, known as "carboxyl." This group is monovalent, and in the simplest organic acid, formic acid (H2CO2), it is attached to a single hydrogen atom, thus, H·COOH. In all other monobasic acids, it is attached to some other monovalent group, usually an alkyl radical, i.e., a radical derived from an alcohol and containing only carbon and hydrogen (as methyl, CH3, ethyl, C2H5, butyl, C4H9, acryl, C2H3, etc.). Hence, the general formula for all monobasic organic acids is R·COOH, the R representing any monovalent radical. In the simplest dibasic acid, oxalic (H2C2O4), two carboxyl groups are united to each other, thus, HOOC·COOH; but in the higher members of the series, the two characteristic acid groups are united through one or more —CH2— groups, or their oxy-derivatives (as HOOC·CH2·COOH, malonic acid; HOOC·CH2·CH2·CH2·COOH, glutaric acid; HOOC·CHOH·CH2·COOH, malic acid, etc.). Polybasic acids, containing three or more carboxyl groups, linked together through one or more alkyl carbon atoms, are also possible, and a few typical ones (as
are found in fruits and other plant tissues.
The H atom of the COOH group may be replaced by metals, in exactly the same way as it is replaceable in inorganic acids, producing either neutral or acid salts, depending upon whether all or only a part of the acid H atoms are replaced by the basic element.
Similarly, the acid H atom of either an organic or an inorganic acid may be replaced by the alkyl group of an alcohol, producing "ethereal salts," or "esters."
Thus, with nitric acid;
| NO2OH (HNO3) | + | C2H5OH | = | NO2OC2H5 (C2H5NO3) | + | H2O |
| Nitric acid | Ethyl alcohol | Ethyl nitrate |
And, with acetic acid;
| CH3·COOH (H4C2O2) | + | C2H5OH | = | CH3·COOC2H5 | + | H2O |
| Acetic acid | Ethyl acetate |