1 I.I.INTRODUCTION Sulphur has a long history of application in medicine as a result of scabicidal, insecticidal, fungicidal and purgative properties1.Organosulphur chemistry has developed very rapidly during the last two decades previously a topic of interest only for specialists and now a day it may be considered as an integral and important part of general organic chemistry. The chemical versatility of organosulphur compounds has lead to its incorporation into a number of projects in several different areas of medicinal chemistry. The discovery of sulphonamide2 as antibacterial drug by a German scientist, Gerhard Domgak, marks an important milestone in the development of medicinal chemistry. This discovery leads to the synthesis of some 15,000 sulphonamides3a. A wide variety of organosulphur compounds show useful biological activity. They have become a regular armoury of pharmaceutical and crop protection chemistry. Some of the OrganoSulphur compounds that have been isolated from natural sources include amino acids, vitamins, harmones and antibiotics, as well as numerous enzymes. Many of the natural products mentioned above enjoy extensive therapeutic usage. In addition, some of the most powerful synthetic drugs are also sulphur containing. Among the best known classes are sulfonamides (anti-infective agents) sunfonyl ureas (oral hypoglycemic agents), 2-thio uracils (anti-thyroid agents), phenothiazines (antihistamines, tranquilizers), thiobarbiturates (analgesics, anesthetics), aromatic surfones (antilepratic and antimalarials), 6-mercaptopurines (anti leukemic agents) etc. The antibiotics like penicillin, ampicillin, and amoxycillin are organosulphur compounds. Anti-ulcer drugs1 ranitidine and cimitidine which are thioethers (organosulphide), and pentaprazole, omeprazole, lansoprazole and rabeprazole which are organosulphones3b are extremely effective and in many cases their use can avoid the need of surgery in the treatment of ulcer. Of the current agrochemicals some 30% contain sulphur in wide variety of oxidation states, because of their usefull biological activity. Some important examples of organosulphur compounds used as agrochemicals1 include thiophosphoryl insecticides like malathion, herbicides like chlorsulphuron, fungicides like dithiocarbamates and caplon and sulphone acaricides like tetradifon. 2 Organosulphur compounds are not only used as drugs but also as dyes and detergents1 Many dyes used in the textile industry contain sulphonic acid group which . imparts water solubility and help to make the dye become fast to the fabric. Sulphur dyes, another class of vat dyes are obtained by heating various organic compounds with sodium polysulphides. Derivatives of 4,4'-diamino-2,2'-stilbenedisulphonic acid such as the phenylamido derivatives are fluorescent whitening agents used to enhance the appearance of white fabrics, e.g. cotton which otherwise tend to turn yellowish with repeated washing. Application of organosulphur compounds is not confined to the fields mentioned above, but of late, it has also plunged into the field of electronics and superconductors4a. Representative examples of molecules are the tetrathiafulvalene derivatives4b, 4c, of which bis (ethylenedithio) tetrathiafulvalene, BEDT-TTF or ET, is the most notable. The derivative of ET with formula k-ET Cu (NCS) is a superconductor4d and has a transition temperature of 2 2 10.4K, making it one of the highest-temperature organic superconductors. Organosulphur compounds include organosulphides (thioethers), sulphoxides and sulphones etc. Of these, the synthesis and structural studies of simple sulphides, sulphones and sulphoxides are well known thing for a long time, but the studies on 1,1-bis (alkyl- or arylthio) ethylenes and their corresponding bis-sulphones and 1,2- bis (alkyl- or arylthio) ethylenes and their corresponding bis-sulphones are of recent origin. The biological studies on sulphones revealed that they can be used in chemotherapy and agriculture. The sulphones of chlorothiazide and hydrochlorothiazide series are frequently used as diuretics. Sulphonal, (CH ) C (SO C H ) , trional and tetranal are used as 3 2 2 2 5 2 sedatives and hypnotics. The discovery of dapsone5 as potential drug against leprosy has revolutionized its whole treatment. Dapsone is also proved to be a potent prophylactic agent. Bis (p-aminophenyl) sulphone was first synthesized by Fromm and Wittman6 and its chemotherapeutic activity was first evaluated by Buttle and his co-workers7 and later Rist8 demonstrated its high anti-bacterial activity. Buttle observed that it is hundred times as active as sulphonilamide. The N,N′-diacetyl and N,N′-digalactoside derivatives of bis (p- aminophenyl) sulphones have been found to be useful as therapeutic agents, similar to the sulphonamides. Sulphenone, 4-chlorodiphenylsulphone and tedion, 2,3,4,5-tetrachloro diphenylsulphone are used as acaricides. 3, 4-Dichlorotetrahydrothiophene-1,1-dioxide has been proposed as nematocide. Promine, [sodium bis (p-aminophenyl) sulphones- N′, N′- bis 3 (glucosesulphonate)], diazone [disodium formaldehyde sulphonate bis (p-aminophenyl) sulphone] were found to be effective tuberculostatic agents, but found to be highly toxic. Streptococci and pneumococci infections9 can be effectively treated with diazsone. Sulphones find application not only in the field of therapy and agriculture but also in textile inustry. Dimethylsulphone or methylsulphonylmethane (MSM) CH SO CH is one of 3 2 3 the best and safe drug10 for the relief of arthritis11, inflammation, lupus and other debilitating and disabling pain conditions and also effective in ameliorating the symptoms of gastrointestinal upset12. Dihydroxy- diethylsulphone, divinyl sulphones and hydroxy ethyl vinyl sulphones are used to give crease resistant finishes. Thiomorpholine-1,1-dioxide and 2- phenyl benzothiophene-3,5-dioxide are optical bleachers.There are many more applications of sulphones such as fuel additives, plasticisers and anti icing additives13 etc. The recently originated unsaturated disulphones revealed from their biological studies that they can be used as effective fungicides14. A few mercapto haloethylene sulphone derivatives14, bis (organosulphonyl) ethylenes16 with the general formula R SO (R ) C=C 1 2 2 (R ) SO R vinylene sulphonyl compounds17 and bis (arylthio) ethylenes18 have been 3 2 4, reported as effective fungicides to protect seed. They are also effective against mildew on cotton-cloth, paint and various plant foliage diseases. The activity of organosulphur compounds of biological importance has been found to vary depending upon the substituents present and also on the stereochemical configurations of the substances. A brief account of the historical development of the chemistry of (organosulphonyl) ethylenes is presented here. It is reported in early 1947, by Schörnberg and Mustafa19 that benzoin (1) react with p-thiocresol (2) in the presence of anhydrous zinc chloride and HCl gas to form α,β-bis (p-tolylmercapto) stilbene (3). H C 3 O OH ZnCl2 S C C H3C SH H HCl S CH3 1 2 3 During the investigation of reactions of carbonyl compounds with mercaptans Romero and Romo20 reported the preparation of cis- and trans-α,α'-benzylthiostilbenes in poor yields. In 1958 the same disulphide was also reported by Bellido21. 4 A convenient method for the preparation of 1,2-bis (alkyl- or arylthio) ethylenes is by the nucleophilic displacement of halogens with thiols from tetrachloroethylene, dichloroethylene, vinylidene halides and vinyl halides. Tetrachloroethylene (4) on refluxion with sodium p-toluenethiolate gave trans-1,2-bis (p-tolylmercapto)-1,2-dichloroethylene (9). By isolating the intermediate product 1-(p- tolylmercapto)-1,2,3-trichloroethylene (7), the following mechanism was suggested. Under forcing condition tetra (p-tolylmercapto) ethylene (10) was also obtained. CH 3 CH 3 S Cl Cl EtOH Cl Cl - Cl S Cl H C SNa 3 Cl Cl Cl Cl Cl Cl 4 5 6 7 p-CH PhSNa / EtOH 3 H3C CH3 H3C H3C Heated in S S sealed tube S Cl S Cl - Cl S S p-CH3PhSNa Cl S Cl S Cl CH H3C 3 CH3 CH 3 10 9 8 The cis-1,2-bis(p-tolylmercapto)ethylene on chlorination gave cis isomer of 1,2-bis(p- tolylmercapto)-1,2-dichloroethylene. Both the cis and trans-1,2-bis (p-tolylmercapto)-1,2- dichloroethylenes on oxidation with peracetic acid yielded the corresponding cis-and trans- 1,2-bis(p-tolylsulphonyl)-1,2-dichloroethylenes.Following a similar procedure for preparation,1,2-bis(propylmercapto)-1,2-dichloroethylene22-25,1,2-bis(ethylthio)-1,2-dichloro -ethylene, 1,2-bis(dodecylthio)-1,2-dichloro ethylene and 1,2-bis(ethylthio)-1,2-difluoro 5 ethylene were reported26. All these disulphides on oxidation yielded the corresponding disulphones which were claimed to be active seed protectants. The preparation of trans-1,2-bis (isopropylthio)-1,2-dichloroethylene was reported in 1963, by Bluestone and Bimber15. Six pairs of cis- and trans-1,2-bis (alkylsulphonyl) ethylenes suitable for use as seed fungicides were also prepared21 by treating 1,2- dichloroethylene with 2 moles of mercaptan and subsequently oxidising the product with peracetic acid. In this reaction, it is reported that cis-1,2-dichloroethylene (11) react readily with nucleophilic agents such as sodium benzenethiolate28a, sodium p-toluenethiolate28b,29 and sodium t-butylmercaptide30, while the trans-isomer, when treated likewise, recovered unchanged. It has been explained that the first step in this reaction is elimination of HCl from cis- 1,2-dichloroethylene (11) to give chloroacetylene (12), which by trans addition of thiol forms the cis-starting material (13). Compound (13) reacts further as shown above to give cis-1,2- bis (alkyl- or arylthio) ethylenes (15), trans-1,2-Dichloroethylene is inert because it does not eliminate HCl under the conditions of the reaction31. The cis-bis-sulphides (15) obtained above isomerise into the corresponding trans-bis-sulphides. All these bis-sulphides on oxidation afforded the corresponding bis-sulphones. Cl Cl -HCl H H EtOH HC CCl RSNa H H RS Cl 11 12 13 -HCl H H RSNa RSC CH RS SR EtOH 14 15 Where R = C H and (CH ) C 6 5 3 3 6 Benati et al.32 in 1963, reported the synthesis of cis- and trans-1,2-bis (p- bromophenylsulphonyl) stilbenes. The addition of p-bromothiophenol to tolan in presence of a base gave trans-1-p-bromophenylthiostilbene. This on bromination yielded cis-and trans-1- bromo-2-p-bromophenylthiostilbenes. These bromophenylthiostilbenes on reaction with p- bromobenzenethiol lead to the formation of cis- and trans-1,2-bis (p-bromophenylthio) stilbenes, which on oxidation gave the corresponding bis-sulphones. Naidu and Peeran reported the synthesis of (E)- and (Z)-1,2-bis(p-toluenesulphonyl) stilbenes33, and seven pairs of (E)- and (Z)-1-alkylsulphonyl-2-p-toluenesulphonylstilbenes34. They have established the geometrical configurations of these isomers through stereospecific synthesis and spectral studies. In 1982, the synthesis of (E)- and (Z)-1,2-bis (phenylsulphonyl) stilbenes was reported by Peeran et al.35. Recently the synthesis of a number of cis- and trans-1,2-bis (alkylthio and arylthio) stilbenes and their corresponding bis-sulphones have been reported36-41. It is reported42a that trans-1,2-dichloro-1,2-bis(4'- chlorophenyl)ethylene (16) reacts with potassium salts of various thiols (17) in dimethylformamide. The chlorine atoms at the double bonds are displaced by thiols giving bis-sulphides (18). All these bis-sulphides (18) on oxidation afforded the corresponding bis- sulphones (19). Weis42a has pointed out that the aliphatic thiols react with trans-1,2-dichloro-1,2- bis(4'-chlorophenyl)ethylene (16) giving trans-bis-sulphides (18) in good yields where as the aromatic thiols either react forming the product in low yields or do not react at all. He has also reported that cis-1,2-dichloro-1,2-bis(4'-chlorophenyl)ethylene does not react with potassium salt of thiols even on long heating. Where R = p-CH C H and (CH ) C 3 6 4 3 3 Recently, Peeran et al.42b have reported the preparation of some trans-1,2- bis(alkylthio)-1,2- bis(4'-bromophenyl)ethylenes and their corresponding bis-sulphones. 7 Cl Cl C C Cl + 2RSK Cl 17 16 DMF SR Cl C C Cl SR 18 H O / AcOH 2 2 SO R 2 Cl C C Cl SO R 2 19 Where R = p-CH C H and (CH ) C 3 6 4 3 3 Flynn and his co-workers30 reported that 1,1-dichloroethylene (20) when treated with thiols (21) under mild conditions, gave trans-1-chloro-2-alkyl- or aryl-mercapto ethylenes (23). This is evidently not the product of elimination-addition which would be cis-isomer of (23) (by trans addition). W. E. Truce et al.31 have suggested an addition-elimination mechanism by the isolation of the addition product (22). Under more vigorous conditions, both (22) and (23) are converted into cis-1,2-bis (alkyl- or arylmercapto) ethylene (25) by an elimination-addition mechanism. Almost the exclusive formation of (23) rather than its cis-isomer is as a result of the greater stability of the trans-form and the transition state leading towards it43. 8 H Cl Base Base RS H R SH R S CH2-C H Cl2 -HCl RSC CH H Cl -HCl H Cl RSH 20 21 22 23 24 Base H H RS SR 25 Where R = p-CH C H and (CH ) C 3 6 4 3 3 It is reported that, nucleophilic displacement of halogens with thiols, also takes place in the case of vinyl type of halides, to give cis-1,2-bis (arylmercapto) ethylenes. Truce et al.31 obtained cis-1,2-bis (p-tolylmercapto) ethylene (29) from both cis- and trans-1-chloro-2-p- tolylmercaptoethylene (26, 27) and p-thiocresol. Similarly, both cis- and trans-1-chloro-2- phenylmercaptoethylenes with thiophenol gave only cis- 1,2-bis (phenylmercapto) ethylene44 and cis- and trans-1-chloro-2-t-butylmercaptoethylene with t-butylmercaptan gave cis-1,2-bis (t-butylmercapto) ethylene. The fact that, both starting materials which are geometrically isomeric gave one and the same product, suggest that they must be reacting via a common intermediate. An elimination-addition mechanism was proposed. RS Cl RSH H H OEt Fast 26 RS SR RSH RSC CH H H OEt RS H 28 RSH 29 H Cl OEt Slow 27 Where R = C H , p-CH C H and (CH ) C 6 5 3 6 4 3 3 9 It is assumed that both cis- and trans-1-chloro-2-alkyl- or arylmercapto-ethylenes (26 and 27) gave alkyl or aryl mercaptoacetylene (28) by elimination of HCl, which by the trans addition of thiols gives rise to the desired product (29). In agreement with this assumption is the fact that alkyl or arylmercapto acetylenes themselves react with thiols to give cis-1,2-bis (alkyl- or aryl-mercapto) ethylene30,31. In 1969, Calo et al.44 reported that unlike the 1-chloro-2-alkyl- or aryl- mercaptoethylenes (26 and 27), the β-halovinyl arylsulphones, ArSO CH=CHX (30 and 31) 2 react with various thiols with total retention of configuration. This is exemplified by the preparation of cis-1-phenylthio-2-arylsulphonylethylenes45, (ArSO CH=CHSC H ) (34) from 2 6 5 cis-1-chloro-2-arylsulphonylethylene, (ArSO CH=CHCl) (30) and thiophenol and trans-1- 2 phenylthio-2-arylsulphonylethylene, (ArSO CH=CHSC H ) (37) from trans-1-chloro-2- 2 6 5 arylsulphonylethylene, (ArSO CH=CHCl) (31) and thiophenol, where Ar = p-CH C H ; p- 2 3 6 4 ClC H and p-O NC H . A possible path explaining retention is shown below. The group 6 4 2 6 4 C H SӨ adds to the olefinic system and ClӨ departs before the intermediate carbanions (32 6 5 and 35) have had time to rotate about the central bonds. The fact that the carbanions shown are propably tetrahedral is likely to be of little consequence, in as much as the two tetrahedral forms of the carbanion are rapidly interconverted by molecular rotation. The resultant sulphide-sulphone (34 and 37) on oxidation gave the corresponding disulphones. 10 H H SO Ar SO2Ar SO2Ar SO Ar 2 2 Fast PhS H + SPh PhS - Cl H H PhS Cl H Cl H Cl H 30 32 33 34 Slow SO Ar 2 H H ArO S H H 2 + SPh PhS Fast PhS - Cl SO2Ar H SO2Ar PhS Cl H Cl H Cl H 31 35 36 37 Nucleophilic substitution in vinyl halides displacement mechanism. It was observed that the addition of thiophenol to p-tolylsulphonylacetylene and p- nitrophenylsulphonylacetylene yielded cis-1-phenylthio-2-p-tolylsulphonylethylene and cis- 1-phenylthio-2-p-nitrophenylsulphonylethylene49 respectively. It is also reported48 that the nucleophilic addition of thiols to ethylsulphonylacetylene in presence of trion B yielded mainly cis-1-ethylsulphonyl-2-alkylthioethylenes. Peeran et al.35 obtained trans-1,2-bis (phenylthio) stilbene from benzoin and excess of thiophenol in the presence of pulverized zinc chloride and HCl gas. Following a similar procedure, Lakshmi Devi51 prepared about six pairs of trans-1,2-bis (alkylthio and arylthio) stilbenes and their corresponding disulphones. Crombie52, in his review on ‘geometrical isomerism about carbon-carbon double bonds’ has dealt extensively with the various methods of preparing geometrical isomers and their physical and chemical properties.