5-arylthianthrenium salts

In 5-alkylthianthrenium salts, the 4- and 6-proton signals are pulled downfield by 0.5-0.9 ppm, and in 5-arylthianthrenium salts, the signals are pulled downfield by 0.4-0.8 ppm. These peri protons are downfield by ----47 ppm with respect to CHCI3 in thianthrene sulfoxides. 

Crivello et al., described the synflieses of 5-arylthianthrenium salts that form efficient triarylsulfonium salt photoinitiators for cationic polymerization. Through the use of electron-transfer photosensitizers, the response of these photoinitiators can be spectrally broadened to the long wavelength ultraviolet-visible light regions of the spectrum. The results obtained suggest that. 5-arylthianthrenium salts are potential replacements for now available triarysulfonium salt photoinitiators in many applications. 

The synthesis of 5-arylthianthrenium salts, 8, [CRI 02a, CRI 04] can be carried out by the condensation of thianthrene-S-oxide with various aromatic compounds bearing electron-donating substituents, R, as depicted in equation [2.1], A mixture of methanesulfonic acid and phosphorous pentoxide serves as an acid catalyst and dehydrating agent for this reaction. Replacement of the methanesulfonate anion by a metathetical reaction with NaMtXn affords the desired active photoinitiator, 8. Depending on the specific R substituent, 5-arylthianthrenium photoinitiators have UV absorption maxima in the range of 300-400 nm. 

Crivello, J.V, Ma, and Jiang, F. (2002) Synthesis and photoactivity of novel 5-arylthianthrenium salt cationic photoinitiators. J. Polym. Sci. Part A,... 

Combining thianthrene radical ion(l+) with free radicals to produce thianthrenium salts has also been achieved. Decomposition of various cumene hydroperoxides (83MI6) and of azobis(2-phenoxy-2-propane) (85MI1) gave 5-arylthianthrenium ions together with 5-(propen-2-yl)thianthrenium perchlorate in the latter case. 

---