Methyl 3,5,5,6,8,8-hexa­methyl-5,6,7,8-tetra­hydro­naphthalene-2-carboxyl­ate (AHTN–COOMe)

Paul Kuhlich; Franziska Emmerling; Christian Piechotta; Irene Nehls

doi:10.1107/S1600536811002601

. 2011 Jan 26;67(Pt 2):o485. doi: 10.1107/S1600536811002601

Methyl 3,5,5,6,8,8-hexamethyl-5,6,7,8-tetrahydronaphthalene-2-carboxylate (AHTN–COOMe)

Paul Kuhlich ^a, Franziska Emmerling ^a,^*, Christian Piechotta ^a, Irene Nehls ^a

PMCID: PMC3051644 PMID: 21523141

Abstract

Crystals of the title compound, C₁₈H₂₆O₂, were grown from ethyl acetate. Due to the racemic precursor, the title compound is also obtained as a racemate. Disorder was observed during structure refinement, originating from two possible half-chair conformations of the non-aromatic ring. The disorder was refined by introducing split positions in the cyclo-hexane ring regarding the two possible R and S-enantiomers at the chiral CH group [ratio 0.744 (3):0.256 (3)]. The crystal structure features pairs of inversion-related molecules connected by pairs of non-classical C—H⋯O hydrogen bonds.

Related literature

For the occurrence of the title compound in human breast milk and the fatty tissue of fish, see: Valdersnes et al. (2006 ▶). The title compound is the product of an esterification of 3,5,5,6,8,8-hexamethyl-5,6,7,8-tetrahydronaphthalene-2-carboxylic acid (AHTN—COOH) with methanol. For the synthesis of the acid, see: Kuhlich et al. (2010 ▶); Valdersnes et al. (2006 ▶). For the crystal structures of AHTN and AHTN–COOH, see: De Ridder et al. (1990 ▶) and Kuhlich et al. (2010 ▶), respectively. For the environmental occurrence and estrogenic activity of AHTN, see: Heberer (2003 ▶); Bitsch et al. (2002 ▶). For puckering parameters, see: Cremer & Pople (1975 ▶).

Experimental

Crystal data

C₁₈H₂₆O₂
M _r = 274.39
Monoclinic,
a = 11.5049 (11) Å
b = 11.9482 (5) Å
c = 12.1078 (13) Å
β = 102.612 (5)°
V = 1624.2 (2) Å³
Z = 4
Cu Kα radiation
μ = 0.55 mm⁻¹
T = 193 K
0.45 × 0.40 × 0.30 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
5083 measured reflections
3062 independent reflections
2856 reflections with I > 2σ(I)
R _int = 0.047
3 standard reflections every 60 min intensity decay: 3%

Refinement

R[F ² > 2σ(F ²)] = 0.054
wR(F ²) = 0.152
S = 1.03
3062 reflections
216 parameters
10 restraints
H-atom parameters constrained
Δρ_max = 0.29 e Å⁻³
Δρ_min = −0.26 e Å⁻³

Data collection: CAD-4 Software (Enraf–Nonius, 1989 ▶); cell refinement: CAD-4 Software; data reduction: CORINC (Dräger & Gattow, 1971 ▶); program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXTL (Sheldrick, 2008 ▶); molecular graphics: PLATON (Spek, 2009 ▶); software used to prepare material for publication: PLATON.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811002601/zl2346sup1.cif

e-67-0o485-sup1.cif^{(25.8KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811002601/zl2346Isup2.hkl

e-67-0o485-Isup2.hkl^{(150.3KB, hkl)}

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
C18—H26⋯O2ⁱ	0.98	2.47	3.397 (2)	157

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Symmetry code: (i) Inline graphic .

Acknowledgments

The authors want to thank Dr Dietmar Pfeifer (BAM, Berlin) for a helpful discussion regarding the interpretation of the NMR data.

supplementary crystallographic information

Comment

The title compound is the product of an esterification of 3,5,5,6,8,8-hexamethyl-5,6,7,8- tetrahydronaphthalene-2-carboxylic acid (AHTN-COOH) with methanol. AHTN-COOH itself is the product of a haloform reaction from 1-(3,5,5,6,8,8-hexamethyl-5,6,7,8- tetrahydronaphthalen-2-yl)ethan-1-one (AHTN) and sodium hypochlorite solution. Two slightly different syntheses of AHTN-COOH are described by Kuhlich et al. (2010) and by Valdersnes et al. (2006). The crystal structure of AHTN-COOH was described previously by Kuhlich et al. (2010). The crystal structure of AHTN was determined by De Ridder et al. (1990).

The title compound can either be obtained in a two-step synthesis, described by Valdersnes et al. (2006) or, as described here, in a one-step procedure (see Experimental).

AHTN itself is a widely used fragrance in cosmetics and cleaning products. It is introduced into the environment mainly via sewage treatment plants and can be found in surface water at low µg/L concentration (Heberer, 2003). It is in focus of interest due to its low estrogenic potential (Bitsch et al., 2002). Due to their structural similarities to AHTN, the title compound and AHTN-COOH might also have estrogenic or even toxic properties themselves.

The title compound was found in human breast milk and piscine fatty tissue by Valdersnes et al. (2006) proofing its ubiquitary occurrence.

The molecule crystallizes in the monoclinic space group P2₁/n. The molecular structure of the compound and the atom-labeling scheme are shown in Fig 1. The structure is disordered in the non aromatic ring. This disorder can be described as pseudo mirror-symmetric with respect to the aromatic ring's plane, resulting in two moieties (ratio 0.744 (3):0.256 (3)).

A general puckering analysis according to Cremer and Pople (Cremer & Pople, 1975) led to a half-chair conformation for both enantiomers. The S-enantiomer (C4-C5-C9-C10B-C11B-C12) has a puckering amplitude (Q) of 0.526 (6) Å and 0.502 (2) Å for the R-enantiomer (C4-C5-C9-C10-C11-C12), respectively. The maximum deviation from planarity for C11/C11B is -0.3587 (39) of the R-enantiomer and 0.3335 (14) of the S-enantiomer, respectively, proofing the nearly mirror-symmetric setup.

Each molecule is surrounded by three next neighbors, whereas the centroids of the molecules are arranged in sheets parallel to the (202) plane.

A detailed description of the disorder treatment can be found in the refinement section. The molecules form pairs via non classical hydrogen bonds (C18—H26···O2) (see dashed green bonds in Fig. 2).

Experimental

The methyl ester of 1-(3,5,5,6,8,8-hexamethyl-5,6,7,8- tetrahydronaphthalen-2-yl)ethan-1-one (AHTN) was synthesized by stirring a solution of 1 mg AHTN dissolved in 100 mL methanol and 50 mL 10% sodium hypochlorite solution at room temperature. After 24 h of stirring precipitated sodium chloride was dissolved with water and the organic compound was extracted three times with 50 mL ethyl acetate each. The organic solvents were combined, washed with water and dried with sodium sulfate. For single-crystal X-ray crystallography white and clear crystals of the title compound were grown by solvent evaporation (ethyl acetate) at ambient temperature over a period of three days [m.p. 348 K]. IR (ν, cm^-1): 1720(s), 1687(s), 1609(s), 1550(s), 1495(s), 1435(s), 1390(s), 1360(s), 1298(s), 1255(s), 1245(s), 1191(s), 1141(s), 1103(s), 1021(s), 980(s), 944(s), 916(s); ¹H-NMR (500 MHz, CD₃OD, TMS): δ = 7.83 (1H, s), 7.23 (1H, s), 3.83 (3H, s), 2.48 (3H, s), 1.85 (1H, ddq, J_H,H'=2.7 Hz, J_H,H''=13.2 Hz, J_H,Me=6.9 Hz), 1.61 (1H, dd, ²J=13.6 Hz, ³J=13.2 Hz), 1.38 (1H, dd, ²J=13.6 Hz, ³J=2.7 Hz), 1.30 (3H, s), 1.26 (3H, s), 1.22 (3H, s), 1.04 (3H, s), 0.98 (3H, d, J=6.9 Hz); ¹³C-NMR (125 MHz, CD₃OD, TMS): δ = 169.7, 151.8, 143.5, 137.8, 131.8, 130.2, 127.8, 52.1, 44.6, 38.9, 35.7, 34.9, 32.6, 32.4, 28.9, 25.1, 21.7, 17.1; (+)-ESI/MS: 275.6 (60) [M+H⁺], 297.5 (100) [M+Na⁺].