Das Diparjun, Rajkumari Kalyani, Rokhum Lalthazuala
Department of Chemistry, National Institute of Technology, Silchar 788010, Assam, India.
Curr Org Synth. 2019;16(7):1024-1031. doi: 10.2174/1570179416666190919152424.
Sustainable production of fine chemicals both in industries and pharmaceuticals heavily depends on the application of solid-phase synthesis route coupled with microwave technologies due to their environmentally benign nature. In this report, a microwave-assisted esterification reaction using polymer-bound triphenylphosphine and 4,4'-dinitroazobenzene reagent system was investigated.
The solvents were obtained from Merck India. Polymer-bound triphenylphosphine (~3 mmol triphenylphosphine moiety/g) was acquired from Sigma-Aldrich. The progress of the reaction was observed by thin-layer chromatography. All the reactions were performed in Milestones StartSYNTH microwave. The NMR spectra were recorded on Bruker Avance III 300, 400, and 500 MHz FT NMR Spectrometers. Using azo compound and polymer-bound triphenyl phosphine as a coupling reagent, esterification of different carboxylic acids with alcohols was performed under microwave irradiation.
Esterification of benzoic acid with 1-propanol under microwave irradiation gave a high yield of 92% propyl benzoate in 60 minutes only. Isolation of the ester products was relatively simple as both the byproducts polymer-bound triphenylphosphine oxide and hydrazine could be removed by simple filtration. The rates of reactions were found to be directly proportional to the pKa of the benzoic acids.
4,4'-Dinitroazobenzene was introduced as a novel coupling reagent, in conjugation with polymer-bound triphenylphosphine, for esterification reactions under microwave irradiation. The low moisture sensitivity of the reaction system, easy separation of the byproducts, and column chromatographyfree isolation of esters help our methods with application significance, particularly from the 'Sustainable Chemistry' perspective.
由于其环境友好的特性，精细化学品在工业和制药领域的可持续生产严重依赖于固相合成路线与微波技术的结合。在本报告中，对使用聚合物负载三苯基膦和4,4'-二硝基偶氮苯试剂体系的微波辅助酯化反应进行了研究。
溶剂购自印度默克公司。聚合物负载三苯基膦（~3 mmol三苯基膦部分/克）购自西格玛奥德里奇公司。通过薄层色谱观察反应进程。所有反应均在迈尔斯通StartSYNTH微波仪器中进行。核磁共振谱在布鲁克Avance III 300、400和500 MHz傅里叶变换核磁共振光谱仪上记录。以偶氮化合物和聚合物负载三苯基膦作为偶联试剂，在微波辐射下进行不同羧酸与醇的酯化反应。
在微波辐射下，苯甲酸与1-丙醇酯化反应仅在60分钟内就得到了产率高达92%的苯甲酸丙酯。酯产物的分离相对简单，因为两种副产物聚合物负载三苯基膦氧化物和肼都可以通过简单过滤除去。发现反应速率与苯甲酸的pKa成正比。
引入4,4'-二硝基偶氮苯作为一种新型偶联试剂，与聚合物负载三苯基膦结合，用于微波辐射下的酯化反应。反应体系的低水分敏感性、副产物的易于分离以及酯的无需柱色谱分离有助于我们的方法具有应用意义，特别是从“可持续化学”的角度来看。
