Carbonate linkage

Polycarbonate is a polyester in which dihydric (or polyhydric) phenols are joined through carbonate linkages. The general-purpose type of polycarbonate is based on 2,2-bis(4 -hydroxybenzene)propane (bisphenol A) and has the general structure ... 

Halogenation. Halogens and halogen acids add readily to the unsaturated carbon linkages of the cyclopentadiene molecule. By such additions a series of halogenated derivatives range, in the case of the chloride, from 3-chlotocydopentene to tetrachlorocyclopentane. Of all the possible chloto derivatives of CPD, only hexachlorocyclopentadiene [77-47-4] ever reached commercial status. It was used as an insecticide, but this use has been discontinued because of its toxicity (see Chlorocarbons and chlorohydrocarbons, toxic aromatics). It can be prepared by a Hquid phase chlorination of CPD below 50°C (29). 

A convenient method of compositional designation uses molar percentages of ester and carbonate linkages coupled with the molar percentages of iso- and terephthalate units in the polymer. A 70% ester, 30% carbonate polyester carbonate with 60 parts of isophthalate and 40 parts of terephthalate is designated 70(60/40)30. Similarly, a standard PC resin is 0(0/0)100, and a polyarjlate resin composed of a 1 1 molar ratio of iso- to terephthalate units esterfied with bisphenol A is designated 100(50/50)0. 

Diyne 66, which possesses a three carbon linkage between the alkynes, also reacts with aldehyde 67 in presence of [Ni(COD)J/SIPr catalytic system (Scheme 5.19). However, the connectivity of the dienone 69 obtained from this diyne was different from those obtained from diyne 60. In the former case, adduct 69 was obtained from a )5-hydride elimination of the nickelacycle 68 instead of a reductive elimination. 

More recently, a C02-soluble chromium(III)-porphyrin catalyst, (344), has been reported to initiate the copolymerization of C02 with CHO.980 Carbonate linkages of >90% are observed and Mw/Mn values are consistently low (1.1-1.4). Complex (344) is highly active, producing 3,900 g polymer/g [Cr] over 18 hours even higher activities have been achieved by supporting the catalyst on polymer beads.981... 

With a concise route to enantiopure 49 identified, Merlic was able to effect desymmetrization by controlled methanolysis to access calphostins B (4b) and C (4c) (Scheme 7.10). The carbonate linkage of calphostin C was installed via reaction of the free alcohol with phosgene and 4-acetoxyphenol, thus completing the first synthesis of calphostin C in 16 steps. 

A nitrogen to carbon linkage is exemplified by the formation of dichloro-1,2,4-thiadiazole (27) from phosphorus tricyanide and sulfur dichloride.32... 

Several syntheses of furans are based upon the use of acetylenes to form carbon-carbon linkages. Of two that employ palladium catalysts,7172 one is outlined in Scheme 11,71 A simpler approach is to treat a 1,3-diketone with... 

Pilcher, G. Thermochemistry of organometallic compounds containing metal-carbon linkages. MTP Review of Science. Series 2. Physical chemistry, Vol. 10. Chapter 2. 1975, p. 45 Cox, J. D., Pilcher, G. Thermochemistry of organic and organometallic compounds. London Academic Press 1970... 

Keywords H-P addition Unsaturated carbon linkage Transition metal complex Homogeneous catalysis... 

Fig. 30. Carbon-carbon linkage of vp ligands in ruthenium complexes...

The term, complex tannin, appears to be established as descriptor for the class of polyphenols in which a flavan-3-ol unit, representing a constituent unit of the condensed tannins (proanthocyanidins), is connected to a hydrolyzable (gallo-or ellagi-) tannin through a carbon-carbon linkage. Since the first demonstration of their natural occurrence, a considerable number of these unique secondary metabolites have been reported. " New additions (Table 11.17) to this series of compounds come exclusively from the groups of Nonaka and Nishioka, and Okuda and Yoshida in Japan. 

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