Green and highly efficient synthesis of perylene and naphthalene bisimides in nothing but water

Article abstract of DOI:10.1039/c6cc06567h

High-purity, symmetrically substituted perylene and naphthalene bisimides were obtained by hydrothermal condensation of monoamines with the corresponding bisanhydride. The hydrothermal imidization proceeds quantitatively, without the need for organic solvents, catalysts or excess of the amines.

Full text of DOI:10.1039/c6cc06567h

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Green and highly efficient synthesis of perylene
and naphthalene bisimides in nothing but water†
Cite this:DOI: 10.1039/c6cc06567h
a
b
c
Bettina Baumgartner, Anastasiya Svirkova, Johannes Bintinger,
c
b
a
Received 9th August 2016,
Christian Hametner, Martina Marchetti-Deschmann and Miriam M. Unterlass*
Accepted 21st November 2016
DOI: 10.1039/c6cc06567h
www.rsc.org/chemcomm
1
1,19
High-purity, symmetrically substituted perylene and naphthalene solvents (e.g. DMF) at high temperatures.
Scarcely used
bisimides were obtained by hydrothermal condensation of mono- alternative routes include the thermal solid-state condensation of
20
amines with the corresponding bisanhydride. The hydrothermal co-crystals of NBA and amines at 160 1C, and direct approaches
imidization proceeds quantitatively, without the need for organic between bisanhydride and the liquid amine using acetic acid as
2
1,22
solvents, catalysts or excess of the amines.
promotor.
While these techniques, especially Langhals’
method, generate NBIs and PBIs in high yields, the products
The development of chemical reactions that minimize environ- have to be purified chromatographically or by recrystallization.
mental impact, as expressed by the principles of ‘‘green chemistry’’, Moreover, typically 4-fold (in some cases up to 20-fold) molar
1
is currently one of the major challenges in synthetic chemistry.
excess of the monoamines are used, which is highly undesirable
This effort is even more important for (i) widely encountered in terms of ‘‘green chemistry’’. Clearly, for both NBIs and PBIs,
chemical functions, (ii) that are typically only accessible via these most common syntheses can be qualified as toxic and
harsh and harmful synthetic procedures. The imide aka diacyl harsh. We recently reported that fully aromatic polyimides can be
2
3
amide function is among such omnipresent chemical moieties. synthesized by so-called hydrothermal polymerization (HTP).
2
Imides are widely used as protecting groups (e.g. phthalimides ), Here, the imide functions are obtained by condensation of
for bioconjugation reactions (e.g. maleimide–thiol coupling ), aromatic diamines with aromatic dianhydrides (or tetracarboxylic
in polymer chemistry (e.g. polyimides, maleimide resins ), acids) in water at 4180 1C and autogenous pressures. For instance,
3
–5
6
,7
8
9
–11
as dyes (e.g. perylene (PBIs) and naphthalene bisimides (NBIs)),
and chromonic liquid crystals (perylene bisimide derivatives).
at 180–200 1C, the autogenous pressure of H O is of only 12–17 bar.
These rather moderate conditions can be generated easily in
2
12–14
The molecular features generating PBIs’ and NBIs’ dye properties, commercial autoclaves and do not require custom-made set-ups.
i.e. aromatic p-systems, also enable energy and electron transfer In the hydrothermal regime, H O becomes increasingly apolar and
ability, and allow for the formation of intriguing supramolecular at the same time shows an increase in its ionic product, i.e. the
2
1
0,11
À
+
assemblies.
3
Symmetrically N-substituted NBIs and PBIs are concentration of both OH and H O ions increases, enabling the
most commonly synthesized by (i) Langhals’ method consisting medium itself to act as both an acid and a base catalyst, which is
2
4
of condensing the naphthalene (NBA) or perylene bisanhydride indeed beneficial for organic condensations. These findings
PBA) with the respective monoamine in molten imidazole prompted us to investigate if HTP conditions could also be
or quinoline) employing zinc acetate or dicyclohexylcarbodiimide applied to small organic molecules.
(
(
15–18
as promotor at high temperatures (180–230 1C).
the addition of Zn salts can be omitted using aprotic polar pare symmetrically substituted PBIs and NBIs in nothing but water.
First, we reacted a series of eleven n-alkyl monoamines (n-C -NH
with PBA (Fig. 1). Specifically, we employed n-C -, n-C -, n-C -, n-C
n-C -, n-C10-, n-C11-, n-C12-, n-C14-, n-C15, n-C16- and n-C18-NH . There-
fore, 1 eq. of PBA and 2 eq. of n-C -NH were stirred in deionized
(ii) Moreover,
In this contribution, we report a novel, green technique to pre-
n
2
)
5
6
7
8
-,
a
Technische Universit ¨a t Wien, Institute of Materials Chemistry, Getreidemarkt 9/BC/2,
A-1060 Vienna, Austria. E-mail: miriam.unterlass@tuwien.ac.at;
Fax: +43-(0)1-58801-165981; Tel: +43-(0)1-58801-165206
9
2
n
2
b
À1
Technische Universit a¨ t Wien, Institute of Chemical Technologies and Analytics,
Getreidemarkt 9/164-IAC, 1060 Vienna, Austria
water (c = 0.03 mol L ) at RT for 15 min. The resulting suspension
was transferred to a non-stirred autoclave that was placed into an
oven preheated at 200 1C. After 24 h, the autoclave was allowed to
slowly cool back to RT, and the crude product was isolated by filtra-
tion, but not subjected to any further purification such as conven-
tional recrystallization or chromatographic separation.
c
Technische Universit a¨ t Wien, Institute of Applied Synthetic Chemistry,
Getreidemarkt 9/163, 1060 Vienna, Austria
†
Electronic supplementary information (ESI) available: Materials & methods,
1
13
ATR-FTIR, SEM, H-NMR, C-NMR, MALDI-TOF-MS, UV-Vis, fluorescence, PXRD.
See DOI: 10.1039/c6cc06567h
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Fig. 1 Hydrothermal condensations of NBIs and PBIs: the dianhydrides
NBA and PBA are reacted with different monoamines in equimolar ratio
(
1 : 2, no excess of RNH
2
). HTW = high-temperature water, here: 200 1C
and autogenous pressure.
Note that all n-C -PBI products, except n-C - and n-C -PBI,
n
16
18
were obtained quantitatively. In the ATR-FTIR spectra of n-C
n
-
PBIs (ESI†), we find the for PBIs characteristic imide modes
Fig. 2 SEM images of hydrothermally synthesized PBIs and PBA. (A) Hydro-
À1
À1
2
(1693 cm and 1654 cm ). Moreover, the NH modes of the
n
thermally treated PBA (24 h, 200 1C). (B–D) n-C -PBIs obtained hydrothermally
n-alkylamines ( n~ (N–H) and intermolecular H-bonding of amine
(
24 h, 200 1C). B = n-C -PBI, C = n-C -PBI, D = n-C12-PBI.
5
8
À1
groups E3330–3200 cm , 2–3 modes) are fully absent in all
cases. n-C
5
-, n-C
8
-, n-C
9
-, n-C10-, n-C14- and n-C15-PBI show
À1
no remaining anhydride modes ( n~ (CQO) E 1772 cm
,
thickness (see Fig. 2B and ESI†). In n-C - and n-C -PBI roundish
7 8
as
À1
n~ s(CQO) E 1733 cm ) related to unreacted PBA. Hence, aggregates of ca. 10–50 mm in diameter coexist with ribbons of
ATR-FTIR analysis indicates both the full consumption of PBA ca. 10 mm  100 nm  1 mm (length  thickness  depth) (see
9
and the absence of perylene monoimide monoanhydride, which Fig. 2C and ESI†). n-C - to n-C15-PBI all form stacks of discoid
would in principle be a possible product. Indeed, Nagao & Misono platelets that are each ca. 5 mm in diameter and ca. 100 nm in
and Huang et al. have used H O/ROH mixtures as solvents for the thickness (see Fig. 2D and ESI†). For longer alkyl-chains in n-C -PBIs,
synthesis of perylene monoimide monoanhydrides, which were the increased hydrophobicity generates the compounds’ drive
in both cases the major products (E80%), and PBIs only formed in to limit the contact with the polar medium H O: the hydro-
Given that these reports (and also Langhals’ thermally formed PBIs minimize their surface area for a given
2
n
2
25,26
minority (E20%).
method) employ important excesses of the monoamines, it is most volume by adopting roundish morphologies. In contrast, PBIs
fascinating that fully condensed PBIs can be obtained hydro- bearing short alkyl chains do not adopt such roundish morphol-
thermally without any additives at equimolar reactant ratio.
While the ATR-FTIR spectra of n-C -, n-C -, n-C11- and n-C12
PBIs show very small remaining CQO anhydride modes, n-C16
5 6
ogies: n-C - and n-C -PBI resemble the morphology of hydro-
thermally recrystallized PBA that we prepared for comparison
(see Fig. 2A and ESI†). Overall, it can be stated that the PBI
6
7
-
-
and n-C18-PBI show considerable anhydride modes (see ESI†). The morphology is strongly influenced by the N-alkyl substitution.
incompleteness of formation of the latter two PBIs is however not Despite the roundish morphologies found in n-C to n-C15, all
related to the basicity of n-C16 and n-C -NH , since the pK values PBIs are highly crystalline as evinced by powder X-ray diffraction
7
18
2
a
of n-alkylamines generally do not vary for different alkyl sub- (PXRD) measurements (ESI†). Since hydrothermal synthesis has
2
7,28
23,24,29
stituents, but all lie in the same range (10.4–10.6).
The been shown to yield outstanding crystallinity for polyimides,
water-solubility is however strongly decreasing with increasing this result comes as no surprise. n-C16- and n-C18-PBI are also
alkyl chainlength. Therefore, we suppose that the hydrothermal highly crystalline in PXRD, but their incompleteness of reaction
formations of n-C16- and n-C18-PBIs are less complete after 24 h, (especially for n-C18-PBI) is further underlined by the presence of
because of n-C16- and n-C18-NH
thus limited availability for reaction. The increase in apolarity
2
’s limited solubility in H
2
O, and reflections corresponding to PBA (ESI†).
The N-substitution of PBIs with alkyl chains is a means
of the n-alkylamines and hence also of the n-C -PBIs is indeed to increase their solubility in organic solvents. Therefore, the
n
reflected by the aspect of the reaction mixtures after hydro- n-C -PBIs could be analyzed by solution NMR for estimating their
n
1
thermal imidization: while the n-C
n
-PBIs bearing short alkyl purity. Representative H-NMR spectra of n-C
8
- and n-C14-PBI are
chains result as homogeneous dispersions, longer alkyl tails lead to shown in Fig. 3 (see ESI† for larger representation and spectra
a precipitate covered by a translucent aqueous phase. Specifically, of the other n-C -PBIs). Both spectra show all expected peaks
n-C to n-C -PBI are obtained as bright blood-red dispersions with and the found integral ratios correspond well to the theore-
no visible phase separation (photographs, see ESI†). n-C and tical ratios (n-C -PBI, H : H : H : H : H expected: 6 : 20 : 4 : 4 : 8,
n-C10-PBI form a ruby-red colored precipitate covered by a turbid found: 6.14 : 21.32 : 3.92 : 4.00 : 8.00; n-C14-PBI, H : H : H : H
red dispersion, and from n-C -PBI onwards, the PBIs fully preci- H expected: 6 : 44 : 4 : 4 : 8, found: 6.21 : 47.16 : 3.87 : 4.11 : 8.00).
n
5
8
9
8
a
b
c
d
e
a
b
c
d
:
11
e
pitate as brownish-red powders, covered by a translucent yellowish While PBA is insoluble in the solvent used for NMR measure-
aqueous phase (ESI†). ments (CDCl /trifluoroacetic acid, 5/1 v/v), remaining mono-
Micromorphological investigations via scanning electron amine would affect the integrals corresponding to CH and
microscopy (SEM) confirm this trend: n-C - and n-C -PBI are CH groups (H , H and H ). It becomes clear from Fig. 3 that
cuboid-like particles of ca. 5–10 mm in length and 1–2 mm in there is no unreacted monoamine present. Note that even for
3
2
5
6
3
a
b
c
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them had been fully characterized. As a positive side effect, the
fact that hydrothermal synthesis allowed us to rapidly synthe-
size this entire series of n-C -PBIs, we could add a considerable
n
amount of to date unreported experimental data on these com-
pounds (see comparison table, ESI†).
Having shown that symmetrically n-alkyl-substituted PBIs
can be obtained quantitatively and with great purity within 24 h
at 200 1C in H
thermal conditions were necessary, or if condensation could
also be achieved in H O at reflux; (ii) If the method was also
2
O, we were interested in studying if: (i) hydro-
2
applicable to other amines (different pK -values, different steric
a
demands) and (iii) to other bisanhydrides (specifically NBA); and
-PBIs lastly (iv) the completeness and reaction time could be improved
1
Fig. 3 H-NMR spectra (600 MHz, CDCl
3
/TFA: 5/1 v/v, 16 scans) of n-C
n
synthesized hydrothermally at 200 1C for 24 h; black = n-C14-PBI, turquoise = adding a non-nucleophilic base as condensation promotor.
n-C -PBI. Solvent residual peak (7.26 ppm) is marked with *.
8
To probe if n-C
we took a closer look at 4 PBIs of different polarity and hence
solubility of both the monoamine and the resulting PBI: n-C
n-C11, n-C14 and n-C18-PBI. The conversion to the PBIs was tested
by ATR-FTIR, after reaction times of 2, 4, 6, 24 and 72 h. In all
2
-PBIs would be obtainable in H O at reflux,
n
5
,
n-C - and n-C -PBI, we did not find residual amines in NMR
1
6
18
(
ESI†), despite the incompleteness, judged from ATR-FTIR, of
the transformation in both cases. We believe, that the remaining
amine was dissolved/dispersed in the aqueous supernatant after
the HT transformation, most likely in its amminium form. Note
that selected n-C -PBI were additionally confirmed by mass
n
spectrometry (ESI†).
Soluble PBIs find tremendous interest for energy-related
applications, e.g. in the field of organic electronics, and as
fluorescence dyes. In both cases, their solubility is required
for processing, and their purity is of prime importance. For
testing the dye quality, we performed UV-Vis absorption and
fluorescence measurements in CH
the fluorescence spectrum of n-C14-PBI are exemplarily shown in
Fig. 4 (see ESI† for spectra of all other n-C -PBIs). Both the absorp-
tion maxima (526 nm, 490 nm, 458 nm) and the fluorescence
maxima (533 nm, 574 nm, 624 nm) are in good agreement with
cases, the n-C -PBIs are forming in considerable amounts, but
n
even after 72 h we still find remaining PBA (ESI†). Therefrom,
it can be concluded that HT conditions are indeed required for
quantitative yields after reasonable reaction times when equi-
molar amounts of the starting compounds are employed. Note
that Tam-Chang et al. could obtain a perylene monoimide
potassium carboxylate, by stirring the parent monoanhydride
1
0
14
potassium salt with N,N-diethylethylenediamine in ambient water.
However, their approach is limited to employing an excess of water-
soluble amines in combination with the increased solubility of the
monoanhydride potassium salt compared to PBA.
Hydrothermal bisimide syntheses additionally employing
H u¨ nig’s base (N,N-diisopropylethylamine, HB) as non-nucleophilic
base, and/or starting from NBA and/or other amines (cyclo-
2 2 3
Cl and CHCl . The UV-Vis and
n
6 2
hexylamine (c-C -NH ), aniline (An)) are summarized in Table 1
9
the literature. The fluorescence quantum yields of all measured
(
ESI† for corresponding ATR-FTIR). First, for n-C -PBIs, it becomes
n
n-C -PBIs are F E 1 (see ESI†). All n-C -PBIs are soluble in a
n
F
n
clear that the addition of 1–2 drops of HB allows for reducing the
reaction time needed for quantitative yield (tR,q) from 24 h (no HB)
to 4 h for both n-C - and n-C14-PBI (Table 1, entries 01–04).
8
However, n-C18-PBI could not be obtained quantitatively by
adding HB (Table 1, entry 06). Nonetheless, the consumption
of PBA was much improved by the HB addition (ESI,† ATR-FTIR).
2 2 3
number of organic solvents (CH Cl ,CHCl , DMSO, DMF, benzene,
nitrobenzene, in the mg/100 mL range) generating strongly colored,
translucent solutions (Fig. 4, ESI†). Since the fluorescence can
be affected by impurities that also show fluorescence, such as
aromatics/heteroaromatics, the hydrothermal imide synthesis
presented here is clearly preferable to condensations in imidazole,
especially since it requires no purification.
n
Second, n-C -NBIs were readily obtainable already without the
addition of HB: tR,q C 16 h was sufficient to generate n-C -NBI
8
While all hydrothermally prepared n-C -PBIs have previously
been prepared by conventional methods by others, not all of
n
without HB, which compares to tR,q C 24 h for n-C -PBI (Table 1,
8
entries 10 and 01). We attribute this to the increased solubility of
NBA in H
addition of HB significantly reduced tR,q by a factor of 4, to 4 h
Table 1, entry 11). Most interestingly, n-C18-NBI was obtained
quantitatively after tR,q C 16 h, without HB (Table 1, entry 12).
Given the high water-insolubility of n-C18-NH , which did not
allow for obtaining n-C -PBI at any tested conditions, this result
2 8
O in the HT regime compared to PBA. For n-C -NBI,
(
2
1
8
is most impressive. Third, cyclohexyl-disubstituted PBI and NBI
were obtained quantitatively only in the presence of HB (Table 1,
Fig. 4 Left: UV-Vis (black) and fluorescence (turquoise) spectrum of
entries 07, 08, 13 and 14), i.e. after only 4 h for c-C
for c-C -PBI. While the pK of c-C -NH (E10.6) is not signifi-
cantly different from that of n-C -NH
6
-PBI and 16 h
n-C14-PBI in CH
Aspect of n-C14-PBI under visible (top) and UV-light (bottom) in the solvents
from left to right): CHCl , CH Cl , DMF, DMSO, THF, TFA.
3
Cl synthesized hydrothermally at 200 1C for 24 h. Right:
6
a
6
2
(
3
2
2
n
2
(E10.4), cyclohexylamine is
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Table 1 Various NBI and PBI syntheses. All reactions were carried out at attribute to the increased solubility of NBA in the hydrothermal
2
00 1C and equimolar anhydride : amine ratio. c-C
amine (pK (c-C -NH ) C 10.6), An = Aniline (pK (An) C 4.6), HB = H u¨ nig’s
base, tR,q = reaction time until bisimides were obtained quantitatively
6 2
-NH = cyclohexyl-
regime. Our approach presents a rapid and easy means for
accessing symmetrically substituted PBIs, which we believe to be
of high interest – especially to non-chemists – for the application of
tR,q [h] these compounds in e.g. energy-related applications.
a
6
2
a
Entry
Bisanhydride
Monoamine
HB
The authors acknowledge TU Wien for funding this project,
and are grateful to Maximilian Raab for preliminary experiments.
Powder X-ray diffraction measurements were carried out at the
X-ray Center of TU Wien (XRC), and SEM was carried out at the
interfaculty electron microscopy facility of TU Wien (USTEM).
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
PBA
PBA
PBA
PBA
PBA
PBA
PBA
PBA
PBA
NBA
NBA
NBA
NBA
NBA
NBA
n-C
n-C
n-C14-NH
n-C14-NH
n-C18-NH
n-C18-NH
8
-NH
-NH
2
—
y
—
y
—
y
—
y
y
—
24
4
24
4
424
417
424
17
417
16
4
16
417
4
17
8
2
2
2
2
2
a
a,b
a
c-C
c-C
An
6
-NH
-NH
2
6
2
a,b
References
n-C
n-C
n-C18-NH
8
-NH
-NH
2
8
2
y
1
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—
—
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—
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a
E 4.6) than the used
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3
0
12 S.-W. Tam-Chang and L. Huang, Chem. Commun., 2008, 1957–1967.
1
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2
719–2726.
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1
2
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1
7 P. Gawrys, D. Boudinet, M. Zagorska, D. Djurado, J.-M. Verilhac,
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1
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to PBI and NBI dye applications – it is exactly these factors that
will have to be considered.
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1
9 S. H u¨ nig, J. Grob, E. F. Lier and H. Quast, Justus Liebigs Ann. Chem.,
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1
20 M. L. Cheney, G. J. McManus, J. A. Perman, Z. Wang and M. J. Zaworotko,
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2
2
at hydrothermal conditions. The hydrothermal imidization lies 23 B. Baumgartner, M. J. Bojdys and M. M. Unterlass, Polym. Chem.,
2
014, 5, 3771–3776.
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2
4 B. Baumgartner, M. J. Bojdys, P. Skrinjar and M. M. Unterlass,
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2
2
2
6 H. Huang, Y. Che and L. Zang, Tetrahedron Lett., 2010, 51, 6651–6653.
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(
such as recrystallization or chromatography) is required. More-
over, the reactions were complete after reasonable reaction
times (max. 24 h) at quantitative yields, with the exception of
very hydrophobic amines (n-C16- and n-C18-PBI), and could be
accelerated by adding a non-nucleophilic base. Lastly, NBIs are
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