4′-Chlorobiphenyl-4-yl 2,2,2-trichloroethyl sulfate

The title compound, C14H10Cl4O4S, is an intermediate in the synthesis of the PCB sulfate monoester of 4′-chloro-biphenyl-4-ol. Both the sulfate monoester and 4′-chloro-biphenyl-4-ol are metabolites of PCB 3 (4-chlorobiphenyl). There are two molecules with different conformations in the asymmetric unit. The solid state dihedral angles between the benzene rings are 18.52 (10) and 41.84 (16)° in the two molecules, whereas the dihedral angles between the least-squares plane of the sulfated benzene ring and O—S (Ar—C—O—S) are 66.2 (3) and 89.3 (3)°. The crystal was an inversion twin with a refined component fraction of 0.44 (7).


Data collection
Nonius KappaCCD diffractometer Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997) T min = 0.679, T max = 0.861 25566 measured reflections 6476 independent reflections 4862 reflections with I > 2(I) R int = 0.063 PCB congeners with a lower degree of chlorination are especially prone to undergo oxidative metabolism to hydroxylated (OH)-PCBs (Letcher et al., 2000). OH-PCBs can be further transformed to glucuronides (Tampal et al., 2002) or sulfates (Liu et al., 2006, Sacco & James, 2005. These PCB metabolites are more hydrophilic than PCBs and OH-PCBs and are expected to be more easily excreted. Despite the potential importance of sulfated PCB metabolites, PCB sulfate monoesters and analogous compounds have not been synthesized experimentally and their detailed molecular structure is unknown. Similarly, only few structures of hydroxylated chlorobiphenyl derivatives (Rissanen et al. 1988a(Rissanen et al. , 1988bLehmler et al., 2001Lehmler et al., , 2002Desiraju et al., 1979;Vyas et al., 2006) and sulfuric acid aryl mono esters (Brandao et al., 2005) have been reported.
Herein we report the crystal structure of the title compound, a trichloro-ethyl PCB sulfate diester intermediate of a putative sulfate metabolite of PCB3 (4-chlorobiphenyl). The asymmetric unit of the crystal structure contains two molecules with different conformations (Fig. 1), an observation that highlights the flexibility of PCB derivatives that lack multiple ortho chlorine substituents. The dihedral angles between the two benzene rings in the biphenyl moiety are 18.52 (10) (Shaikh et al., 2008). The calculated dihedral angle of the title compound is 41.2° (Shaikh et al., 2008), which is comparable to that of molecule B, but significantly larger than that of molecule A. The dihedral angle formed by the least-squares plane of the sulfated benzene ring and O1-S1 (Ar-C4-O1-S1) was 66.2 (3)° and 89.3 (3)° for molecules A and B, respectively. These dihedral angles are larger than the calculated Ar-C4-O1-S1 dihedral angle of approximately 54° (calculated with AM1 as implemented by ArgusLab, Version 4.0.1). Overall, these deviations from the energetically most favorable conformation of the title compound are due to crystal packing effects, which allow the molecule to adopt an energetically unfavorable conformation to maximize intermolecular interactions, and thus the lattice energy in the crystal.

Experimental
The title compound was synthesized from 4-chlorobiphenyl-4-ol by sulfation with 2,2,2-trichloroethyl sulfonyl chloride using 4-dimethylaminopyridine as catalyst (Liu et al. 2004). Crystals of the title compound suitable for crystal structure analysis were obtained from a methanolic solution by slowly evaporating the solvent.

Refinement
H atoms were found in difference Fourier maps and subsequently placed in idealized positions with constrained C-H distances of 0.99 Å (CH 2 ) and 0.95 Å (C Ar H) with U iso (H) values set to 1.2U eq of the attached C atom.
supplementary materials sup-2 The crystal was an inversion twin with a refined component fraction of 0.44 (7), i.e. essentially equal amounts of each component. Fig. 1