Fluoride in drinking water can protect against caries in small doses, but is toxic in high doses. The recommended level of fluoride is quite small, and the contamination of drinking water with higher concentrations is a problem in some parts of the world. To easily detect fluoride in the field, colorimetric methods are convenient.
Tony D. James, Jannis Wenk, Simon E. Lewis, University of Bath, UK, and colleagues have developed selective colorimetric indicators for fluoride that work in water. The team synthesized an azulene with a pinacolborane substituent using an iridium-catalyzed C–H borylation reaction. The boron in this compound can reversibly bind to fluoride, which causes the hybridization at the boron atom to change, and affects the π electron system of the molecule. This, in turn, causes the color to change.
The prepared indicator selectively detects fluoride over other halides. It allows a colorimetric readout both in organic solvents and in water, and could be useful for fluoride detection outside the lab.
- Azulene–boronate esters: colorimetric indicators for fluoride in drinking water,
Carlos M. López-Alled, Adrian Sanchez-Fernandez, Karen J. Edler, Adam C. Sedgwick, Steven D. Bull, Claire L. McMullin, Gabriele Kociok-Köhn, Tony D. James, Jannis Wenk, Simon E. Lewis,
Chem. Commun. 2017.