Other Sulphur-containing Ring Compounds

The crystal structure of pentacarbonyl(tetraphosphorus trisulphide)-molybdenum has been determined.130 The structure shows an intact P4S3 cage molecule attached to a Mo(CO)s moiety through the apical phosphorus atom the i.r. spectrum of the compound suggests that the P4S3 molecule has strong phosphine-like interactions with the Mo(CO)5 system. 

The crystal structure of 2-chloro-l, 3,6,2-trithiarsocan has been determined,131 and shows the eight-membered ring to have a deformed boat conformation (48), with 1,5-transannular As-S interaction. An identical 

A study of the n.m.r. spectrum of a-P4S3l2 has shown the compound to possess the same bicyclic structure in solution as in the solid state. 

data have also been used to show that the compound (C6H6PS)3 has the heterocyclophosphane structure with a five-membered P3S2 ring containing isolated sulphur atoms. One of the directly connected phosphorus atoms is linked to another sulphur atom in an exo-position, in addition to the phenyl group. The above structure has also been confirmed by a second study.  

A series of papers describing the synthesis and substitution reactions of the heterocycle (36) have been published. A later paper d also gives the results of 

Baudler, D. Koch, Th. Vakratsas, E. Tolls, and K. Kipker, Z. anorg. Chem., 1975, 413, 239. 

The five-membered heterocyclic ketone (39) has been prepared by the reaction of dimeric 5,5-dimethyl-l,3A, 2,4,5-dithiadiazastannole (40), obtained by the reaction of S4N4 with tris(trimethylstannyl)amine, with an excess of carbonyl difluoride at room temperature. The cyclic, ketone is the first representative of a new class of compounds that have become readily accessible by this method. 

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A review of saturated, heterocyclic, three-membered rings has been published, and the literature for 1972 concerned with heterocyclic chemistry has been surveyed. The chemistry of three-membered, sulphur-containing rings has been reviewed. " The n.m.r. spectra of small-ring sulphur heterocyclic compounds and other heterocycles have been discussed. Selenium-containing cyclic compounds, including three- and four-membered rings, have been reviewed/... 

Recent work ( ) with model organosulphur compounds has shown that at temperatures above 350 C and pressures in excess of 100 atm (1500 psig), the hydrolytic desulphurisation reaction occurs readily with thioethers, mercaptans and other non-thio-phenic types of organosulphur compounds. Thiophene itself is more resistant to this type of reaction but desulphurisation is significant in the 450 - 500 C range. More complex fused ring sulphur containing aromatic structures, can, however, be more reactive. 

Sulphur has various allotropic forms. Below 95.6°C the stable crystd form is rhombic above this temperature the element transforms into a triclinic form. These crystalline forms both contain cyclic Sb molecules. At temperatures just above its melting point, molten sulphur is a yellow liquid containing Ss rings (as in the soiid form). At about 160°C, the sulphur atoms form chains and the iiquid becomes more viscous and dark brown. If the molten sulphur is cooled quickly from this temperature (e.g. by pouring into cold water) a reddish-brown solid known as plastic sulphur is obtained. Above 200°C the viscosity decreases. Sulphur vapour contains a mixture of S2, S4, Sg, and Ss molecules. Flowers of sulphur is a yellow powder obtained by subliming the vapour. It is used as a plant fungicide. The element is also used to produce sulphuric acid and other sulphur compounds. 

As distinct from benzene and other ring systems which contain carbon as the only ring constituent are a number of heterocyclic ring compounds in which one or more of the carbons is replaced by an oxygen, nitrogen or sulphur atom. These too may be either saturated or unsaturated. 

The pale yellow colour of nitrobenzene or p- nitrotoluene turns more intense when the compound is dissolved in sulphuric acid, while solutions of nitromethane and other nitroparaffins are colourless. The yellow colour of the aromatic nitro compounds is due presumably to an ionic structure containing a quinonoid ring. 

The selenium-sulphur compound Se Si2 has been prepared280 by the reaction of SeCl4 or Se2Cl2 with crude sulphane. A structure determination, using crystals containing 26% selenium, showed that two of the four independent point positions of the Si2 ring are occupied by sulphur atoms, and the two others are occupied by selenium and sulphur at 25 and 75%, respectively. The analytical and structure determinations also showed the existence of a solid solution between the phase which is probably Se2Si0 and S,2. 

The best-known nitrogen-containing compounds (other than those associated with the carboxyl group discussed in Section 10.15) are the aziridines or epimino compounds and the amino compounds derived from these by ring-opening processes. These compounds have a formal resemblance to the epoxides and diols and to the corresponding sulphur compounds. 

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