Study Of 2,6-dichlorotoluene Oxidative Bromination And Oxidation Reactions In A Microchannel Reactor

2,6-dichlorobenzyl bromide and 2,6-dichlorobenzoic acid are important intermediates in organic synthesis,which have a wide range of applications in medicine and agriculture.The former can be synthesized by benzyl bromination of 2,6-dichlorotoluene,and latter can be prepared by oxidation of 2,6-dichlorotoluene.However,the traditional processes for preparing these two substances suffer from the disadvantages of poor economy,environment damage and potential safety hazards.It is necessary to explore new and sustainable methods and processes for the synthesis of these two compounds.Firstly,the synthesis of 2,6-dichlorobenzyl bromide from photocatalytic benzyl oxidative bromination of 2,6-dichlorotoluene was carried in a microchannel reactor with H₂O₂ as an oxidant and HBr as a bromine source.The effects of reaction temperature,molar ratios of reaction materials,residence time,light source,and concentrations of reaction materials on the reaction were investigated,from which optimal reaction conditions were obtained,which are reaction temperature of 70°C,molar ratios of H₂O₂:HBr:2,6-dichlorotoluene of 1.5:1.5:1.0,concentrations of H₂O₂,HBr and2,6-dichlorotoluene to be 7.1wt.%,16.3wt.%and 21.0wt.%,87 W blue light as light source and a residence time of 5.88 min.Under the optimal reaction conditions,the conversion of2,6-dichlorotoluene reached 98.09%with a 2,6-dichlorobenzyl bromide selectivity of93.21%,and the yield of 2,6-dichlorobenzyl bromide was 91.43%.And then,kinetics of oxidative bromination of 2,6-dichlorotoluene to 2,6-dichlorobenzyl bromide in a microchannel reactor was studied.A series of kinetic data were obtained under kinetically controlled conditions by eliminating the mass transfer effects of liquid-liquid phases,and the experimental data were fitted nonlinearly using Matlab software.The results showed that the calculated values based on the kinetic model were in good agreement with the empirical values,and the preexponential factor and activation energy were 635.3 and 24.0KJ/mol,respectively.Secondly,the oxidationof 2,6-dichlorotoluene to 2,6-dichlorobenzoic acid with molecular oxygen as an oxidant under the catalysis of Co（OAc）₂·4H₂O/Mn（OAc）₂·4H₂O/KBr was investigated in a batch reactor.The optimal reaction conditions were obtained which are 2,6-dichlorotoluene of 62.1 mmol,Co/Mn/Br dosaages of 0.52 mol%,0.31 mol%and 0.71 mol%,5.0 g of acetic acid,10μL of water and an oxygen flow rate of 25 m L/min,reaction temperature of 115°C,and reaction time of 22h.Under these conditions,the conversion of 2,6-dichlorotoluene reached up to 99.99%with a 2,6-dichlorobenzoic acid selectivity of 76.45%.Furthermore,the process was explored for the synthesis of 2,6-dichlorobenzoic acid from the oxidation of 2,6-dichlorotoluene in a microchannel reactor with molecular oxygen as an oxidant under the catalysis of Co（OAc）₂·4H₂O/Mn（OAc）₂·4H₂O/KBr.It was found that the the conversion of2,6-dichlorotoluene reached 60.08%with a 2,6-dichlorobenzoic acid selectivity of 41.32%when the reaction was conducted under the conditions of 2,6-dichlorotoluene of 32.05mmol,Co/Mn/Br dosaages of 0.52 mol%,0.31 mol%and 0.71 mol%,acetic acid of 10.0 g,water of 50μL,reaction temperature of 150°C,reaction pressure of 0.9 Mpa,and residence time of 62 min.