BENZYL PHOSPHINES AND THEIR DERIVATIVES. 591 



led to very interesting and important results. In searching for some general method 

 for obtaining the phosphines, Hofmann was influenced by his well-known and beautiful 

 researches on the preparation of the compound ammonias. " The question arose," he 

 says,* "should not the series of phosphines be capable of production by a general reaction 

 similar to that which had yielded me the compound ammonias twenty years ago ? For 

 that purpose it was necessary to allow phosphuretted hydrogen to react upon alcohol 

 iodides under suitable conditions." 



In his first experiments in this direction, Hofmann heated iodide of phosphonium in a 

 sealed tube, in which was also placed a narrower tube containing iodide of ethyl and a 

 little water. The sealed tube thus charged was heated in a horizontal position for several 

 hours to a temperature ranging from 160°-180° C, when a reaction occurred in the desired 

 manner, triethyl phosphine and tetrethyl phosphonium iodide resulting. The yield, how- 

 ever, was very small, owing to the large quantity of hydriodic acid set free. To avoid 

 this, Hofmann took advantage of the fact that phosphonium iodide when heated with 

 alcohol yields phosphuretted hydrogen, iodide of ethyl, and water. Accordingly, he next 

 charged the sealed tubes simply with alcohol and phosphonium iodide. When this 

 mixture was heated for eight hours at 180° C, the reaction was complete. The cooled 

 tubes were found to be full of a snow-white crystalline mass, and on opening them scarcely 

 a trace of gas escaped. On adding water, the solid dissolved to a homogeneous liquid, 

 showing that no iodide of ethyl remained, neither was any alcohol left undecomposed. 

 The crystals showed themselves to consist of a mixture in nearly equal parts, of triethyl 

 phosphine hydriodate, and tetrethyl phosphonium iodide. Their separation presented no 

 difficulty, for on addition of caustic soda, triethyl phosphine separated as a clear liquid, 

 while the solution gave on evaporation beautiful crystals of tetrethyl phosphonium iodide. 



As regards the most favourable proportions of iodide of phosphonium and alcohol 

 (which are of great importance), Hofmann found that one molecular weight of the former 

 should be taken for three molecular weights of the latter. "In this case," he says, "the 

 quantities heated in the tubes can be increased in an extraordinary manner without fear 

 of explosions. In one experiment there was placed in a single tube 25 grms. of phos- 

 phonium iodide and 22 grms. of alcohol." 



Hofmann next investigated the course of the reaction, to decide whether iodide of 

 ethyl was first formed and was then acted upon by the phosphuretted hydrogen, or 

 whether the alcohol and phosphonium iodide acted upon each other directly — 



(1) PH 4 I + 3aH a O=(C 2 H 5 ) 3 PHI + 3H 2 



(2) PH 4 I + 4C 2 H 6 0=(C 2 H 5 ) 4 PI +4H 2 0. 



To decide this question the tubes were heated for four hours only. On cooling, two 

 layers of liquid were visible. The tubes when opened showed great pressure, and on 

 distilling their contents iodide of ethyl passed over in abundance. It may be taken for 

 granted then that the reaction occurs in two phases, in the first of which iodide of ethyl 



* Hofmann, Berichte f iv. (1871) 205. 

 VOL. XXXV. PART II. (NO. 15). 5 C 



