Comment

The title compound, (I), also known as (o-tolyloxy)acetic acid, has been described as an expectorant (Negwer, 1996), and several phenoxyacetic acid compounds are used as herbicides (Cserhati & Forgacs, 1998).

The atomic arrangement in (I) is shown in Fig. 1 and selected geometric parameters are given in Table 1. Apart from the H atoms, the molecule is essentially planar and the torsion angle with the greatest deviation from 0, or 180°, is C2-O1-C7-C8 = 175.6 (2)°.

Carboxylic acids normally form dimers or catemers and here, as expected for a simple monocarboxylic acid, dimers are formed by intermolecular hydrogen bonding involving the carboxylate groups. The pairs of molecules forming the dimers are related by a centre of symmetry and details of the hydrogen bonding are given in Table 2. As well as the dimeric R₂²(8) motif, a weak C-HO contact (Table 2) is present and this links two molecules about a centre of symmetry in an R₂²(14) formation (Fig. 2). Hence, atom O2 acts as both a donor and an acceptor. Indications of C-H bonding (Table 2) are also present as H7A is close to the centroid (Cg1) of the aromatic ring.

There are many similar examples of dimer formation involving carboxylate groups e.g. phenylacetic acid (Hodgson & Asplund, 1991) and 2,4,5-trimethylbenzoic acid (Barcon et al., 1997). The solid-state structures of related compounds, viz. (4-methylphenoxy)acetic acid (Kumar & Rao, 1982) and 3-(2-hydroxyphenyl)propionic acid (Begum et al., 1992), have also been determined.

Figure 1 The atomic arrangement in the molecule of (I), with the the atom-numbering scheme and 50% probability displacement ellipsoids.

Figure 2 A partial packing diagram of (I), showing R22(8) and R22(14) ring formations. [Symmetry codes: (*) -1 - x, -y, 1 - z; (#) -x, -y, 2 - z.]

Experimental

The title compound was obtained from Aldrich and was recrystallized from a mixture of methanol and ethanol.

Crystal data

C9H10O3 Mr = 166.17 Monoclinic, P21/c a = 5.1062 (5) Å b = 22.352 (2) Å c = 7.4014 (9) Å = 108.235 (5)° V = 802.33 (14) Å3 Z = 4 Dx = 1.376 Mg m-3 Mo K radiation Cell parameters from 2909 reflections = 3.0-27.5° = 0.10 mm-1 T = 150 (2) K Plate, colourless 0.40 × 0.24 × 0.06 mm

Data collection

Enraf-Nonius KappaCCD area detector and scans Absorption correction: multi-scan (SORTAV; Blessing, 1995) Tmin = 0.97, Tmax = 0.99 2908 measured reflections 1304 independent reflections 1006 reflections with I > 2(I) Rint = 0.055 max = 27.5° h = -6 5 k = -28 29 l = -9 9

Refinement

Refinement on F2 R[F2 > 2(F2)] = 0.078 wR(F2) = 0.230 S = 1.04 1304 reflections 115 parameters H atoms treated by a mixture of independent and constrained refinement w = 1/[2(Fo2) + (0.1765P)2] where P = (Fo2 + 2Fc2)/3 (/)max < 0.001 max = 0.36 e Å-3 min = -0.53 e Å-3 Extinction correction: SHELXL97 Extinction coefficient: 0.07 (2)

Table 1 Selected geometric parameters (Å, °) O1-C1 1.381 (3) O1-C7 1.415 (3) O2-C8 1.322 (3) O3-C8 1.219 (3) C1-O1-C7 116.32 (19) O1-C1-C2 114.7 (2) O3-C8-O2 124.4 (2) O3-C8-C7 124.8 (2) O2-C8-C7 110.8 (2) O1-C1-C2-C9 3.7 (4) C1-O1-C7-C8 175.6 (2)

Table 2 Hydrogen-bonding geometry (Å, °) D-HA D-H HA DA D-HA O2-H2O3i 0.93 (4) 1.69 (4) 2.618 (3) 172 (4) C6-H6O2ii 0.95 2.56 3.505 (3) 175 C7-H7ACg1iii 0.99 2.60 3.37 134 Symmetry codes: (i) -1-x,-y,1-z; (ii) -x,-y,2-z; (iii) x-1,y,z. Cg1 is the centroid of the aromatic ring.

The crystal diffracted very weakly and decomposed during data collection, hence data completeness is only 71%. The hydroxy (O2) H atom was refined isotropically. The C-H H atoms were allowed to ride on their attached C atoms: C-H distances were 0.95 Å (aromatic), 0.99 Å (methylene) and 0.98 Å (methyl), and U_iso(H) = 1.2U_eq(non-methyl C) or 1.4U_eq(methyl C).

Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: WinGX (Farrugia, 1999).