Solvent-free synthesis of 4,4-diaminotriarylmethanes-leuco malachite materials in the presence of FePO4

Article abstract of DOI:10.1134/S1070427214100176

A fast, efficient and versatile route for the synthesis of 4,4-diaminotriarylmethanes is reported using N,N-dimethyl aniline and aryl aldehydes in presence of FePO₄ under solvent-free condition at 100°C.

Full text of DOI:10.1134/S1070427214100176

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 10, pp. 1507−1510. © Pleiades Publishing, Ltd., 2014.
VARIOUS
TECHNOLOGIES
Solvent-free Synthesis of 4,4'-Diaminotriarylmethanes-Leuco
*
Malachite Materials in the Presence of FePO4
Farahnaz K. Behbahani and Elham Khademloo
Department of Chemistry, Karaj Branch, Islamic Azad University, Karaj, Iran
e-mail: Farahnazkargar@yahoo.com
Received May 15, 2014
Abstract—A fast, efficient and versatile route for the synthesis of 4,4'-diaminotriarylmethanes is reported using
N,N-dimethyl aniline and aryl aldehydes in presence of FePO4 under solvent-free condition at 100°C.
DOI: 10.1134/S1070427214100176
INTRODUCTION
which DTM derivatives were obtained in low to moderate
yields [11]. One of the most useful methods for the
synthesis of DTM is the reaction of arylaldehydes with
N,N-dimethylaniline in the presence of an acid such as
sulfuric acid, HCl, p-TSA, zeolites or montmorillonite
K-10 [12].Although different methods for the preparation
of the aforementioned compounds have been described,
most of them however, suffer from drawbacks such as the
use of corrosive acids or toxic or hazardous chemicals,
excess of solvents and harsh reaction conditions, which
will result in generation of waste streams, complicated
workup procedures, byproducts and isomeric mixtures
and consequently low yields. Therefore, there is still a
need to search for a better catalyst regarding to toxicity,
selectivity, availability and operational simplicity for
the synthesis of triarylmethanes. In addition to cases
mentioned above, FePO4 is cheap, safe and available
reagent [13] that has also been employed for the
selective oxidation of CH4 to CH3OH [14] and benzene
to phenol [15], one-pot synthesis of dihydropyrimidinones
and thiones [16], one-pot three component synthesis
of 2,4,5-trisubstituted imidazoles [17], synthesis of
1,2,4,5-tetra-arylated imidazoles [18], acetylation
of alcohols and phenols with acetic anhydride [19],
synthesis of bis(indolyl)methanes [20] and synthesis of
1,2-disubstituted benzimidazoles [21].
Dyes may be classified according to chemical structure
or by their usage or application method.According to the
chemical structure classification, triarylmethane dyes are
among the most important dyes. Triarylmethane dyes
are monomethine synthetic dyes with three terminal
aryl groups, of which at least one, but preferably
two or three, are substituted by a donor group para
to the methane carbon atom. Due to the importance
of 4,4'-diaminotriarylmethanes (DTM) compounds,
several reviews have disclosed on di- and triarylmethane
derivatives [1–5]. These compounds have a broad
range of applications in color-forming, manufacturing
of novel types of various colorless copying papers,
pressure-sensitive heat-sensitive materials, high-speed
photo duplicating copying papers, light-sensitive papers,
ultrasonic recording papers, electrothermic heat-sensitive
recording papers, inks, crayons, typewritten ribbons,
and photoimaging systems [6]. Accordingly, different
methods for the preparation of the aforementioned
compounds have been described such as those from arene
nucleophiles and triethyl orthoformate, or benzhydrol in
the presence of acid catalysts [7], from condensation of
amines and anilines using acids [8] or zeolites [9] and
also by reaction of anilines with metal catalysts such
as Pd(OAc)2 [10] or clay-mediated oxidative coupling
of disubstituted anilines using microwave radiation, in
In this communication, we wish to report a green
synthesis method for the preparation of DTMs using
arylamines and aldehyde derivatives in the presence of
FePO4 as catalyst (Scheme 1).
* The text was submitted by the authors in English.
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BEHBAHANI, KHADEMLOO
Scheme 1. Synthesis of 4,4'-diaminotriarylmethanes using FePO4 and solvent-free condition
EXPERIMENTAL
was heated in an oil bath at 100°C for 5–6 h, and the
course of the reaction was monitored using TLC on silica
gel with ethyl acetate: n-hexane (1 : 4) as eluent.
Mps were measured by using the capillary tube
method with an electro thermal 9200 apparatus. IR spectra
were recorded on Perkin Elmer FT-IR spectrometer did
scanning between 4000–400 cm–1. 1H NMR spectra were
obtained on Bruker DRX-300MHz NMR instrument in
CDC13. Analytical TLC of all reactions was performed on
Merck precoated plates (silica gel 60F-254 on aluminium).
All compounds are known and spectra and physical data
were compared with those of authentic samples [22–25].
After completion of the reaction, hot ethanol (10 mL)
was added to the reaction mixture, the catalyst was
immediately filtered off, and mother liquor was cooled
to obtain crystals. The desired product was separated
by filtration. For more purification the product was
recrystallized from ethanol.
Recycling of the catalyst. The catalyst separated from
the reaction mixture was washed with hot ethanol and air
dried for the catalyst recovery study. Some reactions were
carried out by recovered catalyst without observation of
appreciable loss in catalyst activity.
Synthesis of 4,4'-diaminotriarylmethane using
iron(III) phosphate procedure: A vial equipped with
a stir bar was charged with aryl aldehyde (0.5 mmol),
N,N-dimethyl aniline (1.5 mmol) and FePO4 (0.05 mmol,
10 mol %) and the vial was capped. The resulting mixture
RESULTS AND DISCUSSION
Our initial attempts to test the feasibility of the reaction
employed benzaldehyde and N,N-dimethyl aniline under
various reaction conditions. To optimize the reaction
conditions, the influence of reaction time, temperature,
solvent and the amount of catalyst was investigated.
Table 1. Optimizing of the catalytic amount of FePO4 for the
synthesis of 4-{[(4-(dimethylamino)phenyl](phenyl)methyl}-N,N-
dimethylbenzenamine
Entry
FePO4, mol %
Time, h
Yield, %
To establish the optimum amount of the catalyst for
this reaction, various ratios of FePO4 were examined
using benzaldehyde (0.5 mmol), N,N-dimethyl aniline
(1.5 mmol) at 100°C as a model reaction (Table 1).
Observed that 20% of the desired products were obtained
in the absence of catalyst over 24 h. As shown in Table 1,
the best results were obtained with 10 mol % of FePO4.
Thus the catalyst is essential component for the synthesis
of 4,4'-diamino)triarylmethanes.
1
2
3
4
5
15
10
5
4
''
82
82
75
70
20
''
2
''
free
24
a
Reaction Condition: Benzaldehyde (0.5 mmol), N,N-dimethyl aniline
(1.5 mmol) at 100 °C.
Table 2. Use of the varying solvents for the synthesis of
4-{[4-(dimethylamino)phenyl](phenyl)methyl}-N,N-dimethyl-
benzenamine
The reaction of N,N-dimethyl aniline with benz-
aldehyde in the presence of FePO4 was carried out in
various solvents such as water, ethanol and under solvent-
free condition. Found solvent-free is the most effective
condition (entry 2, Table 2).
Entry
Solvent
free
Temperature, °C
Yield%a
1
2
3
4
25
–
82
–
The results revealed that a wide variety of substituents
were tolerated on the arene, in different positions. The
aryl aldehydes with electron-withdrawing groups such
as halo-substituents at the para- and nitro-substituents
at the ortho-, meta-, and para positions gave excellent
yields. However with electron-donating groups such as
free
100
H2O
reflux
reflux
EtOH
65
a
Reaction condition: Benzaldehyde (0.5 mmol), N,N-dimethyl aniline
(1.5 mmol) and FePO4 (10 mol%) at 100°C.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 10 2014

SOLVENT-FREE SYNTHESIS
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Table 3. Catalytic preparation of 4-((4-(dimethylamino)phenyl)(phenyl)methyl)-N,N-dimethylbenzenamine in presence of FePO4
mp, °C
Time,
h
Yield,
%
Entry
Ar
Product
found
89–91
reported [ref.]
91–92 [22]
97–98 [22]
88–89 [22]
146–148 [22]
167–68 [23]
Oil [24]
1
2
3
4
5
6
7
8
C6H5
3a
3b
3c
3d
3e
3f
4
5
3
2
5
5
3
2
82
75
92
86
70
68
90
94
4-Me-C6H4
95–97
4-Cl-C6H4
88–90
3-NO2-C6H4
4-N(Me)2-C6H4
3,4-(OMe)2-C6H4
2-NO2-C6H4
4-NO2-C6H4
145–147
166–167
Oil
3g
3h
152–154
170–172
153–154 [22]
170–171 [25]
methyl were obtained lower yields of the desired products
in longer reaction times than those of with electron-
withdrawing groups. These substituents decrease the
electrophilicity of carbonyl group in the corresponding
electrophilic aromatic substitution reactions (Scheme 1).
dimethyl aniline attack to I to give II. After proton
rearrangement to result III, the other N,N-dimethyl
aniline is added to IV-FePO4-activated complex. Loss
of FePO4–OH– to afford V, and deprotonation of V to
give the product VI (Scheme 2).
Areasonable pathway for the synthesis of 4,4'-diamino-
triarylmethanes in the presence of FePO4 is presented in
Scheme 2.
CONCLUSIONS
We have developed a simple, efficient and green
methodology for the synthesis of diaminotriarylmethane
leuco base materials using a catalytic amount of FePO4.
This reaction probably proceeds through the activation
of a carbonyl group by coordination FePO4 as a Lewis
acid to give intermediate I and is followed by N,N-
Scheme 2. Proposed mechanism for the synthesis of 4,4'-diaminotriarylmethanes catalyzed by FePO4
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 10 2014

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BEHBAHANI, KHADEMLOO
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The simple experimental procedure and good yields are
the advantages of the present method.
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