Solvent-free condensation of methyl pyridinium and quinolinium salts with aldehydes catalyzed by DBU

Article abstract of DOI:10.1080/00397911.2010.528573

Methylpyridinium and methylquinolinium salts were condensed under solvent-free conditions with aromatic aldehydes in the presence of 1,8-diazabicyclo[5.4.]undec-7-ene (DBU) as catalyst, by grinding at room temperature. The products are dyes or useful intermediates. The DBU can be easily recycled and reused. Taylor & Francis Group, LLC.

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Solvent-Free Condensation of Methyl
Pyridinium and Quinolinium Salts with
Aldehydes Catalyzed by DBU
Linda Loucif Seiad a b , Didier Villemin a , Nathalie Bar a & Messaoud
Hachemi b
a Laboratoire de Chimie Moléculaire et Thioorganique, UMR CNRS
6507 ENSICAEN and Université de Caen, Caen, France
b Laboratoire de Chimie Moléculaire et Composites, Faculté des
Sciences de l'Ingénieur, Université M'Hamed, Boumerdes, Algéria
Accepted author version posted online: 10 Aug 2011.Version of
record first published: 01 Nov 2011.
To cite this article: Linda Loucif Seiad, Didier Villemin, Nathalie Bar & Messaoud Hachemi (2012):
Solvent-Free Condensation of Methyl Pyridinium and Quinolinium Salts with Aldehydes Catalyzed
by DBU, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 42:5, 650-657
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Synthetic Communications1, 42: 650–657, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.528573
SOLVENT-FREE CONDENSATION OF METHYL
PYRIDINIUM AND QUINOLINIUM SALTS WITH
ALDEHYDES CATALYZED BY DBU
Linda Loucif Seiad,1,2 Didier Villemin,1 Nathalie Bar,1 and
Messaoud Hachemi2
1
´
Laboratoire de Chimie Moleculaire et Thioorganique, UMR CNRS 6507
ENSICAEN and Universite de Caen, Caen, France
´
2
´
Laboratoire de Chimie Moleculaire et Composites, Faculte des Sciences de
l’Ingenieur, Universite M’Hamed, Boumerdes, Algeria
´
´
´
´
GRAPHICAL ABSTRACT
Abstract Methylpyridinium and methylquinolinium salts were condensed under solvent-free
conditions with aromatic aldehydes in the presence of 1,8-diazabicyclo[5.4.]undec-7-ene
(DBU) as catalyst, by grinding at room temperature. The products are dyes or useful inter-
mediates. The DBU can be easily recycled and reused.
Keywords Green chemistry; Knoevenagel condensation; styryl dyes
INTRODUCTION
Styrylpyridinium and styrylquinolinium derivatives constitute an important
group of dyes that have known for a long time; consequently, many applications
of these dyes have been described.[1] Presently, these dyes are useful in studies of
the transport mechanisms through cell membranes and voltage-sensitive probes in
neurones.[2] Fluorescent styryl dyes have been identified as RNA-specific agents in
numerous bioanalytical methods.[3] Some are PDGF receptor tyrosine kinase inhibi-
tors[4] or integrase inhibitors.[5] It was also found that these compounds exhibit a
very good performance as inhibitors for mild steel corrosion[6] and in electrolumines-
cence and photochromism,[7] as fluorophores or optical sensors.[8]
The development of green chemistry[9] and the search for new environmentally
synthetic methods have encouraged us to devise a rapid and effective procedure for
Received June 15, 2010.
Address correspondence to Didier Villemin, Laboratoire de Chimie Moleculaire et Thioorganique,
´
UMR CNRS 6507, INC3M FR 3038 ENSICAEN and Universite de Caen, 4050 Cean, France. E-mail:
didier.villemin@ensicaen.fr
´
650

CONDENSATION OF METHYL PYRIDINIUM AND QUINOLINIUM SALTS
651
the synthesis of styrylpyridinium and styrylquinolinium derivatives using
solvent-free conditions. Solvent-free reactions have gained great importance because
of their high efficiency, operational simplicity, and environmentally benign pro-
cesses. Solventless organic reactions, based on grinding several macroscopic parti-
cles, have been described by Toda[10] in many reaction types (Grignard,
Reformatsky, aldolic, Dieckmann, Knoevenagel condensations, reduction). Most
of these reactions are easily performed at room temperature in a solvent-free
environment using only a mortar and pestle.
RESULTS AND DISCUSSION
The usual synthesis of such styryl derivatives is often carried out by the reac-
tion of 2- or 4-methyl quaternary salts and aromatic aldehydes by reflux for many
hours in the presence of a catalyst (often piperidine) in organic media.[1] This
process needs purification of the product and consumes considerable energy.
The aim of this work is to perform the Knoevenagel condensation[11] of methyl
pyridinium and quinolinium salts (Fig. 1) The Knoevenagel condensation has been
studied and used for the preparation of substituted alkenes in solvent-free con-
ditions.[12] In our work, the condensation may be carried out with the use of
(1,8)-diazabicyclo[5.4.0]undec-7-ene (DBU) as catalyst (Fig. 2). DBU is an effective
and strong base (sterically hindered amidine) that has been used to perform conden-
sation of active methylene compounds.[13] It presents the following advantages: it is
an organobase liquid, soluble in diethylether, while onium salts are insoluble.
Consequently the separation from the products is easier.
Figure 1. Pyridinium and quinolinium iodides.
Figure 2. Structure of DBU.
Figure 3. Aldehydes.

652
L. L. SEIAD ET AL.
Scheme 1. Synthesis of styryl pyridinium and quinolinium iodides.
Table 1. Meltings points, electronic absorptions, and yields of the dyes obtained by grinding
Product
Mp (ꢀC)
Mp lit. (ꢀC)
kmax (e)
Yield (%)
235
235[14]
372 (32000)
60
214
214–215[15]
336 (2600)
30
60
236–237
236–237[16]
571 (13000)
273–274
273–274[17]
465 (33000)
90
258
276
258–259[17]
475 (8000)
523 (7000)
35
73
276[16]
302
302[16]
556 (5000)
50
akmax (nm), e (L molꢁ1 cmꢁ1).

CONDENSATION OF METHYL PYRIDINIUM AND QUINOLINIUM SALTS
653
The Knoevenagel condensation at room temperature of aldehyde (Fig. 3) with
1 equivalent of compound containing active methylene groups in the presence of
DBU as catalyst afforded generally the corresponding trans-styryl derivatives
(Scheme 1) with moderate to excellent yieds (Table 1). Most of the compounds
display high absorption in the ultraviolet–visible range.
1
All the products were characterized by mass spectra, infrared IR, and H and
13C NMR. The sole condensation products detected were the corresponding (E)-
1
isomers, except 1b, which gave a mixture of Z=E stereoisomers (45=55). The H
=
NMR spectra show two characteristic doublets for CH CH trans in the range
7.2–8.6 ppm with coupling constants between 12 and 18 Hz. For signal assignments,
homonuclear two-dimensional (2D) 1H-1H correlation spectroscopy (COSY) spectra
and heteronuclear 2D1H-13C spectra heteronuclear single quantum correlation
(HSQC) and heteronuclear multiple bond correlation (HMBC) were used.
For 1d, no melting point, absorption data, and yield are listed. Compound 1d
was obtained as a complex mixture of Z=E stereoisomers as it was confirmed by MS
spectrum and 1H NMR. Moreover, an additional compound was synthesized under
our experimental conditions. It could be the dimer of (1d) obtained by a cycloaddi-
tion [2 þ 2]. These results are in agreement with those of Andreani [18] obtained with
chloride salts analog of 1d.
Some recycling of the catalytic DBU were then attempted for compound 2a.
The selectivity of the reaction was 90% after the first use, 90% after the second
use, and decreased only after five runs.
EXPERIMENTAL
Materials and Methods
Melting points were determinated on a Kofler apparatus and are uncorrected.
IR spectra were recordered on Fourier transform Perkin-Elmer Spectrum One with
ATR accessory. NMR spectra were recorded at 400 MHz for 1H NMR and
100.6 MHz for 13C NMR with a Bruker Avance III 400 spectrometer in dimethyl-
sulfoxide (DMSO-d6) in parts per million. Mass spectra were recordered on a QTOF
Micro (Waters), ionization electrospray positive (ESI), lockspray orthophosphoric
acid, infusion introduction (10 mL=min), source temperature 80 ꢀC, and desol-
vatation temperature 120 ꢀC. UV–visible spectra were recorded in methanol on
Pharmacia Biotech Nova Spec II UV=vis spectrophotometer.
All starting compounds were commercially available and were used as sup-
plied. The quaternary salts were prepared as previously reported in the literature
by reflux in toluene of the starting compounds with iodomethane or iodoethane,
depending on the structure.[19]
General Procedure
A mixture of the quaternary salt (2 ꢂ 10ꢁ3 mol), aromatic aldehyde (2 ꢂ 10ꢁ3
mol), and DBU (150 mg) was triturated in a mortar for 30 min. The product was
rinsed with diethyl ether (3 ꢃ 15 mL), filtered under reduced pressure, and air dried.
The product was recrystallized from methanol.

654
L. L. SEIAD ET AL.
Recycling
The diethyl ether filtrate was evaporated, and the resulting liquid was used
instead of DBU for performing the same reaction. Six runs were performed with 2a.
Selected Data
(E)-2-(4-Methoxystyryl)-1-methylpyridinium iodide (1a). Yield 60%, mp
235 ꢀC,[14] IR (cmꢁ1): 1680. 1H NMR (ppm): 3.84 (s, 3H, OCH3), 4.34 (s, 3H,
þ
=
N CH3), 7.06 (d, 8.8 Hz, 2H, Ar), 7.44 (d, 16.2 Hz, 1H, CH CH), 7.83 (d, 8.8 Hz,
=
2H, Ar), 7.84 (m, 1H, Ar), 7.92 (d, 16.2 Hz, 1H, CH CH), 8.44 (m, 1H, Ar), 8.47
(m, 1H, Ar), 8.84 (d, 6.4 Hz, 1H, Ar). 13C NMR (ppm): 46.01, 55.50, 114.54 (2C),
114.75, 124.43, 124.46, 127.57, 130.54 (2C), 142.85, 143.93, 145.79, 152.71, 161.44.
EIMS m=z (% relative abundance): 226 (Mþ, 62), 211 (100), 182 (30). HRMS
(ESI-TOF): calcd for C15H16NO 226.1232, found 226.1229.
(E)-1-Ethyl-4-(4-methoxystyryl)pyridinium iodide (1b). Yield 30%, mp
214 ꢀC,[15] IR (cmꢁ1): 1677.1H NMR (ppm): E stereoisomer 1.46 (t, 10.5 Hz, 3H,
CH3), 3.87 (s, 3H, OCH3), 4.50 (m, 2H, NþCH2), 7.14 (m, 2H, Ar), 7.35 (d,
=
=
16.4 Hz, 1H, CH CH), 7.71 (d, 8.8 Hz, 2H, Ar), 8.00 (d, 16.4 Hz, 1H, CH CH),
8.17 (d, 6.8 Hz, 2H, Ar), 8.90 (m, 2H, Ar). Z stereoisomer 1.52 (t, 10.5 Hz, 3H,
CH3), 3.87 (s, 3H, OCH3) 4.50 (m, 2H, NþCH2), 6.75 (d, 8.8 Hz, 2H, Ar), 7.08
(m, 2H, Ar), 7.88 (m, 3H, Ar and CH CH), 8.92 (m, 3H, CH CH and Ar). 13C
NMR (ppm): 16.18, 39.73, 54.7, 111.08, 112.02 (2C), 117.07, 122.55 (2C), 130.26
(2C), 142.08, 143.28 (2C), 151.93, 153.73. EIMS m=z (% relative abundance): 240
(Mþ, 100), 225 (92). HRMS (ESI-TOF): calcd for C16H18NO 240.1388; found
240.1394.
=
=
(E)-2-(4-Methoxystyryl)-1-methylquinolinium iodide (1c). Yield 60%, mp
1
236–237 ꢀC,[16] IR (cmꢁ1): 1678. H NMR (ppm): 3.88 (s, 3H, OCH3), 4.56 (s, 3H,
þ
=
N CH3), 7.12 (d, 8.8 Hz, 2H, Ar), 7.81 (d, 15.2 Hz, 1H, CH CH), 7.95 (t, 8.0 Hz,
1H, Ar), 7.99 (d, 8.8 Hz, 2H, Ar), 8.18 (t, 8.0 Hz, 1H, Ar), 8.25 (d, 15.2 Hz, 1H,
=
CH CH), 8.35 (d, 8.0 Hz, 1H, Ar), 8.55 (d, 8.8 Hz, 1H, Ar), 8.57 (d, 9.2 Hz, 1H,
Ar), 9.03 (d, 9.2 Hz, 1H, Ar). 13C NMR (ppm): 39.7, 55.6, 114.77 (2C), 116.60,
119.29, 120.88, 127.69, 127.69, 128.80, 129.99, 131.42 (2C), 134.75, 139.18, 143.63,
147.19, 156.47, 162.25. EIMS m=z (% relative abundance): 276 (Mþ, 85), 161
(100), 168 (54), 232 (52). HRMS (ESI-TOF): calcd for C19H18NO 276.1388; found
276.1400.
(E)-2-(4-(Dimethylamino)styryl)-1-methylpyridinium iodide (2a). Yield
1
90%, mp 273–2þ74 ꢀC,[17] IR (cmꢁ1): 1630. H NMR (ppm): 3.02 [s, 6H, N(CH3)2],
=
4.30 (s, 3H, N CH3), 6.79 (d, 8.0 Hz, 2H, Ar), 7.24 (d, 15.2 Hz, 1H, CH CH),
=
7.71 (m, 1H, Ar), 7.72 (d, 8.0 Hz, 2H, Ar), 7.93 (d, 15.2 Hz, 1H, CH CH), 8.35 (t,
8.4 Hz, 1H, Ar), 8.46 (d, 8.4 Hz, 1H, Ar), 8.77 (d, 6.0 Hz, 1H, Ar). 13C NMR
(ppm): 39.58 (2C), 45.70, 110.61, 111.78 (2C), 122.34, 123.04, 123.60, 130.75,
143.09 (2C), 144.21, 145.29, 152.11, 153.28. EIMS m=z (% relative abundance):
239 (Mþ, 65), 223 (100), 134 (32). HRMS (ESI-TOF): calcd for C16H19N2
239.1548; found 239.1540.

CONDENSATION OF METHYL PYRIDINIUM AND QUINOLINIUM SALTS
655
(E)-4-(4-(Dimethylamino)styryl)-1-ethylpyridinium iodide (2b). Yield
1
35%, mp 258 ꢀC,[17] IR (cmꢁ1): 1677. H NMR (ppm): 1.51 (t, 10.5 Hz, 3H, CH3),
3.03 (s, 6H, N(CH3)2), 4.45 (m, 2H, NþCH2), 6.79 (d, 10.0 Hz, 2H, Ar), 7.18 (d,
=
=
18.0 Hz, 1H, CH CH), 7.60 (d, 10.0 Hz, 2H, Ar), 7.92 (d, 18.0 Hz, 1H, CH CH),
8.07 (d, 10.0 Hz, 2H, Ar), 8.78 (d, 10.0 Hz, 2H, Ar). 13C NMR (ppm): 16.38, 39.31
(2C), 54.69, 111.98 (2C), 117.2, 122.48 (2C), 128.53, 130.29 (2C), 141.90, 143.40
(2C), 151.97, 153.9. EIMS m=z (% relative abundance): 253 (Mþ, 100), 224 (88),
237 (70), 209 (40). HRMS (ESI-TOF): calcd for C17H21N2 253.1705; found 253.1700.
(E)-2-(4-(Dimethylamino)styryl)-1-methylquinolinium iodide (2c). Yield
1
73%, mp 276 ꢀC,[16] IR (cmꢁ1): 1676. H NMR (ppm): 3.09 (s, 6H, N(CH3)2), 4.45
þ
=
(s, 3H, N CH3), 6.82 (d, 10.1 Hz, 2H, Ar), 7.57 (d, 15.4 Hz, 1H, CH CH), 7.85
(d, 10.1 Hz, 2H, Ar), 7.87 (t, 8,1 Hz, 1H, Ar), 8.10 (d, 7,9 Hz, 1H, Ar), 8.22 (t,
=
7.9 Hz, 1H, Ar), 8.25 (d, 15.4 Hz, 1H, CH CH), 8.50 (d, 8.1 Hz, 1H, Ar), 8.56 (d,
10.2 Hz, 1H, Ar), 8.80 (d, 10,2 Hz, 1H, Ar). 13C NMR (ppm): 39.43 (2C), 53.07,
111.79 (3C), 118.74, 120.30, 122.38, 125.11, 126.8, 128.03, 132.37 (2C), 135.12,
139.56, 142.1, 149.08, 153.09, 156.69. EIMS m=z (% relative abundance): 289 (Mþ,
75), 273 (100), 134 (73). HRMS (ESI-TOF): calcd for C20H21 N2 289.1705 found
289.1703.
(E)-4-(4-(Dimethylamino)styryl)-1-ethylquinolinium iodide (2d). Yield
1
50%, mp 302 ꢀC,[16] IR (cmꢁ1): 1676. H NMR (ppm): 1.57 (t, 8.0 Hz, 3H, CH3),
3.02 (s, 6H, N (CH3)2), 4.91 (m, 2H, NþCH2), 6.84 (d, 8.1 Hz, 2H, Ar), 7.88 (d,
=
8.1 Hz, 2H, Ar), 7.99 (t, 8.0 Hz, 1H, Ar), 8.03 (d, 15.8 Hz, 1H, CH CH), 8.20
=
(d, 15.8 Hz, 1H, CH CH), 8.21 (t, 8.0 Hz, 1H, Ar), 8.36 (d, 8.0 Hz, 1H, Ar), 8.46
(d, 8.0 Hz, 1H, Ar), 9.04 (d, 8.0 Hz, 1H, Ar), 9.16 (d, 8.0 Hz, 1H, Ar). 13C NMR
(ppm): 18.32, 39.58 (2C), 53.17, 111.03 (3C), 114.28, 123.05 (3C), 128.43, 129.01,
134.12, 131.37 (2C), 137.65, 144.08, 144.87, 152.31, 153.26. EIMS m=z (% relative
abundance): 303 (Mþ, 100), 259 (100), 273 (72), 287 (70). HRMS (ESI-TOF): calcd.
for C21H23 N2 303.1861; found 303.1876.
CONCLUSION
The condensation of methylpyridinium and methylquinolinium salts with
aromatic aldehyde takes place at room temperature by grinding in the presence of
DBU as catalyst. The catalyst can be easy reused. This condensation into dyes or
useful intermediates is very simple and efficient.
ACKNOWLEDGMENTS
We gratefully acknowledge the CNRS (National Center for Scientific
Research), the ‘‘Region Basse-Normandie,’’ the University of Boumerdes (Algeria),
the Franco-Algerian program for the Superior Education (PROFS), and the
Algerian-French cooperation for a BAF grant for L. Loucif Seiad. Also the authors
´
thank Remy Legay and Baptiste Rigaud for NMR spectra and Mrs. Karine Jarsale
for ESIMS and HRMS analysis.
´

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REFERENCES
1. For reviews on the old chemistry of styryl dyes, see (a) Doja, M. Q. The cyanine dyes.
Chem. Rev. 1932, 11, 273–321; (b) Mishra, A.; Behera, R. K.; Behera, P. K.; Mishra,
B. K.; Behera, G. B. Cyanines during the 1990s: A review. Chem. Rev. 2000, 100, 1973–
2012; (c) Hamer, F. M. The Cyanine Dyes and Related Compounds; Interscience
Publishers: New York, 1964.
2. Gawinecki, R.; Trzebiatowska, K. The effect of the amino group on the spectral proper-
ties of substituted styrylpyridinium salts. Dyes Pigm. 2000, 45, 103–107.
3. Wang, M.; Gao, M.; Miller, K. D.; Sledge, G. W.; Hutchins, G. D.; Zheng, Q.-H. Simple
synthesis of carbon-11 labeled styryl dyes as new potential PET RNA-specific, living cell
imaging probes. Eur. J. Med. Chem. 2009, 44, 2300–2306.
4. Maguire, M. P.; Sheets, K. R.; McVety, K.; Spada, A. P.; Zilberstein, A. A new series of
PDGF receptor tyrosine kinase inhibitors: 3-Substituted quinoline derivatives. J. Med.
Chem. 1994, 37, 2129–2137.
5. (a) Bonnenfant, S.; Thomas, M. C.; Vita, C.; Subra, F.; Deprez, E.; Zouhiri, F.; Desmae¨le,
D.; D’Angelo, J.; Mouscadet, J. F.; Leh, H. Styrylquinolines, integrase inhibitors acting
prior to integration: A new mechanism of action for anti-integrase agents. J. Virol.
2004, 78, 5728–5736; (b) Mousnier, A.; Leh, H.; Mouscadet, J. F.; Dargemont, C. Nuclear
import of HIV-1 integrase is inhibited in vitro by styrylquinoline derivatives. Mol. Phar-
macol. 2004, 66, 783–788.
6. Noor, E. A.; Al-Moubaraki, A. H. Thermodynamic study of metal corrosion and inhibi-
tor adsorbtion processes in mild steel=1-methyl-4[40(-X)-styryl]pyridinium iodides=hydro-
chloric acid systems. Mat. Chem. Phys. 2008, 110, 145–154.
7. Spalletti, A. Conformer-specific and two-fold adiabatic photoisomerization of Z,Z-1,4-
di-(2-quinolylethenyl)benzene. Photochem. Photobiol. Sc. 2004, 3, 695–699.
8. (a) As fluorophore see Glasbeek, M.; Zhang, H. Femtosecond studies of solvation
and intramolecular configurational dynamics of fluorophores in liquid solution.
Chem. Rev. 2004, 104, 1929–1954; (b) Ambrose, W. P.; Goodwin, P. M.; Jett, J. H.;
Van Orden, A.; Werner, J. H.; Keller, R. A. Single molecule fluorescence spectroscopy
at ambient temperature. Chem. Rev. 1999, 99, 2929–2956; (c) As optical sensor see
McDonagh, C.; Burke, C. S.; MacCraith, B. D. Optical chemical sensors. Chem. Rev.
2008, 108, 400–422.
9. Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University
Press: Oxford, 1988.
10. (a) Tanaka, K.; Toda, F. Solid-free organic synthesis. Chem. Rev. 2000, 100, 1025–1074;
(b) Toda, F. Solid state organic chemistry: Efficient reactions, remarkable yields, and
stereoselectivity. Acc. Chem. Res. 1995, 28, 480–486.
11. For key reviews of the Knoevenagel condensation, see (a) Jones, G. The Knoevenagel
condensation. Org. React. 1967, 15, 204–599; (b) Tietze, L. F.; Beifuss, U. The knoevena-
gel reaction in comprehensive organic synthesis; In B. M. Trost, and I. Fleming (Eds.);
Pergamon: Oxford, 1991; vol. 2, p. 341.
12. Toda, F.; Tanaka, K.; Hamai, K. Aldol condensations in the absence of solvent: Acceler-
ation of the reaction and of the stereoselectivity. J. Chem. Soc. 1990, 11, 3207–3209.
13. Yamanaka, H.; Yokoyama, M.; Sakamoto, T.; Shiraishi, T.; Sagi, M.; Mizugaki, M.
Influence of heteroaromatic amines to Knoevenagel condensation. Heterocycles 1983,
20, 1541–1544.
14. Williams, J. L. R.; Adel, R. E.; Carlson, J. M.; Reynolds, G. A.; Borden, D. J.; Ford, J. A.
Comparison of methods for the preparation of 2- and 4-styrylpyridiniums. J. Org. Chem.
1963, 28, 387–390.

CONDENSATION OF METHYL PYRIDINIUM AND QUINOLINIUM SALTS
657
15. Phillips, A. P. Condensation of aromatic aldehydes with c picoline methiodide. J. Org.
Chem. 1949, 14, 302–305.
16. Bahner, C. T.; Pace, E. S.; Prevost, R. Quaternary salts of styryl pyridines and quinolines.
J. Am. Chem. Soc. 1951, 73, 3407–3408.
17. Phillips, A. P. Condensation of aromatic aldehydes with a picoline methiodide. J. Org.
Chem. 1947, 12, 333–341.
18. Andreani, F.; Andrisano, R.; Tramontini, M. Researches on the reactivity of
Mannich bases, part VIII: Synthesis of N-methyl(vinylaryl)quinolinium salts and their
photosensitivity. J. Heterocycle. Chem. 1967, 4, 171–177.
19. Kramer, D. N.; Bisauta, L. P.; Bato, R. Kinetics of the condensation of N-methyl-4-
picolinium iodide with p-dimethylaminobenzaldehyde in aqueous ethanol. J. Org. Chem.
1974, 39, 3132–3136.