Highly Efficient and Selective N-Alkylation of Amines with Alcohols Catalyzed by in Situ Rehydrated Titanium Hydroxide

Abstract

Catalytic N-alkylation of amines by alcohols to produce desired amines is an important catalytic reaction in industry. Various noble metal-based homogeneous and heterogeneous catalysts have been reported for this process. Development of cheap non-noble metal heterogeneous catalysts for N-alkylation reaction would be highly desirable. Hereby, we propose the N-alkylation of amines by alcohols over a cheap and efficient heterogeneous catalyst -titanium hydroxide. The catalyst provides the selectivity higher than 90% to secondary amines for functionalized aromatic, aliphatic alcohols and amines at high catalytic activity and stability. Mild Brönsted acidity formed by continuous rehydration of Lewis acidity excludes side reactions and deactivation by adsorbed species. The mechanism of the reaction involves dehydration of alcohols to ethers with subsequent C-O bond cleavage by amine with formation of secondary amine and recovery of alcohol.

Integrated design of an amination process of lignin oxygenated model compounds to synthesize cyclohexylamine: catalyst nanostructure engineering and catalytic conditional strategy

“…In the presence of amines, the ether cleaves the C-O bond to form a secondary amine. 134 Consequently, it is very necessary to introduce advanced characterization techniques to elucidate the structural features of catalysts and the heterogeneous catalytic amination process. HAADF-STEM, in situ XPS, and in situ CO-DRIFT can provide information on the morphology, surface composition of catalysts, and the electronic state of metal species.…”

Single Pd–Sx Sites In Situ Coordinated on CdS Surface as Efficient Hydrogen Autotransfer Shuttles for Highly Selective Visible-Light-Driven C–N Coupling

“… − Thus, many well-established routes such as the Ullmann reaction, the Buchwald–Hartwig reaction, and hydroamination have been developed for the synthesis of amines. Compared with these traditional synthesis routes, the direct N-alkylation of amines with alcohols by the borrowing hydrogen (also called hydrogen autotransfer) strategy provides an effective approach for the synthesis of desired amines without any production of toxic waste, − which consists of the initial alcohol dehydrogenation into the corresponding aldehyde with the extrusion of hydrogen, the imine formation with the liberation of water, and the hydrogenation of imine into the desired amine by the hydrogen from alcohols. However, several limitations exist toward this thermal route for N-alkylation of amines with alcohols: (1) requirement of harsh reaction conditions (160–500 °C) for the limiting step of alcohol dehydrogenation; (2) difficulty in selective controlling of the desired product, owing to the overalkylation of amines to the final tertiary amines; − and (3) overconsumption of expensive catalysts during the reaction such as Ru, Pd, Rh, etc.…”

Highly Selective Synergistic N-Alkylation of Amines with ROH Catalyzed by Nickel–Ruthenium

“…In the last few decades, three main strategies have been developed for the N-alkylation of amines with alcohols to afford secondary amines: (i) the “borrowing hydrogen” methodology using either noble or non-noble metal complexes, for instance, Ru, − Pd, Ir, − Rh, Ce, Mn, − Co, − Ni, − and Fe catalysts and some other heterogeneous catalysts. − (ii) Tsuji–Trost-type reactions for allylic alcohols with Pd- or Ni- based metal catalysts. (iii) Lewis-acid-catalyzed reactions employing diverse salts and ligands. , Among the best-performing catalysts, metal triflates and triflimides, including the parent triflic acid (HOTf), were found active for N-alkylation of amines with alcohols based on S N 1 or S N 2 mechanisms . Nevertheless, several disadvantages emerged due to employing expensive nonrecoverable catalysts, difficulties in catalyst–product separation, and the indispensable use of additives or cocatalysts .…”