A structural and spectroscopic investigation of the hydrochlorination of 4,4′-methylenedianiline

Article abstract of DOI:10.1039/b916368a

The hydrochlorination of 4,4′-methylenedianiline, NH ₂C₆H₄CH₂C₆H ₄NH₂ (MDA), in chlorobenzene to produce 4,4′-methylenedianiline dihydrochloride, [H₃NC ₆H₄CH₂C₆H₄NH ₃]Cl₂ (MDA·2HCl) is an important reaction for the production of isocyanates, which are used to manufacture polyurethanes. This reaction is examined here. MDA is moderately soluble in chlorobenzene, whereas MDA·2HCl is effectively insoluble. Controlled addition of anhydrous HCl to MDA in chlorobenzene led to the isolation of a solid whose stoichiometry is MDA·HCl. Crystals obtained from solutions of MDA·HCl in methanol were found by X-ray analysis to consist of the basic hydrochloride salt, [MDAH₂][Cl]₂[MDA]₂H₂O, which is stabilised by complex hydrogen-bonding. The starting material MDA has an H-bonded structure in which the molecules are linked in a one-dimensional chain. Hydrogen-bonding is extensive in MDA·2HCl which contains ladders of [H₃NC₆H₄CH₂C₆H ₄NH₃]²⁺ dications stabilised by N-H...Cl linkages. Energy calculations on the crystalline systems allow an identification of the main factors in intermolecular cohesion; these are related to melting temperature and solubility data. Such improvements in understanding of solute-solute interactions are prerequisites for improving the atom economy of this important stage within the polyurethane manufacture process chain. The solid phase IR spectrum of MDA·2HCl is diagnostic, principally as a result of a Fermi resonance process.

Full text of DOI:10.1039/b916368a

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PAPER
www.rsc.org/pccp | Physical Chemistry Chemical Physics
A structural and spectroscopic investigation of the hydrochlorination
of 4,40-methylenedianilinew
Emma K. Gibson,a John M. Winfield,a Kenneth W. Muir,a Robert H. Carr,b
Archie Eaglesham,b Angelo Gavezzottic and David Lennon*a
Received 10th August 2009, Accepted 8th February 2010
First published as an Advance Article on the web 24th Febuary 2010
DOI: 10.1039/b916368a
The hydrochlorination of 4,40-methylenedianiline, NH2C6H4CH2C6H4NH2 (MDA), in
chlorobenzene to produce 4,40-methylenedianiline dihydrochloride, [H3NC6H4CH2C6H4NH3]Cl2
(MDAꢀ2HCl) is an important reaction for the production of isocyanates, which are used to
manufacture polyurethanes. This reaction is examined here. MDA is moderately soluble in
chlorobenzene, whereas MDAꢀ2HCl is effectively insoluble. Controlled addition of anhydrous
HCl to MDA in chlorobenzene led to the isolation of a solid whose stoichiometry is MDAꢀHCl.
Crystals obtained from solutions of MDAꢀHCl in methanol were found by X-ray analysis to
consist of the basic hydrochloride salt, [MDAH2][Cl]2[MDA]2H2O, which is stabilised by complex
hydrogen-bonding. The starting material MDA has an H-bonded structure in which the molecules
are linked in a one-dimensional chain. Hydrogen-bonding is extensive in MDAꢀ2HCl which
contains ladders of [H3NC6H4CH2C6H4NH3]2+ dications stabilised by N–Hꢀ ꢀ ꢀCl linkages.
Energy calculations on the crystalline systems allow an identification of the main factors in
intermolecular cohesion; these are related to melting temperature and solubility data. Such
improvements in understanding of solute–solute interactions are prerequisites for improving
the atom economy of this important stage within the polyurethane manufacture process chain.
The solid phase IR spectrum of MDAꢀ2HCl is diagnostic, principally as a result of a
Fermi resonance process.
material to form unwelcome hydrochloride salts.5 These
1. Introduction
secondary reactions are outlined as part of Scheme 1.
Methylene diphenyl diisocyanate (MDI) and toluene diisocyanate
There are two features of the scheme which largely determined
(TDI) are the major isocyanates used to make polyurethanes,1
the way in which the study to be described here was carried
having respective shares of the global isocyanate production of
out. First, isolation of the postulated intermediate, methyl-
60 and 34%.1 Flexible foams used in household products such
enedianiline monohydrochloride, [H2NC6H4CH2C6H4NH3]Cl
as furniture and mattresses are made mainly from TDI,2
(MDAꢀHCl) (3) has, as far as we are aware, not been
whereas foams of higher mechanical strength are typically
reported in the open literature previously, although the
made from symmetrical isocyanates such as MDI.3 The
properties of the compound are of potential interest in
primary precursor for MDI is 4,40-methylenedianiline
any modelling studies carried out on the large-scale
(MDA),4 for which the total global production capacity in
phosgenation process. As will be described below, the reaction
2010 will be about 5 million tonnes.
and product characteristics are consistent with two sequential
MDI can be manufactured on the industrial scale by the
hydrochlorination processes. Secondly, the reaction of
phosgenation of MDA in a solvent such as chlorobenzene.
MDAꢀHCl (3) with adventitious water present during
A complicating feature of the phosgenation process is that the
attempted recrystallisation of the compound led unexpectedly
hydrogen chloride liberated reacts with the MDA starting
to the isolation of a hydrate, which we formulate as a basic
hydrochloride salt (4).
Because the hydrochloride salts, MDAꢀHCl and MDAꢀ
a Department of Chemistry, Joseph Black Building,
University of Glasgow, Glasgow, Scotland, UK G12 8QQ.
2HCl, are effectively insoluble in the phosgenation process
solvent, chlorobenzene, the study of their formation presents a
considerable challenge. We have adopted an approach in
which attention is directed to understanding those features
of the solids from which useful information about the
reactions in Scheme 1 can be inferred. The approach used is
identical to that developed to study the hydrochlorination of
the simple aromatic amine, 4-benzylaniline, 4-BA,6 and we
examine here the formation and properties of hydrochloride
salts originating from the industrially relevant MDA. The
E-mail: davidle@chem.gla.ac.uk, d.lennon@chem.gla.ac.uk;
Fax: +44 (0)141 330 4888; Tel: +44 (0)141 330 4372
b Huntsman (Europe) BVBA, Everslaan 45, 3078 Everberg, Belgium
c Dipartimento di Chimica Strutturale e Stereochimica Inorganica,
University of Milano, via Venezian 21, 20133 Milano, Italy
w Electronic supplementary information (ESI) available: Crystallo-
graphic tables for (1), (2) and (4) and crystallographic data for the
structures of MDA (1), MDAꢀ2HCl (2) and [MDAH2][Cl]2[MDA]2-
H2O (4). CCDC reference numbers 740258–740260. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/b916368a
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Scheme 1 Reaction of 4,40-methylene dianiline (1) with HCl to form 4,40-methylene dianiline monohydrochloride (3) and thence, 4,40-methylene
dianiline dihydrochloride (2). Recrystallisation of (3) to give a hydrate, formulated as a basic hydrochloride salt (4).
presence of two –NH2 functional groups in MDA leads to
2. Experimental
complexities that were not found in the 4-BA/HCl/C6H5Cl
system.6 The synthesis of the thermodynamically stable
2.1 Preparation of hydrochloride salts, MDAꢀ2HCl (2) and
MDAꢀHCl (3)
dihydrochloride, MDAꢀ2HCl, is described and the procedure
is modified for preparation of the monohydrochloride,
Chlorobenzene (Sigma-Aldrich, purity 99.8%, o0.005%
water) was purified as described previously.6 Anhydrous HCl
(anhydrous commercial grade, Linde Gas) was dispensed from
a lecture bottle which was fitted with a regulator compatible
with corrosive gases (Praxair, inlet pressure range 0–2.8 ꢂ
104 MPa, outlet range 0–700 MPa) and a stainless steel bonnet
needle valve (Whitey) in order to control the gas flow
into vacuum or flow apparatus. 4,40-Methylene dianiline
(Sigma-Aldrich, purity 97%, mp = 362–364 K, literature
mp = 375 K10) was used without further purification. Melting
points (uncorrected) were determined using a Stuart Scientific
SMP1 instrument. Elemental analyses were obtained using a
CE 440 Elemental Analyser (Exeter Analytical Inc.). The same
procedure and glass reactor/gas manifold unit used to
prepare 4-benzylaniline hydrochloride6 were used to prepare
4,40-methylenedianiline dihydrochloride, MDAꢀ2HCl (2). A
colourless solid, mp = 534 K, precipitated from solution.
Found C, 57.7; H, 5.9; Cl, 26.2; N, 10.2%. C13H16Cl2N2 req. C,
MDAꢀHCl. Whereas
a previous crystallographic study
exists for the diamine,7 no such analysis apparently exists
for the hydrochloride salts and data presented here show
how hydrochlorination dramatically perturbs the structure
of the parent molecule. These structures are compared
with the rather complex hydrogen bonding arrangements
found in the basic hydrochloride salt (4), which is the
product of attempted recrystallisation of MDAꢀHCl from
methanol containing adventitious water (Scheme 1).
The forces acting between molecules in the crystals of MDA
(1) and MDAꢀ2HCl (2) were calculated by the PIXEL
method.8,9 The relative magnitudes of these forces provide
a valuable insight into the factors which influence solubility
and hence mass transport criteria in chlorobenzene.
Such improvements in understanding of solute–solute inter-
actions are prerequisites for improving the atom economy of
this important stage within the polyurethane manufacture
process chain.
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Solubility measurements in chlorobenzene were performed
1
using H NMR spectroscopy in a comparable fashion to that
57.6; H, 5.9; Cl, 26.2; N, 10.3%. Modifications to the appa-
ratus and procedure were necessary for the preparation of 4,40-
methylenedianiline monohydrochloride, MDAꢀHCl (3). Spe-
cifically, a detachable Pyrex cell was charged with a stoichio-
metric amount of HCl on a separate vacuum manifold. The
HCl was then isolated and frozen using an isopentane/liquid
nitrogen slush bath prior to re-connection to the flow appa-
ratus. Controlled and gradual addition of the HCl within a
nitrogen carrier gas feedstream to a degassed, vigorously
stirred solution of MDA in chlorobenzene at 293 K afforded
the reproducible preparation of MDAꢀHCl (3) as a colourless
solid. Found (results from two different samples) C, 66.7, 66.6;
H, 6.5, 6.4; Cl, 15.3, 15.2; N, 11.9, 11.8%. C13H15ClN2 req. C,
66.5; H, 6.4; Cl, 15.1; N, 11.9%. Although a 1 : 1 mole ratio
MDA : HCl was indicated by these analyses, the mp of the
solid occurred over the range 461–498 K. It is possible that
there is a slow loss of HCl when the material is heated.
described in the 4-benzylaniline work,6 which had afforded a
detection limit for 4-benzylaniline of 1 ꢂ 10ꢃ2 mmol dmꢃ3
.
The concentration of solvated MDA (MDA(solv)
) was
determined by integration of the CH2 signal with reference
to an internal standard, CH2Cl2.
Single crystals of MDA (1) were obtained from chloro-
benzene. The solid MDAꢀ2HCl (2) was recrystallised from
methanol (AR grade, purity Z 99.8%) in an atmosphere
of chlorobenzene using a vapour-diffusion crystallisation
procedure. Single crystals of both compounds were mounted
on glass rods and transferred to the cold-gas stream of a
Nonius Kappa CCD X-ray diffractometer for measurement.
The structures were analysed using the WinGX and SHELX-97
software (see Table 1).11–13 The X-ray structural analysis on
the sample obtained by recrystallising MDAꢀHCl (3) from
MeOH established that a chemical change had occurred
and that the composition of the crystal was in fact
[MDAH2][Cl]2[MDA]2H2O (4), i.e. C39H46Cl2N6O, which
requires C, 68.3; H, 6.8; Cl, 10.3; N, 12.3; O, 2.3% and is thus
incompatible with the analytical data obtained for (3) before
recrystallisation (see above).
2.2 Characterisation
Infrared spectra of the solids MDA (1), MDAꢀ2HCl (2) and
MDAꢀHCl (3) were obtained using ATR-FTIR spectroscopy
(Pike MIRacle ATR accessory with diamond/ZnSe element
used within a purged Nicolet Avatar 360 FTIR spectrometer).
1H NMR spectra were obtained on solutions of the reagent
and products using a Bruker Avance 400 MHz spectrometer.
Frequency positions are quoted using the d scale, with d = 0
referenced to TMS. The solutions were prepared by dissolving
a few mg of sample in dimethyl sulfoxide-d6 (Aldrich, 99.9
atom% D, o50 ppm water). The 1H NMR spectra of (1), (2),
(3) and (4) in d6-DMSO were studied in order to provide
chemical shift information for reasonably concentrated
solutions. The spectra were characterised by chemical shifts
for the –NHx (x = 2 or 3) species at d = 4.8, 9.3, 7.9 and
Standard refinement methods were used in the analyses.
Thus, H atoms bonded to N or O atoms were freely refined,
except for (2) where restraining the N–H distances to 0.86(2) A
slightly improved the results; the riding model was used
throughout for C-bonded H atoms. For (1) dispersion is
insignificant; accordingly, Friedel pairs were merged and the
absolute structure was not determined. This contrasts with (4)
where 2291 Friedel pairs were retained as separate observations
and the Flack parameter of 0.01(4) indicates unambiguous
determination of absolute structure.
2.3 Computational studies
1
8.2 ppm respectively. In all cases the aromatic ring H signals
correspond to [AA0BB0]2 spin systems. The d values for the
CH2 signals occurred at d = 3.56, 3.92, 3.77 and 3.78 ppm
respectively.
Intermolecular energies were calculated for the crystal
structures by the PIXEL method,8,9 or by the atom–atom
potential energy method. The former method is based on
Table 1 Crystal data and structure refinements for compounds (1), (2) and (4)a
MDA (1)
MDAꢀ2HCl (2)
[MDAH2][Cl]2[MDA]2H2O (4)
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/A
C13H14N2
198.26
150
Orthorhombic
P212121
5.9003(5)
9.5998(10)
19.1346(15)
C13H16Cl2N2
271.18
150
Monoclinic
P2/n
6.0828(9)
4.5346(9)
24.586(5)
90.694(12)
678.1(2)
2
7360
1194, 0.104
776
C39H46Cl2N6O
685.72
120
Monoclinic
C2
25.6208(5)
5.7067(2)
13.7826(5)
118.962(1)
1763.1(1)
2
15 531
5192, 0.047
4851
b/A
c/A
b/1
V/A3
1083.8(2)
4
6216
1427, 0.080
924
97.4 to 27.5
1427/152
0.059, 0.098
0.114, 0.110
0.18
Z
No. measured
No. unique, Rint
No. observed [I 4 2s(I)]
Completeness (%) to ymax (1)
Data/parameters
R1, wR2 [I 4 2s(I)]
R1, wR2 (all data)
|Dr|max/e Aꢃ3
98.0 to 25.1
1194/90
0.071, 0.120
0.125, 0.136
0.45
98.6 to 30.5
5192/250
0.037, 0.082
0.042, 0.083
0.30
a
All measurements with Mo-Ka X-rays, l = 0.71073 A. Full-matrix least-squares refinement on F2.
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numerical integrations over molecular charge densities
obtained by high-level, correlated quantum mechanical
calculations, to obtain partitioned coulombic, polarization,
dispersion and repulsion energy contributions. The atom–
atom calculations were carried out in the EUNI + EEHT
approximation, whereby total energies consist of a Buckingham-
type 6-exp term and a coulombic term over atomic point
charges calculated using a variant of the extended Huckel
method (see also our previous work6 for more detail).
Fig. 1 A view of the MDA (1) molecule. Here and in Fig. 3 and 5
30% probability ellipsoids are shown and phenyl rings are numbered
cyclically Cn1–Cn6, with Cn1 bound to the central Cn methylene
carbon atom and Cn4 attached to the amine nitrogen atom.
3. Results and discussion
other species.17 There is a single report of a structure containing
the monoprotoꢃnated diamine [p-H3NC6H4CH2C6H4NH2-p]+,
Ph2C(OH)CO2 being the counter-anion.18
3.1 Solubility measurements
The solubility of MDA (1) and MDAꢀ2HCl (2) in chlorobenzene
was investigated by 1H NMR spectroscopy. The saturation
concentration of MDA (1) in chlorobenzene at 298 K was
found to be 0.138 ꢄ 0.007 mol dmꢃ3, with the error represent-
ing 1 standard deviation in 4 replicate measurements. This
value is 34 times smaller than that of its monoamine analogue,
4-benzylaniline (4-BA),6 indicating that the extra amine group
has a modestly detrimental effect on the solubilisation process.
The salt, MDAꢀ2HCl (2), was found to be insoluble in
chlorobenzene at room temperature and even heating at
355 K for 5.8 h did not result in dissolution, as was shown
3.2.1 Crystal structure of MDA (1). The crystal is built
from discrete molecules (Fig. 1) in which the
C12–C11–C1–C21–C22 sequence displays respective torsion
angles of ꢃ17.8(5) and ꢃ66.7(4)1 across the C1–C11 and
C1–C21 bonds.
A search for intermolecular contacts using the WINGX
version of PLATON12 reveals three CgꢀꢀꢀCg distances o5.5 A,
each of which is associated with a X–Hꢀ ꢀ ꢀCg interaction in
which the HꢀꢀꢀCg distance is o3.1 A, Table 2(a).z Furthermore,
the molecules are linked into chains running parallel to the
c-axis by moderate-to-weak19 Nꢀ ꢀ ꢀH–N hydrogen bonds,
Table 2(b) and Fig. 2. The significance of the contacts listed
in Table 2(a) and (b) is best considered in the light of the lattice
energy calculations reported in Section 3.3. However, it is
worth pointing out here that (i) it is not obvious from
Table 2(a) that the intermolecular interaction involving the
C25–H25ꢀ ꢀ ꢀCg1i contact makes a larger contribution to the
lattice energy than that which involves the N1–H111ꢀ ꢀ ꢀCg1ii
contact and (ii) the search failed to find the second most
important contributor to the lattice energy, namely the p–p
interaction between the molecules related by translation along
the short (5.90 A) a-axis: the shortest intermolecular inter-
atomic distance involving the operation 1 + x, y, z, that of
3.07 A between H13ꢀ ꢀ ꢀC16 is 0.17 A greater than the sum of
the H and C van der Waals radii.
1
by the absence of relevant signals in the H NMR spectrum.
Given that the spectral acquisition procedures selected afford a
detection limit of 0.01 mmol dmꢃ3 for 4-benzyl aniline,6 it is
concluded that the solubility of MDAꢀ2HCl (2) is less than
0.01 mmol dmꢃ3 over this temperature range. Moreover, no
amine signals were observed in the NMR spectrum, indicating
that MDAꢀ2HCl did not dissociate under these conditions to
form MDA (or MDAꢀHCl) in solution. The dissolution of
MDAꢀHCl (3) was not investigated. Further, the solid present
in these MDAꢀ2HCl dissolution experiments was not checked
to discover if any solution mediated phase transformation had
taken place.
In contrast, 4-benzylaniline hydrochloride (C6H5CH2C6H4NH2ꢀ
HCl, 4BAꢀHCl) is sparingly soluble in chlorobenzene at
ambient temperature (0.26 ꢄ 0.13 mmol dmꢃ3). Thus, the
significantly reduced solubility of MDAꢀ2HCl (2) in chloro-
benzene, even on warming to 355 K, indicates that the
additional hydrochloride unit, known from the X-ray analysis
to be ionic (see Section 3.2), significantly enhances the cohesive
interactions within the solid, due to the strong coulombic
component between ionic fragments, and thereby works
against solubilisation by non-polar chlorobenzene molecules.
3.2.2 Crystal structure of MDAꢀ2HCl (2). The unit cell
contains [MDAH2]2+ cations and chloride anions. Each
cation (Fig. 3) has exact C2 symmetry, with the diad passing
through the methylene carbon atom C1, so that the two
protonated aniline residues are related by the operation (i)
3/2 ꢃ x, y, 1/2 ꢃ z. The symmetrical conformation of the
cation, defined by the C11i–C1–C11–C16 torsion angle of
71.7(5)1, contrasts with that of free MDA (1) (see Section 3.2.1).
Hydrogen bonding plays an important role, Table 2(c), in
stabilising the crystal; each N–H bond of the cation donates a
proton to a different Clꢃ anion, so that at both ends of the
MDA cation ribbons of H-bonds run parallel to the a-axis
(Fig. 4). Similar ribbons of N–Hꢀ ꢀ ꢀCl bonds occur in
4-BAꢀHCl.6 The geometries of the three N–Hꢀ ꢀ ꢀCl bonds in
MDAꢀ2HCl (2) resemble both one another and those in aniline
3.2 Crystal structure determinations
The structure of MDA (1) at room temperature has previously
been reported; the slight differences between the results of
Bel’skii et al.7 and those obtained by us at 150 K can be
explained by the difference in temperature between the
two experiments. A search of the Cambridge Structural
Database, Version 5.30 of November 2008,14,15 for the
p-N–(C6H4)–CH2–(C6H4)–N-p fragment revealed a number
of recent and relevant structural studies, either of salts of the
[p-H3NC6H4CH2C6H4NH3-p]2+ dication16 or of the neutral
[p-H2NC6H4CH2C6H4NH2-p] diamine co-crystallised with
z Throughout this paper Cg is used to denote the centroid defined by
the six carbon atoms of an aromatic ring.
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Table 2 Geometry of intermolecular interactions (A and 1) in MDA (1) and MDAꢀ2HCl (2)a,b,c
(a) Cgꢀ ꢀ ꢀCg contacts o5.5 A and associated X–Hꢀ ꢀ ꢀCg contacts o3.1 A in MDA (1)
Contact
Distance
j
X–Hꢀ ꢀ ꢀCg
Cgꢀ ꢀ ꢀH
3.03
2.89
2.73
+X–Hꢀ ꢀ ꢀCg
139
166
141
Cgꢀ ꢀ ꢀX
3.80
3.77
3.55
Cg2ꢀ ꢀ ꢀCg1i
Cg1ꢀ ꢀ ꢀCg1ii
Cg1ꢀ ꢀ ꢀCg2iii
5.03
5.22
5.38
58
47
86
C25–H25ꢀ ꢀ ꢀCg1i
N1–H111ꢀ ꢀ ꢀCg1ii
N1–H112ꢀ ꢀ ꢀCg2iii
(b) Hydrogen bonds in MDA (1)
Aꢀ ꢀ ꢀH–D
d(H–D)
d(Aꢀ ꢀ ꢀH)
2.30(4)
d(Aꢀ ꢀ ꢀD)
3.172(5)
+Aꢀ ꢀ ꢀH–D
165(3)
N1ꢀ ꢀ ꢀH221iv–N2iv
0.90(3)
(c) Hydrogen bonds in MDAꢀ2HCl (2)
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
+D–Hꢀ ꢀ ꢀA
N1–H1Nꢀ ꢀ ꢀCl1ii
N1–H2Nꢀ ꢀ ꢀCl1
N1–H3Nꢀ ꢀ ꢀCl1iii
0.87(2)
0.88(2)
0.87(2)
2.35(2)
2.25(2)
2.42(3)
3.190(5)
3.113(5)
3.233(5)
164(5)
165(5)
156(6)
a
Cg1 and Cg2 are the centroids of phenyl rings C11–C16 and C21–C26 and j is the dihedral angle between phenyl rings in contact with one
b
another. Symmetry codes for MDA (1): (i) ꢃx, 1/2 + y, 1/2 ꢃ z; (ii) ꢃ1/2 + x, 3/2 ꢃ y, 1 ꢃ z; (iii) 1/2 ꢃ x, 1 ꢃ y, 1/2 + z; (iv) ꢃ1/2 ꢃ x, 1 ꢃ y,
c
1/2 + z. Symmetry codes for MDAꢀ2HCl (2): (i) ꢃx + 3/2, y, ꢃz + 1/2; (ii) ꢃx + 1, ꢃy + 1, ꢃz + 1; (iii) ꢃx + 2, ꢃy + 1, ꢃz + 1.
Fig. 2 The MDA (1) unit cell viewed along the crystallographic a-axis. Chains of molecules running parallel to the horizontal c-axis are linked by
N–Hꢀ ꢀ ꢀN bonds.
Fig. 3 The MDAꢀ2HCl (2) structure viewed down the diad axis
passing through C1. See Table 2, footnote c for symmetry codes.
hydrochloride (Nꢀ ꢀ ꢀCl 3.16, 3.16 and 3.18 A) which also
contains RNH3+Clꢃ ion pairs.20
Fig. 4 The MDAꢀ2HCl (2) unit cell viewed along the crystallographic
Although the short b-axis of 4.53 A might suggest that the
2+
b-axis, showing the ladder arrangement of MDAH2 cations arising
p–p interaction contributes significantly to the lattice energy,
from N–Hꢀ ꢀ ꢀCl H-bonding.
there are no particularly short individual interatomic contacts
between cations related by translation along b; the shortest is
four distinct species are present and that the crystal is best
the C1–H1ꢀ ꢀ ꢀC16 distance of 2.94 A.
represented by the formula [MDAH2][Cl]2[MDA]2H2O (4).
The diprotonated MDA cation and Clꢃ counter-anion are
3.2.3 Crystal structure determination of [MDAH2][Cl]2-
[MDA]2H2O (4). As previously pointed out, recrystallisation
of MDAꢀHCl (3) from methanol gave diffraction-quality
crystals of a hydrated basic hydrochloride of formal composition
3MDAꢀ2HCl,H2O. The diffraction analysis establishes that
shown, together with the MDA and water molecules in Fig. 5.
The methylene carbon atom of the [MDAH2]2+ cation,
C21, and the water oxygen atom, O1, both lie on crystallo-
graphic diad axes. The conformation of the [MDAH2]2+
cation, defined by the C211i–C21–C211–C216 torsion angle
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outcome is presumably a reflection of the importance of
hydrogen bonding in the solid formed and is rationalised on
the basis that water is a better H-bond acceptor than HCl. The
HCl missing from the structure is believed to have been lost by
evaporation with the methanol. As noted earlier, a salt of the
monoprotonated diamine [p-H3NC6H4CH2C6H4NH2-p]+
presumed to be present in (3) has recently been structurally
characterised.18
In crystals of (4) all four residues are involved in a complex
network of hydrogen bonds (Fig. 6). In considering these, it is
helpful to bear in mind the values of Hꢀ ꢀ ꢀCl distances that are
regarded as typical for various types of XHꢀ ꢀ ꢀCl hydrogen
bond (Table 3). A X–Hꢀ ꢀ ꢀCl interaction has been included in
the list of hydrogen bonds (Table 4) if the Hꢀ ꢀ ꢀCl distance is
less than 3.0 A, the sum of the van der Waals radii of H and Cl.
The –NH3+ nitrogen atom, N21, of the dipositively charged
cation forms four hydrogen bonds: two to neutral amine
nitrogen atoms N12i and N11 (bonds 4 and 6), one to Cl1v
(bond 7) and one to the water O1 atom (bond 5). Bonds 4 and
5 make up a bifurcated H-bond.21 Atoms N11 and N12 of the
two neutral amine groups each form a N–Hꢀ ꢀ ꢀCl H-bond
(bonds 1 and 2) in which the HꢀꢀꢀCl distances, 2.48 and 2.59 A,
respectively, are long compared with the typical values of
Table 3. In addition, N12 participates in a second and
extremely weak interaction with Cl1iv (bond 3, Hꢀ ꢀ ꢀCl =
2.85 A). Furthermore, the free H1A donor atom bonded to
Fig. 5 A view of the [MDAH2]2+, [MDA], Clꢃ and H2O residues in
(4). C21 and O1 lie on crystallographic C2 axes. For symmetry codes
see Table 4, footnote a.
of 38.0(1)1, is appreciably flatter than that in MDAꢀ2HCl (2)
where the corresponding angle is 71.7(5)1, while the torsion angles
of 81.9(2)1 and 47.4(2)1 in the C116–C111–C11–C121–C126
chain of the neutral amine molecule compare with values
of ꢃ17.8(5)1 and ꢃ66.7(4)1 in MDA (1). Evidently these
torsion angles are largely determined by packing requirements.
The formation of (4) corresponds to the reaction between
MDAꢀHCl (3) and water shown in eqn (1).
3MDAꢀHCl(s) + H2O(l) - [MDAꢀ2HCl + 2MDA + H2O](s)
Table 3 Ranges of Hꢀ ꢀ ꢀCl distances in X–Hꢀ ꢀ ꢀCl hydrogen bonds
according to Jeffrey19
+ HCl(g)
(1)
Hꢀ ꢀ ꢀCl/A
Min
It had been assumed that the compound would exist in
methanol without change in stoichiometry (MDAꢀHCl) and
that one amine group of the MDA molecule would be
protonated. The methanol used was analytical reagent grade
(purity Z 99.8%) but was not completely anhydrous. The
Max
H-bond
N+(H2)Hꢀ ꢀ ꢀClꢃ
N(H)Hꢀ ꢀ ꢀClꢃ
OwHꢀ ꢀ ꢀClꢃ
2.12
2.14
2.13
2.15
2.35
2.40
Fig. 6 The structure of [MDAH2][Cl2][MDA]2H2O (4) viewed in projection along the b-axis. In the projection plane a points upwards and c runs
horizontally from right to left. Hydrogen bonds are indicated by the numbers defined in Table 4, except that the operation x, y, ꢃ1 + z has been
applied to the bonds shown radiating from N12. Since N12 links chloride anions related by translation along b, bonds 2 and 3 appear to coincide
in this view.
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Table 4 Hydrogen bond parameters for [MDAH2][Cl]2[MDA]2H2O
(4) [A and 1]a
they do not give rise to any anomalously short, inter-residue
contacts.
It is well-known that monofunctional bases, B, such as
aniline, form hydrochlorides BꢀHCl which are the chloride
salts of the protonated base BH+. Less well known are the
basic salts, B2ꢀHCl, which are also referred to as hemi-
No. D–Hꢀ ꢀ ꢀA
d(D–H) d(Hꢀ ꢀ ꢀA) d(Dꢀ ꢀ ꢀA) +(DHA)
1
2
3
4
5
6
7
8
N11–H1Bꢀ ꢀ ꢀCl1ii 0.91(2) 2.48(2)
3.388(1)
3.373(1)
3.687(2)
2.996(2)
2.803(2)
2.869(2)
3.196(1)
3.118(1)
170(2)
153(2)
158(2)
154(2)
111(2)
161(2)
143(2)
177(2)
N12–H1Cꢀ ꢀ ꢀCl1iii 0.85(2) 2.59(2)
N12–H1Dꢀ ꢀ ꢀCl1iv 0.88(2) 2.85(2)
N21–H2Aꢀ ꢀ ꢀN12i 0.88(2) 2.19(2)
1
2
hydrochlorides, Bꢀ HCl. Aniline, for example, is reported to
N21–H2Aꢀ ꢀ ꢀO1
0.88(2) 2.36(2)
form a hemihydrochloride but, surprisingly, the structure is
not known.24 Indeed, the only structurally characterised
example of the hemihydrochloride of a simple primary amine
appears to be that of cyclohexylamine; the structure
contains equal numbers of neutral cyclohexylamine molecules
and cyclohexylammonium chloride cation/anion pairs.25 The
present study shows that more complex possibilities can arise
for bifunctional bases like MDA.
N21–H2Bꢀ ꢀ ꢀN11 0.96(2) 1.94(2)
N21–H2Cꢀ ꢀ ꢀCl1v 0.90(2) 2.43(2)
O1–H1Wꢀ ꢀ ꢀCl1ii
0.91(2) 2.21(2)
a
Symmetry code: (i) ꢃx + 1, y, ꢃz + 2; (ii) ꢃx + 1/2, y ꢃ 1/2, ꢃz + 1;
(iii) ꢃx + 1/2, y + 1/2, ꢃz + 2; (iv) ꢃx + 1/2, y ꢃ 1/2, ꢃz + 2;
(v) ꢃx + 1/2, y + 1/2, ꢃz + 1.
N11 is 3.05 A from a Clꢃ anion; this interaction is not listed in
Table 4 as the H1Aꢀ ꢀ ꢀCl distance exceeds the sum of the van
der Waals radii of H and Cl. A neutron diffraction study of
bis(2-amino-2-methyl-3-butanone-oximato)nickel(II) chloride
monohydrate22 reports NHꢀ ꢀ ꢀClꢃ bond lengths of 2.301 and
2.445 A and bond angles of 161.9 and 174.01, which can be
compared to those found in [MDAH2][Cl]2[MDA]2H2O. As
previously noted, the water oxygen, O1, accepts an H-bond
3.2.4 Other structural features. Protonation of an aromatic
amine lengthens the Car–N bonds and systematically alters
endocyclic C–C–C angles. Thus, database mean Car–X bond
+
lengths are 1.394 and 1.465 A for XQNH2 and NH3
,
respectively;26 corresponding mean values of 1.412(12) A
and 1.468(6) A in (1), (2) and (4) (see Table 5) agree both
with values of 1.421 and 1.462 A from published MDA17 and
2+ 16
+
MDAH2
1.458(4)
structures and with those of 1.416(5) and
in MDAH+.19 Likewise, the Cn2–Cn4–Cn6
from the N21 NH3 group but it also donates through
H1W to Cl1ii (bond 8); the Hꢀ ꢀ ꢀCl distance of 2.21 A is
A
endocyclic bond angle, where Cn4 is attached to the amine
nitrogen, also changes systematically when the amine is
protonated; the average value of this angle is 121.5(1)1 for
the protonated amine rings in (2) and (4) and 118.4(7)1 for the
unprotonated amine rings in (1) and (4); virtually identical
values apply to published MDA structures.17,18 This change in
bond angle can be attributed to the greater group electro-
unexceptional (see Table 3).
The bifurcated H-bond21 found in the structure of
[MDAH2][Cl]2[MDA]2H2O (4) is common in proton deficient
systems, such as amino acids, carbohydrates and esters. In a
recent survey of 42 structures containing bifurcated bonds
with ester O and amine N as acceptors, mean Hꢀ ꢀ ꢀN and
Hꢀ ꢀ ꢀO distances of 2.31(6) and 2.44(10) A, respectively, were
found.23 Comparing these values with Hꢀ ꢀ ꢀN and Hꢀ ꢀ ꢀO
distances of 2.19(2) and 2.36(2) A in the bifurcated system of
(4) suggests bond 4 contributes more to the stability of (4) than
bond 5. The acute N–Hꢀ ꢀ ꢀO angle of 1111 also indicates that
bond 5 is relatively weak.
+
negativity of NH3 compared with NH2.27 Variations in the
angular geometry of monosubstituted benzene ring derivatives
have been used as the basis of an approach to the estimation of
group electronegativities.28–34 Thus, the acuteness of the mean
C–Cn1–C angle of 117.81 for (1), (2) and (4) (Table 5) reflects
electron release by the methylene group.
The hydrogen bonding scheme presented here for (4) makes
use of all available donor H atoms, provided the very long
Clꢀ ꢀ ꢀNH2 contact of 3.05 A is included, and also of all
acceptor sites on N, O or Cl atoms. It gives rise to {MDAH2,
2MDA} units with C2 symmetry, two of which are shown in
3.3 Intermolecular energies in MDA (1) and MDAꢀ2HCl (2)
crystals
Numerical results are summarised in Table 6, while structures
are depicted in Fig. 7. For MDA, the hydrogen-bonded
molecular pair has a higher coulombic-polarisation energy
and a smaller dispersion contribution than other pairs. The
+
Fig. 6, each held together by four NH3 - NH2 N–Hꢀ ꢀ ꢀN
hydrogen bonds. The structure is then completed through
hydrogen bonding between this unit, water molecules and
Clꢃ anions. Although X–H - p-ring and p–p stacking
interactions undoubtedly contribute to stabilising the crystal,
presence of
a hydrogen bond increases the coulomb-
polarization contribution to the lattice energy in the crystal
Table 5 Selected bond lengths and angles (A and 1) for MDA (1), MDAꢀ2HCl (2) and [MDAH2][Cl]2[MDA]2ꢀH2O (4)
MDA (1)
MDAꢀ2HCl (2)
[MDAH2][Cl]2[MDA]2H2O (4)
Compound
Ring no. n
Cn4–X, X =
1
NH2
2
NH2
1
NH3
11
NH2
12
NH2
21
NH3
+
+
Cn4–N
1.409(4)
1.523(4)
1.388(2)
115.6(2)
117.2(2)
118.4(2)
1.397(4)
1.512(4)
1.384(2)
1.472(6)
1.511(6)
1.380(7)
112.9(6)
117.4(5)
121.6(5)
1.420(2)
1.514(2)
1.393(2)
115.7(2)
117.4(1)
119.1(1)
1.423(2)
1.521(2)
1.394(2)
1.463(2)
1.516(2)
1.390(2)
114.4(2)
119.0(1)
121.5(1)
CH2–CPh
hC–CiPh
C–CH2–C
C–Cn1–C
C–Cn4–C
117.1(3)
117.6(3)
117.7(1)
118.8(1)
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Table 6 Molecule–molecule interaction energies in MDA (1) crystals.
See Fig. 7 for the corresponding molecular structural diagrams
molecules of MDA and water, and chloride anions present
in ratio 1 : 2 : 1 : 2. The present PIXEL implementation
allows only up to two different chemical species in the same
crystal, so a PIXEL calculation for (4) is impossible. However,
using the atom–atom potential method (with atomic point
charges calculated by the more accurate ESP procedure for the
coulombic contribution) an approximation to the lattice
energy was obtained for this complex species too (Table 7).
The heat of sublimation estimated by the atom–atom
approach is nearly identical to the PIXEL values for
MDA (1), and is broadly comparable to the PIXEL value
for MDAꢀ2HCl (2); the inclusion of penetration energies by
PIXEL obviously provides a better estimate. Although the
heat of sublimation calculated for (4) is only an approximation, it
does show that the value lies between those of the free amine
(1) and the hydrochloride (2).
PIXEL energies/kJ molꢃ1
Ecoul
Epol
Edisp
Erep
Etot
Molecular pair
C–H - p ring
ꢃ12
ꢃ5
ꢃ31
18
ꢃ31
1
1
ꢃx, + y, ꢃ z
2
2
p–p stacking
1 ꢃ x, y, z
ꢃ8
ꢃ26
ꢃ11
ꢃ2
ꢃ9
ꢃ5
ꢃ24
ꢃ26
ꢃ21
11
25
18
ꢃ23
ꢃ22
ꢃ19
H-bond
ꢃ ꢃ x, 1 ꢃ y, + z
1
2
1
2
N–H - p ring
1
3
x ꢃ , ꢃ y, 1 ꢃ z
2
2
The combination of information from single crystal X-ray
diffraction and PIXEL calculations of crystal cohesion
energies provides a pointer to the rationalization of the
different solubilities of MDA (1) and MDAꢀ2HCl (2) in
chlorobenzene. The rationale follows that laid out in detail
in our earlier study6 of 4-benzylaniline; the types of solid state
interactions involved in the comparison between MDA and its
hydrochloride salt are the same as those considered pre-
viously6 for the BA vs. BAꢀHCl pair, although, as mentioned
above, the energies involved now cover a wider range. Table 7
shows that the lattice energy of the dihydrochloride salt (2) is
an order of magnitude larger than that of the free base, as
expected for strong ionic bonds against the moderately polar,
or largely dispersive, interactions in the uncharged species.
The one dimensional H-bonding arrangement in MDA (1)
crystals with its medium-strong binding energy is more prone
to dissolution in chlorobenzene; on the other hand, in order to
overcome the substantial stabilization of the solid, dissolution
of MDAꢀ2HCl (2) requires some combination of a large
solvation enthalpy and a favourable entropy of solution, both
conditions being unlikely to be met by a poor donor solvent
like chlorobenzene. As described in Section 2.2, reagents and
products (1), (2), (3) and (4) were all soluble in d6-DMSO,
enabling 1H NMR spectra to be recorded. Thus it is apparent
that dissolution of MDAꢀ2HCl is possible when a better donor
solvent such as DMSO is used, which additionally has a
greater permittivity.
Fig. 7 Structural diagrams for the most relevant molecular-pair
interactions in the crystal of MDA (1): C–H - phenyl ring, p–p
stacking, H-bond and N–H - phenyl ring interactions. See Table 6
for the corresponding interaction energies.
of MDA with respect to the crystal of 4-benzylaniline (4-BA)
[Esub = ꢃ108 kJ molꢃ1].6
The dihydrochloride salt, MDAꢀ2HCl (2), contains one
dipositively charged cation which is balanced by two chloride
anions. The total sublimation energy is the sum of the packing
energy of the ion triad as a whole, plus the energy of the
interaction between the cation and the chloride anions within
the triad. These energies are shown in Table 7. Given that the
corresponding energy for 4-benzylaniline hydrochloride
(4-BAꢀHCl) is ꢃ759 kJ molꢃ1,6 it is clear that the values for
MDAꢀ2HCl (2) are close to twice the corresponding energies
for 4-BAꢀHCl, as expected from the presence of two ionic sites
instead of one.
3.4 FTIR spectroscopy
Infrared spectra in the 4000–2000 cmꢃ1 region for solid MDA
(1) and MDAꢀ2HCl (2) are shown in Fig. 8. Also shown
are spectra for freshly-prepared MDAꢀHCl (3) and for
[MDAH2][Cl]2[MDA]2H2O (4), obtained by recrystallisation
The crystal structure of [MDAH2][Cl]2[MDA]2H2O (4)
contains four chemical residues: a doubly charged cation,
Table 7 Total lattice energies with PIXEL partitioning. The corresponding atom–atom estimates are also shown. Enthalpies of sublimation are
approximated by the negative of the total lattice energies
Ecoul
/
Epot
/
Edisp
/
Erep
/
Etot PIXEL/
kJ molꢃ1
DEsub
/
EUNI+EHT/
kJ molꢃ1
kJ molꢃ1
kJ molꢃ1
kJ molꢃ1
kJ molꢃ1
kJ molꢃ1
MDA (1)
MDAꢀ2HCl (2)
ꢃ74
ꢃ465
ꢃ1027
—
ꢃ33
ꢃ176
ꢃ160
—
ꢃ134
ꢃ201
ꢃ27
—
110
279
115
—
ꢃ130
ꢃ562
ꢃ1099
—
130
1661
ꢃ127
Framework
Cation/Clꢃ
ꢃ1422
[MDAH2][Cl]2[MDA]2H2O (4)
—
ꢃ1331
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(NH2C6H4CH2C6H4NH2ꢀHCl) (3). Although the features in
Fig. 8(c) could correspond to those from a 1 : 1 mole
ratio mixture of (1) and (2), the single crystal XRD data
(Section 3.2.3) from the MeOH recrystallised product (4)
favour its formulation as a single product.
The infrared spectrum of the recrystallised mono-
hydrochloride (4), the composition of which corresponds to
[MDAH2][Cl]2[MDA]2H2O, as determined by XRD (Section
3.2.3), is shown in Fig. 8(d). This spectrum is comparable to
that of MDAꢀHCl (3), Fig. 8(c), but the bands are considerably
broadened. This is attributed to the additional hydrogen
bonding interactions within the [MDAH2][Cl]2[MDA]2H2O
+
(4) structure. Both the NH2 and NH3 units are affected.
The n(N–H) vibration of NH2 is represented by a broad band
about 3280 cmꢃ1; the Fermi resonance about 2600 cmꢃ1 is also
broadened compared with the equivalent bands in (2) and (3).
The difference in the spectral profiles between Fig. 8(c) and (d)
confirms that the monoprotonated base, MDAꢀHCl (3), has
changed on crystallisation; the spectral features in Fig. 8(d),
although not definitive on their own, are consistent with the
formulation [MDAH2][Cl]2[MDA]2H2O (4) derived from the
XRD analysis.
Fig. 8 Reflectance FTIR spectra of solid compounds (1), (2), (3)
and (4), shown in parts (a) to (d), respectively, in the region
4000–2000 cmꢃ1
.
of (3) and characterised by X-ray analysis. A full vibrational
analysis of MDA (1) and MDAꢀ2HCl (2), involving infrared
measurements, periodic DFT calculations and inelastic
neutron scattering experiments and including some on selectively
deuterated molecules, will be published elsewhere.35
4. Conclusions
A variety of methods has been used in this study to examine
some of the factors relevant to the hydrochlorination of 4,40-
methylenedianiline, MDA, to form 4,40-methylenedianiline
dihydrochloride, MDAꢀ2HCl, in chlorobenzene. The main
results can be summarised as follows:
(i) 4,40-Methylenedianiline dihydrochloride can be prepared
from the reaction of solvated HCl and 4,40-methylenedianiline
in chlorobenzene. 1H NMR spectroscopy showed the
saturation concentration of MDA in chlorobenzene at 298 K
to be 0.138 ꢄ 0.007 mol dmꢃ3, whereas MDAꢀ2HCl was
effectively insoluble (o0.01 mmol dmꢃ3) in this solvent. These
values are considerably smaller than those for the analogous
compounds containing one amino group.
In a similar fashion to that observed for the 4-benzylaniline
system,6 the N–H stretching region is highly diagnostic for
discrimination between free amine and the hydrochloride salts.
Fig. 8(a) shows MDA (1) to be characterised by three bands
at 3472, 3435 and 3329 cmꢃ1, attributed to anti-symmetric and
symmetric stretches of the NH2 group.36 On hydrochlorination
to MDAꢀ2HCl (2), Fig. 8(b), these bands disappear and are
replaced by broad bands in the region 3240–2610 cmꢃ1. In
addition, an intense band about 2550 cmꢃ1 can be resolved
into two features at 2574 and 2549 cmꢃ1. Following the
approach presented in our earlier study,6 these two features
about 2550 cmꢃ1 are assigned to Fermi resonance processes
+
(ii) 4,40-Methylenedianiline monohydrochloride, MDAꢀHCl,
can be prepared by controlled addition of HCl to MDA in the
same solvent.
corresponding to combination bands of NH3 deformation
+
modes and NH3 rocking modes. Specifically, the features
arise from (i) a combination band comprising the anti-
+
+
symmetric NH3 deformation at 1498 cmꢃ1 and NH3 rock
at 1061 cmꢃ1 plus (ii) a combination band comprising the
symmetric NH3+ deformation at 1437 cmꢃ1 and a NH3+ rock
(iii) A detailed structural analysis of MDA and MDAꢀ2HCl
shows moderate-to-weak N–Hꢀ ꢀ ꢀN hydrogen bonding in
MDA while in the dihydrochloride each N–H bond donates
a proton to a different Clꢃ anion, resulting in ribbons of
hydrogen bonds at both ends of the [MDAH2]2+ cations and
the production of a coordination framework. Lattice energy
calculations partitioned into coulombic and dispersive factors
provide a rationalisation of the favourable interactions that
contribute to stabilising the crystal structure of the neutral
species and hydrochloride salt in the methylene diphenyl
diisocyanate (MDI) process solvent, chlorobenzene. The
at 1118 cmꢃ1
.
The intermediate compound, MDAꢀHCl (3), depicted in
Fig. 8(c) displays intermediate behaviour between that of
MDA (1) and MDAꢀ2HCl (2). The NH2 stretching modes
are observed ca. 3300 cmꢃ1 in addition to the shifted N–H
+
stretches of the NH3 group ca. 2800 cmꢃ1. More distinctly,
an intense band at 2600 cmꢃ1 is also apparent, corresponding
+
to the NH3 derived, Fermi resonance process described
above. The presence of free amine (NH2 derived modes) and
+
protonated amine (NH3 derived modes) is consistent with
greater lattice energy of the dihydrochloride salt (Elattice
=
ꢃ1661 kJ molꢃ1) compared with that of the free base
(Elattice = ꢃ130 kJ molꢃ1) provides a partial rationalisation
of the solubility differences of the two compounds in
chlorobenzene.
hydrochlorination of a single amine group of the diamine
molecule. This implies that hydrochlorination of the diamine
(1) occurs in a sequential manner, as described by Scheme 1,
where careful addition of one equivalent of HCl to a well-
mixed solution of diamine will yield the monohydrochloride
(iv) X-Ray analysis of crystals obtained from
a
solution of MDAꢀHCl in methanol indicates a composition
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[MDAH2][Cl]2[MDA]2H2O resulting from displacement of
HCl by water. H-bonding is extensive, with eight distinct
H-bonds within the unit cell.
13 Z. Otwinowski and W. Minor, Macromol. Crystallogr., 1997, 276,
307–326.
14 F. H. Allen, Acta Crystallogr., Sect. B: Struct. Sci., 2002, 58,
380–388.
(v) As a collateral result, we confirm that intermolecular
energy estimates, conveniently calculated between molecular
pairs by PIXEL, allow a distinctly more accurate description
and rationalization of crystal structures than is possible by
traditional methods based on detailed consideration of inter-
atomic distances and angles. It is often the case in organic
crystals that relevant interactions are not characterised by
short atom–atom distances, and vice versa.9
15 D. A. Fletcher, R. F. McMeeking and D. Parkin, J. Chem. Inf.
Comput. Sci., 1996, 36, 746–749.
16 (a) R. Nahouane, E. H. Soumhi, I. Saadoune and A. Driss, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2005, 61, 2850–2852;
(b) L.-H. Wei, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2008,
64, 734; (c) Q. Han, Acta Crystallogr., Sect. E: Struct. Rep. Online,
2007, 63, 4456; (d) Z.-L. Wang, L.-H. Wei, M.-X. Li and
J.-P. Wang, J. Mol. Struct., 2008, 879, 150–155.
17 (a) J. Keegan, P. E. Kruger, M. Nieuwenhuyzen, J. O’Brien and
N. Martin, Chem. Commun., 2001, 2192–2193; (b) A. J. Jarvis and
P. G. Owston, J. Chem. Soc. D, 1971, 1403; (c) W. Swardstrom,
D. P. Miller and L. A. Duvall, Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem., 1972, 28, 2510–2514; (d) V. R. Vangala,
R. Mondal, C. K. Broder, J. A. K. Howard and G. R. Desiraju,
Cryst. Growth Des., 2005, 5, 99–104.
(vi) The infrared spectrum for the monohydrochloride,
MDAꢀHCl, is consistent with the hydrochlorination of a single
amine group leading to [NH2C6H4CH2C6H4NH3+]Clꢃ,
implying that hydrochlorination of the diamine is a sequential
process.
18 J. Li, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2005, 61, 2850.
19 G. A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford
University Press, Oxford, 1997, pp. 12, 77.
20 J. F. Malone, C. M. Murray, M. H. Charlton, R. Docherty and
A. J. Lavery, J. Chem. Soc., Faraday Trans., 1997, 93, 3429–3436.
21 G. A. Jeffrey and W. Saenger, Hydrogen Bonding in Biological
Structures, Springer-Verlag, Berlin, 1991.
22 E. O. Schlemper, W. C. Hamilton and S. J. La Placa, J. Chem.
Phys., 1971, 54, 3990–4000.
Acknowledgements
Huntsman Polyurethanes is thanked for the provision of a
studentship (EKG) and research support. Drs David Rycroft
and David Adam (University of Glasgow) are thanked for
assistance with the NMR measurements.
23 K. Molcanov, B. Kojic-Prodic and N. Raos, Acta Crystallogr.,
Sect. B: Struct. Sci., 2004, 60, 424–432.
24 J. C. Speakman, Struct. Bonding, 1972, 12, 141–199.
25 P. G. Jones and B. Ahrens, Eur. J. Org. Chem., 1998, 1687–1688.
26 C. H. MacGillavry and G. D. Rieck, International Tables for X-ray
Crystallography, Physical and Chemical Tables, Kluwer Academic
Publishers, Dordrecht, The Netherlands, 2nd edn, 1999, vol. C,
I.U.Cr, Table 9.5.1.1.
Notes and references
1 Y. Yakabe, K. M. Henderson, W. C Thompson, D. Pemberton,
B. Tury and R. E. Bailey, Environ. Sci. Technol., 1999, 33,
2579–2583.
2 A. Marand, D. Karlsson, M. Dalene and G. Skarping, Anal. Chim.
Acta, 2004, 510, 109–119.
3 S. Subramani, I. W. Cheong and J. H. Kim, Prog. Org. Coat.,
2004, 51, 328–338.
27 A. Domenicano, A. Vaciago and C. Coulson, Acta Crystallogr.,
Sect. B: Struct. Crystallogr. Cryst. Chem., 1975, 31, 1630–1641.
28 A. R. Campanelli, A. Domenicano, F. Ramondo and I. Hargittai,
J. Phys. Chem. A, 2004, 108, 4940.
4 A. Corma, P. Botella and C. Mitchell, Chem. Commun., 2004,
2008–2010.
29 H. Szaty"owicz and T. M. Krygowski, J. Mol. Struct., 2007,
844–845, 200–207.
5 D. Randall and S. Lee, The Polyurethanes Book, John Wiley &
Sons, New York, 2002, p. 77.
30 G. Portalone, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2005,
61, 3083–3085.
6 E. K. Gibson, J. M. Winfield, K. W. Muir, R. H. Carr,
A. Eaglesham, A. Gavezzotti, S. F. Parker and D. Lennon, Phys.
Chem. Chem. Phys., 2009, 11, 288–297.
7 V. K. Bel’skii, V. K. Rotaru and M. M. Kruchinin, Crystallogr.
Rep., 1983, 28, 695–698.
8 A. Gavezzotti, J. Phys. Chem. B, 2003, 107, 2344–2353.
9 A. Gavezzotti, Molecular Aggregation, Oxford University Press,
Oxford, 2007, ch. 12.
31 G. Ploug-Sørensen and E. K. Andersen, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1985, C41, 613–615.
32 L. Gray and P. G. Jones, Z. Naturforsch., 2002, 57b, 61–72.
33 M. Colapietro, A. Domenicano, C. Marciante and G. Portalone,
Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem., 1981,
37, 387–394.
34 A. Dey, R. K. R. Jetti, R. Boese and G. R. Desiraju, CrystEngComm,
2003, 5, 248–252.
10 D. R. Lide, CRC Handbook of Chemistry and Physics, Taylor and
Francis, London, 86th edn, 2005, pp. 3–221.
11 G. M. Sheldrick, SHELX97-Programs for Crystal Structure
Analysis, 1998, (Release 97-2).
12 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
35 E. K. Gibson, J. Callison, A. Sutherland, J. M. Winfield, R. Carr,
A. Eaglesham, S. F. Parker and D. Lennon, to be submitted.
36 D. Lin-Vien, N. B. Colthup, W. G. Fateley and J. G. Grasselli,
The Handbook of Infrared and Raman Characteristic Frequencies of
Organic Molecules, Academic Press, London, 1991.
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