Beilstein J. Org. Chem. 2012, 8, 390–397.
Experimental
3500 RI detector and a Viscotek Viscometer model 250 were
Materials. Randomly methylated (1.8) β-cyclodextrin (m-β- used. The system was calibrated with polystyrene standards
CD) was obtained from Wacker-Chemie GmbH (Burghausen, with a molecular range from 580 Da to 1186 kDa.
Germany). Prior to use, m-β-CD was dried in a CEM Sam 255
Synthesis of 2,3-dibromo-5-(1-butyl-1H-
microwave drying system and stored in a desiccator under
imidazol-3-ium-3-yl)-1,4-benzoquinone-6-
olate (3)
vacuum over sicapent. 1-Butylimidazole (98%), 1,4-dichloro-
butane (97%), and azobisisobutyronitrile (98%) were obtained
from Aldrich Chemicals (Germany). 1-Vinylimidazole (99%)
and tetrabromo-1,4-benzoquinone (p-bromanil) were purchased
from Alfa Aesar and 1-H-imidazole was obtained from
AppliChem (Germany). Dimethylsulfoxide-d6 (DMSO-d6)
99.8 atom % D was purchased from Eurisotop® (France). If not
stated otherwise, all commercially available reagents and
solvents were used without further purification.
Tetrabromo-1,4-benzoquinone (p-bromanil, 1) (0.845 g,
2 mmol) was dissolved in 45 mL of acetonitrile at 60 °C and
1-butyl-1H-imidazole (2) (1 g, 8 mmol) was added. The mix-
ture was heated under reflux for 3 h and was afterwards
hydrolyzed with 40 mL of water. After filtration, acetonitrile
was removed by evaporation and the resulting solution was
cooled at 0 °C until a precipitate was formed. The crude pro-
duct was collected by filtration and was washed three times
with 50 mL of water. After recrystallization from acetic acid, 3
was obtained as a dark red solid. Yield: 247 mg (0.61 mmol,
31%); 1H NMR (500 MHz, DMSO-d6) δ 9.11 (s, 1H,
N(1)CHN(3)), 7.816 (s, 1H, N(1)CHCH), 7.64 (s, 1H,
N(1)CHCH), 4.23 (t, 3JH,H = 7.09 Hz, 2H, N(1)CH2), 1.81 (m,
2H, N(1)CH2CH2), 1.27 (m, 2H, CH2CH3), 0.92 (t, 3JH,H =
7.41 Hz, 3H, CH2CH3) ppm; 13C NMR (125 MHz, DMSO-d6)
δ 175.39 (N(3)–C(CO)CO), 166.76, 163.73 (C=O), 145.01
(CO), 137.31 (N(1)CHN(3)), 131.78 (C–Br), 124.67
(N(1)CHCH), 120.78 (N(1)CHCH), 111.43 (C–Br), 48.46
(N(1)CH2), 31.36 (N(1)CH2CH2), 18.79 (CH2–CH3), 13.26
(CH2–CH3) ppm; IR (cm−1): 3185, 3128, 3066 (CH,
imidazole), 2960, 2915, 2877 (CH3, CH2), 1697 (C=O), 1569,
1552 (C=Carom), 1540 (O–C–C–C–O), 1469, 1338 (δ CH3,
CH2), 1149 (HCC, HCN bending, imidazole), 850, 736, 582;
Anal. calcd for C13H12Br2N2O3: C, 38.64; H, 2.99; N, 6.93;
found: C, 38.65; H, 2.86; N, 6.59.
Measurements. The structures of the synthesized compounds
were evaluated by 1H and 13C NMR spectroscopy by using a
Bruker Avance DRX 500 spectrometer at 500.13 MHz for
proton and 125.77 MHz for carbon. With DMSO-d6 as solvent,
chemical shifts were referenced to the solvent values at δH =
2.51 ppm and δC = 39.52 ppm. C, H and N elemental analysis
was determined by using a Perkin Elmer 2400 CHN analyzer.
Infrared spectra were recorded on a Nicolet 6700 FT-IR spec-
trometer equipped with a diamond single-bounce ATR acces-
sory at room temperature. Thermogravimetric analyses (TGA)
were carried out with a TA 600 Perkin Elmer (TGA combined
with a DTA) in a temperature range between 30 and 800 °C
under an argon atmosphere. The heating rate was 10 °C min−1.
All measurements were baseline corrected and analyzed by
Pyris software. Determination of the type of inclusion complex
and the complexation constant was achieved by UV–vis spec-
troscopy. The UV–vis spectra were recorded on a Nicolet
UV540 spectrometer in the range from 190 to 400 nm in a glass
cuvette with a layer thickness of 1 cm. Furthermore, the change X-ray crystal-structure analysis of 3
of absorbance at a wavelength of λ = 306 nm was determined Single crystals of 3 were obtained by very slow evaporation of
according to the cyclodextrin concentration. Matrix-assisted methylene chloride. They were mounted in inert oil and trans-
laser desorption/ionization-time-of-flight mass spectrometry ferred to the cold gas stream of the diffractometer. Diffraction
(MALDI-TOF-MS) was performed on a Bruker Ultraflex TOF data were collected at 150 K by using an Oxford Diffraction
mass spectrometer. Ions formed with a pulsed nitrogen laser Gemini E Ultra diffractometer [Cu Kα irradiation (λ =
(25 Hz, 337 nm) were accelerated to 25 kV, with the molecular 1.5418 Å)], with an EOS CCD area detector and a four-circle
masses being recorded in the linear mode. 2,5-Dihydroxyben- kappa goniometer. Data integration, scaling and empirical
zoic acid (DBH) in acetonitrile/water (25 mg mL−1) was used as absorption correction was carried out with the CrysAlis Pro
a matrix. The samples (1 mg mL−1 in water) were mixed with program package [14]. The structure was solved by using Direct
the matrix solution at a volumetric ratio of 1:2. Molecular Methods and refined by Full-Matrix-Least-Squares against F2.
weights and molecular weight distributions were measured by The non-hydrogen atoms were refined anisotropically and
size-exclusion chromatography (SEC) with a Viscotek GPCmax hydrogen atoms were placed at idealized positions and refined
VE2001 system that contained a column set up with one by using a model riding mode. All calculations were carried out
Viscotek TSK guard column HHR-H 6.0 mm (ID)_4 cm (L) with the program Olex2 [15]. Brief summary of crystal data:
and two Viscotek TSK GMHHR-M 7.8 mm (ID)_30 cm (L) C13H12Br2N2O3, M = 404.07, Monoclinic, a = 15.0119(6) Å,
columns at 60 °C. N,N-Dimethylformamide (DMF, 0.1 M LiCl) b = 3.99067(18) Å, c = 22.8802(9) Å, β = 93.428(4)°, V =
was used as eluent at a flow rate of 1 mL min−1. A Viscotek VE 1368.24(10) Å3, space group P21/c (No. 14), Z = 4, μ(Cu Kα) =
395