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Logo of actae2this articlesearchopen accesssubmitActa Crystallographica Section E: Crystallographic CommunicationsActa Crystallographica Section E: Crystallographic Communications
 
Acta Crystallogr E Crystallogr Commun. 2017 September 1; 73(Pt 9): 1333–1335.
Published online 2017 August 11. doi:  10.1107/S2056989017011513
PMCID: PMC5588574

Crystal structure of rac-4-[2-(tert-butyl­aza­nium­yl)-1-hy­droxy­eth­yl]-2-(hy­droxy­meth­yl)phenol benzoate

Abstract

The title salt, C13H22NO3 +·C7H5O2 , comprises one salbutamol cation {sys­tematic name: 4-[2-(tert-butyl­aza­nium­yl)-1-hy­droxy­eth­yl]-2-(hy­droxy­meth­yl)phenol} and a benzoate anion. The cation shows disorder of the hy­droxy group [occupancy ratio 0.738 (3):0.262 (3)] at the stereogenic C atom. The non-planar benzoate anion [the dihedral angle between the benzene ring and the carboxyl group is 11.30 (8)°] is linked to the salbutamol cation by a medium-strength O—H(...)O hydrogen bond. Other inter­molecular O—H(...)O and N—H(...)O hydrogen bonds of weaker nature give rise to [001] chains.

Keywords: crystal structure, salbutamol benzoate, hydrogen bonds

Chemical context  

Salbutamol {systematic name: 4-[2-(tert-butyl­amino)-1-hy­droxy­eth­yl]-2-(hy­droxy­meth­yl)phenol} is known as a short-action selective β2-adrenergic receptor agonist for the treatment of pulmonary diseases, including asthma attacks, exercise-induced bronchoconstriction and chronic obstructive pulmonary disease (Saleh et al., 2000  ). However, salbutamol shows poor solubility in aqueous solution, which limits its bioavailability. The production of salt forms is a usual approach to alter the physicochemical properties of pharmaceutical compounds (Surov et al., 2015  ). Salbutamol has been widely studied and some salts of salbutamol have been on the market, such as salbutamol sulfate.

An external file that holds a picture, illustration, etc.
Object name is e-73-01333-scheme1.jpg

We selected various acids and combined them with salbutamol and then investigated the properties of new salt forms. Salbutamol benzoate was found to dissolve and crystallize in water, and it might show different in vitro solubility and dissolution properties. In this work, we report on the crystal structure determination of the title molecular salt salbutamol benzoate, C13H22NO3 +·C7H5O2 .

Structural commentary  

The asymmetric unit of the title compound is shown in Fig. 1  . The mol­ecule of salbutamol (SAL) accepts one proton at the N1 atom from the benzoic acid (BA) and thus forms a 1:1 salt, SAL + BA . The bond lengths of the carboxyl­ate group of the BA anion, C20—O4 and C20—O5, are 1.2617 (15) and 1.2604 (15) Å, respectively. The slight difference may be caused by the role of O4 as an acceptor atom of the O3—H3(...)O4 hydrogen bond with one of the hy­droxy groups of SAL+. The SAL+ cation also has an intra­molecular hydrogen bond between the two hy­droxy functions (O1—H1(...)O3), forming an S(6) ring motif (Fig. 1  and Table 1  ).

Figure 1
The structures of the mol­ecular components in the title compound. Displacement ellipsoids are drawn at the 50% probability level. The dashed line depicts the O—H(...)O hydrogen bond. Both disorder components of the OH group are shown. ...
Table 1
Hydrogen-bond geometry (Å, °)

The BA anion is not planar, indicated by the dihedral angle between the benzene ring and the carboxyl group of 11.30 (8)°. There is some disorder at the stereogenic centre (C8) of the SAL+ cation, but the space group is centrosymmetric and the SAL+ cation is racemic.

Supra­molecular features  

The SAL+ cation is connected to the BA anion via a medium-strength O3—H3(...)O4 hydrogen bond (Table 1  ). In addition, N—H(...)O hydrogen bonds between SAL+ and BA are present, leading to an An external file that holds a picture, illustration, etc.
Object name is e-73-01333-efi1.jpg(12) graph-set motif via N1—H1A(...)O4i and N1—H1B(...)O5ii (for symmetry codes, see Table 1  ). Due to the disorder of the hy­droxy group at C8, there are some variable motifs, including An external file that holds a picture, illustration, etc.
Object name is e-73-01333-efi2.jpg(4) motifs for the O2—H2(...)O4i and O2A—H2A(...)O5i inter­actions, respectively. The variety of N—H(...)·O and O—H(...)O hydrogen bonds leads to [001] chains (Figs. 2  and 3  ).

Figure 2
The crystal packing of the title compound, viewed perpendicular to the bc plane. N—H(...)O and O—H(...)O hydrogen bonds are shown as dashed lines (Table 1  gives the numerical details). Both disorder components ...
Figure 3
The crystal packing of the title compound, viewed perpendicular to the ab plane. N—H(...)O and O—H(...)O hydrogen bonds are shown as dashed lines (Table 1  gives the numerical details).

Database survey  

Six structures containing salbutamol were found in a search of the Cambridge Structural Database (Version 5.38; Groom et al., 2016  ). The structure of salbutamol was reported by Beale & Grainger (1972  ). Salbutamol sulfate was the first salt of salbutamol to be structurally determined some years later (Leger et al., 1978  ). Recently, a new salbutamol sulfate polymorph crystallizing in a different space group (C2/c) was determined (Xie et al., 2010  ). Paluch et al. (2011  ) investigated the co-crystal of a salbutamol hemiadipate salt with adipic acid and also the salbutamol hemisuccinate salt. Moreover, an oxaprozin–salbutamol salt was also reported (Aitipamula et al., 2016  ).

Synthesis and crystallization  

Salbutamol (0.479 g, 2 mmol) and benzoic acid (0.244 g, 2 mmol) were added to 10 ml methanol and stirred for 3 h. The solvent was then evaporated at room temperature to yield salbutamol benzoate. After recrystallization from water, pure crystals were again dissolved in ethanol and the solution filtered. The neat filtrate was evaporated slowly to give colourless block-like single crystals of salbutamol benzoate.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 2  . The hy­droxy group at C8 is disordered over two sets of sites, with refined site occupancies of 0.738:0.262. H atoms were constrained to an ideal geometry, with C—H distances in the range 0.93–0.97 Å, and allowed to ride, with U iso(H) = 1.5U eq(C) for methyl H atoms and U iso(H) = 1.2U eq(C) for all other H atoms. The H atoms of the NH2 group and the hy­droxy group (except for O1—H1, which was refined freely) were also constrained to ideal values and allowed to ride in the refinement, with U iso(H) = 1.2U eq(N) and 1.5U eq(O).

Table 2
Experimental details

Supplementary Material

Crystal structure: contains datablock(s) I, New_Global_Publ_Block. DOI: 10.1107/S2056989017011513/wm5403sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989017011513/wm5403Isup2.hkl

CCDC reference: 1482124

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

C13H22NO3+·C7H5O2Z = 2
Mr = 361.42F(000) = 388
Triclinic, P1Dx = 1.236 Mg m3
a = 8.7525 (16) ÅMo Kα radiation, λ = 0.71073 Å
b = 10.691 (2) ÅCell parameters from 9936 reflections
c = 11.220 (2) Åθ = 2.6–27.5°
α = 79.953 (8)°µ = 0.09 mm1
β = 69.969 (5)°T = 298 K
γ = 87.796 (7)°Block, colourless
V = 971.0 (3) Å30.2 × 0.2 × 0.2 mm

Data collection

Bruker APEXII CCD area detector diffractometer3646 reflections with I > 2σ(I)
ω scansRint = 0.031
Absorption correction: multi-scan (SADABS; Bruker, 2013)θmax = 27.5°, θmin = 2.6°
Tmin = 0.702, Tmax = 0.746h = −11→11
30220 measured reflectionsk = −13→13
4451 independent reflectionsl = −14→14

Refinement

Refinement on F2Hydrogen site location: mixed
Least-squares matrix: fullH atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.042w = 1/[σ2(Fo2) + (0.0446P)2 + 0.2722P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.112(Δ/σ)max = 0.001
S = 1.05Δρmax = 0.20 e Å3
4451 reflectionsΔρmin = −0.16 e Å3
255 parametersExtinction correction: SHELXL2014 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.057 (9)

Special details

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)

xyzUiso*/UeqOcc. (<1)
O10.80860 (14)0.97825 (11)0.26965 (9)0.0546 (3)
O2A0.5973 (5)0.6081 (3)0.8052 (3)0.0434 (11)0.262 (3)
H2A0.62050.58200.86990.065*0.262 (3)
O20.69965 (16)0.73304 (15)0.84687 (13)0.0510 (5)0.738 (3)
H20.69800.66570.89530.076*0.738 (3)
O30.56450 (15)0.87681 (9)0.23563 (9)0.0528 (3)
H30.57370.80610.21530.079*
N10.35552 (12)0.72461 (9)1.00143 (9)0.0322 (2)
H1A0.43360.71731.03610.039*
H1B0.32510.64641.00050.039*
C10.75065 (16)0.91411 (12)0.39463 (11)0.0383 (3)
C20.84945 (16)0.90957 (14)0.46798 (13)0.0436 (3)
H2B0.95340.94620.43130.052*
C30.79551 (15)0.85081 (13)0.59624 (12)0.0391 (3)
H3A0.86230.85050.64530.047*
C40.64238 (15)0.79248 (11)0.65167 (11)0.0329 (3)
C50.54602 (15)0.79462 (11)0.57543 (11)0.0344 (3)
H50.44460.75370.61090.041*
C60.59620 (15)0.85613 (11)0.44730 (11)0.0341 (3)
C70.48166 (18)0.86544 (13)0.37203 (13)0.0436 (3)
H7A0.41100.79040.40170.052*
H7B0.41380.93870.38890.052*
C80.58179 (15)0.72927 (12)0.79268 (11)0.0366 (3)
H8A0.55590.63990.79670.044*0.738 (3)
H8B0.66220.75690.82620.044*0.262 (3)
C90.42675 (15)0.79134 (12)0.86485 (11)0.0366 (3)
H9A0.45020.87950.86390.044*
H9B0.34810.78950.82170.044*
C100.20953 (16)0.78698 (13)1.08980 (12)0.0391 (3)
C110.06894 (18)0.79052 (17)1.03926 (15)0.0544 (4)
H11A0.10080.83950.95400.082*
H11B−0.02280.82871.09490.082*
H11C0.03990.70551.03700.082*
C120.1660 (2)0.70235 (17)1.22185 (13)0.0583 (4)
H12A0.07300.73551.28140.087*
H12B0.25640.70061.25200.087*
H12C0.14110.61771.21520.087*
C130.2593 (2)0.92015 (15)1.09557 (15)0.0532 (4)
H13A0.27990.97321.01310.080*
H13B0.35620.91611.11790.080*
H13C0.17330.95511.15940.080*
O40.56936 (13)0.66457 (10)0.14546 (11)0.0537 (3)
O50.70749 (13)0.52721 (9)0.02270 (9)0.0456 (3)
C140.73821 (15)0.51968 (11)0.22649 (12)0.0360 (3)
C150.86636 (18)0.43726 (15)0.19863 (15)0.0504 (4)
H150.90830.41600.11680.061*
C160.9327 (2)0.38618 (18)0.29166 (17)0.0649 (5)
H161.01850.33040.27210.078*
C170.8726 (2)0.41749 (17)0.41258 (16)0.0612 (4)
H170.91730.38270.47490.073*
C180.7469 (2)0.50006 (17)0.44133 (16)0.0605 (4)
H180.70690.52220.52280.073*
C190.67932 (19)0.55051 (14)0.34893 (14)0.0486 (3)
H190.59320.60590.36930.058*
H10.743 (2)0.9521 (19)0.2336 (19)0.073*
C200.66666 (16)0.57426 (11)0.12434 (13)0.0369 (3)

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
O10.0637 (7)0.0627 (7)0.0279 (5)−0.0049 (5)−0.0088 (4)0.0047 (4)
O2A0.058 (2)0.0273 (17)0.041 (2)0.0088 (15)−0.0153 (17)0.0002 (14)
O20.0418 (7)0.0683 (10)0.0387 (7)0.0011 (6)−0.0185 (6)0.0115 (6)
O30.0895 (8)0.0417 (5)0.0353 (5)0.0097 (5)−0.0304 (5)−0.0105 (4)
N10.0357 (5)0.0334 (5)0.0254 (5)0.0059 (4)−0.0083 (4)−0.0049 (4)
C10.0463 (7)0.0374 (6)0.0245 (6)0.0059 (5)−0.0052 (5)−0.0037 (5)
C20.0368 (7)0.0514 (8)0.0353 (7)−0.0009 (6)−0.0057 (5)−0.0018 (6)
C30.0357 (6)0.0474 (7)0.0326 (6)0.0069 (5)−0.0119 (5)−0.0039 (5)
C40.0357 (6)0.0320 (6)0.0272 (6)0.0091 (5)−0.0069 (5)−0.0044 (4)
C50.0369 (6)0.0333 (6)0.0307 (6)0.0043 (5)−0.0081 (5)−0.0073 (5)
C60.0445 (7)0.0304 (6)0.0289 (6)0.0096 (5)−0.0126 (5)−0.0106 (5)
C70.0578 (8)0.0421 (7)0.0376 (7)0.0127 (6)−0.0225 (6)−0.0143 (5)
C80.0383 (6)0.0385 (6)0.0287 (6)0.0090 (5)−0.0089 (5)−0.0015 (5)
C90.0410 (7)0.0373 (6)0.0263 (6)0.0092 (5)−0.0077 (5)−0.0014 (5)
C100.0391 (7)0.0445 (7)0.0300 (6)0.0090 (5)−0.0058 (5)−0.0109 (5)
C110.0384 (7)0.0745 (11)0.0497 (8)0.0133 (7)−0.0105 (6)−0.0210 (7)
C120.0592 (9)0.0708 (11)0.0310 (7)0.0076 (8)−0.0005 (6)−0.0044 (7)
C130.0613 (9)0.0499 (8)0.0497 (8)0.0127 (7)−0.0148 (7)−0.0230 (7)
O40.0649 (7)0.0524 (6)0.0640 (7)0.0283 (5)−0.0411 (6)−0.0295 (5)
O50.0633 (6)0.0375 (5)0.0384 (5)0.0109 (4)−0.0198 (4)−0.0097 (4)
C140.0367 (6)0.0315 (6)0.0399 (7)0.0014 (5)−0.0135 (5)−0.0053 (5)
C150.0493 (8)0.0534 (8)0.0453 (8)0.0167 (7)−0.0134 (6)−0.0088 (6)
C160.0553 (9)0.0714 (11)0.0636 (10)0.0264 (8)−0.0223 (8)−0.0014 (8)
C170.0624 (10)0.0679 (11)0.0547 (9)0.0054 (8)−0.0310 (8)0.0078 (8)
C180.0762 (11)0.0661 (10)0.0424 (8)0.0097 (8)−0.0252 (8)−0.0093 (7)
C190.0552 (8)0.0480 (8)0.0440 (8)0.0145 (6)−0.0179 (7)−0.0125 (6)
C200.0404 (7)0.0304 (6)0.0428 (7)0.0028 (5)−0.0167 (5)−0.0090 (5)

Geometric parameters (Å, º)

O1—C11.3777 (15)C9—H9A0.9700
O1—H10.88 (2)C9—H9B0.9700
O2A—H2A0.8200C10—C111.518 (2)
O2A—C81.286 (3)C10—C121.5267 (19)
O2—H20.8200C10—C131.523 (2)
O2—C81.3700 (18)C11—H11A0.9600
O3—H30.8200C11—H11B0.9600
O3—C71.4368 (16)C11—H11C0.9600
N1—H1A0.8900C12—H12A0.9600
N1—H1B0.8900C12—H12B0.9600
N1—C91.4980 (15)C12—H12C0.9600
N1—C101.5354 (15)C13—H13A0.9600
C1—C21.3777 (19)C13—H13B0.9600
C1—C61.3964 (19)C13—H13C0.9600
C2—H2B0.9300O4—C201.2617 (15)
C2—C31.3894 (18)O5—C201.2604 (15)
C3—H3A0.9300C14—C151.3827 (19)
C3—C41.3892 (18)C14—C191.3862 (19)
C4—C51.3891 (17)C14—C201.5088 (18)
C4—C81.5234 (16)C15—H150.9300
C5—H50.9300C15—C161.385 (2)
C5—C61.3971 (17)C16—H160.9300
C6—C71.5070 (18)C16—C171.373 (2)
C7—H7A0.9700C17—H170.9300
C7—H7B0.9700C17—C181.370 (2)
C8—H8A0.9800C18—H180.9300
C8—H8B0.9800C18—C191.384 (2)
C8—C91.5175 (17)C19—H190.9300
C1—O1—H1103.7 (13)C8—C9—H9A109.4
C8—O2A—H2A109.5C8—C9—H9B109.4
C8—O2—H2109.5H9A—C9—H9B108.0
C7—O3—H3109.5C11—C10—N1109.36 (10)
H1A—N1—H1B107.3C11—C10—C12110.57 (13)
C9—N1—H1A108.1C11—C10—C13111.26 (12)
C9—N1—H1B108.1C12—C10—N1105.47 (11)
C9—N1—C10116.66 (9)C13—C10—N1109.25 (11)
C10—N1—H1A108.1C13—C10—C12110.75 (12)
C10—N1—H1B108.1C10—C11—H11A109.5
O1—C1—C2117.93 (12)C10—C11—H11B109.5
O1—C1—C6121.77 (12)C10—C11—H11C109.5
C2—C1—C6120.30 (11)H11A—C11—H11B109.5
C1—C2—H2B119.6H11A—C11—H11C109.5
C1—C2—C3120.70 (12)H11B—C11—H11C109.5
C3—C2—H2B119.6C10—C12—H12A109.5
C2—C3—H3A119.8C10—C12—H12B109.5
C4—C3—C2120.42 (12)C10—C12—H12C109.5
C4—C3—H3A119.8H12A—C12—H12B109.5
C3—C4—C8120.65 (11)H12A—C12—H12C109.5
C5—C4—C3118.20 (11)H12B—C12—H12C109.5
C5—C4—C8121.15 (11)C10—C13—H13A109.5
C4—C5—H5118.9C10—C13—H13B109.5
C4—C5—C6122.27 (12)C10—C13—H13C109.5
C6—C5—H5118.9H13A—C13—H13B109.5
C1—C6—C5118.06 (11)H13A—C13—H13C109.5
C1—C6—C7121.60 (11)H13B—C13—H13C109.5
C5—C6—C7120.24 (12)C15—C14—C19118.43 (13)
O3—C7—C6113.03 (12)C15—C14—C20119.93 (12)
O3—C7—H7A109.0C19—C14—C20121.64 (12)
O3—C7—H7B109.0C14—C15—H15119.8
C6—C7—H7A109.0C14—C15—C16120.49 (14)
C6—C7—H7B109.0C16—C15—H15119.8
H7A—C7—H7B107.8C15—C16—H16119.8
O2A—C8—C4111.63 (19)C17—C16—C15120.32 (15)
O2A—C8—H8B103.5C17—C16—H16119.8
O2A—C8—C9122.7 (2)C16—C17—H17120.0
O2—C8—C4111.00 (11)C18—C17—C16119.92 (15)
O2—C8—H8A108.0C18—C17—H17120.0
O2—C8—C9111.94 (12)C17—C18—H18120.0
C4—C8—H8A108.0C17—C18—C19119.93 (15)
C4—C8—H8B103.5C19—C18—H18120.0
C9—C8—C4109.70 (10)C14—C19—H19119.5
C9—C8—H8A108.0C18—C19—C14120.90 (14)
C9—C8—H8B103.5C18—C19—H19119.5
N1—C9—C8111.32 (9)O4—C20—C14118.13 (11)
N1—C9—H9A109.4O5—C20—O4123.67 (12)
N1—C9—H9B109.4O5—C20—C14118.20 (11)
O1—C1—C2—C3177.38 (12)C5—C4—C8—C9−58.81 (15)
O1—C1—C6—C5−179.09 (11)C5—C6—C7—O3−153.65 (11)
O1—C1—C6—C7−2.70 (18)C6—C1—C2—C3−2.0 (2)
O2A—C8—C9—N141.1 (3)C8—C4—C5—C6177.49 (11)
O2—C8—C9—N1−61.14 (15)C9—N1—C10—C1162.74 (15)
C1—C2—C3—C41.8 (2)C9—N1—C10—C12−178.33 (11)
C1—C6—C7—O330.04 (16)C9—N1—C10—C13−59.25 (14)
C2—C1—C6—C50.23 (18)C10—N1—C9—C8173.01 (11)
C2—C1—C6—C7176.62 (12)C14—C15—C16—C17−0.4 (3)
C2—C3—C4—C50.10 (19)C15—C14—C19—C180.0 (2)
C2—C3—C4—C8−179.27 (12)C15—C14—C20—O4−168.35 (13)
C3—C4—C5—C6−1.87 (18)C15—C14—C20—O511.59 (19)
C3—C4—C8—O2A−100.1 (2)C15—C16—C17—C18−0.3 (3)
C3—C4—C8—O2−3.70 (17)C16—C17—C18—C190.8 (3)
C3—C4—C8—C9120.54 (13)C17—C18—C19—C14−0.6 (3)
C4—C5—C6—C11.71 (17)C19—C14—C15—C160.6 (2)
C4—C5—C6—C7−174.73 (11)C19—C14—C20—O411.3 (2)
C4—C8—C9—N1175.17 (10)C19—C14—C20—O5−168.78 (13)
C5—C4—C8—O2A80.6 (2)C20—C14—C15—C16−179.78 (14)
C5—C4—C8—O2176.96 (12)C20—C14—C19—C18−179.68 (14)

Hydrogen-bond geometry (Å, º)

D—H···AD—HH···AD···AD—H···A
O2A—H2A···O5i0.822.092.906 (4)173
O2—H2···O4i0.822.643.1066 (18)118
O2—H2···O5i0.821.892.7029 (16)170
O3—H3···O40.821.832.6340 (15)167
N1—H1A···O4i0.891.992.8538 (14)165
N1—H1B···O5ii0.891.962.8452 (15)171
O1—H1···O30.88 (2)1.78 (2)2.6015 (17)154 (2)

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

Funding Statement

This work was funded by the National Nature and Science Foundation of China grant 21206032. the Science Foundation Henan University of Technology grant 2017RCJH09, 2017QNJH29. the Science Foundation of Henan Province grant 2015GGJS-039.

This paper was supported by the following grant(s):

the National Nature and Science Foundation of China 21206032.
the Science Foundation Henan University of Technology 2017RCJH09, 2017QNJH29.
the Science Foundation of Henan Province 2015GGJS-039.

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Articles from Acta Crystallographica Section E: Crystallographic Communications are provided here courtesy of International Union of Crystallography