Determination of Camphor in Alcoholic Solutions Dinitrophenylhydrazine Method ELMER M. PLEIN
AND
CHARLES F. POE, University of Colorado, Boulder, Colo.
I
N A N INVESTIGATIOX of various methods for determining camphor in spirits and liniments, the dinitrophenylhydrazine reagent suggested by Brady ( I ) , Fernandez and coworkers (45), and Hampshire and Page (4) was used. After trying a number of experiments, the authors were informed that a modified dinitrophenylhydrazine method, in which 5 cc. of the spirit were used, was to be adopted as official in the U. S. Pharmacopmia XI. A number of experiments with the Hampshire and Page method and the suggested U. S. P. X I modification failed to give satisfactory results. Consequently work was undertaken to develop a modified procedure, which is presented below..
dilution. The amount of acid in the method of Hampshire and Page was equivalent to about 9.5 cc. Later, the determination was found to be equally accurate when all the sulfuric acid was added to the reagent test solution, and this addition of acid had the added advantages that very little decomposition took place in the test solution on standing, and that the crystallization of the dinitrophenylhydrazine was reduced to a minimum. Experiments have shown that this modified reagent can be preserved for several weeks. TABLE
Experimental
1 ' . Camphor Present
The first difficulty in both the Hampshire and Page and the modified U. S. P. X I methods was with the dinitrophenylhydrazine reagent, in which 1.5 grams of 2,Cdinitrophenylhydrazine are dissolved in a cooled mixture of 10 cc. of sulfuric acid and 10 cc. of water, and then sufficient water is added to make 100 cc. of solution. Fine crystals appeared soon after the reagent was diluted and cooled. A fine brown decomposition product was also formed after the solution had stood. TABLE
I.
Camphor Present
%
method
%
OF
ADDEDSULFURIC ACID Camphor Found Hampshire and Page method
s. P. X I
method
%
%
%
5 0 5.0 5.0 10.0 10.0 10.0 15.0 15 0 15 0
4.45 4.20 4.39 7.74 7.44 7.23 8.81 8 69 8 65
4.86 4.78 4.83 9.73 9.68 9.78 14.44 14.55 14.51
By using this new test reagent: a number of determinations were made of different samples of spirit of camphor and gave results which were equivalent t o less than the theoretical amounts of camphor (Table 11). The low results in the U. S. P. method (modified by adding more sulfuric acid to prevent the precipitation of the phenylhydrazine) were explained by the fact that a considerable quantity of camphor sublimed in the neck of the flask and in the reflux condenser during the heating process; consequently this camphor was never converted to the hydrazone. In order to overcome this difficulty with the modified U. 8.P. method, various amounts of alcohol were added t o the reaction mixture; the alcoholic vapors condensed and ran down the sides of the condenser and flask and thus washed any sublimed camphor back into the reaction mixture. The optimum amount of alcohol was found to be 15 cc. (Table 111). With more than this amount of alcohol, some of the hydrazone formed was dissolved. All determinations reported below use the new reagent, with added amounts of alcohol. The U. S. P. X I , through a typographical error, recommends the use of 25 cc. of spirit. With this amount of 10 per cent camphor solution, a number of determinations were made, and the maximum amount of camphor found was 3.45 per cent. Not enough dinitrophenylhydraeine is present in the
.\SALYSIS O F SPIRIT OF C . 4 X P H O R
t-,s. P. X I
11. EFFEC'r
Camphor Found Hampshire and Page method
%
A series of samples of spirit of camphor, prepared from camphors obtained from different sources, was carefully made to contain exactly 5.0, 7.5, 10.0, 12.5, and 15.0 grams of camphor in each 100 cc. of solution. The official 95 per cent alcohol was used in making these solutions. The U. S. P. XI was followed in the analysis of 5-cc. amounts of the different spirits. After the mixture had been refluxed, 200 cc. of 1 to 50 sulfuric acid were added, and the mixture was allowed to stand 24 hours. At the end of this period of time in many cases, especially when the spirits contained less than 10 per cent of camphor, numberless small, star-shaped crystals of dinitrophenylhydrazine which could not be separated from the hydrazone formed in the mixture. This condition, of course, caused some of the results to be high, especially in the lower percentage of camphor. With the spirits containing 10 per cent or more of camphor, a greater amount of the phenylhydrazine was used up, and therefore fewer crystals separated out. The lower results were caused by the sublimation of some of the camphor. Similar results were obtained with the Hampshire and Page method (Table I). After completing the heating process, the authors diluted the mixture with various strengths of sulfuric acid, and discovered that 200 cc. of sulfuric acid (3 to 100) would prevent the crystallization of the dinitrophenylhydrazine. This change means that 13.5 cc. instead of 11.5 cc. of sulfuric acid (96 per cent) were present in each reaction mixture after
TABLE
111. EFFECTO F ADDINOALCOHOL Alcohol Added
Camphor Present
Kone
5 cc.
15 cc.
10 cc.
20 cc.
Camphor Found
I
25 cc.
%
%
%
%
%
10.0 10.0 10.0 15.0
7.74 7.74 7.23 8.72
9.12 9.06 9.34 13.25
9.59 9.57 9.68 14.50
9.68 9.75 9.73 14.54
5.0 7.5 10.0
4.45 6.39 8.59 8.41 10.14
4.81 7.19 9.47 9.43 13.99
4.88 7.37 9.79 9.83 14.65
% 9.41 9.72 9.66 14.55
78
50 cc.
%
4.90 7.40 9.82
..
9.SO
,, ,,
14.72
,.
..
%
%
9.55 9.44 9.68 14.60
9.58 9.33 9.65 14.62
... ..
4.78 7.36 9.79 9.75 14.60
.. .. .. .. ,.
4.37 6.78 9.11 9.15 14.33
2-Cc. Sample
10.0 15.0
35 cc.
5-Cc. Sample
,
..
ANALYTICAL EDITION
FEBRUARY 15, 1938
OF TIMEOF HEATING TABLE IV. EFFECTOF VARIATION MIXTURE
Camphor Present 1 hour I
2 houra
Camphor Found (2-cc. samples) 3 hours 4 hours 5 hours
6 hours
9 houri
%
%
%
%
%
%
%
%
5 10 15 15
4.45 8.50 12.33 12.34
4.85 9.66 13.90 13.63
4.92 9.79 14.63 14.49
4.90 9.82 14.76 14.63
4.92 9.80 14.75 14.63
4.95 9.84 14.80 14.78
4.90 9.79 14.75 14 89
OF TABLEv. EFFECT
T-ARI.4TIOS O F
TIMEO F STBSDING
Camphor Found (2-cc. samples)
7
7
Camphor Present
0 hour
24 hours
48 hours
%
%
%
%
96 hours
%
79
limit to the excess that is necessary, as shown by the results with 150 cc. of the reagent solution. The consistently low results might have been caused by the slight solubility of the hydrazone in the reaction mixture. The theoretical amounts of hydrazone which would be formed from the camphor in 2-cc. amounts of the 10.00 and 20.00 per cent spirit were calculated. These amounts of hydrazone were placed in separate flasks and sulfuric acid, alcohol, water, and excess dinitrophenylhydrazine were added in the same amounts which would be present in the reaction flask after being heated in the modified official assay. The mixture was treated exactly as in the modified official determination. The results obtained (Table VII) show that very little solubility takes place. The solubility of the hydrazone was tried also in the alcohol-water-acid mixture without the dinitrophenylhydrazine reagent (Table VII). The results of these latter experiments showed a greater solubility than that obtained when the excess dinitrophenylhydrazine was present. TABLEVII. SOLYHILITIES OF ClhlPHOH DISITROPHEXYLHYDRAZO.\‘E
reagent t o cause all the camphor t o react when sucli a large sample is used. I n all the determinations where 5-cc. amounts were used, results were slightly below the theoretical values. The amount of spirit used in a determination was therefore reduced from 5 t o 2 cc. Different amounts of added alcohol were tried. The optimum amount was 15 cc. with both 2-cc. and 5-cc. samples, and in all determinations reported below, 15 cc. of alcohol were added. When 2-cc. samples were used, the results otained were somewhat nearer those of the theoretical value, especially with the spirit containing 10 per cent or more of camphor, than when 5-cc. samples were used (Table 111). Experiments were conducted next to discover whether or not the length of time of heating had any effect on the determination. The most efficient time seemed to be between 3 and 4 hours. Less than 3 hours’ heating gave results which were considerably too low; and more than 4 hours’ heating did not give results much higher than those obtained after 4 hours’ heating (Table IV). More uniform results seemed to be obtained when the flask containing the reaction mixture was immersed completely in the water during the heating process. Variations of the time of standing after the mixture was diluted were studied (Table V). If the mixture was filtered immediately after dilution, low, nonuniform results were obtained. If the mixtures stood longer than 24 hours, the results were approximately the same as those a t the end of 24 hours. TABLE VI. EFFECTO F VARYING QUANTITIES O F 2,&DINITROPHENYLHYDRAZINE REAGENT
--
Camphor Present
17.4 cc.
-
?.4-Dinitrophenylhydrs.ine Reagent-
20 cc.
,
40 cc. 75 cc. Camphor Found (2-cc. samples)
150 cc.
7%
%
%
%
%
5
3.96 6.25
4.10 6.99
4.67 9.23
4.90 9.80 14.70
4.89 9.74 14.79
15
..
30 Iteagent Added Calculated Hydrazone loss as Added Recovered camphor Gram Gram G./100CC. 0,4332 0.4076 -0.59 0,4241 -0.40 0,4416 0.4191 -0.43 0,4379 0.8830 0.8606 -0.51 0.8509 -0.53 0.8742 0 8648 0.8439 -0.48
The effect of temperature and time of heating were tried on different samples of the hydrazone. The results (Table VITI) show that the time and temperature of heating within reasonable limits have little effect on the hydrazone. A number of blank determinations mere tried. I n these experiments, the reaction flask contained all the reagents except the spirit of camphor. The process was completed and a slight precipitate was obtained. The amounts of these precipitates, when calculated as percentage of camphor never amounted, however, to as much as 0.1 per cent. TABLE VIII.
EFFECTOF HEAT
ON
CAMPHOR 2,4-DI?iITRO-
PHEYYLHTDRAZONE
Continuow Hentiny Temperature Hoitra
0
48 96 120 0 147 210 356 623 664
\o
~~
1
Welpht in G r a m No 2
No 3
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