Kinetic study of addition of some carboxylic acids to 1,2-epoxy-3-phenoxypropane

Article abstract of DOI:10.1021/op9900479

The kinetics of addition of acetic, acrylic, or methacrylic acids to l,2-epoxy-3-phenoxypropane (glycidyl phenyl ether) carried out in the presence of chromium(III) ethanoate have been studied. A kinetic model of the reaction has been proposed. The rate constants as well as the activation parameters have been evaluated. The reactivity of the acids in reactions with GPE and 1-chloro-2,3-epoxypropane (epichlorohydrin) without any solvent are compared. The compositions of reaction mixtures have been carefully determined.

Full text of DOI:10.1021/op9900479

Organic Process Research & Development 1999, 3, 432−436
Kinetic Study of Addition of Some Carboxylic Acids to
1
,2-Epoxy-3-phenoxypropane
Agnieszka Bukowska and Wiktor Bukowski*
Faculty of Chemistry, Rzeszow UniVersity of Technology, Al. Powstancow W-wy 6, 35-959 Rzeszow, Poland
Abstract:
studied for a series of methyl-substituted pyridine derivatives.
The kinetics of addition of acetic, acrylic, or methacrylic acids
to 1,2-epoxy-3-phenoxypropane (glycidyl phenyl ether) carried
out in the presence of chromium(III) ethanoate have been
studied. A kinetic model of the reaction has been proposed. The
rate constants as well as the activation parameters have been
evaluated. The reactivity of the acids in reactions with GPE
and 1-chloro-2,3-epoxypropane (epichlorohydrin) without any
solvent are compared. The compositions of reaction mixtures
have been carefully determined.
An increase in the rate was observed when pyridine was
replaced by 3- or 4-methylpyridine, while 2-methylpyridine
was a less active catalyst than pyridine. Similar dependence
of catalytic activity on the structure of catalyst was observed
for methyl derivatives of quinoline.
2
The kinetics and mechanism of reactions of a series of
glycidyl ethers with caproic or capric acids in chlorobenzene
3
were studied by Sorokin et al. The rate and mechanism of
addition of carboxylic acid to an epoxy ring were found
dependent on the type of catalyst used. The reaction was
slow in the absence of catalyst, and its global order was two;
one for each substrate. The rate of the same reaction carried
out in the presence of sodium or potassium hydroxide was
described by a third-order equation: concentrations of both
reagents and catalyst all appeared in the first power. A
different reaction order was observed for the reaction
catalyzed by trihexylamine. In the presence of this catalyst,
the addition rate did not depend on acid concentration, but
it was found to be proportional to both catalyst and oxirane
concentrations. This finding was in contradiction to the result
Introduction
The reactions of carboxylic acids with 1,2-epoxy-3-
phenoxypropane and its derivatives were the subject of
several kinetic analyses.1-8 The effects of reagent structure,
type of catalyst, and solvent used on the rate and mechanism
of reaction were studied. Mostly the effect of basic catalysts
was studied since these had been most widely utilized in
reactions of carboxylic acids with epoxy compounds. The
reaction mechanisms were found to be pretty complex and
hard to interpret unambiguously. Consequently, the views
on the course of reaction including its order and mechanism
differ from author to author, particularly in the case of tertiary
1
of Tanaka.
Yet another interpretation of kinetic data on the reaction
of 1,2-epoxy-3-phenoxypropane with caproic acid was
1
-5
5
amine catalysts.
published by Matejka and Du sˇ ek. The authors found the
Tanaka et al.1 have found that in the presence of tertiary
amine, substituted glycidyl phenyl ethers reacted with
benzoic acid in xylene, mono-, o-dichlorobenzene, or ni-
trobenzene according to the first order with respect to both
reagents and catalyst. The rate of reactions increased with
the growing acceptor character of the substituent in either
,2,4
first order of the reaction with respect to catalyst and a 0.5
one with respect to both acid and ether concentration.
Despite the different points of view of different authors
on the reaction order, they all seemed to agree that a complex
of the tertiary amine catalyst with carboxylic acid was formed
in the first stage of reaction. This seems quite obvious for
the chemical nature of these compounds. As pointed out by
1
ether or solvent molecules. For the series of aromatic
solvents, toluene, chlorobenzene, o-dichlorobenzene, ni-
trobenzene, or benzene-nitrobenzene mixture, the logarithm
of the rate constant of the addition of benzoic acid to 1,2-
epoxy-3-phenoxypropane catalyzed by pyridine has been
5
Matejka and Du sˇ ek, carboxylic acids in contact with amines
yield an ammonium salt. Formation of such a salt containing
carboxylic anions should result in the same mechanism of
reaction as that observed for sodium acetate catalyst.
An obvious change of the catalyst active form takes place
also when sodium or potassium hydroxide is used. In this
case the neutralization yields the respective carboxylate
which becomes the catalyst of the reaction.
The rate of addition taking place in the presence of alkali
metal hydroxides or carboxylates as well as tertiary amines
should depend on the size of cation in the active form of
catalyst. As the radius of the cation increases, the electrostatic
attraction between counterions becomes weaker, the nucleo-
philicity of carboxylate anions increases and hence increases
the catalytic activity. Such a relationship was observed for
4
found to depend linearly on the solvent dielectric constant.
The effect of catalyst structure on the same reaction rate was
*
Corresponding author. Telephone: (+48-17) 8651338. Fax: (+48-17)
8
543655. E-mail: wbuk@prz.rzeszow.pl.
(
(
(
(
(
(
(
1) Kakiuchi H.; Tanaka, Y. J. Org. Chem. 1966, 31, 1559.
2) Tanaka, Y. J. Org. Chem. 1967, 32, 2405.
3) Sorokin, M. F.; Gershanova, E. L. Kinet. Katal. 1967, 8(3), 512.
4) Tanaka, Y.; Kakiuchi, H. Tetrahedron 1968, 24, 6433.
5) Matejka, L.; Dusek, K. Polym. Bull. 1986, 15, 215.
6) Klebanov, M. S.; Shologon, I. M. Zh. Org. Khim. 1979, 49(4), 812.
7) Klebanov, M. S.; Shoshina, L. V.; Shologon, I. M. Zh. Org. Khim. 1981,
5
3(5), 1131.
(8) Klebanov, M. S.; Kirjazev, F. Yu.; Cervinskii, A. Yu.; Shologon, I. M. Zh.
Org. Khim. 1984, 20(11), 2407.
4
32
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Vol. 3, No. 6, 1999 / Organic Process Research & Development
10.1021/op9900479 CCC: $18.00 © 1999 American Chemical Society and The Royal Society of Chemistry
Published on Web 10/01/1999

9
the reaction of carboxylic acids with 1,2-epoxypropane or
-chloro-2,3-epoxypropane.10 Steric conditions, however,
1
may distort this order. A reduced rate was observed for large
2
cations in the case 2-methylpyridine or 2-methylquinoline.
The differences in the observed reaction order of the
addition of carboxylic acids to glycidyl phenyl ethers
catalyzed by tertiary amines is probably the result of the
equilibrium which is established between the amine and
carboxylic acid. The latter strongly depends on the other
conditions of the reaction.
The basic catalysts, although quite widely used, have
certain disadvantages, the main one being the ability to
1
1
initiate cationic polymerization of epoxy compounds. In a
dilute solution this reaction may be neglected, but in the
systems without a solvent, such as in the commercial
synthesis of hydroxyalkyl esters, the side polymerization
reaction in the alkaline medium may reduce considerably
the reaction selectivity.
Figure 1. The concentration of 1,2-epoxy-3-phenoxypropane
GPE) and of acetic acid (AcOH) versus time in the reaction
(
carried out in the presence of chromium(III) ethanoate cata-
The chromium(III) catalysts, which are effective in the
reactions of carboxylic acids with oxirane, 1,2-epoxypropane,
or 1-chloro-2,3-epoxypropane, are free of this disadvantage.
They exhibit not only a high selectivity, but are usually
more active than basic catalysts.1
-3
lyst (cat); CAcOH,0 ≈ CGPE,0; Ccat ) 0.008 mol‚dm ; temperature
70 °C.
chromatograph with an FFAP capillary column, 10 m/0.53
mm/1 µm).
2-17
The kinetic relationships observed in the addition of
selected carboxylic acids to 1,2-epoxy-3-phenoxypropane in
the presence of such a homogeneous chromium(III) catalyst
in the system without a solvent are presented in this work.
Results and Discussion
Among the products of reaction in the system containing
a carboxylic acid (CA), asymmetric epoxy compound and
catalyst one may expect beside the two isomeric esters with
alcoholic hydroxy groups also the products of dispropor-
tionation of hydroxyesters, subsequent addition of oxirane
to hydroxyesters, polymerization of oxirane or its isomer-
ization to ketone or aldehyde, or even esterification of
carboxylic acid with the addition product. The extent of either
of these reactions depends on the conditions applied and,
primarily, on the kind of catalyst used. Among two isomeric
hydroxyester products, usually the so-called normal product
is formed in excess, i.e., the product of addition to the carbon
atom in epoxy ring which has a lower substitution degree.
In our previous papers on the reactions of carboxylic acids
with 1-chloro-2,3-epoxypropane carried out in the presence
Experimental Section
Materials. Commercially available acetic, acrylic, and
methacrylic acids and 1,2-epoxy-3-phenoxypropane were
purified in the standard manner and distilled prior to use.
Chromic ethanoate was of p.a. grade and used without further
purification.
Procedures. The kinetics of addition were studied in
3
purpose designed glass reactors (50 cm ) equipped with a
heating jacket, reflux condenser, thermometer, and magnetic
stirrer. The content of reactor was brought to desired
temperature with an external thermostat. The equimolar ratio
of carboxylic acid to epichlorohydrin was used. The con-
centration of chromium(III) ethanoate was changed in the
1
7,19,20
of chromium(III) ethanoate
we have shown that in the
-
3
systems without a solvent, most of the above-mentioned side
reactions involving oxiranes do not take place, or their
contribution among products is negligible.
range 2.0-17.0 mmol‚dm and temperature from 60 to 90
°
C at 10° intervals.
The content of unreacted acid in the samples withdrawn
The typical kinetic curves obtained for the reaction of
acetic (1), acrylic (2), and methacrylic acid (3) with 1,2-
epoxy-3-phenoxypropane in the presence of chromium(III)
ethanoate in temperature range 60-90 °C are shown in
Figures 1-3.
from the reactor at predetermined reaction times was
determined by titration. The concentration of 1,2-epoxy-3-
phenoxypropane was determined by Jay’s method. The final
reaction mixtures were carefully analyzed by GLC (HP 5890
18
(
9) Szak a´ cs, S.; G o¨ b o¨ l o¨ s, S.; Nagy, F. J. Chem. Soc., Perkin Trans. 2 1983, 4,
For all systems, the shape of kinetic curves indicates that
the changes of both substrate concentrations are simulta-
neous. This confirms the small contribution of side reactions
in the conditions applied. The same conclusion follows from
results of GLC analysis of the crude reaction products. In
the crude products of reaction two isomeric esters, 2-hy-
droxy-3-phenoxypropyl (n-PHPC) and 1-(hydroxymethyl)-
4
17.
(
10) Bukowska, A.; Guskov, A. K.; Makarov, M. G.; Rokaszewski, E.; Svets,
V. F.. J. Chem. Technol. Biotechnol. 1995, 63, 374.
11) Ellis, B. Chemistry and Technology of Epoxy Resins; Blackie Academic &
Professional: London, 1993.
12) German Patent 1,911,447, 1970.
13) U.S. Patent 3,875,211, 1975.
14) German Patent 2,801,422, 1979.
15) Russian Patent 505,627, 1976.
16) European Patent 1904, 1978.
17) Bukowska, A.; Bukowski, W. J. Chem. Technol. Biotechnol. 1996, 67, 176.
18) Jay, R. Anal. Chim. 1964, 36, 667.
(
(
(
(
(
(
(
(
(19) Bukowska, A.; Bukowski, W. J. Chem. Technol. Biotechnol. 1998, 73, 341.
(20) Bukowska, A.; Bukowski, W. J. Chem. Technol. Biotechnol. 1999, 74, 675.
Vol. 3, No. 6, 1999 / Organic Process Research & Development
•
433

Figure 4. The effect of catalyst concentration on the time
dependence of methacrylic acid (MA) concentration in reaction
with 1,2-epoxy-3-phenoxypropane (GPE) carried out in the
ap tr ue rs ee n 9c 0e °o Cf .c hromium(III) ethanoate; CMA,0 ≈ CGPE,0; temper-
Figure 2. The concentration of 1,2-epoxy-3-phenoxypropane
GPE) and of acrylic acid (AA) versus time in the reaction
carried out in the presence of chromium(III) ethanoate catalyst
(
-
3
CAA,0 ≈ CGPE,0; Ccat ) 0.008 mol‚dm ; temperature 70 °C.
Figure 5. The effect of catalyst concentration on the time
dependence of 1,2-epoxy-3-phenoxypropane (GPE) concentra-
tion in reaction with methacrylic acid (MA) carried out in the
ap tr ue rs ee n 9c 0e °o Cf .c hromium(III) ethanoate; CMA,0 ≈ CGPE,0; temper-
Figure 3. The concentration of 1,2-epoxy-3-phenoxypropane
GPE) and of methacrylic acid (MA) versus time in the reaction
carried out in the presence of chromium(III) ethanoate catalyst;
(
-
3
CMA,0 ≈ CGPE,0; Ccat ) 0.006 mol‚dm ; temperature 70 °C.
The slopes of ln CCA vs time lines depend linearly on the
concentration of chromium(III) ethanoate (Figures 6 and 7)
which means that all reactions are of the first order with
respect to catalyst concentration. The slopes are in fact the
effective rate constants of acid addition to the epoxy
compound. It follows from their values that acrylic acid
reacted with 1,2-epoxy-3-phenoxypropane with the highest
rate and acetic acid with the lowest one among acids studied.
This order of reaction rates coincide with the order of the
2-phenoxyethyl carboxylate (a-PHPC), formed by the addi-
tion of carboxylic acids to 1,2-epoxy-3-phenoxypropane,
dominate:
acidities of acids in water expressed by their pK
a
values.21
No such consistency was observed for 1-chloro-2,3-epoxy-
propane which reacted the fastest with methacrylic acid and
1
7,20
the slowest with acetic acid.
The difference, however,
between the relative reaction rates of methacrylic and acrylic
acids was in both cases pretty small and increased slightly
with temperature.
The data presented graphically indicate that in the
presence of chromium(III) ethanoate the reaction order of
the reaction between carboxylic acids and 1,2-epoxy-3-
phenoxypropane is one with respect to catalyst concentration
As revealed by GLC analysis, the molar fraction of the
abnormal isomer in the crude products only slightly depends
on temperature; its dependence on the type of carboxylic
acid is more pronounced. It increases in the order methacrylic
(8.2%), acrylic (8.8%), and acetic acid (12%). The rate curves
became straight lines in the semilogarithmic plot (Figures 4
and 5) which means that the reaction is of the first order
with respect to substrates.
(21) Weast, R. C. CRC Handbook of chemistry and physics; CRC Press: Boca
Raton, Florida, 1980.
434
•
Vol. 3, No. 6, 1999 / Organic Process Research & Development

the presence of the same catalyst revealed the zero-th order
17
with respect to carboxylic acid concentration. The relevant
rate equation read:
dCCA
dCGPE
dt
-
) -
) kC C
(2)
cat GPE
dt
The rate constants k calculated using eq 2 are shown in Table
. The relative reactivity ratios R ) k /kAcOH for the reaction
1
i
of carboxylic acids with 1,2-epoxy-3-phenoxypropane are
also listed. From their values one can see that the reactivity
of acrylic and methacrylic acid relative to that of acetic acid
reduced 1.2 and 1.5 times, respectively, as temperature
increased from 60 to 90 °C. At 60 °C, the unsaturated acids
had similar reactivity.
The rate constant k in eq 2 is, in fact, a composed rate
constant of formation of two isomeric addition products. If
the molar fractions of these products are known, the partial
rate constants can be calculated from the equation
Figure 6. The effective rate constants (k(MA)) of the reactions
of methacrylic acid with 1,2-epoxy-3-phenoxypropane carried
out in the presence of chromium(III) ethanoate as determined
from the correlation ln CMA vs time. CMA and Ccat are the
methacrylic acid and catalyst concentrations, respectively.
ka-PHPC ) Xa-PHPC
kn-PHPC ) Xn-PHPC
k
k
(3)
(4)
where Xa-PHPC and Xn-PHPC are the molar fractions of products
of normal and abnormal substitution, respectively. The partial
rate constants calculated by using averaged molar fractions
of isomeric hydroxyesters are listed in Table 1. The rate of
formation of the abnormal product seems to depend on the
structure of carboxylic acid. As follows from the values of
X
n-PHPC and Xa-PHPC the rate of formation of the normal
product was the highest among the acids studied. The lowest
rate of the normal product formation had acetic acid.
It seems that the steric effects cause the most bulky
molecule of methacrylic acid to react harder with the more
substituted carbon atom of 1,2-epoxy-3-phenoxypropane than
the smaller acrylic acid, despite the higher overall addition
rate of the latter.
By using linearized forms of Arrhenius and Eyring
equations as well as the temperature dependence of free
energy of activation we have calculated the energy, enthalpy,
and entropy of activation. The results are listed in Table 2.
A clear decrease of values of all these parameters can be
observed in the order acetic acid > acrylic acid > meth-
Figure 7. The dependence of the effective rate constants for
reactions of carboxylic acids (CA) with 1,2-epoxy-3-phenoxy-
propane carried out in the presence of chromium(III) ethanoate
at 70 °C as determined from slopes of the plots ln CCA vs time.
as well as with respect the concentration of one of substrates.
Our previous studies on the reaction order in reaction of
acetic acid with 1-chloro-2,3-epoxypropane carried out in
Table 1. Rate constants of reactions between carboxylic acids and 1,2-epoxy-3-phenoxypropane in the presence of
chromium(III) ethanoate
1
02k,
%
10 ka-PHPC
2
10 kn-PHPC
2
,
acid
acetic
temp, °C
dm mol s-1
3
-1
(a-PHPC)
dm mol s-1
3
-1
dm mol
3
-1 -1
s
i
R ) k /kAcOH
60
0.552 ( 0.030
1.278 ( 0.020
2.540 ( 0.107
5.033 ( 0.213
1.075 ( 0.055
2.217 ( 0.150
4.080 ( 0.058
7.798 ( 0.345
1.068 ( 0.022
1.988 ( 0.045
3.573 ( 0.073
6.347 ( 0.117
12.13 ( 0.85
9.02 ( 1.15
8.19 ( 0.18
0.067
0.155
0.308
0.610
0.097
0.200
0.368
0.703
0.087
0.163
0.293
0.520
0.485
1.0
1.0
1.0
1.0
1.95
1.73
1.61
1.55
1.93
1.56
1.41
1.26
70
80
90
1.123
2.232
4.422
0.978
2.017
3.712
7.095
0.980
1.825
3.280
5.827
acrylic
60
70
80
90
methacrylic
60
70
80
90
Vol. 3, No. 6, 1999 / Organic Process Research & Development
•
435

Table 2. Activation parameters in reactions of carboxylic
acids with 1,2-epoxy-3-phenoxypropane in the presence of
chromium(III) ethanoate
relationship indicates that all addition reactions proceed
according to the same mechanism. A hypothetical mechanism
of the addition taking place in the presence of chromium-
(III) ethanoate has already been discussed in ref 17.17
According to this mechanism, the catalyst is solvated when
dissolved in a carboxylic acid and the exchange of the ligands
takes place in the coordination sphere of chromium(III)
atoms. The rate controlling stage is the activation of oxirane
molecule by creation of a coordination link between epoxy
oxygen and chromium atom which facilitates a quick opening
of epoxy ring by the nucleophilic attack of carboxylate ions
within the coordination sphere. The active complex im-
mediately splits in the presence of a second carboxylic acid
molecule with formation of one of two isomeric hydroxyes-
ters and restitution of the initial form of catalyst. The large
difference in the acidity of substrate and products improves
the reaction selectivity. It limits the extent of subsequent
reactions since the active complex decomposes most easily
in the presence of even a small amount of acidic protons.
Formation of the normal addition product is also favored by
the fact that the addition takes place in the coordination
sphere of the catalyst. The steric effects reduce the possibility
of the nucleophilic attack on the more substituted carbon
atom in epoxy ring. This is evident from the results of the
present work.
acid
acetic
acrylic
methacrylic
-
1
E
∆
∆
a
, kJ‚mol
73.70 ( 1.55 65.39 ( 2.35
70.72 ( 1.55 63.07 ( 1.06
59.57 ( 0.38
56.80 ( 0.35
q
-1
H , kJ‚mol
S , J‚mol K-1 -76.61 ( 4.45 -94.17 ( 3.04 -113.1 ( 1.00
q
-1
Figure 8. The isokinetic plot for the reactions of carboxylic
acids with 1,2-epoxy-3-phenoxypropane(0) or 1-chloro-2,3-
epoxypropane (O) in the presence of chromium(III) ethanoate;
AcOH: acetic acid, AA: acrylic acid, MA: methacrylic acid.
Summary
The addition of a carboxylic acid to 1,2-epoxy-3-phe-
noxypropane carried out in the presence of chromium(III)
ethanoate leads to the formation of two isomeric hydroxy-
esters with the isomer obtained by the addition to the less
substituted carbon atom in the epoxy ring formed in large
excess. The rate of addition does not depend on the con-
centration of carboxylic acid. It is proportional to concentra-
tions of 1,2-epoxy-3-phenoxypropane and catalyst. Among
the acids studied, the most reactive is acrylic acid, and the
least reactive, acetic acid. The amount of the isomer resulting
from abnormal addition depends on acid structure and is the
lowest for methacrylic acid.
acrylic acid. The order is not consistent with the reactivity
order discussed above. The reaction rate which is a function
of the activation energy depends on the ratio of activation
enthalpy and entropy. Although the addition of acrylic acid
to 1,2-epoxy-3-phenoxypropane requires overcoming a slightly
higher activation barrier than that of methacrylic acid, the
entropy of the first reaction is sufficiently high for the overall
rate to be in its favor.
The interrelation between activation energy and entropy
(
the isokinetic plot) is presented in Figure 8. for both the
Received for review May 21, 1999.
OP9900479
systems studied in this work and for reactions with 1-chloro-
2
17,20
,3-epoxypropane reported previously.
The fairly linear
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Vol. 3, No. 6, 1999 / Organic Process Research & Development