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Fumaric acid is (E)-1,4-but-2-enedioic acid, a trans isomer, whereas maleic acid is the corresponding cis isomer, i.e. (Z)-1,4-but-2-enedioic acid (see cis-trans isomerism). Fumaric acid has pK a values of approximately 3.0 and 4.5. By contrast, maleic acid has pK a values of approximately 1.5 and 6.5.
4-Aminobenzoic acid (also known as para-aminobenzoic acid or PABA because the two functional groups are attached to the benzene ring across from one another in the para position) is an organic compound with the formula H 2 NC 6 H 4 CO 2 H. PABA is a white crystalline solid, [3] although commercial samples can appear gray.
pK a values of amino acid side chains play an important role in defining the pH-dependent characteristics of a protein. The pH-dependence of the activity displayed by enzymes and the pH-dependence of protein stability, for example, are properties that are determined by the pK a values of amino acid side chains.
p-Toluic acid (4-methylbenzoic acid) is a substituted benzoic acid with the formula CH 3 C 6 H 4 CO 2 H. It is a white solid that is poorly soluble in water but soluble in acetone . A laboratory route to p -toluic acid involves oxidation of p-cymene with nitric acid.
It also can be prepared by treating benzaldehyde under nitration conditions, a process that initially converts the aldehyde to the acid. 4-Nitrobenzoic acid is a precursor to 4-aminobenzoic acid, which is in turn used to prepare the anesthetic procaine. 4-Nitrobenzoic acid is prepared by oxidation of 4-nitrotoluene.
It may be prepared via the Schiemann reaction, in which a 4-aminobenzoic acid, protected as the ethyl ester, is diazotised and then fluoride introduced using tetrafluoroborate. Hydrolysis of the ester converts it back to the free acid. [2] 4-Fluorobenzoic acid has been observed to form by the aerobic biotransformation of 4-fluorocinnamic acid. [3]
4-Mercaptobenzoic acid (p-mercaptobenzoic acid, p-MBA) is an organosulfur compound with the formula para-C 6 H 4 (−SH)(−COOH). It is used as a ligand in thiolate-protected gold cluster compounds, such as Au 102 ( p -MBA) 44 .
4-Hydroxybenzoic acid, also known as p-hydroxybenzoic acid (PHBA), is a monohydroxybenzoic acid, a phenolic derivative of benzoic acid.It is a white crystalline solid that is slightly soluble in water and chloroform but more soluble in polar organic solvents such as alcohols and acetone. 4-Hydroxybenzoic acid is primarily known as the basis for the preparation of its esters, known as parabens ...