Hydroxy-2,4,5-trimethylimidazole 3- oxide

A solution of diacetyl (4.3 g, 50 mmol) and ethanol (2.2 g, 50 mmol) in methanol (400 ml) is treated with hydroxylamine hydrochloride (2g, 100 mmol) and stirred at room temperature (20 h). The reaction mixture is neutralized with sodium carbonate (15 g), filtered, and concentrated under reduced pressure. The residue crystallizes fiom benzene as tan needles (5.5 g, 83%), m.p. 199-200°C. Similarly prepared is the 2-phenyI analogue (90%). 

5-Dichloroimidazoles can be made by treatment of an arylaldehyde with cyanogen and hydrogen chloride in ethereal solution. The sole by-product appears to be oxamide, which is readily separated because of its sparing solubility in conunon solvents. Yields of 2-aryl-4,5-dichloroimidazoles lie in the range 36-72% [27]. The dichloroimidazolcs are very base-sensitive, and even dilute alkalies convert them into A -methylbenzamides. 

It has been reported that 1-hydroxyimidazoles (rather than imidazoles [28]) are accessible in high yields from reaction of nitrosonium fluoroborate with acetonitrile and the appropriate alkene titanium(III) chloride reduces the hydroxyl function [24]. 

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