Phosphorus Tribromide

• Phosphorus Tribromide [P1743]
• 1-(4,5-Dimethoxy-2-nitrophenyl)ethanol
• Dichloromethane

Phosphorus tribromide (1.63 g, 6.03 mmol) was added dropwise to a solution of 1-(4,5-dimethoxy-2-nitrophenyl)ethanol (1.10 g, 4.83 mmol) in dichloromethane (24 mL) at 0 °C. The mixture was stirred for 3 hours. To the solution was added saturated sodium hydrogen carbonate aqueous solution (18 mL) and washed with water (10 mL, 2 times), dried over sodium sulfate and filtered. The solvent was removed under reduced pressure. The residue was purified by column chromatography (on silica gel, ethyl acetate:hexane = 1:10) to give 1 (952 mg, 68% yield) as a yellow oil.

The reaction mixture was monitored by TLC (hexanes:ethyl acetate = 1:1, Rf = 0.71) and UPLC.
Compound 1 was treated under light shielding throughout the entire process because of its possible photodegradability.
When the sample for NMR of 1 was left under fluorescent light, the color of the solution changed from yellow to dark blue.

Compound 1

¹H NMR (400 MHz, CDCl₃); δ 7.46 (s, 1H), 7.28 (s, 1H), 6.04 (q, J = 5.4 Hz, 1H), 4.02 (s, 3H), 3.95 (s, 3H), 2.07 (d, J = 5.4 Hz, 3H).

• Photolabile Protecting Groups for Nitroxide Spin Labels
  • I. Seven, T. Weinrich, M. Gränz, C. Grünewald, S. Brüß, I. Krstić, T. F. Prisner, A. Heckel, M. W. Göbel, Eur. J. Org. Chem. 2014, 19, 4037.