Dithiets

Theoretical considerations indicate that the thermal conversion of an a-dithione into a 1,2-dithiet is allowed photochemically the thermal processes, both forward and reverse, are forbidden. Model calculations on the dithioglyoxal-dithiet equilibrium show that the Hiickel method predicts the dithioglyoxal to be more stable than the dithiet, whereas the CNDO/2 method predicts the opposite. The potential surface for C2S4 was calculated, and energy minima were predicted for (81), (82), (83), and (84).  

The structure of 3,4-bis(trifluoromethyl)-l,2-dithiet has been determined by electron diffraction. Structures (85), (86), and (87) were said to contribute to the hybrid, but (88) does not. 

Photolysis of diphenylvinylene dithiocarbonate (89) yields diphenyidithiet (90), which is too reactive to be isolated, although it can be trapped as a molybdenum or a nickel complex in the presence of the metal carbonyl.  

Bis-(p-dimethylaminophenyl)dithiet exists in the solid state as the a-dithione, but an equilibrium exists in solution between the two forms. The equilibrium is sensitive to light, temperature, and solvent. 

Snyder, Organic Sulphur Chemistry , ed. C. J. M. Stirling, Butterworths, London, 1975, p. 307. 

2- Dithietans.—1,2-Dithietan (114) is the first isolated derivative in that class. It arises by dimerization of ethyl sulphine, probably by rearrangement of a first-formed sulphenyl sulphinate (see Chap. 3, Pt. II, p. 161). 

2- Dithiets.—Two dithiets (115) and (116) have been isolated, and more observed. ° Benzodithiet is trapped by dimethyl acetylenedicarboxylate to give 

The photochemical decomposition of vinylene dithiocarbonate (226) gave dithiobenzil (227), which was in equilibrium with the corresponding dithiet (228). The activation energy for ring opening of the dithiet was ca. 15 kcal 

Dithiet cation radicals also may be involved in the mass spectrometric fragmentation of l,3-dithiole-2-thiones and the corresponding 2-ones. Treatment of l,2-bis(trifluoromethyl)dithiet with cyclopentadienylindium(i) gave 1,2-dithiolen complexes and with cyclic phosphines and phosphites, phosphoranes (235) 

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Dicyano-l,2-dithiete [53562-16-6] (14) is thought to be an intermediate when BAhr s Salt is oxidi2ed (64,65). If the oxidation is carried out in the presence of vinyl ethers, dihydro dithiins can be obtained in yields up to 60%. 

Measurement of the equilibrium eonstant for the interconvension of the dithiete A and the dithione B yielded the data given below. Calculate AG°, AH°, and AS°. 

Tlie present chapter reviews the chemistry of three- and four-membered ring compounds containing an S—S bond in their ring. Dithiiranes 1,2-dithietanes and 1,2-dithietes are the compounds of this type. Although 1,3-dithietanes are four-membered heterocycles which are prepared much more easily and are seemingly more familiar, they have no S-S bond in the ring and hence are not included in this chapter. 

Tile a-dithione 91, generated by photolysis of 92, is transformed into the dithiin 93 (417o) in the absenee of a trapping agent. The eonversion was proposed to proeeed by a [4 + 2] eyeloaddition of 91 with its dithiete tautomer 94 leading to the dithietane 95, whieh was followed by loss of S2 (85JOC1550). Sueh [4 + 2] dimerizations are often eneountered in the ehemistry of 1,2-dithietes as diseussed later. 

Dithiatopazine 73 serves as a sulfur-transfer reagent under thermal conditions. Tlius, heating 73 and diene 130 in toluene at 100°C formed a cyclic disulfide 131 (25%) and a tetrasulfide 132 (28%) with the formation of the alkene 118 (90%). Under similar conditions, the highly strained acetylene 133 was converted to the 1,2-dithiete 134 (65%) and the congested thiophene 135 (12%) (90JA3029). 

Many stable 1,2-dithietes, which possess at least one bulky substituent, have been isolated. In this system, the strained, reactive double bond of... 

Tire first synthesis of 3,4-di-ferf-butyl-l,2-dithiete (172) was performed by treatment of 173 with Lawesson s reagent (LR). Direct thionation of the diketone 174 failed to yield 172 [82JCR(S)314]. 

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