Colophony (Synonym Rosin) (Resins)

1. Colophony (Synonym Rosin)

Biological Source It is a yellow resin, and abietic anhydride. It is the residue left after distilling off the volatile oil from the oleoresin obtained from Pinus palustris and other species of Pinus belonging to family Pinaceae. Generally, it is offered as wood rosin obtained from southern pine stumps, gum rosin collected as the exudate from incisions in the living tree viz., P. palustris and P. caribaea, and finally from tall oil rosin. It is chiefly produced in the USA.
Characteristic Features Colophony fuses gradually at 100°C and at a higher temperature it burns with a smoky flame, while leaving not more than 0.1% of ash as a residue. The alcoholic solution of colophony turns into milky-white on addition of water. When fragments of rosin are heated with water, they first melt then flow together and ultimately forms a sticky-mass.
It is a pale yellow to amber, translucent fragments, brittle fracture at ordinary temperature. It has a slight turpentine-like odour and taste.
Its acid number is not less than 150 and d 1.07-1.09. It is almost insoluble in water, but freely soluble in ethanol, benzene, ether, glacial acetic acid, oils, carbon disulphide and also soluble in dilute solutions of fixed alkali hydroxides.
Chemical Constituents
1. Colophony contains 90% resin acids known as abietic acid (see Section 2.7.7). The remaining 10% as resene-an inert substance and esters of fatty acids.
2. It also contains a mixture of dihydroabietic acid (C20H30O2) and dehydroabietic acid (C20H28O2).
3. On being heated at 300°C, abietic acid undergoes further molecular rearrangement to produce neo-abietic acid.
Chemical Tests
1. Dissolve 0.1 g of powdered colophony resin in 10 ml of acetic anhydride, add one drop of sulphuric acid and shake well. The appearance of a purple colour which rapidly changes to violet colour.
2. The alcoholic solution of colophony is acidic to litmus paper i.e., it turns blue litmus paper to red.
3. Dissolve 0.2 g of colophony with 5 ml of petroleum ether (60-80°C) and filter to discard the undissolved resin, if any. Shake the resulting clear solution with twice its volume of 0.1% (w/v) cupric acetate solution. The petroleum ether layer attains an emerald-green colouration due to the formation of the copper salt of abietic acid.
Uses
1. Colophony is used in pharmacy for the preparation of zinc oxide plasters, ointments and other adhesive plasters.
2. It is widely used in the manufacture of printing inks, rubber, dark varnishes, sealing wax, linoleum and thermoplastic floor tiles.
3. It also finds its application as varnish and paint dries, cements, soaps, wood polishes, paper, plastics, fireworks, tree wax, sizes, rosin oil
4. It is used for waterproofing cardboard, walls etc.

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