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.
Dilute nitric acid oxidizes it first to para-toluic acid and then to terephthalic acid.
It cannot be prepared by a direct reduction of terephthalic acid.
The A i 4 acid is also obtained by the 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.