Packaging and storage—
Preserve in tight, light-resistant containers.
Identification—
A:
Triturate it with about an equal weight of camphor or menthol: the mixture liquefies.
B:
Dissolve a very small crystal of it in 1 mL of glacial acetic acid, and add 6 drops of sulfuric acid and 1 drop of nitric acid: the liquid shows a deep bluish green color when viewed by reflected light.
C:
Place about 1 g in a test tube, add 5 mL of sodium hydroxide solution (1 in 10), and heat in a water bath: a clear, colorless or pale red, solution is produced, and it becomes darker on standing, without the separation of oily drops. Add to this solution a few drops of chloroform, and agitate the mixture: a violet color is produced.
Melting range 
741
:
between 48
and 51
; but when melted, Thymol remains liquid at a considerably lower temperature.
Limit of nonvolatile residue—
Volatilize about 2 g, accurately weighed, on a steam bath, and dry at 105
to constant weight: not more than 0.05% of residue remains.
Assay—
Transfer about 100 mg of Thymol, accurately weighed, to a 250-mL iodine flask, and dissolve in 25 mL of 1 N sodium hydroxide. Add 20 mL of hot dilute hydrochloric acid (1 in 2), and immediately titrate with 0.1 N bromine VS to within 1 to 2 mL of the calculated endpoint. Warm the solution to between 70
and 80
, add 2 drops of
methyl orange TS, and continue the titration slowly, swirling vigorously after each addition. When the color of the methyl orange is bleached, add 2 drops of 0.1 N bromine VS, shake for 10 seconds, add 1 drop of
methyl orange TS, and shake vigorously. If the solution is red, continue the titration, dropwise and with shaking, until the color is discharged. Repeat the alternate addition of the titrant and the methyl orange TS until the red color is discharged after the addition of the TS. Each mL of 0.1 N bromine is equivalent to 3.755 mg of C
10H
14O.
Auxiliary Information—
Staff Liaison :
Catherine Sheehan, B.Sc., Scientist
Expert Committee : (EM105) Excipient Monographs 1
USP29–NF24 Page 3448
Pharmacopeial Forum : Volume No. 31(3) Page 821
Phone Number : 1-301-816-8262
;)
