The addition reaction of maleate esters and Jeffamine polyetheramines under mild conditions was fairly rapid in the initial period, then it became extremely slow. In the case of the Jeffamine D-230-dibutyl maleate reactant pair, 0.70 conversion was already achieved after 2 h reaction time, but after 1 day, this value was only 0.83. Product inhibition was excluded. Infrared spectroscopic measurements indicated that an amine catalyzed fast isomerization of the maleates to fumarates can be responsible for the unusual slowdown. While heterogeneous catalysts (Cu-, Zn- and Ni-oxides supported by H-beta zeolite, sulfated zirconia, Al2O3, SiO2) had no effect on the reaction rate, the presence of organocatalysts (3,5-dimethylpyrazole, imidazole, quinuclidine, 1,4-diazabicyclo[2.2.2]octane, 1,1′,3,3′-tetramethylthiourea, etc.) enhanced the activity in the low conversion regime. Azole containing reaction mixtures showed about 10 % larger conversion than the catalyst-free one. However, at high conversions (≥0.95), which could be reached after a week the advantage of the catalyst decreased significantly. The effect of organocatalyst can be explained by the inhibition of the maleate-fumarate isomerization.
- Dibutyl maleate
- Diethyl maleate
- Jeffamine D-230
- Jeffamine D-400
- Maleate-fumarate isomerization
ASJC Scopus subject areas
- Physical and Theoretical Chemistry