Study On The Activation Of C-H Bonds Of Alkanes Catalyzed By N-Hydroxyphthalimide

With the rapid development of human society,the demand for fine chemical products is increasing.In order to make the production process more environment friendly,it is particularly urgent to develop a method for efficiently activating alkane C-H bonds,and which is full of great challenges.Since the metal elements has a variable valence state,it is easy to activate molecular oxygen to functionalize the inert alkane C-H bond to alkane oxygenate.Therefore,Metal-based catalysts are widely used for the activation of C-H bonds.However,the dissolution of the metal catalyst during the reaction results in the retention of transition metal ions in the product,which does not meet the development concepts of green chemistry.Research and development of metal-free catalysts for the activation of C-H bonds have become a hot topic in current research.This paper selects N-hydroxyphthalimide as a catalyst to study the metal-free catalytic system from alkane oxidation to alkane oxygenate.The main research work is as follows:(1)A route was developed for one-step aerobic oxidation of cyclohexane to food grade and pharmaceutical grade adipic acid with N-hydroxyphthalimide(NHPI)without any promoter and a metal promoter.The conversion of cyclohexane reached 27.4%,and the selectivity of adipic acid(AA)was as high as 79%.A significant beneficial solvent effect for synergistic reaction is observed because varying polarity and hydrogen-bonding strength can improve catalytic activity and AA selectivity.Cyclic voltammetry measurements and UV-vis spectra of NHPI catalyst are examined in various solvent environments to understand the active role of solvent in influencing the catalytic-site structure(>NOH)of the molecule.(2)The possible mechanism of solvent in the process of NHPI-catalyzed C-H bond activation of alkane was investigated by computational chemistry(DFT).Specifically,the material structure,dissociation energy,reaction intermediates and reaction energy barriers of the reactants and intermediates are calculated by DFT.A PCM continuous model was constructed to predict the reaction energy barrier of the rate control step and to simulate the solvent effect.(3)The N-hydroxyphthalimide was used as a catalyst to activate the C-H bond of other alkanes,and the possible mechanism of NHPI activation of alkanes was inferred.Under the optimizing conditions of 0.6 g NHPI,120 °C and 6 h,the conversion of n-hexane is 42.9% and the selectivity of ketone is up to 64.2%.The results show that the activation effect of NHPI on the C-H bond of alkane is remarkable.