Enzyme-Catalyzed Synthesis, Odor Characteristics and Thermal Analysis of New Pyridine Esters

A new method for the efficient conversion of pyridine methanols and ethyl carboxylates to pyridine esters in air catalyzed by Novozym 435 (N435) was reported. The enzyme catalyzed transesterification reaction was performed under the optimum conditions: N435 (60 mg) as a biocatalyst, acetonitrile (2.5 mL) as a solvent, the molar ratio of pyridine methanols (0.2 mmol) to ethyl carboxylats (1.0 mmol) of 1 : 5, molecular sieve 3 A of 1.00 g, reaction temperature of 50 degrees C, the revolution speed of 150 rpm and reaction time of 36 h. The enzyme still retained a yield of 80 % after repeated use for 10 times. Under optimal conditions, eighteen pyridine esters were synthesized in this paper, containing fifteen esters as novel compounds. The synthesized pyridine esters were analyzed by gas chromatography-mass spectrometry-olfactory (GC-MS-O), of which four pyridyl esters including compounds 3 a, 3 c, 3 g and 3 r possessed strong aromas which were based on peak area in GC-MS. Thermogravimetric analysis (TG) was performed on these four flavor compounds. According to the results of TG analysis, they had good thermal stability at the certain temperature.