Abstract
We recently published details of an effective, reus able and benign heterogeneous amidation catalyst based on thermal treatment of amorphous K60 silica, however the loading of catalyst required was high for some reactions. We report her ein our further development of a series of heterogeneous catalysts based on structured silica (SBA) that retain all the green credentials of the previously described amorphous silica, but with increased efficiency. These catalysts were then utilised in continuous flow systems, achieving excellent conversions with dramatically reduced reaction times.
Highlights
The formation of amides is one of the most important reactions in the pharmaceutical industry, though typically suffers from poor atom economy, with stoichiometric activating agents being required to achieve amide formation.[1]
We present our results for amide synthesis with mesoporous structured silicas (SBA-15), which have very well defined, regular, linear pores, which allow for excellent diffusion
The use of SBA-15 type silicas has proved beneficial in the catalytic formation of amides directly from a range of carboxylic acids and amines, with significantly lower catalyst loadings required than for activated chromatographic K60 silica
Summary
The formation of amides is one of the most important reactions in the pharmaceutical industry, though typically suffers from poor atom economy, with stoichiometric activating agents being required to achieve amide formation.[1]. The rate of reaction in the batch process was highest during the first hour – the average hourly rate of conversion after the 24 hours needed to complete the reactions in batch mode was significantly lower (e.g. for the first example, this can be calculated to be 0.08 g h-1).[7] Secondly, the effect of increasing catalyst quantity in the batch reaction (so that is approaches that of the continuous system) was minimal.
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