Synthesis and characterization of fluorinated derivatives of cresolsulfonphthalein

The reaction between dilute fluorine gas and cresolsulfonphthalein in acetic acid was investigated. The mono-, di-, and trifluorinated cresolsulfonphthalein derivatives were isolated and characterized. These compounds possessed the properties of pH indicators with biologically relevant pKa values (6.4–7.5) and the absorption maxima of the basic forms at 582–592 nm. This method can be used for synthesis of positron-emitting 18F-labeled pH indicators with potential application for non-invasive in vivo pH measurement in biological objects.