Oxidative Cleavage of Methyl Epoxystearate over Al-MCM-41-Assisted WO3∙nH2O for Aldehyde Products

Vegetable oils and their derivatives are of great interest because of their abundance and renewability. This paper prepares nonanal (N) and methyl 9-oxonanoate (M) from methyl epoxystearate (ME) with WO 3 ∙0.33H 2 O, WO 3 ∙H 2 O, and WO 3 ∙2H 2 O as catalysts and H 2 O 2 as the oxidant without the use of organic solvent. The reaction temperature, catalyst amount, H 2 O 2 amount, and reaction time effects on ME conversion and N/M yield are investigated. The results show that WO 3 ∙H 2 O has the best catalytic performance. The optimal reaction conditions are: reaction temperature 60 °C, reaction time 40 min, ME/H 2 O 2 /WO 3 ∙H 2 O molar ratio 1/1.2/0.4, under which the ME conversion and N/M yield reach 95% and 70%, respectively. WO 3 ∙ n H 2 O reacts with H 2 O 2 to form soluble tungsten anions, resulting in severe tungsten loss. Al-MCM-41 materials with different silicon to aluminum molar ratios are added to the reaction system as adsorbents to recover the catalyst by effective adsorption of tungsten anions. The adsorption performance improves as the Si/Al ratio decreases, however, the ME conversion and N/M yield decrease. Thus, 50 is the most suitable Si/Al ratio. The ME conversion and N/M yield can still reach 90% and 60% after four times of use. Practical applications : The nonanal has a natural fragrance and can be used in the cosmetic industry as well as in the preparation of bio-based surfactants. The methyl 9-oxonanoate can be converted into polymer monomers by hydrogenation or amination. The results show that WO 3 ∙ n H 2 O has good catalytic activity, and a satisfying yield of aldehyde products is obtained under mild reaction conditions.