Direct synthesis of p-methyl benzaldehyde from acetaldehyde via an organic amine-catalyzed dehydrogenation mechanism

Abstract

Summary p -Methyl benzaldehyde ( p -MBA) is a class of key chemical intermediates of pharmaceuticals. Conventional industrial processes for p -MBA production involve the consecutive photochlorination, amination, and acid hydrolysis of petroleum-derived p -xylene, while producing vast pollutants and waste water. Herein, we report a direct, green route for selective synthesis of p -MBA from acetaldehyde using a diphenyl prolinol trimethylsilyl ether catalyst. The optimized p -MBA selectivity is up to 90% at an acetaldehyde conversion as high as 99.8%. Intermediate structure and 18 O-isotope data revealed that the conversion of acetaldehyde to p -methylcyclohexadienal intermediates proceeds in an enamine-iminium intermediate mechanism. Then, controlled experiments and D-isotope results indicated that the dehydrogenation of p -methylcyclohexadienal to p -MBA and H 2 is catalyzed by the same amines through an iminium intermediate. This is an example that metal-free amines catalyze the dehydrogenation (releasing H 2 ), rather than using metals or stoichiometric oxidants.

High‐Throughput Screening of Bicationic Redox Materials for Chemical Looping Ammonia Synthesis

“…[ 73–75 ] This will inevitably come at much higher computational costs than those employed in our present study. In light of this, we also note that some recent works have proposed new machine‐learning approaches to expedite the prediction of reaction pathways, [ 76,77 ] bring promise to study the catalytic reactions that involve more complex systems. How the cooperative enhancements in bicationic redox materials are affected by their unique electronic structures will also need to be further examined with detailed DFT calculations.…”

Screening of Catalysts for the Methyl Vinyl Ether Reaction in H2

“…Based on the above information and discussion as well as the relevant literature, a reaction pathway of MVE hydrogenation to methylbenzene over CuO/Al 2 O 3 at 400–450 °C is proposed in Scheme . It starts with hydrocracking of MVE to MeCHO and MeOH on the catalyst’s surface, followed by condensation of MeCHO and/or MeOH to C 3+ aldehydes/ketones, such as propionaldehyde, butyraldehyde, 3-methyl-2-butanone, and 2-butenal reported in the literature, , then dehydration, dehydrogenation, and cyclization of these C 3+ aldehydes/ketones to benzene, methylbenzaldehyde, and trimethylbenzene, − and then hydrodeoxygenation and methylation of methylbenzaldehyde and methylation of benzene and trimethylbenzene by MeOH to hexamethylbenzene. , It is noted that the conversion of C 3+ aldehydes/ketones is far more complex and the products may include heavy polycyclic aromatic hydrocarbons as reported in the literature . It is also reported that the reaction of benzene and MeCHO easily produces heavy polycyclic aromatic hydrocarbons .…”

An automated method for graph‐based chemical space exploration and transition state finding

“…There are alternative methods that also allow bond transformations without relying on expensive quantum‐chemical calculations, 9–22 such as connectivity matrix transformations (also referred to as adjacency matrix transformations or atomic matrix transformations) 15,23–25 . These graph‐based transformations can explore large regions of chemical space by adding or subtracting integer values to connectivity matrices.…”