2.7.6 Preparation of Resins
So far, no general method has either been suggested or proposed for the preparation of resins. In fact, there are two categories of resinous products, namely: (a) Natural Resins; and (b) Prepared Resins, have been duly accepted and recognized. Therefore, this classification forms the basis of the methods employed in the preparation of the two aforesaid resins.
A. Natural Resins:
These resins usually formed as the exudates from various plants obtained either normally or as a result of pathogenic conditions (i.e., by causing artificial punctures), such as: mastic, sandarac. These are also obtained by causing deep incisions or cuts in the trunk of the plant, for instance: turpentine. They may also be procured by hammering and scorching, such as: balsam of Peru.
B. Prepared Resins:
The resins obtained here are by different methods as described below:
(i) The crude drug containing resins is powdered and extracted with ethanol several times till complete exhaustion takes place. The combined alcoholic extract is either, evaporated on a electric water-bath slowly in a fuming cup-board or poured slowly into cold distilled water.
The precipitated resin is collected, washed with cold water and dried carefully under shade or in a vacuum desiccator,
Examples: Podophyllum; Scammony and Jalap.
(ii) In the case of alco-resins, organic solvents with lower boiling points are normally employed e.g., solvent ether (bp 37°C); acetone (bp 56.5°C), for their extraction. However, the volatile oil fraction can be removed conveniently through distillation under vacuo.
(iii) In the instance of gum-resins, the resin is aptly extracted with 95% (v/v) ethanol while leaving the insoluble gum residue in the flask (or soxhlet thimble).
