N‐Doped Yellow TiO₂ Hollow Sphere‐Mediated Visible‐Light‐Driven Efficient Esterification of Alcohol and N‐Hydroxyimides to Active Esters

Abstract

Herein we report a simple synthetic protocol for N‐doped yellow TiO2 (N‐TiO2) hollow spheres as an efficient visible‐light‐active photocatalyst using aqueous titanium peroxocarbonate complex (TPCC) solution as precursor and NH4OH. In the developed strategy, the ammonium ion of TPCC and NH4OH acts as nitrogen source and structure‐directing agent. The synthesized N‐TiO2 hollow spheres are capable of promoting the synthesis of active esters of N‐hydroxyimide and alcohol through simultaneous selective oxidation of alcohol to aldehyde followed by cross‐dehydrogenative coupling (CDC) under ambient conditions upon irradiation of visible light. It is possible to develop a novel and cost‐effective one‐pot strategy for the synthesis of important esters and amides on gram scale using the developed strategy. The catalytic activity of N‐TiO2 hollow spheres is much superior to that of other reported N‐TiO2 samples as well as TiO2 with varying morphology.

Visible Light‐Driven Efficient Synthesis of Amides from Alcohols using Cu−N−TiO2 Heterogeneous Photocatalyst

“…HRTEM images confirmed the presence of crystalline Cu nanoparticles on the surface of the 2D N−TiO 2 sheet. N 2 adsorption‐desorption isotherm of Cu−N−TiO 2 catalyst corresponds to type IV (Figure S2), typically which is similar to that of bare N−TiO 2 [17] . The calculated total BET surface area and average pore size of Cu−N−TiO 2 are 174 m 2 g −1 and 6.5 nm, respectively.…”

“…Sunlight (visible light), prime sustainable energy resources on earth, driven reactions (photo‐catalysis), i. e., conversion of solar energy to chemical energy, using reusable heterogeneous photocatalyst, has been stimulated in recent years, as such reactions proceed smoothly at room temperature (RT) [15–16] . Recently we have reported N‐doped TiO 2 catalyst for the synthesis of N ‐hydroxyimide active ester from alcohol using two equivalent of sacrificial TBHP as an external oxidant [17] . A similar strategy was reported by Xie and Yu groups for Iodide‐catalyzed amide synthesis [18a] and Iron catalyzed esterification [18b] via the N ‐hydroxyimide active ester route.…”

“…N 2 adsorption-desorption isotherm of CuÀ NÀ TiO 2 catalyst corresponds to type IV ( Figure S2), typically which is similar to that of bare NÀ TiO 2 . [17] The calculated total BET surface area and average pore size of CuÀ NÀ TiO 2 are 174 m 2 g À 1 and 6.5 nm, respectively. Although with respect to the bare NÀ TiO 2 no significant change in pore size distribution for CuÀ NÀ TiO 2 took place, a reasonable enhancement of the total surface area, from 155 m 2 g À 1 to 174 m 2 g À 1 was observed, most probably due to the contribution from the metallic Cu nanoparticles on the surface of TiO 2 sheets.…”

“…[15][16] Recently we have reported Ndoped TiO 2 catalyst for the synthesis of N-hydroxyimide active ester from alcohol using two equivalent of sacrificial TBHP as an external oxidant. [17] A similar strategy was reported by Xie and Yu groups for Iodide-catalyzed amide synthesis [18a] and Iron catalyzed esterification [18b] via the N-hydroxyimide active ester route. Although the substrate scope of the reactions has wide under moderately mild conditions, the most critical disadvantage of the reaction was the use of super stoichiometric amounts of TBHP in decane and longer reaction time (24 h).…”

Visible Light-Responsive N-Doped TiO2 Photocatalysis: Synthesis, Characterizations, and Applications

“…These methods usually have the advantages of being cleanroom-free, cost-efficient, and widely applicable. For this purpose, in a typical procedure, the doped N usually originates from nitric acid (HNO 3 ) [65, 66], ammonium hydroxide (NH 4 OH) [67], urea (CH 4 N 2 O) [68,69], ammonium chloride (NH 4 Cl) [70,71], and triethylamine (TEA) [72,73] and the Ti precursors usually include titanium trichloride (TiCl 3 ) [74], titanium tetrachloride (TiCl 4 ) [75], titanium sulfate (Ti(SO 4 ) 2 ) [76], and titanium (IV) Fig. 2 Band structure and density of states of a anatase, b rutile, and c brookite TiO 2 (the Fermi level is set to 0).…”