Quinoxaline-2,3-diones nitration

Quinoxalin-2-one is a very weak base (pK — 1.37) and so the different orientation of substitution in acetic and sulfuric acids may mean that in acetic acid the principal species undergoing nitration is the neutral molecule, and in sulfuric acid, the mono-cation. Treatment of quinoxaline-2,3-dione, or its iViV -dimethyl derivative in sulfuric acid, with 1 equivalent of potassium nitrate, results in nitration at position 6 with 2 equivalents of potassium nitrate, 6,7-dinitro compounds are formed. When quinoxaline is boiled with aqueous nitric acid, 6-... 

The regiospecific oxidative nitration of 3,4-dihydro-6,7-disubstituted quinoxalin-2(l//)-ones utilizing fuming nitric acid in trifluoroacetic acid gives 5-nitro-6,7-disubstituted quinoxa-line-2,3(l/f,4/f)-diones in good yields. 

Nitration of 5-methoxyquinoxaline with potassium nitrate in concentrated sulfuric acid yields the 6,8-dinitro derivative, whereas the 6-methoxy compound is converted to the 5-nitro derivative with the same reagent system. Reaction of 2,3-dimethylquinoxaline with 20% nitric acid yields a mixture of 6-nitro and 6,7-dinitroquinoxaline-2,3(l/f,4//)-dione. The intermediate formation of quinoxaline-2,3(l/f,4//)-dione is proposed. 

Nitration of quinoxaline-2,3(l//,4//)-dione proceeds at the 6- and 7-positions, e.g. nitration with one or two equivalents of potassium nitrate in concentrated sulfuric acid yields the 6-nitro and 6,7-dinitro compounds, respectively. Nitration of 8-(carbamoy methy )su fonyl-benzo[/]quinoxaline-2,3(17/,4//)-dione with potassium nitrate in concentrated sulfuric acid gives the 6-nitro derivative in 52% yield. 

Electrophilic substitution of quinoxaline-2,3-dione and its 1,4-dimethyl derivative occxu at positions 6 and 7. For example, treatment of a solution of quinoxaline-2,3-dione in concentrated sulfuric acid with one equivalent of potassium nitrate yields the 6-nitro derivative, whereas with two equivalents of potassium nitrate 6,7-dinitroquinoxaline-2,3-dione is formed. 6-Bromo and 6,7-dibromoquinoxaline-2,3-dione have been prepared by bromination of the 2,3-dione in sulfuric acid with bromine and silver sulfate, and chlorination is found to occur under similar conditions. Treatment of quinoxaline-2,3-dione with fuming sulfuric acid yields the... 

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