Electrochemical Oxidation Of P-methoxytoluene In Ionic Liquid Media

Anisaldehyde is a kind of important chemical,with widely applications in the fields of food,perfume compositions,pharmaceutical drugs,cosmetic,pharmaceutical and electrodeposite.So it is worthy to study the preparation methods of anisaldehyde.Presently,anisaldehyde was prepared mainly by mediated electrosynthesis method from p-methoxy toluene(p-MT).In the electro-oxidation process,once the methyl group is attacked,it is likely to be further oxidized to the carboxylic acid,or polymer formation,and it is difficult to stop at the aldehyde stage.In order to suppress further oxidation and polymerization,the electrolytes was studied,and anisaldehyde was synthesized by direct electro-oxidation of p-MT in ILs in this paper.Firstly,the ionic liquid was synthesized according to the other researchers,and its electrochemical properties were studied.The electrochemical oxidation behaviors of p-MT were studied in IL—1-butyl-3-methylimidazolium tetrafluoroborate(BMIMBF4)on platinum electrode by cyclic voltammetry(CV),chronoamperometry(CP),constant potential electrolysis and In-situ fourier transform infrared spectroscopy(In-situ FTIRS).The results showed that the electrochemical oxidation of p-MT in IL was irreversible.The four-electrons process was controlled by diffusion,and the diffusion coefficient D was 3.4 ×10-7 cm2·s-1.The main oxidation product was Anisaldehyde.A proper amount of water and suitable temperature were favorable for the anisaldehyde.Meanwhile,the electrochemical oxidation behaviors of p-MT were also studied in BMIMBF4 on graphite and Pb02 electrode.The results showed that the higher selectivity and yield was obtained on graphite electrodes.According to previous study,Electro-oxidation of p-MT was studied on platinum electrode by using CV and constant potential electrolysis in different ionic liquids solutions,such as BMIMHSO4,BMIMSO3CF3,BMIMOOCCH3,BMIMSO3C7H8,and EMIMBF4.The effects of the pH value on the selectivity and yield were studied under the appropriate conditions.The high acidity of BMIMHSO4 might lead to further oxidation of anisaldehyde to anisyl acid,and the selectivity was only 58%.While the oxidation of p-MT was stayed in the first step to alcohol without continuing reaction in the basic ionic liquid(BMIMOOCCH3).The total selectivity to anisaldehyde were 87%,89%,90%and 92%in BMIMSO3PhCH3,BMIMBF4,BMIMSO3CF3 and EMIMBF4 with pH about 3-4,respectively.The selectivity almost were unaffected by the recovery time of the ionic liquid.The ionic liquids were easy to recycle by simple extraction,and its recovery rate was up to 99%.It showed that the ILs had excellent electro-sability.The electrochemical oxidation of aromatic compounds containing methyl under the optimized conditions were stuied on platinum electrode explored in EMIMBF4 solution,the product were detected by GC-MS.It was possible to prepare aromatic aldehydes by the direct electro-synthes is method.In order to determine the intermediate species,collections of in-situ FTIRS of the oxidation processes were acquired.And it was further confirmed that the main products was aromatic aldehydes.