• Resin can be defined as the complex amorphous product of more or less solid characteristics.

• On heating first sets softened and then melt.

• Resins are produced and stored in the schizogenous or schizolysigenous glands or cavities of the plants.

• Isolated resin products which come as an unorganized crude drug in the market are more or less solid, hard, transparent, or translucent materials.

• Resins are insoluble in most polar and nonpolar solvents like water and petroleum ether, respectively, but dissolve completely in alcohol, solvent ether, benzene, or chloroform.

• Chemically, resins are complex mixtures of resin acids, resin alcohols (resinols), resin phenols (resinotannols), esters and chemically inert compounds known as resenes.

• Resins are often associated with volatile oils (oleoresins), with gums (gum-resins) or with oil and gum (oleo-gum-resins). Resins may also be combined in a glycosidal manner with sugars.

• Resins burn with a characteristic, smoky flame.

Two general classes of resinous substances are recognized and this classification is based on the method used in preparing them:

5. Natural resins, occur as exudates from plants, produced normally or as result of pathogenic conditions, as for example

1. By artificial punctures e.g. mastic; or

2. Deep cuts in the wood of the plant e.g. turpentine, or

3. By hammering and scorching, e.g. balsam of Peru.

6. Prepared resins; are obtained by different methods.

1. 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.

2. In the preparation of oleoresins; ether or acetone having lower boiling point are used.

The volatile oil portion is removed through distillation.

3. When the resin occurs associated with gum (gum-resins), the resin is extracted with

alcohol leaving the gum insoluble.

Resins are classified as:

Resins are classified mostly on the basis of two important features, that is, on the basis of their chemical nature and secondly as per their association with the other group of compounds like essential oils and gums.

Chemical classification of resins categorizes these products according to their active functional groups as given below:

1. Resin Acids: Resin acids are the carboxylic acid group containing resinous substances which may or may not have association with phenolic compounds. These compounds are found in free states or as the esters derivatives. Being acidic compounds they are soluble in aqueous solution of alkalies producing frothy solution. Resin acids can be derivatized to their metallic salts known as resinates, which finds their use in soap, paints and varnish industries. The abietic acid and commiphoric acid present in colophony and myrrh respectively are the examples of resin acids.

2. Resin Esters: Resin esters are the esters of the resin acids or the other aromatic acids like benzoic, cinnamic, salicylic acids, etc. They are sometimes converted to their free acids by the treatment with caustic alkali. Dragon’s blood and benzoin are the common resin ester containing drugs.

3. Resin Alcohols: Resin alcohols or resinols are the complex alcoholic compounds of high molecular weight. Like resin acids they are found as free alcohols or as esters of benzoic, salicylic, and cinnamic acids. They are insoluble in aqueous alkali solution but are soluble in alcohol and ether. Resinols are present in benzoin as benzoresinol and in storax as storesinol.

4. Resin Phenols: Resin phenols or resinotannols are also high molecular weight compounds which occur in free states or as esters. Due to phenolic group they form phenoxoids and become soluble in aqueous alkali solution. However they are insoluble in water but dissolve in alcohol and ether. Resinotannols gives a positive reaction with ferric chloride. The resinotannol are found in balsam of Peru as peruresinotannol, in Tolu balsam as toluresinotannol and in benzoin as siaresinotannols.

5. Glucoresins: Resins sometimes get combined with sugars by glycosylation and produce glucoresins. Glycoresins can be hydrolysed by acidic hydrolysis to the glycone and aglycone.

6. Resenes: Chemically inert resin products are generally termed as resenes. They are generally found in free state and never form esters or other derivatives. Resenes are soluble in benzene, chloroform and to some extent in petroleum ether. Resenes are insoluble in water. Asafoetida is an example of resene-containing drug, which contains drug about 50% of asaresene B. Accordingly, other simple classification based on the association of resin with gums and/or volatile oils is given below.

7. Oleoresins: Oleoresins are the homogenous mixture of resin with volatile oils. The oleoresins posses an essence due to volatile oils. A trace amount of gummy material may sometimes be found in oleoresins. Turpentine, ginger, copaiba, Canada resin are few important examples of oleoresins.

8. Gum Resins: Gum resins are the naturally occurring mixture of resins with gums. Due to solubility in water, gums can be easily separated out from resin by dissolving the gum in water. Ammoniacum is an example of natural gum resin.

9. Oleogum Resins: Oleogum resins are the naturally occurring mixtures of resin, volatile oil, and gum. The example includes gum myrrh, asafoetida, gamboage, etc. Oleogum resins oozes out from the incisions made in the bark and hardens.

10. Balsams: Balsams are the naturally occurring resinous mixtures which contain a high proportion of aromatic balsamic acids such as benzoic acid, cinnamic acid, and their esters. Balsams containing free acids are partially soluble in hot water. Some important balsams containing drugs are balsam of Peru, balsam of Tolu, benzoin, and storax. The oleogum resin containing drugs like copaiba and Canada are sometimes wrongly referred to as balsams.

Examples:

1. Resins: colophony, cannabis.

2. Oleoresins: copaiba, ginger.

3. Oleo-gum-resins: asafoetida, myrrh.

4. Balsams: balsam of Tolu, balsam of Peru.

Applications:

1. Resin acids or Resinolic acids are high molecular weight substances, form salts with alkali, with aqueous solution of alkali form soap like solution or colloidal suspension Eg: Abietic acid of Colophony

2. Resin alcohol: They occur in free or in combined form, they are usually tetracyclic or Pentacyclic alcohols, Resinotannols are phenolic in nature.

3. Resin Esters: They are formed by combination of various resin acids, Resins or neutral resins are inert and are not affected by Moisture, Light, Many chemicals

4. Glycoresins or glycosidal resins: Resin glycosides on hydrolysis yield glycone and complex acids. Eg: Jalap Resin, Ipomoea Resin