Synthesis and Langmuir monolayer characterisation of some nitro derivatives of polyphenyl carboxylic acids

Article abstract of DOI:10.3184/030823409X417289

Derivatives of 5′-phenyl-1,1′ : 3′,1″-terphenyl-4- carboxylic acid (PTCA), each with 4'-nitro-substituents (2 and 5) have been synthesised and characterised as Langmuir monolayers at the air/water interface. Surface pressure and electric surface potential

Full text of DOI:10.3184/030823409X417289

JOURNAL OF CHEMICAL RESEARCH 2009
APRILꢁꢀꢇꢇꢈ±228
RESEARCH PAPER 225
Synthesis and Langmuir monolayer characterisation of some nitro
derivatives of polyphenyl carboxylic acids
Patrycja Dynarowicz-Łątka and Piotr Milart*
Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland
Derivatives of 5'-phenyl-1,1':3',1"-terphenyl-4-carboxylic acid (PTCA), each with 4'-nitro-substituents (2 and 5) have
been synthesised and characterised as Langmuir monolayers at the air/water interface. Surface pressure and electric
surface potential measurements of the monolayers under a variety of experimental conditions have been made.
The presence of the nitro-substituent (in 2 cf 2') was found to change the sign of the measured surface potential,
indicating that the nitro-derivative is oriented with the –NO2 group towards the air side, while the carboxylic group
is anchored into the water subphase. Upon introducing two more side phenyl groups into the hydrophobic core of
the nitro derivative 2 to give 5, the measured surface potential (and the resulting apparent dipole moment) change
sign to positive, indicating the prevalence of the dipolar contribution from the hydrophobic moiety over that of the
hydrophilic part of the molecule. Our results show that the contribution of the double layer potential arising from
ionisation of the carboxylic group of the investigated molecules is ~0.1~ꢀV.
Keywords: /DQJPXLUꢀPRQROD\HUVꢁꢀVXUIDFHꢀSUHVVXUHꢁꢀVXUIDFHꢀSRWHQWLDOꢁꢀSRO\SKHQ\OꢀFDUER[\OLFꢀDFLGVꢁꢀDLU±ZDWHUꢀLQWHUIDFH
COOH
Investigations on Langmuir monolayers have mostly been carried
out with amphiphilic molecules containing a polar head group and
a non-polar part composed usually of an alkyl (polymethylene)
chain. Our former studies on the surface behaviour of carboxylic
acids with only benzenoid aromatic hydrophobic moieties,
Y
Y
consisting of non-rigid polyphenyl ring systems, have
proved that purely aromatic amphiphiles, containing no alkyl
chains, are capable of forming stable monolayers at the air-
water interface on their own.1-3 The basic compound for our
investigations, i.e. 5'-phenyl-1,1':3',1"-terphenyl-4-carboxylic
acid, abbreviated as PTCA (Scheme 1), displays on the surface
SUHVVXUHꢂDUHDꢀꢃʌꢄ$ꢅꢀLVRWKHUPVꢀDꢀFKDUDFWHULVWLFꢀSODWHDXꢀWUDQVLWLRQꢀ
that spans the area corresponding to a ratio of ca 2 between
the areas at the start and at the end of the plateau (Fig. 1).1,2
Thorough analysis of electric surface potential measurements
(that enabled effective dipole moment calculation) together
with surface pressure isotherms, complemented with Brewster
angle microscope images, allowed us to conclude that the
inclination of molecules followed by multilayer formation
was the probable cause for the plateau in the isotherm.2 Since
PRQROD\HUꢀFKDUDFWHULVWLFVꢀDUHꢀNQRZQꢀWRꢀEHꢀVWURQJO\ꢀLQÀXHQFHGꢀ
by the structure of molecules, we have also performed studies
RQꢀ WKHꢀ LQÀXHQFHꢀ RIꢀ HLWKHUꢀ Dꢀ K\GURSKRELFꢀ RUꢀ Dꢀ K\GURSKLOLFꢀ
substituent at the 4'-position3-6 as well as on both side rings,7 on
WKHꢀ¿OPꢂIRUPLQJꢀSURSHUWLHVꢀRIꢀDꢀQXPEHUꢀRIꢀ37&$ꢀGHULYDWLYHVꢆ
Z
X
X
PTCA X = H,
2
2'
5
Y = H,
Z = H
Z = NO2
Z = H
X = CH3, Y = H,
X = CH3, Y = H,
X = H,
Y = C6H5, Z = NO2
Scheme 1 Molecular structure of investigated carboxylic acids.
Our results showed that PTCA and its derivatives form stable
Langmuir monolayers, transferable onto solid supports. This
property, together with the fact that the hydrophobic moiety
contains uncondensed polyphenyl ring systems, offers
the potential applications in preparation of well-ordered
conducting layers due to S conjugation. Moreover, since the
K\GURSKRELFꢀ SDUWꢀ LVꢀ EXON\ꢁꢀ VXFKꢀ PROHFXOHVꢀ ±ꢀ DIWHUꢀ IXUWKHUꢀ
IXQFWLRQDOLVDWLRQꢀ ±ꢀ PD\ꢀ EHꢀ XVHGꢀ WRꢀ SUHSDUHꢀ ORZꢂGHQVLW\ꢀ
surfaces, which are advantageous in attaching large molecules.
In this way, both aggregation and undesired steric restrictions
can be avoided.
50
In view of such interesting properties of these compounds
we think it is worth continuing our investigation with other
PTCA derivatives. Herein we present the synthesis and
Langmuir monolayer characteristics of derivatives with 4'-
nitro substituents (Scheme 1, compounds 2 and 5). The results
are compared with those obtained for the derivative without
the nitro group (compound 2').
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0,6
0,5
0,4
0,3
0,2
0,1
0,0
40
30
20
10
0
DV
The preparation of carboxylic acid 2 was accomplished
with a one step procedure from the pyrylium salt 1 reported
in our previous paper (Scheme 2).7 Another approach was
employed for synthesis of carboxylic acid 5. The reaction of
4-carboxybenzaldehyde with an excess of deoxybenzoin gave
the corresponding pentane-1,5-dione 3, which was converted
into the pyrylium bromide 4 according to the procedure
developed by Katritzky et al.8,9 The bulky pyrylium salt
reacted smoothly with nitromethane giving the expected acid
5 (Scheme 3), which is surprisingly soluble in a variety of
organic solvents.
p
0
20
40
o
60
80
100
Area /A2 molecule-1
Fig. 1 Surface pressure/area (S/A) isotherms for PTCA spread
on HCl aqueous solution (pH 3), data reproduced from ref. 2.
6XUIDFHꢀSUHVVXUH±DUHDꢀLVRWKHUPVꢀIRUꢀFRPSRXQGꢀ2 at 20°C
spread on water and on a 10-3 M HCl aq. subphase are
* Correspondent. E-mail: milart@chemia.uj.edu.pl

226 JOURNAL OF CHEMICAL RESEARCH 2009
COOH
COOH
shown in Fig. 2, together with the isotherms for 4''-methyl-
5'-(4-methylphenyl)-1,1':3',1''-terphenyl-4-carboxylic acid
(compound 2', Scheme 1), which have been reproduced
from our previous paper7 for the purpose of comparison.
As has been discussed earlier,7ꢀWKHꢀʌꢄ$ꢀLVRWKHUPꢀIRUꢀFRPSRXQGꢀ
2' does not possess such a clear plateau region, separated
by two condensed regions, as it is observed for the basic,
unsubstituted compound (PTCA) (Fig. 1).1,2 The presence
of two methyl groups on both side phenyl rings of PTCA
PRGL¿HVꢀWKHꢀLVRWKHUPꢀFKDUDFWHULVWLFꢁꢀi.e. after a sharp pressure
increase at a 43 Å2 molecule-1, the surface pressure gradually
increases upon compression, without a clear monolayer
collapse. However, the introduction of an additional polar
substituent (nitro group) at the 4' position (compound 2)
restores the typical isotherm course for PTCA. For compound
2ꢁꢀ QRꢀ VLJQL¿FDQWꢀ GLIIHUHQFHꢀ LQꢀ WKHꢀ VXUIDFHꢀ SUHVVXUHꢀ OLIWꢂRIIꢀ
and plateau surface pressure value is observed upon adding
HCl into the water subphase. To get further insight into the
monolayer behaviour, detailed surface pressure and electric
surface potential measurements have been performed under
Dꢀ YDULHW\ꢀ RIꢀ H[SHULPHQWDOꢀ FRQGLWLRQVꢀ ꢃ)LJꢆꢀ ꢉD±Fꢅꢆꢀ )LUVWO\ꢁꢀ
when different numbers of molecules was deposited onto the
subphase, no change in the onset area for the surface pressure
and the plateau surface pressure was observed, as illustrated
in Fig. 3a. However, the speed of compression was found
to affect the plateau pressure, i.e. the pressure for plateau
decreased with lowering the compression rate (Fig. 3b).
7KHꢀ VXESKDVHꢀ WHPSHUDWXUHꢀ DOVRꢀ KDVꢀ Dꢀ SURQRXQFHGꢀ LQÀXHQFHꢀ
on the plateau surface pressure, i.e. with the increase in
temperature, the plateau pressure decreased (Fig. 3c), similarly
to PTCA and its derivatives.1-7
1) CH3NO2, (C2H5)3N
2) CH3COOH, H2O
O
ClO4
NO2
H3C
CH3
H3C
CH3
1
2
Scheme 2 Synthesis of carboxylic acid 2.
COOH
O
1) KOH, 50% ethanol
2) HCl, H2O
+
O O
HOOC
CHO
3
Br2,
CH3COOH
COOH
COOH
1) CH3NO2, (C2H5)3N
2) HCl, H2O
O
NO2
Br
4
5
Changes in electric surface potential can be observed at
large areas per molecule, with the lift-off (so-called critical
area) occurring when the surface pressure is still zero (Fig. 4).
The surface potential, 'V, of the monolayer of the nitro-
derivative (2) decreased upon compression and attained a
PLQLPXPꢀYDOXHꢀRIꢀ±ꢊꢆꢋꢌꢋꢀ9ꢀRQꢀWKHꢀZDWHUꢀVXESKDVHꢁꢀDQGꢀ±ꢊꢆꢉꢍꢎꢀ
V on 10-3 M HCl. For comparison, the surface potential for
the derivative without the nitro substituent (2'), from previous
work,7 has also been included in the graph. The negative sign
of '9ꢀIRUꢀWKHꢀQLWURꢂGHULYDWLYHꢀPHDQVꢀWKDWꢀWKHꢀ¿OPꢀPROHFXOHVꢀ
are oriented at the interface in such a way that the electron-
withdrawing NO2 group is exposed to the air, giving a negative
contribution to the measured surface potential.
Scheme 3 Synthesis of carboxylic acid 5.
compound 2', water
50
40
30
20
10
0
compound 2', 10-3 M HCl
compound 2, water
compound 2, 10-3 M HCl
Figure 5 presents the results of the other investigated
nitro-derivative, i.e. compound 5. In this case, the course of
the isotherm is different from the other investigated PTCA
derivatives, i.e. it is of liquid-expanded character, without
any plateau region, and collapses at about 30 mN m-1.
10
20
30
40
50
60
o
Area /A2 molecule-1
Fig. 2 Comparison of surface pressure/area (S/A) isotherms
for compounds 2 and 2' spread on water and HCl aqueous
solution (pH 3).
a
b
c
50
50
5 mm min-1
100 mL
10 o
20 o
30 o
C
C
C
50
40
30
20
10
0
25 mm min-1
100 mm min-1
150 mL
40
200 mL
40
30
20
10
0
30
20
10
0
0
20
40
60
0
20
40
60
0
20
40
60
o 2
o
Area /Å2 molecule-1
-1
Area /A2 molecule-1
Area /A molecule
Fig. 3 The influence of spreading volume (a), compression speed (b), subphase temperature (c) on the pressure/area isotherm
for compound 2 spread on water.

JOURNAL OF CHEMICAL RESEARCH 2009 227
water
compound 2', water
10-3 HCl
compound 2', 10-3 M HCl
compound 2, water
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
-0,1
-0,2
-0,3
-0,4
-0,5
0,3
0,2
0,1
0,0
compound 2, 10-3 M HCl
20
40
60
80
100
120
140
20
40
60
80
100
o
Area /A2 molecule-1
o
Area /A2 molecule-1
Fig. 4 Comparison of electric surface potential/area ('/V/A)
isotherms for compounds 2 and 2' spread on water and HCl
aqueous solution (pH 3).
Fig.
7 Electric surface potential/area ('V/A) isotherms for
compound 5 spread on water and HCl aqueous solution (pH 3).
of 0.218 V and 0.318 V are attained on water and 10-3 M HCl
aq, respectively. However, both investigated compounds
have a pronounced difference in the measured surface
potential on water and the acidic subphase, equal to ca |0.1| V.
7KLVꢀ GLIIHUHQFHꢀ LVꢀ GXHꢀ WRꢀ WKHꢀ GRXEOHꢀ OD\HUꢀ SRWHQWLDOꢀ ꢃȥo)
occurring for the ionised monolayer on water, consisting
RIꢀ QHJDWLYHO\ꢀ FKDUJHGꢀ FDUER[\ODWHꢀ DQLRQVꢆꢀ 7KHꢀ YDOXHꢀ RIꢀ ȥo
obtained herein is in a good agreement with the double layer
potential value for monolayers of fatty acids.10
The electric surface potential measurements of Langmuir
monolayers can be interpreted with theoretical models being
able quantitatively to relate measured potentials to molecular
dipole moments (see ref. 11). Such models treat the monolayer
DVꢀDꢀRQHꢂꢁꢀWZRꢂꢀRUꢀWKUHHꢂOD\HUꢀFDSDFLWRUꢆꢀ+LVWRULFDOO\ꢁꢀWKHꢀ¿UVWꢀ
one is the one-layer parallel plate condenser model (Helmholtz
model), which is still frequently applied to the interpretation
of surface potential data. In this model, the surface potential
of a Langmuir monolayer is written as:
The shape of the isotherm is found to be strongly dependent
upon the rate of compression (Fig. 6a) and temperature
ꢃ)LJꢆꢀ ꢏEꢅꢆꢀ +RZHYHUꢁꢀ QRꢀ VLJQL¿FDQWꢀ FKDQJHꢀ ZDVꢀ QRWLFHGꢀ RQꢀ
depositing different numbers of molecules, either on water or
on the acidic subphase.
The shift towards smaller molecular areas on water as
compared to the acidic solution suggests that a loss of
molecules from the surface occurs, resulting from the
enhanced solubility of the compound 5 in water. Surface
potential isotherms are presented in Fig. 7.
Contrary to compound 2 discussed above, having the
negative values of 'V, the compound 5 exhibits positive
surface potential along the compression. The maximum values
water
50
40
30
20
10
0
10-3 M HCl
ꢀ
'V = PA/(AHH0)
(1)
where A is the area per molecule, Hꢀis the dielectric constant
of the monolayer, H0 is the vacuum permittivity and PAꢀis the
so-called effective dipole moment. This equation applies to
QRQꢂLRQLVHGꢀPRQROD\HUVꢆꢀ)RUꢀLRQLVHGꢀ¿OPVꢁꢀWKHꢀGRXEOHꢂOD\HUꢀ
contribution,12ꢀ ȥo, must be taken into consideration. Since
the dielectric constant of the monolayer is unknown, one may
calculate the apparent dipole moment P$ ꢀPAꢁH from the 'V±
A isotherm. The apparent dipole moment values calculated
in this way for the investigated non-ionised monolayers
(spread on the aqueous HCl subphase) at molecular areas
corresponding to maximum _'V_ values (P$max) are compiled
in Table 1.
From the results obtained it is clear that the presence of NO2
JURXSꢀ KDVꢀ Dꢀ VLJQL¿FDQWꢀ LQÀXHQFHꢀ RQꢀ WKHꢀ REVHUYHGꢀ P$ value,
i.e. its value changes from 0.688 D (for compound 2'ꢅꢀWRꢀ±
0.394 D (for compound 2). Very similar effects were obtained
previously for PTCA (0.53 D) and its 4'-nitroderivative (-0.37
D).13 A different effect is observed for compound 5, i.e. values
of experimental surface potentials are positive although this
10
20
30
40
50
60
o
Area /A2 molecule-1
Fig. 5 Surface pressure/area (S/A) isotherms for compound 5
spread on water and HCl aqueous solution (pH 3).
5 mm min-1
10 o
20 o
30 o
C
C
C
25 mm min-1
100 mm min-1
60
50
40
30
20
10
0
50
40
30
20
10
0
A
B
Table 1
Compound
'Vmax/V
Area for 'Vmax
/
Apparent dipole
Å2/molecule-1
moment, P$/Da
0
10 20 30 40 50 60
Area /A2 molecule-1
0
10 20 30 40 50 60
Area /A2 molecule-1
o
o
2
2’
5
–0.3715
0.6477
0.3180
40
40
25
–0.394
0.688
0.211
Fig. 6 The influence of compression speed (a) and subphase
temperature (b) on the surface pressure/area isotherm for
compound 5 spread on water.
aData calculated for non-ionised monolayers spread on acidic
subphase.

228 JOURNAL OF CHEMICAL RESEARCH 2009
(100 mL) with an excess of hydrochloric acid (1:1) (5 mL).
The colourless carboxylic acid was separated by suction. It was
SXUL¿HGꢀ E\ꢀ UHÀX[LQJꢀ LQꢀ DFHWLFꢀ DFLGꢀ ꢃꢎꢊꢊꢀ P/ꢅꢆꢀ7KHꢀ VHSDUDWHGꢀ VROLGꢀ
was washed with acetone and diethyl ether. This compound is almost
insoluble in common organic solvents except for DMSO. It exhibits
DꢀWHQGHQF\ꢀWRꢀIRUPꢀDꢀK\GUDWHꢀRIꢀXQGH¿QHGꢀZDWHUꢀFRQWHQWꢀꢃ1H NMR
signal at 8.04 ppm). An anhydrous sample was obtained by vacuum-
drying (1 mm Hg, 250°C). Yield: 6.90 g (66.0%). M.p. 285–286°C.
IR (KBr) Q = 3437 (–COOH); 3067, 3029, 2672, 2546 (OH +
CH); 1680 (C=O); 1611, 1599 (aromatic rings); 1260 (C–O) cm-1.
1H NMR (DMSO-d6): G[ppm] = 12.60 (s, broad, 1H, –COOH); 7.81
(d, 2H, J = 7.9 Hz); 7.66 (d, 2H, J = 7.9 Hz); 7.52 (d, 2H, J = 7.3 Hz);
7.48–7.44 (m, 6H); 7.36 (t, 2H, J = 7.5 Hz); 7.31 (t, 2H, J = 7.4 Hz);
7.12 (d, 2H, J = 7.8 Hz); 6.96 (t, 2H, J = 7.5 Hz); 6.90 (t, 2H, J = 7.3 Hz);
6.85 (d, 2H, J = 7.3 Hz); 5.66 (d, 1H, J = 10.8 Hz, H at C2 or C4);
5.56 (d, 1H, J = 9.7 Hz, H at C2 or C4); 4.91 (t, 1H, J = 9.9 Hz, H
at C3). The very complicated chemical shifts pattern suggests that
the sterically congested 1,5-diketone exists as a twisted conformer.
Anal. Calcd for C36H28O4 (524.64): C 82.41, H 5.39. Found C 82.39,
H 5.41%.
4-(4-Carboxyphenyl)-2,3,5,6-tetraphenylpyrylium bromide (4):
Bromine (1.6 g, 0.01 mol) dissolved in acetic acid (15 mL) was added
dropwise with stirring to the suspension of 1,5-diketone 3 (5.23 g,
0.01 mol) in acetic acid (50mL) at 110°C. Heating and stirring
were maintained for 8 h. The formation of the yellow precipitate
was observed. The mixture was cooled to room temperature and
the solid was separated, washed with acetic acid and diethyl ether.
7KHꢀFUXGHꢀSURGXFWꢀZDVꢀUHÀX[HGꢀWZLFHꢀLQꢀDFHWLFꢀDFLGꢀꢃꢎꢊꢊꢀP/ꢅꢀIRUꢀ
30 min., separated and dried in air. Due to the extremely low solubility
of the pyrylium salt we were unable to obtain an analytically pure
sample. Nevertheless, the yellow product of technical grade purity
is suitable for further synthesis. Yield: 5.21 g (ca 90%). M.p. 340–
345°C (with decomposition).
4'-Nitro-3',5',6'-triphenyl-1,1':2',1''-terphenyl-4-carboxylic acid
(5): The pyrylium salt 4 (1.17 g, ca. 0.002 mol) and triethylamine
ꢃꢊꢆꢈꢀJꢁꢀꢊꢆꢊꢊꢈꢀPROꢅꢀZHUHꢀUHÀX[HGꢀDQGꢀVWLUUHGꢀLQꢀQLWURPHWKDQHꢀꢃꢎꢊP/ꢅꢀ
for 1 h. The yellowish solution was cooled to room temperature.
On cooling the colourless triethylammonium salt of the prepared acid
precipitated. It was separated and washed with diethyl ether. The salt
was converted into the free acid by addition of hydrochloric acid
(0.5 mL) to its suspension in hot water. An air-dried crude product was
SXUL¿HGꢀE\ꢀUHFU\VWDOOLVDWLRQꢀIURPꢀQLWURPHWKDQHꢀDQGꢀZDVꢀGULHGꢀXGHUꢀ
reduced pressure (1 mm Hg, 150°C). Yield: 0.48 g (ca 46%). M.p.
405–406°C. IR (KBr) Q = 3437 (–COOH); 3061, 3029, 2898, 2672,
2548 (OH + CH); 1693 (C=O); 1605 (aromatic rings); 1533 (–NO2)
cm-1. 1H NMR (DMSO-d6): G[ppm] = 12.75 (s, broad, 1H, –COOH);
7.43 and 7.04 (2d, 4H, AA'BB', JAB = 8.4 Hz, aromatic H of the ring
with –COOH group); 7.19–7.16 (m, 10H, aromatic rings); 6.97–6.86
(m, 20H, aromatic rings); Anal. Calcd for C37H25NO4 (547.63): C
81.14, H 4.61, N 2.56. Found: C 81.07, H 4.68, N 2.44%.
molecule possesses the same polar groups (COOH and NO2)
as compound 2, and moreover, their positions with respect to
the central benzene ring are the same in both cases. Since the
DUHDꢀDYDLODEOHꢀIRUꢀRQHꢀPROHFXOHꢀLQꢀWKHꢀ¿OPꢀLVꢀVLPLODUꢀIRUꢀERWKꢀ
compounds (2 and 5), the same orientation of both molecules
at the air/water interface, i.e. with COOH groups anchored
into water and NO2 group exposed to the air, can be assumed.
Thus, the observed differences in the total value of apparent
dipole moment can be ascribed to a different contribution
of the hydrophobic part, which prevails for compound 5
as compared to compound 2, over the oppositely directed
contribution from the polar groups. Thus, due to a bigger,
positive contribution from the apolar part to the total apparent
dipole moment for compound 5 compared with compound 2,
the resultant apparent dipole moment is positive for compound
5 and negative for compound 2.
Experimental
Melting points were determined with a Mel-Temp II apparatus in
open capillaries and are uncorrected. Elemental analyses were carried
out with a EuroVector EA 3000 analyser. IR spectra were recorded on
1
a Bruker Equinox 55 spectrometer on KBr pellets. H NMR spectra
were taken at 500.13 MHz with a Bruker AMX 500 spectrometer in
DMSO-d6 or CDCl3 with TMS as internal standard.
Spreading solutions were prepared by dissolving the compounds
in spectroscopic grade chloroform. Typical concentrations of the
spreading solutions were ca 0.4–0.5 mg mL-1. Ultrapure water
SURGXFHGꢀE\ꢀDꢀ1DQRSXUHꢀꢃ,Q¿QLW\ꢅꢀZDWHUꢀSXUL¿FDWLRQꢀV\VWHPꢀFRXSOHGꢀ
WRꢀ Dꢀ 0LOOLꢂ4ꢀ ZDWHUꢀ SXUL¿FDWLRQꢀ V\VWHPꢀ ZDVꢀ XVHGꢀ DVꢀ VXESKDVHꢆꢀ7KHꢀ
subphase temperature was controlled thermostatically to within
0.1°C by a circulating water system from Neslab. Monolayer
studies were carried out with a KSV-5000 LB trough (total area =
730.5 cm2) placed on an anti-vibration table in a class 10000 clean
room. After spreading, the monolayers were left for 5 min for the
solvent to evaporate prior to compression. The surface pressure of
WKHꢀÀRDWLQJꢀPRQROD\HUꢀZDVꢀPHDVXUHGꢀWRꢀZLWKLQꢀꢊꢆꢎꢀP1ꢀP-1 using a
Wilhelmy plate (made of chromatography paper, ashless Whatman
Chr 1) connected to an electrobalance. Simultaneously, the surface
potential was recorded using a vibrating plate located ca 2 mm
above the water surface. The reference electrode, made from
platinum foil, was placed in the water subphase. The surface potential
measurements were reproducible to
10 mV. Monolayers were
usually compressed with a barrier speed of 25 mm min-1 (equivalent
to a compression rate of 7.5 u 1017 Å2 min-1) unless otherwise
VSHFL¿HGꢆ
Caution: Pyrylium salts are harmful by inhalation, in contact with
skin (can act as photosensitisers) and if swallowed. Heating of dry
perchlorates may cause an explosion.
Received 22 October 2008; accepted 1 February 2009
Paper 08/0254 doi: 10.3184/030823409X417289
Published online: 29 April 2009
4''-Methyl-5'-(4-methylphenyl)-4'-nitro-1,1':3',1''-terphenyl-4-carboxylic
acid (2): Pyrylium salt 17 (1.43 g, 0.003 mol) and triethylamine
ꢃꢊꢆꢍꢀ Jꢁꢀ ꢊꢆꢊꢊꢍꢇꢀ PROꢅꢀ ZHUHꢀ UHÀX[HGꢀ LQꢀ QLWURPHWKDQHꢀ ꢃꢎꢊꢀ P/ꢅꢀ ZLWKꢀ
constant stirring for 1 h. The dark blue solution was cooled to room
temperature and 50% aqueous acetic acid (10 mL) was added.
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an addition of charcoal. It was then dried under reduced pressure
at 80°C. The colourless pure product forms a glassy phase above
142°C and melts at ca 170°C, Yield: 0.31 g (24.6%). IR (KBr)
Q = 3429 (–COOH); 3031, 2874, 2665, 2540 (OH + CH); 1693 (C=O);
References
1
J. Czapkiewicz, P. Dynarowicz and P. Milart, Langmuir, 1996, 12, 4966.
ꢀ ꢇꢀ 3ꢆꢀ'\QDURZLF]ꢂàąWNDꢁꢀ$ꢆꢀ'KDQDEDODQꢀDQGꢀ2ꢆ1ꢆꢀ2OLYHLUDꢀ-UꢁꢀJ. Phys. Chem.
B, 1999, 103, 5992.
ꢀ ꢉꢀ 3ꢆꢀ '\QDURZLF]ꢂàąWNDꢁꢀ$ꢆꢀ 'KDQDEDODQꢀ DQGꢀ 2ꢆ1ꢆꢀ 2OLYHLUDꢀ -Uꢁꢀ Langmuir,
2000, 16, 4245.
ꢀ ꢋꢀ 3ꢆꢀ '\QDURZLF]ꢂàąWNDꢁꢀ$ꢆꢀ 'KDQDEDODQꢁꢀ$ꢆꢀ &DYDOOLꢀ DQGꢀ 2ꢆ1ꢆꢀ 2OLYHLUDꢀ -Uꢁꢀ
J. Phys. Chem. B, 2000, 104, 1701.
1
1609, 1585 (aromatic rings); 1534 (–NO2) cm-1. H NMR (CDCl3):
ꢀ ꢈꢀ 3ꢆꢀ '\QDURZLF]ꢂàąWND, K. Kita, P. Milart, A. Dhanabalan, A. Cavalli,
D.A. Silva Filho and O.N. Oliveira Jr, J. Colloid Interface Sci., 2001,
239, 158.
G[ppm] = 8.22 and 8.74 (2d, 4H, AA'BB', JAB = 8.3 Hz, aromatic H
of the ring with –COOH group); 7.63 (s, 2H, aromatic H 2' and 6');
7.34 and 7.25 (2d, 8H, AA'BB', JAB = 8.0 Hz, aromatic H of methyl
substituted rings); 2.40 (s, 6H, protons of methyl groups). Anal. Calcd
for C27H21NO4 (423.49): C 76.57, H 5.01, N, 3.31. Found C 76.29,
H 5.07, N 3.21%.
ꢀ ꢏꢀ -ꢆꢀ &]DSNLHZLF]ꢁꢀ 3ꢆꢀ '\QDURZLF]ꢂàąWNDꢁꢀ *ꢆꢀ -DQLFNDꢀ DQGꢀ 3ꢆꢀ 0LODUWꢁꢀ
J. Colloids Surf. A, 1998, 135, 149.
ꢀ ꢍꢀ 3ꢆꢀ'\QDURZLF]ꢂàąWNDꢁꢀ.ꢆꢀ.LWDꢁꢀ3ꢆꢀ0LODUWꢁꢀ$ꢆꢀ'KDQDEDODQꢁꢀ$ꢆꢀ&DYDOOLꢀDQGꢀ
O.N. Oliveira Jr, J. Colloid Interface Sci., 2001, 239, 145.
ꢀ ꢌꢀ $ꢆ5ꢆꢀ .DWULW]N\ꢁꢀ 8ꢆꢀ *UXQW]ꢁꢀ$ꢆ$ꢆꢀ ,NL]OHUꢁꢀ 'ꢆ+ꢆꢀ .HQQ\ꢀ DQGꢀ %ꢆ3ꢆꢀ /HGG\ꢁꢀ
J. Chem. Soc., Perkin Trans I, 1979, 436.
3-(4-Carboxyphenyl)-1,2,4,5-tetraphenylpentane-1,5-dione
(3):
Deoxybenzoin (11.7 g, 0.06 mol) and 4-carboxybenzaldehyde (3.0 g,
0.02 mol) were suspended in ethanol (80 mL). A solution of KOH (3.0
g) in water (15 mL) was added and the mixture was stirred for 2 days.
$ꢀFRORXUOHVVꢀSRWDVVLXPꢀVDOWꢀZDVꢀ¿OWHUHGꢀRIIꢀDQGꢀZDVKHGꢀZLWKꢀHWKDQROꢀ
and diethyl ether. The crude product was suspended in ethanol (150
P/ꢅꢁꢀUHÀX[HGꢀIRUꢀꢎꢀKꢁꢀWKHQꢀFRROHGꢀWRꢀca 50°&ꢀDQGꢀ¿OWHUHGꢆꢀ7KHꢀVDOWꢀ
was converted into free acid by treating its hot aqueous suspension
9
A.R. Katritzky, F. Al-Omran, R.C. Patel and S.S. Thind, J. Chem. Soc.,
Perkin Trans I, 1980, 1890.
10 O.N. Oliveira Jr, PhD Thesis, University of Wales, Bangor (U.K.), 1990.
11 P. Dynarowicz, Adv. Coll. Int. Sci., 1993, 45, 215.
12 J.T. Davies, J. Colloid Sci., 1956, 11, 377.
ꢀꢎꢉꢀ 3ꢆꢀ '\QDURZLF]ꢂàąWNDꢁꢀ $ꢆꢀ &DYDOOLꢁꢀ 'ꢆ$ꢆꢀ 6LOYDꢀ )LOKRꢁꢀ 0ꢆ&ꢆꢀ 6DQWRVꢀ DQGꢀ
O.N. Oliveira Jr, Chem. Phys. Lett., 2000, 326, 39.