Organic acid
An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO2OH, are relatively stronger acids. Alcohols, with –OH, can act as acids but they are usually very weak. The relative stability of the conjugate base of the acid determines its acidity. Other groups can also confer acidity, usually weakly: the thiol group –SH, the enol group, and the phenol group. In biological systems, organic compounds containing these groups are generally referred to as organic acids.
In general, organic acids are weak acids and do not dissociate completely in water, whereas the strong mineral acids do. Lower molecular mass organic acids such as formic and lactic acids are miscible in water, but higher molecular mass organic acids, such as benzoic acid, are insoluble in molecular (neutral) form.
On the other hand, most organic acids are very soluble in organic solvents. p-Toluenesulfonic acid is a comparatively strong acid used in organic chemistry often because it is able to dissolve in the organic reaction solvent.
Exceptions to these solubility characteristics exist in the presence of other substituents that affect the polarity of the compound.
The pKa a logarithmic measure of the acid dissociation constant, categorizes the strength of an acid; the lower or more negative the number, the stronger and more dissociable the acid. It should not be confused with pH, the logarithmic measure of actual hydrogen ion concentration, and thus strength of a particular acid solution. A few examples include: (COOH is the carboxyl group)
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