Abstract Trimeric sulphanuric fluorides have been synthesized successfully from α-sulphanuric chloride and potassium fluoride in acetonitrile, and the so-called “ cis” isomer has been isolated in a state of purity. This compound is more stable with respect to ring cleavage than the sulphanuric chlorides and undergoes a variety of substitution reactions. Reaction with phenyl lithium in diethyl ether in the corresponding mole ratios yields the mono- and diphenyl derivatives, whereas reaction with benzene in the presence of anhydrous aluminum chloride yields the triphenyl derivative in two isomeric forms. Several secondary amines form disubstituted products, each in two isomeric forms. The infra-red spectra of all of these compounds have been determined and evaluated.