Environment-Friendly Reduction of Aromatics to Alicyclic Compounds at Room Temperature Using Superactive Calcined Ni-Al Hydrotalcite Catalysts

Abstract

Calcined Ni-Al hydrotalcite (HT) 2: 1, Cat. A, is a superactive catalyst for reduction of substituted aromatics, i. e. toluene, benzene, nitrobenzene, chloro-, bromo-, and iodobenzene to their respective alicyclic products at room temperature in the presence of molecular hydrogen. Cat. A attained higher conversions compared to calcined Ni-Al hydrotalcites with ratios of 2.5: 1, and 3: 1. Calcined Ni-Al HT is a superactive catalyst whereas catalysts Niγ-Al 2 O 3 or Ni-SiO 2 with Ni contents of 2%, 5%, and 10% resulted in poor conversions. In these cases, Ni in association with the respective oxide is the active precursor for molecular hydrogen initiation in the reduction of aromatics to alicyclic compounds. The objective is to evalua4e Ni as the best catalyst for aromatic ring reduction to alicylic molecule. Quantitative yield were obtained for all the substrates toluene, benzene, nitrobenzene, chloro-, bromo-, and iodobenzene to their respective cyclohexanes. These results indicate that hydrogenation with reusable Ni-Al HT catalysts is a green sustainable process and atom economy efficient for the production of various alicyclic compounds.

Layered Double Hydroxide Catalysts Preparation, Characterization and Applications for Process Development: An Environmentally Green Approach

“…Ni-hydrotalcite catalysts for reductive amination of benzaldehyde with NaBH4, acts as reducing agent to form in situ-Ni-boride which is generated swiftly in the formation of desired product at room temperature. The activity of Ni-Al hydrotalcites for organic transformation discussed above is attributed due to the even distribution of Ni ions for 2:1 ratio of Ni-Al hydrotalcite catalysts and inactivity of 2.5:1, and 3:1 ratio catalyst is due to higher content of Ni in Ni-Al hydrotalcite [107].…”

“…Rahman et al [107] reported the reduction of aromatics to alicyclic molecules with super active 2:1 Ni-Al hydrotalcite catalysts to alicyclic without loss of activity of the catalysts. Osmate intercalated hydrotalcite aimed at selective oxidative bromination of bisphenol-A for asymmetric dihydroxylation of olefins [108] with NMO (N-Methylmorpholine N-oxide) used as co-oxidant in company of molecular oxygen was reported by Choudhary et al [108].…”