DMT [(?)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol], a highly efficient host compound for nitroaromatic guests: selectivity, X-ray and thermal analyses

Article abstract of DOI:10.1007/s10847-018-0853-6

In this work, we reveal that the compound (?)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) is a highly efficient host material for nitroaromatics o-nitrotoluene (o-NT), m-nitrotoluene (m-NT), p-nitrotoluene (p-NT) and nitrobenzene (NB). Each of these guests was included with a 2:1 host:guest ratio. The host displayed selectivity for p-NT and NB when these guests were mixed in equimolar proportions with any one of the other guest solvents, and the host recrystallized from this binary mixture. A selectivity order for the host in these conditions was thus noted to be NB ≈ p-NT > o-NT > m-NT. Furthermore, guests were also mixed in non-equimolar proportions and the host behaviour analysed, the results of which were in accordance with observations from the equimolar studies. Additionally, an equimolar quaternary experiment of all four guests provided a somewhat adjusted host selectivity order [p-NT (39.9%) > NB (30.2%) > m-NT (17.1%) > o-NT (12.8%)]. Single crystal diffraction analyses of all four complexes showed the crystals to share the same host packing, and comparable host–guest interactions were observed in each. However, thermal analyses, both DSC and TG, showed that the preferred guests p-NT and NB formed complexes with increased relative thermal stabilities, and this observation correlated with the selective behaviour of the host in competition experiments.

Full text of DOI:10.1007/s10847-018-0853-6

Journal of Inclusion Phenomena and Macrocyclic Chemistry
https://doi.org/10.1007/s10847-018-0853-6
ORIGINAL ARTICLE
DMT [(−)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol],
a highly efficient host compound for nitroaromatic guests: selectivity,
X-ray and thermal analyses
Benita Barton1 · Eric C. Hosten · Pieter L. Pohl
1
1
Received: 8 June 2018 / Accepted: 5 October 2018
©
Springer Nature B.V. 2018
Abstract
In this work, we reveal that the compound (−)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) is a highly
efficient host material for nitroaromatics o-nitrotoluene (o-NT), m-nitrotoluene (m-NT), p-nitrotoluene (p-NT) and nitroben-
zene (NB). Each of these guests was included with a 2:1 host:guest ratio. The host displayed selectivity for p-NT and NB
when these guests were mixed in equimolar proportions with any one of the other guest solvents, and the host recrystallized
from this binary mixture. A selectivity order for the host in these conditions was thus noted to be NB≈p-NT>o-NT>m-NT.
Furthermore, guests were also mixed in non-equimolar proportions and the host behaviour analysed, the results of which
were in accordance with observations from the equimolar studies. Additionally, an equimolar quaternary experiment of
all four guests provided a somewhat adjusted host selectivity order [p-NT (39.9%)>NB (30.2%)>m-NT (17.1%)>o-NT
(
12.8%)]. Single crystal diffraction analyses of all four complexes showed the crystals to share the same host packing, and
comparable host–guest interactions were observed in each. However, thermal analyses, both DSC and TG, showed that the
preferred guests p-NT and NB formed complexes with increased relative thermal stabilities, and this observation correlated
with the selective behaviour of the host in competition experiments.
Keywords Host–guest chemistry · Inclusion · Complexes · Selectivity · Nitrobenzene · Nitrotoluene
Introduction
reduction to their corresponding toluidines). Specifically,
p-NT is often sulfonated to yield 4-nitrotoluene-2-sulfonic
acid, which may be further utilized as a synthetic interme-
diate, or crystals thereof may be used in optical applica-
tions. The nitrotoluenes are synthesized through nitration of
toluene, a process that affords a mixture of the nitrotoluene
isomers with an o-NT:p-NT ratio of ~1.6 (with m-NT being
the minor product). The boiling points of o-NT (222.0 °C)
and m-NT (232.0 °C) are sufficiently different to allow their
separation through fractional distillation, after which p-NT
may be isolated through crystallization as it has a relatively
high melting point (51.6 °C).
Nitrobenzene (NB), p-nitrotoluene (p-NT), m-nitrotoluene
(
m-NT) and o-nitrotoluene (o-NT) (Scheme 1) are aromatic
compounds that have myriad applications in the chemical
industry [1–5]. Most of the nitrobenzene in production is
converted to aniline, which has a variety of applications,
but nitrobenzene is also sometimes used as a solvent for
certain reactions. Industrially, it is produced through the
mixed acid nitration of benzene. The nitrotoluene isomers
see routine use as building blocks in the production of agri-
cultural chemicals, explosives and dyes (commonly via
Much of the research conducted where one or more of
these compounds behaves as a guest in host–guest appli-
cations deals with chemically sensing them. Examples
include the work of Li et al. [6] who investigated the use of
lanthanide(III) organic frameworks as fluorescent probes for
sensing various nitroaromatics with high selectivity and sen-
sitivity. Other workers considered triptycene-polytriazoles
[7] and dendrimer-derived macromolecules [8] and their
interactions with these guest types.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10847-018-0853-6) contains
supplementary material, which is available to authorized users.
*
Benita Barton
benita.barton@mandela.ac.za
1
Department of Chemistry, Nelson Mandela University, PO
Box 77000, Port Elizabeth 6031, South Africa
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
Table 1 Composition of complexes when DMT was recrystallized
from mixed equimolar guests
NO2
NB
NB
o-NT
m-NT
p-NT
Guest ratios
%e.s.d.’s)
Overall
H:G
MeO
MeO
(
OH
OH
ratio
x
x
66.4:33.6
2.3)
16.8:83.2
1.0)
22.3:77.7
1.1)
2:1
2:1
2:1
2:1
2:1
2:1
2:1
2:1
(
NO2
NO2
x
x
x
x
(
CH3
DMT
x
x
(
CH3
x
x
13.2:20.6:66.2
o-NT
m-NT
(0.3)(0.5)(0.7)
NO2
x
x
x
x
71.9:28.1
HO
HO
(1.2)
OH
OH
x
x
79.7:20.3
(2.6)
x
x
49.6:50.4
CH3
p-NT
(
1.2)
x
30.2:12.8:17.1:39.9
(
0.8)(1.2)(0.7)(1.0)
TETROL
Ratios were determined using GC-MS analyses
Experiments were conducted in triplicate and averages are provided
Scheme 1 Structures of hosts DMT and TETROL, and guests NB,
o-NT, m-NT and p-NT
here, with %e.s.d.’s in parentheses
(
−)-(2R,3R)-2,3-Dimethoxy-1,1,4,4-tetraphenylbutane-
Results and discussion
1
,4-diol (DMT, Scheme 1) has been shown to be a highly
efficient host compound that exhibited selectivity when
recrystallized from mixtures of xylenes [9] and various
anilines [10], with the potential of thus separating such
mixtures. This compound is readily synthesized by meth-
ylation of the secondary hydroxyl groups of host TETROL
Synthesis of DMT
DMT is derived directly from TETROL in moderate yield
(65%) according to published procedures [9, 12].
[
(+)-(2R,3R)-1,1–4,4-tetraphenylbutane-1,2,3,4-tetraol,
Scheme 1]. A comparison of the behaviour of these two
host materials when recrystallized in the presence of iso-
meric toluidine mixtures showed the hosts to possess dif-
fering host ability [11], despite their structural similari-
ties, with DMT displaying significantly poorer selectivity
than TETROL in these conditions. Since DMT is selective
when presented with mixed guests, we investigated the
behaviour of this host compound in the presence of o-NT,
m-NT and p-NT (in addition to NB) to determine whether
their separation would be feasible via host–guest chemis-
try rather than the more usual fractional distillations and
crystallizations. Even though these nitroaromatics are
successfully separated industrially, it remains attractive
to probe alternative separation methodologies.
Assessment of the host potential of DMT for singular
guests NB, o‑NT, m‑NT and p‑NT
After recrystallizing DMT from each of the individual
1
nitroaromatic guests, H-NMR spectroscopy of the iso-
lated solids revealed that DMT clathrated each guest, and
each complex shared the same host:guest (H:G) ratio (2:1).
Competition experiments employing mixed guests
Equimolar guest mixtures
Since each of the guests was clathrated individually, we
conducted competition experiments by mixing guests in
equimolar proportions and recrystallizing DMT from
these mixtures. These experiments were carried out in
order to ascertain whether DMT displayed selectivity
when the guests competed. After GC-MS analyses of
Complexes that formed successfully were subjected to
single crystal diffraction and thermal analyses in order
to ascertain the nature of guest inclusion and the rela-
tive complex stabilities. The results of these studies are
presented here.
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
the crystals formed in this way, Table 1 was populated,
displaying the composition of the complexes. For ease
of distinction, the preferred guest is highlighted in bold
italic font face.
of p-NT (52%, Fig. 1d). A competition experiment com-
prising NB/m-NT (Fig. 1e) resembled that of p-NT/o-NT
(Fig. 1b), and the host was unselective at low concentra-
tions of NB (up until ~ 18%), after which point its pref-
erence for NB increased significantly. Finally, NB/o-NT
mixtures showed DMT to consistently discriminate against
o-NT in favour of NB (Fig. 1f).
In each experiment, the overall H:G ratio remained 2:1
(
Table 1). A binary competition between o-NT and m-NT
resulted in DMT preferentially including o-NT (66.4%).
However, in the presence of o-NT and p-NT, the latter sol-
vent was favoured (83.2%), and remained so also in the pres-
ence of m-NT, where 77.7% of p-NT was extracted from the
mixture. A ternary competition experiment comprising only
the nitrotoluenes resulted in a host selectivity order of p-NT
We also investigated the behaviour of DMT in the simul-
taneous presence of all three of the nitrotoluene isomers.
Once more, the mother liquors (circles, A–G) and crystal-
line solids (squares, A’−G’) were analysed and resulted
in the ternary plot provided in Fig. 2. The general trend
indicates a substantial shift towards higher p-NT concen-
trations in the complexes when compared with the mother
liquors.
(
66.2%)>m-NT (20.6%)>o-NT (13.2%).
NB was also considered in experiments of this type, and
this guest was selected for when competing against o-NT
(
71.9%) and m-NT (79.7%). However, very poor selectivity
was displayed by DMT in a competition between NB and
p-NT (p-NT, 50.4%).
Single crystal X‑ray crystallographic analyses
of complexes of DMT with o‑NT, m‑NT, p‑NT and NB
When we considered only the binary competition experi-
ments, a host selectivity order of NB≈p-NT>o-NT>m-NT
was observed. Interestingly, however, when all four guests
were mixed together, this selectivity order was altered: p-
NT (39.9%)>NB (30.2%)>m-NT (17.1%)>o-NT (12.8%).
We analysed each of the four complexes of DMT using
single crystal diffraction experiments on suitable quality
crystals in order to understand better the mode of reten-
tion of the guests within the host. These experiments were
conducted at 200 K using a Bruker Kappa Apex II dif-
fractometer with graphite-monochromated Mo Kα radia-
tion (λ = 0.71073 Å). APEXII and SAINT were used for
data collection, and cell refinement and data reduction,
respectively [13]. SHELXT-2014 [14] was used to solve
the structures, and refined by least-squares procedures
using SHELXL-2017/1 [14] together with SHELXLE [15]
as a graphical interface. Data were corrected for absorp-
tion effects using the numerical method implemented in
SADABS [13]. All non-hydrogen atoms were refined ani-
sotropically. Carbon-bound hydrogen atoms were added
in idealized geometrical positions in a riding model, and
the hydrogen atoms of the methyl groups were allowed to
rotate with a fixed angle around the C–C bonds to best fit
the experimental electron density. For disordered methyl
groups, the hydrogen atoms were added in idealized
geometrical positions, while the hydrogen atoms of the
hydroxyl groups were allowed to rotate with a fixed angle
around the C–O bonds to best fit the experimental elec-
tron density. The solvent molecules are disordered around
a twofold rotational axis necessitating the use of various
constraints and restraints. The phenyl rings of the disor-
dered solvents were forced into a regular hexagon with bond
lengths of 1.39 Å. The relevant crystallographic data have
been deposited at the Cambridge Crystallographic Data
Centre [CCDC Reference Numbers 1847990 (2DMT·o-
NT), 1847991 (2DMT·m-NT), 1847992 (2DMT·p-NT) and
1847993 (2DMT·NB)].
Non-equimolar guest mixtures
We subsequently varied the mole fractions of guests in
binary mixtures (all combinations) and then recrystallized
DMT from these. After analysing both the resultant crys-
tals (Z) and the mother liquor from which they had formed
(
X) using GC-MS, we plotted the data points (Z vs X) in
order to determine how the host behaviour changed as guest
concentrations changed. The resultant plots are provided in
Fig. 1a–f.
In these figures, the dashed straight-line plot represents
an unselective host, and is hypothetical.
From the p-NT/m-NT competition experiment (Fig. 1a),
it is clear that DMT is consistently selective for the para
isomer over the entire concentration range. However,
p-NT/o-NT mixtures revealed that, at low concentrations
of the para isomer, the host was unselective (up until
approximately 20% p-NT), and only displayed increased
selectivity for p-NT at increased concentrations of this
guest (Fig. 1b). On the other hand, the behaviour of DMT
when recrystallized from o-NT/m-NT mixtures was guest-
concentration dependent, showing preferential inclusion
of m-NT at low concentrations of the ortho isomer, and
preferring o-NT at higher concentrations of this guest. The
point of inflection occurred at approximately 36% o-NT
(
Fig. 1c). The behaviour of DMT in the presence of both
p-NT and NB was comparable to the o-NT/m-NT experi-
ment (Fig. 1c), being guest-concentration dependent, but
the point of inflection occurred at a higher concentration
Table 2 lists the relevant crystallographic and refinement
parameters for these experiments.
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
(
a)
(b)
1
00
100
90
80
70
60
50
40
30
20
10
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
10
20
30
40
50
60
70
80
90
100
0
10
20
30
40
50
60
70
80
90
100
X (p-Nitrotoluene)
X (p-Nitrotoluene)
(
c)
(d)
1
00
90
1
00
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
8
7
6
5
4
0
0
0
0
0
30
20
1
0
0
0
10
20
30
40
50
60
70
80
90
100
X (o-Nitrotoluene)
0
10
20
30
40
50
60
70
80
90
100
X (p-Nitrotoluene)
(
e)
(f)
00
1
00
1
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
9
0
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
0
10
20
30
40
50
60
70
80
90
100
X (Nitrobenzene)
X (Nitrobenzene)
Fig. 1 Selectivity profiles of DMT when recrystallized from a p-NT/m-NT, b p-NT/o-NT, c o-NT/m-NT, d p-NT/NB, e NB/m-NT and f NB/o-
NT mixtures
All four complexes of DMT crystallize in the mono-
clinic crystal system and C2 space group. A close analysis
of unit cell angles and dimensions revealed that each of the
four complexes are, in fact, isostructural. Furthermore, all
guests exhibit well-modelled symmetry-generated disorder.
Figure 3 displays the unit cell for the p-NT complex as rep-
resentative example, where the guest is in ball-and-stick and
the host in stick representation.
manner [9–11]. The geometry of the host molecule is stabi-
lized by 1,3- and 2,4-intramolecular hydrogen bonds which
range between 2.624(2) and 2.679(2) Å (O⋯O) with angles
of 140°–142° (Fig. 3, dashed lines). These are the only clas-
sic hydrogen bonds present in the crystal—no bonds of this
type exist intermolecularly with other host molecules nor
with the guests.
A stereoview was also prepared to illustrate more clearly
the host–guest packing for this complex (Fig. 4).
The isostructural nature of the host packing is a charac-
teristic of DMT, and this host consistently packs in the same
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
The guest molecules are retained in the complexes by var-
ious modes of interaction with the host, and these host–guest
interactions are summarized in Table 3.
All of the guests experience comparable and weak
π–π stacking interactions with the host, with more of
these contact types existing for NB (9 contacts), a highly
preferred guest. Host–guest CH–π interactions are, fur-
thermore, entirely absent in all complexes, while other
short contacts between host and guest are present in the
2
DMT·o-NT, 2DMT·m-NT and 2DMT·NB complexes
(
Table 3). Overall, these data do not convincingly explain
the observed preference of DMT for NB and p-NT, and so
we resorted to analysing the various complexes by means
of thermal analyses.
Thermal analyses
In order to assess the relative thermal stabilities of the
four complexes, these were subjected to thermal analyses
Fig. 2 Ternary plot illustrating the host behaviour when recrystallized
from varying concentrations of the three nitrotoluene isomers
Table 2 Crystallographic data for 2DMT·o-NT, 2DMT·m-NT, 2DMT·p-NT and 2DMT·NB
2
DMT·o-NT
2DMT·m-NT
2DMT·p-NT
2DMT·NB
Chemical formula
Formula weight
Crystal system
Space group
µ (Mo-Kα)/mm
a/Å
b/Å
c/Å
alpha/°
beta/°
2C H O ·C H NO
1046.22
Monoclinic
C2
0.082
17.4337 (9)
12.0313 (7)
14.3683 (8)
90
110.512 (2)
90
2C H O ·C H NO
1046.22
Monoclinic
C2
0.083
17.4167 (10)
12.1276 (7)
14.0545 (9)
90
109.768 (3)
90
2C H O ·C H NO
1046.22
Monoclinic
C2
0.084
17.155 (2)
12.2752 (17)
13.9597 (19)
90
109.557 (6)
90
2C H O ·C H NO
2
1032.19
Monoclinic
C2
0.083
17.2792 (9)
12.0018 (7)
13.9820 (8)
90
108.757 (2)
90
3
0
30
4
7
7
2
30 30
4
7
7
2
30 30
4
7
7
2
30 30
4
6
5
−
1
gamma/°
V/Å3
2822.7 (3)
2
2793.7 (3)
2
2770.1 (6)
2
2745.6 (3)
2
Z
F(000)
Temp./K
Restraints
Nref
1112
200
5
6814
1112
200
2
6824
1112
200
1
6853
1096
200
2
6787
Npar
347
389
359
380
R
wR2
S
0.0475
0.1383
1.06
0.0366
0.0980
1.04
0.0338
0.0886
1.03
0.0340
0.0895
1.02
θ min–max/°
Tot. data
Unique data
Observed data [I>2.0 sigma(I)]
Rint
2.1, 28.3
28,821
6814
5903
0.017
1.5, 28.3
29,120
6824
6040
0.019
2.1, 28.4
27,460
6853
6447
0.017
2.1, 28.3
26,189
6787
6177
0.018
Dffrn measured fraction θ full
1.000
−0.33
0.47
0.999
−0.16
0.20
0.999
−0.23
0.20
0.999
−0.17
0.18
3
Min. resd. dens. (e/Å )
3
Max. resd. dens. (e/Å )
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
o- and m-NT, guests that were discriminated against by DMT.
Furthermore, DSC traces correspond favourably with these
observations: although guest release occurs concomitantly
with the host melt, both NB and p-NT experience this event
at higher temperatures relative to the guests in the other two
complexes (Fig. 5b).
Conclusions
(
−)-(2R,3R)-2,3-Dimethoxy-1,1,4,4-tetraphenylbutane-
,4-diol (DMT) is a highly efficient host compound for
1
nitroaromatic guest compounds, including nitrobenzene
and the three isomers of nitrotoluene, each with a 2:1
host:guest ratio. When two guests were mixed in equi-
molar proportions and the host recrystallized from these
mixtures, it was observed that DMT displayed preferen-
tial behaviour, and the host selectivity order was noted
to be NB ≈ p-NT > o-NT > m-NT. An equimolar mixture
of all four guests, however, showed this order to change
under these conditions [p-NT (39.9%) > NB (30.2%) > m-
NT (17.1%) > o-NT (12.8%)]. Non-equimolar competition
experiments revealed that DMT was selective for p-NT
and NB over the entire concentration range when this host
was recrystallized from p-NT/m-NT and NB/o-NT mix-
tures. p-NT was also preferred when using p-NT/o-NT,
but with the host displaying non-selective behaviour at
low concentrations of this guest. The case was similar for
the NB/m-NT experiment, preferring NB but only after a
certain minimum concentration of this guest in the solu-
tion had been reached. For the o-NT/m-NT and p-NT/NB
experiments, the host preference was guest-concentration
dependent as witnessed by the sigmoidal nature of the
resulting data points. Single crystal diffraction analyses
revealed that NB, a highly preferred guest, experienced
a larger number of π–π stacking interactions but, over-
all, the host–guest interactions were comparable and did
not convincingly explain the selectivity displayed by the
host. However, TG and DSC experiments showed that
complexes containing the preferred guests p-NT and NB
displayed higher relative thermal stabilities than those
comprising o- and m-NT, as mass loss and concomitant
guest release/host melt events occurred at increased tem-
peratures for these complexes. This correlated favourably
with the host selectivity order.
Fig. 3 Unit cell of the 2DMT·p-NT complex (as representative exam-
ple)
Fig. 4 Stereoview to illustrate the host–guest packing in the 2DMT·p-
NT complex (as representative example); intramolecular host–host
hydrogen bonding is shown by means of dashed lines
by heating at 10 °C min−1 in open platinum pans. The so-
obtained thermogravimetric (TG, overlaid for each complex)
and differential scanning calorimetry (DSC, also overlaid)
traces are presented in Fig. 5a, b, respectively.
From the overlaid TG traces in Fig. 5a, it is evident that
p-NT and NB, the preferred guests, are held more tightly in
the host crystal (the onset temperatures for their guest release
processes are higher) relative to the complexes comprising
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
Table 3 Summary of the significant host–guest interactions in the complexes of DMT with o-NT, m-NT, p-NT and NB
Interaction
π–π
2DMT·o-NT
2DMT·m-NT
2DMT·p-NT
2DMT·NB
4.826(4)−5.994(3) Å (7 4.842(2)−5.883(3) Å (8 5.191(1)−5.788(1) Å (8 5.217(4)−5.845(3) Å (9 contacts)
contacts) contacts) contacts)
None None None
None
CH–π
Other short contacts
None
2.61 Å, 134°
2.69 Å, 150°
≪ (host)o-ArC⋯o-
ArH(guest) 2.25 Å,
113°,
2.66 Å, 160°
<
(host)m-ArH⋯O-
N(guest) 2.72 Å, 163°
(host)p-
< (host)p-ArH⋯O-N(guest)
<
ArH⋯ArC(guest)
< (host)m-
2
.33 Å, 153°,
ArH⋯HC(guest)
<
(guest)CH⋯m-
ArH(host)
<
denotes contacts less than the sum of the van der Waals radii, while≪denotes contacts less than this sum minus 0.2 Å
Fig. 5 Overlaid a TG and b DSC traces for the complexes of DMT with o-NT, m-NT, p-NT and NB
Experimental
a reference. High purity nitrogen gas was used as purge
gas. Gas chromatography was performed using an Agi-
lent Technologies 7890 A gas chromatograph system
connected to an Agilent Technologies 5975 C VL MSD
mass spectrometer with a triple-axis detector. High purity
helium gas was used as the carrier gas. An Agilent J&W
Cyclodex-B column was used. From an initial temperature
General methods
Melting points were recorded on an Electrothermal
IA9000 Series digital melting point apparatus and are
uncorrected. Infrared spectra were recorded on a Bruker
Tensor 27 Fourier Transform Infrared spectrophotom-
−
1
of 60 °C, a heating rate of 4 °C min was employed up
to 145 °C with a final hold time of 1 min.
1
13
eter, and H-NMR and C-NMR spectra on a 400 MHz
Bruker Avance Ultrashield Plus 400 spectrometer. Ther-
mal experiments were conducted using a TA SDT Q600
Module system and analysed using TA Universal Analysis
Synthesis of DMT
2
000 data analysis software. Samples were placed in open
DMT was prepared from TETROL according to previous
reports [9, 12].
platinum pans with an empty platinum pan functioning as
1
3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Competition experiments employing mixed guests
Equimolar guest mixtures
TETROL12
A standard Grignard addition reaction to (R,R)-(+)-diethyl
L-tartrate using phenylmagnesium bromide afforded a gum
which crystallized from methanol (68%), mp 148–150 °C
Various combinations of binary, ternary and quaternary
guests were mixed together in equimolar quantities, and
the host dissolved in each of these mixtures. The vials
were closed and stored at 0 °C so that the guest proportions
remained equimolar. After crystallization occurred, the sol-
ids were recovered, washed (petroleum ether, 40–60 °C), and
analysed by means of GC-MS experiments. The results were
provided in Table 1.
2
3
(
lit. [16], mp 150–151 °C); [α]
+163 (c. 3.18, CH Cl )
D
2
2
2
5
−1
{
lit. [16], [α]
+ 154 (c. 1.2, CHCl )}; ν (solid)/cm
3 max
D
3
525–3380 (br, OH), 3392–3146 (br, OH), 3057 (Ar), 3031
(
Ar), 1597 (Ar) and 1493 (Ar); δ (CDCl )/ppm 3.82 (4H,
H 3
br, 2HCOH and 2CPh OH), 4.31 (2H, s, 2HCOH) and
2
7
.00–7.30 (20H, m, Ar); δ (CDCl )/ppm 72.1 (HCOH), 81.7
C 3
(
CPh OH), 125.0 (Ar), 126.1 (Ar), 127.1 (Ar), 127.3 (Ar),
2
1
28.4 (Ar), 128.6 (Ar), 143.9 (quaternary Ar) and 144.2
(
quaternary Ar).
Non-equimolar guest mixtures
DMT9
Two guest solvents were mixed together in a range of non-
equimolar proportions. Here we considered all four of the
relevant guest solvents. The solids that resulted after the host
was dissolved and recrystallized from each of these (also at
Excess sodium hydride, TETROL and methyl iodide
afforded a gum which precipitated out in petroleum ether
(
40–60 °C). This precipitate crystallized from methanol/
0
°C) were treated as before, and also analysed via GC-MS.
petroleum ether to yield DMT (65%), mp 124–126 °C (lit.
Additionally, we analysed the mother liquors from which
these crystals had formed. We then plotted the amounts of
guest 1 in the crystal (Z) against the amount of this guest in
the mother liquor (X) in order to obtain selectivity profiles
for DMT as guest molar ratios varied (see Fig. 1a–f). We
repeated this exercise for a ternary solvent mixture com-
prising the nitrotoluenes, which resulted in the ternary plot
provided in Fig. 2. In this way, we could observe how the
host selectivity changes as the guest concentrations change.
2
3
[
17], mp 125–126 °C); [α]
− 154.5 (c. 0.27, CH Cl )
D
2
2
−
1
{
3
lit. [17], [α] − 153 (c. 0.8, CHCl )}; ν (solid)/cm
D 3 max
576–3271 (br, OH), 3025 (Ar), 2836 (O–CH ), and 1567
3
(
Ar); δ (CDCl )/ppm 2.59 (6H, s, 2OCH ), 4.44 (2H, s,
H
3
3
2
HCOCH ), 4.87 (2H, s, 2CPh OH [disappears upon addi-
3 2
tion of D O]), 7.15 (2H, m, Ar), 7.24 (4H, m, Ar), 7.32
2
(
2H, m, Ar), 7.46 (4H, m, Ar) and 7.63 (8H, m, ortho-
Ar); δ (CDCl )/ppm 61.0 (OCH ), 80.1 (CPh OH), 85.3
C
3
3
2
(
HCOCH ), 125.9 (Ar), 126.1 (Ar), 126.8 (Ar), 127.2 (Ar),
3
1
28.0 (Ar), 128.5 (Ar), 144.9 (quaternary Ar) and 145.6
(
quaternary Ar).
Supplementary data
Assessment of the host potential of DMT for guests
NB, o‑NT, m‑NT and p‑NT
CCDC-1847990 (2DMT·o-NT), 1847991 (2DMT·m-NT),
1
847992 (2DMT·p-NT) and 1847993 (2DMT·NB) con-
tain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via http://www.ccdc.
cam.ac.uk/data_request/cif.
DMT was dissolved in an excess of each individual guest
solvent. In the case of p-NT, which is a solid at room tem-
perature, a co-solvent (ethanol) was necessary to effect this
dissolution. The vials in which these experiments were
conducted were kept open to the atmosphere which allowed
for supersaturation to occur through evaporation of some
solvent. This resulted in crystallization, and each solid was
isolated by means of vacuum filtration, during which the
crystals were washed well with petroleum ether (40–60 °C),
Acknowledgements Financial support is acknowledged from the Nel-
son Mandela University and the National Research Foundation. L. Bolo
is thanked for thermal analyses.
1
and then analysed by means of H-NMR spectroscopy. By
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