A highly efficient synthetic procedure for deuteriating imidazoles and imidazolium salts

Characterization of nonderivatized plant cell walls using high‐resolution solution‐state NMR spectroscopy

“…[26] A modification of this procedure uses methanol-d 4 , which has been shown to give N-alkylation of imidazole in 49% yield. [27] Alkylation by this method in our lab gave an isolated yield of 66% (after vacuum distillation with a microcapillary nitrogen bleed). GC/MS analysis of the product showed complete (-CD 3 ) N-methylation with a distribution of products with the ring protons exchanged, as well.…”

“…[27] In our several attempts with this method, the only position that exchanged to a high degree was H(2) with very little H(4/5) exchange. Since palladium catalysts seem to be quite variable in their activity with this method, our result prompted the search for a more consistent ring proton exchange method for H(4/5).…”

“…Proton spectra of various stages in NMI deuteration: a, 1-methylimidazole; b, 1-methyl-d 3 -imidazole; c, ring deuteration as per Hardacre et al [27] ; d, ring deuteration as per Esaki et al [28] ; e, ring deuteration with combination of methods. HSQC spectra from nonderivatized plant cell walls: a, pine; b, aspen; and c, kenaf at 500 MHz.…”

“…[26,27] Briefly, imidazole (10.89 g, 160 mmol), tributylphosphite (2.30 g, 9.2 mmol), ruthenium chloride hydrate (0.64 g, 3.1 mmol), and methanol-d 4 (20 g, 555 mmol) were sequentially added to dioxane (300 ml) in a 2-l stainless steel Parr reactor vessel. The vessel was sequentially sealed, purged with nitrogen, stirred, heated to 200 °C, and pressurized with nitrogen to 44 bar.…”

“…The product was vacuum distilled (with assistance of a microcapillary) to recover 1-methyl-d 3 This exchange is derived from a combination of prior published methods. [27,28] Briefly, dry palladium catalyst (1 g Pd/C) was well stirred for 1 hr in a double-necked flask purged with nitrogen followed by capping one neck of the flask with a 230-mm round balloon full of hydrogen. A hose, connected to the second neck of the flask, allowed hydrogen to flow through the flask and through a water bath at a rate of ~1 bubble per second via a needle valve.…”