2.5- Dimethyl pyrazine

Fluorobenzene to fluorodihydrocatechol and fluorocatechol Conversion of 2,5-dimethyl pyrazine to 5-metyl pyrazine-2-carboxylic acid, conversion of 5-ethyl-2-methyl pyridine to... 

Methyl- and 2,6-dimethylpyrazines with DMAD in acetonitrile yield the corresponding azaindolizines (249),351 whereas 2,5-dimethyl-pyrazine gives a 1 3-molar adduct less the elements of acetonitrile. This adduct, originally described as an azepine,336 is probably the cyclo-butaindolizine 251,337 and could be formed via 250 by cycloaddition of DMAD across the dihydropyrazine ring and elimination of acetonitrile. 

Trimethyl pyrazine 3-ethyl 2,5-dimethyl pyrazine FIG. 8 Flavor compounds in roasted flaxseed observed by Meyers et al. (2004). 

Sucrose and aqueous /3-aminopropionitiile 2 ethyl- and 2,5-dimethyl pyrazine and other pyrazines 508... 

In the pyrazine series, the Mannich reaction was applied first to 2,5-dimethyl-pyrazine by Linder and Spoerri (715). Of the amines tried, positive reactions were obtained only with dime thy lamine, piperidine, and morpholine, and it was found that one, or more usually two, of the hydrogen atoms of each of the methyl groups could be substituted. Thus 2,5-dimethylpyrazine, dimethylamine hydrochloride, and formalin in refluxing isopentyl alcohol gave 2,5-bis[bis(dimethylaminomethyl)-methyl]pyrazine and 2,5-bis(j3-dimethylaminoethyl)pyrazine. Reaction of 2-methyl-pyrazine with formalin and diethylamine hydrochloride gave 2- 3-diethylamino-ethylpyrazine (716) similarly dimethylamine hydrochloride gave 2-dimethyl-aminoethylpyrazine (17) and some 2-[bis(dimethylaminomethyl)]methylpyrazine (18) (657). 

The isodiazotate salts (19) of 2-amino-3-methyl- and 3-amino-2,5-dimethyl-pyrazines (17, R =R = H R = Me R = R = Me, R = H, respectively) [prepared from the corresponding amine by refluxing with sodium amide in diethyl ether and allowing the resulting sodium salt (18) to react with isoamyl nitrite] on treatment with hydriodic acid gave 2-amino-5-iodo-3-methyl- and 2-amino-5-iodo-... 

Castle and co-workers (1013) showed that 2-chloro-3-methylpyrazine with phosphorus pentasulfide in boiling pyridine afforded 2-mercapto-3-methylpyrazine, and 3-chloro-2,5-dimethylpyrazine similarly treated gave 3-mercapto-2,5-dimethyl-pyrazine. 

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). 

Alkoxypyrazine A-oxides may also be prepared by oxidation of the alkoxypyrazine with peroxyacetic acid. In this way the following have been prepared 3-ethoxypyrazine 1-oxide (100°/20h) (978) 3-(trideuteromethoxy)pyrazine 1-oxide (757l9h) (975) 3-ethoxy-2-methylpyrazine 1-oxide (65-75724h) (978) 3-methoxy-2-phenylpyrazine 1-oxide (55720 h) (817) 3-ethoxy-2,5-dimethyl-pyrazine 1-oxide (56716 h) (872) 3-carbamoyl-2-methoxypyrazine 1-oxide (80720h) (881) and 2-cyano-5-ethoxy-3,6-dimethylpyrazine A-oxide (55720h) (288). 

Heat transforms ketoacids to methylketones like 2-heptanone, 2-nonanone with a green fatty metallic blue cheese note. Hydroxyy acids form the corresponding lactones. The creamy, buttery, coconut-like 5-decanolide, 4-dodecanolide, 5-dodecano-lide contribute to the sweet creamy buttery flavour in cream and butter. Lactose undergoes a caramelisation reaction to develop sweet, caramelic maltol and 4-hy-droxy-2,5-dimethyl-furan-3(2H)-one. Lactose and milk proteins react in a Maillard reaction to roasted, nutty, burnt notes such as 2,5-dimethyl pyrazine. 

In the field of the organic micropollutants, we can establish that the residues of making of beet-sugar, are constitued bassically for nitrogens compounds with heterocycle ring of pyrazine, standing out for its concentration the 2, 5-Dimethyl pyrazine, 2, Ethyl-5, Methyl Pyrazine and 3,-Ethyl-2,5 -Dimethyl Pyrazine. We think these compounds are metabolic pro ducts of the aminoacids present in the beet, mainly of the gly cine and its trimethyl derivates like the betaine... 

The carbonyls are represented by peaks 4, 6, 7, 11 and 16 on Figure 3. They were identified as isobutyraldehyde, isovaler-aldehyde, 2-methyl butanal, pentanal cUid hexanal. The pyrazines are represented by peaks 13, 18, 20, 25 cind 26. They were identified as pyrazine, 2-methyl pyrazine, 2,5-dimethyl pyrazine, 2-ethy1-5-methyl pyrazine and 2-ethyl-3-methyl pyrazine. The authors observed a decrease in carbonyls (which are responsible for harsh green flavor notes) euid increase in pyrazines (which are responsible for roasted notes) with longer roasting time. 

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