research communications
Synthesis and
of a new pyridinium bromide salt: 4-methyl-1-(3-phenoxypropyl)pyridinium bromideaDepartment of Chemistry, Taibah University, 30002, Al-Madina Al-Mounawara, Saudi Arabia, bLaboratoire de Chimie & Electrochimie des Complexes Métalliques (LCECM), USTO-MB, University of Sciences and Technology Mohamed Boudiaf, BP 1505 Oran, El M'nouar, Algeria, and cSchool of Chemistry, University of East Anglia, University Plain, Norwich NR4 7TJ, United Kingdom
*Correspondence e-mail: d.l.hughes@uea.ac.uk, mouslim@mail.be
In the cation of the title molecular salt, C15H18NO+·Br−, the pyridinium and phenyl rings are inclined to one another by 11.80 (8)°. In the crystal, the Br− anion is linked to the cation by a C—H⋯Br hydrogen bond. The cations stack along the b-axis direction and are linked by further C—H⋯Br interactions, and offset π–π interactions [intercentroid distances = 3.5733 (19) and 3.8457 (19) Å], forming slabs parallel to the ab plane. The effects of the C—H⋯X− interaction on the NMR signals of the ortho- and meta-pyridinium protons in a series of related ionic liquids, viz. 4-methyl-1-(4-phenoxybutyl)pyridin-1-ium salts, are reported and discussed.
Keywords: crystal structure; ionic liquids; pyridinium salts; halide; hydrogen bonding; π–π interactions.
CCDC reference: 1581713
1. Chemical context
In the last two decades, ionic liquids (ILs) have gained considerable interest as excellent alternatives to volatile organic compounds (VOCs) because of their unusual range of properties such as negligible vapour pressure, excellent thermal stability in a wide temperature range, no flammability, high ).
and solvation ability (Davis, 2004A wide range of applications using ionic liquids has been reported in many areas such as solvents in organic synthesis (Wang et al., 2007), media for of metals (Endres, 2002), corrosion inhibitors (Ibrahim et al., 2011), electrolytes for electrochemical devices such as batteries (Brennecke & Maginn, 2001), catalysts (Shi et al. 2004), in fuel cells (De Souza et al., 2006), in polymer science (Kubisa, 2004), and in dye-sensitized solar cells (Kawano et al., 2004).
In view of the above mentioned, and of our ongoing research interest in the synthesis of ionic liquids (Messali, 2016, 2015; Messali et al., 2014), we present in this study the preparation and the of the novel title pyridinium halide salt, 4-methyl-1-(3-phenoxypropyl)pyridinium bromide.
2. Structural commentary
The molecular structure of the title pyridinium bromide salt is illustrated in Fig. 1. There is a weak intramolecular C—H⋯O contact present, with an H⋯O distance of 2.52 Å and a C—H⋯O angle of only 100° (see Table 1). The cation consists of two planar groups, a pyridinium ring (N11/C12–C16) and a phenyl group (C1–C6); atom N11 has the expected planar–trigonal conformation. The two aromatic rings are inclined to one another by 11.80 (8)° and there is a step of ca 1.35 Å between the two groups along the C9—C10 bond, see Fig. 2. The C1—O7, C8—C9, C10—N11 and C14—C17 bonds are roughly parallel, so that the two aromatic groups are at opposite ends of an approximately linear cation. This is in contrast to the alignment found in 1-[2-(5-nitro-1H-indol-2-yl)phenyl]methylpyridinium chloride where the cation is U-shaped with the pyridinium ring lying over the pyrrolo ring of the indole moiety (Bremner et al., 2011), possibly as a result of electronic interactions between the two rings.
3. Supramolecular features
In the crystal, the bromide anion is linked to the cation by a C10—H10B⋯Br1i hydrogen bond (Table 1). The anion is surrounded by three other cations with the most significant C-–H⋯Br short contacts varying from ca 3.07 to 3.11 Å (Table 1). The bromide ions are aligned approximately in the planes of the aromatic rings, which is similar to the arrangement found in N-benzylpyridinium bromide (Anders et al., 1990), and in contrast to those in a series of N-(pentafluorobenzyl)pyridinium salts where the anion faces the aromatic rings with formation of anion–π interactions (Giese et al., 2014).
The cations stack head-to-tail, in pairs about centres of symmetry, along the b-axis direction with the aromatic rings being inclined slightly to one another [α = 11.80 (8)° within a pair and 7.52 (16)° between pairs]. As shown in Fig. 3, the pairs are linked by offset π–π interactions, forming slabs parallel to (001): Cg1⋯Cg2iii = 3.8457 (19) Å within a pair, and Cg1⋯Cg2iv = 3.5733 (19) Å between pairs; Cg1 and Cg2 are the centroids of rings C1—C6 and N11/C12–C16, respectively; symmetry codes: (iii) 1 − x, 1 − y, 1 − z; (iv) x − , − y, 1 − z.
4. C—H⋯anion interactions in the 1H NMR spectrum
The C—H⋯anion interactions are clearly manifested in the 1H NMR spectrum (see Section 5. Synthesis and crystallization). Such an effect has previously been shown by a solution study of the C—H⋯Br interaction on the signals of the ortho- and meta-pyridinium protons in the 1H NMR spectra of a series of N-(pentafluorobenzyl)pyridinium salts (Giese et al., 2014). The present study in D2O solvent involves only the pyridinium protons (Ha and Hb) of a series of 4-methyl-1-(4-phenoxybutyl)pyridin-1-ium X− ionic liquids, and the title compound, shown in Fig. 4. The results, given in Table 2, reveal significant shifts for the hydrogen atom Ha in various pyridinium salts, whereas hydrogen atom Hb is only slightly affected by the different counter-anions (Messali, 2015); viz. the study reveals a range of 0.75 p.p.m. for the signals of the ortho-pyridinium protons (Ha) and a shorter range of 0.29 p.p.m. for meta-pyridinium protons (Hb). The determination of the causes behind this variation remains a challenging task for our research group.
5. Synthesis and crystallization
The synthesis of the title compound is illustrated in Fig. 5. To a solution of 1 g of 4-picoline (10.7 mmol) in 20 ml of toluene, were added 2.53 g of (3-bromopropoxy)benzene (118 mmol) at room temperature, followed by stirring at 355 K for 18 h. The completion of the reaction was marked by the separation of a solid from the initially obtained clear and homogeneous mixture of the starting materials. The product was isolated by filtration to remove the unreacted starting materials and solvent. Subsequently, the title picolinium salt was washed with ethyl acetate. The product was finally dried at reduced pressure to remove all volatile organic compounds. The title compound was obtained as a white solid. Colourless prismatic crystals were obtained by slow evaporation of a solution in dichloromethane.
Spectroscopic and analytical data: 1H NMR (D2O, 400 MHz): δ = 2.34 (quint, J = 7.6 Hz, 2H), 2.50 (s, 3H), 3.98 (t, J = 7.6 Hz, 2H), 4.60 (t, J = 7.6 Hz, 2H), 6.72 (d, 2Ar–H), 6.91 (t, 1Ar–H), 7.21 (t, 2Ar–H), 7.66 (d, 2Ar–H), 8.48 (d, 2Ar–H); 13C NMR (D2O, 100 MHz,): δ = 21.2 (CH3), 29.4 (CH2), 58.5 (CH2), 64.5 (CH2), 114.4 (CH), 121.5 (CH), 128.5 (CH), 129.8 (CH), 143.2 (CH), 157.4 (C), 160.1 (C); IR (KBr) νmax 3132 (C—H Ar), 1600–1470 (C=C), 1167(C—N), 1078 (C—O) cm−1; LCMS (M+)–Br− 228.1 found for C15H18NO+. Elemental analysis for C15H18BrNO (308.21); calculated C 58.45, H 5.89, N 4.54%. Found: C 58.51, H 5.82, N 4.49%.
6. Refinement
Crystal data, data collection and structure . The H atoms were included in idealized positions and treated as riding atoms: C—H = 0.93–0.97 Å with Uiso(H) = 1.5Ueq(C-methyl) and = 1.2Ueq(C) for other H atoms.
details are summarized in Table 3Supporting information
CCDC reference: 1581713
https://doi.org/10.1107/S2056989017015481/su5395sup1.cif
contains datablocks I, Global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989017015481/su5395Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989017015481/su5395Isup3.cdx
Supporting information file. DOI: https://doi.org/10.1107/S2056989017015481/su5395Isup4.cml
Data collection: CrysAlis PRO (Agilent, 2014); cell
CrysAlis PRO (Agilent, 2014); data reduction: CrysAlis PRO (Agilent, 2014); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015) and WinGX (Farrugia, 2012).C15H18NO+·Br− | Dx = 1.407 Mg m−3 |
Mr = 308.21 | Mo Kα radiation, λ = 0.71073 Å |
Orthorhombic, Pbca | Cell parameters from 5457 reflections |
a = 10.3615 (3) Å | θ = 3.2–25.6° |
b = 13.8916 (6) Å | µ = 2.82 mm−1 |
c = 20.2121 (8) Å | T = 295 K |
V = 2909.29 (19) Å3 | Prism, colourless |
Z = 8 | 0.60 × 0.19 × 0.10 mm |
F(000) = 1264 |
Oxford Diffraction Xcalibur 3/Sapphire3 CCD diffractometer | 2560 independent reflections |
Radiation source: Enhance (Mo) X-ray Source | 2212 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.048 |
Detector resolution: 16.0050 pixels mm-1 | θmax = 25.0°, θmin = 3.6° |
Thin slice φ and ω scans | h = −12→12 |
Absorption correction: multi-scan (CrysAlis Pro; Agilent, 2014) | k = −16→16 |
Tmin = 0.529, Tmax = 1.000 | l = −24→24 |
38980 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.045 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.087 | H-atom parameters constrained |
S = 1.20 | w = 1/[σ2(Fo2) + (0.0313P)2 + 1.5286P] where P = (Fo2 + 2Fc2)/3 |
2560 reflections | (Δ/σ)max = 0.001 |
164 parameters | Δρmax = 0.27 e Å−3 |
0 restraints | Δρmin = −0.25 e Å−3 |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
Br1 | 0.33702 (3) | 0.68529 (3) | 0.38455 (2) | 0.05802 (14) | |
C1 | 0.3412 (3) | 0.6101 (2) | 0.61560 (14) | 0.0449 (7) | |
C2 | 0.2231 (3) | 0.6169 (2) | 0.58402 (17) | 0.0497 (8) | |
H2 | 0.2174 | 0.6070 | 0.5386 | 0.060* | |
C3 | 0.1146 (4) | 0.6382 (3) | 0.6199 (2) | 0.0665 (10) | |
H3 | 0.0352 | 0.6421 | 0.5986 | 0.080* | |
C4 | 0.1213 (4) | 0.6540 (3) | 0.6864 (2) | 0.0768 (12) | |
H4 | 0.0471 | 0.6694 | 0.7101 | 0.092* | |
C5 | 0.2377 (4) | 0.6470 (3) | 0.71827 (19) | 0.0756 (11) | |
H5 | 0.2422 | 0.6578 | 0.7636 | 0.091* | |
C6 | 0.3494 (3) | 0.6241 (3) | 0.68326 (16) | 0.0567 (9) | |
H6 | 0.4281 | 0.6182 | 0.7050 | 0.068* | |
O7 | 0.44380 (18) | 0.58949 (16) | 0.57589 (10) | 0.0516 (6) | |
C8 | 0.5707 (3) | 0.5894 (2) | 0.60379 (14) | 0.0487 (8) | |
H8A | 0.5792 | 0.5381 | 0.6360 | 0.058* | |
H8B | 0.5880 | 0.6503 | 0.6256 | 0.058* | |
C9 | 0.6631 (3) | 0.5744 (2) | 0.54734 (16) | 0.0514 (8) | |
H9A | 0.6427 | 0.5145 | 0.5250 | 0.062* | |
H9B | 0.7504 | 0.5696 | 0.5644 | 0.062* | |
C10 | 0.6554 (3) | 0.6566 (2) | 0.49855 (15) | 0.0478 (7) | |
H10A | 0.5687 | 0.6602 | 0.4806 | 0.057* | |
H10B | 0.6732 | 0.7167 | 0.5213 | 0.057* | |
N11 | 0.7491 (2) | 0.64405 (17) | 0.44343 (11) | 0.0400 (6) | |
C12 | 0.7086 (3) | 0.6251 (2) | 0.38199 (15) | 0.0440 (7) | |
H12 | 0.6206 | 0.6203 | 0.3734 | 0.053* | |
C13 | 0.7952 (3) | 0.6126 (2) | 0.33169 (15) | 0.0469 (7) | |
H13 | 0.7657 | 0.5996 | 0.2892 | 0.056* | |
C14 | 0.9257 (3) | 0.6192 (2) | 0.34333 (15) | 0.0439 (7) | |
C15 | 0.9652 (3) | 0.6400 (2) | 0.40727 (15) | 0.0500 (8) | |
H15 | 1.0527 | 0.6449 | 0.4169 | 0.060* | |
C16 | 0.8761 (3) | 0.6533 (2) | 0.45620 (16) | 0.0493 (8) | |
H16 | 0.9033 | 0.6688 | 0.4987 | 0.059* | |
C17 | 1.0219 (3) | 0.6050 (3) | 0.28885 (17) | 0.0680 (10) | |
H17A | 1.0431 | 0.5379 | 0.2854 | 0.102* | |
H17B | 1.0986 | 0.6411 | 0.2984 | 0.102* | |
H17C | 0.9856 | 0.6268 | 0.2478 | 0.102* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Br1 | 0.0428 (2) | 0.0664 (2) | 0.0649 (2) | −0.00036 (16) | 0.00019 (15) | −0.00230 (18) |
C1 | 0.0509 (17) | 0.0394 (16) | 0.0444 (17) | −0.0034 (14) | 0.0090 (15) | 0.0015 (14) |
C2 | 0.0513 (18) | 0.0434 (19) | 0.0544 (18) | 0.0051 (15) | 0.0028 (16) | 0.0044 (15) |
C3 | 0.0530 (19) | 0.057 (2) | 0.089 (3) | 0.0066 (18) | 0.014 (2) | 0.012 (2) |
C4 | 0.073 (3) | 0.068 (3) | 0.089 (3) | 0.002 (2) | 0.043 (2) | 0.005 (2) |
C5 | 0.104 (3) | 0.069 (3) | 0.053 (2) | −0.011 (2) | 0.030 (2) | −0.0030 (19) |
C6 | 0.066 (2) | 0.062 (2) | 0.0421 (18) | −0.0088 (17) | 0.0079 (16) | −0.0033 (16) |
O7 | 0.0421 (11) | 0.0718 (16) | 0.0410 (11) | 0.0003 (10) | 0.0042 (10) | −0.0120 (11) |
C8 | 0.0472 (17) | 0.054 (2) | 0.0446 (17) | −0.0009 (15) | −0.0007 (14) | 0.0019 (15) |
C9 | 0.0454 (17) | 0.0531 (19) | 0.0557 (19) | 0.0045 (15) | 0.0050 (15) | 0.0003 (16) |
C10 | 0.0431 (16) | 0.0490 (18) | 0.0513 (18) | 0.0030 (14) | 0.0041 (14) | −0.0031 (15) |
N11 | 0.0347 (12) | 0.0386 (14) | 0.0468 (14) | 0.0002 (10) | 0.0003 (11) | −0.0012 (11) |
C12 | 0.0374 (15) | 0.0456 (18) | 0.0489 (18) | −0.0023 (13) | −0.0103 (14) | 0.0005 (15) |
C13 | 0.0490 (17) | 0.0508 (19) | 0.0407 (16) | −0.0033 (15) | −0.0055 (14) | −0.0008 (14) |
C14 | 0.0466 (16) | 0.0400 (17) | 0.0452 (17) | −0.0042 (14) | 0.0036 (14) | 0.0014 (14) |
C15 | 0.0324 (15) | 0.062 (2) | 0.0554 (19) | −0.0070 (15) | −0.0019 (14) | −0.0028 (16) |
C16 | 0.0410 (16) | 0.061 (2) | 0.0462 (18) | −0.0061 (15) | −0.0059 (14) | −0.0058 (16) |
C17 | 0.062 (2) | 0.082 (3) | 0.059 (2) | −0.007 (2) | 0.0151 (18) | −0.0050 (19) |
C1—O7 | 1.362 (3) | C9—H9B | 0.9700 |
C1—C2 | 1.383 (4) | C10—N11 | 1.488 (4) |
C1—C6 | 1.384 (4) | C10—H10A | 0.9700 |
C2—C3 | 1.371 (5) | C10—H10B | 0.9700 |
C2—H2 | 0.9300 | N11—C12 | 1.337 (3) |
C3—C4 | 1.364 (5) | N11—C16 | 1.347 (4) |
C3—H3 | 0.9300 | C12—C13 | 1.368 (4) |
C4—C5 | 1.371 (6) | C12—H12 | 0.9300 |
C4—H4 | 0.9300 | C13—C14 | 1.375 (4) |
C5—C6 | 1.393 (5) | C13—H13 | 0.9300 |
C5—H5 | 0.9300 | C14—C15 | 1.386 (4) |
C6—H6 | 0.9300 | C14—C17 | 1.498 (4) |
O7—C8 | 1.431 (3) | C15—C16 | 1.365 (4) |
C8—C9 | 1.505 (4) | C15—H15 | 0.9300 |
C8—H8A | 0.9700 | C16—H16 | 0.9300 |
C8—H8B | 0.9700 | C17—H17A | 0.9600 |
C9—C10 | 1.511 (4) | C17—H17B | 0.9600 |
C9—H9A | 0.9700 | C17—H17C | 0.9600 |
O7—C1—C2 | 115.6 (3) | N11—C10—C9 | 111.4 (2) |
O7—C1—C6 | 124.3 (3) | N11—C10—H10A | 109.3 |
C2—C1—C6 | 120.0 (3) | C9—C10—H10A | 109.3 |
C3—C2—C1 | 119.8 (3) | N11—C10—H10B | 109.3 |
C3—C2—H2 | 120.1 | C9—C10—H10B | 109.3 |
C1—C2—H2 | 120.1 | H10A—C10—H10B | 108.0 |
C4—C3—C2 | 120.9 (4) | C12—N11—C16 | 120.2 (2) |
C4—C3—H3 | 119.5 | C12—N11—C10 | 120.9 (2) |
C2—C3—H3 | 119.5 | C16—N11—C10 | 118.9 (2) |
C3—C4—C5 | 119.8 (4) | N11—C12—C13 | 120.6 (3) |
C3—C4—H4 | 120.1 | N11—C12—H12 | 119.7 |
C5—C4—H4 | 120.1 | C13—C12—H12 | 119.7 |
C4—C5—C6 | 120.6 (3) | C12—C13—C14 | 120.7 (3) |
C4—C5—H5 | 119.7 | C12—C13—H13 | 119.7 |
C6—C5—H5 | 119.7 | C14—C13—H13 | 119.7 |
C1—C6—C5 | 118.9 (3) | C13—C14—C15 | 117.6 (3) |
C1—C6—H6 | 120.6 | C13—C14—C17 | 121.3 (3) |
C5—C6—H6 | 120.6 | C15—C14—C17 | 121.1 (3) |
C1—O7—C8 | 119.0 (2) | C16—C15—C14 | 120.3 (3) |
O7—C8—C9 | 106.6 (2) | C16—C15—H15 | 119.9 |
O7—C8—H8A | 110.4 | C14—C15—H15 | 119.9 |
C9—C8—H8A | 110.4 | N11—C16—C15 | 120.6 (3) |
O7—C8—H8B | 110.4 | N11—C16—H16 | 119.7 |
C9—C8—H8B | 110.4 | C15—C16—H16 | 119.7 |
H8A—C8—H8B | 108.6 | C14—C17—H17A | 109.5 |
C8—C9—C10 | 110.9 (3) | C14—C17—H17B | 109.5 |
C8—C9—H9A | 109.5 | H17A—C17—H17B | 109.5 |
C10—C9—H9A | 109.5 | C14—C17—H17C | 109.5 |
C8—C9—H9B | 109.5 | H17A—C17—H17C | 109.5 |
C10—C9—H9B | 109.5 | H17B—C17—H17C | 109.5 |
H9A—C9—H9B | 108.1 | ||
O7—C1—C2—C3 | −179.4 (3) | C9—C10—N11—C12 | 111.0 (3) |
C6—C1—C2—C3 | 0.5 (5) | C9—C10—N11—C16 | −69.8 (3) |
C1—C2—C3—C4 | 0.7 (5) | C16—N11—C12—C13 | 1.5 (4) |
C2—C3—C4—C5 | −1.0 (6) | C10—N11—C12—C13 | −179.3 (3) |
C3—C4—C5—C6 | 0.0 (6) | N11—C12—C13—C14 | 0.1 (5) |
O7—C1—C6—C5 | 178.5 (3) | C12—C13—C14—C15 | −0.8 (5) |
C2—C1—C6—C5 | −1.4 (5) | C12—C13—C14—C17 | 179.5 (3) |
C4—C5—C6—C1 | 1.2 (5) | C13—C14—C15—C16 | 0.0 (5) |
C2—C1—O7—C8 | 174.7 (3) | C17—C14—C15—C16 | 179.6 (3) |
C6—C1—O7—C8 | −5.3 (4) | C12—N11—C16—C15 | −2.4 (5) |
C1—O7—C8—C9 | −174.5 (3) | C10—N11—C16—C15 | 178.4 (3) |
O7—C8—C9—C10 | 62.9 (3) | C14—C15—C16—N11 | 1.6 (5) |
C8—C9—C10—N11 | 178.4 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
C10—H10A···O7 | 0.97 | 2.52 | 2.850 (3) | 100 |
C10—H10B···Br1i | 0.97 | 2.89 | 3.735 (3) | 146 |
C10—H10A···Br1 | 0.97 | 3.11 | 4.043 (3) | 163 |
C12—H12···Br1 | 0.93 | 3.08 | 3.940 (3) | 154 |
C15—H15···Br1ii | 0.93 | 3.07 | 3.931 (3) | 155 |
C17—H17B···Br1ii | 0.96 | 3.08 | 3.956 (4) | 152 |
Symmetry codes: (i) x+1/2, −y+3/2, −z+1; (ii) x+1, y, z. |
Ionic liquid | Anion | Chemical shift for Ha | Chemical shift for Hb |
1 | Br- | d, 9.23 | d, 7.67 |
2 | NO3- | d, 9.22 | d, 7.66 |
3 | CF3CO2- | d, 9.09 | d, 7.65 |
4 | PF6- | d, 8.94 | d, 7.94 |
5 | SCN- | d, 8.82 | d, 7.80 |
6 | N(CN)2- | d, 8.91 | d, 7.75 |
7 | BF4- | d, 8.60 | d, 7.69 |
This study | Br- | d, 8.48 | d, 7.66 |
*Messali (2015). |
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