A new route to adipic acid that uses ozone and ultraviolet light to eliminate the problematic nitrous oxide by-product has researchers intrigued. But once again, issues of scale-up and safety with a greener route to this chemical intermediate—used to make nylon, polyurethane, and plasticizers—temper the good news. Right now, 95% of the world’s adipic acid production uses nitric acid as an oxidant, which releases N2O as a by-product. The gas eats away at Earth’s protective ozone layer and ranks behind only carbon dioxide and methane when it comes to greenhouse gas emissions. Some producers trap and destroy N2O, and emissions have been cut in half since 1990. But significant emissions remain. Chemists have been exploring N2O-free routes to adipic acid for years by using O2 or H2O2 or employing enzymes. These methods tend to be more energy efficient, have better yields, and avoid corrosion problems from using nitric acid, but ...