(S)-(−)-1-Phenyl­ethanaminium hexa­noate

Mary H Wood; Stuart M Clarke

doi:10.1107/S1600536812045746

. 2012 Nov 10;68(Pt 12):o3335. doi: 10.1107/S1600536812045746

(S)-(−)-1-Phenylethanaminium hexanoate

Mary H Wood ^a,^*, Stuart M Clarke ^a

PMCID: PMC3588937 PMID: 23476173

Abstract

A binary mixture of (S)-(−)-1-phenylethanamine and hexanoic acid was allowed to react to form the title salt, C₈H₁₂N⁺·C₆H₁₁O₂ ⁻. This crystal contains a 1:1 stoichiometric mixture of the acid- and amine-derived species and displays a chiral structure with N—H⋯O hydrogen-bonded chains propagating along the c-axis direction.

Related literature

For spectroscopic studies of acid–amine complexes, see: Karlsson et al. (2000 ▶); Paivarinta et al. (2000 ▶); Kohler et al. (1981 ▶); Smith et al. (2001 ▶, 2002 ▶); Klokkenburg et al. (2007 ▶). For recent diffraction studies of acid–amine complexes, see: Jefferson et al. (2011 ▶); Sun et al. (2011 ▶); Wood & Clarke (2012 ▶).

Experimental

Crystal data

C₈H₁₂N⁺·C₆H₁₁O₂ ⁻
M _r = 237.33
Hexagonal,
a = 19.5845 (5) Å
c = 6.6307 (2) Å
V = 2202.49 (10) Å³
Z = 6
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 180 K
0.46 × 0.05 × 0.05 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: multi-scan (SORTAV; Blessing, 1995 ▶) T _min = 0.740, T _max = 0.999
11638 measured reflections
1461 independent reflections
1270 reflections with I > 2σ(I)
R _int = 0.064

Refinement

R[F ² > 2σ(F ²)] = 0.040
wR(F ²) = 0.087
S = 1.06
1461 reflections
157 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.11 e Å⁻³
Δρ_min = −0.14 e Å⁻³

Data collection: COLLECT (Nonius, 1998 ▶); cell refinement: SCALEPACK (Otwinowski & Minor, 1997 ▶); data reduction: DENZO (Otwinowski & Minor, 1997 ▶) and SCALEPACK; program(s) used to solve structure: SIR92 (Altomare et al., 1994 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick 2008 ▶); molecular graphics: Mercury (Macrae et al., 2008 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Click here for additional data file.^{(17.1KB, cif)}

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812045746/mw2095sup1.cif

e-68-o3335-sup1.cif^{(17.1KB, cif)}

Click here for additional data file.^{(72.1KB, hkl)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812045746/mw2095Isup2.hkl

e-68-o3335-Isup2.hkl^{(72.1KB, hkl)}

Click here for additional data file.^{(5.4KB, cml)}

Supplementary material file. DOI: 10.1107/S1600536812045746/mw2095Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O2ⁱ	0.91	1.84	2.753 (3)	176
N1—H1B⋯O1	0.91	1.87	2.768 (3)	167
N1—H1C⋯O1ⁱⁱ	0.91	1.82	2.714 (2)	168

Open in a new tab

Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

The authors thank the Department of Chemistry, the BP Institute and the Oppenheimer Trust for financial and technical assistance and Dr J. E. Davies for collecting and analysing the X-ray data.

supplementary crystallographic information

Comment

The existence of stable acid:amine complexes formed from simple acid and amine reagents has been reported in the literature (Klokkenburg et al., 2007; Karlsson et al., 2000). Many examples adopt a 1:1 stoichiometry, although acid-rich complexes are not uncommon, with both 2:1 and 3:1 adducts observed in some cases (Sun et al., 2011; Kohler et al., 1981). Amine-rich complexes are thought to be inherently instable and thus unlikely to form (Paivarinta et al., 2000), although there is a report of a diamine complex formed between methylamine and dnsa (3,5-dinitrosalicyclic acid) due to deprotonation of the phenolic group in the acid (Smith et al., 2001; Smith et al., 2002).

The stability of complexes such as the title compound derives from the reactive exchange of a proton giving cations and anions with a strong electrostatic attraction. These ions subsequently interact via strong hydrogen-bond formation; each ammonium ion in the s-(-)-α-methylbenzylammonium hexanoate example is able to form three hydrogen bonds (shown in Figures 1, 2 and 3). For the acid-rich complexes, the hydrogen bonding is considered to extend over the three (or more) species involved.

This work follows previous findings of the formation of a 1:1 complex of octanoic acid and decylamine using the same method (Jefferson et al., 2011) as well as a 1:1 complex between benzylamine and hexanoic acid (Wood et al., 2012). This work focuses on the use of a chiral amine, s-(-)-α-methylbenzylamine.

Whilst spectroscopic studies identifying such acid:amine complexes are reasonably common, there still only a few examples of single-crystal X-ray data, as reported here. This may be attributed to the difficulty of growing suitable crystals as outlined in the experimental section.

Experimental

Hexanoic acid and s-(-)-methylbenzylamine, with purities of 99.5% and 99.8% respectively as determined by titration and GC, were purchased from Sigma Aldrich and used without further purification. The crystals were grown by pipetting a small volume (approximately 1 ml) of each into small vials and leaving within a larger vial along with a polypropylene nucleation surface under an inert atmosphere (to minimize amine reaction with atmospheric CO₂ (Sun et al., 2011)). After several weeks abundant crystal growth on the polypropylene surface was observed and a sample selected for X-ray characterization.

Elemental analysis of the crystalline sample gave values of 70.64%, 5.98%, 9.72% and 13.66% for carbon, nitrogen, hydrogen and oxygen respectively. For a 1:1 acid: amine complex, the expected values are: 70.85%, 5.90%, 9.77% and 13.48%, in excellent agreement.

The experimental sample temperature 180 K represents a compromise of improved thermal factors but avoiding sample fracture.