PREPARATION, PURIFICATION, AND PHYSICAL CHARACTERIZATION OF THE ETHYLENE GLYCOL MONOESTERS AND DIESTERS OF CAPRIC ACID

71 Pages·02.285 MB·English

by  NEVIN, CHARLES S

THE PENNSYLVANIA STATE COLLEGE
The Graduate School
Department of Agricultural and Biological Chemistry
PREPARATION, PURIFICATION, AND
PHYSICAL CHARACTERIZATION OF THE ETHYLENE GLYCOL
MONO- AND DIESTERS OF CAPRIC ACID
A Dissertation
by
Charles S. Nevin
Submitted in partial fulfillment
of the requirements
for the degree of
Doctor of Philosophy
August 1950
Approved:
1950
Professor of Agricultural and
.— Biological. Chemistry
1950
Associate Professor of Agricultural
ologlcal Chemistry
Head of Department of Agricultural
and Biological Chemistry
S
TABLE OP CONTENTS
Page
Introduction 1
Historical 2
Statement of Problem 9
Experimental
Preparation and Purification of the Glycol Esters 10
Distilled Ethylene Glycol Monocaprate 10
Distilled Ethylene Glycol Dicaprate 12
Crystallized Ethylene Glycol Monocaprate 13
Crystallized Ethylene Glycol Dicaprate 17
Distilled Crystallized Ethylene Glycol
Monocaprate 19
Distilled Crystallized Ethylene Glycol
Dicaprate 20
Physical Characterization of the Glycol Esters 20
Neutral Equivalents 20
Iodine Numbers 20
Refractive Indices 21
i
Densities 22
Viscosities 21*
Vapor Pressures 25
Discussion and Conclusions 27
Neutral Equivalents 27
Iodine Numbers 28
Refractive Indices 28
Densities 31
TABLE OF CONTENTS
(continued)
Page
Viscosities 33
Vapor Pressures 3^
Molar Refractions 35
Comparison with Ethyl Caprate 36
General Conclusions 36
Tables 39
Figures 60
Acknowledgement 65
Bibliography 66
i
INTRODUCTION
During the past ten years the work of this lab­
oratory1 >9»17, 19,23^3 teen concerned primarily with the
purification and physical characterization of various esters
of short chain monohydrlc alcohols and naturally occurring
fat acids. The purpose of this work was not only to provide
the deficient literature with the physical characteristics
of these compounds, but also to provide information that
would aid ultimately in the preparation or isolation of
purified glycerides and the prediction of the properties
which these glycerides possess.
The logical Intermediate step between the simple
fat acid esters and the glycerides is the study of ethylene
glycol fat acid esters, since these esters possess many of
the characteristics of glycerides yet are far less complex
compounds. Therefore, a study of ethylene glycol esters
was undertaken, the initial investigations of which are
reported in this thesis.
2
HISTORICAL
The first reference found, relative to the prep­
aration of a glycol ester of the fatty acids, is the work
pO
of Wurtz. In 1859 he prepared the distearate of ethylene
glycol from silver stearate and ethylene bromide. Upon
crystallization from ether he obtained a product melting
at 76°C.
In a rather extensive study of fat acids esters,
Kraft^ prepared the glycol esters of the higher fat acids
by heating ethylene chloride together with the potassium
salt of the fat acid for ten hours at 180°C. The diester
was isolated by precipitation from ether solution and then
purified by vacuum distillation. He recorded the following
data.
M.P. .°C_. P.P,, Q BB,
ethylene dilaurate 5** 188
ethylene dimyristate 61* 208
ethylene dipalmltate 72 226
ethylene di stearate 79 21+1
Ethylene glycol dipalmltate was prepared by
Stephenson2^ from palmityl chloride and glycol in the
presence of pyridine and anhydrous chloroform. The reaction
was performed at room temperature for twenty four hours.
After crude purification by hot water washings the ester
was extracted with ether and precipitated by cooling.
Four recrystallizations were carried out using a
chloroform-ethyl alcohol mixture. The final white crystals
gave a constant melting point of 65°C.
The most extensive characterization of ethylene
glycol fat acid esters was carried out in 1915 by Ruttan
21
and Roebuck. They prepared a variety of high molecular
weight fat acid esters including substituted and mixed
esters. Their method was direct esterification of purified
(alcohol recrystallized) fat acids with ethylene glycol at
185°C. for ^ to 7 hours. The products were taken up in
ether solution and washed. After evaporation of the ether
the esters were crystallized from ethyl alcohol. By slow
cooling, they first precipitated the diester (which con­
stituted most of the product), then the monoester (only
a very small amount), and finally, there remained 10 to
15 P®r cent of "almost crystalline, very soluble substance"
(probably the ethyl ester produced by interesterification).
Repeated fractional crystallizations from ethyl alcohol
were necessary in order to obtain constant melting points.
Of the physical characteristics reported the following
are of interest in this study:
M.P. Density Abs. Ethanol Ethyl Ether
Ester °C. gm./cc. *D‘P- gm./lOO gm. ___________
Glycol monopalmltate 51.5 O.8786 l.Mfll 1.62 ( 0°C.) Much more soluble than
(60.5°C.) 2*f.08 (25°c.) either dipalmltate or
monostearate
Glycol dipalmltate 68.7 0.859^ 1.^378 0.018 ( 0°C.) More soluble than
(77.9®C.) 0.087 distearate
0.310 (38°C.)
Glycol monostearate 58.5 0.8780 1.^310 0.67 ( o°c.) Much more soluble than
(60.0°C.) b.17 (25°c.) distearate
10.61 C29°C.)
Glycol distearate 75 0.8581 1A385 0.010 ( 0°C.) Fairly soluble in
(78.06C.) 0.028 (25°c.) cold ether
0.112 0t0°C.)
■r
In 1931 Bhattacharya and Hilditch^ made a study
of mixed glycol esters containing saturated and unsaturated
higher fat acids. In conjunction with this study they
prepared three fully saturated glycol diesters. The
recorded melting points of these esters after recrystalli­
zation from ether are as follows:
glycol dilaurate *f9
glycol dipalmltate 69
glycol distearate 73
Later in 1935 Hilditch and Rigg^ worked out a
method for producing a preponderance of the monoesters of
both glycerol and ethylene glycol. The salient features
of the method consist of; (1) using a large excess of the
polyhydrlc alcohol, (2) using phenol as a mutual solvent
for the immiscible alcohol and fatty acid, and (3) bubbling
dry CO2 gas through the reactants in order to aid mixing
and removal of the water formed. When 3 mols of ethylene
glycol and one mol of palmitic acid were heated at 180°C.
for four hours with 0.1 per cent (based on the weight df
fatty acid) camphor-^-sulfonic acid as a catalyst, a
yield of 89# glycol monopalmltate was obtained. Even
higher yields of the monoester resulted when more catalyst
and a larger proportion of alcohol were used. By using
identical conditions and proportions as stated in the above
example,but without phenol as a solvent, a product con-
tainlng 69# glycol monopalmitate was obtained. Hilditch
and Rigg separated the diesters from their products by
removing successive crops of the crystals from ether
solution. The remaining mother liquor upon evaporation
gave the monoesters which did not change their melting
point upon subsequent recrystallization.
glycol monolaurate 27.5
glycol monopalmitate M-7.5
glycol monostearate 56.0
In connection with other work which they were
if 2*t
doing Staudinger and Schwalenstrocker prepared three
glycol dlesters. The fat acid chlorides and glycol were
used as starting materials. Purification consisted of
high vacuum fractionation followed by numerous
crystallizations from acetone. The following melting
points were reported.
ethylene dilaurate 52
ethylene dimyristate 63
ethylene dipalmltate 70.5
Halasz and Rovira, ^ in a study of glycol
compounds, have prepared and characterized four of the
lower fatty acid glycol esters. They reported the boiling
points, densities, and refractive indices for these
compounds as follows:
ethylene monoformate -
B.P. ?6o 179-180oC. d£8 1.1915? nj8 1.^130
ethylene monoacetate -
B.P. ?6o 187-189 C. d£° 1.1090? nj8 1.^175
ethylene monobutyrate -
B.P. ^ 98-100°C. d*8 1.03215 i£8 1A303
ethylene monononanoate - ^
B.P. lh 1^3-lMf°C. d£7 0.9616; x£9 l.M+Ol
The most recent preparations (19^7) are those of
20
Paqnot. Diesters were synthesized by adding 2 mols of
acid chloride to 1.1 mol ethylene glycol and 2.1 gramatomic
weights of Hg in anhydrous ether solvent. After reaction
water was added to obtain a solid phase and this was
extracted with ether. By direct recrystallizations 90#
yields were obtained. The monoesters were prepared
separately by adding 1 mol of fatty acid to 1 mol of
potassium hydroxide in alcohol solution. To the potassium
soap which formed 1.1 mol of ethylene chlorohydrin
(2-chloroethanol) was added, and the mixture was refluxed
several hours. The potassium chloride which slowly
precipitated was filtered off hot. Upon cooling, the
monoesters precipitated. These were recrystallized from
acetone to give over 90# yield. The following data were
recorded:
A
ethylene dllaurate 52
ethylene dimyristate 63
ethylene dipalmltate 69
ethylene di stearate 7***