Solvent-Free Synthesis of Jasminaldehyde in a Fixed-Bed Flow Reactor over Mg-Al Mixed Oxide

Abstract

In spite of the rapid developments in synthesis methodologies in different fields, the traditional methods are still used for the synthesis of organic compounds, and regardless of the type of chemistry, these reactions are typically performed in standardized glassware. The high-throughput chemical synthesis of organic compounds such as fragrant molecules, with more economic benefits, is of interest to investigate and develop a process that is more economical and industrially favorable. In this research, the catalytic activity of Mg-Al catalyst derived from hydrotalcite-like precursors with the Mg/Al molar ratio of 3 was investigated for the solvent-free synthesis of jasminaldehyde via aldol condensation of benzaldehyde and heptanal. The reaction was carried out in a fixed-bed flow reactor, at 1 MPa, and at different temperatures. Both Brønsted and Lewis (O2− anions) base sites, and Lewis acid sites exist on the surface of the Mg-Al catalyst, which can improve the catalytic performance. Increasing the reaction temperature from 100 °C to 140 °C enhanced both heptanal conversion and selectivity to jasminaldehyde. After 78 h of reaction at 140 °C, the selectivity to jasminaldehyde reached 41% at the heptanal conversion 36%. Self-condensation of heptanal also resulted in the formation of 2-n-pentyl-2-n-nonenal. The presence of weak Lewis acid sites creates a positive charge on the carbonyl group of benzaldehyde, and makes it more prone to attack by the carbanion of heptanal. Heptanal, is an aliphatic aldehyde, with higher activity than benzaldehyde. Therefore, the possibility of activated heptanal reacting with other heptanal molecules is higher than its reaction with the positively charged benzaldehyde molecule, especially at a low molar ratio of benzaldehyde to heptanal.

Biocatalytic Production of Aldehydes: Exploring the Potential of Lathyrus cicera Amine Oxidase

“…However, this procedure is typically limited by their intrinsic lability and low bioaccumulation. Given the high-value applications and large markets for several aldehydes and considering the high demand for "natural" labeled compounds, research on their green and sustainable synthesis is taking center stage [9][10][11]. In this frame, biocatalysis occupies a privileged place, being a valid alternative compared to the conventional physical (extraction) or chemical synthetic routes.…”

Synthesis of odorants in flow and their applications in perfumery

“…It is industrially produced by an aldol condensation of heptanal ( 34 , obtained from castor oil) and benzaldehyde ( 33 ). In the industrial process, stoichiometric amounts of sodium- or potassium hydroxide are used resulting in the formation of large quantities of undesired side products, e.g., enone 36 , the aldol condensation product of two molecules of heptanal [ 9 , 38 ].…”

“…Therefore, Gholami and co-workers developed a flow protocol for the synthesis of jasmonal ( 35 ) by aldol condensation of heptanal ( 34 ) and benzaldehyde ( 33 ) utilizing a magnesium-aluminum mixed oxide catalyst in a fixed bed reactor ( Scheme 8A ) [ 38 ]. To suppress the formation of side product 36 , an excess of benzaldehyde is used.…”

“…To suppress the formation of side product 36 , an excess of benzaldehyde is used. At 140 °C and with a long residence time of 76 h, a moderate heptanal ( 34 ) conversion of 36% was achieved providing jasmonal ( 35 ) in a selectivity of 41% [ 38 ].…”