Methyl methacrylate is an industrially important precursor for the synthesis of various acrylate based plastics. About 75% of the world’s methyl methacrylate consumption is in acrylic plastic production. Acrylic plastic is an optically clear thermoplastic material that is very versatile credit to its durability, impact strength, color and pattern possibilities hence has many applications. A great deal of methyl methacrylate is produced in practice through various industrial processes. The newly developed process (direct oxidative esterification of methacrolein) is accompanied with high raw material availability, less environmental impact, efficient and selective catalysts and feasible process parameters compared to the existing industrial process. The down side being presence of environmentally hazardous waste, production or use of toxic and flammable reagents among others. Therefore, it is imperative that new concepts are developed.
Recently, Umeå University scientists: Dr. Santosh Govind Khokarale and Professor Jyri-Pekka Mikkola proposed a study which, for the first time, involved the introduction of a catalyst free synthesis of methyl propionate and methyl methacrylate, occurring at room temperature through reversible CO2 capture by an organic superbase 1, 8-Diazabicyclo [5.4.0] undec-7-ene (DBU). Their research was published in the journal Green Chemistry.
In brief, the study entailed an initial switchable ionic liquid which was synthesized through interaction of equimolar mixture of DBU and methanol with molecular CO2. In the second step, the formation of methyl propionate, methyl methacrylate was archived through interaction of [DBUH][MeCO3] with equimolar amounts of propanoic or methacrylic anhydride respectively. The molecular CO2 was released in the second step along with the formation of [DBUH][propionate] or [DBUH][methacrylate] as a byproduct upon reaction during methyl propionate or methyl methacrylate synthesis, respectively. The process of reversible CO2 capture and methyl propionate or methyl methacrylate synthesis, were monitored by NMR analysis.
The authors found out that their synthetic approach was fruitfully accomplished in both DMSO as well as methanol where the progress of reaction was not influenced by the choice of the solvent system. In contrast to DMSO as a solvent, methanol facilitated an efficient separation from the reaction mixture along with methyl propionate or methyl methacrylate.
In summary, high recovery level of alcoholic solutions of both esters were achieved. The recovered methyl methacrylate with methanol was polymerized to poly- methyl methacrylate with 87% yield using free radical polymerization process. Here, methanol not only served as reagent and reaction media for CO2 capture process but also assisted in the form of solvent in methyl propionate, methyl methacrylate and poly- methyl methacrylate synthesis. Recovery of the comparatively expensive DBU was further also fruitfully achieved from [DBUH][propionate] and [DBUH][methacrylate]. by using an alkaline sodium chloride saturated aqueous solution. Hence, highly selective, catalyst free, single solvent based, and hence economically favorable synthesis of both methyl propionate and methyl methacrylate is represented. Being catalyst free, room temperature, cheaper and renewable solvent based process, this approach of acrylic plastic precursor synthesis can be explored at industrial level to tackle the drawbacks of currently ongoing industrial processes.
Santosh Govind Khokarale, Jyri-Pekka Mikkola. Efficient and catalyst free synthesis of acrylic plastic precursors: methyl propionate and methyl methacrylate synthesis through reversible CO2 capture. Green Chemistry, 2019, volume 21, pages 2138-2147.Go To Green Chemistry