The Theme of Pollutants in Chemical Reactions
Pollutants: How Can We Help Our Planet?
Pollutants are all around us. Water pollutants. Air pollutants. Soil pollutants. We just can't escape them. But what can we do to decrease them? The easy answer is to stop releasing them into the environment.
The "green chemistry" movement is gaining huge momentum, largely due to increased awareness of the need to reduce pollution. Both new and old industrial processes are being evaluated and examined to try and reduce and even eliminate negative contributions to the environment.
One example of an industry that is starting to become greener is the dry cleaning industry. This industry might not be a huge contributor to global pollution, but it's a great start since lots of little changes can make a difference. Dry cleaners have traditionally dissolved clothing stains with solvents containing chlorine known as perchloroethylenes (PERCs).4
Tetrachloroethylene. (Image from here.)
Not only are these solvents health hazards, but they also stick around in the environment if they enter the soil or natural waterways. Once these bad boys get loose into the environment it's game on and nasty stuff can happen.
(Image from here.)
The dry cleaning industry has been trying a greener approach to stain removal. Instead of chlorine containing solvents some dry cleaners have been using
carbon dioxide or baking soda dissolved in good 'ole fashion water. With this method, most dirt and grease are removed. Baking soda and water are way better for the environment than tetrachloroethylene.
Atom Economy
Not surprisingly, we can't work in the chemical industry without working with chemicals. Where do most of these chemicals come from? Here's a hint: they don't magically appear at the end of a rainbow. That's where we find Lucky Charms. Most chemicals used in industry must be made either in a laboratory on a small scale or at an industrial plant on a large scale.
In many industrial syntheses, a series of reactions are needed to convert the first reactant into the desired final product. For this reason many industries have been reevaluating their atom economy. The goal of the atom economy approach is to send as few atoms as possible into unwanted by-products of these reactions. This would mean fewer harsh chemicals are being created. It also means less waste in general.
Here's an example:
To start, remember that C = good and D = unwanted. If A + B → C + D, it would be great to devise a new method to produce as little of D (the unwanted product) as possible or even A + B → C with no D production at all.
Product D is not necessarily harmful to the environment, although it certainly can be. Think of it this way. Every time Paul go to the grocery store the cashier puts his food in a plastic bag. (This is dating back to the pre-reusable bad days.) Paul doesn't necessarily want the plastic bag, but it comes with the groceries. Eventually Paul has a huge stockpile of plastic bags that he doesn't need or want, and he has to figure out what to do with them. The plastic bags are product D.
A real life example of atom economy is the synthesis of ibuprofen, a popular pain reliever. The original synthesis required six reactions that all together sent 23 H atoms, 7 C atoms, 8 O atoms, 1 Cl atom, 1 Na atom, and 1 N atom into waste products.5 A new greener synthesis requires only three steps and creates waste with only 4 H atoms, 2 C atoms, and 2 O atoms. That's a savings of 33 atoms. Not too shabby.
Industry is starting to do their part to reduce pollutants in our environment. This is a start but more has to be done. This is one of the many challenges for future chemists—any takers?