Piotr LATOS1, Anna CHROBOK1
1Silesian University of Technology, Gliwice, POLAND, Gliwice, Poland
Deep eutectic solvents (DESs) are an emerging class of materials promising for applications as inexpensive “designer” solvents with tunable physicochemical properties. A detailed review of the current literature reveals the lack of predictive understanding of the microscopic mechanisms that govern the structure−property relationships in this class of solvents. Metal oxide are used as substrates for the synthesis of various task-specific materials. Their phase, morphology, particle size and purity, often, are of significant importance for applications, such as catalysis, photovoltaics, and batteries. It is essential to obtain metal oxide particles with defined specific characteristics, which give control over optical and electronic properties. On the other hand the use of solid metal oxides in catalysis causes isolation problems. Metal oxide particles can be suspended in the reaction mixture and a series of unit operations are necessary to separate the catalyst. To overcome this issue metal oxide can be dissolved in DES.
In this work, dissolution experiments were performed in the popular DES choline chloride-urea (molar ratio 1:2) by suspending the ZnO (0,8 wt%) at temperature below 100 °C in order to avoid the decomposition of urea. The driving force of dissolution is the coordination of urea to the metal atom. The amount of zinc oxide was determined by ICP-OES and XRF analysis.
A hybrid system based on DES and ZnO was tested as catalyst in transesterification reaction of dimethyl terephthalate with butanol resulted in the synthesis of alternative non-phthalate plasticizer. Butyl terephthalate was obtained in high yield (92%) and full conversion dimethyl terephtalate, under mild reaction conditions at 100–120 °C and using a 10:1 molar ratio of alcohol to ester and 3.2 wt% of catalyst.
During the reaction course, the formation of the second ester phase was observed what facilitates the reaction progress, shifting the equilibrium towards the ester formation. Lower phase was consisted with catalyst and methanol and the upper phase contained product and unreacted butanol.
Another important parameter for industrial application is the stability of the catalyst and the possibility of its further reuse in following processes. To demonstrate the stability of a hybrid system based on DES and ZnO the post reaction two-phase mixture was separated and the lower phase (containing mainly catalyst) was dried using rotary evaporator and used for the next cycle. The studied catalyst was stable in ten consecutive cycles and could be used without any loss of activity.
In summary, a new catalyst for the synthesis of butyl terephthalate in the presence of hybrid system based on DES and ZnO has been developed. This work contributes to the development of sustainable and environmentally-friendly processes for the production of green plasticizers.
References:
[1] A.P. Abbott, G. Capper, D.L. Davies, K.J. McKenzie, S.U. Obi, J. Chem. Eng. Data, 2006, 51, 1280–1282.
[2] A.P. Abbott, G. Capper, D.L. Davies, R.K. Rasheed, P. Shikotra, Inorg. Chem., 2005, 44, 6497–6499.
This work was financed by the National Science Centre, Poland (grant no. UMO-2020/39/B/ST8/00693).