Carbonic acid derivatives and

Fig. 6. 33. Carbonic acid derivatives and their interconversions (plus cross-reference to a chlorine-free option for the synthesis of isocyanates).

Carbonic Acid Derivatives and Heterocumulenes and Their Interconversion... 

Fig. 8.1. Survey of the interconversion of carbonic acid derivatives and heterocumulenes.

Section 8.3 addresses the aspect of Carbonic Acid Derivatives and Their Interconversion. Figure 8.2 shows how this subject is related to the chemistry of heterocumulenes depicted in Figure 8.1. Carbonic acid derivatives A and heteroatom nucleophiles H-Het3 can react to furnish the carbonic acid derivatives C (see Section 6.4.4). On the other hand, they can react, via the elimination of water, to give the heterocumulene B and subsequently add the heteroatom nucleophile H-Het3. This path also leads to the formation of carbonic acid derivatives C and is described in Section 8.3. 

The former chapter Additions of Heteroatom Nucleophiles to Heterocumulenes, Additions of Heteroatom Nucleophiles to Carbonyl Compounds and Follow-up Reactions has been spht into two separate chapters into Chapter 8 Carbonic Acid Derivatives and Heterocumulenes and Their Interconversion , whose systematic organization should represent a particularly valuable learning aid, and into Chapter 9 Additions of Het-eroatom Nucleophiles to Carbonyl Compounds and Follow-up Reactions—Condensations of Heteroatom Nucleophiles with Carbonyl Compounds. ... 

Almost all recorded purine syntheses from imidazoles involve the cyclization of 5(4)-aminoimidazole-4(5)-carboxylic acid derivatives especially the carboxamides, thiocar-boxamides, carboxamidines, carboxamidoximes, nitriles and esters. The intermediates used for completion of the purine ring are much the same as have been used for Traube cyclization of diaminopyrimidines (Section 4.09.7.3), especially formic and carbonic acid derivatives, and cyclization generally occurs-under much milder conditions. This feature has been of special value in the synthesis of purine nucleosides from imidazole nucleoside precursors. The resultant purine will have variable substituents at C-2 and C-6 and it is convenient to discuss and classify the various preparations largely in terms of the introduced 2-substituents. The C-6 substituents largely reflect the type of carboxylic acid moiety used and do not vary very much between amino, oxo and thioxo. 

Usually, PET processes are preferred to other fragmentation processes in HMPA, but only dialkylthiocarbamates give satisfactory yields of R -H. Again a very good parallel can be drawn between the PET reaction of carbonic acid derivatives and their reduction by dissolving metals in primary amines or HMPA. ... 

Many phosgene equivalents have been designed in order to have the reactivity of phosgene and the leaving group ability of various organic substituents. Formally, and often essentially, they belong to the family of carbonic acid derivatives and, therefore, their chemical behavior and reactivity toward nucleophiles has to be interpreted in terms of this classification [1]. 

This class of polymers is obtained by the reaction of diols with carbonic acid derivatives and the most important polycarbonate, PC, is made from bisphenol A and phosgene. 

C2S2, is a red Hquid (mp —0.5° C, bp 60—70°C at 1.6 kPa (12 mm Hg)) produced by the action of an electric arc on carbon disulfide (1 4). The stmcture has been shown to be S=C=C=C=S on the basis of its reactions to form malonic acid derivatives and on the basis of physical measurements. It is unstable and decomposes ia a few weeks at room temperature it decomposes explosively when heated rapidly at 100—120°C with formation of a black polymeric substance (C2S2) (5,6). Dilute solutions ia CS2 are fairly stable, but photochemical polymerisation to (C2S2) occurs. 

AEyl chloride reacts with sodamide in Hquid ammonia to produce benzene when sodamide is in excess, hexadiene dimer is the principal product, with some trimer and tetramer (C24, six double bonds). AEylation at carbon atoms alpha to polar groups is used in the preparation of a-aEyl-substituted ketones and nittiles. Preparation of P-diketone derivatives, methionic acid derivatives, and malonic ester, cyanoacetic ester, and P-keto-ester derivatives, etc, involving substitution on an alpha carbon between two polar carbonyl groups, is particularly facEe. 

By reaction of polyhydroxy compounds with a carbonic acid derivative, a series of related polymers may be produced with carbonate (—0 C0 0—) linkages, the polymers being referred to as polycarbonates. Carbonic acid, C0(0H)2, itself does not exist in the free state but by means of ester exchange Figure 20.1) (1) and phosgenation techniques (II) it is possible to produce useful products. 

Carothers also produced a number of aliphatic linear polyesters but these did not fulfil his requirements for a fibre-forming polymer which were eventually met by the polyamide, nylon 66. As a consequence the polyesters were discarded by Carothers. However, in 1941 Whinfield and Dickson working at the Calico Printers Association in England announced the discovery of a fibre from poly(ethylene terephthalate). Prompted by the success of such a polymer, Farbenfabriken Bayer initiated a programme in search of other useful polymers containing aromatic rings in the main chain. Carbonic acid derivatives were reacted with many dihydroxy compounds and one of these, bis-phenol A, produced a polymer of immediate promise. 

G. Reactions with Carbon Dioxide and Some Carbonic Acid Derivatives... 

A CSP based on the adsorption of a chiral anthrylamine on porous graphitic carbon successfully resolved the enantiomers of tropic acid derivatives and anti-inflammatory agents in SFC [65]. The carbon-based CSP produced superior results when compared to an analogous silica-based CSP. Occasional washing of the column was necessary to remove highly retained substances. 

Thus unsubstituted (R=H) and substituted (R = alkyl) non-stabilized diyiides 1 react with phenylisocyanate and dicyclohexylcarbodiimide (R NCX), leading to the formation of new monoylide type intermediates. These last ones react in situ with carbonyl compounds through a Wittig type reaction leading respectively to a,)8-unsaturated amides 2 and amidines 3, with a high E stereoselectivity, the double bond being di- or tri-substituted [48,49]. By a similar reactional pathway, diyiides also react with carbonic acid derivatives, with the synthesis as final products of -a,/l-unsaturated esters 4 and acids 5 [50]. 

Biotin is a growth factor for many bacteria, protozoa, plants, and probably all higher animals. In the absence of biotin, oxalacetate decarboxylation, oxalosuccinate carboxylation, a-ketoglutarate decarboxylation, malate decarboxylation, acetoacetate synthesis, citrulline synthesis, and purine and pyrimidine syntheses, are greatly depressed or absent in cells (Mil, Tl). All of these reactions require either the removal or fixation of carbon dioxide. Together with coenzyme A, biotin participates in carboxylations such as those in fatty acid and sterol syntheses. Active C02 is thought to be a carbonic acid derivative of biotin involved in these carboxylations (L10, W10). Biotin has also been involved in... 

We can think of water entering the lake in terms of a titration. A solution of alkali enters a fixed volume of acid the alkaline solution is water entering from the lake s tributary rivers, and the acid is the lake, which contains the weak acid H2CO3 (carbonic acid) deriving from atmospheric carbon dioxide. The alkali in the tributary rivers is calcium hydroxide Ca(OH)2, which enters the... 

The most widely used method for the preparation of [l,2,4]triazolo[3,4-A][l,3,4]thiadiazoles 85 employs 4-amino-5-thio-4/7-[l,2,4]triazoles 83 or 4-amino[l,2,4]-triazole-5(47T)-thiones 84 as starting materials. The reaction of the triazoles 83 or 84 with carbonic acid derivatives furnishes [l,2,4]triazolo[3,4-4][l,3,4]thiadiazoles with a heteroatom substituent (N, O, S) at position 6 the O- and S-functions are formulated as 6-hydroxy and 6-thio derivatives 85a or as thiadiazol-(5/7)6-ones and -thiadiazole-(577)6-thiones 85b, respectively reaction with carboxylic acid derivatives provides the 6-substituted-[l,2,4]triazolo[3,4-4][l,3,4]-thiadiazoles 85c (Equation 20 Table 3). 

Ethyl chloroformate reacts with the isonitroso group of amidoximes to give the corresponding carbonic acid derivative which, on heating, splits off ethanol and yields a 3-substituted 5-hydroxyoxadiazole 27, 28, 103, 104). 

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