Liquid-phase oxidation of toluene by air in acetic acid medium, with cobalt acetate catalyst and sodium bromide or paraldehyde as promoter, has been investigated with a view to developing a process for the production of benzaldehyde with benzoic acid as a coproduct. The effects of various process parameters such as temperature, period of reaction, presswe, and concentrations of the substrate, catalyst, and promoter on the overall conversion and yield of benzaldehyde were studied. Up to 10% conversion, the use of either sodium bromide or paraldehyde as a promoter gave more than 90% yield of benzaldehyde. However, at high conversions, the yield of benzaldehyde decreased markedly. Under suitable conditions. 40% yield of benzaldehyde was obtained at a conversion of 20% in the presence of sodium bromide.
3,4,5-Trimethoxytoluene (TMT) was synthesized, starting from p-cresol, through bromination followed by methylation to give 3,5-dibromo-4-methoxytoluene (DBMT). The methoxylation of the latter with sodium methoxide in methanol was studied under pressure and by continuous distillation of the solvent, methanol. The O-methylation reaction preceding the methoxylation was advantageous from the point of view of separation, purification, and isolation of the desired product and also in reducing the tar formation. The residue obtained was minimized to 0.6-0.7 wt % of the DBMT. The methoxylation reaction with distillative removal of methanol gave a conversion of 98% of DBMT to the mixture of methoxylated products, and the conversion to TMT was 86.5% as compared to 93% and 70.81%, respectively, when the reaction was carried out under pressure in a sealed reactor. However, the overall conversion to TMT based on p-cresol is 64.27% for the methoxylation reaction under pressure and 78.46% for the reaction by continuous removal of methanol calculated as isolated yield. The advantages of the methoxylation of the DBMT over the published literature procedures involving direct methoxylation of 3,5-dibromo-pcresol followed by methylation of the dimethoxy-p-cresol are the ease of separation, purification, and isolation by vacuum fractionation of the desired product TMT.
The selective hydrogenation of cinnamaldehyde and other unsaturated aliphatic aldehydes under a two‐phase liquid system using toluene and aqueous alkaline solution over supported palladium catalysts has been investigated with a view to obtaining the corresponding saturated aldehydes with sufficiently high selectivities. In the case of cinnamaldehyde, the effects of various process parameters on the reaction rate and selectivity with respect to the aldehyde have been investigated. The results obtained are likely to be useful for the rational design of the process for the production of industrially relevant products, such as hydrocinnamaldehyde and citronellal using cinnamaldehyde and citral as the starting materials.
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