The Search For Cyanoform Is Over

Cyanoform, HC(CN)₃, also known as tricyanomethane, is sometimes listed in organic chemistry textbooks as one of the strongest carbon-based acids known (pK_a of –5.1 in water). But after more than a century of chemists trying to make cyanoform, questions have remained as to whether they truly have. The best researchers have been able to do before now is get a fleeting glimpse of the molecule by microwave spectroscopy in the gas phase at very low pressure. Researchers in Germany report they have finally figured out the essential experimental conditions necessary to isolate and fully characterize the celebrated compound and confirm its existence (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201506753). Chemists had assumed cyanoform would be stable at room temperature in water. Among the attempts to make the compound, chemists have tried using sulfuric acid to protonate salts of tricyanomethanide, (NC)₃C^–. Theresa Soltner, Jonas Häusler, and Andreas J. Kornath of Ludwig Maximilian University of Munich instead used anhydrous hydrogen fluoride as a reactant and solvent with calcium tricyanomethanide at low temperature. The team found that cyanoform can be isolated as a crystalline solid, but it’s only stable below –40 °C and is moisture sensitive.