An analysis of 1.3 million chemical reactions listed in patents over four decades has shown that chemists still depend heavily on hazardous solvents, despite a nearly 30-year campaign to make chemistry 'greener' using safer, more sustainable alternatives. The survey is the largest and most comprehensive of its kind. Solvents are workhorse liquids used to dissolve chemical substances during reactions; chemists also use them to extract and purify reaction products. Some of the most common solvents, such as dichloromethane (DCM), are known to have health risks, or are hazardous in other ways ' for instance, many are flammable. Almost all of them are derived from oil or natural gas, giving them a substantial environmental footprint. The patent survey, published this month in Angewandte Chemie1, found that solvents classed as hazardous were used in about 60% of reactions mentioned in patents in 1976, but that by 2016 that proportion had risen to above 70% (see 'Hazardous solvents...
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