TiO₂-Catalyzed n-Valeraldehyde Self-Condensation to 2-Propyl-2-Heptenal: Acid Catalysis or Base Catalysis?

Abstract

Several TiO2 samples with different morphologies and structures, nano/microcomposite of TiO2 (anatase), TiO2 whisker (anatase), and nano-TiO2 (anatase), were prepared and characterized by means of N2 adsorption–desorption, CO2-TPD, and NH3-TPD, and their catalytic performance for n-valeraldehyde self-condensation was investigated. The results indicated that the conversion of n-valeraldehyde was correlated with their acid amount while the selectivity of 2-propyl-2-heptenal was associated with their base amount. Since the catalytic performance of nano-TiO2 (anatase) was the best, its preparation process was further studied and the suitable preparation conditions were obtained. Then the effect of reaction conditions on the catalytic performance of nano-TiO2 (anatase) for n-valeraldehyde self-condensation was investigated and the suitable reaction conditions were obtained as follows: a weight percentage of TiO2 catalyst of 15 wt %, a reaction temperature of 190 °C, and a reaction time of 10 h. Under the above reaction conditions, the conversion of n-valeraldehyde, 2-propyl-2-heptenal yield, and selectivity were 94.6%, 93.7%, and 99.1%, respectively. The TiO2 catalyst could be reused four times without a significant loss in its catalytic performance, which was different from most of the literature. The catalytic stability of TiO2 catalyst was associated with the properties of the active sites, especially acid–base property. Not as some of the literature claimed that their TiO2-catalyzed reactions were base-catalyzed reactions, the TiO2 catalyst used in this work possessed much greater acid amount than base amount. To assess the role of acidic and basic sites in n-valeraldehyde self-condensation, ammonia and carbon dioxide were separately used as a probe molecule for poisoning the corresponding active sites. The results confirmed the key role of acid sites in n-valeraldehyde self-condensation. Therefore, we were convinced that the TiO2-catalyzed n-valeraldehyde self-condensation was mainly an acid-catalyzed reaction.

Aldol Condensation of Cyclopentanone with Valeraldehyde Over Metal Oxides

“…Self-condensation of valeraldehyde gives 2-propylhept-2-enal, which has found applications as an intermediate for production of parfumes [12], and plasticizers [13,14]. Aqueous NaOH is typically applied as a catalyst in industrial scale for this reaction.…”

“…Aqueous NaOH is typically applied as a catalyst in industrial scale for this reaction. It was pointed out [13], that this process causes corrosion and exhibits poor product selectivity. TiO 2 was confirmed to be an efficient heterogeneous catalyst for synthesis of 2-propylhept-2-enal giving very high selectivities to the desired product at 190 °C [13].…”

“…It was pointed out [13], that this process causes corrosion and exhibits poor product selectivity. TiO 2 was confirmed to be an efficient heterogeneous catalyst for synthesis of 2-propylhept-2-enal giving very high selectivities to the desired product at 190 °C [13]. Zhao et al [13] stated that acidity is also required for production of 2-propylhept-2-enal.…”

Ethanol Guerbet Condensation to n‐Butanol or C4‐C8 Alcohols over Ni/TiO2 Catalyst

“…Given an excellent catalytic performance of TiO 2 in aldol condensation reaction and of Ni/TiO 2 in the hydrogenation reaction of α, β-unsaturated aldehyde and a good hydrothermal stability of TiO 2 , [12] it is expected that Ni/TiO 2 has a good catalytic performance in ethanol Guerbet condensation. In this paper, we firstly prepared a Ni/TiO 2 catalyst by an excessive impregnation method and investigated the influence of preparation conditions on its catalytic performance.…”

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

“…Compared with dioctyl phthalate (DOP) derived from 2-ethylhexanol, DPHP has the advantages of low toxicity and volatility and can meet the requirements for health, safety, and environmental protection. 1 Therefore, it is very crucial and urgent to study the synthesis processes of 2-PH. The self-condensation of pentanal to 2-propyl-2-heptenal is an important carbon chain extension reaction in the synthesis of 2-PH.…”