Cyclohexanone(CYC) is a cyclic ketone that can undergo aldol condensation with itself or with other carbonyl compounds. Aldol condensation is a reaction in which two carbonyl moieties react to form a β-hydroxyaldehyde or β-hydroxyketone, and this is then followed by dehydration to give a conjugated enone. Aldol condensation is an important method for the synthesis of complex organic molecules, especially in the field of biofuels.
In this article, we will discuss the aldol condensation of cyclohexanone with furfural, which is a renewable biomass-derived aldehyde. Furfural can be obtained from the hydrolysis of hemicellulose, which is a component of lignocellulosic biomass. The aldol condensation of cyclohexanone and furfural can produce biofuels with high octane numbers and low freezing points.
Catalysts for Aldol Condensation of Cyclohexanone and Furfural
Aldol condensation is usually catalyzed by homogeneous catalysts, such as sodium hydroxide or potassium hydroxide. However, these catalysts have some drawbacks, such as corrosion, waste disposal, and separation problems. Therefore, heterogeneous catalysts are preferred for the aldol condensation of cyclohexanone and furfural. Heterogeneous catalysts are solid materials that can be easily separated from the reaction mixture and reused.
One of the most widely used heterogeneous catalysts for aldol condensation is Mg/Al mixed oxide, which is derived from hydrotalcite. Hydrotalcite is a layered double hydroxide with the general formula [Mg2+ 1−x Al3+ x (OH)2]x+ [An− x/n]·mH2O, where A is an anion such as carbonate or nitrate. Hydrotalcite can be calcined to form Mg/Al mixed oxide, which has a high surface area and basic sites that can activate the carbonyl groups of cyclohexanone and furfural.
Reaction Conditions and Products of Aldol Condensation of CYC and Furfural
The aldol condensation of cyclohexanone and furfural can be performed in a continuous fixed-bed reactor, where the reactants are fed through a packed bed of catalyst at a certain temperature and pressure. The reaction conditions can affect the conversion of furfural, the selectivity of products, and the stability of catalyst.
According to a recent study by Tišler et al., the optimal reaction conditions for the aldol condensation of cyclohexanone and furfural using Mg/Al mixed oxide as catalyst are:
- Temperature: 80 °C
- Molar ratio of cyclohexanone to furfural: 5:1
- Weight hourly space velocity (WHSV): 2 h−1
Under these conditions, the furfural conversion was 100% for more than 55 h, and the yield of products was:
- FCH (4-(2-furyl)-3-buten-2-one): 68%
- F2CH (4-(4-(2-furyl)-3-buten-2-ylidene)-3-buten-2-one): 10%
- Other by-products: 22%
The main product, FCH, is a potential biofuel with a high octane number (RON = 121) and a low freezing point (−76 °C). The secondary product, F2CH, is also a biofuel candidate with a high octane number (RON = 118) and a low freezing point (−63 °C). The other by-products include dimers and trimers of cyclohexanone and furfural.
The table below summarizes the data of the aldol condensation of cyclohexanone and furfural using Mg/Al mixed oxide as catalyst.
| Temperature (°C) | Cyclohexanone/Furfural (mol/mol) | WHSV (h−1) | Furfural conversion (%) | FCH yield (%) | F2CH yield (%) |
|---|---|---|---|---|---|
| 80 | 5 | 2 | 100 | 68 | 10 |
The aldol condensation of cyclohexanone and furfural is an interesting alternative way to obtain biofuels from renewable sources. The reaction can be catalyzed by Mg/Al mixed oxide, which is a heterogeneous catalyst derived from hydrotalcite. The reaction can produce FCH and F2CH, which are biofuels with high octane numbers and low freezing points. The reaction conditions can be optimized to achieve high furfural conversion and product selectivity.
Related Reading:
View Cyclohexanone(CAS 108-94-1) Wikipedia
View Cyclohexanone Product Page
View Method for decomposing cyclohexanone and cyclohexanol
The function and use of cyclohexanone
Experiment of preparing cyclohexanone from cyclohexanol
The Difference Between Cyclohexane and Benzene