Studies On The NHPI-Catalyzed Oxidation Of Aromatics With Hydrogen Peroxide

The selective catalytic oxidation of aromatic hydrocarbons, which can be mainly divided into two significant oxidation of side-chain and aromatic ring, has always attracted extensive attention all the time. In this thesis, two methyl-substituted aromatic hydrocarbons: pseudocumene?TMB? and 2-methylnaphthalene?2-MN? was choosed as the substrates, N-hydroxyphthalimide?NHPI? as the catalyst, H₂O₂ as the oxidant to achieve the direct catalytic oxidation of aromatic ring in a liquid acidic solvent to research the synthetic methodology of the corresponding quinones. The contents of this thesis are presented as follows:Firstly, four aspects of introductions was mainly reviewed: 1) overviews of the selective catalytic oxidation of aromatic hydrocarbons; 2) researches on the NHPI-catalyzed oxidation of aromatic hydrocarbons; 3) studies on the direct catalytic oxidation of TMB to 2,3,5-trimethylbenzoquinone?TMBQ? with hydrogen peroxide; 4) studies on the direct catalytic oxidation of 2-MN to 2-methyl-1,4-naphthoquinone?2-MNQ? with hydrogen peroxide.Secondly, the experiments of liquid phase catalytic oxidation of TMB to TMBQ has been conducted, with NHPI as catalyst, H₂O₂ as oxidant, Ac OH as solvent. A gas chromatography method with internal standard was proposed for the quantitative analysis of TMB and TMBQ, and two standard working curve was established,whereby calculate the conversion rates, yields and selectivities. The effects of NHPI?s amounts, transition metal ions, acids, temperature, oxidant?s amounts, and reaction time have been studied. Integrated optimization of all conditions, the optimum conditions proved to be: NHPI 20mol%, n?TMB?:n?Ac OH? = 1:30,n?TMB?:n?H₂O₂? = 1:5, 80⁹0?, 4⁵h.The studies also show that the presence of the transition metal ions could change the oxidative reaction positions on TMB, which greatly interfere the oxidative reaction to quinone. When transition metal-free, the main oxidation product is TMBQ, while in the presence of transition metal ion, the reaction position is transferred from the benzene ring to the side-chain methyl groups. Since there are three methyl groups of TMB, and their chemical environments are extremely similar to each other, which resulted to a bad regioselectivity for the formation of multiple side-chain oxidative products.Finally, the experiments of liquid phase catalytic oxidation of 2-MN to 2-MNQand 6-MNQ has been investigated, with NHPI as catalyst, H₂O₂ as oxidant,Ac OH/ethyl acetate?EA? as a mixed solvent. A gas chromatography method with internal standard was also proposed for the quantitative analysis of 2-MN and2-MNQ, and two standard working curve was established. The investigations showed that, the addition of EA could increase the selectivity of the naphthoquinones, when EA together with Ac OH as a solvent, the concentration of the substrate 2-MN and the oxidant could be controlled by adjusting the molar ratio of Ac OH and EA, thereby reducing the possibility of the deep oxidation of naphthoquinones, then improving the selectivities of naphthoquinones. The orthogonal experimental method was introduced to the optimum of reaction conditions, and the order of selected factors which could influence the oxidative reaction was obtained, that was proved to be:reaction temperature > reaction time > EA?s amounts > NHPI?s amounts > Ac OH?s amounts. Single factor experiments was investigated to research the effects of various factors on the yields of naphthoquinones, then there was obtained the best oxidative experimental conditions: NHPI 30mol%, m?Ac OH?:m?2-MN? = 20:1,n?EA?:n?2-MN? = 15:1, n?2-MN?:n?H₂O₂? = 10:1, 80?, 5h.