Carboxyl groups and derivatives

Pyridazinecarboxylic acids can also be prepared by hydrolysis of esters, nitriles and amides in the presence of acids or alkali. Another interesting method is partial decarboxylation of 

Pyridazinecarboxylic acids are more acidic than benzoic acids, due to the electronegativity of the pyridazine ring, but oxopyridazinecarboxylic acids are weaker than the corresponding pyridazinecarboxylic acids (Table 11). 

Practically all pyridazine-carboxylic and -polycarboxylic acids undergo decarboxylation when heated above 200 °C. As the corresponding products are usually isolated in high yields, decarboxylation is frequently used as the best synthetic route for many pyridazine and pyridazinone derivatives. For example, pyridazine-3-carboxylic acid eliminates carbon dioxide when heated at reduced pressure to give pyridazine in almost quantitative yield, but pyridazine is obtained in poor yield from pyridazine-4-carboxylic acid. Decarboxylation is usually carried out in acid solution, or by heating dry silver salts, while organic bases such as aniline, dimethylaniline and quinoline are used as catalysts for monodecarboxylation of pyridazine-4,5-dicarboxylic acids. 

Pyridazinecarboxamides are prepared from the corresponding esters or acid chlorides with ammonia or amines or by partial hydrolysis of cyanopyridazines. Pyridazinecarboxamides with a variety of substituents are easily dehydrated to nitriles with phosphorus oxychloride and are converted into the corresponding acids by acid or alkaline hydrolysis. They undergo Hofmann degradation to give the corresponding amines, while in the case of two ortho carboxamide groups pyrimidopyridazines are formed. 

Pyridazinecarbohydrazides are prepared in the normal way from an ester or acid chloride and hydrazine or a substituted hydrazine, generally in good yields. Pyridazines with two ortho alkoxycarbonyl groups give cyclic hydrazides with hydrazine, which are pyridazinopyridazines. 

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A TETRACRGAHOTIN COMPOUNDS CONTAINING CARBOXYL GROUPS AND DERIVATIVES... 

Table 115. Tetorganotin Compounds Containing Carboxyl Groups and Derivatives... 

The next several chapters deal with the chemistry of various oxygen containing func tional groups The interplay of these important classes of compounds—alcohols ethers aldehydes ketones carboxylic acids and derivatives of carboxylic acids— IS fundamental to organic chemistry and biochemistry... 

Systematic names for carboxylic acids are derived by counting the number of car bons m the longest continuous chain that includes the carboxyl group and replacing the e ending of the corresponding alkane by oic acid The first three acids m Table 19 1 methanoic (1 carbon) ethanoic (2 carbons) and octadecanoic acid (18 carbons) illus trate this point When substituents are present their locations are identified by number... 

Broadly speaking, in the study of AB cements derived from poly-carboxylic acids, the band of interest falls in the region 1550-1620 cm (Mehrota Bohra, 1983 Bellamy, 1975). This band is the asymmetric stretch of the carboxylate group and its exact position depends on both the nature of the bonding involved (i.e. whether purely ionic or partially covalent), and the nature of any chelation by the carboxylate group (Bellamy, 1975). 

Enzymatic browning. Phenol-oxidizing enzymes (such as tyrosinase and peroxidase) oxidize tyrosine residues into reactive quinone derivatives, which will condense into colored polymers (melanins). Melanins are rich in carboxyl groups and therefore have high affinity for divalent metal ions such as calcium. 

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