Thiobenzophenones

We proposed new photometric reagent 4,4 -bis(diethylamino)-thiobenzophenone (ethyl derivative of Michler s thioketone, EMT) for the determination of free chlorine and chloramines in drinking water. 

A ring opening of the dithiirane 39 to the thioketone 5-sulfide 35 was proposed for the reaction of thiobenzophenone 5-oxide (40) with the thioketone 41 (81LA187). Tlie conjugation with the phenyl group would stabilize 35 relative to the dithiirane form. 

Reaction of thiobenzophenone with chloromethyl methyl sulphoxide 412 does not give the expected 2,2-diphenyl-3-methylsulphinylthiirane 417, but the a, /1-unsaturated sulphoxide 418 in a 38% yield485 (equation 248). 

Dimethoxy-thiobenzophenon —> Bis-[4-methoxy-phenyl]-dideuiero-methan 74% d.Th. 

Fig. 13. Dependence of half-wave potentials for the reduction of substituted benzenes on the total polar substituent constant, ax- Examples shown benzophenones [pH 0], benzophenone-oximes [pH 0], thiobenzophenones [pH 0], nitrobenzenes [pH 2-0], azo derivatives [pH 2-6]. (Taken from Zuman, 1969.)...

Stock solution Dissolve 1 g 4,4 -bis(dimethylainino)thiobenzophenone (Michler s thioketone) in 100 ml chloroform. 

A dibenzo[fc,react with benzyne, confirming that the [4+2] cycloaddition is preferred to the [2+2] mode <96TL8883>. 

The adducts 41 from 1 and ketones or thiobenzophenone undergo interesting photochemical cycloreversion to afford a silanone or silanethione intermediate 42 in addition to silene 43 both of these intermediates are trapped by ethanol, as shown in Eq. (14).68 71 In the reaction with the thiobenzophenone adduct 41 (R = Ph, X = S), the intermediate silene 43 (R = Ph) was detected by Si NMR.71... 

In the reactions which we have just discussed, the initial reaction involves only the carbonyl group. We therefore looked next at reactions of tetrachlorobenzyne with simpler aldehydes. It is noteworthy that o-carboxybenzenediazonium salts are known to yield 1,3-benzodioxan-4-ones, for example, (129) with carbonyl compounds 166>, and 2,2-diphenyl-3,l-benzo-oxathian-4-one (130) with thiobenzophenone 167>. These products are presumably formed via reactions with the intermediate (128). 

Whenever benzyne is expected to undergo a [2+2] cycloaddition as with ketones,109 it behaves as a dienophile with aromatic thioketones. Reaction of thiobenzophenones with benzyne yields the [4+2] cycloadducts and 1H-2-benzothiopyrans.110,111 Sterically congested thiones,111 thiopivalophenones and 2, react with benzyne to give the [2+2] adducts, 2H-l-benzothietes. 

Tetracyanoethylene (TCNE)175,176 reacts with thiobenzophenones to yield 2,3-dihydrothiophene, thiophene, and 1,2-dithiin derivatives, thus depending on temperature. Okuma suggested a mechanism176 for the formation of 2,3-dihydrothiophenes through [2+2] and [4+2] sequential cycloadditions. 

Four-membered rings. The study of the reaction between thiobenzophenone and methylenetriphenylphosphorane177 pointed out the presence of a reactive intermediate, thiaphosphetane, which decomposed either to a thiirane and triphenylphosphine or to the Witting alkene and a phosphine sulfide, depending on the temperature. 

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