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The Determination of Phenolphthalein in Mineral Oil Emulsion
10
JOURNAL OF THE
AMERICAN PHARMACEUTICAL ASSOCIATION
kspt in a refrigerator for five hours with occasional shaking. It was then allowed to remain undisturbed in the refrigerator for twenty-four hours longer. By filtration of the reaction mixture, 1.4 Gm. (32%) of a light yellow, fine crystalline material was obtained. The crystals decomposed between 250' and 300 ". They decomposed violently if heated over an open flame. The material was used immediately for the next reaction. 4,4'-Bis( acetoxyacetyl)-a,&'-diethy1stilbene.-The bis-diazomethyl ketone (1.1 Gm.; 0.035 mole), obtained in the previous step, was dissolved in a mixture of equal parts of glacial acetic acid and acetic anhydride (25 cc.). Solution took place immediately with vigorous evolution of nitrogen. The reaction mixture was then refluxed for one hour and filtered. After standing in a refrigerator overnight, 0.5 Gm. (34%) of a brownish yellow crystalline product was obtained which crystallized from alcohol in fine, pale yellow needles. M. p. 185-186 ". AnaZ.cCalcd. for C ~ ~ H Z S O C,~ 71.8. : Found: C, 72.1. SUMMARY
stilbene has been prepared by a series of reactions involving the following intermediates: 4,4'dibromo-a,d-diethylstilbene; 4,4'-dicyano-01,01'diethylstilbene; 01,01'-diethyl-4,4'-stilbenedicarboxylic acid ; 01, 01'-diethyl-4,4'-stilbenedicarboxylic acid chloride and 4,4'-bis(diazoacety1) -01, CY' diethylstilbene. The preparation of the intermediate, 4,4'dibromo-a,d-diethylstilbene was carried out by a previously reported procedure, involving the oxidation of p-bromopropiophenone hydrazone with yellow mercuric oxide and conversion of the resulting p-bromophenyl ethyl diazornethane to 4,4'-dibromo-01,a'-diethylstilbene by way of an intermediate sulfone. A method is described for the preparation of the p-bromopropiophenone hydrazone which proved to be quite convenient, productive of good yields and apparently of general applicability. REFERENCES
A new synthetic analog of the adrenal cortical hormones, 4,4'-bis(acetoxyacetyl)-a,a'-diethyl-
31 fi7(i 446)
* The analytical values for hydrogen were somewhat inconsistent: calculated for CzeHnOa: H, 6.46. Found: 7.28.
(2) Solmssen U. V. Chcm. Rev. 37 481(1945). (3) Vargha, i.V. 8;I.d Kovacs, E . h r . 75, 794(1942). (4) Barber, H. J.,'and Slack, R., J: C h e k SOL.,612(1944); J . Pharm. PharLinnell. W. H.. and Sharma. V. R... Ouurt, . mucoZ..'lZ, 263(1939).
(1) Hager, G. P., and Shonle, H. A,, J . A m . Chem. SOL.,68,
-_l. \_---,.
The Determination of Phenolphthalein in Mineral Oil Emulsion* By ALEXANDER T. WARREN, JOHN E. LOGUN, and RAYMOND L. THATCHER A volumetric method based on the iodination of phenolphthalein in an alkaline medium has been applied to the assay for that compound in emulsions. The emulsion is broken by the addition of an acidified solution of sodium chloride. Any glycerin or other solvent capable of absorbing iodine is then removed, the mixture made alkaline with sodium hydroxide, and then treated with an excess of standard iodine solution. After iodination is complete, the excess iodine is determined. phenolphthalein contents of pharmaceutical preparations have been determined by methods based on both gravimetric (I-5), and colorimetric procedures (6). These methods have shortcomings for the purposes of rapid and accurate routine control analysis. The gravimetric methods are lengthy and cumbersome. The colorimetric methods, based on the formation of a red color in alkaline media, suffer inaccuracies because of the absorption of COa from the atmosphere and the subsequent fading of the color. Recently, however, Frederick and Koff HE
*
Received June 24, 1949, from the Quality Control Division, Brooklyn Laboratories, E. R. Squibb and Sons.
(7), have published a colorimetric procedure which results in good color stability in alkaline solutions of 95 per cent alcohol. A volumetric procedure based on the iodination of phenolphthalein in an alkaline medium to tetraiodophenolphthalein (8), has been developed. Substances which will absorb iodine (glycerin, principally) are removed from the emulsion by means of a slightly acidified solution of sodium chloride. The latter breaks the kmulsion, forming a clear, lower aqueous layer and an upper layer consisting of finely divided curds of mineral oil, emulsifying agents and phenolphthalein. After the glycerine has been removed completely, the upper layer is made strongly alkaline with
.
SCIENTIFIC EDITION sodium hydroxide solution and then treated with a known quantity of standard iodine solution. Completion of iodination is indicated b y a color change. The excess iodine is titrated with standard sodium thiosulfate solution in acid medium. EXPERIMENTAL In the extraction process the concentration of acid in the sodium chloride solution is of prime importance. Too strongly acid solutions yield high assay results. This may be due t o the partial hydrolysis of the gum-emulsifying agents which remain in the upper curd layer and which may upon subsequent treatment with strong alkali release simple sugars which absorb iodine. The optimum acid concentration was found t o be 0.25% hydrochloric acid in a 25% sodium chloride solution. The fundamental reaction which takes place between the iodine and the phenolphthalein is as follows: CZOHl404 4- 4Ia 4- 6NaOH
+
GaHd4O4 Na2 44NaI 6Hz0
+
Side reactions between excess IZand excess NaOH also take place but upon acidification before titration with sodium thiosulfate, all iodine not reacting according t o the fundamental equation is reformed as 10. Assay Procedure.-Approximately 10 cc. of the mineral oil emulsion is poured into a 125-cc. separatory funnel from a tared, glass-stoppered weighing bottle, the weight of sample being obtained by difference. Thirty cc. of 25% sodium chloride containing 0.25% hydrochloric acid is added t o the separatory funnel and the mixture shaken continuously for five minutes. The mixture is allowed to separate and the lower aqueous layer is drawn off onto a 12.5-cm. filter paper which has been wetted with distilled water and which contains 1 Gm. of Hyflo Super Cel. The extraction is repeated with 30 cc. of the sodium chloride solution and then with four successive 20-cc. portions, in each case the aqueous layer being filtered through the Hyflo Super Cel. The clear filtrate is discarded The filter paper is finally washed with two 20-cc. portions of the sodium chloride solution and placed in a 500-cc. glass-stoppered Erlenmeyer flask. Thirty cc. of NaOH (U. S. P. XI11 Test Solution) are added t o the material in the separatory funnel and the mixture is shaken for one minute. The contents of the separatory funnel are transferred t o the 500-cc. glassstoppered Erlenmeyer flask containing the filter paper. The separatory funnel is rinsed quantitatively with a total of about 50 cc. of distilled water. The total volume of liquid in the flask should not exceed 125 cc. Fifty cc. of 0.1 N iodine solution (U. S. P. XI11 V. S.) are added from a burette. The flask is stoppered and shaken occasionally until the pink color has been discharged and the mixture assumes a white color with a greenish yellow tint. Fifteen cc. of hydrochloric acid is added to the flask and the excess liberated iodine immediately titrated with 0.1 N sodium thiosulfate solution (U. S. P. XI11 V. S.) using starch (U. S. P. XI11 T. S.) as an indicator. A blank is prepared by adding t o a 500-
11
cc. glass-stoppered Erlenmeyer flask the following: 30 cc. of NaOH (U. S. P. XI11 T. S.), 15 cc. of hydrochloric acid, 75 cc. of distilled water, one 12.5 cm. filter paper, 1 Gm. of Hyflo Super Cel, and 25 cc. of 0.1 N iodine solution (U. S. P. XI11 V. S.). In accordance with the equation, 1 gram equivalent of phenolphthalein reacts with 8 gram equivalents of iodine. Therefore, 1cc. of 0.1 N Na&O, is equivalent t o 0.003979 Gm. of phenolphthalein. The results of several assays using samples of mineral oil emulsion t o which known amounts of phenolphthalein were added are tabulated in Table I. Assay results obtained on several brands of mineral oil emulsion with phenolphthalein are tabulated in Table 11.
TABLE I Phenolphthalein Amount Added, Amount Found,
%
%
A B
0.34 0.34
C
0.34
D
0.34
E
0.34 0.34
0.34 0.32 0.32 0.32 0.32 0.34 0.35 0.35 0.33 0.31 0.32 0.35 0.35 0.33 0.31 0.33
Chemist
F
TABLE I1 Phenolphthalein Amount Found, Label Strength, Sample
A B C
D E F
%
%
0.34 0.34 0.34 0.30 1.00 0.31
0.33 0.33 0.35 0.33 1.08
0.35
SUMMARY
A simple and satisfactory volumetric method for the determination of phenolphthalein iodometrically in mineral oil emulsions is described. REFERENCES
843(1942). ( 5 ) O’Keefe, H. F., ibid., 26, 311(1943). (6) Serrallach, J. A,, and Owen, R. J., THIS JOURNAL, 20,
JOURNAL OF THE
AMERICAN PHARMACEUTICAL ASSOCIATION
kspt in a refrigerator for five hours with occasional shaking. It was then allowed to remain undisturbed in the refrigerator for twenty-four hours longer. By filtration of the reaction mixture, 1.4 Gm. (32%) of a light yellow, fine crystalline material was obtained. The crystals decomposed between 250' and 300 ". They decomposed violently if heated over an open flame. The material was used immediately for the next reaction. 4,4'-Bis( acetoxyacetyl)-a,&'-diethy1stilbene.-The bis-diazomethyl ketone (1.1 Gm.; 0.035 mole), obtained in the previous step, was dissolved in a mixture of equal parts of glacial acetic acid and acetic anhydride (25 cc.). Solution took place immediately with vigorous evolution of nitrogen. The reaction mixture was then refluxed for one hour and filtered. After standing in a refrigerator overnight, 0.5 Gm. (34%) of a brownish yellow crystalline product was obtained which crystallized from alcohol in fine, pale yellow needles. M. p. 185-186 ". AnaZ.cCalcd. for C ~ ~ H Z S O C,~ 71.8. : Found: C, 72.1. SUMMARY
stilbene has been prepared by a series of reactions involving the following intermediates: 4,4'dibromo-a,d-diethylstilbene; 4,4'-dicyano-01,01'diethylstilbene; 01,01'-diethyl-4,4'-stilbenedicarboxylic acid ; 01, 01'-diethyl-4,4'-stilbenedicarboxylic acid chloride and 4,4'-bis(diazoacety1) -01, CY' diethylstilbene. The preparation of the intermediate, 4,4'dibromo-a,d-diethylstilbene was carried out by a previously reported procedure, involving the oxidation of p-bromopropiophenone hydrazone with yellow mercuric oxide and conversion of the resulting p-bromophenyl ethyl diazornethane to 4,4'-dibromo-01,a'-diethylstilbene by way of an intermediate sulfone. A method is described for the preparation of the p-bromopropiophenone hydrazone which proved to be quite convenient, productive of good yields and apparently of general applicability. REFERENCES
A new synthetic analog of the adrenal cortical hormones, 4,4'-bis(acetoxyacetyl)-a,a'-diethyl-
31 fi7(i 446)
* The analytical values for hydrogen were somewhat inconsistent: calculated for CzeHnOa: H, 6.46. Found: 7.28.
(2) Solmssen U. V. Chcm. Rev. 37 481(1945). (3) Vargha, i.V. 8;I.d Kovacs, E . h r . 75, 794(1942). (4) Barber, H. J.,'and Slack, R., J: C h e k SOL.,612(1944); J . Pharm. PharLinnell. W. H.. and Sharma. V. R... Ouurt, . mucoZ..'lZ, 263(1939).
(1) Hager, G. P., and Shonle, H. A,, J . A m . Chem. SOL.,68,
-_l. \_---,.
The Determination of Phenolphthalein in Mineral Oil Emulsion* By ALEXANDER T. WARREN, JOHN E. LOGUN, and RAYMOND L. THATCHER A volumetric method based on the iodination of phenolphthalein in an alkaline medium has been applied to the assay for that compound in emulsions. The emulsion is broken by the addition of an acidified solution of sodium chloride. Any glycerin or other solvent capable of absorbing iodine is then removed, the mixture made alkaline with sodium hydroxide, and then treated with an excess of standard iodine solution. After iodination is complete, the excess iodine is determined. phenolphthalein contents of pharmaceutical preparations have been determined by methods based on both gravimetric (I-5), and colorimetric procedures (6). These methods have shortcomings for the purposes of rapid and accurate routine control analysis. The gravimetric methods are lengthy and cumbersome. The colorimetric methods, based on the formation of a red color in alkaline media, suffer inaccuracies because of the absorption of COa from the atmosphere and the subsequent fading of the color. Recently, however, Frederick and Koff HE
*
Received June 24, 1949, from the Quality Control Division, Brooklyn Laboratories, E. R. Squibb and Sons.
(7), have published a colorimetric procedure which results in good color stability in alkaline solutions of 95 per cent alcohol. A volumetric procedure based on the iodination of phenolphthalein in an alkaline medium to tetraiodophenolphthalein (8), has been developed. Substances which will absorb iodine (glycerin, principally) are removed from the emulsion by means of a slightly acidified solution of sodium chloride. The latter breaks the kmulsion, forming a clear, lower aqueous layer and an upper layer consisting of finely divided curds of mineral oil, emulsifying agents and phenolphthalein. After the glycerine has been removed completely, the upper layer is made strongly alkaline with
.
SCIENTIFIC EDITION sodium hydroxide solution and then treated with a known quantity of standard iodine solution. Completion of iodination is indicated b y a color change. The excess iodine is titrated with standard sodium thiosulfate solution in acid medium. EXPERIMENTAL In the extraction process the concentration of acid in the sodium chloride solution is of prime importance. Too strongly acid solutions yield high assay results. This may be due t o the partial hydrolysis of the gum-emulsifying agents which remain in the upper curd layer and which may upon subsequent treatment with strong alkali release simple sugars which absorb iodine. The optimum acid concentration was found t o be 0.25% hydrochloric acid in a 25% sodium chloride solution. The fundamental reaction which takes place between the iodine and the phenolphthalein is as follows: CZOHl404 4- 4Ia 4- 6NaOH
+
GaHd4O4 Na2 44NaI 6Hz0
+
Side reactions between excess IZand excess NaOH also take place but upon acidification before titration with sodium thiosulfate, all iodine not reacting according t o the fundamental equation is reformed as 10. Assay Procedure.-Approximately 10 cc. of the mineral oil emulsion is poured into a 125-cc. separatory funnel from a tared, glass-stoppered weighing bottle, the weight of sample being obtained by difference. Thirty cc. of 25% sodium chloride containing 0.25% hydrochloric acid is added t o the separatory funnel and the mixture shaken continuously for five minutes. The mixture is allowed to separate and the lower aqueous layer is drawn off onto a 12.5-cm. filter paper which has been wetted with distilled water and which contains 1 Gm. of Hyflo Super Cel. The extraction is repeated with 30 cc. of the sodium chloride solution and then with four successive 20-cc. portions, in each case the aqueous layer being filtered through the Hyflo Super Cel. The clear filtrate is discarded The filter paper is finally washed with two 20-cc. portions of the sodium chloride solution and placed in a 500-cc. glass-stoppered Erlenmeyer flask. Thirty cc. of NaOH (U. S. P. XI11 Test Solution) are added t o the material in the separatory funnel and the mixture is shaken for one minute. The contents of the separatory funnel are transferred t o the 500-cc. glassstoppered Erlenmeyer flask containing the filter paper. The separatory funnel is rinsed quantitatively with a total of about 50 cc. of distilled water. The total volume of liquid in the flask should not exceed 125 cc. Fifty cc. of 0.1 N iodine solution (U. S. P. XI11 V. S.) are added from a burette. The flask is stoppered and shaken occasionally until the pink color has been discharged and the mixture assumes a white color with a greenish yellow tint. Fifteen cc. of hydrochloric acid is added to the flask and the excess liberated iodine immediately titrated with 0.1 N sodium thiosulfate solution (U. S. P. XI11 V. S.) using starch (U. S. P. XI11 T. S.) as an indicator. A blank is prepared by adding t o a 500-
11
cc. glass-stoppered Erlenmeyer flask the following: 30 cc. of NaOH (U. S. P. XI11 T. S.), 15 cc. of hydrochloric acid, 75 cc. of distilled water, one 12.5 cm. filter paper, 1 Gm. of Hyflo Super Cel, and 25 cc. of 0.1 N iodine solution (U. S. P. XI11 V. S.). In accordance with the equation, 1 gram equivalent of phenolphthalein reacts with 8 gram equivalents of iodine. Therefore, 1cc. of 0.1 N Na&O, is equivalent t o 0.003979 Gm. of phenolphthalein. The results of several assays using samples of mineral oil emulsion t o which known amounts of phenolphthalein were added are tabulated in Table I. Assay results obtained on several brands of mineral oil emulsion with phenolphthalein are tabulated in Table 11.
TABLE I Phenolphthalein Amount Added, Amount Found,
%
%
A B
0.34 0.34
C
0.34
D
0.34
E
0.34 0.34
0.34 0.32 0.32 0.32 0.32 0.34 0.35 0.35 0.33 0.31 0.32 0.35 0.35 0.33 0.31 0.33
Chemist
F
TABLE I1 Phenolphthalein Amount Found, Label Strength, Sample
A B C
D E F
%
%
0.34 0.34 0.34 0.30 1.00 0.31
0.33 0.33 0.35 0.33 1.08
0.35
SUMMARY
A simple and satisfactory volumetric method for the determination of phenolphthalein iodometrically in mineral oil emulsions is described. REFERENCES
843(1942). ( 5 ) O’Keefe, H. F., ibid., 26, 311(1943). (6) Serrallach, J. A,, and Owen, R. J., THIS JOURNAL, 20,