Addition reactions of perf1uorothio1acetic acid (TFTAA) with organic and inorganic substrates were studied and six new compounds containing the trif1uoroacety1 group have been prepared. Two types of reactions were observed, free radical and nucleophilic addition. Under the influence of ultraviolet light, TFTAA (CF₃COSH) adds to olefins to form 1:1 adducts. The CF₃COS• radical appears to be the adding species. Three new olefin adducts were prepared: CF₃COSCFHCF₂H, CF₃COSCH₂CF₂H, and CF₃COSCH₂CFH₂. In addition, this was found to be a new way to prepare CF₃COSCH₂CH₃, which had been previously prepared by another route¹. Physical constants, analytical data, infrared, ultraviolet, nmr and mass spectra are presented supporting the proposed structures for these compounds. Nucleophilic addition adducts were formed with TFTAA and some organic and inorganic materials. TFTAA is a strong acid and the CF₃ COS⁻ ion was found to act as a nucleophile with several substrates. With hexafluoroacetone, addition of TFTAA across the carbonyl gave CF₃COSC(CF₃)₂OH. This structure is supported by analytical data, gas chromatographic data, infrared, ultraviolet, nmr, and mass spectra. Ethylene oxide and TFTAA react to produce the alcohol addition product, CF₃COSCH₂CH₂0H, which is supported by analytical data, nmr infrared, and mass spectra. Sulfur trioxide was studied as a representative inorganic molecule. TFTAA adds to this Lewis acid to form the sulfonate, (CF₃COS)₂S0₂. Analytical data, infrared, ultraviolet, nmr and mass spectra are reported here. All of the reactions, except the free radical reactions, occurred spontaneously and exothermically upon mixing the two reactants. A new method of preparing CF₃COSH, by reacting KSH with (CF₃CO)₂O, is also presented ¹M. Hauptschein, C.S. Stokes, and E.A. Nodiff, J. Am. Chem. Soc. 74, 4005 (1952)