6-Amino-3H-isobenzofuran-1-one

The mol­ecule of the title compound, C₈H₇NO₂, also known as 6-amino­phthalide, is essentially planar. In the crystal structure, the mol­ecules are connected into supra­molecular double chains via N—H...O hydrogen bonds that participate in eight-membered (...HNH...O)₂ synthons.

Key indicators

• Single-crystal X-ray study
• T = 153 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.042
• wR factor = 0.105
• Data-to-parameter ratio = 13.5

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S1. Comment

The title compound (I), Fig. 1, was synthesized as a precursor for the corresponding polyamide. The maximum deviation from the least-squares plane through the 11 non-hydrogen atoms in (I) is 0.020 (1) Å, for the C5 atom. The geometric parameters in (I) match closely those reported for the isomeric 5-aminophthalide compound (Yathirajan et al., 2005). The primary intermolecular interactions in the crystal structure of (I) are of the type N—H···O (Table 1). The presence of eight-membered {···HNH···O}₂ synthons leads to the formation of supramolecular double-chains aligned along the a direction (Fig. 2). This arrangement brings π-systems in close proximity and allows for the formation of π···π interactions that provide additional stability to the chains. The closest π···π contact of 3.7360 (15) Å occurs between Cg(O2, C1—C3, C8) and Cg(C3—C8) for symmetry operation: 1 - x, -y, 2 - z. The chains are linked by C—H···O interactions (Table 1) to form layers that stack along the c direction. Contacts between layers are of the type C—H···π so that C4—H4···Cg(C3—C8) = 2.74 Å, C4···Cg(C3—C8) = 3.4663 (18) Å with an angle at H = 134° for symmetry operation: 1/2 - x, -1/2 + y, 3/2 - z.

Related literature

For related literature, see: Yathirajan et al. (2005).

S2. Experimental

The reagents were purchased as indicated and used without further purification: phthalide (98%, Alfa Aesar), N-bromosuccinimide (NBS) (99%, Alfa Aesar), 2,2'-Azobis(2-methylpropionitrile) (AIBN) (98%, Aldrich), benzene (99%, EM Science), sulfuric acid (98%, Mallinckrodt), nitric acid (70%, EMD), acetic acid (99.7%, Mallinckrodt), benzylamine (99%, Aldrich), dichloroethane (Aldrich), ethyl acetate (EMD), hexane (EMD), and methanol (Fisher).

The title compound (I) was obtained from two step nitration-reduction sequence. To a 250 ml round bottom flask, fitted with magnetic stirbar and an ice/water cooling bath, phthalide (21.74 g, 162 mmol) was added. An ice-cold mixture of 70% nitric acid and concentrated sulfuric acid were added at such a rate that the temperature remained below 20°C. The reaction mixture was allowed to stand overnight at room temperature. The clear yellow solution was poured into ice-cold water (300 ml). The yellow precipitate was collected and recrystallized from glacial acetic acid to give 6-nitrophthalide (81%). In a 250 round bottom flask equipped with a stirbar, 6-nitrophthalide (4.90 g, 27.4 mmol) was dissolved in ethanol (100 ml) with heating. At the same time, ammonium chloride (14.78 g, 0.276 mol) was completely dissolved in water (40 ml). To an ethanol solution of iron powder (9.26 g, 0.166 mol) was added the 6-nitrophthalide solution, followed immediately by the ammonium chloride solution. This resulted in an exotherm and the reaction turned brown immediately. The reaction mixture was heated under reflux overnight, and cooled to room temperature. Ethyl acetate was then used to extract the product, and the organic extracts were then washed with sodium bicarbonate and water give a white powder as the product (65%). Light-yellow crystals of (I) were obtained by recrystallization from a methanol solution.

TLC R_f = 0.38 (50/50 hexane/ethyl acetate). ¹H NMR (500 MHz, CDCl₃) δ (p.p.m.) 5.23 (s, 2H, α-CH–), 6.99 (dd, 1H, aromatic 7-H, J₁ = 1.96 Hz, J₂ = 8.30 Hz), 7.14 (d, 1H, aromatic 5-H, J = 2.44 Hz), 7.25 (d, 1H, aromatic 4-H, J = 8.30 Hz). IR (cm^-1) 3500 (–NH₂), 3300 (–NH₂), 1727 (–COO), 1630, 1615, 1505, 1491, 1465, 1329, 1187, 1056, 989.

S3. Refinement

All the H atoms were included in the riding-model approximation, with C—H = 0.95–0.99 Å, N—H = 0.88 Å, and with U_iso(H) = 1.2U_eq(C) and 1.5U_eq(N).

Computing details

Data collection: CrystalClear (Rigaku/MSC, 2005); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Molecular structure of (I) showing atom-labelling scheme and displacement ellipsoids at the 50% probability level (arbitrary spheres for the H atoms).
	Fig. 2. View of the crystal packing in (I) highlighting the supramolecular double-chains mediated by hydrogen bonds, shown as orange-dashed lines. Colour code: red (oxygen), blue (nitrogen), grey (carbon) and green (hydrogen).

6-Amino-3H-isobenzofuran-1-one

Crystal data

C8H7NO2	F(000) = 312
Mr = 149.15	Dx = 1.424 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71070 Å
Hall symbol: -P 2yn	Cell parameters from 1986 reflections
a = 8.396 (2) Å	θ = 2.7–30.2°
b = 5.990 (2) Å	µ = 0.10 mm^−1
c = 14.012 (4) Å	T = 153 K
β = 99.242 (7)°	Prism, light yellow
V = 695.5 (4) Å^3	0.40 × 0.20 × 0.10 mm
Z = 4

Data collection

Rigaku AFC12κ/SATURN724 diffractometer	1370 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.020
Graphite monochromator	θmax = 26.5°, θmin = 2.7°
ω scans	h = −10→10
4579 measured reflections	k = −7→6
1436 independent reflections	l = −14→17

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.105	H-atom parameters constrained
S = 1.13	w = 1/[σ^2(Fo^2) + (0.0459P)^2 + 0.2023P] where P = (Fo^2 + 2Fc^2)/3
1436 reflections	(Δ/σ)max < 0.001
106 parameters	Δρmax = 0.21 e Å^−3
2 restraints	Δρmin = −0.15 e Å^−3

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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
O1	0.74553 (11)	0.30158 (17)	0.91253 (7)	0.0408 (3)
O2	0.71640 (11)	−0.03455 (17)	0.84229 (7)	0.0393 (3)
N1	0.10635 (15)	0.3245 (3)	0.94360 (11)	0.0529 (4)
H1N	0.0067	0.2770	0.9418	0.079*
H2N	0.1367	0.4437	0.9785	0.079*
C1	0.65841 (15)	0.1465 (2)	0.88321 (9)	0.0321 (3)
C2	0.58839 (16)	−0.1970 (2)	0.81381 (11)	0.0386 (3)
H2A	0.6135	−0.3405	0.8479	0.046*
H2B	0.5726	−0.2240	0.7432	0.046*
C3	0.44184 (15)	−0.0911 (2)	0.84286 (9)	0.0301 (3)
C4	0.28242 (16)	−0.1620 (2)	0.83663 (9)	0.0330 (3)
H4	0.2494	−0.3028	0.8091	0.040*
C5	0.17340 (15)	−0.0233 (2)	0.87133 (9)	0.0337 (3)
H5	0.0648	−0.0714	0.8677	0.040*
C6	0.21809 (15)	0.1874 (2)	0.91198 (9)	0.0339 (3)
C7	0.37826 (15)	0.2566 (2)	0.91822 (9)	0.0318 (3)
H7	0.4125	0.3972	0.9455	0.038*
C8	0.48546 (14)	0.1144 (2)	0.88350 (9)	0.0285 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0281 (5)	0.0427 (6)	0.0506 (6)	−0.0048 (4)	0.0037 (4)	−0.0033 (5)
O2	0.0287 (5)	0.0412 (6)	0.0494 (6)	0.0035 (4)	0.0102 (4)	−0.0034 (4)
N1	0.0270 (6)	0.0604 (9)	0.0721 (9)	0.0014 (6)	0.0100 (6)	−0.0306 (7)
C1	0.0268 (6)	0.0359 (7)	0.0334 (7)	0.0028 (5)	0.0044 (5)	0.0026 (5)
C2	0.0338 (7)	0.0351 (7)	0.0479 (8)	0.0029 (5)	0.0094 (6)	−0.0051 (6)
C3	0.0305 (7)	0.0299 (6)	0.0301 (6)	0.0021 (5)	0.0055 (5)	0.0010 (5)
C4	0.0340 (7)	0.0307 (6)	0.0339 (7)	−0.0030 (5)	0.0037 (5)	−0.0018 (5)
C5	0.0264 (6)	0.0399 (7)	0.0347 (7)	−0.0031 (5)	0.0049 (5)	−0.0005 (5)
C6	0.0275 (6)	0.0406 (7)	0.0331 (7)	0.0032 (5)	0.0035 (5)	−0.0053 (5)
C7	0.0274 (6)	0.0339 (7)	0.0330 (7)	0.0012 (5)	0.0018 (5)	−0.0062 (5)
C8	0.0259 (6)	0.0315 (6)	0.0276 (6)	0.0006 (5)	0.0024 (5)	0.0018 (5)

Geometric parameters (Å, º)

O1—C1	1.2123 (16)	C3—C8	1.3808 (18)
O2—C1	1.3535 (17)	C3—C4	1.3937 (18)
O2—C2	1.4570 (17)	C4—C5	1.3810 (19)
N1—C6	1.3726 (18)	C4—H4	0.9500
N1—H1N	0.8801	C5—C6	1.4104 (19)
N1—H2N	0.8801	C5—H5	0.9500
C1—C8	1.4654 (17)	C6—C7	1.3965 (18)
C2—C3	1.4976 (18)	C7—C8	1.3830 (17)
C2—H2A	0.9900	C7—H7	0.9500
C2—H2B	0.9900
C1—O2—C2	110.57 (10)	C5—C4—C3	118.60 (12)
C6—N1—H1N	119.5	C5—C4—H4	120.7
C6—N1—H2N	120.9	C3—C4—H4	120.7
H1N—N1—H2N	118	C4—C5—C6	122.15 (12)
O1—C1—O2	121.26 (12)	C4—C5—H5	118.9
O1—C1—C8	130.08 (12)	C6—C5—H5	118.9
O2—C1—C8	108.67 (11)	N1—C6—C7	120.22 (13)
O2—C2—C3	104.17 (11)	N1—C6—C5	120.95 (12)
O2—C2—H2A	110.9	C7—C6—C5	118.82 (12)
C3—C2—H2A	110.9	C8—C7—C6	118.02 (12)
O2—C2—H2B	110.9	C8—C7—H7	121.0
C3—C2—H2B	110.9	C6—C7—H7	121.0
H2A—C2—H2B	108.9	C3—C8—C7	123.33 (12)
C8—C3—C4	119.09 (12)	C3—C8—C1	108.25 (11)
C8—C3—C2	108.34 (11)	C7—C8—C1	128.42 (12)
C4—C3—C2	132.58 (13)
C2—O2—C1—O1	179.64 (12)	C5—C6—C7—C8	0.33 (19)
C2—O2—C1—C8	−0.42 (14)	C4—C3—C8—C7	−0.49 (19)
C1—O2—C2—C3	0.01 (14)	C2—C3—C8—C7	−179.98 (12)
O2—C2—C3—C8	0.42 (14)	C4—C3—C8—C1	178.81 (11)
O2—C2—C3—C4	−178.97 (13)	C2—C3—C8—C1	−0.68 (14)
C8—C3—C4—C5	0.13 (19)	C6—C7—C8—C3	0.26 (19)
C2—C3—C4—C5	179.47 (13)	C6—C7—C8—C1	−178.90 (12)
C3—C4—C5—C6	0.5 (2)	O1—C1—C8—C3	−179.37 (13)
C4—C5—C6—N1	178.26 (14)	O2—C1—C8—C3	0.70 (14)
C4—C5—C6—C7	−0.7 (2)	O1—C1—C8—C7	−0.1 (2)
N1—C6—C7—C8	−178.63 (13)	O2—C1—C8—C7	179.96 (12)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···O1^i	0.88	2.17	2.9937 (19)	156
N1—H2N···O1^ii	0.88	2.27	3.134 (2)	167
C2—H2A···O1^iii	0.99	2.51	3.477 (2)	164

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