T H E OPTICAL ACTIVITY OF CAMPHOR I N ALCOHOLIC SOLUTIONS CHARLES F. POE
ASD
ELMER M. PLEIS
Department of Chemistry, College of Pharmacy, University of Colorado, Boulder, Colorado Receiiied November 9, 1953
During the course of an investigation of the different methods used for the determination of camphor in spirits of camphor, it was necessary to prepare a large number of alcoholic solutions of camphor. These solutions were read in the polariscope and the specific rotations were calculated. Camphor is one of a number of organic substances which give different values for specific rotation when different strengths of alcohol are used as solvents. The rotation varies also for different amounts of camphor in the same percentage strength of alcohol. One may find a number of references in the literature which give the specific rotations of camphor in ethyl alcohol. Among these may be mentioned Landolt (3), Moreau (5), Kazay (2), Malosse (4), Peacock ( 7 ) , Francois and Luce (l),and Owen (6). However, no comprehensive study in which both factors (percentage camphor and strength of alcohol) are varied has been reported for the complete series of alcoholic solutions of camphor. The samples of camphor used were the purest refined products which could be obtained on the market. The camphor was resublimed at least once; the first ten per cant coming over as sublimate was discarded, as was the last ten per cent remaining in the distilling flask. Pure ethyl alcohol which had been distilled over quicklime was used to make up the various dilutions of alcohol. The camphor solutions varied in strength from 1 per cent to the highest concentration which the particular strength of alcohol used mould dissolve. All solutions were made with the greatest accuracy and at the uniform temperature of 2OOC. The solutions in each case were weight to yolume solutions. Ten readings for each of the solutions were made in the polariscope at 20°C. The specific rotation was calculated by use of the formula
Soecific rotation =
5+2
loo I X C
883
884
CHARLES F. POE AND ELMER Y. PLEIN
4a
46
44
42
I
I
I
4C
3t
g 38
p: .c,
sG
a
P, 3t
34
32
31
M
I
)
z5
I
15
z Percentage Camphor
FIG,
1.
C U R V E S S H O W I N G CH.4SGES IPZ S P E C I F I C ROTATION F O R V A R I O U S ,kMOUNTS O F C A M P H O R DISSOLTED I S DIFFERENT S T R E N G T H S O F ALCOHOL
. OPTICAL ACTIVITY
OF CAMPHOR IN ALCOHOLIC SOLUTIONS
885
where a is the polariscope reading, 1 is the length of the tube in decimeters and
Percentage Strength of Alcohol FIG.2. CURVES SHOWING CHANGES IN SPECIFIC ROTATION FOR VARIOUS AMOUNTS OF CAMPHOR DISSOLVED IN DIFFERENT STRENGTHS OF ALCOHOL
111! The results are shown giaphically in figures 1, 2, and 3. Figure 1shows the curves obtained when the specific rotation is plotted against the percentage camphor. Figures 2 and 3 give the curves obtained when speciik
886
CHARLES F. POE AND ELMER M. PLEIN
30
5-5
6s
75
85
95
Percentage Strength of Alcohol FIQ.3.
C C R V E 6 S H O W I N G C H A N G E S I N S P E C I F I C ROTATION FOR VARIOUS -htOT!NTS OF CAMPHOR
DISSOLVED I N DIFFERENT STRENGTHS
OF
A
4
~
~
~
~
OPTICAL ACTIVITY OF CAMPHOR IN ALCOHOLIC SOLUTIOXS
887
rotation and percentage strength of alcohol are the variable factors. The curves given in these figures offer a practical means of determining an unknown factor when two of the three values-specific rotation, amount of camphor, strength of alcohol-are known. From the figures me may see that the specific rotation varies considerably with a change in the strength of alcohol or with a change in the percentage of camphor dissolved. The values increase as the strength of alcohol increases. The specific rotation when the camphor content is 1 per cent varies from 27.14 for 35 per cent alcohol up to 43.18 for absolute alcohol. In the same strength alcohol the specific rotation increases as the amount of camphor dissolved increases. For instance, in 95 per cent alcohol the specific rotation varies from 40.24 for 1 per cent camphor up to 47.26 for 50 per cent camphor. SUMMARY
1. The specific rotations for alcoholic solutions of camphor have been determined when the percentages of alcohol and camphor are varied over wide limits. 2. Curves have been constructed for determining a third factor when the values of two factors are known. REFERENCES (1) FRANCOIS, M.,AND LCCE,E.: J. pharm. chim. 26, 507 (1922). (2) KAZAY, E. VOX:Pharm. Post 44,495 (1912). (3) LANDOLT, H. VON:Ann. 189, 333 (1877).
(4) MALOSSE, H. : J. pharm. chim. 8, 505 (1913). (5) MOREAV,B. : J. Pharm. 30, 14 (1894). (6) OWES, G . : Trans. Faraday SOC.26, 423 (1930). (7) PEACOCK, D. H . : J. Chem. SOC.107, 1547 (1915).
THE J O U R N A L OF PHYSICAL CHIMJGTRY, VOL. S X X V l I I , X O , 7
