Carboxylic acids groups

As an example, the empirical formula of phenylalanine may be split into a more extended form that shows the presence of a phenyl ring, as well as an amino and a carboxylic acid group (the condensed form in Figure 2-4). 

When the phenol contains a carboxylic acid group, e.g., m- or p-hydroxy-benzoic acid, the acetylated derivative will of course remain in solution as the sodium salt, but is precipitated when the solution is subsequently acidified. Salicylic acid, however, cannot be acetylated under these conditions. 

Heating Kemp s acid with appropriate aromatic diamines yields bis-imides with two convergently oriented carboxylic acid groups on the edges of a hydrophobic pocket. Dozens of interesting molecular complexes have been obtained from such compounds and can be traced in the Journal of the American Chemical Society under the authorship of J. Rebek, Jr., (1985 and later e.g. T. Tjivikua, 1990 B). 

The reaction of aldoses with nitric acid leads to the formation of aldaric acids by oxidation of both the aldehyde and the terminal primary alcohol function to carboxylic acid groups Aldaric acids are also known as saccharic acids and are named by substi tutmg aric acid for the ose ending of the corresponding carbohydrate... 

The most acidic proton is the one of the carboxylic acid group and should have a of approx imately 5... 

Examine the unfilled valences of the carboxylic acid group and find the one marked by a small circle If necessary click on the group to make this circle move to the va lence on carbon... 

The carboxylic acid group has two struc turally distinct valences that can be used to connect this group to the model The active valence is marked by a small cir cle and can be changed by clicking any where on the group... 

A new carbon-carbon bond forms and an entire carboxylic acid group is added to the model... 

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

Carboxylic acid esters Carboxylic acid groups... 

A surprising development involving the 3-position has been presented (61,62). This position traditionally has had a carboxylic acid group and attempts to replace the carboxylate have resulted in lower antibacterial activity. However, it was demonstrated that the carboxylate could be replaced with an isothiazolo ring fused between the 2- and 3-position of the quinolone nucleus. A-62824 [111279-87-9] (22), illustrates this stmctural modification as apphed to ciprofloxacin. 

Carboxylic Acid Group. Reactions of the carboxyl group include decarboxylation, reduction to alcohols, and the formation of salts, acyl hahdes, amides, and esters. 

Carboxylic Acid Group. Sorbic acid undergoes the normal acid reactions forming salts, esters, amides, and acid chlorides. Industrially, the most important compound is the potassium salt because of stabiUty and high water solubiUty. Sodium sorbate [7757-81-5] (E,E form [42788-83-0]) is less stable and not commercially available. The calcium salt [7492-55-9] which has limited solubiUty, has use in packaging (qv) materials. 

Some further transformations involving reduction of the 3-carboxylic acid group are shown in Scheme 21 (66JOC1922, 64JMC483, 70JMC389). 

I. Allyl bromide, Aliquat 336, NaHC03, CH2CI2, 83% yield. The carboxylic acid group of Z-serine (Z = Cbz = benzyloxycarbonyl) is selectively es-terified without affecting the alcohol. 

A terpolymer rubber was introduced by Du Pont in 1975 (Vamac). This is based on ethylene, methyl acrylate and a third, undisclosed, monomer containing carboxylic acid groups to act as the cure site (see Section 11.9). 

More recently, in 1975, Du Pont introduced a terpolymer (Vamac) based on ethylene, methyl acrylate and a third monomer of undisclosed composition which contained a carboxylic acid group to provide a cure site for use with peroxides or amines. Both types of rubber exhibit good heat, oxygen and ozone resistance. 

The transition state for the rapid hydrolysis of the monoanion has been depicted as involving an intramolecular general acid catalysis by the carboxylic acid group, with participation by the anionic carboxylate group, which becomes bound at the developing electrophilic center... 

Hydrolysis of aspirin in H2 0 leads to no incorporation of into the product salicylic acid, ruling out the anhydride as an intermediate and thereby excluding mechanism 1. The general acid catalysis of mechanism III can be ruled out on the basis of failure of other nucleophiles to show evidence for general acid catalysis by the neighboring carboxylic acid group. Because there is no reason to believe hydroxide should be special in this way, mechanism III is eliminated. Thus, mechanism II, general base catalysis of hydroxide-ion attack, is believed to be the correct description of the hydrolysis of aspirin. 

A tertiary amine such as triethylamine is then added to the isocyanate-terminated prepolymer (containing carboxylic acid groups). The tertiary amine reacts with the pendant carboxylic acid groups, forming a carboxylic acid salt. The presence of this salt, together with adequate stirring, allows the dispersion of the prepolymer in water by the so-called melt dispersion process [57]. 

From this discussion, the limitations of the force field should have become clear. There is no such thing as a universal force field which describes every system in every condition. The force field is a function with few adjustable parameters and can, therefore, not be expected to reproduce all properties of all chemical species under all circumstances. This means, for example, that an OH group in an aliphatic alcohol will have to be treated differently from a phenolic OH or from the OH of a carboxylic acid group. Similarly, the density and temperature window of a force field is often limited [22]. 

Homer-Emmons reagents react with trifluoromethyl ketones to form tnfluo romethylated olefins, however, the double bond can isomerize out of conjugation with the carboxylic acid group with the product olefin that bears a y-proton [37] (equation 30)... 

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