Abstract
AbstractAn efficient and green protocol for highly selective reduction of α,β‐unsaturated aldehydes and ketones at room temperature is described in a range of ionic liquids, in the absence of noble metal catalysts, by using NaBH4 as reducing agent. Most notably, using [P6,6,6,14][N(CN)2] ionic liquid, in absence of organic solvent, within 10 min, 97% conversion of cinnamaldehyde was achieved with 100% selectivity towards cinnamyl alcohol. The ionic liquid was easily recycled without any noticeable decline in activity. The reduction protocol was further extended to a variety of α,β‐unsaturated aldehydes and ketones.
Highlights
The selective hydrogenation of α, β-unsaturated aldehydes and ketones is of high importance in the fine chemical industry especially in the production of pharmaceuticals, fragrances and flavours.[1]
High pressure hydrogenation shows lower selectivity since C=C double bond reduction is thermodynamically favoured over carbonyl bond reduction; while hydrogen transfer produces by-products and has lower atom-efficiency besides producing ketone along with the desired unsaturated alcohol. Another attractive alternative for reduction of aldehydes and ketones is by using sodium borohydride, NaBH4 as reducing agent, owing to its ready availability, high stability and easy downstream work-up.[3]
In this study, we have investigated the reduction of α, βunsaturated aldehydes and ketones, using cinnamaldehyde as the model substrate under ambient conditions
Summary
The selective hydrogenation of α, β-unsaturated aldehydes and ketones is of high importance in the fine chemical industry especially in the production of pharmaceuticals, fragrances and flavours.[1]. High pressure hydrogenation shows lower selectivity since C=C double bond reduction is thermodynamically favoured over carbonyl bond reduction; while hydrogen transfer produces by-products and has lower atom-efficiency besides producing ketone along with the desired unsaturated alcohol Another attractive alternative for reduction of aldehydes and ketones is by using sodium borohydride, NaBH4 as reducing agent, owing to its ready availability, high stability and easy downstream work-up.[3] the use of NaBH4 is known over seven decades, the reaction rates are often low, leading to the use of a stoichiometric excess of NaBH4. Virtanen et al have reported selective reduction of C=C double bond in the hydrogenation of cinnamaldehyde to hydrocinnamaldehyde using supported ionic liquid catalysts (SILCAs) using two different ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4Mim][PF6]) and N-butyl4-methylpyridinium tetrafluoroborate ([C4M4Py][BF4]); in presence of palladium particles on active carbon cloth.[19] Amongst the two SILCA catalysts, the system containing [C4M4Py][BF4].
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