You Fei, He Xing, Gao Song, Li Hong-Ru, He Liang-Nian
State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China.
College of Pharmacy, Nankai University, Tianjin 300353, China.
Beilstein J Org Chem. 2020 Mar 10;16:351-361. doi: 10.3762/bjoc.16.34. eCollection 2020.
Raw material from biomass and green preparation processes are the two key features for the development of green products. As a bio-lubricant in metalworking fluids, estolides of ricinoleic acid are considered as the promising substitute to mineral oil with a favorable viscosity and viscosity index. Thus, an efficient and sustainable synthesis protocol is urgently needed to make the product really green. In this work, an environment-friendly Brønsted acidic ionic liquid (IL) 1-butanesulfonic acid diazabicyclo[5.4.0]undec-7-ene dihydrogen phosphate ([HSO-BDBU]HPO) was developed as the efficient catalyst for the production of oligomeric ricinoleic acid from ricinoleic acid under solvent-free conditions. The reaction parameters containing reaction temperature, vacuum degree, amount of catalyst and reaction time were optimized and it was found that the reaction under the conditions of 190 °C and 50 kPa with 15 wt % of the [HSO-BDBU]HPO related to ricinoleic acid can afford a qualified product with an acid value of 51 mg KOH/g (which corresponds to the oligomerization degree of 4) after 6 h. Furthermore, the acid value of the product can be adjusted by regulating the reaction time, implying this protocol can serve as a versatile method to prepare the products with different oligomerization degree and different applications. The other merit of this protocol is the facile product separation by stratification and decantation ascribed to the immiscibility of the product and catalyst at room temperature. It is also worth mentioning that the IL catalyst can be used at least for five cycles with high catalytic activity. As a result, the protocol based on the IL catalyst, i.e. [HSO-BDBU]HPO shows great potential in industrial production of oligomeric ricinoleic acid from ricinoleic acid.
生物质原料和绿色制备工艺是绿色产品发展的两个关键特征。作为金属加工液中的一种生物润滑剂，蓖麻油酸酯具有良好的粘度和粘度指数，被认为是矿物油的有前途的替代品。因此，迫切需要一种高效且可持续的合成方案，以使产品真正绿色化。在这项工作中，开发了一种环境友好的布朗斯台德酸性离子液体（IL）1-丁烷磺酸二氮杂双环[5.4.0]十一碳-7-烯磷酸二氢盐（[HSO-BDBU]HPO），作为在无溶剂条件下由蓖麻油酸生产低聚蓖麻油酸的高效催化剂。对反应温度、真空度、催化剂用量和反应时间等反应参数进行了优化，发现以190℃、50kPa的条件，使用相对于蓖麻油酸15wt%的[HSO-BDBU]HPO进行反应，6小时后可得到酸值为51mg KOH/g（对应低聚度为4）的合格产品。此外，通过调节反应时间可以调节产品的酸值，这意味着该方案可以作为一种通用方法来制备具有不同低聚度和不同应用的产品。该方案的另一个优点是由于产品和催化剂在室温下不互溶，通过分层和倾析可轻松分离产品。还值得一提的是，IL催化剂至少可以循环使用五次，且催化活性高。因此，基于IL催化剂即[HSO-BDBU]HPO的方案在由蓖麻油酸工业生产低聚蓖麻油酸方面显示出巨大潜力。
