Properties of Pyrazine A-Oxides and their C-Alkyl Derivatives

Properties of Pyrazine A-Oxides and their C-Alkyl Derivatives 

Pyrazine monoxide and substituted pyrazine monoxides are somewhat deliquescent or hygroscopic solids which sublime readily (626). 

The strong base-weakening effect of an A-oxide substituent upon a para-situated sp nitrogen atom is exemplified by a comparison of the of pyrazine [0.65 (122)] with that of pyrazine A-oxide [0.05 (745)]. The pKg of 3-methylpyrazine 1-oxide is 0.46 (745). Pyrazine A-oxides form salts thus 2,5-dimethylpyrazine A-oxide forms 1 1 addition products with hydrogen chloride, methyl iodide, and benzyl chloride (625). Thermodynamic parameters for the second protonation of tetramethylpyrazine 1,4-dioxide have been determined from measurements at 25, 40,60,80, and 90° (746). 

Kinetics have been studied for ring D exchange in MeOK-MeOD for pyrazine A-oxide (590), and the first-order rate constant at 120° for H-D exchange for pyrazine A-oxide in liquid ND3 has been determined as 1.0x10 sec (747). 

Unsubstituted 30% HjOj/acetic acid/70-80° Mono- and dioxide 625, 626 

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