| Benzaldehyde is an important intermediate in the organic synthesis. In recentyears, with the development of green chemistry, great attention has been paid on theselective oxidation of toluene to prepare benzaldehyde, using O2 as clean and cheapoxidant. In the present work, we focused on the following aspects.(1) The selective oxidation catalyzed by Co(OAc)2/Mn(OAc)2/NaBr in theacetic acid has been studied and the reaction conditions were optimized. The optimumreaction conditions were as follows: n(Co+Mn)/n(toluene)=0.20％, n(Co)/n(Mn)=28, n(Br)/n(Co)=1.2, reaction time 30min, reaction temperature 110℃, the oxygen pressure0.25MPa. Under these conditions, 29.3％benzaldehyde was obtained with 48.1％selectivity at 40.4％conversion.(2) Oxidation of toluene catalyzed by NHPI/transition metals in the acetic acid hasbeen investigated and the reaction conditions were explored. The optimum conditionswere as follows: n(catalyst)/n(toluene)=10.5％, n(NHPI)/n(MnCl2)=5×10-2, V(acetic acid)/V(toluene)=1, oxygen flow rate 0.05 L/min, reaction temperature 100℃and reactiontime 5 h. Under these conditions, it can obtain the 40.4％conversion, the selectivity ofbenzoic acid and benzaldehyde can reach 71.3％and 12.6％respectively.(3) Oxidation of toluene catalyzed by transition metals/initiator in the ionic liquidreaction medium was studied and the optimum reaction conditions were obtained,which were as follows: n(Co(OAc)2+MnCl2)/n(toluene)=5％, n((Co(OAc)2)/n(MnCl2)=1.5, n(AIBN)/n(toluene)=5％, n(NaBr)/n(toluene)=5％, V([Hmim]·BF4)/V(acetic acid)=0.3, reaction temperature90℃and reaction time 10h. Under these conditions, 24.2％benzaldehyde could beobtained with 40.7％selectivity at 59.4％conversion. |
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