Selective Synthesis of Primary Anilines from NH₃ and Cyclohexanones by Utilizing Preferential Adsorption of Styrene on the Pd Nanoparticle Surface

Abstract

Dehydrogenative aromatization is one of the attractive alternative methods for directly synthesizing primary anilines from NH3 and cyclohexanones. However, the selective synthesis of primary anilines is quite difficult because the desired primary aniline products and the cyclohexanone substrates readily undergo condensation affording the corresponding imines (i.e., N‐cyclohexylidene‐anilines), followed by hydrogenation to produce N‐cyclohexylanilines as the major products. In this study, primary anilines were selectively synthesized in the presence of supported Pd nanoparticle catalysts (e.g., Pd/HAP, HAP=hydroxyapatite, Ca10(PO4)6(OH)2) by utilizing competitive adsorption unique to heterogeneous catalysis; in other words, when styrene was used as a hydrogen acceptor, which preferentially adsorbs on the Pd nanoparticle surface in the presence of N‐cyclohexylidene‐anilines, various structurally diverse primary anilines were selectively synthesized from readily accessible NH3 and cyclohexanones. The Pd/HAP catalyst was reused several times though its catalytic performance gradually declined.

Gold catalysts containing interstitial carbon atoms boost hydrogenation activity

“…The catalytic hydrogenation of aromatic nitro compounds is a cleaner option to produce anilines, but the low selectivity when other reducible groups exist in the reactant molecule is still a drawback, due to the strong adsorption of unsaturated groups on the catalyst surface 55 . Increased activity has been demonstrated on Au/TiO 2 for the conversion of nitrostyrene by Corma et al, but the hydrogenation of nitrostyrene by gold nanoparticles supported on activated carbon or silica shows a very low conversion, and produces both the reduction of the C=C double bond and nitro functional groups 11 .…”

Synthesis of unsymmetrically substituted triarylamines via acceptorless dehydrogenative aromatization using a Pd/C and p-toluenesulfonic acid hybrid relay catalyst

“…Pd/ support catalysts were prepared according to a literature procedure. 20 Substrates (except for 4b and 9b) and solvents were obtained from TCI, Aldrich, Kanto Chemical, FUJIFILM Wako Pure Chemical (reagent grade), or Combi-blocks, and puried prior to use, if necessary. 21 Compounds 4b and 9b were synthesized according to a literature procedure.…”

Continuous Synthesis of Aryl Amines from Phenols Utilizing Integrated Packed‐Bed Flow Systems

“…Thus, consecutive condensation and dehydrogenation would proceed smoothly to afford the desired aryl amines without any by‐products because of the absence of hydrogen. Furthermore, division of the flow reactors would enable the use of a hydrogen scavenger in the second stage to more reliably control product selectivity. This segmentation and integration strategy could significantly improve the amine scope and product selectivity, while some features of flow reactors loaded with heterogeneous catalysts could not only increase reaction efficiency, but also allow reaction conditions milder than those used in the corresponding batch reactions to realize the continuous synthesis of various aryl amines …”