Parachlorophenol

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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The omission of this monograph has been postponed. As of November 1, 2020 this monograph remains official USP text. _{(RB 1-Nov-2020)}

C₆H₅ClO    128.56

Phenol, 4-chloro-;

p-Chlorophenol CAS RN®: 106-48-9; UNII: 3DLC36A01X.

1 DEFINITION

Parachlorophenol contains NLT 99.0% and NMT 100.5% of parachlorophenol (C₆H₅ClO).

2 IDENTIFICATION

A.

Sample solution: 10 mg/mL of Parachlorophenol

Analysis: Add bromine TS dropwise to the Sample solution.

Acceptance criteria: A white precipitate is formed; at first it redissolves, but then it becomes permanent as an excess of the reagent is added.

B.

Sample solution: 10 mg/mL of Parachlorophenol

Analysis: Add 1 drop of ferric chloride TS to 10 mL of Sample solution.

Acceptance criteria: The solution acquires a violet-blue color.

C.

Analysis: Heat a few crystals, held on a copper wire, in the edge of a nonluminous ame.

Acceptance criteria: A green color is imparted to the flame.

D.

Sample: 1 g of Parachlorophenol

Analysis: Mix the Sample and 5 mL of sodium hydroxide solution (1 in 3), then add 1.5 g of monochloroacetic acid. Shake, and heat on a steam bath for 1 h. Cool, dilute with 15 mL of water, and acidify with hydrochloric acid. Extract with 50 mL of ether, wash the ether solution with 10 mL of cold water, then extract the ether solution with 25 mL of sodium carbonate solution (1 in 20). Acidify the solution with hydrochloric acid, collect the resulting precipitate on a filter, and recrystallize it from hot water.

Acceptance criteria: The resulting parachlorophenoxyacetic acid melts between 154° and 158°.

3 ASSAY

Procedure

Sample: 1 g of Parachlorophenol

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Residual titration

Titrant: 0.1 N bromine VS

Back-titrant: 0.1 N sodium thiosulfate VS

Endpoint detection: Visual

Analysis: Transfer the Sample to a 500-mL volumetric flask, and dissolve and dilute with water to volume. Transfer a 25.0-mL portion of the solution to an iodine flask, cool in an ice bath to 4°, and add 20.0 mL of Titrant. Add 5 mL of hydrochloric acid, and immediately insert the stopper. Maintain the flask at a temperature of 4° for 30 min, shaking at frequent intervals. Allow it to stand for 15 min, remove the stopper just sufficiently to introduce quickly 5 mL of potassium iodide solution (1 in 5), taking care that no bromine vapor escapes, and at once insert the stopper in the flask. Shake thoroughly, remove the stopper, and rinse it and the neck of the flask with a small portion of water, allowing the washings to flow into the flask. Shake the mixture, and titrate the liberated iodine with Back-titrant, using 3 mL of starch TS as the indicator. Perform a blank determination. Each mL of 0.1 N bromine is equivalent to 3.214 mg of parachlorophenol (C₆H₅ClO).

Acceptance criteria: 99.0%–100.5%

4 IMPURITIES

4.1 Limit of Nonvolatile Residue

Sample: 1 g of Parachlorophenol

Analysis: Heat the Sample in a tared container on a steam bath until it is volatilized, and dry at 105° for 1 h.

Acceptance criteria: NMT 0.1% of residue remains.

4.2 Limit of Chloride

Sample solution: 10 mg/mL of Parachlorophenol

Analysis: Acidify 10 mL of Sample solution with 2 N nitric acid, and add a few drops of silver nitrate TS.

Acceptance criteria: No turbidity or opalescence is produced.

5 SPECIFIC TESTS

Clarity and Reaction of Solution

Sample solution: 10 mg/mL of Parachlorophenol

Acceptance criteria: Solution is clear and is acid to litmus.

Congealing Temperature 〈651〉: Between 42° and 44°

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant