2- Hydroxy-3,6-dimethylpyrazine 1 -oxide

Aminopyrazine 1-oxide with nitrous acid in sulfuric acid on wanning and dilution with water (108, 547a), and also by treatment with potassium cuprous cyanide (838), has been shown to give 3-hydroxypyrazine 1-oxide. 2-Amino-3,5-dimethylpyrazine 1 -oxide with about 40% sodium hydroxide at reflux in a bath at 140° produced 2-hydroxy-3,5-dimethylpyrazine 1-oxide (524). 

Recently, some interesting photochemical reactions of 2,5-dimethyl-and 2,5-diphenylpyrazine 1-oxide have been reported. Irradiation of a nitrogen-stirred benzene suspension of 2,5-dimethylpyrazine 1-oxide gives 5% 2-acetyl-4-methylimidazole (220) and 15% 2,4-dimethyl -imidazole (221). When the irradiation is carried out in aqueous solution, 10% 2-hydroxy 3,0-dimethylpyrazine (126) and 20% 1-acet-amido-2-formamido-l-propene (222) is formed. The mechanisms in Scheme 49 are suggested for these transformations. 

Dimethylamino-7V-hydroxy-2-pyrazinecarboxamide 6-Dimethylamino-7V-hydroxy-2-pyrazinecarboxamidine 2-Dimethylamino-5-iodopyrazine 2-Dimethylamino-6-iodopyrazine 2-Dimethylamino-5-iodopyrazine 4-oxide 2-Dimethylamino-3-isobutylpyrazine 2-Dimethylamino-6-isobutylpyrazine 2-Dimethylamino-5-methoxy-3,6-dimethylpyrazine 2-Dimethylaminomethyl-3,6-bismethylthiopyrazine 2-Dimethylamino-6-methyl-5-phenylpyrazine 4-oxide 2-Dimethylamino-3-methylpyrazine 2-Dimethylamino-6-methylpyrazine 2-Dimethylamino-3-methylpyrazine 4-oxide Dimethyl 5-amino-6-oxo-1,6-dihydro-2,3-pyrazinedicarboxylate 2-Dimethylamino-5-phenylpyrazine 2-(3-Dimethylaminopropyl)-6-methylpyrazine... 

V-Hydroxy-6-propylthio-2-pyrazinecarboxamide V-Hydroxy-6-propylthio-2-pyrazinecarboxamidine 2- (3-Hydroxyprop-1 -ynyl)-3,6-diisobutylpyrazine 2- (3-Hydroxyprop-1 -ynyl)-3,6-diisobutylpyrazine 4-oxide 2- (3-Hydroxyprop-1 -ynyl)-3,6-diisopropylpyrazine 2- (3-Hydroxyprop-1 -ynyl)-3,6-diisopropylpyrazine 4-oxide 2- (3-Hydroxyprop-1 -ynyl)-3,6-dimethylpy razi ne 2-(3-Hydroxyprop-1 -y nyl)-3,6-dimethylpyrazine 4-oxide 2-(3-Hydroxyprop-l-ynyl)-3,5-diphenylpyrazine 2-(3-Hydroxyprop-l-ynyl)-3,6-diphenylpyrazine 2-(3-Hydroxyprop-l-ynyl)-5,6-diphenylpyrazine 2-(3-Hydroxyprop-l-ynyl)-5,6-diphenylpyrazine 4-oxide 2-(3-Hydroxyprop-l-ynyl)-6-methoxy-5-(2-methylprop-l-enyl)pyrazine 2- (3-Hydroxyprop-1 -ynyl )-6-methoxypyrazine N-Hydroxy-2-pyrazinecarboxamide Af-Hydroxy-2-pyrazinecarboxamide 4-oxide... 

Ramsay and Spring (548) found that treatment of a-chloro-a-hydroxyimino-acetone (13) with sodium hydrogen sulfite gave the bisulfite derivative of pyruvo-hydroxamic acid, which after purification from sodium hydrogen sulfite condensed with aminoacetone to give 2-hydroxy-3,6-dimethylpyrazine 1-oxide (14). 

Ethoxypyrazine 1-oxide refluxed with 40% alcoholic hydrogen chloride yielded 2-ethoxy-5-hydroxypyrazine (1069). Ultraviolet irradiation of 2,5-dimethyl-pyrazine 1-oxide in water afforded 3-hydroxy-2,5-dimethylpyrazine (10%) and 2,5-diphenylpyrazine 1-oxide in benzene gave 3-hydroxy-2,5-diphenylpyrazine (3%) (742). A small yield of 2-ethyI-5-hydroxy-3,6-dimethylpyrazine has been isolated as by-product from the reaction of 2,5-dimethylpyrazine with ethyllithium in ether (615). 

Crystal structures of 3,5,6-tri-t-butyl-2-hydroxypyrazine (1093) 2,5-dichloro-3-methoxypyrazine (915) and 2,3-dichloro-5-ethylamino-6-methoxypyrazine (916) have been determined. The dipole moment of 2-amino-5-bromo-3-methoxypyrazine (2.94D in benzene) is consistent with the S-cis configuration (52) (749) and the polarographic behavior of 3-hydroxy(and methoxy)-2,5-dimethylpyrazine (and their A(-oxides) at various pH values has been investigated (588). 

Methylation (666, 912) of 2-methoxypyrazine with methyl iodide in dimethyl sulfoxide at room temperature gave 3-methoxy-l-methylpyrazinium iodide with a rate of methylation relative to pyrazine of 1.05 (666). 2-Methoxypyrazine with tetracyanoethylene oxide gave a small yield of 3 ethoxypyrazinium dicyano-methylide (53) (1094). Alkylation of 2-methoxypyrazine with ethyl methyl ketone in the presence of sodium in liquid ammonia to give 2-s-butyl-6-methoxypyrazine (17%) has been described (614). The reactions of 3-hydroxy-2,5-dimethylpyrazine and alkylhalides have been examined (1095). 

Preparations of hydroxypyrazine A-oxides by primary syntheses have been included in Chapter III and are summarized briefly as follows Section 1II.3, 2-hydroxypyrazine 1-oxides from a-aminohydroxamic acids and 1,2-dicarbonyl compounds or a,/l-unsaturated a-bromo aldehydes (545-548) Section III.4, 2-hydroxy-3,6-dimethylpyrazine 1-oxide from the bisulfite derivatives of pyruvo-hydroxamic acid and aminoacetone (548) and Section III.5, ring closure of the C-C-N-C-C-N-0 system (545, 546, 548-553). In addition to these preparations... 

Alkoxypyrazine A -oxides may be hydrolyzed with acid to hydroxypyrazine A -oxides. Some examples are the hydrolysis of 3-ethoxy-2,5-dimethylpyrazine 1-oxide at reflux with 3 A hydrochloric acid to give 3-hydroxy-2,5-dimethylpyrazine 1-oxide (872) 2,5-diethoxy-3,6-dimethylpyrazine 1,4-dioxide with 2N hydrochloric acid at 70° gave 2-ethoxy-5-hydroxy-3,6-dimethylpyrazine 1,4-dioxide and 2,5-dibenzyloxy-3,6-dimethylpyrazine 1,4-dioxide similarly treated but at room temperature gave the 2-benzyloxy analogue (842), but with lOAf hydrochloric acid at room temperature it gave 2,5-dihydroxy-3,6-dimethylpyrazine 1,4-dioxide (842). 

Dimethylamino-23-dimethylpyrazine 1-oxide in boiling acetic anhydride gave 2-acetoxymethyl-3-dimethylamino-5-methylpyrazine (793) which was not isolated but saponified directly to 3-dimethylamino-2-hydroxymethyl-5-methylpyrazine (793). 2-Amino-3-cyano-5-methylpyrazine 1,4-dioxide refluxed with (a) acetic anhydride gave 3-acetamido-2-cyano-5-hydroxy-6-methylpyrazine 1-oxide (532) and (6) sodium methoxide gave 3-amino-2-cyano-5-methoxy-6-methylpyrazine 1-oxide (532). 

Chang et al. [73] and Nawar et al. [74] have identified many of the volatiles formed during deep fat frying. They have found numerous acids, alcohols, aldehydes, hydrocarbons, ketones, lactones, esters, aromatics, and a few miscellaneous compounds (e.g., pentylfuran and 1,4-dioxane) as products of deep fat frying. More recently, Wagner and Grosch [75] have studied the key contributors to French fry aroma. The list of key aroma compounds in French fries includes 2-ethyl-3,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 3-isobutyl-2-methoxypyrazine, (E,Z), (E,E)-2,4-decadienal, trans-4,5-epoxy-(E)-2-decenal, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, methylpropanal, 2- and 3-methylbutanal, and methanethiol. If one examines this list, it is obvious that the Maillard reaction (pyrazines, branched chain aldeydes, furanones, and methional), and lipid oxidation (nnsaturated aldehydes) are the primary sources of this characteristic aroma. 

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