Cyclic Sulphonium Research Articles

Extractive Desulphurization of Model Oil Using Sulphonium Based Ionic Liquids

Synthesis of a novel class of cyclic sulphonium based ionic liquids was performed. The ionic liquids were characterized using 1H NMR spectroscopy, FTIR spectroscopy and CHNS elemental analysis. The physicochemical properties of the ionic liquids such as density viscosity and thermal decomposition temperature of the synthesized ionic liquids were determined. The potential of these ionic liquids for the extractive desulphurization of model oil was investigated.

Efficient Clustering of Cyclic Sulphonium Salts Applying Liquid Secondary Ion Mass Spectrometry

Salt-like cluster ions of the ([cation](n)[anion](n-1))(+) type are commonly composed of mono-atomic, inorganic components. Clusters containing organic ions are also known, with nitrogen-centred cations being particularly prominent. However, sulphur-centred analogues, such as organic sulphonium salts, represent a notable exception. Fast atom bombardment and liquid secondary ion mass spectrometry of such compounds show, in general, a low tendency towards the formation of clusters. The present study reveals that sputtering of cyclic sulphonium salts leads to the efficient formation of cluster ions beyond previous observations. Cluster ions are characterised by isotopic pattern analysis and collision-induced dissociation.

One-electron reduction of sulphonium salts in aqueous solution: a pulse radiolysis study

Absolute rate constants have been measured for the reduction of 1-alkylthiolanium (1a–c), 1-alkylthianium (2a–e), 1-(n-carboxyalkyl)thiolanium (3a,b) and 1–(n-carboxyalkyl)thianium (4a,b) salts, and ω-dimethylsulphonioalkanoic acids (5a,b), including biologically active S-methyl-methionine (6) and dimethyl-β-propiothetin (5b), by hydrated electrons in aqueous solutions using the pulse radiolysis method. This reaction was found to occur very rapidly (k in the range 109–1010 dm3 mol–1 s–1), the individual rate constants being dependent on the electron inductive power of the substituents on the positive sulphur centre. The sulphuranyl radical R3S˙, a possible reaction intermediate, could not be detected within the 0.1 µs time resolution of the applied technique. No reaction was observed between S-methylmethionine and CO2˙– or Me2ĊOH under experimental conditions. The one-electron reduction potential of this sulphonium salt has been estimated to be < –1.8 V. C-centred radicals produced upon the reduction of the cyclic sulphonium salts 1-methyl- and 1-ethylthiolanium and 1-methylthianium salts by e–aq were characterized by using p-benzoquinone as a radical scavenger. It was found that ring opening is the predominant process rather than the cleavage of methyl or ethyl radicals.

Preparation, spectroscopic and cyclic voltammetric studies of poly(1,4-naphthalene vinylene) prepared from a cycloalkylene sulphonium salt precursor polymer

Films of poly(1,4-naphthalene vinylene) (P-1,4-NV) were obtained by the thermal elimination of a cycloalkylene sulphonium salt precursor polymer. The ultra-violet/visible (u.v./vis.), fluorescence and Raman spectra and the small-angle X-ray scattering diagrams were examined, and the oxidation and reduction potentials of P-1,4-NV were determined by cyclic voltammetry. The u.v./vis. spectra of P-1,4-NV films made from a sulphonium salt polymer based on the cyclic sulphide, tetrahydrothiophene, which was converted to P-1,4-NV at a temperature about 30°C lower than the temperature needed to obtain P-1,4-NV from the dimethylsulphide sulphonium salt polymer, showed phonon sidebands at room temperature as well as at −200°C. The phonon sidebands were apparently associated with a narrow distribution of crystallite sizes, which had an average long-period spacing of 140Å, and was obtained when P-1,4-NV was made from the cyclic sulphonium chloride precursor polymer. The oxidation potential was found to be 0.75 V vs. SCE (saturated calomel electrode), the reduction potential was found to be −1.60V vs. SCE and the band-gap energy was found to be around 2.05V. The high value for the oxidation potential of P-1,4-NV, in comparison to the oxidation potential of triiodide (0.52V vs. SCE), from which an approximate value of 2 × 10 −8 for the oxidation equilibrium constant was obtained, explains why very low conductivities are obtained when P-1,4-NV is doped with iodine. Films of the cycloalkylene sulphonium salt precursor polymer could be drawn to as much as 1.6 times their original length, and the drawn films showed a significant degree of orientation according to X-ray diffraction and polarized infra-red spectroscopy.

Rhodium carbenoid mediated cyclisations. Part 5. Synthesis and rearrangement of cyclic sulphonium ylides preparation of 6- and 7-membered sulphur heterocycles

Treatment of diazo mercaptans with rhodium(ll) acetate gives six- and seven-membered sulphur heterocycles; diazo sulphides give cyclic sulphonium ylides, which are isolable, or rearrange, depending on the nature of the substituent on sulphur.

MECHANISTIC ASPECTS OF CYCLIC SULPHONIUM SALT FORMATION AND HYDROLYSIS OF 1,n-HALO(ALKYLTHIO) ALKANES

Abstract Cyclization rate constants for various 1,n-halo(alkylthio)alkanes X[sbnd](CH2) n [sbnd]S[sbnd]R with n=4 and n=5 were determined in CH3CN, CH2CI2, C6H14, CDCI3 and H2O/CH3CN (9:1) at T=25°C. The rate of formation of the five- and six-membered cyclic sulphonium salts depends on the halogen atom (I>Br>Cl), the number of methylene groups between sulphur and halogen (n=4>n=5), on the alkyl group R and on the solvent. In aqueous CH3CN hydrolysis becomes competetive. The hydrolysis rate constants of several 1,n-halo(alkylthio)alkanes with n>3 were determined in water at T=25 and 60°C and compared to those of some alkyl halides and the mustard derivative 1-chloro-2-methylthioethane. Hydrolysis of the chloro compounds is slower than of the bromo and iodo analogoues and depends on the number of methylene groups (n) between halogen and sulphur.

Conducting salts of cyclic sulphonium cations with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ): X-ray crystal structure of 1-methyl-1,4-dithianium TCNQ salt, (MDT)1 +(TCNQ)2 ?

Cyclic sulphonium cations (1)–(3) form 1 : 2 salts with TCNQ which are organic conductors at room temperature (σr.t. 1 × 10–3–2.0 S cm–1); the X-ray crystal structure of 1-methyl-1,4-dithianium TCNQ salt (MDT)1+(TCNQ)2–(1) has been determined.

Rhodium carbenoid mediated cyclisations. Synthesis and rearrangement of cyclic sulphonium ylides

Treatment of diazo sulphides with rhodium (II) acetate in benzenegives six- and seven-membered cyclic sulphonium ylides; although the S-benzyl and S-ethyl ylides can be isolated, they rearrange, or eliminate ethylene respectively, on heating; the S-allyl ylides cannot be isolated since they undergo spontaneous [2,3]-sigmatropic rearrangement.

Separation of Sulphonium Salts by Ion Chromatography: Five- and Six-Membered Cyclic Sulphonium Salts

Abstract Several cyclic 5-and 6-membered sulphonium compounds were separated by ion pair chromatography on a opti-dbb ion pair column. The salts show specific retention behavior when using different mixtures of acetonitrile and aqueous sodium perchlorate solutions as eluents. The increase of retention times with extending chain length of the alkyl group R and with ring size is due to an increase of the solute molecular surface areas which were also calculated. The obtained retention parameters give additional information for structural determination.

5-Thiopyranoses. Part 8. Sulphur participation in displacement reactions of sulphonate esters of 5-thio-D-ribose and 5-thio-D-xylose derivatives

The 4-methanesulphonate group of 1,2-O-isopropylidene-3,4-di-O-methylsulphonyl-5-thio-α-D-xylopyranose (3) is displaced by intramolecular attack by sulphur leading to a cyclic episulphonium ion (22) which then reacts with nucleophiles to give ring contracted 4-thio-β-L-arabinofuranose products (4) and (13)–(17) and, in some cases, products (18) and (19) with retained 5-thio-α-D-xylopyranose stereochemistry. Similar reactions with methyl 2,3(3,4)-O-isopropylidene-4(2)-O-methylsulphonyl-5-thio-D-ribopyranosides (24) and (29) also proceed via episulphonium ions (25) and (30) leading to products of retained stereochemistry such as methyl 4-O-benzoyl-2,3-O-isopropylidene-5-thio-β-D-ribopyranoside (26) or of ring contraction e.g., 2,5-dideoxy-2,5-epithio-3,4-O-isopropylidene-D-arabinose dimethyl acetal (32) respectively. The trans-acetal containing methyl 2,3-O-isopropylidene-4-O-methylsulphonyl-5-thio-α-D-xylopyranoside (36) fails to undergo reaction under the same conditions, presumably because of its inability to form the cyclic sulphonium ion (37).

13C13C vicinal coupling constants of sulphonium cations

AbstractThe 13C13C vicinal coupling constants of cyclic sulphonium cations, with the labelled carbon bound to the positively charged sulphur atom, cannotbe related to the dihedral angle ϕ by a Karplus type correlation.

Electron spin resonance studies. Part 60. Detection of radicalcations from vinyl sulphides: evidence for a cyclic structure

Radical-cations have been detected during the oxidation of RSCHCH2(R = Et, Pri) with Cl2˙– or, ˙OH at low pH; e.s.r. parameters indicate that these possess a cyclic sulphonium structure ˙[graphic ommitted]R. Their formation from the hydroxy-adducts may involve anchimeric assistance from the sulphur atom.

Coplanar vs. orthogonal bimolecular substitution at a benzylic carbon

Bimolecular substitution at the benzylic centre in dibenzylethylsulphonium fluoroborate (8) with thiocyanate anion is 8000 times faster than the corresponding reaction in the cyclic sulphonium fluoroborate (4) in which the attacking and leaving groups must remain in approximately the plane of the benzene ring thereby precluding conjugation in the transition state; it is estimated that a ca. thousand-fold increase in rate is attributable to conjugation in unconstrained benzylic substitution.

Competition between oxazolium and sulphonium salt formation in the acid-induced interaction of 2-diazoacetophenones with diaryl sulphides in acetonitrile

Diphenyl sulphide and dibenzothiophen react with 2-diazoacetophenone (1a) and trifluoromethanesulphonic acid in dichloromethane to provide the corresponding phenacylsulphonium salts (3a) and (3c), respectively. Under similar conditions, 4-(diazoacetyl)dibenzothiophen (1c) gives the trifluoromethanesulphonate ester (4c) and not the cyclic sulphonium salt (3f). Interaction of diazoacetophenone (1a) and trifluoromethanesulphonic acid in acetonitrile yields 2-methyl-3-phenacyl-5-phenyloxazolium trifluoromethanesulphonate (7a) by phenacylation of the initially formed 2-methyl-5-phenyloxazole (6a); 4-(diazoacetyl)dibenzothiophen (1c) behaves analogously. 2-Diazoacetophenone (1a), trifluoromethanesulphonic acid, and benzonitrile afford 2,5-diphenyloxazole (6b) which does not undergo phenacylation. Both phenacyl-diphenylsulphonium (3a) and -dibenzothiophenium (3d) salts readily transfer their phenacyl groups to the nitrogen of 2-methyl-5-phenyloxazole (6a).

Novel aspects in the reaction of 2-diazo-2′-(phenylthio)acetophenone with arenesulphenyl chlorides: formation of α-ketoaldehyde thioacetal chlorides via cyclic sulphonium α-(arylthio)phenacylides

Under conditions where 2-diazoacetophenone and benzenesulphenyl chloride provide 2-chloro-2-(phenylthio)-acetophenone, 2-diazo-2′-(phenylthio)acetophenone (1a) with 2-nitro- and 2,4-dinitro-benzenesulphenyl chlorides gives, after treatment with water, 2-(2-nitrophenylthio)- and 2-(2,4-dinitrophenylthio)-3-oxo-1-phenylbenzo[b]thiophenium-2-ides (4b and c) respectively. The structure of these ylides was established by independent syntheses from 3-oxo-1-phenylbenzo[b]thiophenium-2-ide (4a) and the appropriate arenesulphenyl chloride in the presence of triethylamine. In contrast, two molecular proportions of benzenesulphenyl chloride were required to liberate the diazo nitrogen from the phenylthio-diazoketone (1a) when there resulted hydrogen chloride and 2-chloro-2,2,2′-tris(phenylthio)acetophenone (5a). The latter was also prepared from benzenesulphenyl chloride and 3-oxo-1-phenyl-2-(phenylthio)benzo[b]thiophenium-2-ide (4d), which was readily synthesised by condensation of the unsubstituted ylide (4a) with N-(phenylthio)phthalimide in the presence of triethylamine. 2-Chloro-2,2-bis(phenylthio)acetophenones have apparently not been reported previously; evidence in support of such a structure was obtained by hydrolysis, with boiling water, of 2-chloro-2,2,2′-tris(phenylthio)acetophenone (5a) to hydrogen chloride, benzenethiol and S-phenyl [2-(phenylthio)phenyl]thioglyoxylate (8a).

The S-alkylation of sulphides by an activated carbohydrate epimine under acidic catalysis: the formation of α-acetamido-sulphides. Part 2. Reactions with cyclic sulphides and with sulphides bearing an additional nucleophilic sulphur substituent

Methyl 2,3,4-tri-O-acetyl-6,7-acetyleimino-6,7,8-trideoxy-1-thio-D-erythro-α-D-galacto-octopyranoside (1) reacts with cyclic sulphides in the presence of acetic acid to give 7(S)-(ω-acetoxyalkyl)thioamides via attack by acetate ion on the intermediate cyclic sulphonium salts. The co-formation of the 7(S)-{[3-(3-acetoxypropyl)-thio]propyl}thio-derivative (8) from the reaction with thietan demonstrated that collapse of the cyclic sulphonium salt could be occasioned by nucleophilic attack by a sulphide sulphur atom also.αω-Bis(methylthio)alkanes yield monosulphonium salts which collapse to the 7(S)-methylthio-derivative (11) by neighbouring group participation of the sulphide sulphur atom; this participation is inefficient with a 1,3-disubstituted alkane. With ω-(alkylthio)alkanethiols, the efficiency of participation of the thiol sulphur atom again controls the manner of collapse of the intermediate sulphonium salt. With these sulphide–thiol reagents, the co-formation of [(ω-alkylthio)alkyl]thio-derivatives is unexpected.

The 1H and 13C nmr spectra of the “onium” salts of dithiacyclophanes

AbstractThe 1H and 13C nmr spectra of three cyclic sulphonium salts ol dithiacyclophanes have been recorded and compared with those of the open‐chain analogue. The 1H spectra indicate that methylation of the dithiacyclophanes gives a mixture of eonformational isorners with slightly different chemical shifts for the benzylic protons. The 13C spectra indicate that the smaller rings adopt an unsymmetrical conformation with respect to the aromatic ring but that in the larger ring studied, the aromatic carbon atoms are magnetically equivalent. The relevance of these results to the reactivity of the aromatic ring is discussed.

Studies in organic mass spectrometry. XXIII‐Evidence for the occurrence of cyclic sulphonium ions in the gas phase

AbstractFunctional group interaction occurs in the loss of a phenoxy radical from the molecular ions of ω‐phenylthio alkylphenylethers ØO(CH2)nSØ (n = 2–6). Labelling data provide evidence for the S‐phenyl thietanium, S‐phenyl tetrahydrothiophenium and S‐phenyl tetrahydrothiopyranium structures of the decomposing (lifetimes between 10−6 and 10−5 s) [M ‐ ØO]+ ions in the case of n = 3, 4 and 5, respectively.

Cyclic oligomers in the cationic polymerization of cis- and trans-2,3-dimethylthiirane

Under the influence of triethyloxonium tetrafluoroborate in methylene chloride, cis- and trans-2,3-dimethylthiirane are transformed to their corresponding polymers almost instantaneously (at temperatures between 0 and 20 °) but within a few hours these polymers completely degrade to form a mixture of low molecular weight substances. The cis-monomer leads to a mixture of cyclic tetramer, cis-butene and two geometric isomers of 3,4,6,7-tetramethyl-1,2,5-trithiepane. By 1H-NMR it was shown that these two isomers are the trans-cis-trans and the trans-trans-trans forms. The trans-monomer leads to a mixture of trans-butene and 3,4,6,7-tetramethyl-1,2,5-trithiepane which is present as a mixture of the cis-cis-cis and the cis-trans-cis isomers. In both cases, the butene and the trithiepanes were formed in equimolar quantities. The formation of these oligomers is explained by assuming that polymerization occurs via an SN2 propagation reaction between the three-membered cyclic sulphonium ion (the active species) and monomer, followed by a degradation reaction occurring via a back-biting mechanism.

Elimination–addition. Part XXI. Addition–dealkylation reactions of acetylenic sulphonium salts with oxygen, sulphur, and nitrogen nucleophiles

Reactions of nucleophiles with dimethylprop-2-ynylsulphonium and S-prop-2-ynyltetrahydrothiophenium bromides have been investigated. These salts readily isomerise to the allenic isomers ([graphic omitted]·C:C:C), which are susceptible to nucleophilic addition. The initially formed adducts, according to their structure, undergo several types of subsequent reaction. Most commonly, isomerisation of the initial non-conjugated adduct to the conjugated isomer is either followed by addition of a second nucleophile or the nucleophile dealkylates the sulphonium group by attack at carbon adjacent to sulphur. In the case of the cyclic sulphonium salt, dealkylation results in ring cleavage and formation of open-chain sulphides.