Ladenburg (Ann., 1875, 179, p. 163) to be symmetrical trimethyl benzene; terephthalic acid, the remaining isomer, must therefore be the para-compound.
By reducing terephthalic acid with sodium amalgam, care being taken to neutralize the caustic soda simultaneously formed by passing in carbon dioxide, A" dihydroterephthalic acid is obtained; this results from the splitting of a Para-linkage.
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.