Mesoporous Material from Fly Ash as a Catalyst for Stereoselective Reduction of Substituted Cyclohexanones

Abstract

Mesoporous material synthesized using ultrafine coal fly ash as a source for silicon and aluminium with cetyl trimethyl ammonium bromide as the structure directing agent has been found to be a good support for enhancing the stereoselectivity of reduction of some substituted cyclohexanones. Exclusive formation of trans-4-t-butyl cyclohexanol and 4-methyl cyclohexanol is evidenced by the appearance of single peaks in ¹HNMR spectra (δ = 3.5), which are due to axial C–H protons. In other cases, enhancement of stereoselectivity has been observed. Apparently, Lewis/Bronsted acid sites present in the mesoporous material activate such preference for the formation of isomers with an equatorially disposed OH group. A probable transition state has been suggested.

Keywords:

• cetyltrimethyl ammonium bromide
• fly ash
• mesoporous
• stereoselective
• substituted cyclohexanones

Notes

^a For CFA.

^b For mesoporous material: Chemical compositions were determined using XRF technique.

^a Thermodynamically more stable. Ratio of stabler alcohol:less stable alcohol is calculated from the peak integrals of the CH protons (axial/equatorial).

^b Unit in δ.