Mercaptide ion

The reaction with sodium sulfite or bisulfite (5,11) to yield sodium-P-sulfopropionamide [19298-89-6] (C3H7N04S-Na) is very useful since it can be used as a scavenger for acrylamide monomer. The reaction proceeds very rapidly even at room temperature, and the product has low toxicity. Reactions with phosphines and phosphine oxides have been studied (12), and the products are potentially useful because of thek fire retardant properties. Reactions with sulfide and dithiocarbamates proceed readily but have no appHcations (5). However, the reaction with mercaptide ions has been used for analytical purposes (13)). Water reacts with the amide group (5) to form hydrolysis products, and other hydroxy compounds, such as alcohols and phenols, react readily to form ether compounds. Primary aUphatic alcohols are the most reactive and the reactions are compHcated by partial hydrolysis of the amide groups by any water present. 

An important aspect of this is the splitting of the polymer chain with thiol (eq. 5) or mercaptide ion (thiol + base catalyst). In fact, sodium sulfide or organic monothiols, eg, mercaptoethanol or decyhnercaptan, are utilized to lower the molecular weight of polysulftdes or to limit the extent of curing reactions. 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Certain functional groups may be protected from reduction by conversion to anions that resist reduction. Such anions include the alkoxides of allylic and benzylic alcohols, phenoxide ions, mercaptide ions, acetylide ions, ketone carbanions, and carboxylate ions. Except for the carboxylate, phenoxide, and mercaptide ions, these anions are sufficiently basic to be proton-ated by an alcohol, so they are useful for protective purposes only in the... 

Perfluoronaphthalene undergoes an intermolecular substitution followed by intramolecular cyclLzation on reaction with allyl bromide and mercaptide ion to furnish a dihydrothiophene denvative in high yield [34] (equation 23). 

Friedman, M., Cavins, I.F., and Wall, l.S. Relative nucleophilic reactivities of amino groups and mercaptide ions in addition reactions with a.p-unsaturated compounds, J. Am. Chem. Soc., 87(16) 3672-3682,1965. 

Ewens and Gibson (29) reported an early observation on the reaction of the coordinated sulfur atom as a nucleophile (Equation 36), showing the conversion of the mercaptide ion to a thioether function within the coordination sphere. 

In a similar environment, the opisulfide reaction (Kq, 3 ) is not readily terminated by solvent, but instead, a polyethylene sulfide (LXII) is formed. This is understandable when one notes that although the mercaptide ion is a weaker base than the alkoxide ion, it Is a ttim-h stronger nucleophile. Thus the alkoxide ions are depleted in the forma tion of mercaptide ions, and the newly generated mercaptide ions react... 

In 1959, the coordinated mercaptide ion in the gold(III) complex (4) was found to undergo rapid alkylation with methyl iodide and ethyl bromide (e.g. equation 3).9 The reaction has since been used to great effect particularly in nickel(II) (3-mercaptoamine complexes.10,11 It has been demonstrated by kinetic studies that alkylation occurs without dissociation of the sulfur atom from nickel. The binuclear nickel complex (5) underwent stepwise alkylation with methyl iodide, benzyl bromide and substituted benzyl chlorides in second order reactions (equation 4). Bridging sulfur atoms were unreactive, as would be expected. Relative rate data were consistent with SN2 attack of sulfur at the saturated carbon atoms of the alkyl halide. The mononuclear complex (6) yielded octahedral complexes on alkylation (equation 5), but the reaction was complicated by the independent reversible formation of the trinuclear complex (7). Further reactions of this type have been used to form new chelate rings (see Section 7.4.3.1). 

The hydrolysis step is then followed by oxidation of the mercaptide ion to disulfide and the sulfonate ion to sulfonate. Murray and Rayner (42) obtained the following mechanisms for the reaction of DMDS (1.0g/l) in 0.1N NaOH solution at 100 C ... 

Dissolved oxygen rapidly oxidizes simple thiols, through a mercaptide ion intermediate, to disulfides, in the presence of traces of certain metallic... 

Halomercaptans are converted to thietanes by treatment with a as exemplified by the formation of 3-hydroxythietane 21 from 3-chloro-l-mercapto-2-propanol 20 4-thiocyano-2-pentanol 22 is converted to a mixture of cis- and trans-2,4-dimethylthietane 23 by treatment with sodium hydride. The latter reaction involves displacement of cyanate ion by the mercaptide ion. 2,2,4-Trimethylthietane was also prepared by this method. 

Creighton and Owen generated the mercaptide ion by treatment of an (S-acetyl group with base, in the conversions of the thiolacetates (266), (269), and (271) into their respective episulfides (267), (270), and (273). 

The formation of a quaternary salt (7) upon heating 2,3-0-isopropylidene-5-0-(p-tolylsulfonyl)adenosine, observed by Clark, Todd, and Zussman and referred to elsewhere in this review, accounts for the low yield, since this monomolecular quaterni-zation takes place much more rapidly than bimolecular displacement of the p-tolyl-sulfonyloxy group by the methyl mercaptide ion. Recently, this difficulty has been overcome and a good yield of L-2-amino-4-(5-thioaden-5-yl)butyric acid obtained by the reaction of (9b) with the disodium salt of homocysteine in liquid ammonia. This compound had also been prepared enzymically. ... 

The epoxide-mercaptan reaction can be accelerated by amines, which either react with the mercaptan to give a mercaptide ion (Reaction 28) that rapidly adds to the epoxide (Reaction 29), or by the amine first reacting with the epoxide (Reaction 31) to produce a reactive intermediate that then reacts with the mercaptan in a nucleophilic displacement reaction (Reaction 32). 

The attack of the acid (154) on the readily polarizable 1,2-dithiafulvene (155) corresponds to the extremely ready addition of electrophilic reagents to the simple and vinylogous heptafulvene derivatives, which are iso-n-electronic with 155. The opening of the dithiole rings in 156 and 158 under the pressure of the carbanionoid electron pair liberated by the proton abstraction and of the free electron pair on the sulfur, as well as the elimination of elementary sulfur and the intramolecular electrophilic attack of the mercaptide ion (157) on the 5-position to form 158, are simply the typical reactions of 1,2-dithioles that have already been discussed (Section II, B, 3). The reactivity of the 3-methyl group in 154 finds many parallels in the ease of condensation of the methyl-substituted pyridinium, pyrylium, thiopyrylium, and tropylium salts, and particularly... 

Since the S-H bond is only slightly polarized and heterolysis to a proton and a mercaptide ion is thus difficult,19 the addition to olefins is preferably carried out by a radical route induced by benzoyl peroxide12 by irradiation with UV light.13 Alkanethiols and thiophenols can be added under the influence of basic catalysts to strongly polar double bonds such as those in unsaturated carbonyl compounds, nitriles, and carboxylic acids, the C-S bond then being formed to the cationic / -carbon atom ... 

Nucleophilic attack of phosphite on the easily polarizable disulfide linkage displaces a mercaptide ion which is alkylated in a valency expansion of phosphorus to produce a thioether (50,125,143,218,257) ... 

Acyl and aroyl disulfides react by a somewhat different route. Both acetyl disulfide (225) and benzoyl disulfide (125) react exothermically with triethyl phosphite at room temperature to produce 0,0,0-triethyl phosphorothioate and the acyl or aroyl sulfide. This result suggests that the acyl-sulfur linkage in the phosphonium intermediate is more susceptible to cleavage by mercaptide ion than is the alkyl-oxygen bond. 

This reaction actually proceeds through two steps, each a nucleophilic displacement reaction by mercaptide ion on the symmetrical disulfide (I in Equation B), and then on the mixed disulfide (V in Equation C). 

All cleavages of simple disulfides by mercaptans that have been studied kinetically are bimolecular ionic reactions of the SN 2 type, involving direct displacement by mercaptide ion on disulfide [20]. Because the active species in this disulfide scission process is the mercaptide ion [21] rather than the unionized mercaptan, pH is a critical factor. As a consequence, pH can determine the rate-controlling step in the reductive cleavage of cystinyl residues in keratin fibers by mercaptans. For example, in the reaction of wool fiber with dithiothreitol, Weigmann [22] has shown that the ratecontrolling step at pH 7.0 and above is diffusion of the reducing species into... 

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