The order of activity at 150 °C and 1 a The order of activity at 150 °C and 1 a Selectivity to 2-ethyl-2-hexenal was 100% for both pure and mixed isomer feed. Alkali metal zeolites and metal oxides were used for the aldol condensation of n-butanal to 2-ethyl-2-hexenal. Enolate ions are nucleophiles. Among the tested catalysts, SiO 2-Al 2 O 3, Nb 2 O 5 and TiO 2 showed relatively high catalytic activity for the formation of aldol condensation product, 2-ethyl-2-hexenal, whereas all the catalysts deactivated rapidly. What about nucleophilic addition of enolate to aldehyde? RCH 2 CH O + •• OH •• • • – RCHCH O + •• HOH –•••• •• pK a = 16-20 pK a = 16 Some thoughts... •• RCHCH O •• • • – RCH 2 For example, the Robinson annulation reaction sequence features an aldol condensation; the Wieland–Miescher ketone product is an important starting material for many organic syntheses. The condensation of ethanol to butanol was investigated over a commercial hydroxyapatite catalyst in the 350–410 °C temperature range.

The resulting intermediate eventually loses water to give your product, as drawn.

The Aldol Condensation.
Vapor-phase self-aldol condensation of butanal was performed over various solid catalysts.
Vapor-phase aldol condensation of butanal to form 2-ethyl-2-hexenal was carried out over several oxide catalysts such as SiO 2-Al 2 O 3, Al 2 O 3, ZrO 2, and SiO 2. Aldehydes undergo nucleophilic addition. $\begingroup$ The reaction is a self aldol condensation. Give the curly arrows a try and post what you end up with :) $\endgroup$ – NotEvans. If you follow the mechanism closely, you’ll see that a carbanion is formed at the alpha carbon of the carbonyl carbon (which is stabilized by the carbonyl group). Catalysts with moderate and strong acid sites such as Al 2 O 3 and SiO 2-Al 2 O 3 were active for the reaction in the initial period, whereas they deactivated rapidly. An acidic or basic solution can catalyze the condensation of aldol. Aldol condensation is a nucleophile attack on a carbonyl to make a ketone or aldehyde of β-hydroxy. The nucleophile is generally an enolate of an aldehyde or ketone attacking another aldehyde or ketone molecule. A basic solution contains comparable amounts of the aldehyde and its enolate.

Aldol condensations are important in organic synthesis, because they provide a good way to form carbon–carbon bonds. The enolate of the aldehyde attacks a molecule of un-enolised aldehyde.