158 REPORT—1905. 
stitutions of the four isomerides are most probably represented by the 
following formule :— 
H tle H COOH 
*y ee 
18 ae iy fe H, 
a 
H COOH Ee COOH 
YC a 
A?(m.p. 168°) A%(m.p. 244°) 
Serie COOH H 
A 
490% H, H, os 
x | 
H we COOH H Wy Ok 
cis A‘(m.p. 165°) trans H'(m.p. 227°) 
It has not been found possible to isolate even a trace of a dihydroiso- 
phthalic acid from the reduction products, though von Baeyer has shown 
that the products first formed on reduction of phthalic and terephthalic 
acids are always dihydro derivatives. The following considerations are 
suggested as supplying a reason for this curious difference in the behaviour 
of isophthalic acid. 
In the reduction of phthalic and terephthalic acids hydrogen atoms 
always attach themselves in the first instance to the carbon atoms which 
carry the carboxyl groups. Thus the first product of the reduction of 
phthalic acid is +°*°-dihydrophthalic acid— 
A H 
vields = 
" : H 
wv 
and, in a similar manner, the first product of the reduction of terephthalic 
acid is \*‘°-dihydroterephthalic acid— 
& 
yields 
y eae 
8 
If this process be applied to isophthalic acid, it leads to the following 
unsaturated scheme :— 
H 2 
FJ Ss VA 
yields 
fa 
H 
in which the valencies are unable to unite to form double linkings, as,in 
the case of dihydrophthalic and dihydroterephthalic acids. oy 
az 
