General properties and green synthesis of Benzalacetone

General properties of Benzalacetone

Benzalacetone is a white or light yellow crystal, flammable, with coumarin odour, soluble in sulfuric acid, ethanol, ether, benzene and chloroform, slightly soluble in water and petroleum ether ketone compounds. Molecular formula: C10H10O; Density: 1.038; Melting Point: 39-42°C(lit.); Boling Point: 260-262°C(lit.). It acts as a flavouring agent, a spice, a bacterial metabolite and an inhibitor of EC 3.1.1.4 (phospholipase A2). It is mainly used in food additives, flavours and fragrances, as well as a reagent for chemical synthesis or reactions. In addition, the novel hydrophobic benzazepine acetone can also be used to modify lead dioxide electrodes for electrocatalytic degradation of coal tar wastewater.

A green synthesis of Benzalacetone

Claisen–Schmidt (CS) condensation between acetone and benzaldehyde with NaOH as the catalyst is a well-recognized pathway for the synthesis of benzalacetone (BA). However, this process is compromised by a side reaction, i.e., a second CS reaction between benzaldehyde and the BA product. In this work, we designed a stirring-induced emulsion synthesis technique for the cyclic and scaling-up production of BA with 99 ± 1% selectivity, without the use of surfactants. In this approach, the water-soluble acetone and NaOH were separated from the oil-soluble benzaldehyde by the organic–aqueous phase interface, such that the CS condensation could only be executed at the liquid interface. The just-formed BA molecules diffuse to the interior of the oil solvent, where any subsequent CS post-reaction is rendered negligible, owing to the absence of NaOH. The oil phase containing the BA molecules can be easily separated from the aqueous solution by stopping stirring and undisturbed standing, allowing for a large-scale production protocol. As a proof of concept, over 1 kg of BA was produced in the laboratory with high yield and purity.

References：

[1] NAICHUAN YU . Electrocatalysis degradation of coal tar wastewater using a novel hydrophobic benzalacetone modified lead dioxide electrode[J]. Chemosphere, 2022. DOI:10.1016/j.chemosphere.2021.133014.

[2] SUN R, HAN C, XU J. A green synthesis approach toward large-scale production of benzalacetone via Claisen–Schmidt condensation[J]. RSC Advances, 2022. DOI:10.1039/D2RA05320A.