The procedure described below is based on the classical method of Hesse and Zeitschel.121 It depends on the actual separation of the ester from the volatile oil by the formation of the ether insoluble sulfate.
Procedure: Dissolve about 25 to 100 g. of oil in twice the volume of anhydrous ether. Cool the solution well in a freezing mixture, the temperature being reduced to at least 0o. Add,with constant stirring, a solution of 1 volume of concentrated sulfuric acid in 5 volumes of anhydrous ether until no further precipitate forms. Collect the precipitate in a small, wellcooled Buchner funnel and wash with dry, cold ether until odorless. Dissolve this precipitate in water with the aid of alcohol if necessary, and titrate with 0.5 N sodium hydroxide.
Calculate the ester content by means of the following formula :
Percentage of methyl anthranilate = 3.775a/s
where: a = cc. of alkali required;
           s original weight of oil taken in grams.
To this solution add an excess of 0.5 N sodium hydroxide and heat the mixture on a steam bath for 30 min. Titrate the free alkali which is unconsumed with 0.5 N hydrochloric acid. Calculate again the ester content by means of the following formula:
Percentage of methyl anthranilate =  7.55b/s
where : b = cc. of alkali consumed in the saponification ;
            s original weight of oil taken in grams.
If the ester is exclusively methyl anthranilate, a should be twice as large as b.
The procedure as described will determine all basic constituents which form ether insoluble sulfates (e.g., the methyl ester of methyl anthranilic acid) in addition to methyl anthranilate.
For the determination of methyl anthranilate in the presence of methyl N-methyl anthranilate, Erdmann122 has suggested a procedure based on the diazotization of methyl anthranilate, a primary aromatic amine. The ester is washed out of the oil with dilute sulfuric or hydrochloric acid, and the acid solution treated with a 5 per cent sodium nitrite solution to diazotize the amine. The solution is then titrated with an alkaline solution of β-naphthol. (This solution is prepared by dissolving 0.5 g. β-naphthol in 0.5 cc. of sodium hydroxide, at least 30 per cent, and adding a solution of 15 g. of sodium carbonate in 150 cc. of water.) The azo dye thereby formed is insoluble and precipitates out. The titration is continued until no further precipitation occurs.
A combination of the method of Hesse and Zeitschel and that of Erdmann can be used to determine the percentage of methyl anthranilate and of methyl N-methyl anthranilate.
121 Bar. 34 (1901), 296.

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