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Isolation and Purification of Pyrazines Produced by Reaction of Cellulosic-Derived Sugars with NH4OH and Selected Amino Acids.

Various pyrazines have been synthesized via reaction of selected cellulosic-derived sugars, ammonium hydroxide and amino acids at 110°C for 2 hours. Different methods of sample cleanup such as liquid-liquid extraction (LLE), liquid-solid extraction, column chromatography and distillation were employed to isolate pyrazines from the reaction mixture. Effective LLE of pyrazines from aqueous solution using either hexane, methyl-t-butyl ether (MTBE) or ethyl acetate required multiple extraction steps with fresh solvent each time. When hexane was used as the extraction solvent, no imidazole derivatives were extracted with the pyrazines. However, when MTBE or ethyl acetate was employed, 4-methyl imidazole was co-extracted and further cleanup was required. Passing the organic solvent extracts through a column of silica revealed that the silica retained the undesirable imidazoles, such as 4-methyl imidazole. A mixture of 90/10 hexane/ethyl acetate as eluting solvent provided the desirable pyrazines, but it also provided a desirable separation of pyrazines as a function of total alkyl substituent content. Distillation of the aqueous reaction mixture was also used to isolate the pyrazines, leaving the undesirable imidazoles in the undistilled portion of the reaction. Additional chromatographic methods were used to isolate pyrazines from the aqueous distillate including a column packed with C18-bonded silica.