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.
CLASSIFICATION
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:
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.
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.
Resin Alcohols
Resin alcohols or resinols are the complex alcoholic
com-pounds 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.
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.
Glucoresins
Resins sometimes get combined with sugars by glycosylation
and produce glucoresins. Glycoresins can be hydrolysed by acidic hydrolysis to
the glycone and aglycone.
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.
Oleoresins
Oleoresins are the homogenous mixture of resin with
vola-tile 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.
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.
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.
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.
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