The barium salt (+6H 2 0) is very soluble (a distinction between phthalic and terephthalic acids).
Terephthalic acid, formed by oxidizing para-diderivatives of benzene, or best by oxidizing caraway oil, a mixture of cymene and cuminol, with chromic acid, as almost insoluble in water, alcohol and ether; it sublimes without melting when heated.
The A' acid is formed by the direct reduction of terephthalic acid; by boiling the 2 acid with caustic soda; and by the reduction (in the heat) of A I.
It cannot be prepared by a direct reduction of terephthalic acid.
The A 1.5 acid is obtained by boiling the cis- and trans-A 2.5 acids with water, which are obtained on reducing terephthalic acid with sodium amalgam in faintly alkaline solution.