Table Of ContentTHE
DETERMINATION
OF EPOXIDE
GROUPS
B. DOBINSON, B.Sc, Ph.D.
Senior Research Chemist
CIBA (ARL) Ltd., Duxford, Cambridge
W. HOFMANN, D.Phil.
Wissenschaftlicher Experte
Research Department, Plastics Division, CIBA Ltd., Basle
and
B. P. STARK, M.A., Ph.D.
Chief Research Chemist
CIBA (ARL) Ltd., Duxford, Cambridge
THC OUEf N S AWADR
TO INDUSTY R1···
PERGAMON PRESS
OXFORD ' LONDON · EDINBURGH · NEW YORK
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Copyright © 1969
B. Dobinson, W. Hofmann, B. P. Stark
First Edition 1969
Library of Congress Catalog Card No. 68-27156
PRINTED IN GREAT BRITAIN BY D. R. HILLMAN AND SONS LTD., EXETER
08 012788 6
PREFACE
IN THIS short monograph we have summarized the methods which
are at present available for determination of 1,2-epoxide groups
of various kinds, and have tried to indicate the advantages and
limitations of the different procedures, and to suggest which
techniques are most likely to prove successful in a particular
case. We hope that this book will not only be of immediate prac
tical use, but that it will also serve to stimulate further work
towards improved analytical methods.
In Chapter 1, the chemical reactivities of different epoxides
under various conditions are discussed briefly; a knowledge of
the chemical behaviour of a given epoxide under a particular set
of circumstances is of fundamental importance in the choice of
the analytical method to be used. Most of the analytical work
on epoxides has been with procedures involving ring-opening
with HC1 or HBr, and these methods are described in Chapter 2,
in approximate chronological order of their development. Such
"acidic" methods have occasionally proved unsatisfactory, and
alternative techniques involving quantitative rearrangement of
epoxides, or else ring-opening under non-acidic conditions, are
discussed in Chapter 3. The same chapter also contains descrip
tions of various miscellaneous analytical techniques (including
very sensitive methods), and the final section of Chapter 3
comprises a discussion of the use of infrared spectroscopic
techniques for analysis of epoxides and the study of their reac
tions (particularly the cure of epoxy resins). The advantages and
limitations of the various methods are summarized very briefly
in Chapter 4, where the main factors affecting choice of experi
mental procedures are mentioned. Experimental details are given
for the most important analytical procedures, in both Chapters 2
and 3.
We are grateful to Prof. Dr. Hans Batzer and Dr. Walter Wilson
vii
Vili PREFACE
for their encouragement, and to our many CIBA colleagues in
Basle and Duxford who have discussed their results freely with
us, and so greatly assisted the preparation of this book.
Duxford, Cambridge, England B.D.
Basle, Switzerland W.H.
March 1967 B.P.S.
CHAPTER 1
INTRODUCTION
1. General considerations
Compounds which contain the epoxide ring (1.1) have been
given several different kinds of names:*1,2) epoxides, oxirans,
epoxy-compounds, olefin oxides, 1,2-epoxides, a-oxides, 1,2-
oxido-compounds, etc. In this monograph we shall use only the
first three of these terms. Many of the most-investigated epoxy-
compounds contain an epoxide ring of type (1.2), in which three
of the four substituent groups on the heterocyclic ring are hydro
gen atoms; such compounds are frequently called terminal
epoxides.
-CH CH2
(1.2)
(1.1)
CH2C1 (1.3)
O CH,—C—CH.
HJC — CH,
I
CH2C1 (1.5)
(1.4)
Although in this monograph we will be concerned particularly
with the analysis of oxirans, mention will sometimes be made of
oxetans; these are compounds containing a four-membered
cyclic ether group (1.3). Alternative but less common names
for such compounds include: ß-epoxides, 1,3-epoxy-alkanes,
1,3-oxides, and oxacyclobutanes. In general, oxetans undergo
the same types of ring-opening reactions as oxirans, but much less
readily (particularly where non-acidic reagents are involved). It
is therefore understandable that oxetans have so far achieved little
industrial importance. Probably the best known oxetan is 3,3-bis-
1
2 THE DETERMINATION OF EPOXIDE GROUPS
(chloromethyl)oxetan, which is used for production of the
thermoplastic polymer "Penton", having the repeating unit (1.4).t
Ethylene oxide (1.5), the "parent" of the family of epoxides,
was first prepared in 1859 by the French chemist A. Wurtz,(3)
who recognized it to be a "cyclic ether". Because of their high
reactivities in a wide range of ring-opening reactions, epoxides
have achieved industrial importance in many fields, and their
chemical behaviour has been widely studied.
Naturally-occurring epoxides
Numerous naturally-occurring epoxides are known,(4) and their
biological functions have been discussed in an excellent review
by Cross.(5) The existence of epoxide groups in such compounds,
in a wide variety of chemical environments, suggests that new
possibilities for epoxide synthesis still remain to be explored.
It seems certain that many more natural products will be identi
fied as containing epoxide groups, and the biological synthesis,
functions and reactivities of epoxides still require much
investigation.
Synthetic epoxides
Epoxides are frequently synthesized from the corresponding
unsaturated compounds/6,7) The epoxide oxygen atom can either
be introduced directly by oxidation with oxygen or a peracid, or
indirectly by addition of a hypohalous acid to an unsaturated
compound, and subsequent dehydrohalogenation of the resulting
halohydrin. Certain commercially important epoxy resins (p. 7)
are obtained by oxidation of polyunsaturated compounds with
peracetic acid. The three low molecular weight epoxides of
greatest technical importance at present are ethylene oxide (1.5),
propylene oxide (1.6), and epichlorohydrin (1.7) —which is
useful for the synthesis of further epoxides (see below).
A A
H2C—CH CR, H2C— CH CH,C1
(1.6) (1.7)
Ethylene oxide is used principally as a pesticide, and as
tPenton is a product of the Hercules Powder Company.
INTRODUCTION 3
starting material for many important industrial products such as
ethylene glycol, polyols and alkanolamines, as well as textile
auxiliary products and surfactants produced by addition of ethy
lene oxide to various long-chain alcohols or substituted phenols,
etc. Propylene oxide finds its greatest use in the production of
propylene glycol and higher polyoxypropylene polyols. The main
application of epichlorohydrin is in the production of epoxy
resins; these are compounds which contain at least two epoxide
groups, and which under the action of suitable "hardeners"
can be converted into insoluble "cured" materials having a
three-dimensionally cross-linked structure. The epoxy resins
are distinguished by their chemical versatility and their expanding
usefulness in a wide variety of applications. Their most attractive
properties in general are the ability to "harden" (cross-link)
with only very low shrinkage and without the formation of any
volatile reaction products, and the excellent mechanical and
electrical properties of the cross-linked resins. The hardened
products have excellent adhesion to many materials and possess
good resistance to moisture and chemicals.
Much of the analytical work with epoxides so far has been
either with the epoxy resins, or with the simple monoepoxides
(ethylene oxide, propylene oxide, epichlorohydrin) mentioned
above. The types of epoxy resin which have hitherto received
most attention are discussed briefly below: they fall into two
main classes: (a) materials prepared by reaction of epichlorohydrin
with a compound having at least one active hydrogen atom, and
(b) materials prepared by epoxidation of compounds having at
least one C=C double bond.
(a) Epoxy resins prepared from epichlorohydrin
The addition of epichlorohydrin to a compound (X —H)
containing an active hydrogen atom is catalysed by both acids
and bases, and leads to a chlorohydrin (1.8) which can be
dehydrohalogenated (generally with alkali metal hydroxide)
to a terminal epoxide (1.9).(6_8) The hydroxyl group of the inter
mediate chlorohydrin (1.8) can sometimes react to an appreciable
extent with any epichlorohydrin still present, and generate
further chlorohydrin (e.g. 1.10, which on dehydrohalogenation
is converted into a chlorine-containing epoxide, 1.11). This side-
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INTRODUCTION 5
reaction occurs especially during the acid-catalysed additions
of phenols or alcohols to epichlorohydrin; it is much less signi
ficant when phenols react with epichlorohydrin in the presence
of alkalis. Terminal epoxides of the type (1.9) are frequently
termed glycidyl compounds.
(i) Glycidyl ethers
The glycidyl compounds of most industrial importance are the
glycidyl ethers of poly phenols, and especially compounds of
the general formula (1.12), derived by reaction of Bisphenol A
(1.13) with epichlorohydrin. In formula (1.12), the value of n
depends upon the molar ratios of the reactants used. Resins
with values for n in the range 0-3 are viscous liquids or low melting
solids, and are used principally as casting, impregnating, tooling,
laminating or dipping resins, as adhesives, and for production
of moulding powders, foams, and in surface coatings. Epoxy
resins (1.12) with values of n greater than 4 (which can also be
prepared by treatment of lower molecular weight solid(9) or
liquid resins with less than the stoicheiometric amount of Bis-
phenol A) are solids with higher softening points. Such materials
are employed principally for production of surface coatings.
They can either be hot-cured with phenolic, urea- or melamine-
formaldehyde resins, or alternatively can be esterified with
unsaturated fatty acids, to yield air-drying resins (the so-called
"epoxy-esters"). Materials (1.12) with very high n values are
thermoplastic resins, with very low epoxide contents; they are
mainly used for moulding and in surface coatings.
The glycidyl ethers of other polyphenols such as 1,1,2,2-tet-
rakis(/?-hydroxyphenyl)ethane or resorcinol, or novolaks
derived from phenol or cresols, give cross-linked products of
high deflection temperatures.
Polyalcohols form poly glycidyl ethers (which generally contain
"residual chlorine", see above) which are useful as reactive
diluents or flexibilizers for Bisphenol-based epoxy resins (1.12).
Certain water-soluble glycidyl derivatives of polyols have been
recommended for the antistatic finishing of synthetic fibres(10,11)
and for embedding samples for electron microscopy.(12) Mono-
glycidyl ethers of phenols or alcohols are frequently used as
reactive diluents for the polyfunctional epoxy resins (1.12)
derived from Bisphenol A.
6 THE DETERMINATION OF EPOXIDE GROUPS
(ii) G lycidylamines
The only glycidylamines of technical importance are the resins
derived from aromatic amines such as aniline, p-aminophenol
or bis(/?-aminophenyl)methane. These are principally used in
the electrical industry.(13)
(iii) Glycidyl esters
In the cross-linked state, glycidyl esters show a surprisingly
high resistance to strong alkalis and acids.(14)
(iv) Other glycidyl compounds
Various epoxy resins have been prepared from other compounds
with active hydrogen atoms, such as sulphonic acids, sulphona-
mides, and thiols; so far they have achieved very little industrial
importance, however. One of the more attractive resins is the
recently developed triglycidyl isocyanurate.<15)
(b) Epoxy resins produced by epoxidation
ofunsaturated compounds
The two synthetic methods available are: epoxidation with
peracids, and hypohalogenation followed by dehydrohalogenation.
Only the first of these methods is used industrially for epoxy
resin production. The mechanisms(6'7,16_18) of the two procedures
are represented in Fig. 1.1. In the epoxidation of sterically
hindered olefins, the initial attack of peracid or "positive halogen"
YJ£Ì/ -RCO>H VV
hai hai
, /+\ / \l /
-Hhal . \ r
c-c HOH c — c
x c—c
OH
FIG. 1.1.
