Aryl thioketone

Treatment of dienyl aryl ketones with P4S10 affords phosphorus-containing heterocycles which generate dienyl aryl thioketones upon heating262 (equation 28). 

Other thermal 1,3-dipolar cycloadditions are the reactions between nitrile sulfides and electron-deficient aldehydes and ketones forming 1,3,4-oxathiazolines (98 Scheme 19) between aryl thioketones and thiofluorenone 5-tosylimide to yield the 1,3,4-dithiazolidines (204) and between thioketene S-oxides and imines, yielding in one case the 1,2,4-oxathiazolidine (136). 

Thioketones are without exception colored but have a strong tendency to pass into the colorless trithianes, particularly the dialkyl and alkyl aryl thioketones. For instance, thioacetone exists only as the trimer at room temperature but, when heated, is converted into violet vapors of the monomer.403 On the other hand, Baumann and Fromm403 found that acetophenone gives, not only the trimer, but also the monomeric thioketone as an unstable blue oil from which the trimer is formed by pyrolysis. 

Thioketones have been studied more intensively by Andrieu et al. [72] using Raman data to confirm their assignments. Ahphatic thioketones which are not dimerised absorb between 1270 and 1245 cm- and the band position within this range is a function of the sum of the Taft a values of the substituents. With aryl thioketones the frequency falls to 1225—1205 cm-, but there is now no relationship between the frequencies and the Hammett a values of these substituents [76]. These findings have been fully supported by other workers [73, 75]. 

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