(2-Ethoxy­carbonyl-3,5-di­hydroxy­phenyl)­acetic acid monohydrate, an intermediate in the Pechmann reaction

The title compound, C₁₁H₁₂O₆·H₂O, contains a water mol­ecule of hydration and consists of a mostly planar six-membered ring and pendant ester, with a nearly perpendicular orientation of the carboxyl­ic acid group. The structure of this compound was incorrectly reported in the early literature. The crystal structure involves a variety of hydrogen bonds.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.045
• wR factor = 0.113
• Data-to-parameter ratio = 12.3

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

The Pechmann reaction (Cornelius & von Pechmann, 1886) (see Scheme) was one of the earliest biomimetric syntheses, and involves conversion of an aliphatic ester to an aromatic phenolic acid. The reaction and variants find wide application in classical synthetic chemistry. While repeating the reaction of the Scheme (R = Et) following a more recent procedure (Theilacker & Schmid, 1950), we isolated about 5% of a colorless crystalline fraction from the acid hydrolysis that was soluble in hot water but insoluble in chloroform. Initially thought to be inorganic, the material after recrystallization from water fused about 443 K and melted completely by 473 K. The compound slowly turned brown on standing in air.

X-Ray crystallographic analysis revealed the monohydrated structure, (I), shown below, arising in the second step from incomplete hydrolysis and decarboxylation.

Compound (I) was not found in the Cambridge Structural Database (Allen, 2002). However, Jerdan (1899) described a number of intermediates from the Pechmann reaction and their transformation products. He ascribed structure (I) to one of them melting at 417–419 K. Most interestingly, Jerdan described another intermediate, 4-monoethylic hydrogen para-orcinoldicarboxylate, as a monohydrate melting at 463 K that was soluble in water but insoluble in chloroform. He assigned structure (II) to this compound. Since his description closely matches the properties of our product, it is likely that Jerdan's assignments are incorrect. In fact, some of Jerdan's other intermediates were also reassigned (Asahina & Nogami, 1940; Theilacker & Schmid, 1950). Compound (I) was previously used as a reactant to form 2,4-dihydroxy-6-methylbenzoic acid ethyl ester (Asahina & Nogami, 1942).

The water molecule of solvation is stabilized by hydrogen bonds (Table 1), by interaction with the hydroxy groups on the acid as is normally the case with compounds containing water molecules of solvation. This results in a chain structure with the hydroxy part of the acid molecule pointing to and interacting with water molecules of solvation and the hydrophobic end of the acid molecules on adjacent chains facing each other. Parallel chains are held together by the expected carboxylic acid dimerization via hydrogen bonding.

S2. Experimental

Crystals of the title compound were obtained by recrystallization from water of the product obtained following a literature procedure (Theilacker & Schmid, 1950).

S3. Refinement

The water H atoms were refined idependently and resulted in the O—H distances listed in Table 1 and an H—O—H angle of 109 (3)°.

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

Fig. 1. ORTEP-3 (Farrugia, 1997) view of (I), shown with 50% probability displacement ellipsoids. H atoms are represented by spheres of arbitrary radii. Hydrogen bonds are indicated by dashed lines.

(I)

Crystal data

C11H12O6·H2O	F(000) = 544
Mr = 258.22	Dx = 1.418 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 25 reflections
a = 12.091 (3) Å	θ = 10–15°
b = 7.658 (1) Å	µ = 0.12 mm^−1
c = 13.784 (2) Å	T = 293 K
β = 108.57 (1)°	Prism, white
V = 1209.8 (4) Å^3	0.20 × 0.15 × 0.10 mm
Z = 4

Data collection

Enraf Nonius TurboCAD-4 diffractometer	Rint = 0.027
non–profiled ω/2θ scans	θmax = 25.0°, θmin = 1.8°
Absorption correction: ψ scan (North et al., 1968)	h = 0→14
Tmin = 0.976, Tmax = 0.988	k = 0→9
2218 measured reflections	l = −16→15
2113 independent reflections	3 standard reflections every 166 min
1235 reflections with I > 2σ(I)	intensity decay: 2%

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.045	w = 1/[σ^2(Fo^2) + (0.0485P)^2 + 0.1688P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.113	(Δ/σ)max < 0.001
S = 1.01	Δρmax = 0.15 e Å^−3
2113 reflections	Δρmin = −0.20 e Å^−3
172 parameters

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.1839 (2)	0.2728 (3)	0.98609 (17)	0.0351 (6)
C2	0.2156 (2)	0.4505 (3)	1.00941 (17)	0.0352 (6)
C3	0.1719 (2)	0.5364 (3)	1.08049 (19)	0.0390 (6)
O3	0.19671 (18)	0.7060 (2)	1.10699 (14)	0.0577 (6)
H31	0.2347	0.7476	1.0728	0.073 (11)*
C4	0.1003 (2)	0.4521 (3)	1.12645 (19)	0.0408 (7)
H4	0.0719	0.5112	1.1725	0.049*
O5	0.00048 (16)	0.1898 (2)	1.14546 (14)	0.0548 (6)
H5	−0.0199	0.2541	1.1842	0.082*
C5	0.0716 (2)	0.2799 (3)	1.10322 (19)	0.0398 (6)
C6	0.1139 (2)	0.1921 (3)	1.03436 (19)	0.0396 (6)
H6	0.0944	0.0752	1.0203	0.048*
C11	0.2227 (2)	0.1641 (3)	0.91090 (18)	0.0385 (6)
H11A	0.1718	0.0634	0.8914	0.046*
H11B	0.2131	0.2329	0.8497	0.046*
C12	0.3460 (2)	0.1020 (3)	0.9505 (2)	0.0376 (6)
O11	0.38513 (16)	0.0404 (2)	0.87881 (12)	0.0509 (5)
H11C	0.4528	0.0077	0.9045	0.076*
O12	0.40287 (15)	0.1019 (2)	1.04138 (14)	0.0485 (5)
C21	0.2896 (2)	0.5544 (4)	0.96459 (19)	0.0422 (7)
C22	0.4083 (3)	0.5684 (4)	0.8565 (2)	0.0575 (8)
H22A	0.4749	0.6181	0.9086	0.069*
H22B	0.3628	0.6629	0.8162	0.069*
C23	0.4478 (4)	0.4484 (5)	0.7903 (3)	0.0989 (14)
H23A	0.4951	0.5113	0.7579	0.148*
H23B	0.3812	0.4004	0.739	0.148*
H23C	0.4928	0.3556	0.831	0.148*
O21	0.30898 (19)	0.7097 (3)	0.98169 (16)	0.0666 (7)
O22	0.33670 (15)	0.4666 (2)	0.90433 (13)	0.0450 (5)
O100	0.0957 (2)	0.8752 (3)	1.24130 (17)	0.0608 (6)
H101	0.061 (3)	0.970 (6)	1.211 (3)	0.119 (17)*
H102	0.125 (3)	0.824 (5)	1.203 (3)	0.094 (14)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0321 (14)	0.0357 (15)	0.0377 (14)	0.0009 (12)	0.0114 (12)	−0.0033 (12)
C2	0.0356 (15)	0.0352 (15)	0.0383 (13)	0.0000 (12)	0.0168 (12)	−0.0002 (12)
C3	0.0469 (16)	0.0293 (14)	0.0442 (14)	0.0010 (13)	0.0195 (13)	−0.0023 (12)
O3	0.0811 (15)	0.0339 (11)	0.0776 (14)	−0.0105 (10)	0.0529 (13)	−0.0110 (10)
C4	0.0485 (17)	0.0361 (15)	0.0459 (15)	0.0041 (13)	0.0262 (14)	−0.0023 (12)
O5	0.0665 (14)	0.0411 (11)	0.0752 (14)	−0.0074 (10)	0.0487 (12)	−0.0028 (10)
C5	0.0382 (15)	0.0392 (16)	0.0481 (15)	0.0017 (13)	0.0221 (13)	0.0062 (13)
C6	0.0394 (16)	0.0313 (14)	0.0512 (15)	−0.0030 (12)	0.0188 (13)	−0.0053 (13)
C11	0.0387 (15)	0.0377 (15)	0.0417 (14)	−0.0048 (12)	0.0163 (13)	−0.0094 (12)
C12	0.0458 (16)	0.0300 (14)	0.0441 (16)	−0.0030 (13)	0.0245 (14)	−0.0021 (12)
O11	0.0560 (12)	0.0604 (13)	0.0443 (10)	0.0147 (10)	0.0271 (10)	−0.0016 (9)
O12	0.0508 (12)	0.0543 (12)	0.0433 (11)	0.0119 (10)	0.0188 (9)	−0.0049 (10)
C21	0.0447 (17)	0.0406 (17)	0.0443 (15)	−0.0032 (14)	0.0185 (14)	−0.0015 (13)
C22	0.066 (2)	0.057 (2)	0.0620 (18)	−0.0099 (17)	0.0393 (17)	0.0043 (16)
C23	0.140 (4)	0.097 (3)	0.101 (3)	−0.029 (3)	0.095 (3)	−0.018 (2)
O21	0.0930 (17)	0.0403 (13)	0.0894 (15)	−0.0190 (11)	0.0614 (14)	−0.0129 (11)
O22	0.0514 (11)	0.0432 (11)	0.0514 (10)	−0.0050 (9)	0.0319 (10)	−0.0012 (9)
O100	0.0777 (16)	0.0527 (14)	0.0704 (14)	0.0089 (13)	0.0495 (14)	0.0057 (12)

Geometric parameters (Å, º)

C1—C6	1.379 (3)	C11—H11B	0.97
C1—C2	1.422 (3)	C12—O12	1.222 (3)
C1—C11	1.515 (3)	C12—O11	1.312 (3)
C2—C3	1.415 (3)	O11—H11C	0.82
C2—C21	1.472 (3)	C21—O21	1.221 (3)
C3—O3	1.357 (3)	C21—O22	1.330 (3)
C3—C4	1.385 (3)	C22—O22	1.468 (3)
O3—H31	0.82	C22—C23	1.478 (4)
C4—C5	1.375 (3)	C22—H22A	0.97
C4—H4	0.93	C22—H22B	0.97
O5—C5	1.369 (3)	C23—H23A	0.96
O5—H5	0.82	C23—H23B	0.96
C5—C6	1.387 (3)	C23—H23C	0.96
C6—H6	0.93	O100—H101	0.88 (4)
C11—C12	1.494 (4)	O100—H102	0.82 (3)
C11—H11A	0.97
C6—C1—C2	118.8 (2)	C1—C11—H11B	108.6
C6—C1—C11	117.1 (2)	H11A—C11—H11B	107.6
C2—C1—C11	124.1 (2)	O12—C12—O11	123.5 (2)
C3—C2—C1	117.9 (2)	O12—C12—C11	123.1 (2)
C3—C2—C21	116.7 (2)	O11—C12—C11	113.4 (2)
C1—C2—C21	125.3 (2)	C12—O11—H11C	109.5
O3—C3—C4	116.1 (2)	O21—C21—O22	121.3 (2)
O3—C3—C2	122.2 (2)	O21—C21—C2	123.4 (2)
C4—C3—C2	121.7 (2)	O22—C21—C2	115.3 (2)
C3—O3—H31	109.5	O22—C22—C23	107.4 (2)
C5—C4—C3	119.3 (2)	O22—C22—H22A	110.2
C5—C4—H4	120.4	C23—C22—H22A	110.2
C3—C4—H4	120.4	O22—C22—H22B	110.2
C5—O5—H5	109.5	C23—C22—H22B	110.2
O5—C5—C4	122.0 (2)	H22A—C22—H22B	108.5
O5—C5—C6	117.7 (2)	C22—C23—H23A	109.5
C4—C5—C6	120.3 (2)	C22—C23—H23B	109.5
C1—C6—C5	122.0 (2)	H23A—C23—H23B	109.5
C1—C6—H6	119	C22—C23—H23C	109.5
C5—C6—H6	119	H23A—C23—H23C	109.5
C12—C11—C1	114.5 (2)	H23B—C23—H23C	109.5
C12—C11—H11A	108.6	C21—O22—C22	116.3 (2)
C1—C11—H11A	108.6	H101—O100—H102	109 (3)
C12—C11—H11B	108.6

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H31···O21	0.82	1.78	2.514 (2)	147
O5—H5···O100^i	0.82	1.83	2.639 (3)	168
O11—H11C···O12^ii	0.82	1.86	2.678 (3)	171
O100—H101···O5^iii	0.88 (4)	1.94 (4)	2.812 (3)	174 (4)
O100—H102···O3	0.82 (3)	2.01 (4)	2.835 (3)	178 (4)

Symmetry codes: (i) −x, y−1/2, −z+5/2; (ii) −x+1, −y, −z+2; (iii) x, y+1, z.