A methodology for the design and selection of green solvents for organic reactions
Sustainable process-product development & green chemistry
Selection & Use of Organic Solvents (T1-7)
Keywords: green chemistry, organic reactions, solvent design, solvent selection
A methodology for the design and selection of green solvents for organic reactions
M. Folić, R. Gani
CAPEC, Technical University of Denmark, Soltofts Plads, Bygn. 227, 2800 Lyngby, Denmark
C. Jiménez-González and D. J. C. Constable
2GSK, CEHS, Five Moore Drive, PO Box 13398, CS-1152, Research Triangle Park, NC, 27709 , USA
Corresponding author: R. Gani (rag@kt.dtu.dk)
Solvents are widely used in fine chemicals and pharmaceutical industry where they serve to facilitate reaction-based processes by, for example, dissolving reactants and/or bringing them together in suitable concentrations. Reichardt (1988) reports that the reaction between trimethylamine and trimethylsulfonium ion is 119 times faster in nitromethane than in water which is a dramatic influence pointing out the need for knowledge-based choice of solvents for reactions. However, the excessive consumption of solvents leads to disposal of millions of tons of solvents every year. Given this situation, we aim to design and select solvents that, when used as inert media for liquid phase organic reactions, will lead to an increase in reaction rate and simultaneously minimize the environmental impact. Provided the details of an organic reacting system (reactants, products and reaction conditions) are known, our objective is to find solvents that can promote the reaction and rank them according to an established scoring/evaluation system.
The basis for this work is the method developed by Gani et al. (2005) that incorporates industrial practice knowledge in the currently available computer-aided tools for solvent design and property estimation. Essentially, it is a multi-step algorithm, with the solvent selection process occurring in two stages. In the first stage, a list of well-known solvents, if available, is used to identify the solvents that match a sub-set of specified requirements (constraints) and based on this a score is allocated to each solvent. Simultaneously, a computer-aided molecular design (CAMD) technique can also be used to generate a list of solvent candidates, which are then ranked with respect to the corresponding scores. The needed reaction data is provided by the user while the solvents data can either be retrieved from a list of 75 most common solvents or using the hybrid computer aided molecular design (CAMD) technique of Harper and Gani (2000). In the latter case, chemically stable molecules that satisfy the solvent-property requirements are generated and tested. In the second stage, the candidate solvents are further evaluated through more detailed property calculations or by checking the properties databases.
The original method has been extended with application to several case studied of increased complexity involving multi-step organic synthesis reactions. It has also been combined with a CAMD-based methodology for the selection of reaction media developed by Folić et al. (2006) in order to quantify the increase in reaction rates. The methodology of Folić et al. (2006) consists of a simple reaction model based on empirical parameters embedded within the CAMD framework. The model uses as input kinetic data for a small number of solvents for a specific reaction and can then be extrapolated to predict values of reaction rate constants for nearly 8000 molecular structures based solely on their structural parameters. Given the large search space, the optimal potential candidates are easily found.
Results obtained agree well with the solvents commonly used by the user but also give innovative ideas for solvents yet to be tried out. The method allows easy integration process-wide allowing the product recovery operations to potentially be taken into account.
References:
Folić, M., Adjiman, C. S. and Pistikopoulos, E. N., Proceedings of ESCAPE-16, pp. 677-673, 2006.
Gani, R., Jiménez-González, C. and Constable, D. J. C., Computers and Chemical Engineering, Vol. 29, pp. 1661-1676, 2005.
Harper, P. M, and R. Gani, Computers and Chemical Engineering, Vol. 24, pp.677-683, 2000.
Reichardt, C., Solvents and Solvent Effects in Organic Chemistry, VCM Publishers, UK (1988).
Presented Tuesday 18, 10:05 to 10:25, in session Selection & Use of Organic Solvents (T1-7).
