Benzyl xanthate

The first syntheses of 1,2-cfs-thioglycoses (a-D-gluco- and )3-D-manno- derivatives) have been achieved by the reaction in acetone of alkyl or benzyl xanthate or potassium thioacetate with the corresponding l,2-tra s-glycosyl halides [13]. More recently, tetra-O-acetyl-l-S-acetyl-l-thio-a-D-glucopyranose (10a) (Scheme 3) has been obtained i) by reaction of -acetochloroglucose (9 a) with either potassium thioacetate in HMPA or the tetrabutylammonium salt of thio-acetic acid in toluene [14] ii) by peroxide-induced addition of thioacetic acid to the pseudo-glucal (11) [15]. 

Reaction of methyldiphenylphosphine with the benzyl xanthate complexes [M(S2COCH2Ph)2] (M = Pd, Pt) in chloroform yields the dithiocarbonato complexes (43). The platinum complex (43 M = Pt) undergoes a variety of reactions in chloroform solution, e.g. treatment with HC1 yields m-[(Ph2MeP)2PtCl2].149... 

In the thiohydroxamate method, activated acceptors are required for successful addition reactions because the thiohydroxamate is relatively reactive towards alkyl radicals. An ingenious method to circumvent this problem has recently been communicated by Zard.160 Photolysis of benzyl xanthate (40) with a UV lamp in the presence of N-methylmaleimide (NMM) provided the adduct (41) in 40% yield, as illustrated in Scheme 50. In this reaction, the competition reaction between the desired addition to the acceptor and the addition to the precursor still exists. However, addition to the precursor is reversible and,... 

M. Sakata, M. Haga, and S. Tejima, Synthesis and reactions of glycosyl methyl- and benzyl xanthates. A facile synthesis of 1-thioglycosides, Carbohydr. Res., 13 (1970) 379-390. 

Zn benzyl xanthate (C6H5CH20CSS)2Zn Zn n-butyl xanthate (C4H90CSS)2Zn Zn n-amyl xanthate (C5HnOCSS)2Zn... 

Floatability obtained when benzyl xanthate is used as collector is analogous to that of butyl xanthate, However, the conjugated system is larger in C6H4-CH=CH-CH20CSSNa than in CeHs. Comparison of thiophenols with various structures is listed in Table 5.14. 

The modification of cellulose with alkaline carbon disulfide to introduce xanthate groups has been extensively exploited in the industrial production of viscose. Early work on the preparation and properties of starch xanthate has been discussed. Xanthate derivatives of cellulose and starch have been discussed with respect to general xanthate chemistry, and the xanthation of cellulose in homogeneous medium is known to be a second-order reaction. Cellulose xanthate shows some potential as a matrix for enzyme insolubilization, " and stable derivatives of this xanthate may be prepared by transesterification. Thermal decomposition of cellulose allyl- and benzyl-xanthates gives 5,6-cellulosene. Some thiocarbonyl derivatives of polysaccharides have been prepared. "... 

Benzyl xanthate Butyl xanthate Cinnamyl xanthate (-amyl xanthate Benzyl xanthate Butyl xanthate Cinnamyl xanthate i-amyl xanthate... 

The first reported synthesis of peracetylated 1-thio-a-D-glucopyranose started from the Brigl s anhydride [9] but traditionally, 1,2-cw-thioglycoses have been generated from the 1,2-tranj-glycosyl halides by reaction of alkyl or benzyl xanthates in acetone [13], potassium thioacetate in hexamethylphosphoramide (HMPA) [14], or the tetrabutylammonium salt of thioacetic acid in toluene [15] (Scheme 1). A recent alternative is the peroxide-induced addition of thioacetic acid to hydroxy-glucal derivatives [16]. 

When exposed to ait, the sodium salts tend to take up moisture and form dihydrates. The alkah metal xanthates are soluble ia water, alcohols, the lower ketones, pyridine, and acetonitrile. They are not particularly soluble ia nonpolar solvents, eg, ether or ligroin. The solubiUties of a number of these salts are Hsted ia Table 4. Potassium isopropyl xanthate is soluble ia acetone to ca 6 wt %, whereas the corresponding methyl, ethyl, / -propyl, n-huty isobutyl, isoamyl, and benzyl [2720-79-8] xanthates are soluble to more than 10 wt % (12). The solubiUties of the commercially available xanthates ia water are plotted versus temperature ia Figure 1 (14). 

Esters derived from the primary alcohols are the most stable and those derived from the tertiary alcohols are the least stable. The decomposition temperature is lower in polar solvents, eg, dimethyl sulfoxide (DMSO), with decomposition occurring at 20°C for esters derived from the tertiary alcohols (38). Esters of benzyl xanthic acid yield stilbenes on heating, and those from neopentyl alcohols thermally rearrange to the corresponding dithiol esters (39,40). The dialkyl xanthate esters catalytically rearrange to the dithiol esters with conventional Lewis acids or trifluoroacetic acid (41,42). The esters are also catalytically rearranged to the dithiolesters by pyridine Ai-oxide catalysts (43) ... 

Certain, Y, Y-dialkyl dithioearbamates [e,g. benzyl A)/V-diethyl dithiocarbamate (14)] and xanthates have been used as photoinitiators. Photodissociation of the C-S bond of these compounds yields a reactive alkyl radical (to initiate polymerization) and a less reactive sulfur-centered radical (to undergo primary-radical termination) as shown in Scheme 9.9.30 41 4 ... 

The processes described in this section should be contrasted with RAFT polymerization (Section 9.5.3), which can involve the use of similar thioearbonylthio compounds. A. A -dialkyl dithiocarbamates have very low transfer constants in polymerizations of S and (mctb)acrylatcs and arc not effective in RAFT polymerization of these monomers. However, /V,A -dialkyl dithiocarbamates have been successfully used in RAFT polymerization of VAc. Certain O-alkyl xanthates have been successfully used to control RAFT polymerizations of VAc, acrylates and S. The failure of the earlier experiments using these reagents and monomers to provide narrow molecular weight distributions by a RAFT mechanism can he attributed to the use of non-ideal reaction conditions and reagent choice. A two part photo-initiator system comprising a mixture of a benzyl dithiocarhamate and a dithiuram disulfide has also been described and provides better control (narrower molecular weight distributions).43... 

Transformation of 2-deoxysugar derivatives into glycosyl xanthates can be performed by the treatment of O-benzyl-protected hemiacetal derivative with diphe-nylphosphoryl chloride, followed by the reaction with O-ethyl potassium xanthate in the presence of a base (NaOH, PTC reaction or NaH in appropriate organic solvent). High yields and selectivities in such reactions were observed when using sodium hydride in anhydrous THF [401],... 

Methyl 6-0-(3-0-Acetyl-2-Azido-4,6-0-Benzylidene-2-Deoxy-a- and 3-D-Galactopyrano-syl)-2,3,4-Tri-0-Benzyl-a-D-Galactopyranoside (110) A solution of xanthate 108 (1.2 mmol), glycosyl acceptor 11 (372 mg, 0.8 mmol) and activated 4-A powdered... 

Xanthate 169 with oxaziridine 33 gave -benzyl 0-isopropyl carbonothioate 172 and iJ-benzyl 0-isopropyl carbono(dithioperoxoate) 173 in a ratio of 93 7 <1997J(P1)2019>. The reaction is believed to go through sulfur oxidation to give sulfine intermediate 170 that rearranges to an oxathiirane 171 intermediate (Scheme 5). 

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