2-Chloroquinoxaline, with thiourea

Quinoxalinyl, 4-cinnolinyl, and 1-phthalazinyl derivatives, which are all activated by a combination of induction and resonance, have very similar kinetic characteristics (Table XV, p. 352) in ethoxylation and piperidination, but 2-chloroquinoxaline is stated (no data) to be more slowly phenoxylated. In nucleophilic substitution of methoxy groups with ethoxy or isopropoxy groups, the quinoxaline compound is less reactive than the cinnoline and phthalazine derivatives and more reactive than the quinoline and isoquinoline analogs. 2-Chloroquinoxaline is more reactive than its monocyclic analog, 2-chloropyrazine, with thiourea or with piperidine (Scheme VI, p. 350). 

Chloroquinoxaline (1) affords quinoxaline-2(l/f)-thione (16) in 73% yield upon treatment with thiourea in methanol, followed by hydrolysis of the intermediate isothiuronium salt with sodium hydroxide. ... 

Quinoxaline-2-thione (2) is prepared from 2-chloroquinoxaline by treatment with thiourea in methanol, followed by hydrolysis of the resulting isothiouronium salt (1) with 2.5 M sodium hydroxide. A number of other quinoxaline-2-thiones have been prepared by this method, in most cases without the isolation of the intermediate isothiouronium salt. 3-Hydrazinoquinoxaline-2-thiones are obtained from the corresponding 2-chloro-3-hydrazinoquinoxalines by treatment with an aqueous solution of alkali sulfide or alkali hydrogen sulphide.3-Amino-quinoxaline-2-thione has been prepared similarly by treating 2-amino-3-chloroquinoxaline with methanolic potassium hydrogen sulfide in an... 

Various 3-substituted aminoquinoxaline-2-thiones have been prepared from quinoxaline-2,3-dithione. For example, treatment of the dithione with methylamine yields 3-methylaminoquinoxaline-2-thione, and the corresponding reaction with hydrazine hydrate yields 3-hydrazino-quinoxaline-2-thione. The latter compound is also obtained by treatment of 2,3-dichloroquinoxaline with thiourea and then with hydrazine hydrate. When 2-chloroquinoxaline 1-oxide is heated with thiourea in methanol at room temperature, an unidentified solid m.p. 184-185° is obtained alkaline hydrolysis of methanol-soluble products gives quinoxaline-2-thione in 41% yield. A method of some general applicability is illustrated by the preparation of the thioxo compound 4 from o-anilinoaniline (3). °... 

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