NaBH4 Reduction Difference Spectra

The carbonyl reactivity of pyrrole-, furan-, thiophene- and selenophene-2- and -3-carbaldehydes is very similar to that of benzaldehyde. A quantitative study of the reaction of Af-methylpyrrole-2-carbaldehyde, furan-2-carbaldehyde and thiophene-2-carbaldehyde with hydroxide ions showed that the difference in reactivity between furan- and thiophene-2-carbaldehydes was small but that both of these aldehydes were considerably more reactive to hydroxide addition at the carbonyl carbon than A-methylpyrrole-2-carbaldehyde (76JOC1952). Pyrrole-2-aldehydes fail to undergo Cannizzaro and benzoin reactions, which is attributed to mesomerism involving the ring nitrogen (see 366). They yield 2-hydroxymethylpyrroles (by NaBH4 reduction) and 2-methylpyrroles (Wolff-Kishner reduction). The IR spectrum of the hydrochloride of 2-formylpyrrole indicates that protonation occurs mainly at the carbonyl oxygen atom and only to a limited extent at C-5. 

Kg. 4.1.9. Difference spectrum of oak (Quercus obtusata) obtained by subtracting the spectrum of MWL from the spectrum of the same MWL after NaBH4 reduction. (Instrument Nicolet 20SX D, 4cm 1 resolution, 32 scans, KBr pellet technique)... 

Other difference spectra (e.g., NaBH4 reduction, ethanolysis, hydrogenation, and photo-reduction) are obtained similarly by subtracting from the spectrum of chemically treated lignin in the sample cuvet, the spectrum of the untreated lignin at an equal concentration. 

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