中文摘要：

分别以丙氨酸和2-氨基丁酸为起始原料,经Dakin-West和Robinson-Gabriel两步反应合成2,4,5-三甲基噁唑和4-乙基-2,5-二甲基噁唑两种食用香料。考察催化剂、原料物质的量比、反应温度、反应时间、环化缩合剂种类等因素的影响,确定2,4,5-三甲基噁唑的较佳合成工艺：第一步Dakin-West反应,丙氨酸与乙酸酐的物质的量之比1：11,二甲基氨基吡啶和无水乙酸钠作催化剂（二甲基氨基吡啶用量为丙氨酸物质的量的10%、无水乙酸钠用量为丙氨酸物质的量的2.5倍）,130℃反应5h,得产物Ⅰ（α-乙酰氨基酮）;第二步Robinson-Gabriel反应,以多聚磷酸为环化脱水剂,产物Ⅰ与PPA物质的量比1：4,150℃反应2h,得产物Ⅱ。产物Ⅱ减压蒸馏纯化得2,4,5-三甲基噁唑,两步反应的总产率为30.5%。按上述条件合成4-乙基-2,5-二甲基噁唑,两步反应的总产率为28.8%。2,4,5-三甲基噁唑和4-乙基-2,5-二甲基噁唑均具有烤香、清香香气特征。产品结构通过质谱、红外光谱和核磁共振进行确认。本合成工艺路线以氨基酸为原料,具有原料易得、操作简单、产品香气纯正的优点,具有较好的工业化开发前景。

英文摘要：

Flavoring compounds such as 2,4,5-trimethyloxazole and 2,5-dimethyl-4-ethyloxazole were synthesized by Dakin-West and Robinson-Gabriel reactions using alanine and 2-aminobutyric acid as the starting materials. The optimal synthesis processing of 2,4,5-trimethyloxazole was explored through evaluating the effects of catalysts, reaction temperature, reaction time and reactant mole ratio on the yield of 2,4,5-trimethyloxazole. During Dakin-West reaction for synthesizing product Ⅰ （α-acylaminoketone）, the optimal reaction conditions were alanine-acetic anhydride ratio of 1：11 （mole/mole）, dimethylamino pyridine and anhydrous sodium acetate as the catalysts, dimethylamino pyridine-alanine ratio of 1：10, anhydrous sodium acetate-alanine ratio of 2.5：1, reaction temperature of 130 ℃ and reaction time of 5 h. During Robinson-Gabriel reaction for synthesizing product Ⅱ （2,4,5-trimethyloxazole）, the optimal reaction conditions were polyphosphoric acid as cyclic dehydration agent, product Ⅰ-PPA ratio of 1：4, reaction temperature of 150 ℃ and reaction time of 2 h. The product Ⅱ（2,4,5-trimethyloxazole） was purified by vacuum distillation. The total yield of 2,4,5-trimethyloxazole was 30.5%. Similarly, according to above synthesis conditions, the total yield of 2,5-dimethyl-4-ethyloxazole was 28.8%. The 2,4,5-trimethyloxazole and 2,5-dimethyl-4-ethyloxazole had the characteristics of roasted and fragrant aroma. Both product structures were elucidated by IR, MS and 1H NMR. This synthesis processing has the advantages of easily available raw materials, simple operation and purely aromatic products, which will have widely prospects for industrial development.