Pyrazine hydrogen-deuterium exchange

Kinetic studies of hydrogen-deuterium exchange in pyrazine (590, 591) and... 

Hydrogen-deuterium exchange rates of H2 and in some 3-substituted pyrazine 1 -oxides in Na0D-D20 have been correlated with a constants, and the log of the H2 exchange rates have been shown to be rectilinearly related to the pK values of these compounds (745). A considerable exchange-rate enhancement was caused by replacement of the =C4-H function in a pyridine A-oxide by a =N4 with formation of a pyrazine A-oxide (745). 

Dipole moments of 3-aminopyrazine 1-oxide (3.43D, dioxane) (749) and 3,5-bisdimethylaminopyrazine 1-oxide (4.87, benzene) (663) have been measured. Second-order rate constants for hydrogen-deuterium exchange of H2 and in sodium deuteroxide-deuterium oxide solutions of 3-amino- and 3-dimethylaminopyrazine 1-oxides have been determined as 2.3 x 10 , 1.1 x 10 , and 3.3 x 10 and 4.5 x 10 l/mol min, respectively. These results (and those of other 3-substituted pyrazine 1-oxides) have been correlated with o constants, and the log of the H2 exchange rates has been shown to be linearly related to the p/fa values of these compounds (745). 

Proton magnetic resonance techniques have been used for the measurement of rates of hydrogen-deuterium exchange of pyrazine (in CHsOD-CHsONa at 164.6") (591) for a study of protonation of pyrazine (1472) for analysis of the reaction mixture from quatemization of 2-substituted pyrazines with methyl iodide (666) for elucidation or confirmation of the structures of alkylpyrazines obtained by alkylation of pyrazines with aldehydes and ketones in the presence of a solution of an alkali or alkaline earth metal in liquid ammonia, or a suspension of these metals in other solvents (614) for a study of changes in chemical shifts produced on ionization of 2-methyl and 2-amino derivatives of pyrazine in liquid ammonia (665) for characterization of methoxymethylpyrazines (686) for the determination of the position of the A -oxide function in monosubstituted pyrazine V-oxides and the analysis of V-oxidation reactions (838) for a study of the structure of the cations of fV-oxides of monosubstituted pyrazines (1136) and for the determination of the structure of the products of peroxyacetic and peroxysulfuric acid iV-oxidation of phenyl- and chlorophenylpyrazines (733b). 

A recent paper has shown that imidazo[l,2-a]pyrazine undergoes electrophilic substitution, as expected, at the 3-position. Thus N-bromosuccinimide afforded a 72% yield of 3-bromoimidazo[l,2-ojpyrazine from the parent heterocycle. Base-catalyzed proton-deuterium exchange was shown to occur at the 3- and 5-positions (PMR evidence). On heating with phosphorus pentachloride at 265° in a sealed tube, imidazo[l,2-a]pyrazine yielded its perchloro derivative in 55% yield. Reaction of this product with sodium methoxide resulted in nucleophilic substitution at the 5- and 8-positions. The remaining chlorines in the molecule proved to be removable by catalytic hydrogenation. Apart from this study there has been little work on the reactions of this ring system. 

Second-Order Rate Coefficients for Base-Catalyzed Deuterium-Hydrogen Exchange in 3-Substituted Pyrazine N-Oxides ... 

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