We report a simple gram scale synthesis of several imidazolinium salts (Br, Cl, PF6 and BF4). This particular protocol describes the synthesis of N,N’–bis–(2,4,6–trimethylphenylamino)ethane dihydrochloride
Azolium salts have become indispensable starting materials in N–heterocyclic carbene (NHC) chemistry. From being a laboratory curiosity, NHCs occupy now an important position in contemporary organometallic chemistry as powerful ligands for many catalytic reactions (ie: Negishi, Kumada–Tamao–Corriu, Sonogashira and Suzuki–Miyaura cross–coupling reaction, Buchwald–Hartwig amination, aerobic oxidation, CuAAC reaction …) as well as organocatalysts. Although diverse strategies have been developed to synthesize imidazolinium salts, they generally require the reduction of an intermediate diimine. This usually involves stoechiometric borohydride in a exothermic process which could present difficulties and hazards to scale–up. We report a simple gram scale synthesis of several imidazolinium salts (Br, Cl, PF6 and BF4). Through a direct double alkylation of 1,2–dibromethane, the corresponding diamine is obtained which serves as convenient starting material for the salts described above using convenient known procedures.
The following protocol have been obtained from http://www.nature.com/protocolexchange/protocols/2484 and is republished in accordance with the Creative Commons license Attribution-NonCommercial 3.0 Unported license. The protocol have been reordered to comply with the MolMeth format and have not undergone review by the listed author for correspondence, Arnaud Gautier (email@example.com). Articles listed as references for the protocol are listed separately1.
- 37.8 g (82.5 mmol) of N,N’–bis–(2,4,6–trimethylphenylamino)ethane dihydrobromide
- 600 mL of diethyl ether
- 25 g (235.8 mmol) of solution of sodium carbonate
- 200 mL water
- 200 mL of ethanol
- 19.0 g (242 mmol) of acetyl chloride
- Round-bottomed flasks (500 mL,1 L)
- Teflon-coated stirring bars
- Filtration funnels
- Thermally controlled stirring plate
- A distillation apparatus
- A thermometer.
- A separation funnel.
- Weigh out 37.8 g (82.5 mmol) of N,N’–bis–(2,4,6–trimethylphenylamino)ethane dihydrobromide in a 1 L round–bottomed flask.
- Add 500 mL of diethyl ether and 25 g (235.8 mmol) of solution of sodium carbonate in 200 mL water.
- Stir vigorously the solution for 2 h.
- Separate the organic layer, extract the aqueous phase with 100 mL of diethyl ether and dry the combined phases over anhydrous Na2SO4.
- Add 200 mL of ethanol in a 500 mL round–bottomed flask immerged in a water bath.
- Add 19.0 g (242 mmol) of acetyl chloride dropwise while maintaining the temperature close to room temperature. Then stir the solution for 30 minutes at room temperature.
- Add the ethanolic HCl solution to the ether.
- PAUSEPOINT : A white solid forms immediately.
- Filter off the solid and dry it to constant weight in an oven (90°C).