Mathias

Publication date: 9 June 2022

Source: Chem, Volume 8, Issue 6

Author(s): Juan Wang, Chen Cheng, Qi Yuan, Hao Yang, Fanqi Meng, Qinghua Zhang, Lin Gu, Jianlei Cao, Leigang Li, Shu-Chih Haw, Qi Shao, Liang Zhang, Tao Cheng, Feng Jiao, Xiaoqing Huang

Tailoring mesoporous TiO₂ at the mesoscopic and microscopic level has been advancing in the last decade as its unique nanoscale architectures are of great importance for various applications. This Review surveys and discusses how to synthesize a series of novel mesoporous TiO₂ materials, with the aim of highlighting how precise control can be achieved over the mesostructure and also potential synthetic directions.

Abstract

Mesoscale TiO₂ structures have realized many technological applications—ranging from catalysis and biomedicine to energy storage and conversion—because of their large mesoporosities offering desirable accessibility and mass transport. Tailoring mesoporous TiO₂ structures with novel mesoscopic and microscopic configurations is envisaged to offer ample opportunities for further applications. In this Review, we explain how to synthesize novel mesoporous TiO₂ materials and present recent examples. An emphasis is placed on a “monomicelle assembly” strategy as an emerging and powerful approach to direct the formation of mesostructured TiO₂ with precise control over its structural orientations and architectures. Furthermore, typical examples of mesoporous TiO₂ for applications in batteries and photocatalysis are highlighted. The Review ends with an outlook towards the synthesis of mesoporous TiO₂ with tailored architectures by self-assembly, which could pave the way for developing advanced energy conversion and storage devices.

An overview of the latest generation of halogen-containing agrochemicals introduced into the market over the past 10 years is provided. Manufacturing approaches of current halogen-containing development candidates are described.

Abstract

To ensure sustainability, the agrochemical industry is faced with enormous challenges, from provision of high-quality food to water use, environmental impact and growing world population. The loss of agrochemicals due to consumer perception, changing grower needs and everchanging regulatory requirements is higher than the number of active ingredients being introduced into the market. Therefore, the development of new agrochemicals is essential, that can provide improved efficacy and favorable environmental profiles. In this context, introduction of halogen atoms into a molecule is an important tool to influence its physico-chemical properties. Since 2010, around 81 % of the launched agrochemicals contain halogen atoms. This Review gives an overview of the latest generation of halogen-containing agrochemicals introduced into the market over the past 10 years and describes manufacturing approaches of current halogen-containing development candidates.

Pining for catechol: A catalytic route is developed to synthesize bio-renewable catechol from pinewood-derived lignin-first monomers. The two-step process consists of O-demethylation of 4-n-propylguaiacol over acidic beta zeolites in hot pressurized liquid water, delivering 4-n-propylcatechol, and gas-phase C-dealkylation of 4-propylcatechol providing catechol and propylene over acidic ZSM-5 zeolites in the presence of water.

Abstract

A catalytic route is developed to synthesize bio-renewable catechol from softwood-derived lignin-first monomers. This process concept consists of two steps: 1) O-demethylation of 4-n-propylguaiacol (4-PG) over acidic beta zeolites in hot pressurized liquid water delivering 4-n-propylcatechol (4-PC); 2) gas-phase C-dealkylation of 4-PC providing catechol and propylene over acidic ZSM-5 zeolites in the presence of water. With large pore sized beta-19 zeolite as catalyst, 4-PC is formed with more than 93 % selectivity at nearly full conversion of 4-PG. The acid-catalyzed C-dealkylation over ZSM-5 zeolite with medium pore size gives a catechol yield of 75 %. Overall, around 70 % catechol yield is obtained from pure 4-PG, or 56 % when starting from crude 4-PG monomers obtained from softwood by lignin-first RCF biorefinery. The selective cleavage of functional groups from biobased platform molecules through a green and sustainable process highlights the potential to shift feedstock from fossil oil to biomass, providing drop ins for the chemicals industry.

A metal-free DDQ catalyzed depolymerization strategy was developed to transform lignin models or natural lignin into various benzimidazole containing compounds (up to 94 % yield). Both β-C and γ-C atoms of lignin can be also utilized to produce desirable products. More importantly, this method can realize the oxidation, degradation and valorization of natural lignin in an one-pot manner.

Abstract

It is a challenging task to simultaneously achieve selective depolymerization and valorization of lignin due to their complex structure and relatively stable bonds. We herein report an efficient depolymerization strategy that employs 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant/catalyst to selectively convert different oxidized lignin models to a wide variety of 2-phenylbenzimidazole-based compounds in up to 94 % yields, by reacting with o-phenylenediamines with varied substituents. This method could take full advantage of both C_β and/or C_γ atom in lignin structure to furnish the desirable products instead of forming byproducts, thus exhibiting high atom economy. Furthermore, this strategy can effectively transform both the oxidized hardwood (birch) and softwood (pine) lignin into the corresponding degradation products in up to 45 wt% and 30 wt%, respectively. Through a “one-pot” process, we have successfully realized the oxidation/depolymerization/valorization of natural birch lignin at the same time and produced the benzimidazole derivatives in up to 67 wt% total yields.

The number of methods that exploit transition-metal-catalyzed C(sp³)−H activations for the assembly of cyclic systems is steadily growing. This Minireview covers the most relevant cyclization and cycloaddition approaches, discussed from a mechanistic perspective.

Abstract

The selective functionalization of C(sp³)−H bonds using transition-metal catalysis is among the more attractive transformations of modern synthetic chemistry. In addition to its inherent atom economy, such reactions open unconventional retrosynthetic pathways that can streamline synthetic processes. However, the activation of intrinsically inert C(sp³)−H bonds, and the selection among very similar C−H bonds, represent highly challenging goals. In recent years there has been notable progress tackling these issues, especially with regard to the development of intermolecular reactions entailing the formation of C−C and C−heteroatom bonds. Conversely, the assembly of cyclic products from simple acyclic precursors using metal-catalyzed C(sp³)−H bond activations has been less explored. Only recently has the number of reports on such annulations started to grow. Herein we give an overview of some of the more relevant advances in this exciting topic.

Synthesis
DOI: 10.1055/a-1579-2190

Nickel boride catalyst prepared in situ from NiCl2 and sodium borohydride allowed, in the presence of an aqueous solution of TEMPO-oxidized nanocellulose (0.01 wt%), the reduction of a wide range of nitroarenes and aliphatic nitro compounds. Here we describe how the modified nanocellulose has a stabilizing effect on the catalyst that enables low loading of the nickel salt pre-catalyst. Ni-B prepared in situ from a methanolic solution was also used to develop a greener and facile reduction of organic azides, offering a substantially lowered catalyst loading with respect to reported methods in the literature. Both aromatic and aliphatic azides were reduced, and the protocol is compatible with a one-pot Boc-protection of the obtained amine yielding the corresponding carbamates. Finally, bacterial crystalline nanocellulose was chosen as a support for the Ni-B catalyst to allow an easy recovery step of the catalyst and its recyclability for new reduction cycles.
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