This figure is taken from Green chemistry: state of the art through an analysis of the literature by V. Dichiarante, D. Ravelli and A. Albini. Green Chemistry Letter and Reviews Vol. 3, No. 2, June 2010, 105-113.
As the label indicates, the pie chart shows a distribution of green chemistry topics as analyzed by articles produced in the year 2008. The majority of the pie chart (about 50%) is attributed to catalysis – or starting a reaction, under more favorable conditions that require less resources, whether those resources are heat, energy, reagents etc. Specifically, metal catalysts were the most cited catalysts used in many different reactions, specifically in those involving enzymes. Acids are also seen in this category, and according to the article, are used mainly in condensation reactions. The next largest section of the pie (about 40%) is attributed to media, or where/in what the reaction takes place. Many reactions require some liquid for a reaction to take place. Many of these liquids, especially in organic chemistry, are volatile or toxic compounds. As a result, most of the research done with green chemistry and the media of reactions use either no solvent, which allows for most reduction of waste. Water has also gained a prominent role in green chemistry literature as it is our universal solvent and usually can be recycled in a reaction. Ionic liquids are the third major media hit; they are liquids that have charged compounds in the solution to help guide a reaction. Ionic liquids are usually not volatile and are stored more easily compared to their organic counterparts. Finally, the last 10% of the pie chart goes to ‘new methods,’ or novel ways to do old reactions. Using microwaves to start and maintain a reaction is the most prominent method, followed by some research advances in photochemistry and ultrasounds, using light or sound respectively in reactions.