Synthesis of N,N’–bis–(2,4,6–trimethylphenylamino)ethane dihydrobromide

Abstract

We report a simple gram scale synthesis of several imidazolinium salts (Br, Cl, PF6 and BF4), the synthesis of N,N’–bis–(2,4,6–trimethylphenylamino)ethane dihydrobromide is described in this protocol

Introduction


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.

Legal disclaimer
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 (arnaud.gautier@univ-bpclermont.fr). Articles listed as references for the protocol are listed separately1.

Reagents

  • 40.5 g (0.3 mol) of 2,4,6–trimethylaniline
  • 22.5 g (0.125 mol) of 1,2–dibromoethane
  • 80 mL of methanol
  • 100 mL of ethyl acetate

Equipment

  • Round-bottomed flasks (250 mL)
  • Teflon-coated stirring bars
  • Filtration funnels
  • Thermally controlled stirring plate
  • A distillation apparatus
  • A thermometer.
  • A separation funnel.

Instructions

  1. Weigh out 40.5 g (0.3 mol) of 2,4,6–trimethylaniline in a 250 mL round–bottomed flask equiped with a stirring bar.
  2. Add 22.5 g (0.125 mol) of 1,2–dibromoethane.
  3. Add 30 mL of methanol.
  4. Stir the reaction mixture under reflux for 24 h.
  5. PAUSEPOINT : a solid forms during the reaction, usually after 18 h.
  6. The solution is cooled down to room temperature and stirred for an additional 2 h.
  7. Filter off the formed brownish precipitate, wash it with 50 mL of methanol, 100 mL of ethyl acetate, 100 mL of diethyl ether and dry under an air flux for one hour to obtain a white powder.

Citation:
Gautier A. Cisnetti F. Diez-Gonzalez S and Gibard C. Synthesis of 1,3–bis(2,4,6–trimethylphenyl)–imidazolinium salts : SIMes.HCl, SIMes.HBr, SIMes.HBF4 and SIMes.HPF6. Protocol Exchange Published online 10 October 2012 doi:10.1038/protex.2012.048