Thermal dehydration of amides to nitriles catalyzed by vanadium on hydrotalcite
Among methods for amide dehydration, this is particularly convenient: heterogeneous catalyst, purely thermal reaction in mesitylene at reflux. Sueoka,
Mitsudome, Mizugaki, Jitsugawa and Kaneda, attached.
The authors prepare the catalyst by depositing VCl3 on hydrotalcite:
| Quote: | | V/HT was synthesized as follows. HT (1.0 g) was added to 100 mL of an aqueous VCl 3 solution (4 mM) and then the mixture was stirred at room
temperature for 3 h. The obtained slurry was filtered, washed with deionized water and dried overnight at room temperature in vacuo to yield V/HT (V:
1.9 wt%) as a pale gray powder. |
High yields of nitriles are obtained for aromatic, aliphatic and alpha-branched primary amides with a long (24-72 hours) reflux in mesitylene (bp
165). The catalyst loading is low, but reuse results in reduced efficiency (yield loss ~10%).
Presumably xylene (bp 144) would require an even longer reflux, too slow to be practical. Diiodomethane has a closer boiling point (162), as do cymene
(177) and dimethylacetamide (165).
The preparation of mesitylene from acetone and concentrated sulfuric acid is given on Orgsyn involving multiple purifications for 12-15% yield.
Alternatively, mesitylene is prepared from toluene or xylene by disproportionation with AlCl3.
Surprisingly, even though the catalyst is prepared with vanadium (III), the authors report that the catalyst soft X-ray absorption (photoelectron
energies) is consistent with sodium orthovanadate (V).
Attachment: sueoka2010.pdf (599kB)
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edit: replaced limonene with cymene due to possible instability
[Edited on 1-12-2022 by clearly_not_atara]
[Edited on 04-20-1969 by clearly_not_atara]
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