Solid fly-ash:h2so4 catalyzed microwave assisted solvent-free condensation:synthesis of some trifluoromethyl-imines

Article abstract of DOI:10.4067/S0717-97072013000400071

Good yield of trifluoromethyl-imines have been synthesized by Fly-ash:H2SO4 catalyzed condensation of anilines and phenyl trifluoromethyl ketone in microwave irradiation under solvent free conditions.

Full text of DOI:10.4067/S0717-97072013000400071

J. Chil. Chem. Soc., 58, Nº 4 (2013)
SOLID FLY-ASH:H2SO4 CATALYZED MICROWAVE ASSISTED SOLVENT-FREE CONDENSATION:SYNTHESIS
OF SOME TRIFLUOROMETHYL-IMINES
G. THIRUNARAYANAN*, 1, P. MAYAVEL1, K. THIRUMURTHY1, G. VANANGAMUDI2 K. G. SEKAR3 AND
K. LAKSHMANAN3
1Department of Chemistry, Annamalai University, Annamalainagar-608 002, India.
2PG and Research Department of Chemistry, Government Arts College, C-Mutlur, Chidambaram-608102, India
3Department of Chemistry, National College, Tiruchirappalli-620 001, India.
(Received: March 22, 2013 - Accepted: May 20, 2013)
ABSTRACT
Good yield of trifluoromethyl-imines have been synthesized by Fly-ash:H2SO4 catalyzed condensation of anilines and phenyl trifluoromethyl ketone in mi-
crowave irradiation under solvent free conditions.
Keywords: Fly-ash:H2SO4, Greener synthesis, Trifluoromethylimines, Anilines.
bottle and capped. The purities of this catalyst were confirmed by SEM analy-
sis and infrared spectroscopic data.
INTRODUCTION
General procedure for synthesis of phenyltrifluoromethylimines
An appropriate equi-molar quantities of aryl amines (2 mmol), phenyl
trifloromethyl ketone (2 mmol) and fly-ash: H2SO (0.5 g) were taken in Bo-
rosil glass tube and tightly capped. The mixture w4as subjected to microwave
irradiation for 6-8 minutes in a microwave oven (Scheme 1) (LG Grill, Inte-
llowave, Microwave Oven, 160-800W) and then cooled to room temperature.
The organic layer was separated with dichloromethane and the solid product
was obtained on evaporation of solvent. The solid, on recrystallization with
benzene-hexane mixture gave glittering solid. The insoluble catalyst was re-
cycled by washing the solid reagent remained on the filter by ethyl acetate (8
mL) followed by drying in an oven at 100°C for 1h and it was reused for further
reactions. The purities of synthesized imines were checked by their physical
constants and spectral data published earlier in literature. The reactants, reac-
tion time, percentage of yield, analytical, physical constants and mass frag-
ments of imines have been presented in Table 1. The spectral data of unknown
compounds are summarized in Table 2.
Chiral imine derivatives possess multipronged biological activities such
as antimicrobial1, anticancer2, antiplasmodic-antihypoxic3, antitubularcular4,
nematicidal, insecticidal1e5, anti-inflammatory, and lipoxygenase6. The imine
moieties are important intermediate and versatile starting materials for synthe-
sis of chiral amines7-13pyrimidine derivatives, phenylhydrazones, azomethines,
indoles, quinoxalines, imidazoles, by hydrogenation14, nucleophilic addition
with organometallics15and cycloaddition reaction16. The unique condensation
of carbonyl compounds with amines is a well-known reaction. Many reagents17
were used for synthesis of optically active imines such as Lewis acids, mo-
lecular sieves in ionic liquids, infrared18-25 and ultrasound radiation26. These
catalysts were applied for synthesis of chiral amines by oxidative coupling
of amines27 with carbonyl compounds5,28,29, alcohols30 and acid chlorides31,32
.
The use of microwave heating in synthetic methods has become popular for
academic and pharmaceutical areas, due to this is a new enabling technology
for new for growing of drug discovery research and developments33. Chemists
and scientists21, 34, 35, 21 preferred solvent free microwave synthetic method for
synthesis of organics, due to shorter reaction time, operational simplicity, easy
workup procedure, less hazards to environment, and better yields. There is
no report on synthesis of imines with fly-ash:H2SO4 catalyst under microwave
heating in literature in the past. Therefore the authors have taken efforts to
synthesize some phenyl trifluoromethylimines from phenyl trifluoromethyl
ketones and substituted anilines in the presence of Fly-ash:H2SO4 catalyst in
microwave irradiation under solvent-free conditions. When compared to the
commercially available catalyst mere Fly-ash, and laboratory made catalyst
such as anhydrous sodium acetate the use of Fly-ash: H2SO4 catalyst in the pre-
sent investigation gave more yield of imines up to 30 to 40%. The motivation
and interest to select the catalyst for the present investigation is attributed to the
less toxicity, lesser hazardousness, supporting pollution free environment, easy
handling procedure, techniques, environmentally benign process and good per-
centage of yields.
Scheme 1: Synthesis of trifluoromethyl-imines.
RESULTS AND DISCUSSION
The waste air-pollutant fly-ash has many chemical species21, 34, 35, 36 SiO2,
Fe2O3, Al2O3, CaO, MgO and insoluble residues. The waste fly-ash is conver-
ted into useful catalyst fly-ash: H2SO4 by mixing fly-ash and sulphuric acid.
The fly-ash: H2SO4 catalyst was used for synthesis of imines. The fly ash par-
ticles are in the silt-sized range of 2-50 microns38. Glass, mullite-quartz, and
magnetic spinel are the three major mineralogical matrices identified in fly ash.
Si, Al, Fe, Ca, C, Mg, K, Na, S, Ti, P, and Mn are the major elemental consti-
tuents of fly ash. The solubility of fly ash has been extensively investigated and
it is largely dependent on factors specific to the extraction procedure. Literature
study reveals that the long-term leaching studies predict that fly ash will lose
substantial amounts of soluble salts over time, but simulation models predict
that the loss of trace elements from fly ash deposits through leaching will be
very slow. Small amounts of radioisotopes are found to be the constituents of
fly ash which do not appear to be hazardous.
The phenyl trifloromethylimines were synthesized by microwave irradia-
tion of appropriate equi-molar quantities of substituted aryl amines (2 mmol),
phenyl tirluoromethyl ketone(2 mmol) and fly-ash: H2SO4 (0.5 g) in borosil
glass tube. The sulphuric acid group and chemical species present in the fly-
ash have enhanced the catalytic activity. During the course of the reaction
these species are involved for the promoting effects on condensation between
EXPERIMENTAL
Materials and methods
All chemicals used were procured from Sigma-Aldrich and E-Merck. The
Fly-ash was collected from Thermal Unit-II, Neyveli Lignite Corporation,
Neyveli, Tamilnadu, India. Infrared spectra (KBr, 4000-400 cm-1) have been
recorded on BRUKER (Thermo Nicolet) Fourier transform spectrophotometer.
The NMR spectra of all imines have been recorded on JEOL-400 spectrometer
operating at 400 MHz for recording 1H spectra and 100 MHz for 13C spectra in
CDCl3 solvent using TMS as internal standard. Mass spectra have been recor-
ded on SHIMADZU spectrometer using chemical ionization technique.
Preparation of fly-ash:H2SO catalyst36
In a 50mL Borosil beaker, 1g 4of fly-ash and 0.8 mL (0.5 mol) of sulphuric
acid were taken and mixed thoroughly with glass rod. This mixture was heated
on a hot air oven at 85°C for 1h, cool to room temperature, stored in a borosil
e-mail: drgtnarayanan@gmail.com
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J. Chil. Chem. Soc., 58, Nº 4 (2013)
the aryl amines and trifloromethyl ketone group leading to the formation of
imines by condensation of amines. The proposed general reaction mechanism
is shown in Figure 1. The components of fly ash vary considerably, but all fly
ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous
and crystalline) and calcium oxide (CaO). Hence the reaction takes place in
the only in the heterogeneous phase. In these experiments the products were
isolated and the catalyst was washed with ethyl acetate, heated to 100°C then
reusable for further runs of reaction. There was no appreciable change in the
percentage of yield of imines in further runs. In this protocol the reaction gave
better yields of the imines during the condensation without any environmental
discharge. The purities of synthesized imines were checked by their physical
constants and spectral data published in earlier in literature. The same experi-
ment was carried out with conventional heating method with ethanol medium.
The yields of the imines were found to be 50-65% only.
Further we have investigated the catalytic effect of fly-ash: H2SO4 on the
synthesis of imines (Entry 1) by varying the catalyst quantity from 0.2 to 1.5g.
As the catalyst quantity is increased from 0.25 to 0.5g, the percentage of yield
of the product gets increased from 85 to 86%. There is no significant increase
in the percentage of the product by even after increasing 0.5g of the quantity of
the catalyst. This catalytic effect is shown in Figure 2. The optimum quantity
of catalyst loading was found to be 0.5g for the synthesis of imines from amine
with 2 mmol of ketone. The reusability of this catalyst was studied the reaction
of aniline and trifluoromethyl ketone. The reusability of catalyst on condensa-
tion reaction of amines and ketones is given in Table 3. From the Table 3, first
two runs gave 86% product. The third, fourth and fifth runs of reactions gave
the yields 85.8%, 85.7% and 85.5 % of imines. There was no appreciable loss
in its effect of catalytic activity was observed up to fifth run.
Table 1. Synthesis of trifluoromethyl-imines by microwave assisted fly-ash:H2SO4 catalyzed solvent free conditions from trifloromethyl ketone and various
amines(R).
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J. Chil. Chem. Soc., 58, Nº 4 (2013)
Table 2. The spectral data of selective trifloromethyl-imines.
Figure 1. Proposed mechanism for synthesis of trifluoromethane–imines by condensation of amines
in presence Fly-ash:H2SO4 catalyst.
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J. Chil. Chem. Soc., 58, Nº 4 (2013)
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Figure 2. Effect of loading of catalyst fly-ash: H2SO4 versus percentage
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Table 3. Reusability of catalyst on condensation of trifluoromethyl-imine
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In conclusion, we have developed an efficient method for synthesis of
trifloromethyl-imines by condensation of amines, using solvent free environ-
mentally greener catalyst fly-ash: H2SO4 under microwave irradiation between
phenyl trifloromethyl ketone and amines. This reaction protocol
offers a
simple, economical, environmentally friendly, non-hazards, easier work-up
procedure and good yields.
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ACKNOWLEDGEMNT
The authors thank to SAIF, IIT Chennai for recording NMR spectral of
compounds.
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