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NOV 2 9 1920
The Esterification of Acetic and Prop-
ionic Acids by Methyl, Ethyl,
Propyl, Isobutyl and Iso-
amyl Mercaptans
A DISSERTATION
SUBMITTED TO THE BOARD OF UNIVERSITY STUDIES OF THE
JOHNS HOPKINS UNIVERSITY IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
By
EDGAR M. FABER
BALTIMORE, MARYLAND,
June, 1917
EASTON, PA.,
ESCHENBACH PRINTING CO.
1919
The Esterification of Acetic and Prop-
ionic Acids by Methyl, Ethyl,
Propyl, Isobutyl and Iso-
amyl Mercaptans
A DISSERTATION
KUR
SUBMITTED TO THE BOARD OF UNIVERSITY STUDIES OF THE
JOHNS HOPKINS UNIVERSITY IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
By
ene
EDGAR M. FABER
BALTIMORE, MARYLAND,
June, 1917
EASTON, PA,
ESCHENBACH PRINTING Co.
1919
CONTENTS.
Page.
..............................................
...........................................
Acknowledgment ..........
Historical
Materials.
Method of Work......
Experimental.......
Results............
Summary of Results .
Discussion of Results..
Conclusions .......
Biography.
a Bocowaner
.......................
....
...
..
.....
......................
....
....
................
Peclina. M1: 6-24-37
ACKNOWLEDGMENT.
The author wishes to take this opportunity to express his gratitude to
Drs. Morse, Frazer, Lovelace, Gilpin, Swartz and the late Dr. Jones for
valuable instruction and advice received in both lecture room and labora-
tory.
Special thanks are due Dr. Reid, at whose suggestion and under whose
guidance this investigation was carried out.
The Esterification of Acetic and Propionic
Acids by Methyl, Ethyl, Propyl, Isobutyl
and Isoamyl Mercaptans
Historical.
Ever since Berthelot and Pean de St. Gillest so carefully investigated the
formation of esters, the problem of esterification, with and without a
catalyst, has been one of great interest to the chemist.
This was followed by the work of Menschutkin? in which the question
of the influence of the structure of both the acid and of the alcohol was
extensively studied.
Reidin a study of the mechanism of esterification found that mercaptan
esterifies benzoic acid and that a well-defined limit is reached.
This work was extended by Pratt and Reid4 who studied the esterifi-
cation of benzoic acid by various mercaptans, and further by Sachs and
Reid and Kimball and Reid who took up the question of isomerism of the
acids and of the mercaptans.
All of this work on mercaptans has gone to show that mercaptans esterify
acids as do alcohols and that the relations between the limits reached are
1 Ann. chim. phys., [3] 65, 385 (1862); 66, 5 (1862); 68, 225 (1863).
2 Ber., II, 1510 (1878); Ann. chim. phys., 23, 58 (1881).
: Am. Chem. J., 43, 489 (1910).
* J. Am. Chem. Soc., 37, 1934 (1915).
• Ibid., 38, 2746 (1916).
• Ibid., 38, 2757 (1916).
D
much the same with mercaptans as with alcohols, but up to the present
only aromatic acids have been used with mercaptans.
The present investigation was undertaken to extend the work to the
aliphatic acids. The esterification of acetic, propionic and butyric acids
by methyl, ethyl, propyl, isobutyl and isoamyl mercaptans has been
studied.
Materials.
Acids.—The acetic acid used was prepared by cooling a pure glacial
acetic acid to its freezing point and effecting crystallization by the in-
troduction of an acetic acid crystal.
After pouring off the unsolidified portion the process was repeated until
the acid, by titration with standard alkali, showed a high degree of purity.
The propionic acid was obtained by fractionating a standard commercial
product.
Mercaptans.-The methyl and ethyl mercaptans used in this work were
made by Reid. Both were freed from sulfides, dried and distilled, the
best fractions only being used. The methyl mercaptan boiled at 6°,
the ethyl at 35.5° to 36.1°.
The propyl, isobutyl and isoamyl mercaptans were standard commercial
products.
Ethyl Alcohol.-To free the ethyl alcohol from carbonic and other acids
which the commercial material usually contains it was distilled from
caustic potash.
Heating.-The furnace employed was that constructed by Pratt and
Reid, electrically controlled and heated, it maintained the temperature
constant within 3°
Standard Solutions. The standard barium hydroxide was kept in a
large stock bottle from which it was run through a siphon, fitted with a
stopcock, into the buret. The tops of the bottle and buret were
protected from the carbon dioxide of the air by soda-lime tubes.
For the standard hydrochloric acid solution a similar apparatus was
used, except that the stock bottle and buret were protected by tubes con-
taining acid of the same strength.
Both solutions were approximately 0.1 N and were standardized at
intervals of two weeks.
Method of Work.
Pyrex glass tubes about 6 X 75 mm., closed at one end, were washed with
hot chromic acid, filled with a dilute solution of hydrochloric acid and
allowed to stand in a boiling solution of the same for a period of six hours.
They were then washed and boiled in distilled water for an hour, after
which they were washed with distilled water and thoroughly dried in an
air bath.
Each tube was weighed and, after introducing the acid by means of a
T
capillary pipet controlled by a rubber exhaustion bulb, drawn out to a
narrow neck and weighed again. The mercaptan was then added, the
tube being placed in a mixture of ice and salt, and the tube sealed.
The tube and tip were then weighed. After this the tubes were placed
in the furnace and heated to 197–203° for the desired length of time.
When the furnace had cooled they were removed and analyzed. To do
this the tube was scored with a file, the tip broken off and thrown into a
120 cc. Erlenmeyer flask. By means of a pipet, similar to the one used
to introduce the acid, the content of the tube was transferred to the flask,
the former washed out four times with alcohol (distilled from KOH) and
the washings added to the main portion.
Sufficient alcohol was then added to the reaction mixture to bring the
volume to 25 CC.
The mercaptan not entering into the reaction was eliminated by drawing
carbon dioxide-free air through the solution, the flask containing the latter
being immersed in water heated to 50°. Preliminary experiments with
known amounts of acid and mercaptan showed that it is necessary to pass
air through the solutions 15 minutes to remove methyl and ethyl mercap-
tans; 25 minutes for the propyl; 30 minutes for the isobutyl, and 45 min-
utes for the isoamyl. The amount of acid in the solution was then de-
termined by titration with standard barium hydroxide solution using
phenolphthalein as indicator.
Experimental.
Since, according to the usual reasoning in the consideration of reversible
reactions, the amount of ester formed in unit time is equal to (acid X
mercaptan) K, and the amount of ester decomposed in the same time is
equal to (water X ester) K' (the expressions in parentheses represent con-
centrations), and since, at equilibrium, these opposing velocities are:
equal, we have:
[acid] x [mercaptan K
= = = 71
(water] x [ester] K
This is for the general case in which the ainounts of acid and inercaptan
are not equivalent. If the mass law holds, the value of r will be the same
whatever the relative concentrations of acid and mercaptan and we can
use the value of 1 found in one case to calculate the equilibrium in any
other. The case that has been most frequently studied in esterification
is the special case in which the initial concentrations are equal.
Since the two reacting substances are used up at the same rate and since
equivalent amounts of the products are formed, the final concentrations
of acid and mercaptan are equal, as are the concentrations of water and
ester, and we may write
1 Am. Chem. J., 43, 499 (1910); Bonz, Z. Physik. Chem., 2, 865 (1888).
المسم
[acid] x [mercaptan] _ (acid ]
{ester] x [water] [ester]2
_K'
K
[acid] colo
{ester]
when x% of the acid has reacted, the ester will be *% and the acid re-
maining, 100 — *%. Then
100 - X
100
= Vī
or
x = -
- Vrti
In this, x is the percentage of an equivalent mixture which would have
reacted when equilibrium has been reached. We may call x, the limit for
equivalent quantities or, for general purposes, simply the esterification
limit, understanding that it is calculated for equivalent concentrations
from values of r obtained working with other than equivalent concentra-
tions. This is the percentage of esterification, or limit, that has been cal-
culated in all of the articles of this series.
In tabulating the results, the data are arranged as follows:
a. Acid in grams weighed in.
b. Millimols of acid at start.
6. Mercaptan in grams weighed in.
d. Millimols of mercaptan at start.
e. Cubic centimeters of standard alkali required for titration.
f. Millimols of acid present at end calculated from e.
g. Millimols of mercaptan remaining, d --- m = g.
m. Millimols of ester, equals water, b -- f = 111.
% Percentage of esterification, or x, calculated by the above formula
for equivalent quantities of mercaptan and acid.
The data are given in full in the first run but after that, to save space,
the weights in g. of the acid and mercaptan, a and c, and the titration fig.
e, are omitted.
RESULTS.
Series I.-48 Hours at 200°.
CH3COOH + CH,SH.
a, Acid, g............ 0.0848 0.0872 0.1006 0.0909 0.1033 0.0924
b, Acid, m. mols...... 1.413 1.453 1.676 1.514 1.721 1.539
€, Mercap., g......... 0.0869 0.0947 0.0622 0.0899 0.0527 0.0922
d, Mercap., m. mols.. 1.807 1.969 1.293 1.869 1.096 1.917
e, Ba(OH)2, cc........ 12.60 12.83 1 5.67 13.54 16.31 13.84
f, Acid left.......... 1.159 1.180 1.442 1.246 1.500 1.273
g, Mercap. left....... 1.553 1.696 1.059 1.600 0.875 1.651
m, Ester = water.... 0.2535 0.2724 0.2344 0.2687 0.2204 0.2661
Vr................. 5.295 .195 .26 5.25 5.19 5.44
%......... ........ 15.89 16.15 15.96 16.00 16.13 15.51
Mean, 15.94%
W
Tau
VT......
•
•
•
•
b, Acid in m. mols.... 2.417 2.192 1.684 2.132 2.116 2.094
d, Mercap., m. mols... 3.147 3.062 2.040 2.780 3.046 2.568
f, Acid left.......... 2.075 1.877 1.451 1.826 1.791 1.811
g................... 2.805 2.747 1.807 2.474 2.721 2.285
m, Mercap. left...... 0.3425 0.3153 0.2329 0.3066 0.3248 0.2833
... 7.04 7.20 6.95 6.93 6.79 7.17
%.................. 12.43 12.20
12.20 12.57 12.61 12.82 12.23
Mean, 12.48%
CH3COOH + C3H,SH.
1.453 1.444 1.944 1.658 1.609 1.404
... 1.505 1.379 1.328 1.429 1.426 1.514
1.272 1.284 1.757 1.472 1.430 1.227
1.325 1.219 1.141 1.243 1.247 1.337
0.1804 0.1601 0.1870 0.1656 0.1797 0.1772
. 7.19 7.81 7.57 7.29 7 .42 7.22
......... 12.20 11.35 11.66 12.06 11.86 12.10
Mean, 11.87%
CH3COOH + (CH3)2CHCH2SH.
...... 2,107 1.926 1.784 1.951 1.996
.... 1.757 1.755 1.709 1.551 1.750
1.874 1.702 1.579 1.741 1.775
... 1.524 1.531 1.504 1.340 1.529
0.2335 0.2239 0.2056 0.2103 0.2211
.. 7.23 7.20 7.49 7.26 7.45
... 12.14 12.18 I1.77 12.10 11.83
Mean, 12.00%
•
•
•
.. 1.094
.. 4.847
...... 0.759
.......... 4.512
... 0.3355
Vr........ 5.51
%.......... 15:38
Series II.-96 Hours at 200°.
CH,COOH + CH.SH.
1.264 1.494. 1.644 1.791 2.537 2.342
2.073 3.019 2.356 2.086 3.200 3.080
1.004 1.141 1.320 1.468 2.084 1.904
1.812 2.666 2 .032 1.763 2.747 2.642
0.2608 0.3536 0.3241 0.3226 0.4535 0.4380
5.35 4.93 5.05 4.98 5.07 5.12
15.74 16.86 16.52 16.70 15.96 16.34
Mean, 16.21%
... 1.781
...
. 1.478
1.571
. 1.268
0.2100
6.72
... 12.95
2.417
1.832
2.142
1.557
0.2752
6.63
13.10
2.171 2.204 2.001
1.600 1.832 1.901
1.926 1.941 1.751
1.355 1.569 1.651
0.2448 0.2629 0.2500
6.60 6.63 6.80
13.15 13.10 12.81
Mean, 13.02%
IO
...............
..............
.
.....
.....
....
.
*1.
................
................
12.0
CH3COOH + CH SH.
2.382 2.091 2.364 2.216 2,167 2.127
1.608 1.667 1.751 1.848 1.943 2.116
2.129 1.862. 2.104 1.960 1.907 1.859
g................... 1.354
1.354 1.438 1.491 1.592 1.682 1.848
0.2536 0.2288 0.2600 0.2562 0.2603 0.2682
6.69 7.15 6.8 6.89 6 .88 6.89
12.90 (12.27) 12.80 12.67 12.70 12.67
Mean, 12.75%
CH3COOH + (CH3)2CHCH,SH.
.. 1.892 1.848 2.036 1.861 2.112
1.475 1.500 1.348 1.401 1.371
1.702 1.650 1.834 1.665 1.905
1.285
1.303
1.146 1.205 1.163
0.1906 0.19710.2017 0.1957 0.2077
.......................... 7.75
7.75 7.43 7.18 7.23 7.16
%........
.(11.42) 11.85 12.21 12.14 12.24
Mean, 12.11%
...
möösi bio
&............................
>
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...........
............
TV...
.........
....
CH3COOH + (CH3)2CHCH2CH2SH.
2.141 1.902 2.229 2.162 1.832
1.094 1.048 1.001 1.128 0.984
1.711 1.518 1.853 1.755 1.453
0.6647 0.6641 0.6256 0.7208 0.6055
0.4297 0.3842 0.3757 0.4072 0.3794
..... 7.84 8.26 9.06 8.73 7.81
.. 11.30 10.8 9.94 10.28 11.34
Mean, 10.73%
CH3COOH + CH3SH–192 Hours at 200°.
1.566 1.518 1.474 1.448 1.796 1.743 1.218
2.102 2.200 1.840 2.484 1.505 1.825 1.561
1.273 1.225 1.201 1.143 1.398 1.446 1.002
b...
d...
f...
1.608
1.773
1.329
m.. 0.27830.2927
Vr. 5.12 5.18
%.. 16.33 16.17
0.2923
5.23
16.05
0.2729
5.02
16.59
0.3051
5.17
16.2
0.3975 0.2964 0.2150
(3.12) 5.01 5.40
(24.23) 16.62 15.62
Mean, 16.23%
1
.
Selle
Series III.-45 Hours at 200°.
CH,CH2COOH + CHESH.
hoa s os
1.573
1.661
1.335
1.423
0.2386
.. 5.77
.. 14.76
1.477
1.928
1.224
1.674
0.2536
5.64
15.05
1.715
2.212
1.420
1.918
0.2947
5.60
15.15
1.483 1.550. 1.611
2.655 2.990 2.389
1.188 1.223 1.313
2.361 2.663 2.091
0.2944 0.3275 0.2978.
5.68 5.51 5.56
14.95 15.72 15.23
Mean, 15.14%
>
II
od sios >60
moj si bio >
:
:
. .
rojsi bo
.
:
.
:
CH3CH2COOH + C2H SH.
· 1.507 1.472 1.3491.373 1.508 1.402
. 2.553 2.908 2.724 2.602 2.922 2.753
1.287 1.246 1.146 1.168 1.278 1.207
2.334 2.681 2.521 2.397 2.692 2.559
: 0.2195 0.2263 0.2030 0.2049 0.2302 0.1942
7.89 8.07 8.37 8.16 8.05 9.05
. 11.24 11.02 10:67 10.91 11.04 (9.94)
Mean, 10.97%
CH,CH,COOH + C3H,SH.
1.508 1.402 1.295 1.258 1.323 1.287
1.644 1.355 1.309 1.220 1.291 1.288
1.361 1.262 1.156 1.123 1.191 1.152
1.497 1.216 1.171 1.085 1.158 1.153
. 0.1471 0.1396 0.1387 0.1356 0.1328 0.1353
... 9.7 8.87 8.39 8.328 .84 8.51
(9.34) 10.00 10.65 10.72 10.16 10.51
Mean, 10.41%
CH3CH2COOH + (CH3)2CHCH2SH-48 Hours at 200°
..... 1.815 1.747 1.653 1.858 1.714
. 1.700 1.753 1.728 1.773 1.689
... 1.630 1.554 1.469 1.669 1.537
1.515 1.560 1.545 1.584 1.513
0.1853 0.1929 0.1836 0.1886 0.1767
: 8.48 8.07 8.20 8.62 8.63
%..........
...... 10.55 I1.02 10.86 10.40 10.39
Mean, 10.64%
Series IV.-96 Hours at 200°.
CH,CH,COOH + CH3SH.
1.250 1.458 1.349 1.514 1.658 1.703
2.536 2.177 2.609 2.349 2.395 2.954
0.989 1.192 1.061 1.221 !.368 1.361
2.275 1.910 2.321 2.057 2.105 2.612
0.2617 0.2667 0.2877 0.2924 0.2898 0.3417
5.73 5.65 5.45 5.42 5.85 5.51
%........ ....... 14.86 15.03 15.49 15.58 (14.59) 15.34
Mean, 15.26%
CH,CH,COOH +- C,H.SH.
1.872 1.758 1.830 1.676
. 2.281 2.431 1.639 1.594
. 1.631 1.519 1.603 1.485
2.041 2.192 1.412 1.403
0.2406 0.2391 0.2268 0.1912
.... 7.58 7.63 6.63 7.54
%............ .......
.... 11.65 11.58 (13.1). 11.70
Mean, 11.64%
.
:
.
:
.
noosios
.
.
.
.
>
.
.
noras do Š>00
: : iila
I 2
CH3CH2COOH + C3H,SH.
1.700 1.826 1.766 1.642 1.791 1.777
.. 1.786 1.841 1.794 1.751 1.828 1.765
1.503 1.624 1.574 1.448 1.580 1.579
1.589 1.640 1.602 1 .556 1.618 1.568
0.1968 0.2017 0.19250.1944 0.2103 0.1977
..... 7.85 8.09 8 .24 7.72 7.60 7.95
11.29 11.00 (10.81) II.40 11.60 11.16
Mean, 11.29%
CH3CH,COOH -+- (CH3),CHCH,SH.
.... 1.308 1.474 1.916 1.615 1.607
1.408 1.433 1.292 1.445 1.475
.. 1.163 1.339 1.757 1.440 1.434
. 1.262 1.298 1.133 1.270 1.303
: 0.1455 0.1354 0.1588 0.1751 0.1726
. 8.32 9.73 8.88 7.72 7.92
· 10.72 (9.31) 10.12 11.46 11.20
Mean, 10.87%
CH3CH,COOH + (CH3)2CHCH.CH.SH.
... 1.492 1.349 1.558 1.696 1.727 1.423
... 1.185 1.175 1.148 1.102 1.163 0.981
1,151 1.008 1.217 1.375 1.395 1.138
: 0.8433 0.8339 0.8072 0.7812 0.8310 0.6958
0.3413 0.3411 0.3409 0.3209, 0.3325 0.2853
. 9.12 8.49 9.19 10.21. 10.23 9.86
9.88 10.52 9.80 8.92 8.90 9.20
Mean, 9.53%
%.....
m.....
%........
9.5.3
SUMMARY OF RESULTS.
Acetic Acid with Mercaptans.
Time.
Methyl Ethyl. Propyl. Isobutyl. Isoamyl.
48 Hours,.
.. 15.94 12.48 11.87 12.00
96 Hours.........
16.21 13.02 12.75 12.11 10.73
192 Hours.......... ......... 16.23
..... ......
Propionic Acid with Mercaptans.
48 Hours.......... ......... 15.14 10.97 10.41 10.64.
96 Hours............
15.26 11.64 11.29 10.87
Discussion of Results.
From the foregoing results it is noticed that a good degree of concordance
exists between the individual results in a table, considering the experimental
errors involved in using mercaptans and the variations in proportions of
active materials used.
Preliminary experiments conducted to ascertain the time necessary
to reach the limit showed that 96 hours was sufficient. This is brought out
in the small increase in the limit for acetic acid and methyl mercaptan at
192 hours, over that at 48 hours, they being, respectively, 16.23% and
16.21%.
Alcohols with
acetic acid.i
.66.57
S
Below is a comparison of the limits obtained using mercaptans with
those found by Menschutkin with acetic acid and various alcohols in
equimolecular quantities at 154°, and with the limits found by Pratt and
Reid and Kimball and Reid for mercaptans with benzoic acid.
Mercaptans with
Acetic acid. Propionic acid. Benzoic acid.
Methyl............... 69.52
16.21
15.62
18.72
Ethyl..........
13.02
11.64 14.78
Propyl................ 66.85
12.75
11.29
14.12
Isobutyl............... 67.38
12.11 10.87 13.638
As has been found in all the work with mercaptans the limits using
mercaptans are much lower than those with alcohols. With both mer-
captans and alcohols the limits are much higher for methyl than for any
other.
With the alcohols, ethyl gives the lowest limit and then there is a slight
rise with increase of molecular weight, but with mercaptans there is a
continual lowering of the limit as we go up the series. The values quoted
for mercaptans with benzoic acid show the same relations.
Then, too, it is seen that the limits reached with acetic acid are slightly
higher than those with propionic. Menschutkin4 found this same re-
lation between the rates, when acetic and propionic acids were heated one
hour with isobutyl alcohol by obtaining 44.4% for the former and 41.2%
for the latter. In all of the tubes except those containing the methyl
esters, slight decomposition was shown by the presence of hydrogen sul-
fide. Judging from the extent of discoloration of the lead acetate paper
the amount of decomposition seemed to increase with rise in molecular
weight.
Conclusions.
I. The limits of esterification of acetic and propionic acids with inethyl,
ethyl, propyl, isobutyl and isoamyl mercaptans have been determined at
200°.
2. The limits for propionic acid were found to be somewhat lower than
those for acetic.
3. The limits obtained were found to be much lower than those for
corresponding alcohols.
4. The proportions of reacting substances seemed to have but little
influence on the limit.
5. The stability of the esters was found to decrease with increase in
molecular weight.
BALTIMORE, MD.
i Ber., 11, 1510 (1878).
2 J. Am. Chem. Soc., 37, 1947 (1915).
8 Ibid., 38, 2766 (1916).
* Ann. chim. Phys., 23, 58 (1881).
BIOGRAPHY.
Edgar M. Faber was born at Gettysburg, Pennsylvania, April 21, 1890.
His early education was obtained in the public schools of that place. In
1911 he entered Pennsylvania College, graduating in 1914 with the degree
of B.S. From 1914-1917 he has been pursuing graduate studies in chem-
istry in Johns Hopkins University. During the years 1914-1915 and
1916–1917 he was laboratory assistant to Dr. Lovelace and for his last
year he was awarded a University Scholarship.

UNIVERSITY OF MICHIGAN
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