The Mixed Aldol Condensation

The aldol condensation is versatile in that the enolate anion of one carbonyl compound can be made to add to the carbonyl carbon of another, provided that the reaction partners are carefully selected. Consider, for example, the reaction between acetaldehyde and benzaldehyde, when treated with base. Only acetaldehyde can form an enolate anion (benzaldehyde has no a-hydrogen). If the enolate ion of acetaldehyde adds to the benzaldehyde carbonyl group, a mixed aldol condensation occurs. 

Some recent aiternatives for water treatment inciude using the dissolved organic carbon, nitrates, and other components in the water as a food source to grow algae. Then such algal biomass can be harvested in order to capture the cell wall constituents, which include lipids and triglycerides (Chapter 1 5). The lipids can be converted 

When ketones are treated with halogens (CI2, Br2,12), they undergo a-halogenation. This is illustrated above for acetone (2-propanone) and chlorine. Enolization of the acetone is followed by the reaction of enol with chlorine to provide a-chloroacetone. The enol (or enolate) of acetone behaves as a nucleophile and the chlorine behaves as an 

In this particular example, the resulting mixed aldol eliminates water on heating to give cinnamaldehyde (the flavor constituent of cinnamon). 

Write the structure of the mixed aldol obtained from acetone and 

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The mixed aldol condensations that are the most synthetically useful are those m which... 

As actually carried out the mixed aldol condensation product 1 3 diphenyl 2 propen 1 one has been isolated in 85% yield on treating benzaldehyde with ace tophenone in an aqueous ethanol solution of sodium hydroxide at 15-30°C... 

The mixed Claisen condensation of two different esters is similar to the mixed aldol condensation of two different aldehydes or ketones (Section 23.5). Mixed Claisen reactions are successful only when one of the two ester components has no a hydrogens and thus can t form an enolate ion. For example, ethyl benzoate and ethyl formate can t form enolate ions and thus can t serve as donors. They can, however, act as the electrophilic acceptor components in reactions with other ester anions to give mixed /3-keto ester products. 

The starting materials for the mixed aldol condensation—benzaldehyde and propanal—are... 

Butadiene is one of the given starting materials the a,j8-unsaturated ketone is the mixed aldol condensation product of 4-methylbenzaldehyde and acetophenone. 

B-12. Benzalacetone is the mixed aldol condensation product formed between benzaldehyde (C6H5CH=0) and acetone [(CH3)2C=0], What is its structure ... 

In the aldol condensation, an enolate anion acts as a carbon nucleophile and adds to a carbonyl group to form a new carbon-carbon bond. Thus, the a-carbon of one aldehyde molecule becomes bonded to the carbonyl carbon of another aldehyde molecule to form an aldol (a 3-hydroxyaldehyde). In the mixed aldol condensation, the reactant with an a-hydrogen supplies the enolate anion, and the other reactant, usually without an a-hydrogen, supplies the carbonyl group to which the enolate ion adds. The aldol reaction is used commercially and also occurs in nature. 

We showed, over two different series of Al(Ga)PON oxynitrides catalysts, that the nitridation of phosphate precursors has a positive effect on the selectivity to jasminaldehyde for the mixed aldol condensation reaction of heptanal with benzaldehyde. The influence of nitridation on the product distribution was interpreted in terms of changes in the relative density of acid and basic sites on the catalyst surface. Decreasing the acidity and increasing the basicity through nitridation enhances the simultaneous activation of benzaldeyde and heptanal and favors the cross condensation reaction between those two aldehydes, rather than the self-condensation of heptanal. 

The starting materials for the mixed aldol condensation— benzaldehyde and propanal—are prepared by oxidation of benzyl alcohol and 1-propanol, respectively. 

Analogous to the mixed aldol condensation (Sec. 9.18), mixed Claisen condensations are possible. Predict the structure of the product obtained when a mixture of ethyl benzoate and ethyl acetate is heated with sodium ethoxide in ethanol. 

The aldol reaction (aldol condensation) is one of the fundamental reactions of organic chemistry, since it leads to the formation of a new carbon-carbon bond and is broadly applicable. A condensation reaction is one in which two molecules are joined with the concomitant expulsion of a small stable molecule, usually water or an alcohol. The aldol reaction may be used to condense various combinations of aldehydes and ketones. The mixed aldol condensation of an aldehyde having no a-hydrogen atom with a ketone is specifically known as the Claisen-Schmidt reaction. This variation of the aldol condensation is illustrated here in the synthesis of dibenzalacetone. 

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