Micellar catalysis in the systems arylamine-diphenylamine-NO 2-

Article abstract of DOI:10.1134/S1070363208110066

By methods of UV and IR spectroscopy and thermogravimetry reactions of diazotizaion and azo coupling were studied in the systems of primary arylamine (p-nitro-, p-carboxy- and p-sulfoaniline)- diphenylamine -nitrite ion in water and micellar media on the basis of surfactants. The micellar catalysis effect of sodium dodecylsulfate in the micellar media was revealed. Rate of diazotization was shown to be independent of the surfactants of various types. Formation of ionic associates of azo dyes with dodecylsulfate anions in premicellar region was established and physicochemical characteristics of the associates were estimated.

Full text of DOI:10.1134/S1070363208110066

ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 11, pp. 2019–2024. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © S.Yu. Doronin, R.K. Chernova, 2008, published in Zhurnal Obshchei Khimii, 2008, Vol. 78, No. 11, pp. 1783–1788.
Micellar Catalysis
in the Systems Arylamine–Diphenylamine–NO2
–
S. Yu. Doronin and R. K. Chernova
Chernyshevskii Saratov State University,
ul. Astrakhanskaya 83, Saratov, 410026 Russia
Received May 19, 2008
Abstract—By methods of UV and IR spectroscopy and thermogravimetry reactions of diazotizaion and azo
coupling were studied in the systems of primary arylamine (p-nitro-, p-carboxy- and p-sulfoaniline)–
diphenylamine –nitrite ion in water and micellar media on the basis of surfactants. The micellar catalysis effect
of sodium dodecylsulfate in the micellar media was revealed. Rate of diazotization was shown to be
independent of the surfactants of various types. Formation of ionic associates of azo dyes with dodecylsulfate
anions in premicellar region was established and physicochemical characteristics of the associates were
estimated.
DOI: 10.1134/S1070363208110066
Reactions of diazotization and azo coupling found
wide application in organic [1] and analytical [2]
chemistry. The reactions of diazotization of primary
arylamines followed by azo coupling of the formed
diazonium salts with amines and phenols have been
well enough studied and some general conditions for
these reactions were formulated [1–3]. However, effect
of surfactants of various types on the physicochemical
parameters of such reactions remains practically not
studied. It is known that in the presence of micellar
nanoreactors, the micelles of surfactants, micellar
catalysis is possible [4] that affects some physico-
chemical characteristics of the system including its
stability, degree of formation of azo dye, and others.
involving diazonium cation and azo components
bearing different charges allowed to conclude that
micellar effects are controlled by formal charges of
both reactants.
In [8] the effect of sodium dodecyldulfate micelles
on the azo coupling reactions was studied of twelve
benzenediazonium tetrafluoroborates (XC H BF ,
6
5
4
where Х = Н, p,m-NO , p,m-Cl, p,m –Br, p,m-CH ,
2
3
p,m-OCH and p-OC H ) with 1-naphthol-4-sulfonic
3
2
5
acid. In all cases a decrease was observed in the reac-
tion rate with anionic micelles by 1.41 to 11.82 times.
Sallo and Tomescu treated the reaction deceleration
from the viewpoint of Hartley’s “sign rule.”
Despite a significant contribution of Coulomb inter-
action of diazonium ions with azo components in these
reactions, no unambiguous prediction was suggested
with respect to the effect of surfactants on the stage of
the azo coupling. This situation suggests a necessity of
detailed experimental study of the influence of
surfactants on the kinetics of each azo coupling reac-
tion in dependence on the nature of reactants. Earlier
we revealed micellar catalysis effect of sodium
dodecylsulfate in the Griss reaction [9] leading to more
than 2-fold decrease in the reaction rate due to
separating effect of micellar nanoreactors on the
reactive forms of the reactants. Now we present the
results of the complex study of the effect of micelles as
well as ions of surfactants on the reactions of
Pubished data on the micellar catalysis of diazotize-
tion and azo coupling reactions are scanty and
contradictory [5–8]. In a review [5] results were
presented of the study of kinetics of several azo
coupling reactions. In the presence of micelles of
sodium dodecylsulfate and hexadecyltrimethylammo-
nium bromide a deceleration (up to 15-fold) occurred
of azo coupling reactions of 4-nitrobenzenediazonium
with 1-naphthol-6-sulfoacid and 2-naphthol-3,6-di-
sulfoacid. On the contrary, sodium dodecylsulfate
micelles accelerate azo coupling reactions of 4-
methoxybenzenediazonium with 1-naphthylamine and
1
-amino-2-methylnaphthalene (up to 1100-fold). The
data of the study on the azo coupling reactions
2019

2
020
DORONIN, CHERNOVA
diazotization and azo coupling in the systems of
primary arylamine–diphenylamine–nitrite ion.
well soluble. Besides, by varying рН it was possible to
vary electrostatic properties of the chosen arylamines
(
protonated and non-protonated –COOH and –SO H
3
–
We studied three model systems: (I) NO –p-
groups) that was significant for the consideration of the
phenomenon of micellar catalysis. The choice of
diphenylamine as an azo component was stipulated by
its pronounced hydrophobic character governing its
low solubility in water and hence good solubility in the
micelles of surfactants. Diphenylamine being a
secondary amine is not capable of diazotization, hence
some side reactions are excluded (in particular, the
autocoupling that is characteristic, e.g., of 1-naph-
thylamine [1], see the scheme).
2
–
nitroaniline–diphenylamine; (II) NO –p-aminobenzoic
acid–diphenylamine; (III) NO –sulfanilic acid–di-
phenylamine. This choice of amines for diazotization
is defined by their high reactivity and by difference in
the nature of substituents of the second type (-NO2,
2
–
2
-
COOH and -SO H) in para-position of benzene ring,
3
enhancing the electrophilicity of the diazonium cation.
The substituent nature affects also the solubility of
arylamine, p-aminobenzoic acid derivatives are poorly
soluble in water while derivatives of sulfanilic acid are
_
2
+
N+
NH + NO + 2H
N
2
R
R
H
N
H
N
_H+
+
N
N +
N
N
_
H O
R
2
R
A
H
H
N
H
H+
N
N
NH
N
N
+
+
R
R
B
C
We studied stage by stage the effect of various
types of surfactants (anionic, sodium dodecylsulfate;
cationic, cetylpyridinium chloride; non-ionic, oxy-
ethylated alkylphenol OP-10) on the diazotization of p-
nitroaniline, p-aminobenzoic and sulfanilic acids and
on the coupling of the respective diazonium salts with
diphenylamine.
Azo coupling stage. In the systems I and II at рН >
1 the azo coupling reaction does not occur, at рН = 1
azo dyes A formed (see the scheme) precipitate in 15–
20 min (Fig. 2) due to their low solubility. Therefore
photometric analysis in aqueous medium at the
–5
concentration of reagents above 2×10
M is
impossible. In system III the azo dye А is soluble in
water (pH = 1). Formation of solid phase in such
systems occurred after 24 h, or in 2–3 h when sul-
Diazotization stage. Diazonium salts formed in
solution at рН 1 (Fig. 1) are characterized by
absorption peaks with λmax 260, 265 and 270 nm for
the systems I, II and III, respectively, in agreement
with the data in [10]. The spectra character and
intensity of absorption peaks do not suffer any change
at the transfer from aqueous medium to micellar one
regardless the surfactant type. In addition, in the
micellar media formed with different type surfactants
did not change the rate of formation of diazonium salt
compared with the aqueous medium. Thus, we can
conclude that micelles formed by the surfactants of
various type do not influence the step of diazotization,
due to a sufficiently high rate of this reaction
proceeding either in the aqueous medium, or in the
presence of a surfactant micelle.
–
2
fanilic acid concentration was above 1×10 M.
The precipitates formed in the systems I–III were
isolated and identified by IR spectroscopy (Fig. 3c)
after preliminary termogravimetric investigation
(Fig. 3a). The analysis of IR spectra of the synthesized
azo compounds by an example of system I (Fig. 3c)
–
revealed the presence of characteristic bands of NO
2
–
1
group at 1515, 1333 cm , of secondary amino group
>NH at 3401 cm , and of the system of conjugated
bonds including –N=N– in the region of 1600–1400
–
1
–
1
cm . Besides, in the IR spectrum there are two bands
–
1
in the region of 3500–3300 cm characteristic of
primary amino group of the parent arylamine. The
study showed that the product of azo coupling reaction
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 11 2008

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2
MICELLAR CATALYSIS IN THE SYSTEMS ARYLAMINE–DIPHENYLAMINE–NO
2021
(
a) (b)
A
A
1
.2
.0
.8
.6
.4
.2
0
1.2
1
0
0
0
0
1.0
0.8
0.6
0.4
0.2
0
1
2
3
,4,7,10
,5,8,11
,6,9,12
1
2
3
,4,7,10
,5,8,11
,6,9,12
2
20 260 300 340
c)
380
420
2
20 240 260 280 300 320 340
λ, nm
λ, nm
(
A
1
.2
1
0
0
0
0
.0
.8
.6
.4
.2
0
1
2
3
,4,7,10
,5,8,11
,6,9,12
2
20 240 260 280 300
320 340
λ, nm
Fig. 1. Electron absorption spectra of model systems (a) I, (b) II, and (c) III. (1–3) aqueous medium, (4–6) in dodecylsulfate
–
2
–3
–4
solution, 2×10 M, (7–9) in dodecylsulfate solution, 1×10 М, (10–12) in the solution of cetylpyridineium chloride in 5×10
–4
М
–4
–4
2
solution of OP-10. Concentration of NaNO : 0 (1, 4, 7, 10); 1×10 М (2, 5, 8, 11); 5×10 М (3, 6, 9, 12). c(arylamine) 1×10 М,
pH 1, l 1 cm.
in the system I is 1-(4-diphenylamino)-4-nitroazo-
benzene, in the systems II and III were obtained related
azodyes of А type (see the scheme). Thus, the poorly
soluble azo dyes А formed in aqueous medium
decrease the concentration of the most colored
Preliminary examination showed that introducing to
the model systems the micelles of anionic type sur-
factants (sodium dodecylsulfate) leads to a change in
the azo coupling reaction rate, to stabilization of
optical density of the solutions under photometry for
several hours, and to hyperchromic and bathochromic
effects in electron absorption spectra. As seen from
(
photometrically meaningful) protonated forms B and
C (see the scheme).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 11 2008

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022
DORONIN, CHERNOVA
kinetic curves (Fig. 2), the formation of precipitate in
A
the systems I' and II' does not occur, the solutions are
homogenous, and the optical density is stable for 24 h.
0
.9
.8
.7
.6
.5
.4
.3
.2
.1
0
I'
0
0
0
0
0
0
0
0
Contrary to the effect of sodium dodecylsulfate
micelles, at the concentration of this surfactant below
III
–3
critical for the micelle formation (0.1–1)×10 M, in
the systems I'–III' occurred formation of the solid
phase as strongly colored precipitate, the associate of
azo dye protonated form C (see the scheme) with
dodecylsulfate ions. The formed precipitates were
isolated and identified by analogy with the azo dyes А
II'
I
III'
precipitate
II
precipitate
(
Figs. 3b, 3d).
0
10 20 30 40 50 60 70 80
τ, min
In the IR spectrum of ionic associate appear
–
2
–1
Fig. 2. Plots А–τ for systems I, II and III in aqueous
medium and for systems I', II' and III' in micellar medium
of sodium dodecylsulfate, 2×10 М. Concentrations of
2
arylamine and diphenylamine are 1×10 М, с(NaNO )
characteristic bands of NO group at 1515, 1333 cm
–
2
and of conjugated bonds system in the region of 1600–
–1
–1
–
3
1400 cm . Two bands in the region of 3500–3300 cm
characteristic of NH group of the parent arylamine
–
5
2
×10 М, pH 1, λmax 530 nm.
2
–1
ν, cm
4
00
Т
DTG
00
3
70
600
800
7
00
9
DTA
(c)
(d)
1
50
(
a)
1
1
300
500
TG
Т
6
10 730
DTG
340
20
900
DTA
2
1
50
1
2
800
500
(
b)
3
500
TG
Т, %
Fig. 3. Derivatgrams and IR spectra of (a, c) 1-(4-diphenylamino)-4-nitroazobenzene and (b, d) its ionic associate with
dodecylsulfate ion.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 11 2008

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MICELLAR CATALYSIS IN THE SYSTEMS ARYLAMINE–DIPHENYLAMINE–NO
2023
were not observed. Compared to the IR spectrum of
azo dye (Fig. 3d), in the IR spectrum of associate
reaction; that is understandable from the viewpoint of
the orientation theory. Total concentration of diphenyl-
amine is a sum of concentrations of protonated and
nonprotonated forms.
appear characteristic bands of CH groups at 2940–
2
–
1
2
1
915, 2870–2845 cm and of SO group at 1440–1350,
230–1150 cm . The characteristic band of secondary
–1
+
с
i
= [B] + [BH ].
(2)
–
1
amino group at 3401 cm is not observed, owing
probably to the formation of an intramolecular
hydrogen bond. Analysis of IR spectra of the syn-
thesized products suggests the formation of
dodecylsulfate ions associates with protonated quinoid
form of azo dyes C. Thus, in the model systems I, II,
and III are formed ion pairs of azo dyes with
dodecylsulfate ions. The ion pairs are poorly soluble in
water but are well solubilized by sodium
dodecylsulfate micelles that leads to the shift of the
reaction equilibrium to the side of maximal formation
of azo dyes in analytical form C providing strong
coloration of the micellar solutions in the systems I–
III.
Here с is the total concentration of diphenylamine, [B]
i
is the equilibrium concentration of nonprotonated form
+
of diphenylamine, [BH ] is the equilibrium concentra-
tion of protonated form of diphenylamine. Introducing
protonation constant we can express concentration of
protonated form of diphenylamine as:
+
[
B][H ]
.
k
a
=
(3)
+
[
BH ]
Here k is the constant of diphenylamine protonation.
a
+
[
B][H ]
+
[
BH ] =
.
(4)
k
a
Solubility of azo dye and its associate with
dodecylsulfate ion is determined qualitatively on the
example of system I. The solubility both of the dye
itself and of its ion pair with dodecylsulfate under
optimal conditions in going from aqueous medium
Hence
+
+
[B][H ]
a
k [B] + [B][H ]
,
C
i
= [B] +
=
(5)
(6)
k
a
k
a
–
6
–1
+
+
(
molar solubility 2×10 mol l ) to micellar one (molar
i
C k
a
= k [B] + [B][H ] = [B](k + [H ]),
a
a
–
4
–1
solubility 1.6×10 mol l ) increases approximately
0-fold, resulting from the solubilization with the
i a
C k
8
[
B] =
.
(7)
+
sodium dodecylsulfate micelles.
a
k + [H ]
As follows from Fig. 2, transfer from aqueous
medium to micellar one changes the rates of the
studied reactions. In the model systems I and II the
reaction rate grows, in system III falls. For quantitative
characterization of reaction rates we investigated
kinetics of these reactions and calculated respective
rate constants.
Introducing relation (7) into Eq. (1) we obtain the
equation of the reaction kinetics.
b
d[C]
i a
C k
a
=
k[A]
.
+
dt
a
k + [H ]
Insofar as the reaction rate depends on the con-
centrations of both diazonium salt and diphenylamine,
we had to study the reaction order with respect to each
reagent. The reaction orders, estimated according to
Van’t Hoff differential method [11], were found to
equal unity both with respect to diazo and azo
components. Therefore for all the studied systems the
general kinetic equation is expressed as follows:
Rate of formation of azo compounds depends on
the concentration of reacting components. The kinetics
equation is as follows:
d[C]
a
b
=
k[A] [B] .
(1)
dt
d[C]
i a
C k
Here d[C]/dt is rate of azo coupling raction, k is the
rate constant, [A] and [B] are equilibrium concentra-
tions of diazo compound and diphenylamine, respect-
tively.
=
k[A]
.
+
dt
a
k + [H ]
The reaction rate constant is:
υ
It is known that in acid media diphenylamine
k =
.
i a
C k
undergoes protonation (рK 0.9). However, only the
а
ε l[A]
+
a
k + [H ]
nonprotonated form enters into the azo coupling
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 11 2008

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DORONIN, CHERNOVA
Reaction rate constants for systems I–III in water and
sodium dodecylsulfate micelles
The chemicals used were: NaNO of “chemically
2
pure” grade, 4-nitroaniline, 4-aminobenzoic and sul-
fanilic acids were twice recrystallied from hot water;
diphenylamine of “analytically pure” grade was
recrystallized from petroleum ether; sodium dode-
cylsulfate “pure” of grade corresponding to Technical
Requirments TU 6-09-07-1816-93 and other surfa-
ctants were not additionally purified. Acetate–chloride
buffer solutions were of рН in the range 0.65–4.0.
2
–2
–1
s
k , l mol min
System
Н
2
О
Dodecylsulfate micelles
I
80±5
35±1
38±4
271±19
85±2
II
III
7.20±0.17
Here ε is the molar extinction coefficient of analytical
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2
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–
2
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~
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 11 2008