Episulfides formation

Benzenediazonium fluoroborate, 2-carboxy-xanthone synthesis from, 3, 838 Benzenediazonium ions phenyl azide formation from, 5, 839 Benzenediazonium salts, o-(imidazol-l-yl)-intramolecular diazo coupling, 5, 404 Benzene-1,2-disulfonimides N-substituted reactions, 6, 930 Benzene episulfide formation, 7, 577 Benzeneimine... 

Enzymatic hydrolysis exposes the sulfide, which undergoes episulfide formation releasing the phosphate. This method was developed for... 

The deaoetylation of viNual hydroxy-thiethyl aoetate (XV), the isomeric S aoetyl compound (XVI), and the diaoetate (XVII) yield ethylene sulfide when treated with diiiiti-alkali (Eq. 13). 

The S( D) atoms in the X = 2490 A. photolysis of COS in the presence of ethylene produces ethylene episulfide (ES) and vinyl mercaptan (VM) as the principal products. For this system the rates of product formation are given in Table V. The following features of the reaction should be noted (a) CO fonnation gradually decreases with increasing olefin pressure to a value nearly half of that obtained from pure COS (6) the rates of both vinyl mercaptan and episulfide formation rise with pressure to a flat maximum (c) the rate ratio (Rvu/R s) attains a limiting... 

On these bases, the steps shown in eqs. (28)-(29) merit consideration for the primary interaction. Step (28a) is 85 kcal./mole exothermic and steps (28c) and (28d) would also be about equally exothermic. The exo-thermicity of episulfide formation via triplet atom addition, step (30), is only 60 kcal/mole. 

The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

In the oxidative Eschenmoser sulfide contraction (Scheme 11), thioamide 59 is oxidized by benzoyl peroxide to give either a symmetrical disulfide or the O-benzoate of the thiolactam-S-oxide. In any event, the once-nucleophilic thioamide sulfur atom is now forced to adopt the role of electrophile a reactivity umpolung has, in effect, been achieved.13 The nucleophilic enamide 65 attacks the sulfur atom leading to the formation of sulfur-bridged intermediate 66. The action of a phosphine or a phosphite thiophile on the putative episulfide then gives vinylogous amidine 67. 

Copolymerization is a facile method to diversify the structure of polymer materials. However, if the polymerizabiHties of comonomers are far from each other, copolymerization is essentially difficult, resulting in the formation of a mixture of the homopolymers and/or the copolymer with block sequences. This is the case for the anionic copolymerization of epoxide and episulfide, where the po-lymerizabihty of episulfide is much higher than that of epoxide, and the copolymer consisting mostly of -S-C-C-S- and -O-C-C-O- homo sequences is formed [87]. As mentioned in the previous sections, the zinc complex of /-methylpor-phyrin brings about polymerization of both epoxide and episulfide. 

The desulfurative C-C bond formation process developed by Eschenmoser [217] is somewhat akin to the Ramberg-Backlund rearrangement. An episulfide intermediate is formed, which on being attacked by a phosphine, begets a carbon skeleton with polarity alternating sequence. 

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