Carbonic acid mixed derivatives

A huge number of ester and carbonate derivatives of polynitroaliphatic alcohol have been synthesized driven by the search for new explosives and energetic plasticizers and oxidizers for propellant and explosive formulations. Most of these are derived from 2-fluoro-2,2-dinitroethanol and 2,2,2-trinitroethanol ° and have excellent oxygen balances. Some examples are illustrated above (168-174) but more comprehensive lists can be found in numerous reviews. " " Direct esterification of polynitroaliphatic alcohols with nitric acid, mixed acid, or acetic anhydride-nitric acid has been used as a route to mixed polynitroaliphatic-nitrate ester explosives. ... 

Importantly, TV-carbamoyl derivatives of primary amines obtained from photolabile benzoins exist in varying proportions as cyclic hydroxyoxazolidinone tautomers. Therefore, the preparation of TV-carbamoyl derivatives of benzoins is applicable only for secondary amines and TV-alkylated amino acids. 244 At basic pH unsymmetrical benzoins, such as 3,5-dimethoxybenzoin, their mixed carbonate and carbamate derivatives, tend to equilibrate to the isomeric forms. Nevertheless, in TFA and aqueous solutions at pH 8 the structural integrity is fully maintained. 244 Preparation of 3,5-dimethoxybenzoin-derived carbamates of secondary amines and amino acids can be mediated by either CDI/methyl triflate in ni-tromethane 246 or 4-nitrophenyl chloroformate/DMAP in dry THF. 244 ... 

All other carboxylic acid derivatives in Table 6.1, in which the leaving group is bound to the carboxyl carbon through an O atom, are increasingly better acylating agents than carboxylic acid alkyl esters (entry 3) in the order carboxylic acid phenyl ester (entry 4) < acyl isourea (entry 7) < mixed carboxylic acid/carbonic acid anhydride (entry 8) < carboxylic acid anhydride (entry 9) < mixed carboxylic acid anhydride (entry 10). 

The last of these special examples of SN reactions of heteroatom nucleophiles at the carboxyl carbon of a carboxylic acid derivative is given in Figure 6.21. There, the free carboxyl group of the aspartic acid derivative A is activated according to the in situ procedure of Figure 6.14 as a mixed carbonic acid/carboxylic acid anhydride B that is then treated with N,0-dimethylhydroxyl amine. This reagent is an N nucleophile, which is thus acylated to give the... 

A mixed gas of 60-75 percent C02 derived from mixing the 40 percent C02 from the kilns and the 90 percent C02 from the calcinations of bicarbonate, is fed to the bottom of these crystallizing units. Absorption of C02 in the highly alkaline ammoniated brine results in crystallization of crude sodium bicarbonate. Because of the heat evolved in the absorption and neutralization of the carbonic acid gas and from crystallization of the sodium bicarbonate, the temperature of the liquor in the column rises from 38°C to a maximum of about 62-64°C. In normal operation, the temperature of the discharge slurry is maintained at about 27°C by automatic adjustment of the water flow through the cooling tubes. A tower such as that shown in Fig. 26.2 has a capacity for producing 50 tons per day of finished soda. 

The mixed esters of carbonic acid [see Table I, type (a)] were formerly designated carboalkyloxy, but this term is now avoided, since it was often confused with carboxyalkyl [—(CHj) —CO2H]. A, the mixed esters of dithiocarbonic acid [see Table I (e) R = alkyl] have been termed alkyl xanthogenates or alkyl xanthates, thus relating them to the corresponding acid dithiocarbonates (R = metal), industrially called xanthates, but more precisely termed 0-(/Si-metal thiolthiocarbonyl) derivatives. Of the mixed-ester types and acid types indicated in Table I, examples of (a), (b), (e), (f), and (g) of the former, and (a), (b), and (e) of the latter have so far been reported. For intermolecular esters, examples of (i) and (k), and, for cyclic esters, examples of (0) and (t), have been described. 

All anhydrides derived from an amino acid, other than a symmetrical anhydride, are mixed anhydrides . However, in the field of peptide chemistry, the term mixed anhydride is commonly used to refer to anhydrides derived from an amino acid and either a carboxylic acid 1 or a carbonic acid 2 (Scheme 1). Other mixed anhydrides will be addressed separately. The use of mixed anhydrides 1 and 2 for peptide synthesis encompasses two distinct reaction steps, as outlined in Scheme 2. The first step is the formation of the mixed anhydride, the activation step, which is the reaction of an amino acid derivative 8 with an acid chloride 9, in the presence of a tertiary amine, in an inert solvent to give the mixed anhydride 10. The second step is the condensation of the mixed anhydride 10 with the amine of an amino acid derivative 11 to give peptide product 12 and the carboxylic acid 13. 

Although N-protected amino acid mixed anhydrides, and particularly mixed carbonic anhydrides, have been by far the most commonly used mixed anhydrides in peptide synthesis, a number of additional mixed anhydrides derived from acids of phosphorus, arsenic, and sulfur have been reported and used in peptide synthesis t l however, these reagents have not found general applicability in routine peptide synthesis. 

An example of such a polyketide is cubensic acid 76 from Xylaria cubensis [115]. From an initial viewing of this structure it could be considered to derive from a mixed acetate/propionate pathway. Feeding studies however clearly demonstrate that the underlying carbon chain is derived from eleven acetate units with all of the eight methyl branches having their origin in L-methionine (Fig. 8). 

Amidines also react with carbonic acid derivatives to provide mixed substituted 1,3,5-triazines. Thus, treatment of aryl amidines, e.g. 3, with phosgene gives 4,6-diaryl-l,3,5-triaz.in-2-ols.318... 

Hydrolysis of this substance leads by intermediate steps to sulfamide (Scheme 1). Ammonolysis, on the other hand, yields a cyclic mixed derivative of sulfuric acid and carbonic acid (LXXXIII). Sulfuryl amide gives salts and also numerous organic derivatives. A silver salt (AgNH)2S02... 

Polycarbonates are actually polyesters formed by the reaction of carbonic acid derivatives with aromatic, aliphatic, or mixed diols. Two routes have been developed and commercialized. There is the direct reaction of phosgene with a diol in accordance with the Schotten-Baumann reaction shown... 

Mixed anhydride method, a procedure of peptide coupling using reactive species resulting from the carboxylic moiety of a N-acylated amino acid and alkyl chlorocar-bonates (alkyl chloroformates), especially isobutyl chlorocarbonate (isobutyl chloro-formate), that readily reacts with an amino component. The nucleophilic amino component attacks the carboxy group of the amino acid component, with formation of the desired peptide derivative and release of the unstable isobutyl carbonic acid which immediately decomposes into carbon dioxide and isobutanol [J. Meienhofer, in The Peptides Analysis, Synthesis, Biology,... 

In RP-HPLC, the stationary phase is less polar than the mobile phase and is usually comprised of spherical silica particles (typically, 3-5 pm in diameter). The acidic functionalities on the silica material have been modified by deriv-atisation with alkyl (C2 to C18), phenyl, cyano and amino groups. Typical mobile phases used in RP-HPLC consist of mixtures of aqueous buffers mixed with water-miscible organic solvents, such as methanol and acetonitrile. In addition to modified silica stationary phases, other new developments in RP-HPLC are now available, e.g. porous polymeric, carbon and mixed modal phases. 

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