Structure of 2,3,5,6-Tetraiodo-1,4-Benzenedicarboxylic Acid and Features of the Thermolysis of Iodinated Terephthalic Acids

The crystal structure of 2,3,5,6-tetraiodo-1,4-benzenedicarboxylic acid dihydrate is described and the following structural features are established by XRD: C 8 H 6 I 4 O 6 , M 705.73; monoclinic crystal system, P 2 1 / n space group; unit cell parameters: a = 5.78160(10) Å, b = 15.0976(2) Å, c = 17.3437(3) Å; α = 90°, β = 94.602(2)°, γ = 90°; V = 1509.02(4) Å 3 , Z = 4, ρ calc = 3.106 g/cm 3 . Some features of the thermolysis of terephthalic acid and its iodine derivatives are described. Diiodoterephthalic acid is the least thermally stable, tetraiodoterephthalic acid is the most stable. The iodinated terephthalic acids have similar heats of fusion. The largest amount of carbon residue is formed during the decomposition of 2,3,5,6-tetraiodo-1,4-benzenedicarboxylic acid.