Study On The Green Hydroxylation Of Toluene To Cresols

Cresols are important fine chemical intermediates,And other organic compounds which use it as raw materials has widely used in medicine,pesticide,spices and so on.A single cresol has more application,and it who has a good quality has always been in short supply and has a high market value.Many different ways have been researched to synthesize the cresol,but it is a research focus in the field of organic synthetic chemistry research using the toluene as the starting material to synthesize cresol,which conforms with the requirement of green chemistry.In this paper,toluene was used as starting materials,Al-TPP prepared by ourselves and porphyrin as catalyst and hydroperoxides and oxygen as oxidants to prepare cresol.In this reaction,the oxidants included hydrogen peroxide,t-butyl hydroperoxide?TBHP?and cyclohexanone peroxide?CYHPO?,which were used to produce cresol from toluene in different oxidation system.The GC was used to detect the yield and NMR was used to approve product structure in different reactions.At the same time this paper has explored to obtain a single cresol with high selectivity through the optimization of reaction conditions.Firstly,hydrogen peroxide was employed as oxidant,toluene was employed as a substrate without any solvent.It was found that acetic acid certain effect on the increase in toluene conversion,and when the dosage of acetic acid was 0.019eq?relative to toluene?,the effect was best with the conversion of toluene increased by 10%.Then,we focused on the influence of the solvent on the reaction of toluene hydroxylation,and found that the solvent had very important effect on the selectivity of cresols in the reaction.Under mild conditions,with self-made Al-TPP as catalyst and hydrogen peroxide as oxidant,the best solvent was t-butyl alcohol to generate p-cresol and acetonitrile to generate o-cresol.With t-butyl alcohol as solvent,toluene conversion could be obtained 4.7% yield under the optimal reaction condition,meanwhile the effective utilization of hydrogen peroxide was 36.8%.Under the best conditions,with the solvent replaced by acetonitrile,we could get the toluene conversion was 3.3%,the effective utilization of hydrogen peroxide was 28.9%,and the selectivity of o-cresol was more than 90%.Then,TBHP and CYHPO was used as oxidant respectively to oxidize toluene.Experiment found that the energy needed for hydroxylation of benzene ring was high,and TBHP's oxidizability was not strong enough to make the hydroxylation of benzene ring,so the conversion of toluene was too low.However,a satisfactory result was obtained with CYHPO as oxidant,the effective utilization of CYHPO was 34.4%.We found that solvent had a great influence on the reaction.When the solvent changed,the conversion of toluene was changed,and the product was changed.Acetonitrile was the best solvent to produce o-cresol.We also found the quantity of oxidant had an impact on the conversion.The more the oxidant,the higher the conversion of toluene,but the lower the effective utilization of CYHPO.Reaction temperature on the reaction was crucial.The reaction almost did not occur at low temperature.When the temperature was 100?,the reaction was good.Finally,oxygen was empioyed as oxidant,TiO₂ loaded TCPPFeCl was empioyed as catalyst in the reaction of photocatalytic oxidation of toluene.We got o-cresol and benzaldehyde,but the yield was too low,only 440 ppm of o-cresol.When the temperature was too low,there were no cresol in the reaction of photocatalytic oxidation of toluene with TCPPMnCl as catalyst and oxygen as oxidant.When the temperature was 35?,about 0.5% of toluene was converted to cresols.