Studying in Synthesis and Catalytic Activity of the NHPI Derivatives with the Structure of Quaternary Ammonium
|Keywords||quaternary ammonium salt N-hydroxyphthalimide(NHPI) catalyticoxidation ethylbenzene|
Catalytic aerobic oxidation of hydrocarbons into their corresponding oxy-functionalizedcompounds with high activity, such as alcohols, aldehydes, ketones, acids and epoxides, is akind of familiar reaction in organic chemistry, and plays an important role in theindustrial and basic research. The success of the oxidation reaction largely depends on thedevelopment of catalysts, which can improve the oxidative capacity, the reaction rate andproduct selectivity. The stoichiometric oxidants are used in traditional method such aspotassium permanganate, potassium dichromate, which lead to the generation of a largenumber of inorganic salts and environment pollution. During the past decades, theN-hydroxyphthalimide (NHPI) caught a lot of attention in oxidation reaction between freeradicals and oxygen as a new organic catalyst. Generally, NHPI is usually supplemented bytransition metal or small organic molecules to act as a catalyst, however, the toxicity andexpensive of metals restrict the wide application. Catalytic oxidation by NHPI combinedwith small organic molecules overcome the shortcomings of the metal catalyst, whichbecome a research hotspot. The quaternary ammonium salts display well in the catalyticoxidation reaction beaucase of its small molecule weight, simple structure and synthesismethod, which are considered ideal as co-catalyst synergistic with NHPI. Aerobic oxidation ofC-H catalyzed by NHPI use the multi-component catalyst system combined with NHPI andcocatalyst normally, therefore, it is innovative to put NHPI and cocatalyst into one molecule assingle component catalyst.Eight kinds of NHPI derivatives with the double structure of quaternary ammonium saltand NHPI and six kinds of quaternary ammonium salts were designed and synthesized withhigh purity (monitored by HPLC,>98.0%). Moreover, the structures of target substances werecharacterized by IR, Elemental Analysis and1H NMR. The new compounds were appliedto the catalytic oxidation of ethylbenzene, and satisfactory results were achieved.It can be found that:(1) the NHPI derivatives and quaternary ammonium salts/NHPI canbe used in catalytic oxidation reaction of ethylbenzene, showing good performance under mildconditions;(2) ethylbenzene can be converted into acetophenone in high conversion (85.7%)and selectivity (90.2%) by the NHPI derivatives(10mol%) under0.3MPa of dioxygen in10mL acetonitrile at80°C in20h through the study of various impact factors. These new catalyistsexhibit catalytic activities and selectivities in the oxygenation of different kinds ofhydrocarbons.(3)82.2%conversion of ethylbenzene with87.8%selectivity for acetophenonecan be obtained by the catalyst of NHPI (10mol%) combined with the new quaternaryammonium salts(1mol%) under0.3MPa of dioxygen in acetonitrile at80°C in7h.It is studied that the NHPI derivatives of ester-containing as catalyst is better than thebenzyl NHPI derivatives, because the solution of the former is good with long carbon chain.Similarly, the catalytic results are also different with different tertiary amines as raw materials,and the solubility of the catalysts is increased in the derivatives synthetic ofdidecylmethylamine with longer carbon chain than those of other tertiary amines.