These are amorphous products of complex chemical nature.

They are considered as end products of metabolism, and are believed to arise by oxidation of polymerized terpenoids metabolites forming complex mixtures.

Resins are found as exudations from the trunk of various trees.

Resins and their combinations are formed in the plant as normal physiological products, but their production is increased by injury.

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RESINS

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. They are also dissolve in volatile oils, fixed oils, and chloral hydrate

They occur as: transparent or

translucent solids, semi-solids or

liquid substances.

Resins when heated, they soften and ultimately melt.

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Resins are classified mostly on the

basis of two important features, that

is:

1. On the basis of their chemical nature.

(functional groups).

2. Secondly as per their combination with the

other group of compounds like essential

oils and gums.

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CHEMICAL CLASSIFICATION

Chemical classification of resins categorizes these products according to their active

functional groups as given below:

Resin acids: these includes abietic acid, copaivic acid, oxycopaivic acid and

commiphoric acid, found in a free state or as esters.

Resin alcohol “Resinols”: Resin alcohols are found free or in combination with

aromatic acids such as benzoic, salicylic and cinnamic acids. These include high

molecular weight alcohols of two types:

1. Resinols: these are simple alcohols such as benzoresinol and

storesinol.

2. Resinotannols: these are complex alcohols of high molecular weight

and they give a tannin reaction with iron salts. Examples of these

alcohols include peruresinotannol and sumaresinotannol.

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CHEMICAL CLASSIFICATION

• Resenes: these are complex neutral substances devoid of

characteristic chemical properties (chemically inert compounds).

Asafoetida is an example of resene-containing drug, which

contains drug about 50% of asaresene B.

• Glycoresins: these are complexes of sugars and resin acids and

on hydrolysis they yield sugars and complex resin acid.

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The different forms and combinations in which resins occur include:

• Resins: these are the resins which are not combined with other substances. Examples of these resins include colophony, guaiacum, and podophyllum.

• Oleo-resins: these are mixtures of resins and volatile oils. Natural oleoresins are exemplified by turpentine and copaiba. Some pharmaceutical oleoresins are derived from ginger and capsicum.

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• Gum-resins: these are mixtures of resinous compounds and gums e.g. gamboge.

• Oleo-gum-resins: these are mixture of resinous compounds, gums and volatile oils, e.g. myrrh, asafoetida, galbanum, and olibanum.

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• Balsams: They are the naturally occurring resinous mixtures which contain a high proportion of aromatic balsamic acids such as benzoic acid, cinnamic acid, and their esters. E.g. balsam of Peru, balsam of Tolu and benzoin.

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A part from their common pharmaceutical uses, resins and their combinations find wide application in aromatherapy and as fixatives in the perfumery industry, e.g. olibanum from Boswellia frereana, and the volatile oil distilled from wood of Cedrus deodora.

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Plant resins are valued for the production of varnishes, adhesives, and food glazing agents.

The ancient Chinese, Japanese, Egyptians, and others used resins in preparation of lacquers and varnishes.

Synthetic resins are industrially produced resins, typically viscous substances that convert into rigid polymers by the process of curing. Important examples are bisphenol A diglycidyl ether, which is a resin converted to epoxy glue upon the addition of a hardener. Silicones are often prepared from silicone resins via room temperature vulcanization.

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• The process of the isolation of resin from crude drug can be a difficult task due to the presence of various combinations.

• However the most generalized technique can be the extraction of the drug with alcoholic solvents and then subsequent precipitation of resin by adding concentrated alcoholic extract to a large proportion of water.

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Pharmaceutical resins are obtained

from the plants and animals by one of

the following methods:

By extraction with alcohol and precipitation

with water, e.g. jalap, podophyllum,…etc.

By distillation for separation of oil, e.g. copaiba,

colophony,…etc.

By heating the plant part, e.g. guaiacum.

As plant exudates by incisions, e.g. myrrh,

asafoetida, balsams,…etc.

By collecting fossil resins, e.g. copal,

kauri,…etc.

By processing the encrustations i.e. shellac.

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