The X-ray Structure of 4-Aminobenzyl alcohol (4-Aminophenylmethanol)

Article abstract of DOI:10.1007/s10870-018-0748-9

A second polymorph of 4-aminobenzyl alcohol [orthorhombic, a = 8.95051(15), b = 5.8248(1), c = 12.1645(2) ?, space group Pna2₁] shows a “herringbone” structure with stacks of hydrogen-bonded molecules when viewed down the b-axis. Graphical Abst

Full text of DOI:10.1007/s10870-018-0748-9

Journal of Chemical Crystallography
https://doi.org/10.1007/s10870-018-0748-9
ORIGINAL PAPER
The X-ray Structure of 4-Aminobenzyl alcohol
(4-Aminophenylmethanol)
R. Alan Aitken1 · Lewis Davidson1 · Alexandra M. Z. Slawin1
Received: 8 July 2018 / Accepted: 30 October 2018
© The Author(s) 2018
Abstract
A second polymorph of 4-aminobenzyl alcohol [orthorhombic, a =8.95051(15), b=5.8248(1), c=12.1645(2) Å, space
group Pna21] shows a “herringbone” structure with stacks of hydrogen-bonded molecules when viewed down the b-axis.
Graphical Abstract
H
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A new polymorph of 4-aminobenzyl alcohol adopts a “herringbone” structure with stacks of hydrogen bonded molecules viewed down the
b-axis.
Keywords 4-Aminobenzyl alcohol · Hydrogen bonding · Herringbone structure
Introduction
In connection with current studies on functionalised ana-
Electronic supplementary material The online version of this
logues of azophenine, we recently prepared 4-aminobenzyl
alcohol 1. Although this compound was first reported in
1895 [1], we initially believed that its X-ray structure had
not hitherto been determined. The combination of amino and
hydroxyl groups with a benzene ring gives interesting oppor-
tunities for the formation of hydrogen-bonded networks and
article (https://doi.org/10.1007/s10870-018-0748-9) contains
supplementary material, which is available to authorized users.
* R. Alan Aitken
raa@st-and.ac.uk
1
EaStCHEM School of Chemistry, University of St Andrews,
St Andrews, Fife KY16 9ST, UK
Vol.:(0123456789)
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Journal of Chemical Crystallography
such features have already been noted for both the meta-
isomer 2 [2] and the ortho-isomer 3 [3]. In addition, hydro-
gen-bonding patterns in structures of the closely related
ortho-, meta- and para-hydroxybenzyl alcohols 4–6 have
been examined in detail [4, 5] (Scheme 1). We determined
the X-ray structure and, at that stage, found a previously
published structure [6] but the two were markedly different.
In this paper, we describe the crystal and molecular structure
of the new polymorph of 1 and compare the observed hydro-
gen-bonding patterns with those for the originally reported
polymorph and related compounds.
least-squares against F2 (SHELXTL [9]). Carbon-bound
hydrogen atoms were assigned riding isotropic displacement
parameters and constrained to idealised geometries while
OH and NH hydrogen atoms were refined freely. Table 1
summarises the X-ray data.
Table 1 Crystal data and structure refinement details for 1
CCDC deposit no.
Empirical formula
Formula weight
Crystal system
Space group
Temperature (K)
Crystal form
1566675
C7H9NO
123.15
Orthorhombic
Pna21
Experimental
125(1)
Colourless plate
0.15×0.15×0.02 mm
a=8.95051(15) Å
b=5.8248(1) Å
c=12.1645(2) Å
634.19(2)
4-Nitrobenzyl alcohol (20 g, 0.12 mol) was added to a boil-
ing suspension of zinc dust (80 g, 1.22 mol) and calcium
chloride (8 g, 0.07 mol) in water (400 mL). The resulting
solution was boiled for 30 min and then filtered hot. On
cooling the filtrate, a reddish solid appeared and this was
filtered off and discarded. Sodium carbonate was then added
to the filtrate to precipitate the calcium salts, which were
then filtered off. The filtrate was evaporated down to dry-
ness. The resulting oil was then recrystallized from toluene
to afford a pale yellow solid (3.69 g, 23%) m.p. 60–61 °C,
(lit. [7] 58–61 °C).
Unit cell dimensions
Volume (Å3)
Z
4
Dc (g cm−3
)
1.290
Absorption coefficient
Radiation type, wavelength
F(000)
0.703 mm−1
Cu Kα, 1.54187 Å
264
θ range
Limiting indices
7.28°–75.31°
δH (Bruker AV400, 400 MHz, CDCl3) 7.18 (2H, d,
J=8.5 Hz, ArH) 6.69 (2H, d, J=8.5 Hz, ArH), 4.57 (2H, s,
CH2OH) and 3.65 (2H, s, NH2) (agreement with lit. values
[8]).
−11≤h≤11,
−6≤k≤7,
−15≤l≤14
Reflections collected/unique
Rint
6342/1280
0.0188
Data were collected using a Rigaku XtalLAB P200 and a
Mercury CCD (confocal optics Cu-Kα radiation) at 125 K.
Intensity data were collected using ω/ϕ steps accumulating
area detector frames spanning at least a hemisphere of recip-
rocal space (data were integrated using CrystalClear). All
data were corrected for Lorentz, polarisation and long-term
intensity fluctuations. Absorption effects were corrected on
the basis of multiple equivalent reflections. The structure
was solved by direct methods and refined by full-matrix
Data/restraints/parameters
Data with I>2σ(I)
1280/4/95
1279
1.035
0.0608, 0.1293
0.0611, 0.1294
0.39 and −0.53
0.03(9)
Goodness of fit on F2
R1, wR2 [data with I>2σ(I)]
R1, wR2 (all data)
Largest diff. peak/hole (e Å−3
Flack parameter
)
Scheme 1 Synthetic route used
to compound 1, and structures
of related compounds 2–6 with
CCDC Ref Codes
Zn, CaCl2, H2O
OH
OH
H2N
O2N
1 (UHEVUZ)
OH
OH
OH
OH
OH
OH
6 (DOJFEN01)
HO
NH2
3 (SAGTOL)
OH
NH2
2 (EVIWOW)
4 (FOVQOX,
FOVQOX01))
5 (FACCOB01,
FACCOB02)
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Journal of Chemical Crystallography
Results and Discussion
We first attempted to prepare 1 by reduction of the readily
available ethyl 4-aminobenzoate (benzocaine) using lithium
aluminium hydride. Although this reaction does not appear
to have been reported, the closely related reduction of methyl
4-aminotetradeuteriobenzoate with LiAlD4 is reported to
afford the hexadeuteriated 4-aminobenzyl alcohol in 47%
yield [10]. However in our hands the ethyl ester was recov-
ered completely unchanged after prolonged boiling with a
large excess of LiAlH4 in either diethyl ether or THF. We
deduce that binding of the amino group to aluminium occurs
and inhibits reduction. We therefore reverted to the original
1895 synthesis [1], and found that treatment of 4-nitrobenzyl
alcohol with zinc dust in the presence of calcium chloride
in boiling water gave the product in acceptable yield and in
good purity after recrystallization from toluene. The crystals
obtained were directly suitable for X-ray diffraction and the
molecular structure of 1 is shown in Fig. 1.
Fig. 1 The molecular structure of the new polymorph of 1 showing
numbering system used
Table 2 Bond lengths for 1
Bond
Length (Å)
C(7)–O(7)
O(7)–H(7)
C(1)–N(1)
N(1)–H(1A)
N(1)–H(1B)
C(1)–C(2)
C(1)–C(6)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(4)–C(7)
C(5)–C(6)
1.421(4)
0.980(7)
1.417(2)
0.976(7)
0.976(7)
1.394(3)
1.400(2)
1.390(3)
1.396(2)
1.398(3)
1.510(2)
1.395(3)
The molecular structure has bond lengths (Table 2) and
angles that are unremarkable but the crystal structure is
much more interesting with a regular “herringbone” pattern
featuring stacks of hydrogen-bonded molecules. A section
of the structure viewed along the b-axis is shown in Fig. 2
and the equivalent schematic representation is in Fig. 3.
Each OH and NH2 group is involved in one donor and one
acceptor interaction, with the oxygen lone pair interacting
with an NH and the nitrogen lone pair interacting with an
OH. One NH in each molecule is not involved in hydrogen
bonding but appears to interact with the π-electrons of a
Fig. 2 Hydrogen bonding pattern in the crystal structure of 1 viewed along the b-axis
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Journal of Chemical Crystallography
H
O
H
O
H
O
H
H
H
H
N
H
H
N
N
O
O
H
O
H
H
O
H
H
O
H
O
N
H
H
N
H
H
N
H
H
H
H
H
H
N
H
H
N
N
O
O
H
O
H
O
H
O
H
H
O
H
N
H
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N
H
H
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N
H
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N
H
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N
N
O
H
O
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O
O
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O
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H
N
H
H
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N
H
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N
H
H
H
H
H
N
H
H
N
N
O
O
H
O
H
H
N
H
H
N
H
H
N
H
H
Fig. 3 Schematic hydrogen bonding pattern in the crystal structure of 1
benzene ring. The geometric parameters for this pattern are
given in Table 3.
Table 3 Geometric parameters for intermolecular hydrogen bonding
in 1
The hydrogen-bonding pattern is remarkably different
from those involved for the previously reported structure of
1 [6], and the other isomers 2 and 3. We attribute the isola-
tion of a second form of 1 to recrystallization of our sample
D–H⋯A
d(D⋯A) d(D–H) d(H⋯A) <(D–H⋯A)
O(7)–H(7)⋯N(1)
N(1)–H(1B)⋯O(7) 3.040(2) 0.98(2)
2.845(2) 0.98(3)
1.89(4)
2.14(2)
165(3)
153(2)
Fig. 4 Hydrogen bonding pattern in the previously reported polymorph of 1 viewed along the c axis [6]
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Journal of Chemical Crystallography
Fig. 5 Hydrogen bonding pattern in the crystal structure of 2 [2]
Fig. 6 Hydrogen bonding pattern in the crystal structure of 3 [3]
from toluene which apparently gives a new polymorph. The
literature structure used commercially available material
with no indication of the recrystallization solvent (if any) in
its manufacture. The two polymorphs of 1 differ most obvi-
ously in that the previous structure is centrosymmetric with
head-to-tail hydrogen bonded dimers which are then linked
by further hydrogen bonding interactions in chains (Fig. 4).
As is the case for our structure, each OH and NH is involved
in one donor and one acceptor interaction with one NH not
involved in hydrogen bonding. For the meta-isomer 2 [2],
each OH and NH2 group is again involved in one donor and
one acceptor interaction, with the oxygen lone pair interact-
ing with an NH and the nitrogen lone pair interacting with
an OH, but the molecules are all aligned in the same orien-
tation (Fig. 5). In the ortho-isomer 3 [3], the molecules are
arranged in antiparallel lines with an oxygen lone pair to
NH interaction linking adjacent molecules within the line
and one nitrogen lone pair to OH interaction per pair of
molecules linking the two lines in centrosymmetric dimers
(Fig. 6). The remaining nitrogen lone pair to OH interactions
then link to further lines of molecules behind and in front
of the plane giving an infinite layer with a hydrogen bonded
interior and hydrophobic exterior.
Comparison with the structures adopted by the isomeric
hydroxybenzyl alcohols 4–6 [4] is also interesting. The
structures adopted by the two ortho-isomers 3 and 6 are
1 3

Journal of Chemical Crystallography
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closely analogous with centro-symmetric dimers involved
in further hydrogen bonding in each case, while for the
two meta-isomers, 2 and 5, there is again a good degree of
similarity, with molecules all aligned in the same way and
connected in a two-dimensional hydrogen bonded network.
When we come to the para-isomers 1 and 4 however,
the situation differs markedly. Although each hydrogen
bonded group is involved in one acceptor and one donor
interaction in both structures, the herringbone pattern of 1
is replaced in 4 by a three-dimensional hydrogen bonded
network featuring spirals of molecules along the c-axis
with a four molecule repeat unit.
References
1. Fischer O, Fischer G (1895) Ber Dtsch Chem Ges 28:879–881
2. Betz R, Gerber T, Hosten E (2011) Acta Crystallogr Sect E
67:o2118
3. Zipp CF, Fernandez MA, Marques HM, Michael JP (2012) Acta
Crystallogr Sect E 68:o174
4. Lemmerer A, Esterhuysen C (2011) CrystEngComm
13:5773–5782
Conclusion
5. Liu W-S, Wei R-P, Tang X-L, Wang W-H, Ju Z-H (2009) Acta
Crystallogr Sect E 65:o1689
6. Bacchi A, Carcelli M, Chiodo T, Cantoni G, De Filippo C, Pipolo
S (2009) CrystEngComm 11:1433–1441
The crystal structure for this new polymorph of 1 is quite
different from the previous polymorph and those previ-
ously reported for the isomers 2 and 3. It also differs mark-
edly from that of the closely similar hydroxy analogue 4.
Despite significant progress in being able to predict the
X-ray structures of simple aromatic compounds containing
OH and NH2 groups [11], it is clear that further work is
required to fully understand the forces that determine the
structure adopted in a given case.
7. Grice R, Owen LN (1963) J Chem Soc 1963:1947–1954
8. Lawson T, Gannett PM, Yau W-M, Dalal NS, Toth B (1995) J
Agric Food Chem 43:2627–2635
9. Sheldrick GM (2014) Acta Crystallogr Sect A 64:112–122
10. Pfister R, Ihalainen J, Hamm P, Kolano C (2008) Org Biomol
Chem 6:3508–3517
11. Dey A, Kirchner MT, Vangala VR, Desiraju GR, Mondal R, How-
ard JAK (2005) J Am Chem Soc 127:10545–10559
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