3- Ethyl-2,5-dimethylpyrazine oxidation

Polyurethanes (PU) The odor of many polyurethanes is caused by fishy smelling low molecular weight amines, mostly methylamines like trimethylamine, degradation products of the amine catalysts used during production. In some cases after evaporation of the fishy smelling amines, other odor qualities remain. One noticeable odor of PU samples was earthy, nutty, which can often be attributed to substituted pyrazines, formed by condensation of two a-aminoketones, subsequent oxidation or alkylation by aldehydes. One example is 2-ethyl-3,5-dimethylpyrazine (Mayer and Breuer, 2006). 

Chloro-3,6-dimethylpyrazine (124) gave 2-ethyl-3,6-dimethylpyrazine (125) [Et2Zn, NiCl2.(Ph2PCH2)2CH2, THF, A, 20°C, 3 h 71%] 55 2-ethyl-3,6-di-methylpyrazine 1-oxide (126) (46%) was made similarly 1594 and analogues likewise.551594... 

Ethylthio-2-pyrazinecarbonitrile 6-Ethylthio-2-pyrazinecarbonitrile 6-Ethylthio-2-pyrazinecarbothioamide 3-Ethylthio-2-pyrazinecarboxamide 6-Ethylthio-2-pyrazinecarboxamide 3-Ethylthio-2-pyrazinecarboxylic acid 6-Ethylthio-2-pyrazinecarboxylic acid 3-Ethylthio-2,5-pyrazinedicarboxamide 2-Ethylthiopyrazine 1-oxide 2-Ethyl-3,5,6-trimethylpyrazine 2-Ethyl-3,5,6-triphenylpyrazine 2-Ethyl-3-vinylpyrazine 2-Ethynyl-3,6-dimethylpyrazine 2-Ethynyl-3-methylpyrazine 2-Fluoro-5,6-dimethoxy-3-methylpyrazine 2- Fluoro- 5,6-dimethoxypyrazine 2-Fluoro-3,6-dimethylpyrazine 2-Fluoro-3-(l-hydroxyethyl)pyrazine 2-Fluoro-3-iodopyrazine 2-Fluoromethyl-5-methyl-3,6-diphenylpyrazine 2- Fluoro- 5-phenylpyrazine 2-Fluoro-3-phenylthiopyrazine... 

Some 2 -dialkylpyrazines have been oxidized in one step with sodium dichromate in acetic acid, in good yields, to the corresponding 2-acyl-3-alkylpyrazines (678). Thus 2-ethyl-3-methylpyrazine gave 2-acetyl-3-methylpyrazine, 23-diethylpyrazine gave 2-acetyl-3-ethylpyrazine, and 2-ethyl-3,5(or 3,6)-dimethylpyrazine gave 2-acetyl-3,5(or 3,6)-dimethylpyrazine (678). 

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). 

The total neutral essential oil from M. oleifera leaves is composed of 44 constituents and include toluene, 5-ter/-butyl-l,3-cyclopentadiene, benzaldehyde, 5-methyl-2-furaldehyde, benzeneacetaldehyde, linaloloxide, 2-ethyl-3,6-dimethylpyrazine, undecane, a-isophorone, benzylnitrile, 2,6,6-trimethyl-2-cyclohexane-l, 4-dione, 2,2,4-trimethyl-pentadiol, 2,3 -epoxycarane, p-menth-1 -en-8-ol, 2,6,6-trimethylcyclohexa-1,3 -dienecarbaldehyde, indole, tridecane, a-ionone, l,l,6-trimethyl-l,2-dihydronaphthalene, a-ionene, (1-damascenone, 3-ionone, ledene oxide, 2-ter/-butyl-l,4-dimethoxybenzene, ( )-6,10-dimethylundeca-5,9-dien-2-one, 4,6-dimethyl-dodecane, 3,3,5,6-... 

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. 

Acetic acid, transAmaXooX oxide (furanoid), 3-ethyl-2,5-dimethylpyrazine 815.2 889.23 65 4-Ethenyl-2-metlioxyplienol 22.43 92.85... 

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