1. Methanol (500 mL), 2,6-diisopropylaniline (63.8 mL, 340 mmol), glyoxal (40 wt% aqueous solution, 19 mL, 170 mmol), and formic acid (1 mL) were added to a 1000 mL round bottom flask. The reaction mixture was stirred at room temperature for 3 hours.
2. The reaction mixture was filtered and the yellow precipitate (3) was collected and washed with cold methanol. The precipitate was dried under vacuum overnight to give product (3) (70% yield, 44.2 g, 238 mmol).
3. The product (3) (200 g, 532 mmol) and ethyl acetate (2 L) were added to a 5 L round bottom flask and stirred until completely dissolved. Cool the solution to 0°C.
4. To a 500mL conical flask was added paraformaldehyde (20.7g, 690mmol) and a dioxane solution of 4N HCl (212mL, 851mmol), stirred for 10 minutes and then added to the above cooled solution.
5. The reaction mixture was stirred at room temperature for 2 hours and the precipitate was collected by filtration.
6. The precipitate was dissolved in methanol (200 mL), sodium bicarbonate (15.0 g) was added and stirred for 1 hour or until no bubbles were produced.
7. The solids were removed by filtration and the filtrate was reprecipitated by adding diethyl ether (250 mL) to the filtrate.
8. The product was collected by filtration, washed with ethyl ether and dried under vacuum to afford 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (IPr-HCl, 4) as a white powder (70% yield, 158.25 g, 371 mmol).
9. The product was characterized by 1H NMR (CDCl3, 400 MHz) and 13C NMR (CDCl3, 400 MHz) and the data were consistent with the expected structure.
