1. Resin Acids
Synonyms Resinolic Acid.
The resin acids essentially
contain a large portion of carboxylic acids and phenols. However, they occur
both in the free state and as their respective esters. They are
usually found to be soluble in aqueous solutions of the alkalies, thereby
forming either soap like solutions or colloidal suspensions.
Resinates, i.e.,
the metallic salts of these acids find their extensive usage in the manufacture
of inferior varities of soaps and varnishes.
A few typical examples of resin
acids are enumerated below:
Out of all the six commonly
found resin acids Abietic Acid shall be discussed here under:
Abietic Acid (Synonym Sylvic
Acid)
Chemical Structure 13-Isopropylpodocarpa-7,
13-dien-15-oic acid; (C20 H30O2).
It is a tricyclic diterpene embedded
with four isoprene units. It is studded with four methyl moieties and a
carboxylic acid function. Besides, it also has two double bonds one each in
ring-Band ring-C of the phenanthrene nucleus.
Preparation It is a widely
available organic acid, prepared by the isomerization of rosin.* It may also
be synthesized from dehydroabietic acid.**
The commercial grade of abietic
acid is normally obtained by heating either rosin alone or with mineral acids.
The product thus achieved may be glassy or partly crystalline in nature. It is
usually of yellow colour and has a mp 85°C i.e., much lower than the
pure product (mp 172-175°C).
Characteristic Features It
is obtained as monoclinic plates from alcohol and water. Its physical parameters
are: mp 172-175°C; [α]24D -106° (c = 1 in absolute
alcohol); UVmax 235, 241.5, 250 nm (ε 19500, 22000, 14300). It is
practically insoluble in water, but freely soluble in ethanol, benzene, chloroform,
ether, acetone, carbon disulphide and also in dilute NaOH solution.
Identification It
readily forms the corresponding methyl ester as methyl abietate (C21
H32O2), which is colourless to yellow thick liquid bp
360-365°C, d2020 1.040, and n20D 1.530.
Uses
1. It is used for manufacture
of esters (ester gums), such as: methyl, vinyl and glyceryl esters for use in
lacquers and varnishes.
2. It is also employed
extensively in the manufacture of ‘metal resinates’ e.g., soaps,
plastics and paper sizes.
3. It also assists in the
growth of butyric and lactic acid bacteria.
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* Harris, Sanderson, Org. Syn. Coll. Vol. IV,
1 (1963); and Fieser and Fieser, The
chemistry of Natural Products Related
to Phenanthrene (New
York, 3rd. edn., 1949).
** A.W. Burgastahler, and
L.W. Worden., J.
Am. Chem. Soc., 83, 2587, (1961) E. Wenkert et al., ibid, 86, 2038, (1964)Source:Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar
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