Features of acetal interchange of 1,1-dialkoxyalkanes with 1,2-propylene glycol in neutral solutions

Article abstract of DOI:10.1023/A:1012361419351

Reactions fo 1,1-dimethoxymethane, 1,1-dimethoxyethane, and 1,1-dimethoxypropane with 1,2-propylene glycol at 25°C in neutral solutions were studied by ¹³C NMR spectroscopy. Under these conditions, 1,1-dimethoxymethane does not react with the g

Full text of DOI:10.1023/A:1012361419351

Russian Journal of General Chemistry, Vol. 71, No. 5, 2001, pp. 752 755. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 5, 2001,
pp. 802 805.
Original Russian Text Copyright
2001 by Balashov, Krasnov, Danov, Chernov.
Features of Acetal Interchange of 1,1-Dialkoxyalkanes
with 1,2-Propylene Glycol in Neutral Solutions
A. L. Balashov, V. L. Krasnov, S. M. Danov, and A. Yu. Chernov
Dzerzhinsk Branch, Nizhni Novgorod State Technical University, Dzerzhinsk, Russia
Received July 7, 1999
Abstract Reactions fo 1,1-dimethoxymethane, 1,1-dimethoxyethane, and 1,1-dimethoxypropane with
1,2-propylene glycol at 25 C in neutral solutions were studied by 13C NMR spectroscopy. Under these
conditions, 1,1-dimethoxymethane does not react with the glycol. Only the primary OH group of the glycol
participates in the acetal interchange. The reactions of 1,1-dimethoxyethane and 1,1-dimethoxypropane with
the glycol, along with the linear acetals, yielded 2-alkyl-4-methyl-1,3-dioxolanes. The product ratio depends
on the molar ratio 1,1-dialkoxyalkane : glycol. In the system 1,1-dimethoxypropane 1,2-propylene glycol,
the equilibrium concentration of the cyclic acetal slightly increases with temperature in the range 25 80 C.
Acetal interchange of linear acetals (1,1-dialkoxy-
alkanes) with 1,2-glycols is a convenient route to
1,2-dioxolanes [1, 2]. The advantage of this procedure
over the other routes is that significant amounts of the
target product are formed already on mixing the react-
ants in a neutral solution [3]. Previously we studied
the reaction of linear acetals with ethylene glycol [3]
and elucidated the influence of the structure of the lin-
ear acetal on the composition of the reaction mixture.
With increasing volume of the alkoxy group in the
initial acetal, the reaction selectivity with respect to
1,3-dioxolane increases. Variation of the structure of
the alkyl radical in the aldehyde moiety has virtually
no effect on the equilibrium yield of the cyclic acetal.
the composition of the reaction products, we studied
in this work, using 13C NMR spectroscopy, the reac-
tions of 1,1-dimethoxyalkanes RCH(OCH3)2 [R = H
(I), CH3 (II), C2H5 (III)] with 1,2-propylene glycol
(IV) in neutral solution at 25 80 C.
Previously it was suggested [1] that the mechanism
of acetal interchange is similar to the mechanism of
formation and hydrolysis of acetals. Study of the reac-
tions of carbonyl compounds with ethylene glycol and
1,2-propylene glycol in neutral solution showed that
the major reaction products are various hemiacetals
[4, 5]. On mixing of 1,2-propylene glycol with an
aldehyde, the OH groups of the glycol participate in
the reaction with the carbonyl group, with the second-
ary OH groups being less reactive.
To elucidate the influence of the structure of 1,2-
glycol on its reactivity in acetal interchange and on
13
0
0
Fig. 1. C NMR spectrum of the mixture 1,1-dimethoxyethane (II) 1,2-propylene glycol (IV) (25 C, c 5.457, c 5.479 M).
II
IV
1070-3632/01/7105-0752$25.00 2001 MAIK Nauka/Interperiodica

FEATURES OF ACETAL INTERCHANGE OF 1,1-DIALKOXYALKANES WITH 1,2-PROPYLENE GLYCOL 753
13
0
0
Fig. 2. C NMR spectrum of the mixture 1,1-dimethoxypropane (III) 1,2-propylene glycol (IV) (25 C, c 4.802, c 5.459 M).
III
IV
The spectra of the equilibrium mixtures II IV and
III IV are shown in Figs. 1 and 2. In analysis of the
composition of the equilibrium mixtures and structure
of the products, we leaned upon the spectra of the
pure reactants and of equilibrium reaction mixtures of
linear acetals with ethylene glycol [3] and of carbonyl
compounds with ethylene glycol and 1,2-propylene
glycol [4, 5]. Table 1 gives the assignments for the
groups of signals whose integral intensities were used
to obtain quantitative data on the composition of the
reaction mixtures. Among the reaction products, we
detected mixed acetal V, acetal VI, and the cyclic
acetal, 2-alkyl-4-methyl-1,3-dioxolane VII.
OCH3
RCH
OCH2CH(CH3)OH
RCH
OCH2CH(CH3)OH
OCH2CH(CH3)OH
V
VI
OCH2
RCH
OCHCH3
VII
Table 1. Signal assignment in the 13C NMR spectra of mixtures 1,1-dimethoxyethane 1,2-propylene glycol and
1,1-dimethoxypropane 1,2-propylene glycol at 25 C (the carbon atoms giving the indicated signal are printed italic)
,
Correction
factor
,
C
ppm
Correction
factor
C
Assignment
Assignment
ppm
1,1-Dimethoxyethane 1,2-propylene glycol
1,1-Dimethoxypropane 1,2-propylene glycol
48.33 CH3OH
51.06 CH3CH(OCH3)2
66.81 HOCH2CH(CH3)OH
67.31 HOCH2CH(CH3)OH
70.00 CH3CH(OCH3)OCH2CH(CH3)OH
CH3CH(OCH2CH(CH3)OH)2
70.89 CH3CHOCH2CH(CH3)O
0.9969
1.0042
0.8293
0.6453
0.8240
48.33 CH3OH
1.0404
0.9299
0.6938
0.7994
1.1303
51.32 CH3CH2CH(OCH3)2
66.89 HOCH2CH(CH3)OH
67.36 HOCH2CH(CH3)OH
70.06 CH3CH2CH(OCH3)OCH2CH(CH3)OH
CH3CH2CH(OCH2CH(CH3)OH)2
70.87 CH3CH2CHOCH2CH(CH3)O
0.9955
1.7103
1.4557
1.1155
1.4260
1.4471
71.00 CH3CHOCH2CH(CH3)O
71.13 CH3CH2CHOCH2CH(CH3)O
72.11 CH3CH(OCH3)OCH2CH(CH3)OH
CH3CH(OCH2CH(CH3)OH)2
71.96 CH3CH2CH(OCH3)OCH2CH(CH3)OH
CH3CH2CH(OCH2CH(CH3)OH)2
99.68 CH3CHOCH2CH(CH3)O
1.3066
103.71 CH3CH2CHOCH2CH(CH3)O
1.1284
100.45 CH3CH(OCH3)2
100.67 CH3CH(OCH2CH(CH3)OH)2
0.9353
1.0335
104.56 CH3CH2CH(OCH3)2
105.02 CH3CH2CH(OCH2CH(CH3)OH)2
1.0047
0.9087
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 5 2001

754
BALASHOV et al.
Table 2. Equilibrium composition of reaction mixtures obtained by mixing of linear acetals with 1,2-propylene glycol
at 25 C
Initial concentrations
Concentrations of components of equilibrium reaction mixture, M
of reactants, M
linear
acetal
1,2-propylene
glycol
linear
acetal
1,2-propylene
glycol
acetal
V
acetal
VI
dioxolane
methanol
VII
Compound II
1.541
2.978
4.285
5.457
11.33
9.014
7.068
5.479
8.828
4.723
2.520
0.9656
3.082
5.048
6.084
5.856
0.9609
1.594
1.249
1.238
0.5801
0.7573
1.537
0.2811
0.9865
2.181
0.3461
0.5127
0.6964
1.341
Compound III
1.261
2.630
3.661
4.802
4.802a
4.802b
11.25
9.039
7.389
5.459
5.459
5.459
9.144
5.187
2.709
0.7026
0.1396
0.0057
2.522
0.8454
1.433
1.660
1.448
1.817
1.86
0.4156
0.9278
1.140
1.253
1.201
1.424
0.2114
0.6415
1.493
1.300
1.209
4.779
5.819
6.011
6.520
6.877
0.0579
0.2197
0.6074
0.4844
0.3093
a
b
Reactants mixed at 65 C.
Reactants mixed at 80 C.
Similar to the system with ethylene glycol, the
of the appropriate signals, are listed in Table 2. Simi-
lar to the system with ethylene glycol [3], an increase
in the molar ratio dialkoxyalkane compound IV (A)
results in increased concentrations of the linear acetal,
alcohol, mixed acetal V, and dioxolane VII. The equi-
librium conversion of the linear acetal decreases with
increasing its initial concentration (Fig. 3). In going
from ethylene glycol to 1,2-propylene glycol, the
equilibrium conversion of the linear acetal changes
insignificantly. Such a low sensitivity to the structure
of 1,2-glycol was observed previously in direct acetal-
ization of carbonyl compounds with 1,2-glycols [4 7].
With both glycols, replacement of the C2H5 group in
the aldehyde moiety of dimethoxyalkane by C3H7 has
virtually no effect on its equilibrium conversion in
acetal interchange.
spectrum of the mixture dimethoxymethane (I) com-
pound IV contains only the signals of the initial com-
ponents; no reaction products are detected.
The concentrations of the components of the reac-
tion mixtures, calculated from the integral intensities
In going from dimethoxyethane to dimethoxyprop-
ane, the equilibrium yield of the corresponding 2-al-
kyl-4-methyl-1,3-dioxolane, acetal V, and acetal VI
in the reaction with 1,2-propylene glycol slightly
increases (Table 2), which is well consistent with data
obtained for the reaction of linear acetals with ethyl-
ene glycol [3]. In going from ethylene glycol to prop-
ylene glycol, the equilibrium yields of the products
change dramatically: The equilibrium yields of the
cyclic product and acetal V decrease, and the yield of
acetal VI increases.
Fig. 3. Influence of the initial molar ratio [linear acetal] :
[glycol] (A) on the equilibrium conversion of linear acetals
II and III: (1) 1,2-propylene glycol + II, (2) 1,2-propylene
glycol + III, (3) ethylene glycol + II [3], and (4) ethylene
glycol + III [3].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 5 2001

FEATURES OF ACETAL INTERCHANGE OF 1,1-DIALKOXYALKANES WITH 1,2-PROPYLENE GLYCOL 755
Increase in the temperature in the range 25 80 C
also affects to some extent the equilibrium composi-
tion of the reaction mixture. The equilibrium concen-
trations of the linear acetal and compound IV decrease
and that of free methanol increases, which indicates
that the equilibrium conversion of the reactants in-
creases. With increasing temperature, the concentra-
tions of the products vary differently: The content of
acetal V decreases, whereas the equilibrium concen-
trations of acetal VI and dioxolane somewhat in-
crease.
The 13C NMR spectra were taken on a Varian
Gemini-300 Fourier spectrometer at 25 C using the
INEPT technique. For stabilization of the resonance
conditions, a thin ampule of D2O was placed inside
the ampule with the reactants. The internal reference
was (CD3)2SO (
39.7 ppm). In quantitative anal-
ysis, correction faCctors were introduced to allow for
incomplete spin relaxation and the nuclear Overhauser
effect.
REFERENCES
Thus, formation of cyclic acetals in reactions of
1,1-dialkoxyalkanes with 1,2-glycols is favored by
equal reactivity of the hydroxy groups in the glycol
and by elevated temperatures. If a glycol contains
both primary and secondary hydroxy groups, the
CH2OH group is more reactive, and along with the
heterocycle (reactant ratio 1 : 1) the reaction yields
large amounts of linear acetal VI (reactant ratio
1 : 2).
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Linear acetals were prepared from alcohols and
aldehydes by standard procedures. The acetals were
washed with aqueous NaOH and distilled twice in a
column. Chemically pure grade 1,2-propylene glycol
was used without additional purification (weight frac-
tion of water 0.2 0.3%, as determined by Fischer
titration). After mixing, the reaction solutions were
kept at 25 C for no less than 24 h.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 5 2001