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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Khimiya atsetalei (Acetal Chemistry), Moscow: Nauka,
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pp. 1478 1483.
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nov, A.Yu., and Kvashennikov, A.I., Zh. Obshch.
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EXPERIMENTAL
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Zh. Fiz. Khim., 1997, vol. 71, no. 6, pp. 1016 1019.
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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