Preparation Of Natural Benzaldehyde From Cinnamaldehyde Oxidized By H₂O₂

Benzaldehyde is the world’s second largest perfume that has been applied widely in food, beverage, pharmaceutical, cosmetic and other fields. With the improvement of people’s living standards, attention on food safety and quality are increasing. Natural benzaldehyde, with good market value and market prospects, is increasingly favored by more and more consumers.Based on the rich resources of Guangxi, the present dissertation used cinnamaldehyde or cinnamon oil as raw material, hydrogen peroxide as the green oxidant, sodium carbonate or sodium bicarbonate (NaHCO3 or Na2CO3) as the non-toxic, cheap and easy to get high performance catalyst to synthesize natural benzaldehyde in non-toxic alcohol solvent under mild conditions. The process accords with the requirements of green chemistry which strongly advocated currently.1) Benzaldehyde is prepared by oxidation of cimmaldehyde by hydrogen peroxide in low-boiling alcohol (ethanol) solution under relatively mild conditions. A small amount of sodium bicarbonate can efficiently catalyze the reaction, which demonstrated high catalytic performance and selectivity of up to 74% for benzaldehyde.2) Propylene glycol has also been employed as the reaction solvent. With sodium bicarbonate catalyzed oxidation of cinnamaldehyde by H2O2 under mild conditions, the selectivity of benzaldehyde can reach up to 90%. Low reaction temperature can avoid decomposition of H2O2 at higher temperatures which leads to the risk of explosion by H2O2. The low temperature is also beneficial for maintaining natural degree of benzaldehyde.3) The oxidation reaction mechanism has been investigated from thermodynamic and kinetic results as well as instrumental characterization e.g. GC, LC, GC/MS. The plausible reaction mechanism is:NaHCO3 reacts with H2O2 to form HCO4- first. Then, HCO4- attacks the C=C bond of cinnamaldehyde nucleophilically to form cinnamaldehyde epoxide (3-phenyl-2,3-epoxy propanal). The epoxy was then oxidized continuously to produce benzaldehyde and glyoxalic acid.