46 



SECTIONAL ADDRESSES 



This is in keeping with their formation from equimolecular quantities of 

 dialkylmonobromogold compounds and tribromogold and with their 

 physical and chemical properties. Slowly, on standing, more rapidly, in 

 a current of an inert gas at the ordinary temperature, and still more rapidly, 

 when heated at a temperature just above the boiling point of the alkyl 

 bromide, they decompose quantitatively into alkyl bromide and gold 

 monobromide, thus : 



R 



Br 



Au 



^^ / 



Br 



Au 



= 2 RBr+Au 



Br 

 / ^ 



Au 



/ \ / 



R 



Br 



Br 



\ 



Br 



This decomposition also seems to afford chemical evidence concerning 

 the constitution of the aurous halides to which reference has already been 

 made. The aurous bromide (monobromogold) is left in a state of purity 

 as highly crystalline apparently pseudomorphs of the monoalkyldibromo 

 compound, and, prepared in this way, it is suitable for X-ray investigation 

 to which such an aurous compound does not yet appear to have been 

 submitted. 



Chemically, the monoalkyldibromogold compounds behave as equi- 

 molecular mixtures of gold tribromide and the dialkylmonobromogold. 

 For example, in contact with the many solvents which decompose them 

 they yield dialkylmonobromogold compounds and the solvents are either 

 brominated or oxidised and aurous bromide is left as a yellow precipitate. 

 With hydrobromic acid, they yield hydrobromoauric acid and the dialkyl 

 monobromogold compound and with aqueous solutions of alkali halides 

 the reaction is similar. With ethylenediamine, they yield equimolecular 

 quantities of the ethylenediaminodialkylgold bromide, [R2AU en] Br, and 

 diethylenediaminogold tribromide (Gibson and Simonsen 1930, Gibson 

 and CoUes 193 1), having the constitution : 



■CH2— HgN 



CH.-H^N 



Au 



NH^— CH- 



NHo— CH, 



Br 



This is a crystalline yellow salt which is highly soluble in water and 

 insoluble in ethanol. It is readily prepared by the action of ethylene- 

 diamine on gold tribromide or on a suitable salt of hydrobromoauric acid. 

 It constitutes one of the few examples known in which the 4-covalent 

 auric gold complex is a tervalent cation in halide salts. It is analogous to 

 tetraamminoauric nitrate, [Au(NH3)4](N03)3, the corresponding phos- 

 phate, iJPO^.Hp, the oxalonitrate, R{^Q^{Z^O^, the chlorate, i?(C103)3, 

 the perchlorate, i?(C104)3, the oxaloperchlorate, i?(C104)(Co04), the 

 sulphonitrate, i?(N03)(S04), and the chromate R.^(Q,xO^.^ where R = 

 [Au(NH3)4]+++ (Weitz 1915). Like the above diethylenediamino com- 

 pound, these are very stable salts ; they retain their ammonia even in the 



