148 Royal Society : — 



February 24.— Sir Benjamin C. Brodie, Bart., Pres., in the Chair. 



The following communications were read : — 



"Researches on the Phosphorus-Bases." — No. V. Diphospho- 

 nium-Compounds. By A. W. Hofmann, LL.D., F.R.S. &c. 



In a note* ou the deportment of dibromide of ethylene with tri- 

 ethylphosphine, I have stated that the reaction between these two 

 substances gives rise to the production of 



Bromide of triethylbromethylene- 1 r/n ti \ //-. tt t> \TnT> 

 phosphonium j [(C,H,)3 (C.H.Br) P] Br, 



whilst two other bromides, viz. 

 Bromide of triethylphosphonium [(C,H5)3HP]Br and 



Bromide of triethylvinyl-phos- 1 r,p tt x /p tt ^p^^lr 

 phonium / L(^4H,)3(C,H3)P]Br, 



are generated in consequence of secondary processes. But I did not 

 fail to remark in the same note, that in addition there is formed in 

 this reaction a fourth bromide, the nature of which, at that time, I 

 had been unable to fix by experiment. 



I have continued the study of this substance, which has led to the 

 following results. 



All attempts to eliminate the bromide in question by frequently 

 recrystallizing the direct product of the action of dibromide of ethyl- 

 ene on triethylphosphine have entirely failed. Considerable sacri- 

 fice of precious material and often repeated analyses of the different 

 crops of crystallization taught me nothing, except that the body 

 which I endeavoured to grasp is most abundantly produced when 

 the triethylphosphine is rather in excess. Indeed, it would appear, 

 that under those conditions, the bromide in question constitutes the 

 principal product of the reaction. 



Not more successful was an attempt to increase the chances of 

 separation by reducing the number of the bromides. 



As I have previously stated, treatment with oxide of silver de- 

 stroys the triethylated bromethylene-phosphonium, converting it into 

 a basic compound, which contains no longer any bromine, whilst 

 the same agent transforms the bromide of triethylphosphonium into 

 the oxide of argento-triethylphosphonium, and the dioxide of tri- 

 ethylphosphine. On saturating again by hydrobroraic acid the liquid 

 thus produced, the solution now contained only the new bromide, the 

 bromide of the debrominated body, and the dibromide of triethyl- 

 phosphine, the extreme solubility of which rendered its presence al- 

 most harmless. The task was thus virtually reduced to the separation 

 of two bromides. Unfortunately, the two substances resemble each 

 other to such an extent, that this hope also had to be abandoned. 



A modification, however, of this process led to the solution of the 

 difficulty. On saturating the alkaline solution, produced by the action 

 of oxide of silver upon the crude bromides, with hydriodic instead of 

 hydrobromic acid, a mixture of the corresponding iodides was ob- 

 tained, the separation of which could be easily accomplished. 



On moderately concentrating this solution, a beautiful iodide of 

 * Phil. Mag. vol. xvii. p. 134. 



