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Reaction of glycidyl benzoate with acid in the presence of tertiary amines as the catalyst.

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Die Angem&
Makromolekhre Chemie 12 (1970) 157-165 (Nr. 155)
From the Institute of Chemical Technology Pardubice and the Research Institute
of Synthetic Resins and Lmquers, Pardubice, Czechoslovakia
Reaction of Glycidyl Benzoate with Acid in the
Presence of Tertiary Amines as the Catalyst
By VLaDmiR FIALA*
and MILOSLAVLIDA%K**
(Eingegangen a m 19. Dezember 1969)
SUMMARY:
The reaction of epoxides with carboxylic acids catalysed by tertiary aminea has
been discussed. The mechanism of the reaction has been deduced and confirmed,
using experimental results, on the example of the reaction of glycidyl benzoate
with benzoic acid in xylene, catalysed by benzyldimethylamine. The reaction
occurs vie a combined ionic mechanism as well as via a complex formation, thus
explaining the abnormal dependence of the reaction conetent on the dielectric constant of the milieu and the found non-integer orders of reaction with reapect to the
emine and to the acid.
ZUSAMMENFASSUNG:
Es wurde die Umsetzung von Epoxydverbindungen mit Carbomdiuren unter der
Katalyse mit tertiiiren Aminen diskutiert. Auf Grund von experimentellen Resultaten wurde der Reektionsmechanismw am Beispiel der Umsetzung von Glycidyl.
benzoat mit Benzoesiiure unter der Katelyse durch Benzyldimethylamin in Xylol
abgeleitet und bestiitigt. Die Umeetzung verkuft nach einem kombinierten Ionenmechanismus und iiber Komplexbildung. Damit k h e n die abnormale Abhiingigkeit der Reektionskonetante von der Dielektrizitiitskonshte des Mediums und
die nicht ganzzahligen Ordnungen beziiglich Amin und Siiure erkliist werden.
A considerable number of papers has been concerned with the reaction of
electrophilic compounds with epoxides, namely both m-th respect to the curing
of epoxide resins 1-10 and to the preparation of polyester resins 11-21. It has
been found, that the reaction is catalysed by electron-donating substances
**
Institute of Chemical Technology, Pardubice, Czechoslovakia, present addrese
University Kyoto, Japan.
Research Institute of Synthetic Resins and Lequers, Pardubice, Czechoslovakia.
167
V. FIALA
and M. LID&K
such as alkaline hydroxides, alkaline salts of weak acids and, above all, by
tertiary amines and quaternary ammonium salts 4,22.
The following reactions may theoretically occur in the case of the reaction
of the carboxylic acid with the epoxide group :
R-COOH
+CHAH\O/
I
+CHAH-
MOO-CHAH-OH
‘O/
IGCOOH
I
+ R--COO4HcCH--OH
+ H2O
CHAH\O/
I
+ H2O
MOO--CH~CH-OH
I
-----*
R--COO--CH&H-OH
-
I
I
R-COO-CHAH-O-CH-CH-OH
I
+
M 0 0 - - C H - - C H ~ O O G R Ha0
(2)
(3)
I
--+
HO4HcCH-OH
-
WOOH
(4)
I
+ HO--CH2-CH-OH
( 51
The reaction (2) is known as not taking place when catalysed by tertiary
amines5. The reaction (3)occurs a t higher temperatures only (above2OOoC)4-23
or with excess of alcohol. The reactions (4) and (5) are known, as well, as not
taking place when catalysed by tertiary amines. The tertiary amines are not
engaged in the reaction considering that they are desactivated by the large
excess of acid. The summar reaction (1)may be thus the basic reaction.
An ionic mechanism has been considered for this reactions :
R-COOH
R-COO-
+ base. R-COO- + H+
+CHAH-
--+
R-COO-CH~CH-0-
I
‘O/
R--COO--CHAH-O-
I
(6)
+ H+
--+
R-COO--CH&H-OH
I
(8)
Other papers suggest a mechanism involving the formation of a transitory
complex9 :
R-COOH
168
+ base
-
[R-COOH . . . .base]
(9)
Reaction of Qlycidyl Benzodte
A aeries of arguments is mentioned by the authors for both mechanisms; it
is likely that the real mechanism may be the combination of both of them.
In this paper we studied the reaction of the epoxide group with the carboxylic acid catalysed by a tertiary amine, e. g., the reaction of glycidyl benzoate
with benzoic acid catalysed by benzyldimethylamine. The benzoic acid was
chosen for being the most simple aromatic carboxylic acid (the curing agents
of epoxy resins being on the baais of aromatic carboxylic acids or of their anhydrides), glycidyl benzoate waa used also with respect to the study of the influence of the ester group on the reactivity of the glycidyl group, and benzyldimethylamine is one of the mostly used tertiary amines in the reactions of
this type. The choice of these compounds cannot, according to the recent
knowledge within the range of the reactions of epoxide compounds, affect the
general validity of the found conclusions for the class of the reactions of aromatic carboxylic acids with glycidylic compounds of glycidyl ether- or glycidyl
ester type catalysed by tertiary amines.
As mentioned above, the mechanism of the reaction of carboxylic acids with
epoxides catalysed by tertiary amines is not quite clear aa yet, and that with
respect both to the progress of the reaction and to the influence of the concentration of the single reaction constituents on its total velocity. We attempted
in this work to obtain, from the course of the reaction, the necessary kinetic
data and to elucidate them then on the base of a theoretical elaboration of
the single reactions which might be expected in the reaction mixture.
Experimental
Used chemicals
Glycidylbenzoate waa prepared by the described method84 and bi-distillated
through a 70 cm column filled with glass ringa. B. p. 110 “C at 6 Torr, ng = 1.5263.
Analysis: epoxy-oxygen content 8.79% (theory: 8.98yo), C: 66.62% (theory
67.41y0), H: 5.99% (theory 5.66y0).
Benzoic acid - Anal R’grade, purchased from Lachema, Brno.
Benzylamine - Anal R’grade, bi-distillated through 20 cm WIDMERcolumn.
Xylene Anal R’grade wcw shaken successively with sulfuric acid and a sodium
bicarbonate solution, then dried with calcium chloride, and distilled on a column.
Chlorbenzene - Anal R’grade, waa shaken repeatedly with portions of sulfuric
acid, then waahed with a sodium bicarbonate solution, dried with calcium chloride
and distilled on a column.
Nitrobenzene - Anal R’grade, waa purchased from Lachema, Brno, and purified
by distillation on a column.
169
V. FIALA
and M. LIDA&
Acetophenone - Anal R’grade, waa purchased from Lachema, Brno, and purified
by distillation on a column.
o-Nitrotoluene was prepared by nitration of toluene, and distilled on a column.
Analytical Methods
The epoxide-oxygenwas analytically determinatd by the DURBET~KI
methodas.
The analytical determination of carboxylic groups was carried out by direct
titrating with KOH. T h e necessary amount of the sample waa diluted with 20 ml
acetone and with 10 ml water, and titrated with 0,l N KOH using phenolphthalein
as indicator.
Reaction
The solution of glycidyl benzoate and the solution of benzoic wid with dimethylamine were thermostated, separately, a t the reaction temperature. The solutions
were then mixed in the thermostated reaction flesk and maintained under steady dry
pure nitrogen gaa stream. The aamples were tsken out at determined intervals
using vacuum. Aliquots were pipetted out from the separated ice-cooled sample
into the titration flasks and concentration of epoxide and carboxylic groups was
determined.
M e a s u r e d a n d calculated v a l u e s
From the mutual relationship of the loss of the epoxide-and carboxylic groups
(the studied lose of the epoxide groups was equivalent to the loss of the carboxylic
groups) a t various initial concentrationsof the benzoic acid, of the glycidyl benzoate
and of benzyldimethylamine in xylene, the order of reaction was determined with
respect to the single constituents (Fig. 1, Table l), i. e., to amine: 0.60;to glycidyl
benzoate: 1.06 and to the benzoic acid: 0.52. From the temperature-dependence
of the reaction constant (Fig. 2) was determined, similarly, the activation energy
of reaction E h = 16.9 kcal/mol (Table 2).
Table 1. The orders of reaction with respect to the single constituents.
c (mole/l)
calculated
constituent
log c
benzoic acid
0.802%1
0.6508-1
0.4771-1
1.5
1.o
0.7
0.52
glycidyl benzoate
0.8195-1
0.6395-1
1.5
1.0
1.06
benz yldimethylamine
0.875CL-2
0.6990-2
0.1761-2
0.3010-2
0.175
0.05
0.015
0.02
0.60
160
Order
Reaction of Glycidyl Benzoate
temperature
"C
k * 102
9s
110
124
0.505
0.972
2.27
0.2
-
0.1
-
log k
+ 2 (1112
*
-
mol-l/2 min-1)
0.7033-1
0.9877-1
0.3666
I
'
0.01
I
I
1
,
,
,
,
0.6
0.7
7
0.75
m
+
>=
-
0
Ol
,
-0.11,
0.4
,
0.5
,
0.6
0.7
log c + 1
,
1
0.8
c) The determination of the or-
der of reaction With respect to
benzyldimethylamine.
1.(
g*5
1
1.0
b) The determination of the order of reaction with respect
to glycidyl benzoate.
0.9
l
Fig. 1 b
Fig. la
Fig. 1. a) The determination of the order of reaction With respect to
the benzoic acid.
0.8
log C +
1
- 0.0
-Os5
,
1
0.0
0.5
1.0
log c + 2
1.5
Fig. 1 c
161
V. Flaw and M. L I D A ~
Fig. 2. The temperature-dependence
of the reaction constant of the reaction of the benzoic acid with glycidyl
benz08t.8 CaMyWd by benzyldimethylamine.
The dependence of the milieu on the reaction rate was studied on the progress
of the reaction in solvents which differ by their dielectric constant: in nitrobenzene,
o-nitrotoluene, acetophenone, chlorobenzene and xylene. The found results are
summarized in Table 3 and in Figs. 3 and 4.
Table 3. The dependence of the reaction on the dielectric constant of the milieu
a t 110°C.
solvent
nitrobenzene
0-nitrotoluene
acetophenone
chlorobenzene
xylene
log k + 2
(11/2 . mol-lle . --I)
0.4282
0.3802
0.2421
0.1024
0.9974-1
D-1
l'D
0.0441
0.0683
0.0716
0.2300
0.4270
2D
+1
0.468
0.451
0.448
0.346
0.236
log D
1.3560
1.2934
1.1461
0.6365
0.3698
Similarly as in the reaction of phenyl glycidyl ether with the benzoic acid
b (Fig.4), where a
a t similar conditions*, the relationship log k'= a log D
and b are constants, was found to hold better in the studied reaction for the
dependence of the dielectric conatant of used solvent (D) on the reaction con1)-1.
stant (k)than the relationship log k - 1/D or log k - (11-1) (2 D
The amumption is thereby confirmed that the reaction mechanism is affected
by the combination of ionic mechanisms or by the formation of complexes,
which is in good agreement with the suggested mechanism.
+
-
162
+
.
N
c
X
I
0
Y
Fig. 3.
Reaction of 0.48 M glycidyl benzoate with 0.48 M benzoic acid C8tdyBed
by 0.12 M benzyldimethylemine in various solvents at 110OC.
El xylene
A nitrobenzene
0 chlorobenzene
o-nitrotoluene
0 acetophenone
1.5.
-1.5.
Fig. 4.
The dependence of the reaction rate constant of the reaction of benzoic
acid with glycidylbenzoete catalyeed by benzyldimethylamine on the dielectric constent of the milieu.
163
V. FIALA
and M. LIDA%K
The found non-integer order of reaction with respect to the catalytic amine
can be explained 7.10 by the formation of a complex with the acid, for the
formation of which in xylene there are fundamental presumptions at given
conditions.
It is possible, on the basis of the found experimental and literature data, to
suggest for the reaction of benzoic acid with glycidyl benzoate catalysed by
benzyldimethylamine the following reaction schema :
M O O -
I
+C H A H
R-COO-CH&H-O-
I
'0'
c4
I
R-COO-CHAH-0c6
c6
c3
I
+ NR;R"H+
+ NR;R"
R-COO-CHAH-OH
c7
c5
c2
(13)
When we express the suggested equations by kinetic equations, then
The member ks c4 CQ can be, consequently, neglected.
In the equilibrium c4 is given by the catalytic amount of the amine, this
reaction being thus = 0. For the same reason it can be thought that c4 = c5.
Then
dc6
- - ksc4cs -k4cjc4 and
dt
164
-dc6
dt
dc7
=
= -k3c3
dt
V
G+
Reaction of alycidyl Benzoate
The found reaction orders in the first stage with respect to the single constituents can be explained by the analysis of the kinetics of the studied reaction, use being made of simplifications baaed on previous papers published in
this field.
The obtained result is in good agreement with the found kinetic values of
the reaction. The suggested mechanism may be therefore considered aa the
most probable one.
Y. TANAKA
and H. KAKIUCHI,
J. appl. Polymer Sci. 7 (1963) 1063.
Y. TANAKA
and H. KAKIUCHI,
J. Polymer Sci. A 2 (1964) 3405.
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J. appl. Chem. 6 (1956) 429.
4 L. SHECHTER
and J. WYNSTRA,
Ind. Engng. Chem. 48 (1956) 86.
N. 5. ISMCS
and E. R. PARKER, J. chem. SOC.[London] 1960, 3497.
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and H. KAKIUCHI,
J. Polymer Sci. A-1 4 (1966) 109.
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and H. -CHI,
J. Macromol. Chem. 1 (1966) 307.
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J. org. Chem. 31 (1966) 1955.
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ISHII,
~ Y J.
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et al., Vysokomol. Soedin. 7 (1865) 1024.
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~ , GULBINS
et al., Makromolekulare Chem. 51 (1962) 53.
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~,
Technische Hochschule Stuttgmt 1957.
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and M. F. SOROKIN,
Lakokras. mat. 5 (1965) 79.
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Makromolekulare Chem. 89 (1965) 177.
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and W. HOFMANN,
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2
165
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