(met'' a kree' sol).
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C7H8O 108.14

3-Hydroxytoluene [108-39-4].
» Metacresol contains not less than 95.0 percent and not more than 101.0 percent of C7H8O.
Packaging and storage— Preserve in tight, light-resistant containers.
Clarity of solution—
A: Add 10 mL of it to 10 mL of solvent hexane, and mix: a clear solution is obtained.
B: Add 1.0 mL of it to 20 mL of 1 N sodium hydroxide, and mix: a clear solution is obtained.
Identification— Shake 10 mL of it with 30 mL of water in a separator, and allow to separate. The lower layer is clear; the upper layer clears slowly. To 5 mL of the upper layer add a drop of ferric chloride TS: a bluish color is produced. To a separate 5-mL portion of the upper layer add bromine TS dropwise: a white precipitate is obtained.
Assay— Transfer about 10 drops of Metacresol to an accurately tared 100-mL volumetric flask, and weigh to determine the amount, in mg, added. Add about 50 mL of 1 N sodium hydroxide, shake to dissolve, dilute with 1 N sodium hydroxide to volume, and mix. Transfer 10.0 mL of this solution to an iodine flask, add about 50 mL of water and sufficient 18 N sulfuric acid to neutralize the solution to litmus, and cool to 20. Add 25.0 mL of 0.1 N bromine VS and 15 mL of hydrochloric acid, and immediately insert the stopper. Shake the flask, and cool under running water. Allow to stand in a cool, dark place for 30 minutes, shaking every 10 minutes. Cool to 20, quickly add 5 mL of potassium iodide solution (1 in 5) to the collar of the flask, gently lift the stopper momentarily, and allow the solution to be drawn into the flask, shake thoroughly, remove the stopper, and rinse it and the inside neck of the flask with a small quantity of water so that the washing flows into the flask. Add 1 mL of chloroform, shake, and titrate the liberated iodine with 0.1 N sodium thiosulfate VS, adding 3 mL of starch TS as the endpoint is approached. Perform a blank determination (see Residual Titrations under Titrimetry 541). Each mL of 0.1 N bromine is equivalent to 1.802 mg of C7H8O.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Feiwen Mao, M.S.
Senior Scientific Liaison
(SM32010) Monographs - Small Molecules 3
USP35–NF30 Page 3825
Pharmacopeial Forum: Volume No. 37(4)