124 UNIVERSITY OF COLORADO STUDIES 



Their mineral acid salts are characterized by an intense, usually red, 

 color. No marked increase in basicity over the normal quinoxalines 

 has been observed in the case of these dihydro-compounds. The hydro- 

 gen of the imido group is replaceable by the hydrocarbon, acetyl, and 

 nitroso groups. 



The tetrahydroquinoxalines, as far as investigated, do not show 

 fluorescence. They are basic in character. 



Besides the above-mentioned dihydro-compounds of the general 

 formula 



vV 



HR' 



there is possible, theoretically, another series corresponding to the gen- 

 eral formula, 



(TV 



It is the purpose of this paper to describe the first member of this 

 series to be isolated. 



GENERAL AND THEORETICAL PART 



If orthophenylene-diamine is dissolved in an excess of dry acetone 

 and treated with a current of dry hydrochloric acid gas, a solid sub- 

 stance separates out, which proves to be the hydrochloric acid salt of a 

 new base. The diamine reacts in the same way when mesityloxide is 

 used instead of acetone, proving that the first reaction, in the case of 

 acetone, is a condensation of the ketone to mesityloxide, which then 

 reacts with the diamine. The free base crystallizes in large mono- 

 clinic prisms from benzene. It is very slightly soluble in water, easily 

 soluble in ether, alcohol, chloroform, carbon bisulphide, the hydrocar- 

 bons, and in acids. It dissolves in benzene, xylene, etc., in the cold 

 to a colorless solution, which turns to a golden yellow on heating. If a 



