Mercaptide synthesis

Stabilizer Synthesis. The selected alkyltin chloiide intermediate reacts with either a carboxyhc acid or a mercaptan in the presence of an appropriate base, such as sodium hydroxide, to yield the alkyltin carboxylate or alkyltin mercaptide heat stabihzet. Alternatively, the alkyltin chloride can react with the base to yield the alkyltin oxide, which may or may not be isolated, for subsequent condensation with the selected carboxyhc acid or mercaptan. 

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). 

Halothiophenes, which are not activated through the presence of —I—M-substituents, undergo substitution smoothly under more forcing conditions with copper salts in pyridine or quinoline. Hence 3-cyanothiophene and 5-methyl-2-cyanothiophene have been obtained from the corresponding bromo compounds. 2-Bromothiophene reacts readily with aliphatic cuprous mercaptides in quinoline at 200°C to give thioethers in high yields. The use of the copper-catalyzed Williamson synthesis of alkoxythiophenes from iodo- or bromo-thiophenes and alcoholate has been mentioned before. The reaction of 2-bromothiophene with acetanilide in nitrobenzene in... 

Perfluorohalogenoorganosulfenyl halides are, like thiols, mercaptides, and thioketones, key compounds for the synthesis of new perfluorohalo-genoorganomercapto derivatives. The high reactivity of the S—X bond (X = Cl, Br) toward electrophilic as well as nucleophilic reagents causes them to be highly valued starting materials for the synthesis of new derivatives. The chemistry of the not very stable sulfenyl fluorides has... 

The synthesis of a large number of metal complexes of mercaptoamines by Busch and coworkers (6, 15, 17, 24) has opened the way for detailed study of the reactions of the coordinated mercaptide function. Mercaptoamine complexes provide the first extensive series of complexes of known structure in which the effect of varying structural parameters on the reactivity of the mercaptide group can be subjected to investigation. 

Lippard et al. have reported on the synthesis and structural characterization of the Fe2(SR)2(S2CSR)4 (162) and Co2(SR)2(S2CSR)4 (405, 409) complexes (see also Sections II.C.8a and II.C.8b). In these complexes the Fe2S2 and Co2S2 planar units contain mercaptide bridges. 

Formation of a symmetrical sulphide (a) (e.g. dipropyl sulphide, Expt 5.204), is conveniently effected by boiling an alkyl halide (the source of carbocations) with sodium sulphide in ethanolic solution. Mixed sulphides (b) are prepared by alkylation of a thiolate salt (a mercaptide) with an alkyl halide (cf. Williamson s ether synthesis, Section 5.6.2, p. 583). In the case of an alkyl aryl sulphide (R-S Ar) where the aromatic ring contains activating nitro groups (see Section 6.5.3, p. 900), the aryl halide is used with the alkyl thiolate salt. The alternative alkylation of a substituted thiophenol is described in Section 8.3.4, p. 1160. The former procedure is illustrated by the preparation of isobutyl 2,4-dinitrophenyl sulphide (Expt 5.205) from l-chloro-2,4-dinitrobenzene and 2-methylpropane-1-thiol. 

Early syntheses of SeMet were tedious, non-stereospecific or limited to small-scale preparations. Klosterman and Painter (1947), for example, first reacted 5-((3-bromoethyI)- hydantoin with benzyl selenol to yield y-benzylselenoho-mocysteine. The latter was converted to the sodium salt of DL-selenohomo-cysteine with sodium in liquid ammonia, and reacted with methyl iodide to yield DL-SeMet. Plieninger (1950) obtained DL-SeMet by the reaction of sodium selenomethyl mercaptide with a-amino-y-butyrolactone in an inert solvent at 170°C. A synthesis of DL-SeMet from acrolein was also described (Zdansky, 1968). The first stereospecific synthesis of L-SeMet via esters of tosylated homoserine was reported by Pande et al. (1970). 

A synthesis of XIV was accomplished as follows (9) /J-carboline-1-carboxylic acid chloride was condensed with the magnesium ethoxy derivative of malonic ester to yield, after acid hydrolysis, 4-hydroxy-canthin-6-one (XV). This compound, with phosphorous oxychloride followed by heating in a sealed tube with potassium methyl mercaptide, gave the alkaloid XIV. If 4-hydroxycanthin-6-one is condensed with phosphorous oxychloride-phosphorous pentachloride, 4,5-dichlorocan-thin-6-one and 4-hydroxy-5-chlorocanthin-6-one are formed. 

The addncts derived from carbodiimides and nncleophiles also undergo thermal elimination reactions to regenerate the carbodiimide, and they are therefore of limited preparative value. For example, the elimination of hydrogen chloride from carbonimidoyl dichlorides is used in the synthesis of arenesulfonylcarbodiimides (see Section 9.2.2). Of course, isoureas and isothioureas also undergo elimination reactions. When the elimination of isothioureas is conducted in the presence of heavy metal ions, the insoluble metal mercaptides are precipitated to facilitate the in situ generation of the carbodiimides. 

Figure 4.87 Synthesis of a mercaptide functionalised NHC palladium(ll) complex by insertion of palladium into a C-S bond of levamisolium triflate.

Figure 4.89 Synthesis of a mercaptide functionalised NHC ligand in the coordination sphere of nickel (II).

The reduction of a carboxyl group to an aldehyde group can be effected by a reductive desulfurization of the thiol ester with Raney nickel. The thiol esters are prepared by the reaction of the acyl chloride with an excess of ethyl mercaptan in pyridine or by reaction with lead mercaptide in dry ether. The hydrogenolysis is then carried out by refluxing an ethanol ic solution of the thiol ester with Raney nickel for 6 hours. By this new synthesis, propionaldehyde and benzaldehyde have been prepared in 73% and 62% yields, respectively. ... 

This type of reaction was reported for tris(2-methoxyethyl)aminei and for the tetraamine tris(2-diethylaminoethyl)amine (Etetren). The latter was also obtained by alkylation of A, A-diethylethylenediamine with (C2H5)2NCH2CH2-Cl. 7 The corresponding methyl derivative tris(2-dimethylaminoethyl)amine (Mestren) was prepared by methylation of tris(2-aminoethyl)amine (tren). Similarly, methylation of tris(2-thiolethyl)amine was used to prepare tris(2-methylthioethyl)amine (D = SCHs). The method reported here (Sec. C) seems more efficient, in that it avoids the intermediate synthesis of N(CH2CH2-SH)a and is based on the reaction above with NaSCHs the sodium methyl-mercaptide is either prepared in advance or in situ by the reaction of CH3SH with NaOCHa. 

Mercapto or methylthio nitrogen heterocycles are either obtained by direct treatment of hydroxy-nitrogen heterocycles with reagents such as phosphorus pentasulfide or Lawesson reagent (78BSB223 79T2433), or by treatment of activated intermediates such as chloro-nitrogen heterocycles with mercaptide anions as well as by total synthesis. 

The Chemistry of Ring A.—Two methods have been described for smoothly hydrolysing the highly-hindered axial C-4 methyl esters such as methyl 0-methyl podocarpate. The first uses boron trichloride in methylene chloride, and the otherlithium n-propyl mercaptide in hexamethylphosphoramide. The oxidative decarboxylation of dehydroabietic acid and 0-methyl podocarpic acid affords a mixture of C-4 olefins which are separable over 10 % silver nitrate by t.l.c. Thus in a partial synthesis of callitrisic acid, the 4(19)-epoxide prepared... 

A partial synthesis of this metabolite has also been reported by Buehi and Wo-gan84, proceeding to the optically active natural product (18) by means of demethyla-tion (lithium alkyl mercaptides) of natural aflatoxin Bt (i) in good yield. 

In order to realize the synthesis of ( )-isozonarol (86), the ketone (82) was treated with excess methyllithium in ether. The resulting alcohol on dehydration with dimethyl sulfoxide followed by chromatographic purification over 15% silver nitrate on silica gel afforded ( ) isozonarol dimethyl ether (85). Its demethylation with lithium n-butyl mercaptide in hexamethylphosphoric triamide furnished ( )-isozonarol (86). 

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