| Cycloalkanes are a series of important petrochemical products,and can be converted to various chemical intermediates through catalytic oxidation,such as cycloalkanols,cycloalkanones,cycloalkyl hydroperoxides and aliphatic dicarboxylic acids,which have been applied widely in the chemical industry.Among these oxidation products,cycloalkanols and cycloalkanones are irreplaceable raw materials in the preparation of polyamide polymers and other fine chemical products,and aliphatic dicarboxylic acids are the direct materials for the syntheses of polyamide polymers.In the current industrial processes,the most typical oxidation of cycloalkanes is the catalytic oxidation of cyclohexane,which was conducted at 150oC?170oC employing Co???salts or Mn???salts as catalysts and O2 as the oxidant.The main problems in the current industrial oxidation of cyclohexane are the high reaction temperature,low substrate conversion,poor selectivity to target products,and unclear reaction mechanism,especially for the formation of aliphatic dicarboxylic acids which could not be inhibited effectively and resulted in the unsatisfying selectivity to KA oil.The origins of above problems are as followings.?1?High reaction temperature.?2?The oxidation of cycloalkanes with O2 is a relatively disordered free radical diffusion process with poor controllability.?3?The oxidation intermediates,cycloalkyl hydroperoxides,are transformed to cycloalkanols and cycloalkanones through thermal decomposition,which increases the uncontrollability of the reaction and reduces the selectivity to KA oil.In order to overcome these problems,the model compounds of cytochrome P-450,metalloporphyrins with confined domain were employed as catalysts in this dissertation to decrease the disordered diffusion of free radicals meanwhile Zn???salts were introduced to enhance the transformation of cycloalkyl hydroperoxides at the reaction temperature not higher than 120oC with the purpose to improve the selectivity of cycloalkanols and cycloalkanones.Due to the confined catalytic domain and the relay catalysis between bimetal centers,not only the selectivity to cycloalkanols and cycloalkanones were improved,but also the conversion of cycloalkanes were enhanced obviously.The selectivity toward the target products and the conversion of substrates were improved simultaneously.The main contents of this dissertation are as followings.5,10,15,20-Tetraphenylporphyrin?TPP?,5,10,15,20-tetrakis?1-naphthyl?porphyr-in?T1-Na P?,5,10,15,20-tetrakis?2-naphthyl?porphyrin?T2-Na P?,5,10,15,20-tetrakis?9-phenanthryl?porphyrin?T9-Ph P?,5,10,15,20-tetrakis?1-pyrenyl?porphyrin?T1-Py P?and their bromides were synthesized through Adler-Longo method employing benzaldehyde,1-naphthalene aldehyde,2-naphthalene aldehyde,9-phenanthrene aldehyde,1-Pyrene aldehyde and pyrrole as raw materials.The corresponding porphyrin cobalts of above ligands were obtained in the isolated yields of 10.8%,9.50%,10.0%,6.50%,2.90%,5.90%,4.90%,5.30%,2.80%and 1.10%based on the aromatic aldehydes.All the porphyrins and metalloporphyrins above were characterized and confirmed through 1H NMR,13C NMR and ESI-MS.The obtained metalloporphyrins were applied in the oxidation of cycloalkanes as catalysts with O2 as oxidant,and the effects of the confined catalytic domain,the amount of catalyst and O2 pressure on the catalytic oxidation of cycloalkanes and the apparent kinetics of these oxidation processes were studied systematically.It was demonstrated that with the confined catalytic domain increasing from TPPCo???to T1-Py PCo???,the ratio between alcohols and ketones increased dramatically.For cyclohexane as substrate,when the confined catalytic domain increased from TPPCo???to T1-Py PCo???,the ratio between cyclohexanol and cyclohexanone in the oxidation products increased from 0.76 to 0.91,and the conversion of cyclohexane remained at about 4.36%with the total selectivity toward cyclohexanol,cyclohexanone and cyclohexyl hydroperoxide?KA oil?of about 84.5%.And when the confined catalytic domain increased from TPPBr Co???to T1-Py PBr Co???,not only the ratio between cyclohexanol and cyclohexanone increased from 0.80 to 1.27,but also the conversion of cyclohexane reached up to about 5.00%with the total selectivity of about 86.4%toward KA oil.Due to the existence of confined catalytic domain,the catalytic oxidation of cycloalkanes were enhanced significantly,which also is a strong evidence for the rationality of the original design in this study.Zn???salts were employed to form bimetallic catalysis systems with the porphyrin cobalts???mentioned above in the purpose to enhance the catalytic transformation of the oxidation intermediates cycloalkyl hydroperoxides in the catalytic oxidation of cycloalkanes,and the effect of amount of Zn???and the mechanism in the relay catalysis of bimetal centers were studied systematically.It was demonstrated that due to the employment of Zn???salts,not only the selectivity toward KA oil was increased obviously,but also the conversion of cyclohexane was increased dramatically.For T2-Na PBr Co???as catalyst,the selectivity toward KA oil was increased from 87.3%to 95.8%with the conversion of cyclohexane increasing from 5.29%to 6.21%.Thus,the optimized catalytic system was obtained in this study:the reaction mixture was stirred at 120oC and 1.0 MPa O2 for 8.0 h with T2-Na PBr Co???(1.2×10-3%,mol/mol)and Zn?OAc?2?2.0 mg/mmol?as catalysts in which the conversions of cyclohexane,cycloheptane,cyclooctane and cyclododecane were 6.21%,20.6%,26.1%and 30.5%respectively with the total selectivity of cycloalkanols,cycloalkanones and cycloalkyl hydroperoxides being 95.8%,98.0%,98.5%and 100.0%respectively.MOFs?PCN-224-p,PCN-224-m,PCN-224-d,PCN-222-p,PCN-222-m and PCN-222-d?with confined domain were synthesized through solvothermal method with 5,10,15,20-tetrakis?4-carboxyphenyl?porphyrin cobalt????T?4-COOH?PPCo?,5,10,15,20-tetrakis?3-carboxyphenyl?porphyrin cobalt????T?3-COOH?PPCo?and 5,10,15,20-tetrakis?4-?4-carboxyphenyl?phenyl?porphyrin cobalt????T?4-COOH?PPCo?as metalloporphyrins units.The obtained materials were characterized and confirmed through FT-IR,XRD,SEM,TEM,EDS,XPS and TGA.The bimetallic catalysis systems were obtained based on above MOFs and Zn?OAc?2,and applied in the catalytic oxidation of cycloalkanes with O2 in which the confined domain in MOFs were employed to decrease the disordered diffusion of free radicals and Zn???salts were introduced to enhance the catalytic transformation of cycloalkyl hydroperoxides with the purpose to improve the selectivity of target products.The optimized catalytic system in this study was obtained as following:the reaction mixture was stirred at 120oC and 1.0 MPa O2 for 8.0 h with PCN-222-d?0.07mg/mmol?and Zn?OAc?2?2.0 mg/mmol?as catalysts in which the conversions of cyclohexane,cycloheptane,cyclooctane and cyclododecane were 5.51%,16.6%,20.8%and 22.4%respectively with the total selectivity of cycloalkanols,cycloalkanones and cycloalkyl hydroperoxides being 94.4%,96.8%,98.8%and100.0%respectively.The satisfying selectivity toward cycloalkanols and cycloalkanones,and the better substrate conversions in this study were mainly attributed the effective inhibition of the disordered free radical diffusion in the confined catalytic environment and the catalytic transformation of cycloalkyl hydroperoxides by Zn???.Compared with the current documents on the catalytic oxidation of cycloalkanes with O2,the main advantages of this study are:?1?Low reaction temperature;?2?Solvent-free and additive-free;?3?High total selectivity toward cycloalkanols and cycloalkanones;?4?The increase in conversion did not consume the total selectivity toward cycloalkanols and cycloalkanones,and the conversion and selectivity toward target products were improved simultaneously. |
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