n-Butyraldehyde Self-Condensation Catalyzed by Sulfonic Acid Functionalized Ionic Liquids

Abstract

Self-condensation of n-butyraldehyde to 2-ethyl-2-hexenal is one of the important processes for the industrial production of 2-ethylhexanol. In the present work, several sulfonic acid functionalized ionic liquids (SFILs) were synthesized. Their acid strengths were determined by the Hammett method combined with UV–vis spectroscopy, and their catalytic performances in n-butyraldehyde self-condensation were investigated. The results show that the conversion of n-butyraldehyde correlated well with the acid strength of the SFILs with the same cation. The SFILs with triethylammonium cations showed a better catalytic performance than those with imidazolium cations or pyridinium cations, and [HSO3-b-N­(Et)3]p-TSA (“b”, butyl) exhibited the highest selectivity. Under the optimal reaction conditions of the mass ratio of [HSO3-b-N­(Et)3]p-TSA to n-butyraldehyde = 0.1, reaction temperature = 393 K, and reaction time = 6 h, the conversion of n-butyraldehyde was 89.7% and the selectivity to 2-ethyl-2-hexenal was 87.8%. [HSO3-b-N­(Et)3]p-TSA could be reused four times without a significant loss in its catalytic performance. A kinetic analysis result showed that this is a reversible second-order reaction. Compared with the kinetic parameters from the reaction catalyzed by an aqueous base or acid catalyst, the pre-exponential factor is lower due to the restriction of the high viscosity of [HSO3-b-N­(Et)3]p-TSA. Finally, a possible reaction mechanism for n-butyraldehyde self-condensation catalyzed by [HSO3-b-N­(Et)3]p-TSA was proposed.

Green synthesis of benzonitrile using ionic liquid with multiple roles as the recycling agent

“…36 In order to explore the relationship between the catalytic performance and properties of the ionic liquids, which were combined in the (NH 2 -OH) 2 $ILs, their acid strengths were measured according to the method reported previously. 38 The results were shown in Table 3 and Fig. S1, † from which we can see that the acid strength order is as follows: [HSO 3 -b-Py]$HSO 4 , which was in accordance with their catalytic activity.…”

Ir/C and Brφnsted acid functionalized ionic liquids: an efficient catalytic system for hydrogenation of nitrobenzene to p-aminophenol

“…In order to explore the relationship between the catalytic performance and the acidity of BFILs, the acidity of BFILs was measured by an acid-base titration method. 43 Phenolphthalein was used as an indicator, and the concentration of NaOH aqueous solution was 2 mol L À1 .…”

Silica‐immobilized acid ionic liquid: An efficient catalyst for pentanal self‐condensation

“…Functionalized ionic liquids not only have the advantages of solid inorganic catalysts (easy separation and environmentally friendly), organic-inorganic composite materials (outstanding designability and easy adjustment), and liquid catalysts (good mobility, high density, and uniform distribution of active sites), but they also play the role of solvents, so they are widely used in catalysis, organic synthesis, and other fields. [7][8][9][10] The functionalized ionic liquids have been used to catalyze aldol condensation reactions. For example, acid ionic liquids were used for butanal self-condensation and for aldol condensation of aromatic aldehydes with ketones, [10][11][12][13] basic ionic liquids were employed for aldol condensation of aldehydes with ketones, [14][15][16] and several acid-base bifunctional ionic liquids were synthesized for catalyzing pentanal self-condensation.…”

“…[7][8][9][10] The functionalized ionic liquids have been used to catalyze aldol condensation reactions. For example, acid ionic liquids were used for butanal self-condensation and for aldol condensation of aromatic aldehydes with ketones, [10][11][12][13] basic ionic liquids were employed for aldol condensation of aldehydes with ketones, [14][15][16] and several acid-base bifunctional ionic liquids were synthesized for catalyzing pentanal self-condensation. 17 We separately evaluated the catalytic performance of an acid ionic liquid [HSO 3 -b-N(Et) 3 ]p-TSA in butanal self-condensation and the catalytic performance of an acid-base bifunctional ionic liquid [PEmim]Cl-0.5Zn(CH 3 COO) 2 in petanal self-condensation.…”

“…Fairly good results were obtained: 2-ethyl-2-hexenal selectivity of 87.8% was achieved at a butanal conversion of 89.7% over [HSO 3 -b-N(Et) 3 ]p-TSA, while 2-propyl-2-heptanal selectivity of 86.6% was obtained at a pentanal conversion of 94.7% over [PEmim]Cl-0.5Zn(CH 3 COO) 2 . 10,17 However, some problems arose, such as a large ionic liquid dosage (higher than 10 wt%), boredom separation, and purification operation, among others. To solve these problems, immobilized ionic liquid catalysts have been prepared via physical adsorption method or bonding method.…”