Centre in Green Chemistry and Catalysis (CGCC)

The solvents are compounds that play an auxiliary role in the preparation of chemicals. In chemical production processes, solvents are responsible for the majority of waste generated. Their removal and elimination requires supplemental energy and additional waste will be released eventually in the environment. Consequently, evaluation of alternatives to conventional solvents is one of the mandates of the CCVC. Ideally, a green solvent should be non-toxic, readily available and inexpensive but, above all, it should have additional attributes such as providing a milieu where chemical reactivity is increased, improving chromatographic separations or facilitating catalyst recycling. In this context, researchers are evaluating the use of green solvents such as water, supercritical CO2 and ionic liquids in reactions relevant to synthesis, while others are studying the reactions obtained during the C-H bond activation using supercritical CO2 as a solvent.
New applications of supercritical fluid chromatography (SFC) are also being considered in the context of enantiomer separation. This work will provide alternative methods with low environmental impact to convert raw materials into useful products or synthetic intermediates.

Conventionally, attaining the highest yield and product selectivity are the governing factors of chemical synthesis. Little consideration is given to the use of multiple reagents in stoichiometric quantities or of chiral auxiliaries, which often are not incorporated into the target molecule and can result in significant side products. It is now recognized that it is highly desirable that all atoms of the starting materials and of the reagents be included in the product. This concept, referred to as "atom-economy," is a key principle in the "Twelve Principles of Green Chemistry" and has altered the way many chemists design and plan their syntheses. Catalysis plays a central role in attaining high atom-economy for reactions, since, in a well-conceived reaction, minute amounts of catalysis can convert a starting material into a product with significantly increased structural complexity.

Heterogeneous catalysts have significant Green advantages over their homogeneous counterparts, given the easier removal of the metal catalyst from the reaction mixture. This also helps to ensure that there is no contamination of the product by the metal. CGCC researchers are exploring two types of heterogeneous systems: homogeneous catalysts immobilized on solid supports and high-surface area nanoparticle catalysts. Each can provide a platform to further enhance both the Green and economic profile of a number of the homogeneous catalytic reactions developed above and induce a large number of collaborations. Both approaches take advantage of the expertise in surface chemistry that exists in CGCC.

Not only will novel heterogeneous catalyst systems be developed, but the mechanistic aspects of the processes will also be studied. CGCC researchers have already had significant success in using a state-of-the-art surface science/mechanistic approach to understanding key catalytic reactions. For example, scanning tunneling microscopy (STM) was used to achieve sub-molecular resolution imaging of asymmetric intermolecular interactions on a catalyst surface. This type of study yields profound new insights into the mechanism of asymmetric synthesis on surfaces.

Heterogeneous catalysis is often believed to be too difficult to study in a fundamental way. However, in the present global context of pressing concerns related to a sustainable development, the study of heterogeneous catalysis is undergoing an explosive renaissance. CGCC is very well placed to take part in this worldwide effort in catalysis and to lead to breakthroughs in a number of Green chemistry catalytic processes.

As an alternative to synthetic catalysts, Nature has created extraordinarily effective catalysts for biological and chemical transformations, which, in almost all cases, operate in the Green solvent, water. A major thrust of Green chemistry involves the use of biological catalysts or mimics of biocatalysts in chemical syntheses and processes. The desirable features of enzyme-catalyzed reactions for chemical synthesis include high substrate specificity, high regio-, stereo- and enantioselectivities, and mild reaction conditions in aqueous media. Some groups will collaborate by using enzymes to catalyze the regio- and stereoselective hydroxylations of unactivated C-H bonds in water. These are key reactions in the synthesis of many fine chemicals and pharmaceuticals, but are usually difficult to reform. The mechanistic aspect of the enzymatic reactions will also be pursued as part of CGCC's program. For instance, the study of the directed evolution of enzymes in order to gain a better understanding of enzymatic catalysis, to create novel biosynthetic activities, and to contribute to the improvement of the strategies will be undertaken.

Traditional synthetic methods use multiple steps to create the levels of molecular complexity desired in products. From a Green perspective, these methods have significant limitations: they rely on reagents that are not fully incorporated into products, require repeated solvent use, suffer from diminishing yield with increase in number of reaction steps, and require repeats of the sequence to generate variants of the products to tune properties. An intriguing alternative approach would be to prepare products directly from readily available resources. CGCC researchers are developing new non-catalytic Green transformations that comply as much as possible with the atom-economy principle. These efforts provide a set of transformations that are easy to perform (one step), create minimal waste, and offer access to molecular diversity for the synthesis of new polymers, drug scaffolds, and new materials, all in a Green manner.

The creation of alternative methods and synthetic platforms to convert feedstock into useful products and/or synthetic building blocks via Green methods must also undergo careful scrutiny. While these may be effective processes relative to traditional synthetic methods, whether they are indeed environmentally benign must be carefully examined. Ultimately, in each of these Green chemistry studies, it is critical that we determine if the processes and the new chemicals synthesized are truly Green. The pollution potential of both the native form and degradation products/eco-metabolites of Green replacement molecules or processes are under investigation.

A notable feature of CGCC is the inclusion of management and policy experts as members. These researchers study how the processes by which public concerns are (or are not) generated, how controversies are resolved, and how policy changes result when policy-makers and other stakeholders are faced with new environmental and health risks. The evolution of technology is also being considered, especially how the chemical and pharmaceutical industries adopt new synthetic methods or alternative products. The centre, while impacting on all steps leading to a chemistry more respectful of the environment, allows researchers to become involved in innovation beyond the strictly scientific aspects.