N,N′-(Hexane-1,6-diyl)bis(4-methyl-N-(oxiran-2-ylmethyl) benzenesulfonamide): Synthesis via cyclodextrin mediated N-alkylation in aqueous solution and further Prilezhaev epoxidation

Article abstract of DOI:10.3762/bjoc.9.318

N-alkylation of N,N′-(hexane-1,6-diyl)bis(4-methylbenzenesulfonamide) with allyl bromide and subsequent Prilezhaev reaction with m-chloroperbenzoic acid to give N,N′-(hexane-1,6-diyl)bis(4-methyl-N-(oxiran-2-ylmethyl) benzenesulfonamide) is described. Thi

Full text of DOI:10.3762/bjoc.9.318

N,N'-(Hexane-1,6-diyl)bis(4-methyl-N-(oxiran-2-
ylmethyl)benzenesulfonamide): Synthesis via
cyclodextrin mediated N-alkylation in aqueous
solution and further Prilezhaev epoxidation
Julian Fischer, Simon Millan and Helmut Ritter*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2013, 9, 2834–2840.
Institute of Organic Chemistry and Macromolecular Chemistry,
Heinrich-Heine-University Düsseldorf, Universitätsstraße 1, D-40225
Düsseldorf, Germany
doi:10.3762/bjoc.9.318
Received: 02 October 2013
Accepted: 18 November 2013
Published: 09 December 2013
Email:
Helmut Ritter* - h.ritter@hhu.de
This article is part of the Thematic Series "Superstructures with
cyclodextrins: Chemistry and applications".
* Corresponding author
Keywords:
Associate Editor: C. Stephenson
alkylation; cyclodextrins; epoxy; rheology; sulfonamides
© 2013 Fischer et al; licensee Beilstein-Institut.
License and terms: see end of document.
Abstract
N-alkylation of N,N'-(hexane-1,6-diyl)bis(4-methylbenzenesulfonamide) with allyl bromide and subsequent Prilezhaev reaction
with m-chloroperbenzoic acid to give N,N'-(hexane-1,6-diyl)bis(4-methyl-N-(oxiran-2-ylmethyl)benzenesulfonamide) is described.
This twofold alkylation was performed in aqueous solution, whereby α-, and randomly methylated β-cyclodextrin were used as
adequate phase transfer catalysts and the cyclodextrin–guest complexes were characterized by 1H NMR and 2D NMR ROESY
spectroscopy. Finally, the curing properties of the diepoxide with lysine-based α-amino-ε-caprolactam were analyzed by rheological
measurements.
Introduction
Various diepoxides easily react with amines or diamines to usually several side products and oligomers are formed in
form cross-linked, cyclic or linear addition-polymers, which are significant concentrations [10-12]. An alternative route is a two-
implemented in construction, electronic, aerospace, medical and step reaction via N-allylation and further Prilezhaev epoxida-
dental industries [1,2]. Hereby, bisphenol A diglycidyl ether tion with peroxides [13-15]. The solubility of hydrophobic reac-
(BADGE) is often used [3,4]. However, non-bisphenol A based tants in water can be increased significantly by cyclodextrins
diepoxides are subject to intensive research [5-9]. The indus- (CD) and thereby the use of organic solvents can be reduced
trial synthesis of BADGE and other commercially available [16-18]. To our best knowledge, CD mediated N-alkylation of
diepoxides proceeds mainly by using epichlorohydrin, whereby sulfonamides is not yet described. Generally, only a few exam-
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ples are known in literature about CD assisted alkylation of was conducted in N,N-dimethylformamide as solvent, as well as
amines in aqueous solution [19-22]. Hence, in this work, we in aqueous solution via CD-complexation (Scheme 1).
wish to present our direct and CD mediated method to alter-
native sulfonamide based diepoxides, focusing on one charac- Unmodified 3 is neither in a neutral nor in a basic milieu
teristic example. Furthermore, the polymerization of these types significantly soluble. However, by complexation of 3 with two
of diepoxides was investigated with lysine-based α-amino-ε- equivalents of randomly methylated β-cyclodextrin (β-CD) to
caprolactam through rheological measurements.
give 3β, water solubility could be increased distinctively. Char-
acterization of the inclusion complex of β-CD with 3 in D2O
solution was conducted using 2D NMR ROESY spectroscopy
Results and Discussion
N,N'-(Hexane-1,6-diyl)bis(4-methylbenzenesulfonamide) (3), as (Figure 1).
precursor for the subsequent N-alkylation and further Prilezhaev
epoxidation, was synthesized easily from p-toluenesulfonyl Thereby, proton signals at 7.0 and 7.4 ppm can be assigned to
chloride (1) and hexamethylenediamine (2) [23]. The resulting the aromatic protons of 3. Furthermore, the protons of its
crystalline sulfonamide was first described in 1927 prepared p-methyl moiety demonstrate a singlet signal at 2.1 ppm. As
from 1,6-dibromohexane and p-toluenesulfonamide [24]. The illustrated in Figure 1, interaction of these protons with the
subsequent two-fold N-alkylation of 3 with allyl bromide (4) inner protons of β-CD in the range of 3.3 to 3.8 ppm is visible.
Scheme 1: Synthesis of sulfonamide 3, N-alkylation of 3 in organic solution and of CD-complex (3β) in aqueous phase to obtain 5 and the subse-
quent epoxidation with m-chloroperbenzoic acid (mCPBA) to yield product 6.
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Figure 1: 2D NMR ROESY spectrum of the complex of 3 with β-CD in D2O, displaying the interaction of the tosyl protons with the β-CD protons.
This strongly indicates a self-agglomeration of the tosyl groups Two-fold N-alkylation of β-CD-complexed N,N'-(hexane-1,6-
of 3 with β-CD. Further confirmation of these findings is a diyl)bis(4-methylbenzenesulfonamide) (3β) with 4α in aqueous
perceivable downfield shifting of the proton signals of 3β solution gave N,N'-(hexane-1,6-diyl)bis(N-allyl-4-methylben-
compared to 3 suspended in D2O, since they are magnetically zenesulfonamide) (5), which could easily be precipitated and
shielded by the β-CD cavity.
separated from the CD-complex by heating, since decomplexa-
tion occurred over 70 °C. The remaining aqueous CD-solution
Additionally, the water solubility of 4 is limited as well can be reused in principle, since in an alkaline milieu CD-rings
(3.83 g L−1) [25]. Since the stability of CD–guest complexes are stable. A comparison of the 1H NMR spectra of 5 received
often depends on the size of the guest molecule relative to the in organic and in aqueous solution, respectively is given in
CD cavity, stability constants of unbranched alkyl chains or Supporting Information File 1 (Figure S2) to show no signifi-
vinyl groups are the highest with α-CD (six glucose units) and cant differences. Also, CD signals in the range of 3.0 to 4.0 ppm
for tosyl groups with β-CD (seven glucose units), respectively are not observable. That indicates complete CD-decomplexa-
[18]. Therefore, the water solubility of 4 was increased by add- tion of 5. Subsequently, 5 was epoxidized in a Prilezhaev reac-
ition of α-CD (4α). 2D NMR ROESY spectroscopy was also tion with m-chloroperbenzoic acid (mCPBA) in methylene chlo-
performed for 4α. As expected, the protons of the allyl-group at ride to obtain N,N'-(hexane-1,6-diyl)bis(4-methyl-N-(oxiran-2-
5.9 ppm, 5.1 ppm and 4.0 ppm correlate with the α-CD protons ylmethyl)benzenesulfonamide) (6). The proceeding reaction
in the range of 3.9 to 3.5 ppm (Figure S1, Supporting Informa- was monitored by means of 1H NMR spectroscopy, since the
tion File 1).
allyl protons of 5 in the range of 5.0 to 5.7 ppm vanish on
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conversion (Figure S3, Supporting Information File 1). To illus- modulus G’’, exhibits low four-digit values at 50 °C. However,
trate the curing properties of the synthesized diepoxide, 6 was η* increases further on time until the sol–gel-transition
reacted in a ring-opening polymerization with the primary (gelpoint), where G’ is equal to G’’, is reached after about 40 to
amine α-amino-ε-caprolactam (8). 8 was synthesized by 45 min (Figure 2B). Generally, by passing this point the mix-
cyclization of lysine (7) (Scheme 2). Hence, an increase of the ture is no longer capable of flowing. Shortly after reaching the
reactivity of the primary amino group towards the epoxide func- gelpoint, η* is not significantly rising further, which is a sign
tion compared to the amino groups in native lysine was for completed conversion. The resulting poly-adduct 9 exhibits
expected [26-28].
a glass transition temperature (Tg) of around 49 °C. Equivalent
measurements of standard BADGE demonstrated a gelpoint
after about 99 min and a Tg of about 74 °C (Figure S4,
Supporting Information File 1). Thus, the curing properties for a
mixture of 6 with 8 are relatively comparable to a mixture of
BADGE with 8, whereby the observed differences can be
caused by different reactivity of the oxirane moieties or unequal
solubility of the respective diepoxide with 8.
By means of IR spectroscopy, ring opening polymerization of
epoxides with amines can be monitored. The spectrum of 6
exhibits weak bands at 1253 and 895 cm−1, which can be
assigned to the C–O-stretching vibration and the symmetric ring
deformation vibration, respectively, of its epoxide groups. On
curing at 50 °C, a broad band between 3100 and 3600 cm−1
Scheme 2: Cyclization of L-(+)-lysine monohydrochloride to give race-
mate 8.
As illustrated in Figure 2A, oscillatory measurements display an appears which is caused by hydrogen bonded hydroxy
initial high viscosity for a mixture of 6 and 8, since its complex stretching vibrations originating from epoxide ring opening.
viscosity (η*), calculated from storage modulus G’ and loss The epoxide bands seem to vanish after curing, which is a sign
Figure 2: Oscillatory rheological measurements of an equimolar mixture of 6 and 8 at 50 °C. Illustrated is the complex viscosity (A), as well as G’ and
G’’ (B) in dependence of time. The polymer 9 is displayed as an idealized structure (R = H or polymer network; crosslinking via addition of epoxide
moieties to the hydroxy functions is likely [2]).
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for high conversion. However, due to overlaps of broader bands determined using a Mettler Toledo DSC 822e equipped with a
in adjacent areas, no clear statement can be made in this regard sample robot TSO801RO. For calibration, standard tin, indium,
(Figure S5, Supporting Information File 1). Based on this work, and zinc samples were used. Heating and cooling curves were
future research could focus on conducting the entire synthesis determined between −30 and 130 °C at a heating rate of
of 6 CD mediated in aqueous solution. Also, the presented 15 °C/min. The Tg value was taken from the inflection point of
pathway for alkylation in aqueous media could be transferred to the second heating curve. Electrospray ionization mass spec-
the solvent saving synthesis of further alkylated products.
trometry (ESIMS) was conducted on a Bruker maXis 4G mass
spectrometer. Melting points were obtained using a Büchi
Melting Point B-545 apparatus at a heating rate of 5 °C/min.
Conclusion
An alternative route for the synthesis of N,N'-(hexane-1,6-
diyl)bis(4-methyl-N-(oxiran-2-ylmethyl)benzenesulfonamide) Synthesis of 5 in organic solution: 7.0 mmol of 3 were
(6) via N-alkylation of N,N'-(hexane-1,6-diyl)bis(4-methylben- dissolved in 25 mL dried N,N-dimethylformamide and the solu-
zenesulfonamide) (3) and further oxidation was described. For tion was cooled to 0 °C in an ice bath. The apparatus was set
the first time, the CD-mediated N-alkylation of a sulfonamide under constant nitrogen-flow and 17.2 mmol of sodium hydride
was conducted, whereby water solubility of 3 and 4 were were added. Afterwards, the suspension was stirred for 2 h and
increased by adding β-CD and α-CD, respectively. By applying subsequently, 35 mmol of allyl bromide (4), which was filtrated
oscillatory rheological measurements, a mixture of 6 and 8 through neutral aluminium oxide, was added dropwise. The
reached the gelpoint after about 40 to 45 min at 50 °C. Thus, an resulting mixture was stirred at 50 °C for 18 h and after cooling
environmentally more sustainable route for the synthesis of a to room temperature it was diluted with 40 mL of saturated
bisphenol A free diepoxide was presented, which appears to be solution of ammonium chloride. The aqueous phase was
a suitable substitute for technically employed bisphenol A washed threefold with 40 mL of ethyl acetate, the organic
diglycidyl ether.
phases were combined and the solvent was evaporated under
reduced pressure. After drying, 5.3 mmol (76% yield, not opti-
mized) of brown slurry were received. The raw product was
Experimental
All reactants were commercially available and unless otherwise purified by column chromatography (n-hexane/ethyl acetate
stated used without further purification. All solvents used were 2:1) to give 3.98 mmol (57% yield, not optimized) of 5. 1H
of analytical purity or freshly distilled. β-CD and α-CD were NMR (300 MHz, DMSO-d6, δ) 7.68 (d, J = 8.3 Hz, 4H, Ar-H),
obtained from Wacker Chemie GmbH and were used after 7.40 (d, J = 7.9 Hz, 4H, Ar-H), 5.60 (ddt, J = 6.3, 10.1, 17.1 Hz,
being dried with a vacuum oil pump over P4O10. p-Toluenesul- 2H, H2C=CH-CH2-), 5.19 (dd, J = 17.0, 1.6 Hz, 2H, CH2,
fonyl chloride (98%) was obtained from Alfa Aesar, allyl bro- trans), 5.11 (dd, J = 10.1, 1.6 Hz, 2H, CH2, cis), 3.73 (d, 4H, J
mide (99%), 3-chloroperoxybenzoic acid (70–75%), 1,6- = 6.4 Hz, allyl-CH2-), 2.99 (t, J = 7.4 Hz, 4H, N-CH2-), 2.39 (s,
hexanediamine (99.5+%) and L-(+)-lysine monohydrochloride 6H, Ar-CH3), 1.38 (m, 4H, -CH2-), 1.14 (m, 4H, -CH2-); 13C
(99+%) were purchased from Acros Organics, bisphenol A NMR (75 MHz, DMSO-d6, δ) 143.0 (2C, Ar(C)-CH3), 136.6
diglycidyl ether and deuterium oxide (99.9%) were provided (2C, RO2S-(C)Ar), 133.5 (2C, R-CH=CH2), 129.8 (4C, Ar(C)),
from Sigma Aldrich, chloroform-d (99.80%) was obtained from 126.9 (4C, Ar(C)), 118.5 (2C, RHC=CH2), 50.1 (2C, N-CH2-
Euriso-Top and dimethyl sulfoxide-d6 (99.9%) was purchased CHR), 47.0 (2C, N-CH2-CH2R), 27.5 (2C, -CH2-), 25.5 (2C,
from Deutero. 1H NMR, 13C NMR and 2D ROESY spectra -CH2-), 20.9 (2C, -CH3); IR (diamond) ν (cm−1): 2951, 2916,
were recorded on a Bruker Avance DRX 300 and a Bruker 2855 (m, -CH2-, Ar-CH3), 1652 (w, C=C), 1597 (m, Ar), 1336,
Avance III – 600 by using deuterium oxide, dimethyl sulfoxide- 1155 (v, R-SO2-NR2), 1090 (m, Ar-S-), 965 (v, -CH2-), 934 (m,
d6 or chloroform-d as solvents. The chemical shifts (δ) are R-SO2-NR2), 816 (s, Ar-H (neighbouring)); ESIMS m/z: 505.4
given in parts per million (ppm) using the solvent peak as an [M + H]+, 527 [M + Na]+; mp 70 °C.
internal standard. FTIR spectra were recorded on a Nicolet 6700
FTIR spectrometer equipped with an ATR unit. Oscillatory Synthesis of 5 CD mediated in aqueous solution: 6.8 g of
rheological measurements were performed on a Haake Mars II randomly methylated β-CD and 25 mmol of sodium hydroxide
rheometer by ThermoFisher Scientific. For this purpose a plate- were dissolved in 15 mL double distilled water and 2.4 mmol of
plate construction (MP35, PP35Ti) was used. The temperature 3 were added. The initial suspension was stirred at 45 °C for
was set to 50 °C and was determined in the measuring plate some minutes until a homogenous solution was achieved.
with an accuracy of ±0.1 °C. The Sol–gel-transmission was Simultaneously, a homogenous solution of 1.15 mmol of 4,
determined by the first intersection of G’ and G’’. Graphs were 13.8 mmol of sodium hydroxide and 1.6 mmol of α-CD in
plotted using reduced data, calculated by the median of three 10 mL of double distilled water was prepared. Subsequently,
following values. The glass transition temperature (Tg) was the solution of 4α was added dropwise to the solution of 3β.
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