Sulphoxides—

Sulphoxides L Large numbers of sulphoxides have been 

This band was found to be not only very intense but also remarkably constant in position in dilute solution. Thus both cyc/ohexylmethylsulphoxide and phenylmethylsulphoxide absorb strongly at 1055 cm in dilute solution in carbon tetrachloride, and even in unsaturated materials such as diallyl sulphoxide (1047 cm ) the frequency is not diminished. This is due to the fact that the n clouds of any attached double bonds do not lie in the same plane as those of the S=0 link so that conjugation does not occur. The frequency then depends only on the inductive properties of the substituents, so that in some cases aromatic substitution leads to a small frequency rise [51]. 

The sulphoxide bond is therefore readily identifiable in both the infra-red and Raman by the presence of a strong band in the 1050 cm region, and Cymmerman and Willis [12] have used the 

S=0 Groups attached to other elements. The S=0 frequency is determined wholly by the inductive effects of the substituents and these are related to their effective electronegativities. Probably the most useful measure of these is the tt values derived by Thomas in relation to the P=0 vibration which is also solely determined by these factors. If therefore one considers compounds with two identical substituents the values of others with mixed substituents can be derived with reasonable accuracy. 

The thionyl halides range from 1308 cm for thionyl fluoride, through 1233 for thionyl chloride [52] to 1121 cm for the bromide [85]. Nitrogen substitution also raises s=o as there is no resonance. Sulphinamides have been studied by Smith and Wu [86], by Keat et al. [87] and by Steudel [84]. With A -alkyl groups on both sides of the sulphur atom the frequency is close to 1120 cm , but lower values are found for structures such as R—NHSO—R (1060—1037 cm ) [86]. In these the bands are usually doubled which may indicate dimerisation as in the amides. Two sulphur atoms attached to the S=0 group give frequencies close to 1105 cm-i. 

Garlic is used for a variety of reasons, and some of the attributes associated with it, e.g. for cancer prevention, or to reduce heart attacks, may not be substantiated. Other properties such as antimicrobial activity, effects on lipid metabolism, and platelet aggregation inhibitory action have been demonstrated. Ajoene has been shown to be a potent antithrombotic agent through inhibition of platelet aggregation. 

Lancini GC and Lorenzetti R (1993) Biotechnology of Antibiotics and Other Microbial Metabolites. Plenum, New York. 

Lancini G, Parenti F and Gallo GG (1995) Antibiotics - A Multidisciplinary Approach. Plenum, New York. 

Niccolai D, Tarsi L and Thomas RJ (1997) The renewed challenge of antibacterial chemotherapy. Chem Com-mun 2333-2342. 

Russell AD (1998) Mechanisms of bacterial resistance to antibiotics and biocides. Prog Med Chem 35, 133-197. 

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DMF, Me2NC(0)H. Dimethyl formamide. DMSO, Mc2SO. Dimethyl sulphoxide. 

Once the presence of a sulphonate group has been estabhshed (and, if possible, the phenol isolated), the compound may be characterised by the preparation of a derivative. It must be remembered that both sulphoxides RSOR and sulpJiones RSOjR yield sulphur dioxide on fusion with caustic alkali and acidification. 

The following classes of sulphur compounds occur in Solubility Groups II, III and VII sulphonic acids and derivatives, ArSO,OR sulphinic acids and derivatives, ArSOOR mercaptans, RSH thiophenols, ArSH sulphides or thioethers, RSR disulphides, RSSR sulphoxides, RR S->0 ... 

Sulphinic acids. Aromatic sulphinic acids are found in Solubility Group II. They may be detected by dissolving in cold concentrated sulphuric acid and adding one drop of phenetole or anisole when a blue colour is produced (Smiles s test), due to the formation of a para-substituted aromatic sulphoxide. Thus the reaction with benzenesulphinic acid is ... 

Sulphoxides. These are usually solids of low m.p. They may be oxidised in glacial acetic acid solution by potassium permanganate to the corresponding sulphones, and reduced to the sulphides by boiling with tin or zinc and hydro chloric acid. 

In hexadeuteriodimethyl sulphoxide the compound which is labelled as 3-methyl-pyrazolone gives NMR spectra 16. In what form is this compound present in this solution ... 

Crystallisable polymers have also been prepared from diphenylol compounds containing sulphur or oxygen atoms or both between the aromatic rings. Of these the polycarbonates from di-(4-hydroxyphenyl)ether and from di-(4-hydroxy-phenyl)sulphide crystallise sufficiently to form opaque products. Both materials are insoluble in the usual solvents. The diphenyl sulphide polymer also has excellent resistance to hydrolysing agents and very low water absorption. Schnell" quotes a water absorption of only 0.09% for a sample at 90% relative humidity and 250°C. Both the sulphide and ether polymers have melting ranges of about 220-240°C. The di-(4-hydroxyphenyl)sulphoxide and the di-(4-hydroxy-phenyl)sulphone yield hydrolysable polymers but whereas the polymer from the former is soluble in common solvents the latter is insoluble. 

The laboratory preparation of the Udel-type polymer has been described. Bis-phenol A is mixed with chlorobenzene (solvent) and dimethyl sulphoxide (active solvent) and heated to 60°C to obtain a clear solution. Air is displaced from the system by nitrogen or argon and an aqueous solution of caustic soda added. This results in a two-phase system, one predominantly chlorobenzene the... 

The condensation reaction is promoted by certain polar solvents and of the many which have been tested dimethyl sulphoxide appears to be the most effective. As usual with linear condensation polymers molecular equivalence and near-absence of monofunctional material is necessary to ensure a high molecular weight. Moisture and alcohols can also have a devastating effect on the molecular weight. In the case of water it is believed that 4-chlorophenyl 4-hydroxyphenyl sulphone is formed which functions as an effective chain terminator. Gross contamination with air is also believed to reduce the maximum attainable molecular weight as well as causing intense discolouration. 

Alkyl sulphoxides occur widely in small concentrations in plant and animal tissues. No gaseous sulphoxides are known and they tend to be colourless, odourless, relatively unstable solids soluble in water, ethyl alcohol and ether. They are freely basic, and with acids form salts of the type (R2S0H) X. Because sulphoxides are highly polar their boiling points are high. Their main use is as solvents for polymerization, spinning, extractions, base-catalysed chemical reactions and for pesticides. 

The corrosion of tin by nitric acid and its inhibition by n-alkylamines has been reportedThe action of perchloric acid on tin has been studied " and sulphuric acid corrosion inhibition by aniline, pyridine and their derivatives as well as sulphones, sulphoxides and sulphides described. Attack of tin by oxalic, citric and tartaric acids was found to be under the anodic control of the Sn salts in solution in oxygen free conditions . In a study of tin contaminated by up to 1200 ppm Sb, it was demonstrated that the modified surface chemistry catalysed the hydrogen evolution reaction in deaerated citric acid solution. 

N— compounds used as acid inhibitors include heterocyclic bases, such as pyridine, quinoline and various amines. Carassiti describes the inhibitive action of decylamine and quinoline, as well as phenylthiourea and dibenzyl-sulphoxides for the protection of stainless steels in hydrochloric acid pickling. Hudson e/a/. refer to coal tar base fractions for inhibition in sulphuric and hydrochloric acid solutions. Good results are reported with 0-25 vol. Vo of distilled quinoline bases with addition of 0 05m sodium chloride in 4n sulphuric acid at 93°C. The sodium chloride is acting synergistically, e.g. 0-05m NaCl raises the percentage inhibition given by 0-1% quinoline in 2n H2SO4 from 43 to 79%. Similarly, potassium iodide improves the action of phenylthiourea . 

Direct measurements on metals such as iron, nickel and stainless steel have shown that adsorption occurs from acid solutions of inhibitors such as iodide ions, carbon monoxide and organic compounds such as amines , thioureas , sulphoxides , sulphidesand mer-captans. These studies have shown that the efficiency of inhibition (expressed as the relative reduction in corrosion rate) can be qualitatively related to the amount of adsorbed inhibitor on the metal surface. However, no detailed quantitative correlation has yet been achieved between these parameters. There is some evidence that adsorption of inhibitor species at low surface coverage d (for complete surface coverage 0=1) may be more effective in producing inhibition than adsorption at high surface coverage. In particular, the adsorption of polyvinyl pyridine on iron in hydrochloric acid at 0 < 0 -1 monolayer has been found to produce an 80% reduction in corrosion rate . 

Reaction of adsorbed inhibitors In some cases, the adsorbed corrosion inhibitor may react, usually by electro-chemical reduction, to form a product which may also be inhibitive. Inhibition due to the added substance has been termed primary inhibition and that due to the reaction product secondary inhibition " . In such cases, the inhibitive efficiency may increase or decrease with time according to whether the secondary inhibition is more or less effective than the primary inhibition. Some examples of inhibitors which react to give secondary inhibition are the following. Sulphoxides can be reduced to sulphides, which are more efficient inhibitorsQuaternary phosphonium and arsonium compounds can be reduced to the corresponding phosphine or arsine compounds, with little change in inhibitive efficiency . Acetylene compounds can undergo reduction followed by polymerisation to form a multimolecular protective film . Thioureas can be reduced to produce HS ions, which may act as stimulators of... 

Sulphide and sulphoxide complexes have been extensively studied since cis-RuC12(DMSO)4 (DMSO, dimethyl sulphoxide, (Me)2SO) was found to have anti-tumour properties and to be a precessor for radiosensitizing agents. Such complexes can act as catalysts for the oxidation of sulphides with molecular oxygen. 

Apart from DMSO complexes, others including those with tetramethylene sulphoxide have been increasingly examined, but the account here focuses on DMSO. 

Ruthenium(III) sulphoxide complexes were less well authenticated until recently [111] some syntheses are found in Figure 1.41. 

Again both S- and O-bonded sulphoxides are found. mer-[RuCl3(Ph2SO)3] has one S-bonded sulphoxide and two O-bonded sulphoxides (one trans to Cl, one trans to S) [112], The imidazole-substituted complexes are being studied as possible radiosensitizers and for anti-tumour activity. 

Carbonyl derivatives of ruthenium sulphoxide complexes have been made [113]. 

RuCl3(DMSO)3 reacts with sulphides to form mixed sulphide/sulphoxide complexes that are catalysts for oxidation of thioethers to sulphoxides [114a] ... 

Complexes of O-donors are relatively rare, explicable by the soft nature of the divalent ions. A telling indication is that sulphoxide ligands will only bind through O if steric effects make S-bonding impractical. The most important complexes are diketonates and carboxylates (for the aqua ions see section 3.5). 

An ambidentate ligand has the choice of using two different types of donor atom. Two that have been extensively studied in their bonding to platinum and palladium are sulphoxides and thiocyanate. 

Steric crowding increases as bigger alkyl groups are introduced so that [Pt[(Me2CHCH2CH2)2S0]4](C104)2 has only O-bonded sulphoxides (IR). IR spectra can be used to distinguish between S- and O-bonded sulphoxide ... 

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