Thiobenzophenone 4-

After standing for one-half hour, water is added and the solution is extracted with ether. The ether solution is dried over calcium chloride and the ether is distilled. The residue is distilled under reduced pressure in an atmosphere of carbon dioxide (Note 3). Thiobenzophenone boils at i74°/i4 mm. it distils as a blue oil which, if pure and dry, forms beautiful blue crystals on cooling. The yield of crude product is 10-12.5 g. (50-63 per cent of the theoretical amovmt) (Note 4). 

This product is approximately 75 per cent pure and is purified further by recrystallization from petroleum ether (b. p. 70-90 ). The yield of purified product melting at 53-54° is 8.4-9.9 g. (42-49 per cent of the theoretical amount). 

For preservation, the thiobenzophenone is sealed in a glass tube with dry carbon dioxide and placed in the dark. 

The benzophenone dichloride was prepared by heating equivalent molecular quantities of benzophenone and phosphorus pentachloride to 145-150° for two hours and then fractionating the mixture under reduced pressure. The product used for this preparation boiled at 201-202°jmm. 

It is necessary to have an excess of the chloride present at aU times in order to prevent the formation of dibenzohydryl-disulfide, due to reduction of the thioketone with the hydrosulfide. If the chloride is added to the sodium hydrosulfide solution, a 70 per cent yield of the pure disulfide is obtained and no thioketone is formed. 

CH3CH2ONa + H2S - C2HflOH + NaSH CgHsCClaCuHr, + aNaSH - CuHsCSCuHr, + aNaCl + H2S 

Submitted by H. Staudinger and H. Freudenberger. Checked by Roger Adams and E. H. Woodkubf. 

An alcoholic solution of sodium hydrosulfide is prepared by dissolving 4.6 g. of sodium (0.2 mole) in 150 cc. of absolute alcohol and saturating the solution with dry hydrogen sulfide. 

In a 3-I. three-neck flask, equipped with a mechanical stirrer and a reflux condenser, is placed 25 g. (o.ri mole) of benzophe-none dichloride (Note 1). An inert atmosphere is obtained by passing carbon dioxide through the flask. The sodium hydrosulfide solution is added slowly (Note 2). A vigorous reaction occurs and it is controlled by cooling. The solution becomes deep blue in color. 

---

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. 

---