DE. A. W. HOFMANN ON THE PHOSPHOEHS-BASES. 
453 
that of triethylphosphine, I always used, in commencing the study of this reaction, the 
former substance in excess. The triethylphosphine is quickly fixed by the dibromide 
of ethylene, and the action may be considered as terminated when the presence of the 
free phosphorus-base in the mixture is no longer indicated by disulphide of carbon. As 
soon as this point is attained, the crystalline bromides may be thrown on a filter, the 
ether allowed to run ofF, and the crystals freed from excess of bromide of ethylene by 
washing them for a while with anhydrous ether, in which they are quite insoluble. 
The crystals thus obtained dissolve vdih great facility in water and in ordinary 
alcohol, somewhat less readily in boiling absolute alcohol. This solution on cooling 
deposits well-developed crystals, which sustain a heat of 100° without decomposition, 
but show a slight tendency to deliquesce in the air. The analysis of these crystals, and 
their behaviour with reagents, showed unmistakeably that, in the action of dibromide 
of ethylene on triethylphosphine, two bromides at least are formed. The determination 
of the bromine by means of nitrate of silver in the products of different preparations, 
purified by successive crystallizations from alcohol, gave the following percentages of 
bromine : — 
I. II. III. IV. V. VI. VII. VIII. IX. 
Bromine . . 32*10 29*58 28*30 28*05 27*46 27*30 27*15 26*85 25*94. 
On again repeating the crystallization, fhe amount of bromine precipitated by nitrate 
of silver did not exhibit any further diminution. 
The complete analysis of the crystals, purified by a great number of crystallizations 
from alcohol, which will be given in a subsequent paragraph of the paper, has led me 
to the simple expression 
Cg P Br, = Cg PIi 5 P+C 2 Br„ 
whence it appears that the body is produced by the combination of one molecule of 
triethylphosphine with one molecule of the bromine-compound. 
The purification of the second substance, yielding with nitrate of silver a larger pro- 
portion of bromine, which remains in the mother-liquor of the compound just described, 
is somewhat complicated. As 1 shall have to return to this body in the description of 
the individual compounds, I content myself in this place with just setting forth the 
general character of the reaction by quoting the formula deduced from its examination. 
The analysis of this bromine-compound, together with those of a whole series of bodies 
derived from it, has led to the formula 
H34 P2 Br^ = 2 Ce P + C2 H4 Br^, 
showing that the body is a compound of two molecules of triethylphosphine and one 
molecule of dibromide of ethylene. 
These observations are sufiicient to establish the peculiar nature of the reaction in ^ 
question. There are clearly two successive phases to be distinguished, according as the 
bromide of ethylene lays hold of one or two molecules of triethylphosphine ; secondary 
products may likewise be formed, which for the present may be left out of consideration, 
