Catalysis helps us:
- reduce reaction time, which in turn saves energy
- selectively carry out parallel reactions, which again saves time and money required for separation of the side-products. Some side-products are harmful and dangerous. So it also keeps us safe.
- replace stoichiometric reagents with catalytic amounts of a substance, which helps us save resources and money. Some stoichiometric reagents are harmful and also create problems due to its existence. For example, aluminum chloride is a reagent used in Friedel–Crafts reaction, is a highly corrosive substance and also ends up acidifying the waste stream. Separation of AlCl3 is lengthy and expensive and it cannot be recycled due to its corrosive nature. A greener alternative for this can be explained with an example. Catalytically effective amount of a mixture of bismuth tri-halide and of perfluoroalkanesulfonic acid can be used for sulfonation reactions instead of AlCl3.
By and large, catalysts are a way to make a reaction go green. But, if one can find a way to turn a reaction greener without using a catalyst, even better. How can one do that? Alternative energy options such as microwave and ultrasound often can help us carry out reactions without using a catalyst or a solvent.
Ionic liquids are a fairly new class of catalysts. A part of the research community is cautious about using them as catalysts. Even though they are non-volatile unlike common solvents, they can be hazardous. From cradle to grave approach, that is from synthesis to its disposal, these can prove to be extremely harmful to us and the environment. Are they?