Four acids of this composition are known, namely dextroand laevo-tartaric acids, racemic acid and mesotartaric acid, the two last being optically inactive (see Stereo-Isomerism).
Berzelius by the dry distillation of tartaric or racemic acids (Pogg.
Their constitution follows from their formation from dibromosuccinic acid and from their synthesis from glyoxal cyanhydrin, these two methods producing the inactive racemic form which may then be split into the active components.
Absence of rotary power when asymmetric carbon atoms are present, may be caused by an internal compensation within the molecule as with the inactive tartaric acid (mesotartaric acid), or may be due to the fact that the compound is an equimolecular mixture of leftand right-hand varieties, this being the case with racemic acid that was broken by Louis Pasteur into laevoand dextro-tartaric acid (see Stereo-Isomerism).
The trans-acid is a racemic compound, which on heating with acetyl chloride gives the anhydride of the cis-acid.
The trans compound is perfectly asymmetric and so its mirror image (I) should exist, and, as all the trans compounds synthetically prepared are optically inactive, they are presumably racemic compounds (see 0.