3-[(Z)-(4-Diethyl­amino-6-oxocyclo­hexa-2,4-dien-1-yl­idene)methyl­amino]benzoic acid

M T Swamy; B Narayana; H S Yathirajan; B K Sarojini; Maciej Kubicki

doi:10.1107/S1600536807064446

. 2007 Dec 6;64(Pt 1):o163–o164. doi: 10.1107/S1600536807064446

3-[(Z)-(4-Diethylamino-6-oxocyclohexa-2,4-dien-1-ylidene)methylamino]benzoic acid

M T Swamy ^a, B Narayana ^b, H S Yathirajan ^c, B K Sarojini ^d, Maciej Kubicki ^e,^*

PMCID: PMC2915231 PMID: 21200729

Abstract

The title compound, C₁₈H₂₀N₂O₃, crystallizes as the keto tautomer, unlike the vast majority of similar structures that have been reported that contain the hydroxy tautomer. There are two strong hydrogen bonds in the crystal structure, both accepted by the same carbonyl group: one intramolecular N—H⋯O and one intermolecular O—H⋯O. As a result, the carbonyl C=O distance is long, at 1.310 (2) Å, which may suggest the molecule has a significant zwitterionic character. The dihedral angle between the benzene ring planes is 15.05 (7)°. As a result of the intramolecular hydrogen bond, the bridging C—C=N—C group is almost coplanar with the benzene ring that has the diethylamino substituent [dihedral angle 2.35 (15)°].

Related literature

For related structures, see: Büyükgüngör et al. (2007 ▶); Odabaşoğlu et al. (2007 ▶); Yathirajan et al. (2007 ▶). For biological applications, see Hodnett & Dunn (1970 ▶); Misra et al. (1981 ▶); Agarwal et al. (1983 ▶); Varma et al. (1986 ▶); Singh & Dash (1988 ▶). For related literature, see: Allen (2002 ▶).

Experimental

Crystal data

C₁₈H₂₀N₂O₃
M _r = 312.36
Monoclinic,
a = 9.0904 (13) Å
b = 9.8993 (9) Å
c = 17.8208 (19) Å
β = 100.068 (2)°
V = 1579.0 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 295 (1) K
0.3 × 0.2 × 0.2 mm

Data collection

KUMA KM4CCD diffractometer
Absorption correction: none
12993 measured reflections
3514 independent reflections
2464 reflections with I > 2σ(I)
R _int = 0.020

Refinement

R[F ² > 2σ(F ²)] = 0.041
wR(F ²) = 0.124
S = 0.98
3514 reflections
283 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.25 e Å⁻³
Δρ_min = −0.17 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2006 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997 ▶); molecular graphics: XP (Siemens, 1989 ▶); software used to prepare material for publication: SHELXL97and WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536807064446/cs2063sup1.cif

e-64-0o163-sup1.cif^{(18.9KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536807064446/cs2063Isup2.hkl

e-64-0o163-Isup2.hkl^{(168.8KB, 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
N7—H7⋯O10	0.91 (2)	1.81 (2)	2.578 (2)	140 (2)
O1A2—H1A2⋯O10ⁱ	1.07 (3)	1.40 (3)	2.467 (1)	173 (2)
C5—H5⋯O1A1ⁱⁱ	0.98 (2)	2.48 (2)	3.449 (2)	174 (2)
C8—H8⋯O1A1ⁱⁱⁱ	0.96 (2)	2.63 (2)	3.436 (2)	142 (1)
C11—H11⋯O1A2^iv	0.98 (2)	2.60 (2)	3.244 (2)	124 (1)
C16—H16A⋯O1A1^v	1.00 (2)	2.60 (2)	3.570 (2)	163 (1)

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) .

Acknowledgments

MTS thanks Sambhram Institute of Technology for the research facilities.

supplementary crystallographic information

Comment

Schiff bases are used as substrates in the preparation of number of industrial and biologically active compounds via ring closure, cycloaddition and replacement reactions. Some Schiff base derivatives were reported to possess antimicrobial, anti-inflammatory and central nervous system activities. Moreover, Schiff bases are also known to have biological activities such as antimicrobial, antifungal, antitumor and as herbicides (e.g. Hodnett et al., 1970, Singh & Dash, 1988, Varma et al., (1986)). In the course of our studies of Schiff bases (e.g. Büyükgüngör et al., 2007; Odabaşoğlu et al., 2007; Yathirajan et al., 2007), the title compound, C₁₈H₂₀N₂O₃ was synthesized and its crystal structure is reported.

The title compound crystallizes as the keto-tautomer (Fig. 1), unlike the majority of the similar compounds. In the CSD (Allen, 2002) the hydroxy tautomers were found in 218 compounds while the keto ones only in 17 compounds (Version Nov. 2006, updates up to August 2007; only organic compounds). In this case the presence of the certain tautomer is proven by the succesful location and refinement of the hydrogen atom bonded to N7 nitrogen atom (Fig. 2a). Short and relatively linear intramolecular N—H···O hydrogen bond forms an almost planar (maximum deviation 0.017 (1) Å) six-membered ring. The same O10 oxygen atom which accepts the intramolecular hydrogen bond is involved in a very short (O···O distance is 2.467 (1) Å) intermolecular O—H···O hydrogen bond. As a result the C10—O10 bond of 1.310 (2)Å is significantly longer than a typical C?O double bond. CSD search results show that such elongation is typical for similar compounds, the mean C—O distance being 1.348 (17)Å for hydroxy tautomers, but it may also be as large as 1.299 (17)Å also for the keto-tautomers. Together with the observation of bond lengths around N7 atom this implies some degree of zwitterionic character of the molecule, with partial positive charge at N7—H7 group and negative at O10 atom. These perturbations disturb also the benzene ring. The ring A (C1 - C6) is closer to planarity than the ring B (C9 - C14). Maximum deviations from the least-squares planes are 0.0103 (11)Å for ring A and 0.0219 (12)Å for ring B. Also the bond lengths and angles are much more uniform within the ring A than in ring B.

The conformation of the molecule is described by the dihedral angles between benzene ring planes of 15.05 (7)°. As a result of the intramolecular hydrogen bond, the bridging C—C?N—C group is almost coplanar with the ring B (dihedral angle 2.35 (15)°). The COO group is significantly, by 21.73 (10)°, twisted with respect to its parent ring's plane. On the other end of the molecule, the C—N—C fragment is twisted by 17.0 (2)°, while the terminal C—C bonds are almost perpendicular to the CNC plane.

In the crystal structure the molecules are connected by strong intermolecular O—H···O hydrogen bonds into tapes along the y-direction. The O—H bond is significantly elongated, to 1.07 (3)Å due to the formation of the hydrogen bond (cf. Fig. 2 b). The tapes are connected by relatively strong inter-tape C—H···O hydrogen bonds into the layers (Fig. 3). Some additional C—H···O interactions (Table 1) also play a role in the building of the crystal structure.

Experimental

A mixture of 3-aminobenzoic acid (1.37 g, 0.01 mol) and 4-(diethylamino)-2-hydroxybenzaldehyde (1.92 g, 0.01 mol) in 25 ml of absolute ethanol containing 2 drops of 4 M sulfuric acid was refluxed for about 5 h. On cooling, the separated solid was filtered and recrystallized from DMF (m.p.: 483–485 K). The expected product was 3-({(1E)-[4-(diethylamino)-2-hydroxyphenyl]methylene}amino)benzoic acid, but the obtained product was the tautomeric form 3-({(Z)-[4-(diethylamino)-6-oxocyclohexa-2,4-dien-1-ylidene]methyl} amino)benzoic acid. Analysis for C₁₈H₂₀N₂O₃: Found (Calculated): C: 69.12 (69.21); H: 6.38 (6.45); N: 8.90% (8.97%).