Selective Hydrogenation of Phenol and Derivatives over Polymer‐Functionalized Carbon‐Nanofiber‐Supported Palladium Using Sodium Formate as the Hydrogen Source

Abstract

Selective hydrogenation of phenol to cyclohexanone over a catalyst of polyaniline‐functionalized carbon‐nanofiber‐supported palladium (Pd‐PANI/CNF) with sodium formate as the hydrogen source has been studied. Phenol conversion exceeding 99 % was achieved with a cyclohexanone selectivity of >99 % in aqueous media. In an extension to Pd‐PANI/CNF, polymers such as polypyrrole (PPY), poly(4‐vinylpyridine) (PVP), and poly(1‐vinylimidazole) (PVI) were further applied to a catalyst of Pd‐polymer/CNF for selective phenol hydrogenation. All of the Pd‐polymer/CNF catalysts showed excellent to good performance toward selective phenol hydrogenation. However, Pd‐PANI/CNF was considerably more active and selective to afford the desired cyclohexanone than Pd‐PPY/CNF, Pd‐PVP/CNF, and Pd‐PVI/CNF. Moreover, a series of phenol‐derived compounds were selectively hydrogenated in high yields under the investigated aqueous conditions. The research highlights an environmentally benign and effective process for the selective reduction of phenol derivatives with sodium formate as an alternative hydrogen source.

Continuous‐Flow Palladium‐Catalyzed Synthesis of Cyclohexanones from Phenols using Sodium Formate as a Safe Hydrogen Source

“…[2] Large production of cyclohexanonei sb ased on either the oxidation of cyclohexane under Co catalysis or the partial hydrogenation of phenol in the presence of different transition-metal catalysts (Scheme1). [11] Some examples of phenol reductionw ith the use of formic acid, [12] sodium formate, [13,14] and potassium formate [15] under batch conditions were reported recently.A lthough very attractive, some of these protocols feature some limitations, such as the requirement for an inert atmosphere [12] or microwaveh eating. To define milder and more energy efficient one-step processes, the use of selectiveh omogeneous and heterogeneous catalysts hasb een investigated in the liquid phase and has resulted in many successful examples mainly based on single or mixed Pd, [3] Pt, [4] Ru, [5] Rh, [6] andN i [7] catalysts on different supports.…”

“…To define milder and more energy efficient one-step processes, the use of selectiveh omogeneous and heterogeneous catalysts hasb een investigated in the liquid phase and has resulted in many successful examples mainly based on single or mixed Pd, [3] Pt, [4] Ru, [5] Rh, [6] andN i [7] catalysts on different supports. [13] Following our interest in developing sustainable protocols based on the use of safe media, heterogeneous catalysis, [16] and the applicationo fflow technology, [17] we report herein our approacht owardst he definition of ac ontinuous-flow protocol by using commerciallya vailableP d/C for the catalyzed selective transfer hydrogenation of phenol to cyclohexanone in water by using sodium formate as ah ydrogen source.In ap reliminaryo ptimization study in batch, we investigated the best reaction conditions suitable for transfer to af low pro-Scheme1.Reactionsteps in at ypical phenol hydrogenation process. The chemical strategy to reduce phenol selectively is based on controlling the desorption of cyclohexanone from the catalyst surface beforef urther hydrogenation leads to cyclohexanol.…”

“…In terms of ad ifferent approach startingf rom phenol, the industrial process towardc yclohexanone comprises an initial reductive step to access cyclohexanol, which is furtherd ehydrogenatedt oc yclohexanonei nahigh-temperature gas-phase Pd-or Pt-catalyzed process. [11] Some examples of phenol reductionw ith the use of formic acid, [12] sodium formate, [13,14] and potassium formate [15] under batch conditions were reported recently.A lthough very attractive, some of these protocols feature some limitations, such as the requirement for an inert atmosphere [12] or microwaveh eating. [8] Considering the commonly proposed mechanism for the hydrogenation of phenol on supported palladiumc atalysts, reductiono ccurs on the phenolate ion adsorbed on the support in proximity of the metal particles, which are responsible for the activation of hydrogen.…”

“…[8] Considering the commonly proposed mechanism for the hydrogenation of phenol on supported palladiumc atalysts, reductiono ccurs on the phenolate ion adsorbed on the support in proximity of the metal particles, which are responsible for the activation of hydrogen. [13] Following our interest in developing sustainable protocols based on the use of safe media, heterogeneous catalysis, [16] and the applicationo fflow technology, [17] we report herein our approacht owardst he definition of ac ontinuous-flow protocol by using commerciallya vailableP d/C for the catalyzed selective transfer hydrogenation of phenol to cyclohexanone in water by using sodium formate as ah ydrogen source. [9] The use of formic acid derivativesa sahydrogen sourcei n combination with ap alladium catalyst is ap romising, safe, and sustainable alternative to classic methods.…”

“…To define milder and more energy efficient one-step processes, the use of selectiveh omogeneous and heterogeneous catalysts hasb een investigated in the liquid phase and has resulted in many successful examples mainly based on single or mixed Pd, [3] Pt, [4] Ru, [5] Rh, [6] andN i [7] catalysts on different supports. [11] Some examples of phenol reductionw ith the use of formic acid, [12] sodium formate, [13,14] and potassium formate [15] under batch conditions were reported recently.A lthough very attractive, some of these protocols feature some limitations, such as the requirement for an inert atmosphere [12] or microwaveh eating. The chemical strategy to reduce phenol selectively is based on controlling the desorption of cyclohexanone from the catalyst surface beforef urther hydrogenation leads to cyclohexanol.…”