The Preparation of Carbonates

The only example of an O-(chloroformyl) carbohydrate isolated from a base-catalyzed phosgene reaction was supplied by Freudenbei and his 

Three examples of the direct synthesis of intermolecular carbonates from carbohydrate derivatives by the action of phosgene in pyridine have been reported. Von Vargha condensed l,2 5,6-di-0-isopropylideue-D-glucofu-ranose with the calculated quantity of phosgene in a benzene-pyridine medium and selectively hydrolyzed the 5,6-0-isopropylidene group in the product XXXI with warm, 80% acetic acid, to give bis(1,2-0-isopropyli- 

The bis(methyl 3, 4-0-isopropylidene- 9-D-arabinopyranoside) 2,2 -car-bonate obtained by Foster and Wolfrom from methyl 3,4-0-isopropyli- 

Haworth, Porter, and Waine examined the reaction of D-galactose and of D-xylose with phosgene in acetone, and isolated, respectively, 6-0-(chloroformyl)-l,2 3,4-di-0-isopropylidene-D-galactopyranose (XIV) and 1,2-0-isopropylidene-D-xylofuranose 3,5-carbonate (X). The reactive chloroformyl compound could be converted to the 6-0-(phenylaminocar-bonyl) derivative XXXVI by treatment with aniline, or to the 6-0-(meth-oxycarbonyl) derivative with methanol, and its possible use in the optical 

Anderson, Goodman, and Baker employed an O-(methoxycarbonyl) protecting group in an analogous manner for their synthesis of methyl 2,3-anhydro-D-ribofuranoside (XLV). Treatment of 1,2-0-isopropylidene-D-xylofuranose (XLI) with methyl chloroformate in pyridine gave, by preferential esterification of the least-hindered alcohol group (at C5), predominantly 1,2-0-isopropylidene-5-0-(methoxycarbonyl)-D-xylofuranose (XLII) a small proportion of the 3,5-di-0-(methoxycarbonyl) derivative was separated by fractional recrystallization. Subsequently, the C3-hydroxyl was esterified with tosyl chloride, and the resulting 3-0-tosyl ester XLIII 

---

Synthetic chemical approaches to the preparation of carbon-14 labeled materials iavolve a number of basic building blocks prepared from barium [ CJ-carbonate (2). These are carbon [ C]-dioxide [ CJ-acetjlene [U— C]-ben2ene, where U = uniformly labeled [1- and 2- C]-sodium acetate, [ C]-methyl iodide, [ C]-methanol, sodium [ C]-cyanide, and [ CJ-urea. Many compHcated radiotracers are synthesized from these materials. Some examples are [l- C]-8,ll,14-eicosatrienoic acid [3435-80-1] inoxn. [ CJ-carbon dioxide, [ting-U— C]-phenyhsothiocyanate [77590-93-3] ftom [ " CJ-acetjlene, [7- " C]-norepinephrine [18155-53-8] from [l- " C]-acetic acid, [4- " C]-cholesterol [1976-77-8] from [ " CJ-methyl iodide, [l- " C]-glucose [4005-41-8] from sodium [ " C]-cyanide, and [2- " C]-uracil [626-07-3] [27017-27-2] from [ " C]-urea. All syntheses of the basic radioactive building blocks have been described (4). 

Table 1. Nutritive Sweeteners Used in the Preparation of Carbonated Beverages...

Using a method suggested by Saint-Flour and Papirer [100], Schultz and Lavielle obtained A// -values for the interaction of several vapors of differing donor numbers and acceptor numbers with various treated and untreated carbon fibers used in the preparation of carbon fiber-epoxy matrix composites. was expressed as ... 

Discussion. The hydroxides of sodium, potassium, and barium are generally employed for the preparation of solutions of standard alkalis they are water-soluble strong bases. Solutions made from aqueous ammonia are undesirable, because they tend to lose ammonia, especially if the concentration exceeds 0.5M moreover, it is a weak base, and difficulties arise in titrations with weak acids (compare Section 10.15). Sodium hydroxide is most commonly used because of its cheapness. None of these solid hydroxides can be obtained pure, so that a standard solution cannot be prepared by dissolving a known weight in a definite volume of water. Both sodium hydroxide and potassium hydroxide are extremely hygroscopic a certain amount of alkali carbonate and water are always present. Exact results cannot be obtained in the presence of carbonate with some indicators, and it is therefore necessary to discuss methods for the preparation of carbonate-free alkali solutions. For many purposes sodium hydroxide (which contains 1-2 per cent of sodium carbonate) is sufficiently pure. 

Not only hydrocarbon systems, but also silicon rubbers (Lee 1986), can be pyrolyzed to obtain silicon-based membranes. Details of the pyrolysis are mainly reported for nonmembrane applications. A recent example is the paper of Boutique (1986) for the preparation of carbon fibers used in aeronautical or automobile constructions. 

Pharmacokinetic and metabolic investigations of indolidan [82] and the preparation of carbon-14- and deuterium-labelled indolidan have been described [83]. The major metabolite isolated from monkey urine has been shown to result from oxidation of the dihydropyridazinone core to the pyri-dazinone system. 

Heteronuclear Pt-Ru binary carbonyl clusters have been used for the preparation of tailored PtRu bimetallic electrocatalysts. The use of carbonyl complexes such as Ru4Pt2(CO)i8 and closely related carbide and hydride carbonyl-derived clusters, that is, Ru5PtC(CO)i6 and Ru6Pt3(CO)2i( X3-H)( x-H)3, has allowed the preparation of carbon- and y-Al203-supported catalysts in which the presence of RugPts, RusPt and Ru4Pt2 clusters or nanoparticles has been reported [62-65]. 

Fullerenes have potential applications in the preparation of carbon support catalyts and diamond films. They have high electrical conductivity and chemical reactivity. 

Control of the pH and temperature of the precipitating solution is important to provide optimised conditions for stoichiometric, homogeneous, fluorhydroxyapatite formation. Similar conditions and set-up can be used for the synthesis of fluoride-substituted apatite crystals with varying size, crystallinity and morphology depending on the preparation temperature [124] a purge of the synthesis system with nitrogen gas ensures the preparation of carbonate-free fluorhydroxyapatite at ambient temperature [125]. 

It can be seen from the above discussion that the oxidation of piperidines can be a useful and often mild method for the preparation of carbon-substituted piperidines. 

Carbon Dioxide. Acquaint yourself with the design of a Kipp gas generator (Fig. 33) and charge it for the preparation of carbon dioxide. Remove stopper with cock 1 and charge middle sphere 2 up... 

When a concentrated solution of ferric chloride is rapidly mixed with fifty to one hundred times its volume of aqueous hydrogen sulphide solution the liquid assumes a transient blue colour, sulphur subsequently precipitating in the ordinary yellowish-white form.2 Sulphur with a blue coloration is also obtained in the interaction of carbon disulphide and sulphur chloride, for the preparation of carbon tetrachloride, under the catalytic influence of ferric chloride,... 

Among the classic methods for the extension of the aldose chain by one carbon atom from the reducing end [9J, the Kiliani-Fischer cyanohydrin synthesis [10] is a milestone in carbohydrate chemistry. However after 110 years from discovery and numerous applications [11], including the preparation of carbon and hydrogen isotopically labeled compounds for mechanistic and structural studies [12], there are still several drawbacks that make the method impractical. These are the low and variable degree of selectivity and the harsh reaction conditions that are required to reveal the aldose from either the aldonic acid or directly from the cyanohydrin. Synthetic applications that have appeared in recent times confirmed these limitations. For instance, a quite low selectivity was registered [13] in the addition of the cyanide ion to the D-ga/acfo-hexodialdo-l,5-pyranose derivative 1... 

Alcohols and phenols can be attached to support-bound alcohol linkers as carbonates [467,665,666], although few examples of this have been reported. For the preparation of carbonates, the support-bound alcohol needs to be converted into a reactive carbonic acid derivative by reaction with phosgene or a synthetic equivalent thereof, e.g. disuccinimidyl carbonate [665], carbonyl diimidazole [157], or 4-nitrophenyl chloro-formate [467] (see Section 14.7). The best results are usually obtained with support-bound chloroformates. The resulting intermediate is then treated with an alcohol and a base (DIPEA, DMAP, or DBU), which furnishes the unsymmetrical carbonate. Carbonates are generally more resistant towards nucleophilic cleavage than esters, but are less stable than carbamates. Aryl carbonates are easily cleaved by nucleophiles and are therefore of limited utility as linkers for phenols. 

The preparation of carbonates is mechanistically closely related to the synthesis of carbamates, and similar reagents can be used for this purpose (Table 14.10). Resin-bound alcohols can be directly converted into carbonates by treatment with a chloro-formate (see Experimental Procedure 14.2), in two steps by activation with phosgene or a synthetic equivalent thereof followed by reaction with an alcohol in the presence of a base, or by treatment of a resin-bound alcohol with carbon dioxide and an alkyl halide under basic reaction conditions [125]. Thiocarbonates can be prepared from... 

A case in point involves the electrochemical oxidation of vicinal diacids. A standard synthetic method for the preparation of carbon-carbon double bonds occurs by the bis-decarboxylation of such diacids. Even relatively strained, synthetically inaccessible double bonds have been introduced in this way, e.g., eqn 6. 

The preparation of carbon disk-shape UMEs is similar to that of the carbon fibre UME. The only difference is that the active part is sealed on epoxy resin. With this purpose, a micropipette tip (1 mL) is glued to the head-tip of a carbon fibre UME. The carbon fibre is maintained in vertical position with a metal hook and the micropipette tip (1 mL) is filled with epoxy resin. Once the resin is cured, the tip is cross-sectioned with a microtome or a blade. Then, the disk carbon UME is ready. 

Palladium-catalysed reactions of dimetallic compounds 358 such as X2B—BX2, R3Sn—SnR3, R3S11—SiR3 or R3Si—SiR3 with halides via oxidative addition and transmetallation are useful for the preparation of carbon main group metal bonds 359. 

For laboratory-scale use, the preparation of carbon monoxide is best accomplished by the thermal decomposition of formic acid or sodium formate ... 

A brief note lacking details claims the preparation of carbon oxide telluride in very low yields by the action of carbon monoxide on tellurium. Carbon oxide telluride is a gas at room temperature1. 

Carbon ditelluride has not yet been prepared. Attempts to prepare this compound from carbon tetrachloride and hydrogen telluride, carbon tetrabromide or tetraiodide and silver telluride, carbon and tellurium2, or dichloromethane and tellurium3 were unsuccessful. The claim of the preparation of carbon ditelluride by sputtering tellurium from a tellurium/graphite electrode in a DC-arc under carbon disulfide4 was withdrawn5. 

Of the many possible types of carbohydrate thiocarbonates, only a few have been synthesized. The essential difference between the preparations of carbonates and thiocarbonates is that, in the former case, one method may introduce different types of substituents, whereas, with the thiocarbonates, this complication has not so far arisen. The methods are thus classified according to the different types of thiocarbonate. 

Vator in 1935. Hochstetter reported the preparation of carbonates of D-glucose, D-mannitol, sucrose, and starch by heating the appropriate carbohydrate to 130° with diphenyl carbonate in a medium of molten resorcinol or catechol. The products, the first two of which were crystalline, were purified by removal of the liberated phenol in high vacuum, followed by repeated solvent extraction. No characterization appears to have been carried out, apart from noting that boiling water slowly hydrolyzes the derivatives to carbon dioxide and the original carbohydrate. 

The preparation of carbon monoliths has challenged many researchers. Integral carbon monoliths are prepared by extrusion of the carbon precursor, mixed with additives to make the resin extrudable. 

Radical chemistry has been widely exploited for the modification of carbohydrates. In particular, tributyltin hydride-promoted deoxygenation provides a convenient method for the effective removal of hydroxyl groups without intervention of other functionalities. Stereoselective carbon-carbon bond formation at the anomeric center has also revealed its apphcability for the preparation of carbon analogues of 0-glycosides. The majority of this work has been reviewed in earlier publications and hence will not be covered in this account. Instead a selection of newer appHcations is provided here, which have been categorized according to the type of radical reaction carried out. 

Biocatalysts are being applied widely in the industry, including the preparation of carbon-carbon bonds. Stereoselective oxidation with biocatalysts is an area where chemistry will find it hard to compete. A need still exists for new catalysts to replace stoichiometric reagents, as in the reduction of an amide to an amine, amide formation, and substitution of an alcohol (Mitsunobu reaction) (258). In both arenas of catalysis, the overall goal for green chemistry and stereoselectivity must be carbon-hydrogen bond activation. 

One of the most significant steps in the preparation of carbon fibers from acrylic precursor fibers is the oligomerization of the nitrile groups. This reaction has originally been studied in context with the problem of thermal discoloration of PAN (e.g. McCarthney Grassie and McNeill Grassie and Hay It was supposed to lead to a so-called ladder structure ... 

This is a topic of great practical interest because of water treatment and metal recovery applications. Its fundamental aspects are also important for the preparation of carbon-supported catalysts [22], where the catalyst precursor is typically dissolved in water prior to its loading onto the porous support. 

L. Coppi, A. Mordini and M. Taddei, Tetrahedron Lett., 1987, 28,969 for the preparation of carbon-centered optically active allylsilanes, see L. Coppi, A. Ricci and M. TaMei, Tetrahedron Lett., 1987,28,965. 

---