Zirconium‐β Zeolite‐Catalyzed Continuous‐Flow Friedel‐Crafts Acylation Reaction

Improved Process for the Continuous Acylation of 1,3-Benzodioxole

The acylation of 1,3-benzodioxole was studied in a continuous process using a recyclable heterogeneous substoichiometric catalyst. In a short time period (30 min), at 100 °C, the conversion rate was 73%, with a selectivity of 62% of the desired acylated product; the reaction was run continuously for 6 h, showing excellent stability and selectivity. Moreover, the unreacted starting material, 1,3-benzodioxole, can be easily separated by distillation and recycled.

Efficient construction of a β-naphthol library under continuous flow conditions

A β-naphthol library has been efficiently constructed utilizing a mild continuous flow procedure, relying on a tandem Friedel-Crafts reaction and starting from readily available arylacetyl chloride and alkynes. Multiple functionalized β-naphthols can be acquired within 160 s in generally high yields (up to 83%). Using an electron-rich phenylacetyl chloride derivative (4-OH- or 4-MeO-) provides spirofused triene dione as the primary product. A scale-up preparation affords a throughput of 4.70 g h-1, indicating potential large-scale application. Herein, we present a rapid, reliable, and scalable method to obtain various β-naphthols in the compound library.

Regioselective Friedel-Crafts Acylation Reaction Using Single Crystalline and Ultrathin Nanosheet Assembly of Scrutinyite-SnO2

Peculiar physicochemical properties of two-dimensional (2D) nanomaterials have attracted research interest in developing new synthetic technology and exploring their potential applications in the field of catalysis. Moreover, ultrathin metal oxide nanosheets with atomic thickness exhibit abnormal surficial properties because of the unique 2D confinement effect. In this work, we present a facile and general approach for the synthesis of single crystalline and ultrathin 2D nanosheets assembly of scrutinyite-SnO₂ through a simple solvothermal method. The structural and compositional characterization using X-ray diffraction (Rietveld refinement analysis), high-resolution transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and so on reveal that the as-synthesized 2D nanosheets are ultrathin and single crystallized in the scrutinyite-SnO₂ phase with high purity. The ultrathin SnO₂ nanosheets show predominant growth in the [011] direction on the main surface having a thickness of ca. 1.3 nm. The SnO₂ nanosheets are further employed for the regioselective Friedel-Crafts acylation to synthesize aromatic ketones that have potential significance in chemical industry as synthetic intermediates of pharmaceuticals and fine chemicals. A series of aromatic substrates acylated over the SnO₂ nanosheets have afforded the corresponding aromatic ketones with up to 92% yield under solvent-free conditions. Comprehensive catalytic investigations display the SnO₂ nanosheet assembly as a better catalytic material compared to the heterogeneous metal oxide catalysts used so far in the view of its activity and reusability in solvent-free reaction conditions.

Development of Trifluoromethanesulfonic Acid-Immobilized Nitrogen-Doped Carbon-Incarcerated Niobia Nanoparticle Catalysts for Friedel-Crafts Acylation

Heterogeneous trifluoromethanesulfonic acid-immobilized nitrogen-doped carbon-incarcerated niobia nanoparticle catalysts (NCI-Nb-TfOH) that show excellent catalytic performance with low niobium loading (1 mol %) in Friedel-Crafts acylation have been developed. These catalysts exhibit higher activity and higher tolerance to catalytic poisons compared with the previously reported TfOH-treated NCI-Ti catalysts, leading to a broader substrate scope. The catalysts were characterized via spectroscopic and microscopic studies.

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

Due to their intrinsic physical properties, which includes being able to perform as volatile liquids at room and biological temperatures, fragrance ingredients/intermediates make ideal candidates for continuous-flow manufacturing. This review highlights the potential crossover between a multibillion dollar industry and the flourishing sub-field of flow chemistry evolving within the discipline of organic synthesis. This is illustrated through selected examples of industrially important transformations specific to the fragrances and flavours industry and by highlighting the advantages of conducting these transformations by using a flow approach. This review is designed to be a compendium of techniques and apparatus already published in the chemical and engineering literature which would constitute a known solution or inspiration for commonly encountered procedures in the manufacture of fragrance and flavour chemicals.

p-Toluenesulfonic acid functionalized imidazole ionic liquids encapsulated into bismuth SBA-16 as high-efficiency catalysts for Friedel-Crafts acylation reaction

Bismuth SBA-16 catalyst was synthesized by the hydrothermal method. Four kinds of p-toluenesulfonic acid functionalized imidazole ionic liquids were prepared by a two-step method and their molecular structures were characterized by 1H NMR and MS. The post-synthesis impregnation method was used to functionalize the Bi(10)-SBA-16 silicon mesoporous material with the ionic liquids and the obtained materials were characterized by FT-IR, XRD, BET, XPS, and TG. The results show that the volume and pore size of SBA-16 were changed by loading Bi and ionic liquids, while the three-dimensional cubic pore structure of SBA-16 was not destroyed. The composite catalyst was evaluated in Friedel-Crafts acylation of anisole with acetic anhydride. The effects of reaction temperature and the ratio of anisole and acylating agent on the acylation of anisole were investigated by experimental design. The results showed that 1.2ILc@Bi(10)-SBA-16 was used as the catalyst, the conversion of anisole was 85.41% and the yield of aromatic ketone was 69.19% under the conditions of a reaction temperature of 100 °C, a catalyst dosage of 0.5 g, a time period of 4 h and a molar ratio of 1 : 1.5. After 5 recycling runs, the reduction in the overall ratio of reactant conversion and product yield did not exceed 7.5%, indicating that 1.2ILc@Bi(10)-SBA-16 has good stability and reusability.

Well-Dispersed Trifluoromethanesulfonic Acid-Treated Metal Oxide Nanoparticles Immobilized on Nitrogen-Doped Carbon as Catalysts for Friedel-Crafts Acylation

Although strong acid-treated metal oxides are useful heterogeneous superacid catalysts for various organic transformations, they usually have a limited density of acidic sites due to their low surface areas. Herein, heterogeneous trifluoromethanesulfonic acid immobilized nitrogen-doped carbon-incarcerated titanium nanoparticle (NP) catalysts have been developed that are composed of well-dispersed, small Ti NPs (ca 7 nm) that are otherwise difficult to achieve using acid-treated metal oxides. The catalysts showed high activity for Friedel-Crafts acylation with low titanium loading (2 mol%, <1 mg of metal for 1 mmol of substrate). A range of microscopic, spectroscopic and physicochemical studies revealed that the nitrogen-doped carbon immobilized the trifluoromethanesulfonic acid and that the addition of metals further changed the nature of the acidic species and enhanced catalytic activity.

Brønsted acid/visible-light-promoted Markovnikov hydroamination of vinylarenes with arylamines

A Brønsted acid/visible-light-promoted Markovnikov hydroamination of vinylarenes with arylamines in the presence of TPT and CF₃CO₂H has been developed. This transformation provides a green approach to alpha-amino-substituted arylalkanes under metal-free conditions.