Propyl 4-amino­benzoate

Gutzwiller, A.J.; Hermann, C.K.F.; Harakas, G.N.

doi:10.1107/S2414314626004566

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 11| Part 5| May 2026| x260456

https://doi.org/10.1107/S2414314626004566

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Propyl 4-aminobenzoate

Alexander J. Gutzwiller,^a Christine K. F. Hermann ^a and George N. Harakas ^a ^*

^aPO Box 6949, Radford University, Radford, Virginia 24142, USA
^*Correspondence e-mail: [email protected]

(Received 28 April 2026; accepted 30 April 2026; online 7 May 2026)

The structure of the title compound, C₁₀H₁₃NO₂, shows the n-propyl group to be perpendicular to the remaining part of the molecule; carboxylate-C—O—C—C(n-propyl) torsion angle = −87.05 (19)°. In the crystal, amine-N—H⋯O(carbonyl) and weaker amine-N—H⋯N(amine) hydrogen bonding occurs within double layers parallel to the ab plane. The hydrogen atoms of the methyl group are disordered over two sets of sites in the ratio 0.89 (3) to 0.11 (3).

Keywords: crystal structure; hydrogen bonding.

CCDC reference: 2550860

Structure description

The reaction of 4-aminobenzoic acid with 1-propanol yielded the title compound n-propyl 4-aminobenzoate (risocaine). Risocaine, its isomer, isopropyl 4-aminobenzoate, and amines with similar structures have medical applications such as pain relievers (Priyanka et al., 2022 ).

The crystal structure we report complements the physical and spectroscopic data collected as part of a guided inquiry undergraduate Organic Chemistry laboratory experiment (Hermann et al., 2026 ). In this guided inquiry experiment, students synthesized and characterized solid esters, selected for ease of purification and handling. Students were provided with a list of possible carboxylic acids and alcohols but not the specific reactants assigned to each group. After synthesis, they compared the observed melting point range of their product to a reference table. Furthermore, students recorded the IR,¹H NMR, and ¹³C NMR spectra of their product to confirm their conclusions from the melting point range.

Referring to Fig. 1, the C9 atom of the n-propyl group is close to perpendicular to the carboxylate residue as seen in the C7—O1—C8—C9 torsion angle of −87.05 (19)°. The equivalent torsion angles for one of the terminal –CH₃ groups in isopropyl 4-aminobenzoate (two independent molecules) are −77.8 (4) and −86.5 (4)°, while the other –CH₃ groups approach coplanarity, i.e. 159.5 (3) and 152.5 (4)° (Priyanka et al., 2022). The carboxylate [the C2—C1—C7—O2 torsion angle = 176.86 (17)°] and amine [C2—C3—C4—N1 = 174.94 (17)°] groups are close to coplanar to the benzene ring to which they are connected.

Figure 1
The molecular structure of the title compound showing displacement ellipsoids at the 30% probability level. Only the major component of the disordered hydrogen atoms on C10 are shown.

The molecular packing (Fig. 2) shows hydrogen-bonding interactions between the amine functional group and the carbonyl group of the ester and weaker amine-N—H⋯N(amine) hydrogen bonding; distances and angle are listed in Table 1. The hydrogen bonding occurs within double layers that stack along the c axis.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯N1ⁱ	0.88 (2)	2.55 (2)	3.397 (3)	162 (2)
N1—H1B⋯O2ⁱⁱ	0.88 (2)	2.09 (2)	2.964 (2)	173 (2)
Symmetry codes: (i) $[-x-{\script{1\over 2}}, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) .

Figure 2
Crystal packing viewed along the b axis. Hydrogen-bonding interactions are shown as dashed lines.

Synthesis and crystallization

Referring to Fig. 3, the title compound was synthesized through a Fischer esterification. A mixture of 4-aminobenzoic acid (1.5 g), 1-propanol (10 ml), and concentrated sulfuric acid (1 ml) was refluxed in a 50 ml boiling flask for 1 h. The reaction mixture was allowed to cool; a solution of 10% sodium carbonate was added until a pH of 8 was obtained. The solution was chilled in an ice bath until a solid product was formed. The solid was isolated by vacuum filtration.

Figure 3
Reaction scheme for the title compound.

The yield was 0.864 grams (57.0%) with a melting point of 72.7°C, which compared to a literature value of 73–75°C. The IR and NMR spectra confirmed the structure (Hermann et al., 2026).

X-ray quality crystals were produced by dissolving the product into methanol, followed by adding an equal volume of hexanes. The solvent was allowed to evaporate over several days. A single-crystal was coated with NVH oil and mounted on a MiTeGen loop then cooled to −40 °C for data collection.

Refinement

Crystal data, data collection, and structure refinement details are summarized in Table 2. The hydrogen atoms on the methyl-C10 atom are disordered over two positions and refined to a 0.89 (3) to 0.11 (3) occupancy ratio.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₀H₁₃NO₂
M_r	179.21
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	233
a, b, c (Å)	8.5011 (3), 5.8300 (2), 19.7631 (8)
β (°)	95.453 (2)
V (Å³)	975.05 (6)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.09
Crystal size (mm)	0.41 × 0.21 × 0.21

Data collection
Diffractometer	Bruker D8
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.966, 0.982
No. of measured, independent and observed [I > 2σ(I)] reflections	37794, 2427, 2283
R_int	0.039
(sin θ/λ)_max (Å⁻¹)	0.668

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.069, 0.159, 1.17
No. of reflections	2427
No. of parameters	126
No. of restraints	5
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.39, −0.27
Computer programs: APEX3 and SAINT (Bruker, 2019 ), SHELXT2018/2 (Sheldrick, 2015a ), SHELXL2019/2 (Sheldrick, 2015b ) and ShelXle (Hübschle et al., 2011 ).

Structural data

CCDC reference: 2550860

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314626004566/tk4124sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314626004566/tk4124Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314626004566/tk4124Isup3.cml

checkCIF report

Computing details top

Propyl 4-aminobenzoate top

Crystal data top

C₁₀H₁₃NO₂	F(000) = 384
M_r = 179.21	D_x = 1.221 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 8.5011 (3) Å	Cell parameters from 9986 reflections
b = 5.8300 (2) Å	θ = 3.7–28.3°
c = 19.7631 (8) Å	µ = 0.09 mm⁻¹
β = 95.453 (2)°	T = 233 K
V = 975.05 (6) Å³	Block, colourless
Z = 4	0.41 × 0.21 × 0.21 mm

Data collection top

Bruker D8 diffractometer	2427 independent reflections
Radiation source: sealed tube	2283 reflections with I > 2σ(I)
Flat graphite monochromator	R_int = 0.039
Detector resolution: 7.391 pixels mm^-1	θ_max = 28.3°, θ_min = 3.7°
ω and φ scans	h = −11→11
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −7→7
T_min = 0.966, T_max = 0.982	l = −26→26
37794 measured reflections

Refinement top

Refinement on F²	Primary atom site location: Intrinsic Phasing
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.069	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.159	w = 1/[σ²(F_o²) + (0.0557P)² + 0.6285P] where P = (F_o² + 2F_c²)/3
S = 1.17	(Δ/σ)_max < 0.001
2427 reflections	Δρ_max = 0.39 e Å⁻³
126 parameters	Δρ_min = −0.27 e Å⁻³
5 restraints

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
O1	0.41184 (15)	0.7084 (2)	0.39339 (8)	0.0407 (4)
O2	0.52677 (15)	0.3933 (2)	0.35610 (7)	0.0420 (4)
N1	−0.21045 (19)	0.1716 (3)	0.29235 (10)	0.0450 (4)
H1A	−0.220 (3)	0.028 (3)	0.2790 (13)	0.068*
H1B	−0.287 (2)	0.229 (4)	0.3145 (13)	0.068*
C1	0.24626 (19)	0.4106 (3)	0.35136 (8)	0.0300 (4)
C2	0.1139 (2)	0.5332 (3)	0.36787 (10)	0.0362 (4)
H2	0.127429	0.673133	0.391334	0.043*
C3	−0.0363 (2)	0.4507 (3)	0.35001 (10)	0.0389 (4)
H3	−0.124141	0.534562	0.361780	0.047*
C4	−0.0597 (2)	0.2444 (3)	0.31471 (9)	0.0324 (4)
C5	0.0731 (2)	0.1194 (3)	0.29957 (9)	0.0327 (4)
H5	0.059756	−0.022164	0.276956	0.039*
C6	0.2229 (2)	0.2018 (3)	0.31749 (9)	0.0320 (4)
H6	0.310763	0.116125	0.306731	0.038*
C7	0.4082 (2)	0.4970 (3)	0.36686 (9)	0.0313 (4)
C8	0.5655 (2)	0.8188 (3)	0.40383 (11)	0.0403 (4)
H8A	0.551542	0.985495	0.400907	0.048*
H8B	0.629878	0.771708	0.367673	0.048*
C9	0.6508 (2)	0.7587 (4)	0.47167 (11)	0.0471 (5)
H9A	0.680761	0.596304	0.472127	0.057*
H9B	0.580694	0.783509	0.507594	0.057*
C10	0.7985 (3)	0.9069 (5)	0.48517 (14)	0.0621 (7)
H10A	0.866055	0.885591	0.448792	0.093*	0.89 (3)
H10B	0.855180	0.862316	0.528067	0.093*	0.89 (3)
H10C	0.768012	1.066875	0.487229	0.093*	0.89 (3)
H10D	0.793444	0.990931	0.527267	0.093*	0.11 (3)
H10E	0.804318	1.014205	0.447992	0.093*	0.11 (3)
H10F	0.891486	0.809646	0.488829	0.093*	0.11 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0293 (6)	0.0326 (7)	0.0598 (9)	0.0002 (5)	0.0014 (6)	−0.0065 (6)
O2	0.0275 (6)	0.0401 (8)	0.0582 (9)	0.0056 (5)	0.0037 (6)	−0.0025 (6)
N1	0.0287 (8)	0.0482 (10)	0.0585 (11)	−0.0060 (7)	0.0061 (7)	−0.0119 (9)
C1	0.0271 (8)	0.0291 (8)	0.0336 (8)	0.0033 (6)	0.0022 (6)	0.0025 (7)
C2	0.0315 (8)	0.0311 (9)	0.0457 (10)	0.0040 (7)	0.0017 (7)	−0.0074 (8)
C3	0.0270 (8)	0.0363 (10)	0.0538 (11)	0.0090 (7)	0.0054 (7)	−0.0077 (8)
C4	0.0273 (8)	0.0354 (9)	0.0344 (8)	0.0002 (7)	0.0035 (6)	0.0025 (7)
C5	0.0347 (9)	0.0290 (8)	0.0345 (8)	0.0001 (7)	0.0040 (7)	−0.0042 (7)
C6	0.0278 (8)	0.0311 (9)	0.0375 (9)	0.0057 (7)	0.0051 (6)	−0.0016 (7)
C7	0.0295 (8)	0.0299 (8)	0.0344 (8)	0.0032 (7)	0.0021 (6)	0.0042 (7)
C8	0.0355 (9)	0.0317 (9)	0.0534 (11)	−0.0063 (8)	0.0025 (8)	0.0034 (8)
C9	0.0427 (11)	0.0492 (12)	0.0489 (11)	−0.0090 (9)	0.0010 (9)	0.0010 (9)
C10	0.0493 (13)	0.0730 (17)	0.0619 (14)	−0.0224 (12)	−0.0059 (10)	−0.0058 (13)

Geometric parameters (Å, º) top

O1—C7	1.338 (2)	C2—C3	1.379 (3)
O1—C8	1.453 (2)	C3—C4	1.395 (3)
O2—C7	1.212 (2)	C4—C5	1.400 (2)
N1—C4	1.382 (2)	C5—C6	1.376 (2)
C1—C6	1.394 (2)	C8—C9	1.504 (3)
C1—C2	1.398 (2)	C9—C10	1.527 (3)
C1—C7	1.470 (2)

C7—O1—C8	116.80 (14)	C3—C4—C5	118.45 (16)
C6—C1—C2	118.51 (16)	C6—C5—C4	120.56 (16)
C6—C1—C7	119.17 (15)	C5—C6—C1	121.01 (16)
C2—C1—C7	122.30 (16)	O2—C7—O1	122.63 (16)
C3—C2—C1	120.55 (17)	O2—C7—C1	124.79 (17)
C2—C3—C4	120.88 (16)	O1—C7—C1	112.57 (14)
N1—C4—C3	120.56 (16)	O1—C8—C9	111.97 (16)
N1—C4—C5	120.92 (17)	C8—C9—C10	110.04 (19)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···N1ⁱ	0.88 (2)	2.55 (2)	3.397 (3)	162 (2)
N1—H1B···O2ⁱⁱ	0.88 (2)	2.09 (2)	2.964 (2)	173 (2)

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

References

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