Classification and Isolation of Resins

Content

Classification and isolation of Resins

Objective

At the end of this lecture, student will be able to

• Explain the physical and chemical nature of resins

• Identify families of resin containing drugs

• Classify resins

• Explain various isolation methods of resins

Resins

• Amorphous products of complex chemical nature

• Mixtures of essential oils, oxygenated products of terpenes and carboxylic acids

• Produced in plants during normal growth or secreted as a result of injury to the plants

• Usually occur in schizogenous or schizolysigenous cavities or ducts

Distribution in plants:

• Resins and resinous substances are more or less extensively distributed throughout the entire plant kingdom, specifically the Spermatophyta

The most important resin containing families are

• Pinaceae- Colophony or Rosin

• Leguminosae- Tolu balsam or Balsam of peru

• Burseraceae- Myrrh

• Umbelliferae- Asafoetida

Occurrence of Resins:

In plants resins usually occur in different secretary zones

• Resin cells- Ginger

• Schizogenous ducts or schizolysogenous ducts- pine wood

• Glandular hairs- Cannabis

Physical properties of Resins:

• Amorphous, hard and brittle

• Transparent or translucent solids, semi solids or liquid substances

• Most of the resins are heavier than water

• Soluble in alcohol, volatile oils, fixed oils and non-polar solvents like benzene and ether

• Insoluble in water

• Electrically non-conductive and combustible

• When heated they soften and ultimately melt

• Resins burn with a characteristic, smoky flame by virtue of the presence of a large number of c-atoms

• Formed in schizogenous or schizolysigenous ducts as end products of metabolism

Chemical nature of Resins:

• Chemically resins are not pure substances but complex mixtures of several resinous substances as resin acids, resin alcohols, resin esters, and neutral resins

• Resins do not contain nitrogen elements, may contain few oxygen

Classification of Resins

Resins are classified in three different ways

1. Taxonomical classification According to botanical origin, e.g. Berberidaceae resins- podophyllum, Coniferous resins- colophony etc

2. Chemical Classification e.g. Resin acid, Resin ester, Resin alcohol, Resenes etc

3. According to the portion of the main constituents of the resin or resin combination e.g. Oleoresins, Oleo-gum-resins, Balsams, Glycoresins

Chemical Classification of Resins:

1. Acid resins

• Carboxylic acid group containing resinous substances

• May or may not have association with phenolic compounds

• Soluble in aqueous solution of alkalis producing frothy solution

• Found in Free State or as the ester derivatives

• Derivatized to their metallic salts (Resinates)

Examples –

Colophony – Abietic acid

Sandrac - Sandracolic acid

Myrrh - Commiphoric acid

Copaiba - Copaivic acid

2. Resin esters

• Esters of the resin acids or the other aromatic acids like benzoic, cinnamic, salicylic acid etc

• Converted to free acids by the treatment with caustic alkali

Example –

• Benzoin contains benzyl benzoate

• Storax contains cinnamyl cinnamate

3. Resin alcohols (Resinol)

• Complex alcoholic compounds of high mol wt

• Found in Free State or as the ester of benzoic, salicylic and cinnamic acids

• Insoluble in aqueous alkali, but soluble in alcohol and ether

Examples –

• Balsam of peru with peruresinotannol

• Guaiaccum resin with guaicresinol

4. Resenes

• Chemically inert

• Found in Free State and never form salt or other derivatives

• Insoluble in water, soluble in benzene and chloroform

Example- Asafoetida (asaresene-B)

Classification of Resins based on combination with other constituents

Oleoresins - Resins and volatile oil in homogenous mixtures – capsicum

Oleogumresin - Resin, v.oil and gum – homogenous mixture – Myrrh, guggul and asafoetida

Glycoresins - Resin and sugars - – homogenous mixture – Jalap

 Balsam - Mixture of benzoic and cinnamic acid – balsam of tolu, balsam of peru, storax

Classification Based on association of resin with other groups

1. Oleoresins

• Homogenous mixture of resin with volatile oil

• Posses essence due to volatile oil

• Trace amount of gummy material may sometimes be found

Eg: Turpentine, ginger, copaiba

2. Gum resins

• Naturally occurring mixture of resin with gum

• Gum can be easily separated from the resin by dissolving in water

Eg: Ammoniacum

3. Oleogum resins

• Naturally occurring mixture of resin, volatile and gum

• Oozes out from the incisions made on the bark

Eg: Asafoetida, gummyrrh, gamboage

Balsams

• Balsams are resinous mixtures that contain large proportions of cinnamic acid, benzoic acid or both or their esters

• Balsams containing free acids are partially soluble in hot water

• The term “balsam” is often wrongly applied to oleoresins and should be reserved for such substances as balsam of Peru, balsam of Tolu and storax

Isolation of resins

1. Natural resins occur as exudates from plants, produced normally or as a result of pathogenic conditions

Eg: Myrrh, asafoetida, balsams

2.  In case of oleoresins, ether or acetone having lower boiling point are used and oil is separated by distillation

Eg: Colophopny, copoiba

3.  In case of gum resins, the resin is extracted with alcohol leaving gum insoluble

Eg: Ammoniacum

4.  By heating the plant part

Eg: Guaiacum

5.  By collecting fossil resins

Eg: Copal, kauri

6. By processing the encrustations

Eg: Shellac

7. The drug containing resins is powdered and extracted with alcohol till exhaustion.

The Concentrated alcoholic extract is either evaporated or poured into water and the precipitated resin is collected, washed and carefully dried

Eg: Jalap, podophyllum, ipomoea

Summary

• Amorphous mixtures of essential oils, oxygenated products of terpenes and carboxylic acids

• Distribution – Pinaceae, Leguminosae, Burseraceae and Umbelliferae

• Occurance - Schizogenous ducts or schizolysogenous ducts, glandular hairs

• Amorphous, hard, brittle, transparent or translucent, heavier than water

• Soluble in alcohol, fixed oils and non-polar solvents, Insoluble in water

• Chemical – Resin acid, resinol, resin ester and resene

• Resin combination – Oleo resin, gum resin and oleo gum resin

• Balsams - Large proportions of cinnamic acid, benzoic acid or both or their esters

• Isolation of resin – As exudates Distillation

                                  - By heating the plant part

                                  - By collecting fossil resin

                                  - By processing the encrustations

                                  - Extracting with alcohol and precipitation with water