Derivatives of Carbonic Acid

Carbonic anhydrase is an enzyme that interconverts water and carbon dioxide with carbonic acid. A carbonate dianion is shown in red within the structure of carbonic anhydrase above. 

Carbonic acid, HO OH is an unstable compound that decomposes spontaneously to produce carbon dioxide and water and, therefore, cannot be isolated. However, many acyl chlorides, esters, and amides that are derived from carbonic acid are stable compounds that have important applications. 

Carbonyl dichloride (CICOCI), a highly toxic compound that is also called phosgene, can be thought of as the diacyl chloride of carbonic acid. Carbonyl dichloride reacts by nucleophilic addition-elimination with two molar equivalents of an alcohol to yield a dialkyl carbonate  

A tertiary amine is usually added to the reaction to neutralize the hydrogen chloride that is produced. 

Carbonyl dichloride reacts with ammonia to yield urea (Section I.IA)  

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Polycarbonates form a rather specialised class of linear polyesters, since they are formed from a diol, usually an aromatic diol, with a derivative of carbonic acid. The commercially useful products also differ from other types of polyester in that they are generally non-crystalline, melt-processable polymers of high 7J, possessing very high optical clarity and toughness. 

Being formally a derivative of carbonic acid, 4,5-bis(ethylenedithio)-l,3-dithiol-2-one 188 is opened into the dipotassium salt 192 by the action of potassium ethoxide in THF (Equation 20) <1974JOC511>. 

Hydrolytic Cleavage. As a derivative of carbonic acid the urethane group can be cleaved hydrolytically but only under rigorous conditions (40). It is more stable than an ester group but can react similarly with alcohols and amines (20, 35). However, such conditions are unlikely to prevail in a propellant. 

The most general method of preparing 2-carbonyl derivatives is to react 3-aminopropanols with difunctional derivatives of carbonic acid.1 2-Oxo derivatives of tetrahydro-1,3-oxazine being both 8-lactams and 8-lactones differ in their chemical properties from those of tetra-hydro-1,3-oxazines. 

Pocker, Y., and Guilbert, L. J. Carbonic anhydrase catalysed hydrolysis and decarboxylation. Kinetic studies of enzyme-catalysed decomposition of mono- and disubstituted derivatives of carbonic acid. Biochemistry 13, 70-78 (1974). 

Practically all methods which have been proposed for the preparation of guanidine salts involve either ammonation or ammonolysis of some derivative of carbonic acid. Phosgene,1 chloropicrin,2 and esters of orthocarbonic acid2 react with aqueous ammonia to give small yields of guanidine. The hydrochloride is obtained when carbon tetrachloride3 is acted upon by liquid ammonia under pressure. Urea4 is partially ammonolyzed in the presence of ammonium chloride. 

Polycarbonate resins are a variety of polyester in which a derivative of carbonic acid is substituted for adipic, phthalic, or other acid and a diphenol is substituted for the more conventional glycols. 

The synthesis of 2(3//)-oxazolones by incorporation of carbon atom 2 into a four-atom chain is exemplified by the condensation of phenacylaniline with ethyl chloroformate (equation 138). Benzoxazolones are similarly prepared from o-aminophenols and derivatives of carbonic acid, such as phosgene, diethyl carbonate, urethane (Et02CNH2) or urea (equation 139). The analogous condensation of carbon disulfide or cyanogen bromide with o-aminophenols leads to benzoxazolethiones or 2-aminobenzoxazoles, respectively (equation 140). 

These too are made by carbonyl substitution reactions, but this time the nucleophile is aromatic and the electrophile is an aliphatic derivative of carbonic acid such as phosgene (COCI2) or a carbonate diester [CO(OR)2]. The aromatic nucleophile is a diphenol but the two OH groups are on separate rings joined together by an electrophilic aromatic substitution. This compound is called bisphenol A and has many other applications. 

Condensations followed by silyl migrations are achieved easily with carbon acid chlorides, imid chlorides (7, 26-28), and adequate derivatives of carbonic acid such as phosgene [Eq. (5a)] and isocyanide dichlorides [Eq. (5b)] (29-31). After the primary condensation to the... 

This acid is not known in the free state but as the ethyl ester. As will be shown later chlor formic acid may also be considered as a derivative of carbonic acid and as this is its most important relation a fuller discussion will be deferred until carbonic acid is discussed (p. 428). 

Semi-carbazid is an important reagent forming derivatives with aldehydes and ketones. Its name indicates that it is a hydrazine derivative of carbonic acid or of carbamic acid. It is also amino urea. 

Much of the chemistry of the functional derivatives of carbonic acid is already quite familiar to us through our study of carboxylic acids. The first step in dealing with one of these compounds is to recognize just how it is related to the parent acid. Since carbonic acid is bifunctional, each of its derivatives, too, contains two functional groups these groups can be the same or different. For example ... 

III general, a derivative of carbonic acid containing an group is unstable, and dedomposes to carbon dioxide. For example ... 

Most derivatives of carbonic acid are made from one of three industrially available compounds phosgene, urea, or cyanamide. 

The dithio derivative of carbonic acid is xanthogenic acid (1), unknown in the free state, the anhydride of which, carbon disulfide, is in itself an active substance with very good biological properties. 

Carbamic ester RNM—COOR, an amide derivative of carbonic acid with common name urethane. 

Carbamic acid, HOOCNH, the monoamide derivative of carbonic acid, is not known in the free state and usually occurs in the form of salts. Carbamate coordination chemistry is much less extensive than the ligands so far considered, which contain the ligating group O2CX. This is principally for two reasons firstly the synthetic routes to these complexes are often limited to carbon dioxide reactions with dialkylamide complexes, and secondly the unstable character of the complexes themselves due to reaction (7). Carbamate complexes are electronically and sterically similar to monocarboxylate systems, although the presence of two alkyl groups per ligand enhances their solubility. 

Urea is a di-amino derivative of carbonic acid, known as carbonic diamide. Urea may also be considered an amide of carbamic acid, according to the formal sequences suggested in Figure 5.7. This figure also indicates that when an ammonia molecule reacts with urea, it produces guanidine, an organic imide molecule. 

Fig. 5.7. Formal reaction diagram showing the formation of amino derivatives of carbonic acid...

Derivatives of carbonic acid, which are commonly used in organic synthesis as protective groups or reaction intermediates, might be good ctmdidates for photoinduced reduction of... 

Polycarbonates are the second largest by volume engineering thermoplastics next to polyamides. Their preparation involves the linking together of aromatic dihydroxy compounds, usually 2,2-bis(4-hydroxy-phenyl) propane or bisphenol A, by reacting them with a derivative of carbonic acid such as phosgene (Equation 2.33) or diphenyl carbonate (Equation 2.34). 

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