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Theses and Dissertations
1914
The specific rotation of ethyl tartrate in methyl and
ethyl alcohols and in their binary mixtures
Roscoe Harrison Carter
State University of Iowa
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Recommended Citation
Carter, Roscoe Harrison. "The specific rotation of ethyl tartrate in methyl and ethyl alcohols and in their binary mixtures." MS (Master
of Science) thesis, State University of Iowa, 1914.
http://ir.uiowa.edu/etd/3870.
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THE SPECIFIC ROTATION OF ETHYL TARTRATE IN M ETHYL AND
ETHYL ALCOHOLS AND IN THEIR BINARY MIXTURES.
THESIS
Presented to the Faculty of the Graduate College of the
State University of Iowa in Partial fulfillment
of the Requirements for the Degree of
Master of Science.
by
ROSCOE HARRISON CARTER
Iowa City, Iowa.
1914.
A C K N O W L E D G M E N T
The author desires to express his sincere
appreciation for the assistance and inspiration of
Dr. J. N. Pearce at whose suggestion and under whose
direction this investigation was made. The writer also
desires to thank Dr. E. W. Rockwood and Dr. W. J.
Karslake for their instruction.
To Dr. L. P. Sieg of the Department of Physics
we are also indebted for the use of a polarimeter which
made possible this investigation.
R. H. C.
1.
THE SPECIFIC ROTATION OF ETHYL TARTRATE IN METHYL AND
ETHYL ALCOHOLS AND IN THEIR BINARY MIXTURES.
According to Landolt^optically active bodies
i
are divisible into three groups:- First, those which are
active only in the crystalline form and lose this property
when fused or dissolved in an inactive liquid.
These are
either single refracting or uniaxial double refracting
crystals, whose rotatory power depends entirely on the
crystalline structure.
Second, those which are active only
in the amorphous condition,
i.e., fused or in solution.
Among these are numerous carbon compounds occurring in
plants and animals.
Some of these substances and their
derivatives have been produced synthetically.
Substances
of this class, like camphor, have no rotatory power in the
crystalline state, although, as in the case of sugar which
has been fused, they retain that power in the solid
amorphous condition.
Third, those which are active in both
the crystalline 3tate and in solution.
Hydrated strychnine
sulphate and amylamine alum are two examples of this class.
The activity of the
members of the second class
is the property of the molecules and depends upon the
arrangement of the molecules.
This is conclusively
o
shown by the fact that turpentine oil and camphor
possess
the same rotatory power in the gaseous and liquid states.
1.
2.
Ann., 189, 241 - 337,
1878.
Biot, Mem, d. 1' Acad., II., 114.
2.
Among the factors which influence the specific rotation
of an optically active compound in solution are temperature,
concentration and the nature of the solvent.
The specific rotation of levulose in aqueous
solutions has been found to decrease to the extent of
"to
.5057°for each degree of rise in temperature. The rotary
power of an alcoholic solution oif camphor is independent
c
o
of the temperature betwesn 10 and 40 . On the other hand,
increasing temperature is accompanied by a rapid increase
in the values of the specific rotation of alcoholic
solutions of tartaric acid. The rate of this increase
becomes less pronounced at temperatures above 27.8°.
In dilute aqueous solutions of ethyl tartrate,
the specific rotation diminishes almost linearly with
rise in temperature. The same author finds that for
solvents which raise the^>ecific rotation above that of
the pure ester, an increase in temperature causes a
decrease in the specific rotation and vice versa. The
specific rotation for ethyl tartrate in the aromatic
nitro-derivatives increases with rise in temperature and
passes through a maximum value.
In these solvents the
maximum rotation increases in value and moves toward a
lower temperature as the dilution becomes greater.
1. Tuchschmid, Zeit. f. Chem.,
(2), VII., 230,
2. Patterson, J. Chem.§oc., 85, 1129,
1904.
3.
1909.
Ibid.,
93, 1836,
1872.
3. :
The relation between the maximum rotation and the
temper?ture at which it occurs was found to be much the
same in different solvents and is thus, in a sense,
independent of the concentration and the nature of the
solvent.
The influence of the concentration upon the
specific rotation of the dissolved optically active
substance is determined by the nature of the solvent.
Ethyl tartrate^in benzene gives the same specific rotation
at concentrations at five and twenty-five grams of the
ester per hundred grams of solution. For a given temperature,
o
the specific rotation ’of the same ester in nitro-benzene,
nitro-naphthalene, o-and m-nitro-toluene decreases with
increase in concentration. Similar relations3were obtained
for the ester in ethyl and methyl alcohols and water solutions.
The concentration-rotation curve for ethyl tartrate in
ethyl alcohol exhibits at first a marked decrease in
rotation and then gradually approaches a straight line
upon further increase in concentration. The influence of
slight concentrations of the ester in water and methyl
alcohol is similar but less pronounced.
According to Oudeman and Hesse4 "when an optically
active compound is dissolved in a mixture of two solvents
its specific rotary power assumes a new value which has
1.
2.
3.
4.
Patterson,
Patterson,
Patterson,
Ann., 176,
Ber., 38, 4090,
1905.
J. Chem.Soc., 93, 1836,
J. Chem.Soc., 85, 112,9,
219,
1875.
1908.
1901.
4.
no evident relation to the values obtained when either
solvent is used separately.” Using alcoholic solutions
of cinchonine they found that about one-half the
alcohol can be replaced by chloroform without affecting
the rotation. On the other hand, if in a chloroform
solution even one-three-hundredth of the solvent is
replaced by alcohol, a difference of 4°in the specific
rotation is produced. The specific rotation of this
alkaloid attains a maximum value in binary mixtures of
these solvents containing 90rfo of chloroform.
Patterson and Montgomerie^determined the specific
rotary power of ethyl tartrate in mixtures of ethylene
bromide and nitro-benzene and in mixtures of quinoline
and ethylene bromide. The specific rotation in the binary
mixtures of these solvents is lower than the values
calculated according to the law of mixtures. Each pair
r\
of these liquids show an expansion on mixing. Patterson*0
had previously shown that the specific rotation of ethyl
tartrate in various alcohols and water is greater, the
smaller the solution volume of the ester in these
solvents. The conclusion^ reached from this investigation
is that the influence of mixtures of nitro-benzene and
ethylene bromide is proportional to the volume, but not
the weight composition of the mixed solvent. On the other
1.
2.
J. Chem. Soc., 95, 1128,
J. Ohem. Soc., 79,
190,
1909.
1901.
5.
hand, tha influence of mixtures of quinoline and ethylene
bromide is proportional neither to the volume nor weight
composition of the mixed solvent. These authors also find
that volume and temperature changes attending the mixture
of certain liquids are related,
in that,
if mixing is
accompanied by liberation of heat, there is a volume
contraction and vice versa.
Pribram-*- studied the influence of mixtures of
ethyl alcohol with benzene, toluene, xylene and cymene
upon the specific rotation of ethyl tartrate. He found
that, for concentrations of five grams in forty c.c. of
the binary solvent, the specific rotation in equal
mixtures of these solvents and ethyl alcohol are -0.410°;
-0.619°; -0.652°; -0.791°, respectively. For the same
concentration in the alcohol alone the rotation is -*- 0.379°
thus showing that the effect of the added solvent is to
reverse the sign of rotation.
The effect of mixtures of ethyl acetate and
benzene upon the specific rotation of camphor and of
mixtures of alcohol and acetic acid upon the specific
rotation of turpentine were investigated by Piimbach.'
In both cases for concentrated solutions he found that
the specific rotation of the active substance in the
mixture could be calculated from the equation,
(A)
= ( A ^ P - l -H ( A ) 2P2 ,
1. Ber., 22, 6,
1889.
2. Z. physik. Chem., 9, 698,
1892.
6.
where P.,, Pr are the quantities of the component liquids
in unit weight of the mixed solvent and (A)^,
(A),, are
the specific rotations of the same concentration in the
3ingle solvents. This equation representing the law of
mixtures holds best in solutions containing about 50}o
of the solute. The observed values agree very closely
with those calculated from observations on the simple
solutions, on the assumption that the optical rotation
is in no way influenced by mixing the solvents. At lower
concentrations a minimum curve was obtained for solutions
in both paiis of solvents. However, in the turpentine
solutions this minimum value is so very nearly equal to
that calculated according to the law of mixtures as to
be almost within the limits of experimental error.
Various theories have been advanced to explain
the anomalous results obtained for the specific rotation
of optically active compounds in different solvents.
Thomsen1 advanced the theory that there is
probably some action between solvent and solute which
results in the formation of molecular compounds.
Preundler also inclines toward this theory. He claims
that it is supported by the fact that an increase in
temperature increases the specific rotary power of a
compound bringing it nearer to its normal value as conditions
become more favorable for the dissociation of these
1. Ber., 14, 203, 1881.
2. Bull. Soc. Chem.,(3) 9, 409, 1893.
7.
compounds. On tlia other hand, a decrease in rotation
for an increase in concentration is accounted for by the
increased difficulty of forming these molecular compounds.
According to W a l d e n H h e r e is a relation between
the molecular weight of a compound in solution and its
~ta.
specific rotary power, If the solvent causes the liquid
molecules of the solute to associate or polymerize, there
will be a decrease in the value of the specific rotation
and vice versa.
This view is not shared by Patterson^because
ethyl■tartrate dissolved in benzene, despite its increase
in molecular w e i ght, as determined by the boiling- and
freezing- point methods, gives the same specific rotation
for five and twenty-five grams of the ester per hundred
grams of solution. In dilute aqueous solutions the molecular
weight of the ester remains constant for all changes in
concentrationybut its specific rotary power decreases
nr
steadily with increase in concentration. The same author1-'
considers the formation of molecular compounds as improbable,
since the relation between the maximum rotation a n d the
temperature at which it occurs in different solvents is
independent of the concentration and the nature of the
solvent. According to Patterson^the changes in the
specific rotation of optically active compounds are due
1.
2.
3.
4.
Bar., 38, 345, 1905.
Ber., 38, 4090, 1905.
J. Chem. Soc., 93, 1838, 1908.
J. Chem. Soc., 87,
313, 1905.
8.
to changes in the internal pressure
on the molecule or
to changes in the solution volume. If the solution volume
decreases, the greater pressure on the molecules will
increase the distortion and the specific rotation will
increase with increasing concentration. Conversely,
if
the solution volume increases there will be less pressure
on the dissolved molecules of the solute
and correspond-
ingly a decrease in the specific rotery power. In solutions
of ethyl tartrate in chloroform the specific rotation
rapidly diminishes with increasing dilution, while the
molecular solution volume increases. On the other hand,
the specific rotation of ethyl tartrate in solutions in
water, ethyl alcohol, and methyl alcohol} methylene chloride,
ethylidene chloride and carbon tetrachloridesdecreases
while the molecular solution volume increases with increasing
concentration.
The object of this investigation was to make a
systematic study of the effects of temperature, concentration
and solvent upon the specific rotation of ethyl tartrate
in ethyl and methyl alcohols and in binary mixtures of
these solvents.
1.
2.
J. Chem. Soc., 85, 1129,
1901.
Proc. Chem. Soc., 23, 263,
1906.
9.
MATERIALS AND APPARATUS
DIETHYL TARTRATE.
Kahlbaum's best grade of the
ester was distilled under reduced pressure and only the
middle fraction passing over at 228°- 230° and 720 - 725
m.m. was collected for this work.
ALCOHOLS.
Ordinary 95$ ethyl alcohol was
refluxed for eight to twelve hours over good lime and
then distilled. The distillate was allowed to stand for
three weeks over anhydrous copper sulphate and again
distilled. After refluxing with metallic calcium the
alcohol wa3 again fractionated and the middle fraction
passing over at 76.9° C .(uncorrected) collected.
Kahlbaum's acetone-free methyl alcohol was
purified in the same manner, except that the refluxing
with lime was omitted. Only the middle fraction passing
over at 65° (uncorrected) was collected.
POLARIlvlETER.
The instrument^used in this
investigation was of the half shadow type, manufactured
by E. W. Wilson, London. Its scale was graduated in degrees
and half degrees and was provided with two verniers which
permitted readings to£0.0l'.
Several methods for maintaing constant
temperatures in the observation tube were attempted before
1. Kindly loaned to us by the Department of Physics of
the State University of Iowa.
10.
a satisfactory one was found. The apparatus finally
devised consisted of a circular galvanized iron bath
about fifteen inches high and ten inches in diameter. In
the center of the bottom of this bath was soldered a
circular cup three inches high and three inches in diameter,
inside of which rotated a motor-driven stirrer. Just below
the water level was soldered a tube, one centimeter in
diameter, which was connected directly with one end of
the water jacket surrounding the observation tube. The
other end of the jacket was connectedw ith a similar tube
inserted in the center of the bottom of the large bath
and directly in the center of the inside cup. The motordriven stirrer making about five hundred revolutions per
minute inside the cup and directly over the inlet tube
exerted suction sufficient to cause a rapid circulation
of water through the jacket of the observation tube.
By
this means the solution under observation was kept at
temperatures which were constant and approximately the
3ame as that of the bath for any desired period of time.
The large bath which was electrically heated and the
temperature electrically controlled gave temperatures
constant to t 0.02? A cooling coil connected with the
w^ter system also made it possible to maintain
constant temperatures below that of the room. To
prevent radiation the tubes were wrapped with sheet
11.
asbestos and the whole apparatus, including polarimeter
and bath was enclosed in a large plaster-board case
provided with glass windows for reading the temperatures.
Electric light bulbs were also placed inside the case to
prevent the increased radiation at higher temperatures.
All temperatures in the observation tube were
read on a certified AnshiStz mercury thermometer graduated
in 0.2° and permitting estimations accurate t o ±0.02?
Temperatures in the large bath were read on a certified
mercury thermometer graduated in 0.10° and readable to
*0 .01?
Sodium light alone was used. It was produced
by allowing the flame of a strong Bunsen burner to
pass through a circular opening in a piece of heavy asbestos
board. This opening was surrounded by a ring of pure
sodium chloride. The brilliant yellow light thus furnished
was further rendered monochromatic by filtration through
a two centimeter layer of a saturated solution of
potassium dichromate.
The solutions were made up by weight at laboratory
temperature in the following manner. A small dropping
bottle containing the ester was carefully weighed,
approximately the amount desired was poured into a two
hundred and fifty c.c. flask and the bottle weighed again.
The amount of solvent necessary to make the solution
12 .
contain the desirsd numbar of grams of the estar per
one hundred grams of solution was then calculated and
weighed into the flask. The weights of solvent used
were accurate to the second; those of the ester to the
fourth decimal place.
A series of eighteen readings were taken with
water to determine the zero reading of the polarimeter.
The mean value of the observed angles of rotation was
94.586° with a probable error of ± .0016?
The polarimeter tube was carefully cleaned and
dried, filled with the solution and stoppered with a onehole rubber stopper carrying the Anschutz thermometer.
It was then placed in the polarimeter connected with the
heating apparatus and allowed to stand until the desired
constant temxjerature had been reached. The readings were
taken at temperatures as near twenty, thirty, forty and
fifty degrees as could be done conveniently. To be sure
that the rotation did not change on standing several
solutions were allowed to remain in the tube from one to
eight hours and readings taken again. The variations over
such intervals were within the limits of experimental
error.
As soon as the rotation for one temperature
had been determined the temperature of th.
large bath
13 .
was raised by means of a Bunsen burner and then regulated
exactly to the temperature desired. The same solution was
left in the tube for a series of readings except when a
long interval of time elapsed between readings. In no case
were readings taken from solutions which had stood in the
tube tore than four hours.
The densities of the solutions were determined
in duplicate at the four constant temperatures of the
large bath. When corrected for water at 4°the resulting
densities for a given solution agree within four units
in the fourth decimal place. These were plotted against
temperature and the density of a solution at any
temperature read directly from the curve. Small Ostwald
pyknometers were used, each having a capacity of about
10 c.c. and provided with a bulb to allow for expansion
of the solution.
Eight readings of the observed angle of rotation
were made for each concentration at each temperature and
the mean of these used to calculate the values of the
specific rotation. By the *.ethod of least squares the mean
error and the probable error of the mean were calculated.
These were so small that the corrections were deemed
unneccessary.
The specific rotations were calculated by means
of t h e equation
(A)t
_ 10QJL.
(a ;e _ i-p-d.
14 .
(A)p r the specific rotation for yellow light at the
temperature t.
a I the mean observed rotation.
1 = the length of the tube in decimeters,
p Z the number of grams of the ester per one hundred grams
of solution.
d* = the density of the solution at the temperature t
referred to the density of water at 4°C.
RESULTS AND DISCUSSION.
When the specific rotation is plotted as the
ordinate against temperature as the abscissa the resulting
curve ie practically a straight line.
This is true both
for solutions in the single solvents and in the binary
mixtures.
Patterson1 , however, found that the rotation -
temperature curves for this ester in methyl and ethyl
alcohols are slightly concave toward the temperature axia.
Assuming that the specific rotation for a given
concentration is a linear function of the temperature,
the specific rotations were calculated for intervals of
ten degrees between 0° and 50° by means of the equation,
( A ) p = a + bt,
where -a and b are constants.
1.
J. Chem. Soc., 79, 167, 1901.
15 .
The values of these constants for a given
concentration were determined by the method of least
squares^from the observed values of the specific
rotation at the four temperatures. The agreement between
the observed and calculated values is very close. For
convenience and brevity only the calculated values are
recorded in the tables. The specific rotations for the
six concentrations in the five solvents at a given
temperature are given in Tables I to VI.
It will be
observed that the specific rotation is at all temperatures
greatest in the most dilute solutions.
This decrease is
most rapid at first and then less and les3 rapid with
further increase in concentration.
These results in
general agfee with those <8f Patterson? although his
values are higher in all
cases.
Tables VII. to XII. represent the specific
rotations for a given concentration at the six
temperatures in each of the five solvents.
These not
only show the general increase in rotation with rise in
temperature, but they also show the effect of the solvent
upon the specific rotation produced by a given
concentration at a given temperature.
1. Mellor: Higher Mathematics forStudents of Chemistry
and Physics*, p. 327.
2. J. Chem. Soc., 79, 167,
1901.
16.
TABLE
T A B L E
I.
Specific Rotation at 0°
Concen­
tration.
3
66
9
15
25
50
100 Ethyl
10.404
6.691
6.335
5.838
5.861
5.375
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
25 Ethyl
75 Methyl
8.229
6.561
6.726
5.914
5.863
5.708
8.031
6.470
6.346
5.665
5.732
5.800
7.615
7.168
6.563
6.751
6.211
6.171
T A B L E
100 Methyl
11.503
8.801
8.463
8.255
6.764
II.
Specific Rotation of 10°
Concen­
tration.
3
6
9
15
25
50
100 Ethyl
11.721
7.759
7.202
6.734
6.763
6.2.05
75 E t h y l - 50 Ethyl
25 Methyl
50 Methyl
9.340
7.561
7.292
6.737
6.645
6.499
T A B L E
9.165
7.497
6.922
6.436
6.610
6.615
25 Ethyl
75 Methyl
8.447
8.045
7.343
7.638
7.016
6.927
100 Methyl
12.814
9.558
9.426
9.050
7.564
I I I .
Specific Rotation of 20°
Concen­
tration.
100 Ethyl
3
13.038
8.828
8.070
7.630
7.666
7.035
6
9
15
25
50
75 Ethyl
25 Methyl
10.452
8.562
7.859
7.559
7.428
7.291
50 Ethyl
50 Methyl
10.299
8.525
7.498
7.206
7.489
7.530
25 Ethyl
75 Methyl
9.279
8.923
8.123
8.525
7.822
7.683
*
100 Methyl
14.125
10.315
10.390
9.844
8.364
17.
T A B L E
IV.
Specifio Rotation at 30?
Concen­
tration.
3
6
9
15
25
50
100 Ethyl
14.355
9.896
8.938
8.526
8.568
7.865
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
11.563
9.563
8.425
8.382
8.211
8.082
11.432
9.553
8.074
7.977
8.367
8.244
'
T A B L E
25 Ethyl
75 Methyl
10.111
9.800
8.903
9.412
8.627
8.439
100 Methyl
15.436
11.072
11.343
10.639
9.164
V.
Specific Rotation at 40?
Concen­
tration.
3
6
9
15
25
50
100 Ethyl
15.673
10.965
9.806
9.423
9.470
8.695
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
12.674
10.563
8.991
9.204
8.993
8.873
12.566
10.581
8.650
8.748
9.245
9.059
T A B L E
25 Ethyl
75 Methyl
10.945
10.478
9.683
10.299
9.433
9.195
100 Methyl
16.747
11.830
12.316
11.433
9.963
VI.
Specific Rotation at 50?
Concen­
tration.
3
6
9
\5
25
50
100 Ethyl
16.990
12.033
10.674
10.319
10.373
9.525
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
13.785
11.564
9.559
10.027
9.776
9.664
13.700
11.609
9.226
9.518
10.124
9.874
25 Ethyl
75 Methyl
11.776
11.555
10.463
11.186
10.238
9.951
100 Methyl
18.058
12.587
13.279
12.228
10.763
18 .
T A B L E
VII.
3 g. of ester per 100 g. of solution.
Temperature
100 Ethyl
(A)D
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
(A)d
(a )d
25 Ethyl
75 Methyl
(A)d
100 Methyl
(A)D
0°
10
20
30
40
50
10.404
11.721
13.038
14.355
15.673
16.990
8.229
9.340
10.452
11.563
12.674
13.785
8.031
9.165
10.299
11.432
12.566
13.700
7.615
8.447
9.279
10.111
10.945
11.776
11.503
12.814
14.125
15.436
16.747
18.058
b
.13173
.11111
.11339
.08322
.13110
T A B L E
VIII.
6 g. of ester per 100 g. of solution.
Temperature
100 Ethyl
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
25 Ethyl
75 Methyl
(A) d
100 Methyl
(A)d
(a )D
(A) d
30
40
50
6.691
7.759
8.828
9.896
10.965
12.033
6.561
7.561
8.562
9.563
10.563
11.564
6.470
7.497
8.525
9.553
10.581
11.609
7.168
8.045
8.923
9.800
10.478
11.555
8.801
9.558
10.315
11.072
11.830
12.587
b
.10685
.10007
.10278
.08775
.07572
0°
10
20
T A B L E
(A )d
IX.
9 g. of ester per 100 g. of solution.
Temperature
100 Ethyl
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
25 Ethyl
75 Methyl
100 Methyl
(a )e
(a )d
20
30
40
50
6.335
7.202
8.070
8.938
9.806
10.674
6.726
7.292
7.859
8.425
8.991
9.559
6.346
6.922
7.498
8.074
8.650
9.226
6.563
7.343
8.123
8.903
9.683
10.463
8.463
9.426
10.390
11.343
12.316
13.279
b
.086786
.056634
.057603
.078000
.096311
0°
10
(A)d
(a ) d
(A)d
19.
T A B L E
X.
15 g. of ester per 100 g. of solution.
Temperature
100 Ethyl
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
25 Ethyl
75 Methyl
100 Methyl
(a )d
(a )d
(a )d
0°
10
20
30
40
50
5.838
6.734
7.630
8.526
9.423
10.319
5.914
6.737
7.559
8.382
9.204
10.027
5.665
6.436
7.206
7.977
8.748
9.518
6.751
7.638
8.525
9.412
10.299
11.186
8.255
9.050
9.844
10.639
11.433
12.228
b
.08962
.082258
.077061
.088691
.079446
T A B L E
(A)D
(a )d
XI.
25 g. of ester per 100 g. of solution.
Temperature
100 Ethyl
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
25 Ethyl
75 Methyl
(A)D
(a )d
(A )p
0°
10
20
30
40
50
5.861
6.763
7.666
8.568
9.470
10.373
5.863
6.645
7.428
8.211
8.993
9.776
5.732
6.610
7.489
8.367
9.245
10.124
6.211
7.016
7.822
8.627
9.433
10.238
6.764
7.564
8.364
9.164
9.963
10.763
b
.090247
.078266
.087840
.080543
.079982
T A B L E
(a )d
100 Methyl
XII.
50 g. of ester per 100 g. of solution.
Temperature
0°
10
20
30
40
50
b
100 Ethyl
75 Ethyl
25 Methyl
50 Ethyl
50 Methyl
(a )d
25 Ethyl
75 Methyl
(a )d
(a )d
5.375
6.205
7.035
7.865
8.695
9.525
5.708
6.499
7.291
8.082
8.873
9.664
5.800
6.615
7.530
8.244
9.059
9.874
6.171
6.927
7.683
8.439
9.195
9.951
.083014
.079129
.081489
.075606
(a )d
(a )d
20.
The relative effect of concentration at the
different temperatures andin the five solvents is best
shown by Figs. I. to VI..
In these figures curve I.
represents solutions in pure ethyl alcohol, II. solutions
in 75 ethyl-25 methyl, III. solutions in 50ethyl-50methyl,
IV. solutions in 25 ethyl-75 methyl and V. solutions in
pure methyl alcohol.
The red line represents the values
of the specific rotation for pure ethyl tartrate as found
by Winther^
A comparison of the values of the ordinates
for a given temperature in the six figures gives at once
the relative effect of concentration in e a c h of the five
solvents. It will be observed that in all concentrations
and at all temperatures the specific rotation is greatest
in pure methyl alcohol.
In the remaining solvents the
relative position of the temperation-rotation curves
change not only with temperature, but also with increasing
concentration.
In the three percent solutions,
(Fig.I.)
curve I. representing the values in ethyl aJLcQhol, lies
just below and parallel with that for the solution in
methyl alcohol(V.), while curve IV., representing the
specific rotations in the seventy-five percent methyl
alcohol mixture, falls below all the others.
It is
evident that the solvents when mixed in this proportion
exert
1.
a
relatively much greater depression of the
Z. physik. Chem., 41, 176, 1902.
21.
specific rotation than at any higher concentration. As
the proportion of ethyl alcohol increases the values of
the specific rotation for this concentration continue to
increase up to the values for the ester in pure ethyl
alcohol.
This order is contrary to what we should
expect in view of the fact that the specific rotation is
greatest in the metjuyl alcohol alone.
Further, it
should be noted that the specific rotation increases
with rise in temperature, but at different rates in the
different solvents.
With this discussion of figure I.
we can the more easily follow the effect of concentration
as represented in the remaining figures of this set.
Beginning with the six percent concentration
the influence of methyl aloohol tends'to increase
relatively the specific rotation in those mixtures in
which it predominates.
On the other hand, the influence
due to the ethyl alcohol decreases with increasing
concentration.
It should be understood that at a given
temperatiire we have to deal with two opposing factors,
first, the influence of the alcohols, more especially the
methyl alcohol tending to increase the specific rotation
and, second, the influence of increasing concentration
tending at the same time to decrease the specific
rotation.
The values of the specific rotation at a
given temperature will depend, therefore, upon- the relative
magnitude of these two influences.
22.
The relative values for the rotation in
mixtures containing seventy-five and fifty percent of
ethyl alcohol retain for the most part their respective
relations to the values in ethyl alcohol up to and through
solutions containing fifteen percent of the ester.
Owing
to the difference in the temperature coefficients the c
curves for the different solvents must necessarily cross.
In Figures II.* III.* and V. we observe the gradual
change in the position of curves I. and IV., representing
the specific rotation in ethyl alcohol and its twentyfive percent mixture,respectively.
Points of inter­
section of the temperature-rotation curves indicate
those temperatures at which the specific rotation for the
same concentration in the two solvents are identical.
These points move towards specific rotations of higher
values with increase in concentration.
In concentrations
containing fifty percent of the ester (Fig.VI.) the
specific rotation values at low temperatures are lower
in ethyl alcohol than in all other solvents.
Similar,
but less pronounced, changes may be observed in the
specific rotation in the remaining solvents.(curves II.
and III.)
The values in these two mixtures are very
close at all temperatures and concentrations.
Up to and
through the fifteen percent ester solutions the specific
rotations, except at higher temperatures in the six
23.
rjercent solution, are higher in the seventy-five
percent ethyl than in the fifty percent ethyl mixtures.
With further increase in the proportion of methyl alcohol
(II.and III., Figs. V. and VI.) the influence due to the
concentration increases less rapidly.
The specific rotation
in the fifty percent mixture now lie for the most part
above those in the mixed solvent containing seventy-five
percent o f e t h y l alcohol.
It is evident from Figure VI.
that, if the concentration is still further increased,
the specific rotations in pure ethyl alcohol will at all
temperatures lie below those in the other solvents.
The
general relation will then be that the specific rotation
will increase regularly and almost linearly with increase
in the proportion of methyl alcohol.
In the most dilute solutions the specific
rotations are for all temperatures and solvents
considerably higher than that for the pure ester at
corresponding temperatures. With increase in concentration
in a given solvent, the specific rotation decrease
rapidly and approach the values for the pure ester, this
decrease being the more rapid at the higher temperatures.
Beginning with the nine percent es.er solution we note
the gradual decrease in the rotatory power until first
in the mixtures and finally in ethyl alcohol, the
specific rotations of the solutions at the higher
temperatures becomes less than those of the pure ester.
24.
At low temperatures the specific rotation is for all
concentrations in all solvents higher than for the ester.
A clearer idea of the effect of solvent upon
the specific rotation is given by Figures VII. to XII..
Here the specific rotation is plotted isothermally
©
against the percentage composition of the solvent as
abscissa.
Starting with the three percent solution in
pure methyl alcohol and successively adding small
quantities of Jth yl alcohol, the specific rotation
rapidly decreases and passes through a minimum value.
This minimum occurs approximately in the solvent of
seventy-five methyl- twenty-five ethyl composition.
From this mixture on the specific rotation increases
rapidly at first to approximately the fifty percent solvent
mixtures, then more slowly and finally very rapidly as
the percent of ethyl alcohol increases.
The minimum
becomes more pronounced as the temperature increases.
As the concentration of the ester is increased
the minimum is gradually displaced towards solvents
containing a higher percent of ethyl alcohol.
This is
accompanied by a flattening tendency on the part of the
isothermal curves.
At concentrations containing fifty
percent of the ester these isothermal curves have become
practically straight lines, the rotatory power increasing
linearly with increasing percentage of methyl alcohol.
25.
It is further expected that as the concentration
approaches that of the pure ester, the temperature-rotation
curves will in turn assume a form concave to the temperature
axis.
On account of the lack of time and an insufficient
supply of the ester, however,
it was impossible to carry
the investigation further.
SUMMARY
The specific rotation of di-ethyl tartrate
in ethyl alcohol, methyl alcohol and three binary
mixtures has been determined at four temperatures between
20°and 50°.
Six concentrations were used in each solvent.
The observed temperature-rotation curves when
plotted appeared to be straight lines.
Assuming, therefore,
that the specific rotation is a linear function of the
temperature, the specific rotation for each concentration
in each solvent has been calculated for temperatures at
intervals of ten degress between 0°and 50°.
It has been
found that the relation between temperature and specific
rotation is expressed by the equation:
(A)p =- a-f-bt.
The constants a and b have been derived by the method of
least squares.
The agreement between the observed and
calculated specific rotations is sufficiently close to
indicate the correctness of the assumption.
26.
The values of the specific rotation decrease
with increasing concentration of the ester in each
solvent.
This increase is more rapid in very dilute
♦
solutions and becomes less a n d less rapid as the
concentration increases.
At higher concentrations the
specific rotation in all the solvents approach the value
for the pure ester at the corresponding temperatures.
The effedt of concentration on the rate of decrease on
the values of specific rotation is not the same in all
solvents, being most marked relatively in solutions in
ethyl alcohol.
The specific rotation passes through a minimum
value when plotted isothermally against the percentage
composition of the solvent.
This minimum is most marked
in dilute solutions in the twenty-five ethyl-seventy-five
methyl mixtures and is displaced toward mixtures of a
higher percent of ethyl alcohol as the concentration of
the ester increases.
At concentrations of fifty grams
of the ester per one hundred grams of solution the
isothermal curves become practically straight lines, the
specific rotation then increasing linearly with increase
in the percent of methyl alcohol.
A new method has been devised for maintaining
constant temperatures in the observation tube of a
polarimeter.
BIOGRAPHY
Roscoe Harrison Carter was born near Glenwood,
Mills County, Iowa in 1889.
He received his early
education in the country schools and in Whiting, Iowa;
he was graduated from the Whiting High School in 1905.
In 1907 he attended Morningside Academy for one
semester and in 1908 matriculated in Morningside College,
receiving from that institution the degree of Bachelor
of Arts in 1912.
During the year 1911-12 he was under­
graduate assistant in Chemistry in Morningside College.
He spent the years 1912-1914 as Assistant in Chemistry
in the State University of Iowa.
During this time he
also carried on graduate work leading to the Master of
Science degree.