Pentasulfide, cyclic

The reagent does not replace nitrogen atoms, and N-alkyl or N-aryl anthranilic acids yield 2,l-benzisothiazoline-3-thiones (94) on heating with phosphorus pentasulfide in xylene. Curiously, when alkyl iV-arylanthranilates are treated in the same way, only a very small proportion—less than 10%— of 94 is obtained. The major product (80%) is the cyclic phosphorus-containing compound (95), the identification of which gives some clue about the structures of possible intermediates.122... 

Recent developments in the chemistry of cyclic selenium sulfides have revealed that sulfur and selenium form a very complex binary system. Cyclic eight-membered molecules with the general formula Se Ss can be prepared from the molten mixtures of sulfur and selenium and also by a variety of chemical reactions. In all cases mixtures of different selenium sulfides are formed which it has not yet been possible to separate, In the reaction of titanocene pentasulfide with dichlorodiselane, however, the resulting mixture is simple enough to allow the major component to be identified as 1,2,3-86385... 

The synthesis of specific sulfur allotropes is achieved by reactions of titano-cene pentasulfide Cp2TiSs with dichlorosulfanes S Cl2 ( = 2, 4, 6) or sulfuryl chloride SO2CI2 [see eqns (2.1) and (6.1)]. The X-ray structures of many of these cyclic sulfur allotropes have been determined (see Figure 6.2 in Section 6.1). In general, they adopt puckered molecular conformations, e.g. the crown-shaped cyclo-Sg, which minimise repulsions between non-bonding electron pairs on... 

In the reaction of cyclic trisulfide 133 with chloro(triphenylmethyl)trisulfide or triphenylthiosulfenyl chloride, only two of the three sulfur atoms were ultimately delivered resulting in the pentasulfide 134 in 30% yield. This apparently reflected the overall stability of pentasulfide versus the hexasulfide (Equation 23) <2000TL7809, 2000TL7169>. 

Analogous chemistry was reported [215] with thioaldehyde intermediates generated from a non-classical thermal reaction of a sulfoxide via a sulfe-nate ester (Table 3, entry 2). The reaction of cyclic tetra- or pentasulfides with stabilised phosphoranes is also a good source of thioaldehydes [216], trapped by dienes (Table 3, entry 2). 

Figure 3. Structure obtained by x-ray diffraction of cyclic pentasulfide formed by interaction of sulfur and dicyclopentadiene...

It is possible that this polymer is formed by ring-opening polymerization of the cyclic pentasulfide or other cyclic polysulfides. In a separate experiment, heating the trisulfide gave a similar chain polymer. We have not been able to separate the fraction VRE = 0.72 which was formed in much smaller quantities than other fractions. 

Preparation of a Cyclic Heptasulfane Using Titanocene Pentasulfide as Sulfur-... 

Titanocene pentasulfide (1) has been used as a transfer reagent for the S5 unit to prepare numerous inorganic homo- and heterocycles. More recently, cyclic organic polysulfanes have also been obtained from (1) by reaction with bis(sulfenyl chlorides) (equation 99). ... 

Vogel and coworkers have succeeded in preparing two geometrically isomeric [30]annulene pentasulfide macrocycles, namely 6.59a and 6.59b.These two macrocycles were prepared via the McMurry-type reductive carbonyl coupling of 3,4-diethyl-2,5-diformylthiophene (Scheme 6.5.2). They were isolated in a combined yield of 1.5% from a mixture of products that included a cyclic trimer, tetramer, and two isomeric cyclic hexamers (discussed in Chapters 2, 4, and 7, respectively). Separation of isomer 6.59a from 6.59b was achieved by fractional crystallization. However, this separation was complicated by the fact that the two isomers obtained appeared to interconvert readily under normal laboratory conditions. 

The other approach to 2-thioxo-l,2-thiaphospholanes 108 and 110 is based on the direct reaction of an unsaturated hydrocarbon, phosphorus pentasulfide and a thiophosphoric acid halide under drastic conditions (autoclave, 150-200 °C, 10-18 h) [142, 143], When cyclic alkenes (e.g. cyclohexene) are used as the starting substrates, bicyclic compounds are formed with one of the rings representing 1,2-thiaphos-pholane (Scheme 64). These reaction products are used as antioxidant additives for motor oils, polymers and agrochemicals. 

Phosphorus pentasulfide (s. a. under C H N) Replacement of cyclic oxygen by cyclic sulfur... 

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