Formation of flavor compounds by the reactions of carbonyls and ammonium sulfide under mild conditions

Model systems composed of carbonyls including alpha-hydroxyketones (3-hydroxy-2-butanone, 1-hydroxy-2-propanone and 1-hydroxy-2-butanone) and alpha-dicarbonyls (2,3-butanedione and 2,3-pentanedione) and ammonium sulfide, were set up to study the formation of heterocyclic flavor compounds under mild conditions.; In the model reaction of 3-hydroxy-2-butanone and ammonium sulfide, four interesting intermediate compounds, namely, 2-(1-hydroxyethyl)-2,4,5-trimethyl-3oxazoline, 2-(1-mercaptoethyl)-2,4,5-trimethyl-3-oxazoline, 2-(1-hydroxyethyl)-2,4,5 trimethyl-3-thiazoline, 2-(1-mercaptoethyl)-2,4,5-trimethyl-3-thiazoline have been identified by GC/MS in addition to other heterocyclic flavor compounds including 2,3,5,6-tetramethylpyrazine, 2,4,5-trimethyloxazole, 2,4,5-trimethylthiazole and 2,4,5-trimethylimidazole. Studies under six different temperatures (25, 50, 75, 100, 125 and 150°C) showed that at the temperature lower than 75°C, 2-(1-hydroxyethyl)-2,4,5-trimethyl-3-oxazoline was the most dominant product, whereas 2,3,5,6-tetramethylpyrazine was the major product at or higher than 75°C.; Other alpha-hydroxyketones including 1-hydroxy-2-propanone and 1-hydroxy-2-butanone were also studied in model reactions. Only two intermediate compounds from each reaction were identified by GC/MS. They were 2-(1-hydroxymethyl)-2,4-dimethyl-3-oxazoline and 2-(1-hydroxymethyl)-2,4-dimethyl-3-thiazoline from 1-hydroxy-2-propanone reaction and 2-(1-hydroxymethyl)-2,4-diethyl-3-oxazoline and hydroxymethyl)-2;4-diethyl-3-thiazoline from 1-hydroxy-2-butanone reaction.; In the model reaction of 2,3-butanedione and ammonium sulfide, a pair of interesting intermediate isomers, 5-hydroxy-2,4,5-trimethyl-3-thiazolines, were tentatively identified by GUMS. Other interesting compounds including 3-hydroxy-2-butanone, 3-mercapto-2-butanone, acetamide, thioacetamide, 2,4,5-trimethyloxazole, 2,4,5-trimethylthiazole, 2,3,5,6-tetramethylpyrazine and 2,4,5-dimethylimidazole were identified.; Another alpha-dicarbonyl, 2,3-pentanedione was also used in the study. Four pairs of oxazoles and thiazoles, namely, 4-ethyl-2,5-dimethyloxazole and 5-ethyl-2,4-dimethyloxazole, 2,4-diethyl-5-methyloxazole and 2,5-diethyl-4-methyloxazole, 4-ethyl-2,5-dimethylthiazole and 5-ethyl-2,4-dimethylthiazole, and 2,4-diethyl-5-methylthiazole and 2,5-diethyl-4-methylthiazole were tentatively identified by GC/MS. Other volatile compounds, including acetamide and thioacetamide, propanamide and thiopropanamide, 3-mercapto-2-pentanone and 2-mercapto-3-pentanone, 2,5-diethyl-3,6-dimethylpyrazine and 2,6-diethyl-3,5-dimethylpyrazine, and 4-ethyl-2.5-dime thylimidazole and/or 5-ethyl-2,4-dimethylimidazole and 2,4-diethyl-5-methylimidazole and/or 2,5-diethyl-4-methlylimidazole were also tentatively identified in this system.