The first named of these two compounds was obtained by Klepl, in
addition to the didepside, by heating _p_-hydroxybenzoic acid. Fischer
and Freudenberg obtained a beautifully crystalline form in the following
way: carbethoxyhydroxy-benzoyl chloride was coupled with
_p_-hydroxybenzoyl-_p_-hydroxybenzoic acid in alkaline solution, the
compound dissolved in a mixture of pyridine and acetone, and ammonia
added for the purpose of removing the carbethoxy group. The tridepside
was then obtained as long needles by re-dissolving in acetone.

Both tridepsides melt well above 200 C., are practically insoluble in
water, and are but sparingly soluble in practically all organic
solvents. In alcoholic solution they give colour reaction with ferric
chloride similar to those given by _p_-hydroxybenzoic acids.


Preparation of Tetradepsides
[Footnote: Fischer and Freudenberg, Liebig's _Ann._, 1910, 372, 32.]

Here, again, two forms are known, _e.g._,
tri-_p_-hydroxybenzoyl-_p_-hydroxybenzoic acid--

HO.C_5H_4.COO.C_6H_4.COO.C_6H_4COO.C_6H_4 COOH

and vanilloyl-di-_p_-hydroxybenzoyl-_p_-hydroxybenzoic acid--

HO
} C_6H_3.COO.C_6H_4.COO.C_6H_4.COO.C_6H_4.COOH
CH_3O

The former has been prepared from