2- Hydrazino-3-hydroxy-5,6-diphenylpyrazine

A notable characteristic of the pyrazine nucleus is its resistance to electrophilic substitution but some hydroxypyrazines may be nitrated. Nitration of 5-hydroxy-23-diphenylpyrazine with fuming nitric acid in acetic acid gave the readily purified 2-hydroxy-3-nitro-5,6-diphenylpyrazine (71) (1065) [which reacts readily with hydrazine to give 2-hydrazino-3-hydroxy-5,6-diphenylpyrazine (1124)]. 3-Hydroxy-2,5-diphenylpyrazine undergoes random nitration under a variety of strongly acidic conditions (1065) but brief boiling of an acetic acid solution of equivalent amounts of 34iydroxy-2,5-diphenylpyrazine and nitric acid produced 2-hydroxy-5-nitro-3,6-diphenylpyrazine (75%) (817). 

Dihydroxy-5,6-diphenylpyrazine refluxed with aqueous hydrazine hydrate gave 2-hydrazino-3-hydroxy-5,6-diphenylpyrazine, which was also obtained by heating 2-hydroxy-3-nitro-5,6-diphenylpyrazine with aqueous hydrazine (1124). Distillation of the compound claimed by Japp and Knox (317) to be 3-hydroxy-2,5-diphenylpyrazine (317, cf. 282) with zinc dust produced 2,5-diphenylpyrazine (317) reduction of the former with hydriodic acid and red phosphorus at 200 for 6 hours gave what was regarded as 2,5-diphenyl-3,4-dihydropyrazine (317). 

A solution of 2-hydroxy-3-nitro-5,6-diphenylpyrazine in dry pyridine treated dropwise with thionyl chloride gave a slightly exothermic reaction and after standing for 18 hours gave the zwitterion of 24iydroxy-5,6-diphenyl-3-pyridinio-pyrazine (12) (863) and 23-dihydroxy-5,6-diphenylpyrazine with boiling 50% aqueous hydrazine gave 2-hydrazino-3-hydroxy-5,6-diphenylpyrazine (13) (which was also prepared from 2-hydroxy-3-nitro-5,6-diphenylpyrazine) (1124). 

Hydroxy-3-nitro-5,6-diphenylpyrazine heated with aqueous hydrazine gave 2-hydrazino-34iydroxy-5,6-diphenylpyrazine (1124) whereas when refluxed with hydrazine and Raney nickel in methanol it gave 2-amino-3-hydroxy-5,6-diphenyl-pyrazine (1065). 

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