Packaging and storage—
Preserve in tight, light-resistant containers. Store at 25
, excursions permitted between 15
and 30
.
Identification—
Place about 1 mL of Iophendylate, 15 mL of water, and 7 g of potassium dichromate in a round-bottom, 50-mL flask. Carefully add 10 mL of sulfuric acid, moderating the ensuing vigorous reaction by cooling the flask with tap water. When the reaction has subsided, reflux the mixture for 2 hours. Pour the cooled contents of the flask into 25 mL of water, filter the mixture with suction, and wash the precipitate with a small quantity of cold water. Crystallize the precipitate from 10 mL of diluted alcohol, and sublime the solid so obtained: the sublimate of
p-iodobenzoic acid melts between 268
and 272
.
Free acids—
Transfer about 4 g, accurately weighed, to a small flask, and add 20 mL of alcohol. Swirl to dissolve the test specimen, add 5 drops of phenolphthalein TS, and titrate with 0.050 N alcoholic potassium hydroxide to a pink color that persists for 30 seconds: not more than 0.60 mL of 0.050 N alcoholic potassium hydroxide is required for neutralization, correction being made for the amount of 0.050 N alcoholic potassium hydroxide consumed by a blank (0.3% as iodophenylundecanoic acid).
Free iodine—
Determine its absorbance in a 4-cm cell, at 485 nm, with a suitable spectrophotometer, using water as the blank: the absorbance is not greater than 0.16 (7.5 ppm).
Saponification value—
Transfer about 1 g, accurately weighed, to a 250-mL flask, add 25.0 mL of 0.5 N alcoholic potassium hydroxide VS, and reflux the mixture on a steam bath for 1 hour. Cool, add 25 mL of water and 0.7 mL of
phenolphthalein TS, and titrate with 0.5 N hydrochloric acid VS. The saponification value (see
Fats and Fixed Oils 
401
) is between 132 and 142.
Assay—
Dissolve about 50 mg of Iophendylate, accurately weighed, in 5 mL of toluene contained in a 125-mL separator fitted with a suitable, inert plastic stopcock. Add 15 mL of sodium biphenyl, and shake vigorously for 2 minutes. Extract gently with three 10-mL portions of 5
M phosphoric acid, combining the lower phases in a 125-mL iodine flask. Add 1 N sodium hypochlorite dropwise to the combined extracts until the solution turns brown, and then add an additional 0.5 mL. Shake intermittently for 3 minutes, add 5 mL of freshly prepared, saturated phenol solution, mix, and allow to stand for 1 minute, accurately timed. Add 1 g of potassium iodide, shake for 30 seconds, and titrate rapidly with 0.1 N sodium thiosulfate VS, adding 3 mL of
starch TS as the endpoint is approached. Each mL of 0.1 N sodium thiosulfate is equivalent to 6.939 mg of C
19H
29IO
2.
;)
-methyl-, ethyl ester.