Crystal structure of potassium (1S)-d-lyxit-1-ylsulfonate monohydrate

The anion has an open-chain structure in which the S atom, the C atoms of the sugar chain and the oxygen atom of the hydroxymethyl group form an essentially all-trans chain. A three-dimensional bonding network exists in the crystal structure involving coordination of two crystallographically independent potassium ions by O atoms (one cation being hexa- and the other octa-coordinate, with each lying on a twofold rotation axis), and extensive intermolecular O—H⋯O hydrogen bonding.


Chemical context
In aqueous solution, the bisulfite anion HSO 3 À exists in a complex, pH-dependent equilibrium with sulfurous acid H 2 SO 3 and the sulfite anion SO 3 2À . These sulfur compounds are widely used in the preservation of foodstuffs because of their anti-oxidant and antimicrobial properties. Dissolution of sodium or potassium metabisulfite (Na 2 S 2 O 5 or K 2 S 2 O 5 , respectively) in water affords a mixture of such compounds, along with sulfur dioxide, and they are widely used (e.g. as food additive E223) for their anti-oxidant, bactericidal and preservative properties. The reaction of the bisulfite ion with carbonyl compounds to give hydroxysulfonic acids has long been known as a method of aldehyde purification; less well recognized generally is that reaction of an aldehydo-sugar, which exists predominantly in a cyclic, hemi-acetal form, with a bisulfite anion affords the open-chain form of the carbohydrate in which the carbonyl group has undergone addition of the sulfur nucleophile. A possible role in the stabilization of food stuffs led to early studies (Gehman & Osman, 1954) and evidence for the acyclic nature of such compounds was first provided by Ingles (1959), who reported on such adducts from d-glucose, d-galactose, d-mannose, l-arabinose and l-rhamnose. However, conclusive proof of the acyclic nature of these bisulfite adducts was first given through the X-ray studies of Cole et al. (2001) who reported the crystal structures of d-glucose-and d-mannose-derived potassium sulfonates. Later studies by X-ray crystallography on the sodium sulfonate derived from d-glucose (Haines & Hughes, 2012) and the potassium sulfonates from d-galactose (Haines & Hughes, 2010) and d-ribose (Haines & Hughes, 2014) proved their acyclic nature and allowed, in each case, the configuration at the newly formed chiral centre to be determined.
The crystallization of the bisulfite adducts of aldoses requires reactions to be conducted in concentrated solution, and success can be dependent on the particular aldose and the choice of the alkali metal ion. Thus, we have prepared the potassium adduct from l-arabinose as described by Ingles (1959), having properties in agreement with those reported, but despite prolonged efforts have not succeeded in obtaining suitable crystals for X-ray determination. Our attempts to make a crystalline potassium sulfonate from d-xylose have not been successful. In contrast, d-ribose readily afforded suitable crystals (Haines & Hughes, 2014) and we were therefore prompted to investigate the reaction of the remaining pentose, d-lyxose, with the bisulfite ion, from which we isolated the nicely crystalline title product (see Scheme). We report here its crystal structure.

Structural commentary
The systematic name for the salt is potassium (1S,2S,3S,4R)-1,2,3,4,5-pentahydroxypentane-1-sulfonate monohydrate. The anion has an open-chain structure in which the S atom, the C atoms of the sugar chain and the O atom of the hydroxymethyl group form an essentially all-trans chain with the corre-sponding torsion angles lying between absolute values of 178.61 (12) (for C2-C3-C4-C5) and 157.75 (10) (for S1-C1-C2-C3). The newly formed chiral centre at C1 has the S configuration ( Fig. 1). For each lyxose residue, all hydroxy groups act as hydrogen-bond donors (Table 1). Atom H2O is involved in a bifurcated hydrogen bond to O11 in the same molecule and to O1 in a neighbouring molecule (at x, y, z À 1). Atom H1O is involved in hydrogen bonding to atom O9 of a water molecule, the H atoms of which are hydrogen-bonded to O5 and O12 of adjoining molecules. Two crystallographically independent potassium ions are present, each one lying on a twofold rotation axis, with one cation possessing a coordination sphere of six O atoms (assuming a cut-off distance of 3 Å ), four coming from two different sulfonate residues and two from O atoms of hydroxymethyl groups. The other cation is octacoordinate with oxygen atoms arising from two water molecules, two O atoms at new chiral centres at C1, and from two pairs of O atoms from different sulfonate residues. The  View of a molecule of a d-lyxose-KHSO 3 adduct and water molecule, indicating the atom-numbering scheme. The coordination spheres of the two potassium ions (both lying on twofold rotation axes), and the hydrogen bonds (dashed lines) on the lyxose unit, are shown. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Packing diagram, viewed along the c axis, showing the approximately parallel alignment of the d-lyxose chains between sheets of potassium ions and water molecules. Hydrogen bonds are shown as dashed lines; the fine line bonds are of bifurcated hydrogen bonds. Please note that the atoms labelled O2, O4 and O11 are eclipsing the real atoms of those names.
range of cation-oxygen bond lengths in the coordination spheres lie in the range 2.7787 (12) to 2.9855 (12) Å , but it should be noted that the designated hexacoordinate potassium ion does have two further neighbouring O atoms at 3.1131 (12) and 3.3824 (13) Å . Variability in the coordination spheres of potassium ions in related coordination environments was observed in the d-galactose bisulfite (Haines & Hughes, 2010), d-glucose bisulfite (Cole et al. 2001;Haines & Hughes, 2012) and dehydro-l-ascorbic acid bisulfite (Haines & Hughes, 2013) adducts, where the potassium ion is, respectively, six-, seven-and eight-coordinate. A view along the c axis ( Fig. 2) indicates the approximately parallel but alternating alignment of the d-lyxose chains between sheets of potassium ions and water molecules, with hydrogen bonds shown as dashed bonds except for the bifurcated hydrogen bonds which are denoted by fine line bonds. Cation coordination with d-lyxose sulfite anions and water molecules is depicted in Fig. 3 and a view along the a axis ( Fig. 4) shows the approximately parallel alignment of the d-lyxose chains.

Supramolecular features
A three-dimensional network exists in the crystal structure through coordination of (i) a hexacoordinate potassium ion with O atoms from four different d-lyxose bisulfite residues, (ii) an octacoordinate potassium ion with O atoms from four different d-lyxose bisulfite residues and two different water molecules, (iii) intermolecular hydrogen bonding between hydroxy groups of the d-lyxose moieties, and (iv) hydrogen bonding between a water molecule and two different lyxose residues. Despite spectroscopic evidence for a diastereoisomeric adduct in solution, only the 1S stereoisomer crystallized from the reaction mixture.

Spectroscopic findings
High-resolution mass spectrometry in negative-ion mode showed no significant peak for ([C 5 H 11 O 8 S 1 ] À ) at the calculated m/z of 231.0180, but a significant peak was observed at 213.0073 ([C 5 H 11 O 8 S -H 2 O] À ). A similar loss of water from the parent anion was observed in the case of the d-ribose adduct (Haines & Hughes, 2014). A peak at 149.0457 ([C 5 H 9 O 5 ] À ) arose from the parent sugar and the base peak was at 299.0979 ([C 10 H 19 O 10 ] À ). The latter corresponds to the ion of the product formed by reaction between the bisulfite adduct and d-lyxose with displacement of potassium bisulfite.
The 1 H NMR spectrum of the adduct in D 2 O showed the presence theand -pyranose forms of d-lyxose and the major and minor forms of the acyclic sulfonate in the % ratios of 35.48 : 11.29 : 48.39 : 4.84. The adduct undergoes partial hydrolysis in aqueous media; notably, it is present in a larger proportion in the more concentrated solution used for 13 C NMR spectroscopy (see below). A large J 2,3 coupling of 9.4 Hz suggests the conformation about the C2-C3 bond is similar in solution and the crystalline state.
In the 13 C NMR spectrum, signals for C1 nuclei allow identification of theand -pyranose forms of d-lyxose and the major ( C 82.20) and minor ( C 84.26) adducts in the ratios of 17.05 : 5.43 : 71.32 : 6.20, respectively.

Synthesis and crystallization
Water (0.5 ml) was added to potassium metabisulfite (0.37 g) which did not completely dissolve even on warming but which  View (slightly offset from along the c axis) of the sheets of potassium ions which are linked through coordinating d-lyxose-sulfite anions and water molecules. Symmetry codes are as in Fig. 1.

Special details
Experimental. CrysAlisPro, Agilent Technologies, Version 1.171.36.21 Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.