Bull. SOC. Chim. Belg. vo1.87/n04/1978

STUDIES ON ORGANOPHOSPHORUS COMPOUNDS XXIV. * THE FORMATION OF DISULFIDES FROM SULFOXIDES

J.B.RASMUSSEN, K.A.JBRGENSEN and S.-0.LAWESSON

Department of Organic Chemistry, Chemical Institute University of Aarhus, 8000 Aarhus C

DENMARK

Received 11/4 /78 - Accepted 19/4 /78

ABSTRACT - The reaction of DMSO with the dimer of p-methoxyphenylthionophos- phine sulfide, 1, produces dimethyl disulfide and causes partly deoxygenation of DMSO to give dimethyl sulfide. P 4 S l o and DMSO give dimethyl disulfide in lower yield, a result not observed in recent The cyclic sulfox- ide, tetrahydrothiophene sulfoxide, 2 , also reacted with 1 to give the cyc- lic disulfide, l,Z-dithiane, 2 .

Sulfur compounds seem to become of utmost importance in organic synthe- sis, and the removal of oxygen from a sulfoxide by deoxygenation' is an im- portant reaction. In connection with our work on the new thiation reagent 1,

we have found that ketones,= amides,3 esters,4 and thiolesters4 are easily transformed into the corresponding thiocarbonyl compounds. It was also found that 1 or P,Sl0, when reacted with sulfoxides, produces the corresponding sulfide and disulfides. Two recent reports6Ie prompt us to report our preli- minary findings.

The dimer 1 does react quite violently with DMSO, being complete within 5 minutes when the reaction temperature is kept at 30-35 "C. After immediate work-up of the reaction mixture by distillation, both dimethyl sulfide and dimethyl disulfide are isolated and characterized (see experimental section). From GLC the yield of dimethyl sulfide was found to be quantitative (95-lOOqb) while that of dimethyl disu1fi.de was estimated (by three experiments) to be 43-48 4 6 ) . When P,S1, was used instead of 1, dimethyl disulfide was isolated in less than 10 '$ yield. A l s o in this reaction it was important to isolate the products immediately after reaction; otherwise not a trace amount of di- methyl disulfide would be found. Other non-cyclic sulfoxides have been react-

*Part XXIII. S.SCHEIBYE, B.S.PEDERSEN and S.-O.LAWESSON, Bull. OC. him.Belg. ( 1 9 7 8 )

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ed with ' or P,S,, giving the same results.

Tetrahydrothiophene sulfoxide gives ring-enlargement upon reaction with - 1. The products were characterized by comparison with authentic samples (see

experimental section).

Q + ' - CJ n + f-J+SB

2 2 - EXPERIMENTAL

lH NMR spectra were recorded at 60 MHz on a Varian A-60 spectrometer and 13C NMR spectra were recorded at 2 0 MHz on a Varian CFT-20 spectrometer. TMS was used as internal reference and chemical shifts are expressed in 6-values. CDCL, was used as solvent. IR spectra were recorded on a Beckmann IR-18 and 180 Perkin-Elmer/spectrometer. MS were recorded on a Micromass 7070 F mass spectrometer operating at 70 eV, using a direct inlet. Silica gel 60 (Merck) was used for column chromatography. Mp.s and bp.s are uncorrected.

Compound 1 was prepared as reported." The reaction between 1 and DMSO. 1 (0 .028 mole) was added in small portions

and with stirring to 20-mL of DMSO T0.28 mole). A violent reaction was noted. After about 4-5 min, the reaction mixture was distilled and fractions up to bp.140 "C were collected. GLC (10 '$ PEG 4000) showed that a quantitative yield of dimethyl sulfide (based on the assumption that three out of four sulfurs were exchanged3) and 43-48 $ of dimethyl disulfide (based on several experi- ments) were formed. Dimethyl sulfide was characterized by GLC and NMR and al- s o as the 2(CH3),S - 3 HgCL, complex; mp. 154 "C (lit.' 150-151 " C ) . Dimethyl disulfide was purified by distillation and shown to be identical in all re- spects with an authentic sample (MS, NMR, .;"= 1.5250, lit. nio= 1.5259). The reaction between P,s, and DMSO. As described above, P,S,, (0.02 mole)

was added to DMSO (0.7 mole7 and after the exothermic reaction had ceased ( 2 - 3 min), the reaction products were distilled off and collected. Besides dime- thy1 sulfide, dimethyl disulfide was isolated in 6-8 '$ yield (based on three experiments) and characterized as above. The reaction between 1 and tetrahydrothiophene sulfoxide. 1.04 g. (0.01mole)

of tetrahydrothiophene sulfoxide was dissolved in 20 ma on anhydrous benzene at r o o m temp. and 4.8 g (0.012 mole) of was added with stirring. The tempe- rature increased to 25 "C and the reaction mixture was then kept at 70 "C with stirring for 2 h. Silica gel was added to bind the acidic P,S-residues andto diminish polymerization of the cyclic disulfide. Most of the solvent was then stripped off. GLC (5 '$ SE 30, silized DMCS) showed the same retention timeas that of authentic 1,Z-dithiane.' The MS showed the following peaks (120 (M') 87 86 84 79 78 73 64 60 59 55 (bate peak) 54 53 47 46 44 41 39) identicalwith the MS of authentic 1,2-dithiane. IR (CS,) showed absorption at 520 cm-',ty- pica1 for disulfides (500-525 cm-l). In one experiment, when a large excess of tetrahydrothiophene sulfoxide was used, it was possible to precipitate 1,2- dithiane as white crystals (mp.33 " C ) , free from polymers, and identical (mp. MS, NMR, IR) with authentic and sublimed 1,Z-dithiane (from G.Claeson). In both experiments tetrahydrothiophene and S, were characterized by TLC and MS, respectively. Acknowledgement - Thanks are expressed to Dr.G.Claeson, AB Kabi, Gothenburg, Sweden, for a sample of 1,2-dithiane.

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