BENZYL PHOSPHTNES AND THEIR DERIVATIVES. 535 



though its boiling point is high. Similar compounds of bromine and iodine have been 

 obtained. 



Compounds of tri-methyl and tri-ethyl phosphine with mustard oils, are formed 

 easily, and give crystalline hydrochlorates. They no doubt have the constitution, 



S = C = <^E S 



[_Note. — Some of the aromatic tertiary phosphines, especially tri-phenyl phosphine, 

 have properties which differ materially from those of other tertiary phosphines. Thus 

 tri-phenyl phosphine is a crystalline solid having scarcely any odour, and it does not 

 oxidise spontaneously. It is remarkably stable, and is not attacked by chlorine even 

 when heated. The hydriodate and hydrochlorate are formed when it is dissolved in the 

 warm concentrated hydracids, and are crystalline, but on adding water they dissociate. 

 By treating the phosphine with bromine and an alkali, or by oxidising it with hydrochloric 

 acid and chlorate of potash, the hydrate (C 6 H 5 ) 3 P(OH) 2 is obtained as a crystalline 

 solid. This when heated to 100° readily loses water, and is converted into the oxide, a 

 substance which is not acted upon by bromine, oxygen, sulphur, &c. By dissolving the 

 phosphine in fuming nitric acid a nitrate of the formula (C 6 H 5 ) 3 P(N0 3 ) 2 is obtained.] 



Tertiary phosphines, apparently without exception, unite with alkyl iodides to form 

 phosphonium salts. 



General Properties of Quaternary Compounds (Phosphonium Salts). 



So many of these bodies have been obtained that a list appears inadvisable. It would 

 include derivatives of the series C n H 2n+1 to the 5th term, one or two of the series 

 C n H 2n _7, and a large number of mixed phosphoniums containing various radicals, among 

 which are vinyl, allyl, and ethylene. 



The phosphonium salts are the most stable of all organic phosphorus compounds. 

 None are decomposed by water, and most of them can be obtained readily in the crystal- 

 line state by evaporating their solutions. 



As a rule, they are soluble in water and in alcohol. They are readily prepared from 

 their iodides, either by double decomposition with a silver salt, or by first obtaining 

 their hydrates (by the action of hydrate of silver), and subsequently neutralising the 

 solution with the acid. 



The hydrates EJPOH are solid substances, having a powerful alkaline reaction and 

 many properties similar to those of an alkali. Indeed, in the case of tetrethyl phos- 

 phonium hydrate, the only remarkable point of difference between it and caustic potash 

 (so far as its reactions with metallic salts, &c, are concerned) is that when added to a 

 zinc or aluminum salt, the zinc or aluminum hydrate, which is at first precipitated, is 

 insoluble in an excess. Phosphonium hydrates are decomposed when heated, and in 

 some cases, when their solutions are boiled or at the moment of production, into a 

 tertiary phosphine oxide and a hydro-carbon, 



R 4 POH = R 3 PO + R-H. 



VOL. XXXV. PART II. (NO. 15). 4 T 



