Cyclic carbon

Cp = weight per cent of paraffinic carbon % = weight per cent of cyclic carbon... 

The cyclic carbonate of benzoin (4,5-diphenyl-l,3-dioxol-2-one, prepared from benzoin and phosgene) blocks both hydrogen atoms of primary amines after dehydration acid stable, easily crystallizable Sheehan oxazolinones are formed, which are also called Ox derivatives. The amine is quantitatively deblocked by catalytic hydrogenation in the presence of 1 equiv. of aqueous acid (J.C Sheehan, 1972, 1973 M.J. Miller, 1983). An intelligent application to syntheses of acid labile -lactams is given in the previous section (p. 161). 

Propargylic alcohol, after lithiation, reacts with CO2 to generate the lithium carbonate 243, which undergoes oxypalladation. The reaction of allyl chloride yields the cyclic carbonate 244 and PdC. By this reaction hydroxy and allyl groups are introduced into the triple bond to give the o-allyl ketone 245[129]. Also the formation of 248 from the keto alkyne 246 with CO2 via in situ formation of the carbonate 247 is catalyzed by Pd(0)[130]. 

Formation of Cyclic Carbonates. In the absence of water, chlorohydrins such as 2-chloroethanol and l-chloro-2-propanol react with an alkah carbonate or bicarbonate to produce cycHc carbonates such as ethylene carbonate [96-49-1] and propylene carbonate [108-32-7] ia yields of up to 80%... 

Treatment of cyclic carbonates of 1,2-diols with thiocyanate ion at temperatures of 100 °C or higher yields thiiranes (Scheme 145) (66CRV297, 75RCR138). Thiourea cannot replace thiocyanate satisfactorily, and yields decrease as the carbonate becomes more sterically hindered. The reaction mechanism is similar to the reaction of oxiranes with thiocyanate (Scheme 139). As Scheme 145 shows, chiral thiiranes can be derived from chiral 1,2-diols (77T999, 75MI50600). 

Acetates, benzoates, and cyclic carbonates are stable to these hydrolysis conditions. [Cyclic carbonates are cleaved by more alkaline conditions (e.., dil. NaOH, 20°, 5 min, or aq. Pyr, warm, 15 min, 100% yield).] ... 

Cyclic carbonates and cyclic boronates have also found considerable use as protective groups. In contrast to most acetals and ketals the carbonates are cleaved with strong base and sterically unencumbered boronates are readily cleaved by water. 

Cyclic carbonates are veiy stable to acidic hydrolysis (AcOH, HBr, and H2SO4/ MeOH) and are more stable to basic hydrolysis than esters. 

Cyclic carbonates have been used to a limited extent only (since they are readily hydrolyzed) to protect the catechol group in a polyhydroxy benzene. 

The cyclic carbonate is easily cleaved by refluxing in water for 30 min. It can be converted to the 1,2-dimethoxybenzene derivative (aq. NaOH, Me2S04, reflux, 3 h). ... 

Polycarbonates were first prepared by Einhom in 1898 by reacting the dihydroxybenzenes, hydroquinone and resorcinol, separately with phosgene in solution in pyridine. The hydroquinone polycarbonate was an infusible and insoluble crystalline power whereas the resorcinol polymer was an amorphous material melting at about 200°C. The third dihydroxybenzene, catechol, yields a cyclic carbonate only, which is not surprising bearing in mind the proximity of... 

Cyclic carbonates are prepared directly from epoxides with LiBr, CO2, NMP (l-methyl-2-pyrrolidinone), 100°. ... 

Easily prepared from the appropriate monosaccharide, a glycal is an unsatu-rated sugar with a C1-C2 double bond. To ready it for use in potysaccharide synthesis, the primary -OH group of the glycal is first protected at its primary -OH group by formation of a silvl ether (Section 17.8) and at its two adjacent secondary - OH groups by formation of a cyclic carbonate ester. Then, the protected glycal is epoxidized. 

The chain and branched chain saturated hydrocarbons make up a family called the alkanes. Some saturated hydrocarbons with five carbon atoms are shown in Figure 18-11. The first example, containing no branches, is called normal-pentane or, briefly, n-pentane. The second example has a single branch at the end of the chain. Such a structural type is commonly identified by the prefix iso- . Hence this isomer is called /50-pentane. The third example in Figure 18-11 also contains five carbon atoms but it contains the distinctive feature of a cyclic carbon structure. Such a compound is identified by the prefix cyclo in its name—in the case shown, cyclopentane. 

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