Classification of Resins: Resins are amorphous products of complex chemical nature. They are simply extractions of plant material, are taken either from the whole plant or from specific parts of the plant (bark of trees, flowers of herbs, and buds of shrubs) depending on the availability and desired effect. They are produced in special resin cells known as schizogenous cells in the plants or at the site of injury of the plants and oozes out through the bark and hardens on exposure to air. Commercial resins are collected from fossil materials. Resinous substances may occur alone or in combination with essential oils or gums. They consist primarily of secondary metabolites or compounds that play no role in the primary physiology of a plant. Resin production is widespread, but only a few families are of commercial importance viz. Anacardiaceae, Burseraceae, Dipterocarpaceae, Guttiferae, Hammamelidaceae, Leguminosae, Liliaceae, Pinaceae, Styracaceae and Umbelliferae. Resin is dark brown and it has different levels of hardness and opacity, based on the clarity. Resins are collected from the wood or the bark of the plants that secrete it or ooze out, and they are often collected from plants when the tissues are leached by alcohol. Raw resins are distilled to take away the terpene elements to make products.
- Resins are transparent or translucent solids, semisolids, or liquid substances.
- They are brittle solid.
- They are fusible and flammable organic substances.
- They are not soluble in water but heavier than water.
- They are soluble in volatile oils, ether, and alcohol.
- They become harden when exposed to air.
- They are generally produced by woody plants.
- They do not play a role in the fundamental processes of the plant.
- When heated, they form a smoky flame.
- Resins are a mixture of essential oils.
- They are oxygenated products of terpene and carboxylic acid.
- Chemically they contain esters, acids, and alcohols.
- Some resins are chemically inert, known as resenes.
- Resins generally form soap when boiled with alkali.
- With heat, they become soft, clear and form adhesive fluids.
- Resins are also combined in a glycosidic manner with sugar.
- They are non-nitrogenous compounds.
- The common terpenes in resin are the bicyclic terpenes alpha and beta-pinene and sabinene, the monocyclic terpenes limonene and terpinolene, and smaller amounts of the tricyclic sesquiterpenes.
- They are associated with volatile oils (oleoresins), with gum (gum resins), or with oil and gum (oleo-gum resins).
- Electrically they are non-conductive masses.
- Specific gravity is 0.90-1.25.
Sources of Resins: They are mainly three types that are given in Fig.1.
(a) Natural Sources: The resins that are obtained from plant and animal sources are known as natural sources resins. They are obtained in different parts of plants and by various methods depending on the nature of the resins. They are found inside plants or are exuded by plants, such as sap, latex, or mucilage forms. Some examples of plant source resins are Asafoetida, Myrrh, Balsam, Benzoin, Ginger, Colophony, Jalap, Podophyllum, etc. Some examples of animal source resins are Shellac or Lac. Sometimes animal and plants resins are obtained from fossils, they are known as fossilized resin. Example: Amber which is fossilized tree resin, often known as Copal.
(b) Chemical resins: They are synthetic resins and are useful in various preparations like nail polish. It is made up of organic compounds. They are generally liquid monomers of thermosetting plastics. Typical examples of synthetic resins are epoxy resin, acrylic phenolic resin, urea-formaldehyde resin, etc.
(c) Derived Resins: They are transparent or translucent mass, derivatives of the resins that are not produced directly from plants or animals, e.g., rosin. It is prepared by solidified resin from which the volatile terpene components have been removed by distillation. It has a vitreous fracture and a faintly yellow or brown color, non-odorous or having only a slight turpentine odor and taste. It is insoluble in water but soluble in alcohol and other organic solvents like ether. It melts under the influence of heat and burns with a bright smoky flame.
Preparation of Resin:
As per the method of preparation, resins are classified as follows:
(a) Natural Resins: They occur as exudates from plants, are produced normally, or as a result of pathogenic conditions. It may happen by artificial punctures e.g., mastic or deep cuts in the wood of the plant e.g., turpentine, or by hammering and scorching like balsam of Peru.
(b) Prepared Resins: The resins are 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 dried. Depending on the solvent used in the extraction they are further classified as Oleoresins and gum resins. Ether or acetone is used for the extraction of oleoresins whereas alcohol is used for the extraction of gum resins.
Occurrence in Plants: Based on the sources, resins are collected from different parts of plants namely, resin cells (Ginger), Schizogenous cells (Pine), and glandular hairs (Cannabis).
Classification of Resins
Resins are classified into three types which are tabulated below Fig.2.
Taxonomical Classification: As per the botanical origin, the resins are classified, as Coniferous resins: Colophony, Berberidaceae resins: Podophyllum, etc.
Chemical Classification: These types of resins are classified as per the predominating chemical constituents present in the resin structure:
Acid Resins: They are mixtures of carboxylic acids, found in a tree. They have the basic skeleton of three fused rings fused with the empirical formula C19H29COOH. Resin acids are tacky, yellowish gums that are water-insoluble. They are used to produce soaps.
Examples: Abietic acid from Colophony, Commiphoric acid from Myrrh, Alleuritic acid from Shellac, etc.
Ester Resins: Ester groups are present in the basic structure of the resins.
Examples: Benzyl benzoate in Benzoin, Cinnamyl cinnamate in Storax, etc.
Alcohol Resins: High molecular weight alcoholic group and present in the structure of resins. They sometimes form complex and are found either in a free state or as ester form.
Examples: Peruresinotannol from Balsam of Peru, Guaicresinol from Guaiam, Gurjuresinol from Gurjan etc.
he alcohol that gives specific tannin reaction with iron salts. They are of various types like Aloe resinotannoil (e.g: Aloes), Ammo resinotannol (eg: Ammoniacum), Galba resinotannol (e.g.: Galbanum), Peru resinotannol (e.g.: Balsam of Peru), Sia resinotannol (e.g.: Benzoin) and Tolu resinotannol (e.g.: Balsam of Tolu).
Resinols: They are the resins that give sowing negative specific tannin reaction with iron salts. They are of different types like Benzo resinol (e.g.: Benzoin), Sto resinol (e.g.: Storax), Gurju resinol (e.g.: Gurjun balsam) and Guaia resinol (e.g.: Guaiacum resin).
Glycoresins: They are a combination of resin and sugar.
Examples: Jalap resin from jalap, Podophylloresin from dried roots, and rhizome from Podophyllum hexandrum, etc.
Resenes Resins: They are chemically inert substances and have no chemical properties. They do not undergo hydrolysis or any salt formation.
Examples: Dracoresens from Dragon’s blood, Fluavil from Gutta-percha, Mastic from Pistacia lentiscus, etc
Classification Based on Constituents of Resin: They are classified as per the major constituents present in the resins or resin combinations. They are further sub-classified as:
Resins: They are unorganized hydrocarbon compounds present in the plants. They are produced in resin ducts and are excreted through canals or glands.
Examples: Colophony, Cannabis.
Oleoresins: They are a concentrated liquid form of spice. Oleoresins can be defined as the true essence of the spices and can replace whole/ground spices without impairing any flavor and aroma characteristics.
A naturally occurring mixture of essential oils and a resin, extracted from various plants. They were obtained by extraction with a non-aqueous solvent followed by removal of the solvent by evaporation and by supercritical fluid extraction.
Examples: Copaiba, Ginger, Pine, Balsam.
Advantages of Oleoresins:
- Easy to store and transport.
- More stable when heated.
- More economical to use.
- Easier to control quality and cleaner than the equivalent ground spices.
- Free from contamination.
- Concentrated form reduces storage space and bulk handling and transport requirements.
- The concentrated and moisture-free form ensures longer shelf life due to minimal oxidative degradation or loss of flavor.
Oleo Gum Resins: It is a solid plant exudation consisting of a mixture of volatile oil, gum, and resin. It is a combination of oleo gum and resin. Therefore, an oleo-gum- resin has a nature that is partially soluble in water and alcohol and looks oily.
Examples: Asafoetida, Myrrh, Turmeric.
Balsams: They are also known as turpentine. They are the resinous exudate or sap from certain kinds of trees and shrubs. They mainly contain cinnamic and benzoic acid or their esters in the structures. They are oily and odorous substances. Among the true balsams are the Balm of Gilead, or Mecca, which is cultivated in Arab, Egypt, and Syria and they are extremely costly. The Copaiva balsam, Balsam of Peru, and Tolu are found chiefly in South America.
Examples: Balsam of Tolu, Balsam of Peru, Balsam of Mecca (Liquid balsam obtained from the tree Commiphora gileadensis).
Uses of Resins: Broadly resins are used for paints, varnishes, perfumery preparations, and various pharmaceutical aids. Therapeutic graded resins are used for expectorants, antiseptics, flavoring agents, carminatives, stomachic, etc.
Chemical Tests of Resins:
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