Disulfides aliphatic, oxidation

Under aprotic conditions, prototropic transformations of thiols are relatively slow, so one can observe distinct waves of the oxidation of the protonated form and of its parent base [19, 20]. Normally, the oxidation of thiols (aliphatic, aromatic, and heteroaromatic) affords diorganyl-disulfides. So various aliphatic and aromatic thiols are easily converted into the corresponding disulfides upon oxidation in MeOH/MeONa with the yields ranging... 

Miscellaneous. Reagent prepared by the Syntex procedure has been used to oxidize pyridine methanols to the corresponding aldehydes, mercaptans to disulfides, aliphatic a-ketols to a-diketones, and N-phenylhydroxylamine to nitrosobenzene. A suspension of the dioxide in an ethereal solution of the substrate was stirred vigorously for 5-6 hrs. and the oxide was removed, and washed with ether. The filtrate and washings were concentrated under reduced pressure and the product isolated by distillation or crystallization. 

Polythiosemicarbazide disulfide is the most efficient aliphatic polyamine disulfide for inhibiting the thermal oxidative breakdown of polypropylene, while polyimi-noaniline disulfide and polydiiminodiphenyloxide disulfide (Fig. 3) are the most efficient aromatic polyamine disulfides. In contrast to polyethylene, the thermal oxidative breakdown period increases as the concentration increases (Fig. 4), Depending on the concentration, the flow-melt index at 230°C increases at a lower rate than in the case of commercial stabilizer Santanox (Table 2)-... 

In an earlier experiment, Jori et al. (14) reported that methionyl residues are important in maintaining the tertiary structure of lysozyme. The introduction of a polar center into the aliphatic side chain of methionine, as a consequence of the conversion of the thioether function to the sulfoxide, may bring about a structural change of the lysozyme molecule which, in turn, reduces the catalytic efficiency. When ozonized lysozyme was treated with 2-mercaptoethanol in an aqueous solution according to the procedure of Jori e al. (14), the enzyme did not show any increase in its activity. This may be explained in two ways. In one, such reactions are complicated by many side reactions, e.g. sulfhydryl-disulfide interchange, aggregation and precipitation of the modified enzyme (24-26). In the other, the failure to recover the activity of the enzyme may by associated with the extensive oxidation of other residues. 

This study indicates that the sulfur of our sulfide samples was susceptible to bacterial attack in two of the three cases. The aliphatic sulfides could be ranked in the order of their ease of oxidation as di-ferf-butyl polysulfide > di-fert-butyl disulfide > di-tert-butyl sulfide. 

A-Phenyltriazolinedione is an efficient and chemoselective reagent for the oxidation of thiols to their corresponding symmetrical disulfides. The method is applicable to aromatic, aliphatic, and bifunctional thiols and excellent yields are obtained. A two-step mechanism (Scheme 6) has been proposed.109... 

Note Confirmed human carcinogen Nonpolar, aromatic solvent sweet odor very flammable and toxic confirmed human carcinogen soluble in alcohols, hydrocarbons (aliphatic and aromatic), ether, chloroform, carbon tetrachloride, carbon disulfide, slightly soluble in water incompatible with some strong acids and oxidants, chlorine trifluoride (zinc in the presence of steam) decomposes at high temperature to form biphenyl. Synonyms cyclohexatriene, benzin, benzol, phenylhydride. These are the most common, although these are many other synonyms. 

A third method of access to sulfines is the oxidation of thiocarbonyl compounds. When the starting material is available it is an attractive route. There has been some dispute in the past whether enethiolisable thiocarbonyl derivatives would lead to the corresponding sulfines or to divinyl disulfides [101, 102]. It is now clear from our research that, even if the C=S molecules bear highly acidic a-protons, oxidation occurs on C=S and does not touch the a-protons. There are many examples of this behaviour. The most easily enethiolised compounds are thioketones. We have shown that their reaction with a peroxycarboxylic acid, mCPBA, is very fast at 0°C and quantitatively provides the corresponding sulfines [103]. In many examples the aliphatic sulfines are not very stable and have to be used in subsequent reactions that will be faster than their decomposition (t1/2 from some hours to days). 

Alkyl sulfides and thiols. Some alkyl thiols and sulfides, notably those from commonly ingested Allium sativum (garlic) and Allium cepa (onion) (Alliaceae), are variously bioactive as odorants and antimicrobials. Propanethial S-oxide (CH3-CH2-CH=S=0) is a lachrymatory irritant principle of onion. Allicin (S-oxodiallydisulfide CH2=CH—CH2-SO-S-CH2— CH=CH2), diallyldisulfide (CH2=CH-CH2-S-S-CH2-CH=CH2) and diallylsulfide (CH2=CH—CH2—S—CH2-CH=CH2) are major odorants of garlic that are reactive and irritant because of the allyl groups. Dimethyl disulfide (CH3—S—S-CH3), dipropyl disulfide (CH3-CH2-CH2-S-S-CH2-CH2-CH3), methyl allyl disulfide (CH3-S-S-CH2-CH=CH2) and propane-1-thiol (CH3-CH2—CH2—SH) are further Allium odorants. Methane thiol (methyl mercaptan CH3—SH) is a widespread plant volatile and notably derives from anaerobic bacterial degradation of cysteine as in human flatus and bad mouth odour. The aliphatic disulfides allicin and ajoene inhibit proinflammatory expression of iNOS. 

It has been observed that PCC will rapidily dimerize aromatic, but not aliphatic, thiols to their corresponding disulfides in good yield (Table 8, entry S). Sulfides may undergo oxidation to give sulfones (Table 8, entry 10). ... 

The tetraalkylammonium chromates prepared by Gelbard and coworkers a q)eared to be equally effective for all types of alcohols, but under the conditions of Santaniello et al., tetra-n-butylammonium chlorochromate was found to be a selective benzylic and allylic oxidant. It also efficiently converts aliphatic and aromatic thiols to disulfides. Trimethylammonium chlorochromate has also bera reported for the oxidation of allylic alcohols in DMF. ... 

The oxidadon of thiols to disulfides by molecular oxygen or air is believed to proceed via two routes as shown in Scheme 3. Thus, the reaction may be enhanced under basic conditions but more stable anions react at a slower rate, while aliphatic thiols are oxidized faster than aromatic ones. 7... 

Oxidation. Triphenylbismuth carbonate suspended in CH2CI2 is a heterogeneous oxidant for a variety of functional groups. Allylic alcohols are efficiently oxidized to the corresponding unsaturated aldehydes or ketones, even in the presence of a thiol, which is itself oxidized by this reagent to a disulfide, cis- and Irani-1,2-Glycols are cleaved to dialdehydes hydrazones are oxidized to diazocompounds oximes are cleaved to ketones and 1,2-dialkylhydrazines are oxidized to azo compounds. Phenylhydrazones, semicarbazones, tosylhydrazones, aromatic and aliphatic amines, enamines, and enol ethers are inert to 1. 

More recently, the oxidation of aliphatic disulfides could be modulated (one-electron or two-electron process) according to the applied potential [295,296] and has afforded (Scheme 64) a convenient synthesis of amides. 

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