Pyrazine methiodide

The and N relaxation rates and the deuterium quadrupole coupling constant for pyrazine have been reported (1503) but the motion of this molecule could not be analyzed. N-H Spin coupiings in pyrazine methiodides have been determined (704). 

Hydrogenation of 2,3,5,6-tetramethylpyrazine over platinum oxide was unsuccessful in alcohol or in ethyl acetate, and proceeded only to small extents in acetic acid. However, the anhydrous hydrochloride of the pyrazine was rapidly and quantitatively hydrogenated in absolute ethanol with the addition of acetic acid.162 The methiodide of the tetramethylpirazine was also successfully hydrogenated over platinum oxide in ethanol with the addition of a little water.163... 

Rates of methylation (from n.m.r. studies) of 2-fluoro- and 2-chloropyrazines with methyl iodide in dimethyl sulfoxide at room temperature relative to pyrazine have been determined as 0.16 and 0.15, respectively (666). Methylation of 2-chloropyrazine with methyl iodide in benzene at reflux gave one methiodide (912). 2-Chloropyrazine also formed a p-fluorophenacyl bromide salt (913). 

Methylation of 2-amino-3-hydroxypyrazine (62) with methyl iodide and sodium methoxide afforded 3-amino-l-methyl-2-oxo-1,2-dihydropyrazine (63), and when an excess of methyl iodide was used, a mixture of compound (63) and its methio-dide (64) was isolated. Reaction with dimethyl sulfate and alkaU gave compound (63) and l,4-dimethyl-2,3-dioxo-l,2,3,4-tetrahydropyrazine (66) the latter was presumed to be formed by hydrolysis of an intermediate quaternary salt since it was also obtained by treatment of the methiodide (64) with aqueous sodium hydroxide. Reaction of 2-amino-3-hydroxypyrazine with ethereal diazomethane produced a mixture of N- and 0-methyl derivatives, (63) and 2-amino-3-methoxy-pyrazine (65). With methyl toluene-p-sulfonate the quaternary salt 2-amino-3-hydroxy-1-methylpyrazinium toluenesulfonate (67) was obtained on alkaline hydrolysis it gave 3-hydroxy-l-methyl-2-oxo-l,2-dihydropyrazine (68) (832). Pulcherriminic acid with diazomethane gave a dimethyl derivative (99). 

The ultraviolet spectra in aqueous solution (821) of the methiodides isolated from the methylation of 2-amino- and 2-dimethylaminopyrazines with methyl iodide in methanol (821) differed from those obtained by protonation of 2-amino-and 2-dimethylaminopyrazine, respectively. This methiodide of 2-aminopyrazine was rapidly decomposed by aqueous alkali but did not form l-methyl-2-oxo(or imino)-l, 2-dihydropyrazine or 2-methylaminopyrazine (821). These and other observations were consistent with protonation of 2-amino(2-methylamino or 2-dimethylamino)pyrazine at N, and with the methiodides isolated involving quater-nization at N4 (821). It has been claimed from studies of ultraviolet and infrared spectra and from reactions with cyanoguanidine that in 2-aminopyrazine p-toluenesulfonate, the amino group is protonated (1189). 

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