Synthesis of Amidation Agents and Their Reactivity in Condensation Reactions

Article abstract of DOI:10.1055/a-1334-6916

Nowadays, the development of new approaches which smartly bypass the use of harsh reaction conditions and hazardous chemicals covers a pivotal role. In this research paper the synthesis, characterization, and application of novel libraries of triazine bis-quaternary ammonium salts, employed as coupling agents to produce amides is reported. Full characterization of the novel compounds by ¹H and ¹³C NMR, FT-IR spectroscopy, ESI-HRMS, and elemental analysis is provided. Furthermore, a comparison in terms of activity of the preformed triazine compounds versus in situ formulations has been evaluated for the formation of amides in the presence of phenylethylamine and different aliphatic or aromatic acids. A possible correlation between the chemical structure of the triazine and their reactivity for the formation of the triazine bis-quaternary ammonium salts is also reported. Moreover, best performing condensation agents have been further tested for the cross-linking of collagen powder as possible wet white tanning systems, for sustainable and environmentally friendly leather tanning.

Full text of DOI:10.1055/a-1334-6916

SYNTHESIS
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
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021, 53, 1672–1682
paper
1672
en
Synthesis
R. Sole et al.
Paper
Synthesis of Amidation Agents and Their Reactivity in Conden-
sation Reactions
Roberto Sole◊a
Lodovico Agostinis◊a
Silvia Concaa
Vanessa Gattoa,b
Noemi Bardellaa
Andrea Morandinia
Chiara Buranelloa
Valentina Beghetto*a,b
a
Dipartimento di Scienze Molecolari e Nanosistemi, Università
Ca’ Foscari Venezia, Via Torino 155, 30172, Venezia, Italy
beghetto@unive.it
Crossing s.r.l., Viale della Repubblica 193/B, 31100, Treviso,
b
Italy
◊
These authors contributed equally
Corresponding Author
Received: 08.11.2020
Accepted after revision: 10.12.2020
Published online: 10.12.2020
for amide synthesis, triazine-based quaternary ammonium
salts such as 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-meth-
ylmorpholinium chloride (DMTMM) are gaining increasing
DOI: 10.1055/a-1334-6916; Art ID: ss-2020-t0576-op
4
5
interest for the synthesis of amides, peptides, collagen,
Abstract Nowadays, the development of new approaches which
smartly bypass the use of harsh reaction conditions and hazardous
chemicals covers a pivotal role. In this research paper the synthesis,
characterization, and application of novel libraries of triazine bis-qua-
ternary ammonium salts, employed as coupling agents to produce am-
cross-linked carboxymethylcellulose2,6 and grafted amine.7
Albeit the strategic importance of amides, most meth-
ods commonly employed for their synthesis still lack both
in economic and environmental sustainability, have low
atom efficiency, generate large quantities of hazardous
waste products, and require complicated purification
1
ides is reported. Full characterization of the novel compounds by H and
13
C NMR, FT-IR spectroscopy, ESI-HRMS, and elemental analysis is pro-
vided. Furthermore, a comparison in terms of activity of the preformed
triazine compounds versus in situ formulations has been evaluated for
the formation of amides in the presence of phenylethylamine and dif-
ferent aliphatic or aromatic acids. A possible correlation between the
chemical structure of the triazine and their reactivity for the formation
of the triazine bis-quaternary ammonium salts is also reported. More-
over, best performing condensation agents have been further tested for
the cross-linking of collagen powder as possible wet white tanning sys-
tems, for sustainable and environmentally friendly leather tanning.
8
steps. Compared to other conventionally employed cou-
pling agents such as carbodiimides, quaternary ammonium
salts derived from 2-chloro-4,6-dialkoxy-1,3,5-triazines are
known for their higher stability, lower cost, and reduced
2,4,6
hazard.
Nevertheless, DMTMM, the only 2-chloro-4,6-
dialkoxy-1,3,5-triazine-derived quaternary ammonium salt
commercially available, should be improved to implement
the use of these products on industrial scale. Our research
group has long been involved in the study of innovative sus-
Key words 1,3,5-triazine bis-quaternary ammonium salts, amidation
agents, collagen cross-linking, green chemistry, sustainable leather tan-
ning
9
tainable processes for fine chemistry. Recently, our studies
have focused on the development of new condensation
agents.
One of the most important reactions in organic chemis-
try and biochemistry is still today the synthesis of amides
due to their wide application for the production of pep-
tides, pharmaceuticals, biologically active compounds, and
This in mind, the scope of this work is to verify if the
synthesis of bis-quaternary ammonium salts, synthesized
by reaction of 6-substituted 2,4-dichloro-1,3,5-triazines
with a tertiary amine (Ams), could generate new families of
efficient condensation agents.
Compared to 4,6-disubstituted 2-chloro-1,3,5-triazine-
derived quaternary ammonium salts, one of the major ad-
vantages of triazine bis-quaternary ammonium salts, is the
presence of two active reaction sites for amide synthesis,
1
industrial polymers, detergents and lubricants. Conse-
2
quently, many different physical and chemical protocols
have been developed for the synthesis of amides by dehy-
dro-condensation reaction of a carboxylic acid and an
3
amine. Within the chemical dehydro-condensation agents
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2020. Thieme. All rights reserved. Synthesis 2021, 53, 1672–1682
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

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Synthesis
R. Sole et al.
Paper
which should allow to reduce triazine consumption, syn-
thetic costs, implementing atom efficiency and overall sus-
tainability of the process.
The activity of the isolated triazine bis-quaternary am-
monium salts will be compared with the activity of con-
densation agents prepared by adding directly to the reac-
tion mixture a 6-substituted 2,4-dichloro-1,3,5-triazine
and a tertiary amine. Advantages foreseen will be evaluated
for the condensation of different aromatic, aliphatic, ,-
unsaturated carboxylic acids and an amine.
rived from MMT, MEAT, and MIAT have been prepared by
reaction with N-ethyl- or N-methyl-substituted tertiary
amines at 0 °C (Scheme 1). The seven different tertiary
amines employed are N-methylmorpholine (NMM), N-eth-
ylmorpholine (NEM), N-methylpiperidine (NMP), N-eth-
ylpiperidine (NEP), N-methylpyrrolidine (MPD), trimethyl-
amine (TMA), and triethylamine (TEA). All the triazine bis-
quaternary ammonium salts isolated are reported in Figure
1 with the respective yields.
The stability of MMT-Ams, MIAT-Ams, and MEAT-Ams
1
Finally, most efficient triazine bis-quaternary ammoni-
um salts will be tested for bovine collagen powder (BCP)
cross-linking. Easy to use and inexpensive, BCP has been
previously employed as standard substrate for preliminary
cross-linking (or tanning) tests to verify the efficacy of a
coupling compound as tanning agent. This methodology
has been demonstrated to be easily implementable from
laboratory to industrial scale for bovine hides tanning, to
was monitored by H NMR over a period of over 34 weeks
both in pure form and in water solution (see Supporting In-
formation). It is interesting to note that, except for MMT-
MM, the stability of the triazine bis-quaternary ammonium
salts synthesized in this work was highly superior com-
1
2
pared to DMTMM.
Yields and stability data highlight differences in the re-
activity of MMT, MIAT, and MEAT in the presence of the
tert-amines tested. For example, quaternarization of MIAT
and MEAT took place only in the presence of N-methyl-sub-
stituted amines and in no case with N-ethyl-amines, while
MMT was highly reactive both with NEM and NEP allowing
to synthesize very stable MMTEM and MMTEP in high
yields (89% and 94%, respectively).
6a,10
produce metal, formaldehyde, and phenol-free leather.
The different 6-substituted 2,4-dichloro-1,3,5-triazines
and derived bis-quaternary ammonium studied in this
work are reported in Figure 1. Only the synthesis of 2,4-di-
chloro-6-methoxy-1,3,5-triazine (MMT) has been previous-
11
ly reported, but, to the best of our knowledge, no bis-qua-
ternary ammonium salt of MMT has yet been studied.
Moreover, also the synthesis of 2,4-dichloro-6-(diisopro-
pylamino)-1,3,5-triazine (MIAT) and 2,4-dichloro-6-(di-
ethylamino)-1,3,5-triazine (MEAT), the preparation of the
corresponding quaternary ammonium salts of MMT, MIAT,
and MEAT and their use as condensation agents has never
been reported. MMT, MIAT, and MEAT have been synthe-
sized by reaction of cyanuric chloride with methanol, or a
secondary amine, in the presence of an acid scavenger, ac-
cording to the general synthetic strategy reported in
Scheme 1. Bis-quaternary ammonium salts of the three dif-
ferent 6-substituted 2,4-dichloro-1,3,5-triazines were pre-
pared similarly to triazine mono-quaternary ammonium
TMA gave very stable triazine bis-quaternary ammoni-
um salts by reaction with MIAT and MEAT, while MMTTMA
resulted very unstable.
MIATMM and MEATMM were considerably more stable
than the corresponding MMTMM, respectively 15 and 13
weeks compared to few days for MMTMM (see Supporting
Information), while in the presence of MPD, MMTMPD and
MIATMPD were isolated in approximately 70% yield but no
formation of MEATMPD was observed. It is interesting to
note that almost a dozen stable products were achieved by
reaction of 6-substituted 2,4-dichloro-1,3,5-triazine with
two equivalents of a tertiary amine.
According to the literature, the stability of mono-qua-
ternary ammonium salts derived from 2-chloro-4,6-dime-
thoxy-1,3,5-triazine (CDMT) and NMM strongly depends on
1
1
salts such as DMTMM and other triazine derivatives. In
particular, all triazine bis-quaternary ammonium salts de-
2
Cl
OMe
acetone
OMe
N
Cl
MeOH
2 equiv NR1R2R3
N
N
N
N
N
0
°C, 1 h
0 °C, 40 min
NaHCO3
3
2
1
1
2
3
Cl
N
Cl
R R R N
N
NR R R
Cl
N
Cl
MMT
2
Cl
R
HN
R
R
N
N
N
R
Cl
N
acetone
2 equiv NR R R
R
N
N
R
1
2 3
acetone
N
N
N
+
2
N
r.t., 30 min
3
2
1
1
2
3
0
°C, 40 min
R R R N
NR R R
Cl
Cl
Cl
N
Cl
R = H MEAT
R = CH3 MIAT
Scheme 1 Synthesis of MMT, MEAT, and MIAT and triazine bis-quaternary ammonium salts
©
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Synthesis
R. Sole et al.
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ring (Scheme 2). In particular, 13C NMR studies reported by
Kunishima et al. indicate that the reaction between NMM
and CDMT may occur if the triazine ring is in equatorial po-
Cl
N
mono-substituted
R
N
X
12
triazines
Cl
Ams
N
N
N
N
N
X
X
N
N
sition respect to the alkyl chain (CH ) of NMM. Then, this
3
Y
Y
Ams
rather strained structure spontaneously rearranges to a
more stable chair conformation with the flattened triazinyl
group in the axial position. Consequently, when the nucleo-
philic substitution and the conformational rearrangement
are hindered by a -alkyl group present on the tert-amine,
the formation of the corresponding triazine mono-quater-
nary ammonium salt may be critical. For this reason,
DMTMM may be easily synthesized, while DMTEM and
DMTEP are more difficult to produce.
Y = OMe, NEt2, N(i-Pr)2
X = O, CH2
R
Ams =
N
X
Scheme 2 Reaction pathway for the formation of triazine bis-quater-
nary ammonium salts in the presence of cyclic N-methyl or N-ethyl-
amine
the possibility of equatorial to axial conformational inter-
change with respect to the six-membered cyclic tert-amine
Since no data were available in the literature on triazine
bis-quaternary ammonium salts reported in Figure 1, we
tert-amines (Ams)
N
N
N
O
N
O
N
N
N
1
2 3
NR R R
=
NMM
NEM
NMP
NEP
MPD
TMA
TEA
Cl
CDMT and mono-
quaternary ammonium
salts
Cl
Cl
OMe
OMe
OMe
OMe
N
N
N
N
N
N
N
N
MeO
N
N
MeO
N
N
MeO
N
N
MeO
N
Cl
O
O
CDMT
DMTMM
DMTEM
DMTEP
Novel dichloro triazines
OMe
N
N
N
N
N
N
N
N
N
N
Cl
N
Cl
Cl
Cl
Cl
Cl
MMT
MIAT
MEAT
Triazine bis-quaternary
ammonium salts
2
Cl
2Cl
2Cl
2Cl
N
N
N
N
2Cl
OMe
OMe
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
O
O
O
O
O
O
O
O
MMTEM
9%
MIATMM
8%
MIATMP
85%
MMTMM
MEATMM
90%
8
8
8
7%
2Cl
2Cl
2Cl
2Cl
2Cl
2
Cl
N
N
N
N
OMe
N
N
N
OMe
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
MEATMP
8%
MMTMPD
3%
MMTEP
4%
MIATMPD
72%
MIATTMA
70%
MEATTMA
96%
7
9
7
Figure 1 General formula of tertiary amines, mono-quaternary salts derived from CDMT and bis-quaternary ammonium salts derived from MMT, MIAT,
and MEAT
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Synthesis
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deemed it interesting to verify if analogous conclusions on
conformational stability could be inferred also for these
compounds. This in mind, 13C NMR characterization of the
bis-quaternary ammonium salts of 6-substituted 2,4-di-
chloro-1,3,5-triazines was carried out. Chemical shifts of
N
N
Cl
N
acetone
N
N
N
N
+
10 HN
DIAT
reflux, 96 h
Cl
N
Cl
Cl
the carbon atoms of the N-CH methyl and secondary car-
3
bons (N-CH CH ) of the -alkyl substituents present on the
2
3
tert-amine in MMT-Ams, MIAT-Ams, and MEAT-Ams are re-
ported in the Supporting Information (see Table 2 in the SI).
Based on literature data,12 from the  value of the N-CH3
and N-CH CH their equatorial or axial position may be in-
N
Cl
N
acetone
N
N
N
N
+
8
HN
DEAT
reflux, 2 h
2
3
Cl
N
N
Cl
Cl
1
1
ferred considering that generally, when the alkyl group
present on the tert-amine is a -CH , a chemical shift below
3
5
0 ppm corresponds to an axial position, while  values
OMe
N
Cl
N
OMe
N
above 50 ppm are characteristic of an equatorial position.
Additionally, the chemical shift of the secondary carbon
atom of N-CH CH falls above 60 ppm when in equatorial
acetone
MAT
MeOH
N
N
N
N
NaHCO3
0 °C
2 HN(i-Pr)2
Cl r.t., 3.5 h
2
3
Cl
N
N
Cl
Cl
Cl
N
position, while axial conformations have  values below 60
ppm. According to the data reported in Table 2 of the Sup-
porting Information, MMTEM and MMTEP have  values of
Scheme 3 Synthesis of DIAT, DEAT, and MAT
6
5.0 and 64.7 ppm, respectively, indicating that also for
these triazine bis-quaternary ammonium salts, the most
stable conformation is the one with the N-alkyl chain in the
equatorial position and the triazine ring in axial position, in
agreement with the literature.12
the seven different tertiary amines previously employed for
the synthesis of bis-quaternary ammonium salts as above
described, but without any success. Recently Kitamura et
13
al. reported that the presence of electron-withdrawing or
It may be inferred that the presence of a less crowded
substitution pattern on MMT compared to CDMT, MEAT, or
MIAT allowed nucleophilic attack by both NEM and NEP on
MMT, and consequently the rearrangement to the equatori-
al conformation giving MMTEM and MMTEP in good yields.
Moreover, all 6-substituted 2,4-dichloro-1,3,5-triazines
bis-quaternary ammonium salts, having a tertiary amine
with a -CH3 in the  position, showed  values for -CH3
above 50 ppm, indicating a conformation with the methyl
group in equatorial position and the triazine moiety in axial
position.
electron-donating groups strongly influences the reactivity
of triazine quaternary ammonium salts and correlated this
behavior to the Hammett substituent constants. In particu-
14
lar, according to the Hammett substituent constants -OCH3
and -OCH CH have a m respectively of +0.12 and +0.10,
2
3
while m of -N(CH CH ) is –0.16 and –0.26 for -N[CH(CH ) ] ,
2
3
2
3 2 2
thus the decrease in reactivity of DEAT and MAT may be at-
tributed to the reduced electron-withdrawing nature of the
substituents present in DEAT and MAT, compared to, for ex-
ample, CDMT and 2-chloro-4,6-diethoxy-1,3,5-triazine
(CDET). As far as the mono-substituted MIAT and MEAT are
concerned, the strong electron-withdrawing nature of the
two Cl atoms (m +0.37) efficiently counterbalances the
negative Hammett substituent constants of -N(CH CH )
In order to further highlight the reactivity of MMT, MI-
AT, and MEAT in comparison to mono-quaternary ammoni-
um salts, disubstituted 2-chloro-4,6-(diisopropylamino)-
2
3 2
1
,3,5-triazine (DIAT), 2-chloro-4,6-(diethylamino)-1,3,5-
(m –0.16) and -N[CH(CH ) ] (m –0.26) allowing to syn-
3 2 2
triazine (DEAT), and 2-chloro-4-(diisopropylamino)-6-me-
thoxy-1,3,5-triazine (MAT) were synthetized (Scheme 3).
While CDMT is a very well known compound employed for
the synthesis of DMTMM and other quaternary ammonium
salts, DIAT, DEAT, and MAT had never been reported previ-
ously in the literature and were synthesized with a protocol
analogous to the one adopted for other disubstituted tri-
azine compounds. Moreover, MAT could be alternatively
prepared first by nucleophilic substitution of methanol, fol-
lowed by reaction with diisopropylamine or vice versa
without any significant difference (yield 70%, see Support-
ing Information for further details).
thesize the bis-quaternary ammonium salts reported in
Figure 1.
All synthesized triazine compounds, were tested in or-
der to verify their activity for the synthesis of amides.
Moreover, coupling agents prepared in situ by addition of 6-
substituted 2,4-dichloro-1,3,5-triazines and a tert-amine in
the reaction mixture, have also been tested. This methodol-
ogy has seldom been employed in the literature and may
constitute a valid alternative to the isolated quaternary am-
monium salts allowing to reduce processing costs, solvents,
and time. The activity of different MMT-Ams, MIAT-Ams,
MEAT-Ams (preformed), MMT/tert-amine, MIAT/tert-
amine, and MEAT/tert-amine (in situ formulation) was test-
ed employing benzoic acid (1a) and phenylethylamine (2a)
The 4,6-disubstituted 2-chloro-1,3,5-triazine com-
pounds, DIAT, DEAT, and MAT, were further reacted with
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Table 1 Dehydro-condensation Reaction between Benzoic Acid (1a) and Phenylethylamine (2a) by Isolated Bis-quaternary Ammonium Salts or
a
MMT/tert-Amine, MIAT/tert-Amine, and MEAT/tert-Amine In Situ Protocol
Coupling agentb
Yield (%) of 3a after 15 min/1 h Entry
c
Coupling agentb
Yield (%) of 3a after 15 min/1 h
c
Entry
1
2
3
4
5
6
7
8
9
MMTMM
65/68
82/89
48/52
51/55
49/57
55/60
32/34
47/51
25/33
29/33
11
12
13
14
15
16
17
18
19
20
MIAT/NMP
MIATMPD
MIAT/MPD
MEATMM
17/20
38/42
47/51
39/44
38/40
52/57
26/28
45/47
42/46
17/19
MMTMMd
MMT/NMM
MMT/NMP
MMTMPD
MMT/MPD
MMT/TMA
MIATMM
MEAT/NMM
MEATMP
MEAT/NMP
MEAT/MPD
MEATTMA
MEAT/TMA
MIAT/NMM
MIATMP
10
a
Reaction conditions: benzoic acid (1.2 mmol), phenylethylamine (1.2 mmol), MeOH (6 mL), 25 °C.
Coupling agent: 6-substituted 2,4-dichloro-1,3,5-triazine (0.6 mmol) and tertiary amine (1.2 mmol) were added; for isolated MMT-Ams, MIAT-Ams, and MEAT-
b
Ams (0.6 mmol) were used.
c
Yield in 3a was measured by GLC using mesitylene as internal standard after 15 min and 1 h.
MMTMM (0.83 mmol).
d
O
Figure 1, most of the isolated MMT-Ams, MIAT-Ams, and
MEAT-Ams showed good stability, allowing to compare the
two different protocols (preformed and in situ formula-
tion), with the exception of MMTMP, MMTTMA, and MEAT-
MPD which were not stable enough to be isolated. Addi-
tionally, the synthesis of bis-quaternary ammonium salts
prepared from 6-substituted 2,4-dichloro-1,3,5-triazine
and N-ethyl tertiary amines was generally unsuccessful, ex-
cept for MMTEM and MMTEP, thus N-ethyl tert-amines
were not further investigated in this work.
OH
1
a
O
condensation agent
+
N
solvent
r.t.
H
3a
H2N
2
a
Scheme 4 Dehydro-condensation reaction for the synthesis of amide
3a
O
Cl
–
O
Cl–
N
N
N
as standard substrates (Scheme 4 and Table 1). All data re-
ported in Table 1 are the mean values achieved for a set of at
least three experiments monitored after 15 min and 1 h.
For example, the in situ formulation in the presence of
MMT/tert-amine foresees: dissolution of 1.2 mmol of ben-
zoic acid (1a) in the reaction solvent, followed by addition
of 0.6 mmol of MMT, 1.2 mmol of tert-amine NMM, and 1.2
mmol of phenylethylamine (2a) (Table 1, entry 3). Analo-
gous conditions were employed for the formulation of
MIAT/tert-amine and MEAT/tert-amine. The yield of amide
solvent
N
N
N
N
O
3
2 CH Cl
N
N
O
N
O
O
Scheme 5 Demethylation of DMTMM
The isolated triazine bis-quaternary ammonium salts
and 6-substituted 2,4-dichloro-1,3,5-triazine/tert-amine in
situ formulation allowed to obtain 3a in comparable yields
(see, for example, Table 1, entries 1, 3 and 5, 6 or entries 14,
15). MMT/tert-Ams gave better yields in amide 3a com-
pared to MIAT/tert-Ams (cf. Table 1, entries 3 and 9) or
MEAT/tert-Ams (cf. Table 1, entries 3 and 15). Isolated
MMTMM was the most efficient amidation agent for the
synthesis of 3a reaching yields up to 68% in 1 h (Table 1, en-
try 1). It is important to consider that, in the literature ami-
dation reactions carried out in the presence of DMT-Ams or
CDMT/tert-amine employ a molar ratio between the car-
boxylic acid and the coupling agent of 1:1 (mol/mol). In this
work the ratio between 1a and the triazine derivative was
2:1 (mol/mol), reducing by half the amount of condensa-
3
a was monitored by GLC after 15 min and 1 h. For a set of
preliminary experiments, the reaction mixture was moni-
tored by GLC also after 24 h; since no significant difference
was observed between the yield in amide 3a after 1 h and
2
4 h, all further reactions were monitored within 1 h.
It is well known that depending on the tert-amine used,
the corresponding triazine quaternary ammonium salt may
be unstable and decompose leading to the formation of tri-
azine derivatives which are totally inactive as dehydro-con-
4
a,15
densation agents (see Scheme 5).
On the contrary, for
the triazine bis-quaternary ammonium salts reported in
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1677
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R. Sole et al.
Paper
2
Cl–
X
N
X
R''NH3+
R''NH2
O
Cl–
O
N
N
N
N
R'
O–
+
1 2 3
+
+
R'
O
NR R R
3
2
1
1
2
3
R R R N
N
NR R R
+
HNR R R Cl–
1 2 3
X = OMe, NEt2, N(i-Pr)2
NR R R = NMM. NEM, NMP; NEP, MPD, TMA, TEA
R"NH2
1
2 3
O
R'
NHR''
O
X
N
X
N
X
N
R''NH3+
R'
NHR''
R''NH2
+
O
Cl–
+
N
N
N
N
N
N
O
R'
O–
+
HO
OH
HNR R R Cl–
1
2
3
HO
NR R R
1 2 3
HO
O
R'
R"NH2
Scheme 6 Formation of the mono and bis-ester intermediate
tion agent employed. These data may be rationalized con-
sidering that the dichloro-triazine derivatives such as MMT-
Ams, MIAT-Ams, or MEAT-Ams, may originate two interme-
diate active ester species allowing to activate up to two
equivalents of carboxylic acid for each equivalent of triazine
present in the reaction mixture (Scheme 6). Although part
of the triazine bis-quaternary ammonium salts tested give
conversions in 3a below 50% by 1 h (see, for example, Table
philicity of the carboxyl group of 1c and 1d compared to 1a,
which disfavors the formation of the active ester (Table 2,
entries 3 and 4).
Data reported in Tables 1 and 2 confirmed that 2,4-di-
chloro-6-methoxy-1,3,5-triazine and a tert-amine allow to
achieve reasonably good yields in amides 3a–e with a sig-
nificant reduction in consumption of triazine and solvents
required for the synthesis and recovery of isolated bis-qua-
ternary ammonium salts. These features are particularly
important for some specific applications as for example, for
their use as collagen cross-linking agents.
1
, entries 7, 9, or 10–12), when conversions above 50% are
achieved it indicates that, for each equivalent of triazine
present, more than one equivalent of 1a reacted. In other
words, considering, for example, Table 1, entry 1, 1.2 mmol
of 1a were reacted with 0.6 mmol of MMTMM, producing
In a recent paper, we reported a study on the economic
and environmental sustainability of DMTMM as a tanning
0
.82 mmol of 3a (yield 68%). This implies that one of the
chlorine atoms (0.60 mmol) was 100% active in the reaction
conditions tested, while the other chlorine atom was effi-
cient for over 36% (0.22 mmol), substantiating that lower
consumption of these quaternary ammonium salts may be
achieved, compared to 4,6-disubstituted 2-chloro-1,3,5-tri-
azine derivatives. Moreover, if the molar ratio between 1a
and MMTMM was slightly increased, the yield in 3a raised
to 89% in 1 h (Table 1, entry 2), which is comparable to val-
O
MMT/MPD
R1-COOH
+
R1
N
H2N
MeOH, T (°C)
5 min, 60 min
H
1
1
2a
3
1
R : Ph
(1a)
CH2Ph
(1b)
(1c)
(1d)
(1e)
CH2(CH2)5CH3
CH=CH(CH2)4CH3
CH=CH2
1
2
ues obtained with DMTMM or CDMT/NMM system.
To widen the scope of the coupling agents synthesized,
dehydro-condensation reactions for the synthesis of differ-
ent amides were tested (Scheme 7) ranging from aliphatic,
aromatic, sterically hindered, and ,-unsaturated acids.
Only MMT/MPD was further tested since, comparing data
reported in Table 1, this coupling system showed compara-
ble activity to MMTMM, higher than MMT/NMM and more-
over could be easy formulated in the reaction mixture,
without isolation of the triazine quaternary ammonium
salt.
O
O
N
H
N
H
3
a
3b
O
O
N
N
H
H
3
c
e
3d
O
Changing from benzoic acid to phenylacetic acid (1b),
no substantial variation in the overall yield of amide 3b was
observed (cf. Table 1, entry 1 and Table 2, entry 1). For the
synthesis of 3c and 3d slightly lower yields were obtained,
N
H
3
Scheme 7 Condensation reaction between phenylethylamine (2a) and
carboxylic acids 1a–e with MMT/MPD system
4
2% and 54% respectively, probably due to reduced nucleo-
©
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1678
Synthesis
R. Sole et al.
Paper
Table 2 Condensation Reaction between 2a and Acids 1b–1e in the
Presence of MMT/MPD
salt (preformed or in situ formulation), as previously re-
ported for DMTMM.
a,b
10,17
Cross-linking experiments were carried out according
c
10,18
Entry
Acid
Amide
Yield (%) after 15 min/1 h
to the protocol optimized in our previous work,
simply
by adding to a water suspension of BCP, the triazine bis-
quaternary ammonium salts or a 6-substituted 2,4-di-
chloro-1,3,5-triazine and a tert-amine in 1:2 molar ratio.
Preliminary tests were carried out with a molar ratio
between COOHcoll and 6-substituted 2,4-dichloro-1,3,5-tri-
1
2
3
1b
1c
1d
1e
3b
3c
3d
3e
59/65
33/42
52/54
33/34
4
a
Reaction conditions: acid 1b–1e (1.2 mmol), phenylethylamine (2a; 1.2
azine of 4:1 (mol/mol), corresponding to half the amount
mmol), MeOH (6 mL).
10,18
normally employed with DMTMM.
In Table 3 only the
b
Coupling agent: 2,4-dichloro-6-methoxy-1,3,5-triazine (MMT; 0.6 mmol)
and MPD (1.2 mmol).
results achieved for amidation agents giving Ts values above
0 °C are summarized.
c
Yields were measured by GLC using mesitylene as internal standard after
7
15 min and 1 h.
Table 3 Shrinkage Temperature of Collagen Cross-linking by Different
Triazine Bis-quaternary Ammonium Salts
agent.6a When these chemical agents are employed to stabi-
lize the collagen structure, cross-linked amide bonds are
a
Coupling agentb
Ts (°C)c
formed between the pendant carboxylic and amine resi-
Entry
dues present in the protein chains (Scheme 8).7
,16,17
As far as
1
2
3
4
5
6
–
55
70
71
80
75
79
71
this specific application is concerned, the efficiency of
these agents in terms of condensation activity is only one of
the features which have to be taken into consideration to-
gether with ease of use, versatility, low cost, and environ-
mental impact. Thus, further experiments were carried out
in order to verify the efficiency of the triazine derived bis-
quaternary ammonium salts reported in Figure 1 as colla-
gen cross-linking agents. In particular, bovine collagen
powder (BCP) was selected as standard substrate for the
preliminary cross-linking (or tanning) tests. According to
the literature, 1.0 g of BCP contains 1.2 mmol of free car-
boxylic acid groups (COOHcoll) and 0.8 mmol of free amine
MMTMM
MMT/NMM
MMT/NMP
MIATMM
MEATMM
MEAT/NMM
7
a
Reaction conditions: collagen (250 mg, 0.3 mmol COOH), r.t., 4 h.
Coupling agent: 6-substituted 2,4-dichloro-1,3,5-triazine (0.075 mmol)
b
and tertiary amine (0.150 mmol); for isolated MMT-Ams, MIAT-Ams, and
MEAT-Ams (0.075 mmol) were used.
c
Shrinkage temperature was calculated by DSC (see experimental section).
1
6b
groups (NH2Coll
)
and these functional groups will be
cross-linked by an amidation agent to form covalent amide
bonds, influencing the shrinking temperature (Ts) of the
treated collagen. Generally, collagen Ts should increase from
From data in Table 3, it is possible to observe that Ts of
collagen samples cross-linked by isolated MIATMM (entry
5) and MEATMM (entry 6) were higher compared to MMT-
MM (entry 2). Moreover, MMT/NMM (entry 3), MMT/NMP
(entry 4), and MEAT/NMM (entry 7) were also efficient for
collagen cross-linking reaching values as high as 80 °C,
comparable to some of the most efficient synthetic tanning
agents industrially employed today. It should be further
underlined that from an industrial point of view, the possi-
bility to reduce triazine consumption by half is a great ad-
vantage since lower chemical consumption not only implies
reducing material costs, but also expenses due to the treat-
ment of wastewater after tanning.
In conclusion, in this work three different new families
of triazine bis-quaternary ammonium salts have been syn-
thesized and fully characterized. Isolated MMT-Ams, MIAT-
Ams, and MEAT-Ams have been studied as well as a simpli-
fied methodology for the use of these compounds for cou-
pling reactions. In particular, both isolated and in situ tri-
azine bis-quaternary ammonium salts proved to be effi-
cient for the synthesis of amides, reaching, in best reaction
conditions, yields in 3a of up to 89%. The activity of
MMT/MPD was further investigated for the synthesis of ali-
5
0–55 °C for native collagen to Ts above 75 °C, to be suffi-
18,19
ciently stabilized for further processing.
MeO
N
OMe
2
0
N
N
Cl
N
O
O
O
H2N
N
H
OH
OH
N
NH Cl
O
N
N
MeO
OMe
Collagen
Collagen
Collagen
Collagen
DMTOH
Scheme 8 Chemistry likely involved in collagen cross-linking promot-
ed by DMTMM
Variations in BCP shrinking temperature (Ts) were mea-
sured before and after the reaction to evaluate the cross-
linking efficiency of the triazine bis-quaternary ammonium
©
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1679
Synthesis
R. Sole et al.
Paper
phatic, aromatic, sterically hindered, and ,-unsaturated
acids reaching yields in the different amides up to 65%.
Main advantage of these compounds relies in the presence
of two active condensation sites present on the 6-substitut-
ed 2,4-dichloro-1,3,5-triazine, which, in best reaction con-
ditions, may reduce the consumption of triazine up to al-
most 50%. To assess the possible industrial application of
these new amidation agents, cross-linking experiments of
bovine collagen powder were carried out and increase in
collagen shrinking temperature measured to evaluate the
efficiency of the different triazine agents used. MMT/NMP
gave very good Ts up to 80 °C. This data is comparable to
some of the most efficient tanning agents employed indus-
trially today, such as, for example, aldehydes and natural or
synthetic tannins. The possibility to stabilize collagen with-
out the use of chrome salts, formaldehyde, or phenols con-
(monitored by GC), and then the solvent was removed by reduced
pressure evaporation. Acetone (30 mL) was added and the suspension
filtered to remove NaCl. The acetone was evaporated to give MMT
(
10.5 mmol, 97%) as a white solid; mp 88 °C.
FT-IR (KBr): 1528, 1258, 815 cm–1
1H NMR (300 MHz, acetone-d
):  = 4.17 (s, 3 H).
C NMR (75 MHz, acetone-d ):  = 172.7, 172.7, 57.4.
.
6
1
3
6
2,4-Dichloro-6-(diisopropylamino)-1,3,5-triazine (MIAT) and 2,4-
Dichloro-6-(diethylamino)-1,3,5-triazine (MEAT)
To a 100-mL flask, equipped with magnetic stirrer, was added cy-
anuric chloride (2.0 g, 10.8 mmol) in acetone (20 mL). Then, the
amine (21.6 mmol, 2 equiv) was added dropwise to the solution and
the reaction was stirred at r.t. for 30 min (monitored by GC). The sus-
pension was filtered to remove ammonium chloride and mother li-
quors were concentrated to dryness. The obtained solid was charac-
1
13
terized by H NMR, C NMR, FT-IR, and mp.
stitutes a great advantage of triazine derivatives from a sus-
tainability point of view.6
a,19,21,22
Moreover, the amount of
MIAT
MMT/NMP employed to reach Ts of 80 °C is by far lower
compared to other triazine based cross-linking agents
known to date for the tanning of hides, reducing both costs
in reagents and chemical load in wastewater.
Yield: 10.26 mmol (95%); yellow solid; mp 103 °C.
FT-IR (KBr): 1525, 1333, 1229, 808 cm–1
.
1
H NMR (300 MHz, acetone-d ):  = 4.51 (m, 2 H), 1.39 (d, 12 H).
6
1
3
C NMR (75 MHz, acetone-d ):  = 169.2, 164.2, 47.7, 19.4.
6
+
ESI-HRMS: m/z [M – Cl] calcd: 213.0907; found: 213.0712.
Anal. Calcd for C H Cl N (249.14): C, 43.39; H, 5.66; N, 22.49. Found:
C, 44.12; H, 6.54; N, 23.71.
9
14
2
4
All chemicals were purchased from Sigma Aldrich (St. Louis, MO,
USA). Bovine collagen powder was purchased from Filk (Research In-
1
13
stitute of Leather and Plastic Sheeting, Freiberg, Germany). H and
NMR spectra were recorded on a Bruker Avance AC 300 spectrometer
Billerica, MA, USA) operating at 300.21 and 75.44 MHz, respectively.
C
MEAT
(
Yield: 9.94 mmol (92%); white solid; mp 77 °C.
FT-IR spectra were recorded using a Perkin-Elmer Spectrum-One
spectrophotometer using KBr disks. Melting points were measured
with a Buchi 235 model. Differential scanning calorimetry (DSC) of
collagen samples was performed on a Netzsch STA 409 cell (Selb, Ger-
many) fitted with an air-cooling compressor at r.t. and a controller
Netzsch TASC 414/3. The instrument temperature was calibrated us-
ing indium as the standard. Collagen samples (about 7.0 mg) were
weighed (about 0.1 mg) into aluminum pan melting pots and sealed.
Samples were heated from 30 °C to 120 °C at a scanning rate of 10
FT-IR (KBr): 1521, 1336, 1235, 811 cm–1
.
1
H NMR (300 MHz, acetone-d ):  = 3.71 (m, 4 H), 1.22 (d, 6 H).
6
13C NMR (75 MHz, acetone-d
):  = 169.9, 164.4, 42.7, 12.2.
6
+
ESI-HRMS: m/z [M – Cl] calcd: 185.0594; found: 185.0612.
Anal. Calcd for C H Cl N (221.09): C, 38.03; H, 4.56; N, 25.34. Found:
7
10
2
4
C, 37.53; H, 4.89; N, 24.11.
2-Chloro-4,6-bis(diisopropylamino)-1,3,5-triazine (DIAT)
°
C/min. A sealed melting pot (about 7.0 mg) filled with Al O3 (about
2
7
.0 mg) was used as the reference. Gas-chromatography analysis were
To a two-necked 100-mL flask, equipped with magnetic stirrer and
bubble condenser, was added cyanuric chloride (1 g, 5.42 mmol) in
acetone (30 mL). The system was cooled to 0 °C and a solution of di-
isopropylamine (7.6 mL, 54.20 mmol) in acetone (30 mL) was added.
The solution was heated to reflux and stirred for 96 h (monitored by
GC). Every 24 h, acetone (10 mL) was added. At the end of this period,
the precipitate was filtered off and organic phase was evaporated to
dryness. Finally, in order to remove unreacted amine, the obtained oil
recorded with an Agilent Technologies 6850 gas chromatograph
equipped with FID detector and capillary column HP-5 (cross-linked
5% phenylmethylsilicone) or HP-1 (100% dimethylsiloxane). Analyses
were registered with following temperature ramps: HP-1 column: Ti:
5
5
0 °C × 1 min, rate: 20 °C/min, Tf: 230 °C × 35 min. HP-5 column: Ti:
0 °C × 4 min, rate: 20 °C/min, Tf: 230 °C × 30 min. ESI-MS analyses
were performed using a Finnigan LCQ-Duo ion-trap instrument, op-
erating in positive ion mode (sheath gas N , source voltage 4.0 KV,
was washed and dried with CH
2 2
Cl (×4) to give DIAT (4.33 mmol, 80%)
2
capillary voltage 21 V, capillary temperature 200 °C). All mass spectra
were recorded on freshly prepared solutions. Elemental analyses (C,
H, N) were carried out using a Fison EA1108 microanalyzer.
as a yellowish solid; mp 111 °C.
FT-IR (KBr): 1521, 1330, 1236, 810 cm–1
.
1
H NMR (300 MHz, CDCl ):  = 4.38 (m, 4 H), 1.33 (d, 24 H).
3
1
3
C NMR (75 MHz, CDCl ):  = 167.4, 163.6, 45.7, 20.5, 20.2.
3
2
,4-Dichloro-6-methoxy-1,3,5-triazine (MMT)
+
ESI-HRMS: m/z [M + H] calcd: 313.2033; found: 313.1943; m/z [M +
To a 100-mL flask, equipped with magnetic stirrer, was added
NaHCO3 (0.91 g, 10.8 mmol) in MeOH (30 mL). The suspension was
cooled to 0 °C with an ice-cold water bath and cyanuric chloride (2.0
g, 10.8 mmol) was slowly added. The reaction stirred at 0 °C for 1 h
+
Na] calcd: 336.1082; found: 336.1985.
Anal. Calcd for C15
H28ClN (313.87): C, 57.40; H, 8.99; N, 22.31. Found:
5
C, 56.92; H, 8.12; N, 23.01.
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1680
Synthesis
R. Sole et al.
Paper
+
2-Chloro-4,6-bis(diethylamino)-1,3,5-triazine (DEAT)
ESI-HRMS: m/z [M – Cl] calcd: 346.1646; found: 346.1622.
To a two-necked 100-mL flask, equipped with magnetic stirrer and
bubble condenser, was added cyanuric chloride (1 g, 5.42 mmol) in
acetone (30 mL). The system was cooled to 0 °C and a solution of di-
ethylamine (4.5 mL, 43.36 mmol) in acetone (30 mL) was slowly add-
ed. The solution was heated to reflux and stirred for 2 h (monitored
by GC). At the end of this period, the precipitate was filtered off and
organic phase was evaporated to dryness. Finally, in order to remove
Anal. Calcd for C14H25Cl N O (382.28): C, 43.99; H, 6.59; N, 18.32.
Found: C, 43.44; H, 6.01; N, 18.07.
2
5
3
4,4′-(6-Methoxy-1,3,5-triazine-2,4-diyl)bis(4-ethylmorpholin-4-
ium) Dichloride (MMTEM)
Yield: 1.78 mmol (89%); white solid; mp 87 °C.
FT-IR (KBr): 1571, 1370, 1288, 1263, 1135 cm–1
.
unreacted amine, the obtained oil was washed and dried with CH Cl2
2
1
(
×4) to give DEAT (4.33 mmol, 80%) as a dark yellow oil; mp 94 °C.
H NMR (300 MHz, D O):  = 4.57 (d, 4 H), 4.20 (d, 4 H), 3.96 (q, 4 H),
2
FT-IR (KBr): 1519, 1334, 1231, 813 cm–1
3.85 (m, 8 H), 3.39 (s, 3 H), 1.25 (t, 6 H).
.
1
3
1
C NMR (75 MHz, D O):  = 168.8, 167.6, 65.0, 62.0, 57.9, 48.8, 7.0.
H NMR (300 MHz, CDCl ):  = 3.52 (q, 8 H), 1.14 (t, 12 H).
2
3
+
1
3
ESI-HRMS: m/z [M – Cl] calcd: 374.1959; found: 374.1967.
C NMR (75 MHz, CDCl ):  = 168.9, 164.0, 41.6, 41.3, 13.3, 12.7.
3
+
Anal. Calcd for C16H29Cl N O (410.34): C, 46.83; H, 7.12; N, 17.07.
2 5 3
Found: C, 46.55; H, 6.88; N, 16.84.
ESI-HRMS: m/z [M + H] calcd: 257.1406; found: 257.1501; m/z [M +
+
Na] calcd: 280.1323; found: 280.4873.
Anal. Calcd for C11H20ClN (257.77): C, 51.26; H, 7.82; N, 27.17. Found:
C, 52.06; H, 8.37; N, 26.71.
5
1
,1′-(6-Methoxy-1,3,5-triazine-2,4-diyl)bis(1-ethylpiperidin-1-
ium) Dichloride (MMTEP)
Yield: 1.88 mmol (94%); white solid; mp 73 °C.
2
-Chloro-4-methoxy-6-(diisopropylamino)-1,3,5-triazine (MAT)
FT-IR (KBr): 1579, 1371, 1288, 1259 cm–1
.
To a 100-mL flask, equipped with magnetic stirrer, was added
NaHCO (0.23 g, 2.71 mmol) in MeOH (30 mL). Then, the system was
1
3
H NMR (300 MHz, D O):  = 4.48 (d, 4 H), 3.82 (q, 4 H), 3.54 (t, 4 H),
2
cooled to 0 °C and cyanuric chloride (0.5 g, 2.71 mmoL) was slowly
added. The solution was stirred for 1 h (monitored by GC). At the end
of this period, solvent was removed by reduced pressure evaporation,
then acetone (30 mL) was added, and the suspension obtained was
filtered to remove NaCl. Next, diisopropylamine (0.76 mL, 5.42 mmol)
was added to the solution and the reaction was stirred at r.t. for 3.5 h.
Finally, the suspension was filtered, and mother liquors were evapo-
rated to dryness to give MAT (1.62 mmol, 60%) as a white solid; mp 81
3.38 (s, 3 H), 1.95 (m, 4 H), 1.75 (m, 8 H), 1.20 (t, 6 H).
13
C NMR (75 MHz, D O):  = 170.2, 168.9, 64.7, 59.9, 49.3, 21.5, 21.3,
2
7
.8.
+
ESI-HRMS: m/z [M – Cl] calcd: 370.2373; found: 370.2367.
Anal. Calcd for C18H33Cl N O (406.39): C, 53.20; H, 8.19; N, 17.23.
2
5
Found: C, 53.09; H, 7.98; N, 17.02.
°
C.
1
,1′-(6-Methoxy-1,3,5-triazine-2,4-diyl)bis(1-methylpyrrolidin-1-
FT-IR (KBr): 1521, 1336, 1261, 1232, 803 cm–1
.
ium) Dichloride (MMTMPD)
1
Yield: 1.46 mmol (73%); white solid; mp 63 °C.
FT-IR (KBr): 1551, 1343, 1289, 1275 cm–1
.
H NMR (300 MHz, acetone-d ):  = 4.61–4.39 (m, 2 H), 3.93 (s, 3 H),
.38–1.31 (d, 12 H).
6
1
1
3
1
C NMR (75 MHz, acetone-d ):  = 170.8, 170.0, 165.5, 54.8, 47.1,
H NMR (300 MHz, D O):  = 3.56 (m, 4 H), 3.26 (s, 3 H), 2.97 (m, 4 H),
6
2
46.8, 19.7, 19.6.
2.83 (s, 6 H), 2.07 (m, 4 H), 1.92 (m, 4 H).
+
13
ESI-HRMS: m/z [M + H] calcd: 244.1091; found: 244.1783; m/z [M +
C NMR (75 MHz, D O):  = 155.8, 151.5, 57.0, 56.2, 41.0, 23.3.
2
+
Na] calcd: 267.0988; found: 267.0823.
+
ESI-HRMS: m/z [M – Cl] calcd: 314.1747; found: 314.1735.
Anal. Calcd for C10H17ClN O (244.72): C, 49.08; H, 7.00; N, 22.89.
Found: C, 48.67; H, 8.50; N, 22.16.
4
Anal. Calcd for C14H25Cl N O (350.29): C, 48.00; H, 7.19; N, 19.99.
Found: C, 47.89; H, 6.91; N, 19.85.
2
5
Preparation of Triazine Bis-quaternary Ammonium Salts Derived
from 6-Substituted 2,4-Dichloro-1,3,5-triazine; General Procedure
4
,4′-[6-(Diisopropylamino)-1,3,5-triazine-2,4-diyl]bis(4-methyl-
morpholin-4-ium) Dichloride (MIATMM)
To a 50-mL flask, equipped with magnetic stirrer, was added 6-substi-
tuted 2,4-dichloro-1,3,5-triazine (MMT, MIAT, MEAT; 2.0 mmol) in
acetone (20 mL). The solution was cooled to 0 °C and the amine (4.0
mmol, 2 equiv) was slowly added (in the case of TMA, a 45% wt. aq
solution was used). The reaction was stirred for 40 min, then the pre-
cipitate was filtered and dried under vacuum. The solid product ob-
Yield: 1.76 mmol (88%); yellowish solid; mp 68 °C.
FT-IR (KBr): 1518, 1341, 1271, 1231, 1134 cm–1
.
1
H NMR (300 MHz, D O):  = 4.59 (m, 2 H), 4.59 (m, 4 H), 4.21 (d, 4 H),
2
3.95 (m, 8 H), 3.60 (s, 6 H), 1.42 (d, 12 H).
13
C NMR (75 MHz, D O):  = 169.0, 164.2, 62.2, 60.4, 55.2, 49.9, 19.2.
2
1
tained was characterized by H NMR, FT-IR, and mp, when possible
+
the 13C NMR spectrum was acquired as well. 13C NMR spectrum of
MMTMM was not acquired due to its low stability.
ESI-HRMS: m/z [M – Cl] calcd: 415.2588; found: 415.2591.
Anal. Calcd for C19H36Cl N O (451.44): C, 50.55; H, 8.04; N, 18.62.
2 6 2
Found: C, 50.32; H, 7.98; N, 18.21.
4
,4′-(6-Methoxy-1,3,5-triazine-2,4-diyl)bis(4-methylmorpholin-
4-ium) Dichloride (MMTMM)
1,1′-[6-(Diisopropylamino)-1,3,5-triazine-2,4-diyl]bis(1-methyl-
piperidin-1-ium) Dichloride (MIATMP)
Yield: 1.74 mmol (87%); white solid; mp 73 °C.
FT-IR (KBr): 1521, 1336, 1288, 1261, 1129 cm–1
Yield: 1.70 mmol (85%); white solid; mp 70 °C.
.
FT-IR (KBr): 1532, 1351, 1267, 1222 cm–1
.
1
H NMR (300 MHz, D O):  = 4.53 (m, 4 H), 4.16 (m, 4 H), 3.87 (m, 8
2
H), 3.39 (s, 3 H), 2.87 (s, 6 H).
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1681
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R. Sole et al.
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1
2
2
2
4
4
4
H NMR (300 MHz, D O):  = 4.61 (brm, 2 H), 4.51 (d, 4 H), 3.68 (t, 4
6-(Diethylamino)-N ,N ,N ,N ,N ,N -hexamethyl-1,3,5-triazine-2,4-
2
H), 3.44 (s, 6 H), 1.98 (m, 4 H), 1.73 (m, 8 H), 1.41 (d, 12 H).
diaminium Dichloride (MEATTMA)
1
3
C NMR (75 MHz, D O):  = 169.5, 164.6, 62.2, 55.4, 49.6, 21.5, 20.8,
Yield: 1.92 mmol (96%); yellowish solid; mp 72 °C.
2
1
9.4.
FT-IR (KBr): 1563, 1368, 1268, 1215 cm–1
.
+
ESI-HRMS: m/z [M – Cl] calcd: 411.3002; found: 411.3001.
1
H NMR (300 MHz, D O):  = 3.81 (q, 4 H), 3.62 (s, 18 H), 1.27 (t, 6 H).
2
Anal. Calcd for C21H40Cl N (447.49): C, 56.37; H, 9.01; N, 18.78.
Found: C, 57.12; H, 9.21; N, 19.01.
13
2
6
C NMR (75 MHz, D O):  = 171.1, 164.5, 54.4, 44.4, 11.1.
2
+
ESI-HRMS: m/z [M – Cl] calcd: 303.2063; found: 303.2061.
Anal. Calcd for C13H28Cl N (339.31): C, 46.02; H, 8.32; N, 24.77.
Found: C, 45.98; H, 8.20; N, 24.52.
2
6
1
,1′-[6-(Diisopropylamino)-1,3,5-triazine-2,4-diyl]bis(1-methyl-
pyrrolidin-1-ium) Dichloride (MIATMPD)
Yield: 1.44 mmol (72%); white solid; mp 68 °C.
Coupling Reactions
FT-IR (KBr): 1540, 1345, 1279, 1215 cm–1
.
1
H NMR (300 MHz, D O):  = 4.61 (m, 2 H), 4.43 (m, 4 H), 3.91 (d, 4 H),
.56 (s, 6 H), 2.34 (m, 8 H), 1.42 (d, 12 H).
2
Dehydro-condensation Reactions in the Presence of MMT/tert-
Amine System; Typical Procedure
3
1
3
C NMR (75 MHz, D O):  = 169.9, 163.7, 65.5, 51.3, 48.9, 21.9, 18.8.
Acid 1a (146.5 mg, 1.2 mmol) was dissolved in solvent (MeOH, 6 mL)
and subsequently MMT (107.9 mg, 0.6 mmol), tert-amine (1.2 mmol),
and amine 2a (145.4 mg, 1.2 mmol) were added. The yield of amide
2
+
ESI-HRMS: m/z [M – Cl] calcd: 383.2689; found: 383.2685.
Anal. Calcd for C19H36Cl N (419.44): C, 54.41; H, 8.65; N, 20.05.
Found: C, 54.56; H, 8.12; N, 20.07.
2
6
3
a was monitored by GLC using mesitylene as internal standard after
1
5 min and 1 h. To isolate 3a, the mixture was filtered and the yellow-
ish solid recovered was dissolved in CH Cl and extracted with water
2
2
2
2
2
4
4
4
6
-(Diisopropylamino)-N ,N ,N ,N ,N ,N -hexamethyl-1,3,5-tri-
(
3 × 30 mL). The combined organic phase was dried (MgSO ), filtered,
4
azine-2,4-diaminium Dichloride (MIATTMA)
and concentrated in vacuo to give 3a as a white solid. Analogous reac-
tion conditions were employed with MEAT and MIAT in the presence
of a tert-amine.
Yield: 1.40 mmol (70%); yellowish solid; mp 73 °C.
FT-IR (KBr): 1540, 1340, 1271, 1211 cm–1
.
1
H NMR (300 MHz, D O):  = 4.63 (m, 2 H), 3.63 (s, 18 H), 1.42 (d, 12
2
Dehydro-condensation Reaction in the Presence of Isolated Qua-
ternary Ammonium Salts; Typical Procedure
H).
1
3
C NMR (75 MHz, D O):  = 176.6, 170.0, 59.9, 50.0, 20.0.
2
Acid 1a (158.7 mg, 1.2 mmol) was dissolved in MeOH (6 mL) and the
preformed amidation agent (0.6 mmol) and amine 2a (145.4 mg, 1.2
mmol) were added. The yield of amide 3a was monitored by GLC us-
ing mesitylene as internal standard after 15 min and 1 h. The proce-
dure to isolate 3a was the same as mentioned above.
+
ESI-HRMS: m/z [M – Cl] calcd: 331.2376; found: 331.2371.
Anal. Calcd for C15H32Cl N (367.36): C, 49.04; H, 8.78; N, 22.88.
Found: C, 48.50; H, 8.31; N, 22.52.
2
6
4,4′-[6-(Diethylamino)-1,3,5-triazine-2,4-diyl]bis(4-methyl-
morpholin-4-ium) Dichloride (MEATMM)
Cross-Linking of Bovine Collagen Powder; Typical Procedure
Yield: 1.80 mmol (90%); white solid; mp 86 °C.
FT-IR (KBr): 1531, 1361, 1268, 1219, 1130 cm–1
The cross-linking of BCP in the presence of MMTMM is reported as an
example (Table 3, entry 2): bovine collagen powder (300.0 mg, 0.36
mmol COOHcoll) was dispersed in water (30 mL) under magnetic stir-
ring. After 30 min, MMTMM (199.2 mg, 0.72 mmol) was added to the
suspension and stirring was continued for a further 4 h; the collagen
powder was then recovered by filtration, air dried, and analyzed by
DSC.
.
1
H NMR (300 MHz, D O):  = 4.49 (d, 4 H), 4.10 (d, 4 H), 3.82 (q, 8 H),
2
3.70 (q, 4 H), 3.48 (s, 6 H), 1.16 (t, 6 H).
1
3
C NMR (75 MHz, D O):  = 169.1, 164.0, 61.8, 59.9, 55.1, 44.13, 11.4.
2
+
ESI-HRMS: m/z [M – Cl] calcd: 387.2275; found: 387.2271.
For MMT/NMM the same procedure was performed adding MMT
Anal. Calcd for C17H32Cl N O (423.38): C, 48.23; H, 7.62; N, 19.85.
Found: C, 48.10; H, 6.89; N, 6.42.
2
6
2
(
129.6 mg, 0.72 mmol) and NMM (145.6 mg, 1.44 mmol).
1
,1′-[6-(Diethylamino)-1,3,5-triazine-2,4-diyl]bis(1-methylpiperi-
Supporting Information
din-1-ium) Dichloride (MEATMP)
Yield: 1.56 mmol (78%); white solid; mp 86 °C.
FT-IR (KBr): 1531, 1361, 1268, 1219, 1130 cm–1
Supporting information for this article is available online at
.
https://doi.org/10.1055/a-1334-6916.
S
u
p
p
orti
n
gI
n
f
orm
a
ti
o
n
S
u
p
p
orti
n
gI
n
f
orm
a
ti
o
n
1
H NMR (300 MHz, D O):  = 4.53 (d, 4 H), 3.79 (q, 4 H), 3.65 (t, 4 H),
2
3
.43 (s, 6 H), 1.96 (m, 4 H), 1.75 (m, 8 H), 1.26 (t, 6 H).
References
1
3
C NMR (75 MHz, D O):  = 169.5, 164.4, 61.1, 55.1, 43.8, 20.9, 20.2,
2
1
1.5.
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(
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Anal. Calcd for C19H36Cl N (419.44): C, 54.41; H, 8.65; N, 20.04.
Found: C, 54.10; H, 8.43; N, 8.56.
2
6
©
2020. Thieme. All rights reserved. Synthesis 2021, 53, 1672–1682

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