In this way all hydroxybenzoic acids may be carbomethoxylated. ❋ Georg Grasser (N/A)
In analogy with peptides and saccharides, the names di -, tri -, and polydepsides of hydroxybenzoic acids would be suitable for these substances. ❋ Georg Grasser (N/A)
They readily form esters with alcohols, which on subsequent saponification with alkali are converted into the esters of the free hydroxybenzoic acids. ❋ Georg Grasser (N/A)
Amongst the small number of synthetically prepared ester anhydrides of hydroxybenzoic acids, a few occur exhibiting the properties of the natural tannoids. ❋ Georg Grasser (N/A)
The fact that hydroxybenzoic acids are constantly encountered together with the products obtained on hydrolysis of the tannins, seems to point toward the conclusion that anhydrides of hydroxybenzoic acids are frequent constituents of the natural tannoid molecules. ❋ Georg Grasser (N/A)
From the point of view of the chemistry of the tannins, therefore, the starting-point would naturally be that of synthesising the ester anhydrides of hydroxybenzoic acids. ❋ Georg Grasser (N/A)
The principles underlying the synthesis of depsides are the following: -- If the chlorides of carbomethoxy (or carbethoxy) hydroxybenzoic acids are coupled with the sodium salts of hydroxybenzoic acids, esters are formed, _e. g. ❋ Georg Grasser (N/A)
Similarly to sugar, the true glucosides can be coupled with hydroxybenzoic acids, which is proved by the preparation of tetra-galloyl - [Greek: a] - methyl glucoside; this substance, also, exhibits tannoid character. ❋ Georg Grasser (N/A)
On subsequently removing the carbo-methoxy group derivatives of hydroxybenzoic acids are obtained, _e. g. ❋ Georg Grasser (N/A)
This simple procedure, however, is not applicable to most other hydroxybenzoic acids which are decomposed at the high temperature necessary to induce reaction. ❋ Georg Grasser (N/A)
The chlorides may be coupled with free hydroxybenzoic acids, and on removing the carbomethoxy group didepsides are obtained. ❋ Georg Grasser (N/A)
The most common decomposition products of the natural tannoids are hydroxybenzoic acids, notably gallic and proto-catechuic acids; furthermore, other aromatic and aliphatic hydroxy compounds frequently occur. ❋ Georg Grasser (N/A)
Of the three classes of isomeric anhydrides which can be formed from hydroxybenzoic acids, the chemistry of the natural tannins is only concerned with the class comprising the ester anhydrides. ❋ Georg Grasser (N/A)
From a physiological standpoint the recognition of tannins as esters of glucose and hydroxybenzoic acids, possessing characteristics similar to those of tannin, is of great importance. ❋ Georg Grasser (N/A)
These investigators found that by the condensation of phenols and hydroxybenzoic acids with formaldehyde, diphenylmethane derivatives were formed; pyrogallol yields hexahydroxydiphenylmethane -- ❋ Georg Grasser (N/A)
If the carboxyl of the first molecule combines with a hydroxyl of the second molecule (ester formation), then a substance possessing character similar to that of a hydroxybenzoic acid is formed, which is capable of combining up with a further molecule in the same way. ❋ Georg Grasser (N/A)
The production of synthetic tannins employs two quite distinct methods; one is to synthesise the most simple tannin, viz., the tannic acid contained in galls (tannin), or to build up substances similar in character to the tannins, from hydroxybenzoic acids. ❋ Georg Grasser (N/A)
The method of preparation employed in the synthesis of pentagalloyl glucose may be easily applied to other hydroxybenzoic acids, _e. g._ penta [_p_-hydroxybenzoyl] glucose ❋ Georg Grasser (N/A)
The chlorides, being for the most part solids, the mode of procedure is as follows: -- the hydroxybenzoic acid required for coupling is dissolved in normal or double-normal alkali (the volume calculated per molecule acid), a little acetone added, and the mixture well cooled; ❋ Georg Grasser (N/A)
The preparation of pentagalloyl glucose has proved this compound to be nearly identical with tannin obtained from galls (_tannin_); a few other natural tannins belong to this type which Fischer terms acyl compounds of sugar with hydroxybenzoic acids. ❋ Georg Grasser (N/A)
