liquid in the flask was poured off and distilled under 

 diminished pressure. It was completely volatile at the ordinaiy tem- 

 perature, except a minute trace of phosphorous acid, which remained 

 as a residue, and gave the ordinaiy qualitative tests. 



The scum above alluded to became a hard, brittle substance on 

 cooling. After freeing from all traces of phosphorus trichloride it 

 was completely soluble in water, except for a small quantity of a 

 bright yellow substance, which readily ran through an ordinary filter 

 paper, though it was retained by papers of specially close grain. This 

 substance was at first taken to be amorphous phosphorus, but the fact 

 that even after Avashing it evolved for weeks the odour of phosphine 

 suggested that it was a compound of phosphorus, probably a suboxide. 

 A quantitative analysis of the solution obtained above showed that it 

 contained both phosphorous and phosphoric acids. 



The yellow substance mentioned above was purified for analysis 

 by frequent decantation washings. It was then collected and dried 

 in vacuo for several days. Two analyses gave 79 "63 per cent, and 

 77 "74 per cent, of phosphoi^iis. These numbers agree appreciably with 

 the value required for the suboxide P2O, which requires 79 "23 per cent of 

 phosphorus, and which was obtained by Besson by the interaction of 

 phosphorus trichloride and phosphorous acid. (J. Chem. Soc, 



