Study On The Oxidation Characteristics Of Trans-anethole And Selectivity Of Anisaldehyde

Traps-anethole is the main component of star anise oil.The study on the oxidation characteristics of traps-anethole had important theoretical and practical value for the production,storage and deep processing of star anise oil and trans-anethole.In this paper,oxidation characteristics of trans-anethole with oxygen and selectivity of anisaldehyde were investigated.The main research contents and results were as follows:(1)The temperature and pressure of trans-anethole oxidation with oxygen was determined by self-designed mini closed pressure vessel device(MCPVT).The process and oxidation characteristics of the oxidation reaction were reasearched.In nitrogen,pressure in the vessel was stable,thermal decomposition of trans-anethole didn't occur.But in oxygen,trans-anethole absorbed oxygen.Oxygen was absorbed slowly in the range of 0.15 hour and 0.9 hour,then trans-anethole oxidation reaction became rapid(0.9?3.0h),finally,oxidation process went to slow(3.0?5.5h)in 60? for 5.5h.With the increase of reaction temperature,the initial reaction time decreased(1.0h(55?)>0.5h(75?)>0.25h(95?)),but the consumption of oxygen increased(1.23×10-3mol(55?)<4.08×10-3mol(75?)<6.09×10-3mol(95?)).(2)Peroxide was measured by iodimetry and thin-layer chromatography(TLC).The results showed that:In atmosphere,the optimal conditions for the pure traps-anethole with oxygen generated peroxides(peroxide concentration = 85.07mmol/kg)were:T=95?,t=4h.There were at least three kinds of peroxides.Under high pressure,peroxide concentration increased sharply when temperature over 80?.At the same time,peroxide concentration was effected by the change of reaction time and n(traps-anethole)/n(O2).(3)Constituents of oxidation products were detected by gas chromatography-mass spectrometry(GC-MS).Also,the selectivity of anisaldehyde was investigated.The oxidation products were anisaldehyde(14.33%),acetaldehyde(1.44%),anethole epoxide(4.72%),anethole diol(0.77%)and P-anisil(0.12%)at n(traps-anethole)/n(O2)=1,55? for 3h.The oxidation products were anisaldehyde(25.56%),acetaldehyde(1.22%),anethole epoxide(0.68%),4-Methoxyphenylacetone(22.59%),anethole diol(3.39%)and P-anisil(1.25%)at n(trans-anethole)/n(O2)?1,210? for 3h.Compare with the products in low temperature,a large number of 4-Methoxyphenylacetone was generated in high temperature.So the possible oxidative pathway for traps-anethole was offered.The selectivity of anisaldehyde was higher in low temperature through calculation.Reaction time was optimized.The selectivity of anisaldehyde was 70.36%at 55 ? for 7h,which provided a new idea for the oxidation of trans-anethole to anisaldehyde.(4)MCPVT determined the pressure behavior,and then oxidation kinetics was calculated.The results showed that:The oxygen consumption kinetics was zero-order in gas phase,the equation was lnki=-3.97×103·T-1-3.09,the coefficient of correlation was 0.9964.The trans-anethole oxidation kinetics was first-order in liquid phase,lnk2=-5.04×103·T-1+8.60,R2=0.9990.With the increase of reaction temperature,macyoscopic mass transfer coefficient improved.It was benefited for oxidation reaction,because more oxygen dissolved in liquid phase.