198 Proceedings of Boyal Society of Edinburgh. [sess. 
method. The phenomena observed were exactly the same as those 
previously described, and the melting-point of the acid obtained 
after precipitation with hydrochloric acid and two recrystallisations 
from alcohol was found to be 192° C., which is the melting-point of 
pure dibenzyl-phosphinic acid. Our previous observation is thus 
fully confirmed. The reaction in all probability occurs as follows: — 
(C 7 H 7 ) 3 PO + KHO = C 7 H 8 + (C 7 H 7 ) 2 KP0 2 . 
The occurrence of oxide of tribenzyl-phosphine among the pro- 
ducts of Hofmann’s sealed tube reaction led us to suspect that 
tribenzyl-phosphine had been formed in the first instance, but was 
subsequently oxidised by atmospheric oxygen. It became necessary, 
therefore, to search for the tertiary phosphine in the original product. 
The investigation was attended with considerable difficulties, as we 
had already proved that the products of the sealed tube reaction 
are a highly complex mixture, and contain, among other substances, 
resinous bodies which are exceedingly difficult to get rid of. We 
succeeded at last in isolating a liquid which grows hot on exposure 
to air, with production both of oxide of tribenzyl-phosphine, and 
of dibenzyl-phosphinic acid ; which is precipitated by hydriodic 
acid, forming solid compounds ; and which in contact with sulphur 
gives rise to a crystalline compound, which we believe to be tri- 
benzyl-phosphine sulphide. Moreover, the liquid acts energetically 
upon crystallised iodide of benzyl to give iodide of tetrabenzyl- 
phosphonium. The liquid appears, in fact, to be a mixture of the 
secondary and tertiary phosphines. Continuing our investigations, 
we have succeeded in obtaining from the liquid two solid substances 
which are easily separated from each other. The first is almost 
insoluble in ether, and has either the formula (C 7 H 7 ) 3 P0 2 or 
(C 7 H 7 ) 3 PS.* The second is undoubtedly tribenzyl-phosphine 
itself. It crystallises easily from alcohol, and unites with sulphur 
at ordinary temperature and with oxygen also. We have not as 
yet obtained it in sufficient quantity to thoroughly investigate its 
properties. 
* We give this last formula partly because the first is improbable, and partly 
because the substance in question has the same melting-point and properties 
as the sulphide of tribenzyl-phosphine. But, on the other hand, we have not 
as yet detected sulphur in it, and unless that element was present in the crude 
products used, its occurrence is incomprehensible. 
