In chemistry, carboxylic acids (also called alkanoic acids) are organic acids characterized by the presence of a carboxyl group. Carboxylic acids thus have the structure
where R is a hydrogen or an organic group. In chemical formulas, this is also written as RCOOH.
Carboxylic acids are typically weak acids, with only about 1% of RCOOH molecules dissociated into H+cation and RCOO-anions at room temperature in aqueous solution. The anion RCOO- is usually named with the suffix "-ate", so acetic acid, for example, becomes acetate ion.
The two electronegative oxygen atoms tend to pull the electron away from the hydrogen of the hydroxyl group, and the remaining proton H+ can more easily leave. The remaining negative charge is then distributed symmetrically among the two oxygen atoms, and the two carbon–oxygen bonds take on a partial double bond character (i.e., they are delocalised).
This is a result of the resonance structure created by the carbonyl component of the carboxylic acid, without which the OH group does not as easily lose its H+ (see alcohol).
The presence of electronegative groups (such as _OH or -Cl) next to the carboxylic group increases the acidity. So for example, trichloroacetic acid (three -Cl groups) is a stronger acid than lactic acid (one -OH group) which in turn is stronger than acetic acid (no helping group).
Carboxylic acids react with bases to form carboxylate salts, in which the hydrogen of the -OH group is replaced with a metal ion. Thus, ethanoic acid (the same as acetic acid) reacts with sodium bicarbonate (baking soda) to form sodium ethanoate (sodium acetate), carbon dioxide, and water:
To form covalent bonds with the functional group on a protein, one may use as a chemically reactive group (reactive entity) a wide variety of active carboxyl groups, particularly esters, where the hydroxyl moiety is physiologically acceptable at the levels required to modify the insulinotropic peptides.
To form such bonds, one may use as a chemically reactive group coupled to the ITP a wide variety of active carboxyl groups, particularly esters, where the hydroxyl moiety is physiologically acceptable at the levels required.
Such carboxy protecting groups are well known to those skilled in the art, having been extensively used in the protection of carboxyl groups in the penicillin and cephalosporin fields as described in U.S. Pat.
B is a labile atom or group, hydroxy, amino or an ether, thioether or aminegroup; and
As examples of phenyl radicals having 1 or 2 sulpho or carboxygroups there may be mentioned phenyl; 2-, 3- or 4-sulphophenyl; 2,4-, 2,5- or 3,5-disulphophenyl; 2-methyl-4-sulphophenyl; 2-methyl-5-sulphophenyl; 4-methyl-2-sulphophenyl; 2-sulpho-5-methylphenyl; 2-methoxy-5-sulphophenyl; 4-methoxy-2-sulphophenyl; 2-chloro-4-sulphophenyl; 2-chloro-5-sulphophenyl; 2,5-dichloro-4-sulphophenyl; 4-nitro-5-sulphophenyl; 5-nitro-2-sulphophenyl; 2-carboxy-5-sulphophenyl; and 3,5and 3,4-dicarboxyphenyl.
As Examples of particularly preferred naphthyl radicals having 1, 2 or 3 sulpho or carboxygroups there may be mentioned 4-, 5-, 6- or 7-sulphonaphth-l-yl; 1- or 6-sulphonaphth-2-yl; 3,8- or 4,8-disulphonaphth-l-yl; 4,8- or 5,7-disulphonaphth-2-yl; 2,5,7- or 3,5,7-trisulphonaphth-2-yl; 1,5,7 or 3,6,8-trisulphonaphth-2-yl; 6-carboxy-8-sulphonaphth-2-yl and 6-carboxynaphth-2-yl.
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