Molecular sieve abstract
The present invention provides an improved process for synthesis
of porphyrin compounds of the general formula 1 ##STR1## from pyrrole
and aromatic aldehyde over zeolite molecular sieve catalysts using
microwave heating, (solvent free) to provide an eco-friendly, economical,
faster and selective heterogeneous method.
Molecular sieve claims
We claim:
1. A process for synthesizing a tetraphenyl porphyrin compound
comprising reacting a pyrrole with an aromatic aldehyde in the presence
of a zeolite molecular sieve catatyst under microwave radiation
at a frequency effective to obtain the tetraphenyl porphyrin compound.
2. A process as claimed in claim 1 wherein the zeolite molecular
sieve catalyst is in alkali ion form, ammonium ion form or proton
form.
3. A process as claimed in claim 2 where the zeolite molecular
sieve catalyst is in alkali ion form and comprises an alkali ion
selected from the group consisting of sodium and potassium.
4. A process as claimed in claim 1 wherein the zeolite molecular
sieve catalyst is selected from the group consisting of MCM-41
Al-MCM-41 HY, SAPO-5 ZSM 5 and HZSM-5.
5. A process as claimed in claim 1 wherein the aromatic aldehyde
is of the formula RPhCHO, wherein R in the ortho, meta and para
positions is selected from the group consisting of methoxy, N, N,
dimethyl, hydroxy and nitro.
6. A process as claimed in claim 1 wherein the aromatic aldehyde
is selected from the group consisting of benzaldehyde, o/m/p-methoxy
benzaldehyde, o/m/p-methyl benzaldehyde, o/m/p-nitro benzaldehyde,
m/p-hydroxy benzaldehyde, N, N, dimethyl benzaldehyde and 345
tri methoxy benzaldehyde.
7. A process as claimed in claim 1 wherein the pyrrole and the
aldehyde are reacted at a pyrrole to aldehyde molar ratio in the
range of 1:1 to 1:4.
8. A process as claimed in claim 1 wherein the catalyst is regenerated
by burning out carbon deposited thereon by passing air through a
layer of the catalyst at a temperature in the range of 450.degree.
C. to 550.degree. C.
9. A process as claimed in claim 1 wherein the time period for
the microwave radiation is in the range of 3 minutes to 30 minutes.
10. A process as claimed in claim 1 wherein the process is conducted
so as to yield at least 23.5% of the tetraphenyl porphyrin compound,
said compound having the formula 1:
Molecular sieve description
FIELD OF INVENTION
The present invention relates to a process for synthesis of a porphyrin
compound using a molecular sieve catalyst under microwave radiation.
More particularly, the present invention relates to a process for
synthesis of tetraaryl porphyrin by reacting pyrrole and aromatic
aldehyde under microwave irradiation, which is a solvent free system
using a specific zeolite catalyst. The invention also relates to
a process for the synthesis of tetraphenyl porphyrin by reacting
pyrrole with benzaldehyde in presence of zeolite molecular sieves
under microwave irradiation. The present invention relates to synthesis
of porphyrin compounds over solid acid catalyst.
This invention provides a non-corrosive, eco-friendly process,
where the catalyst can be recyclable and reuse for many times, no
work up procedure, no-wastage of the compounds (i.e. high atom selectivity),
simple sample extraction and high selectivity of products.
BACKGROUND OF THE INVENTION
Porphyrin compounds as well as methods for synthesising the same
are well recognised in the art. However, porphyrin compounds and
other pyrrole compounds are expensive. For example porphyrine is
offered at costs as high as $15000/g. Even though many catalysts
such as organic and inorganic acid catalysts are known for the synthesis
of porphyrins, the catalysts have at best limited facility for reuse
and the yields are very low. Another disadvantage of the prior art
processes for the synthesis of porphyrins using such catalysts is
that impure corroles are formed making it difficult to separate
the pure compound.
The first such report of synthesis of porphyrin molecules under
microwave irradiation by A. Petit et al (Synthetic Communication
22 (8) (1992) 1139) employed silica alumina, clay and montmorillonite
as a catalyst. However, the results were very poor and not more
than 10%.
It is therefore important to develop a process for the synthesis
of porphyrins with good yield and where catalyst is reusable thereby
resulting in economy of costs.
Zeolite catalysts are known in the art for several processes. Zeolites
of ZSM series are available from Conteka, Swedan. Methods for producing
them are described in detail in U.S. Pat. No. 3702886 (ZSM-5).
C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J.
S. Beck, Nature 359 (1992) describe the synthesis of MCM-41 by an
aqueous solution of aluminum isopropoxide. An aqueous solution of
sodium hydroxide (0.3 g) was added to aluminum isopropoxide (0.38
g) in 50 ml beaker and stirred in hot conditions, till a clear solution
was formed. Then 9.4 ml of tetraethyl ammonium hydroxide (TEAOH)
and Ludox colloidal silica (9.26 g) were added drop wise while stirring
at room temperature. Then hexadecyl tri-methylammonium bromide (10.55
g) was added slowly to the above solution. The pH of the mixture
was maintained at 11.0-11.5. Finally, the gel mixture was transferred
into an autoclave and heated at 100.degree. C. for 24 h. The solid
product was recovered by filtration, washed with deionized water
and dried in air. All the as-synthesized samples were calcined at
773 K in air.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a selective,
solvent free, eco-friendly, economical process for synthesis of
tetraaryl porphyrines.
This and other objects of the invention have been achieved by using
a zeolite molecular sieve as the catalyst for the microwave radiation
method for the synthesis of porphyrins.
SUMMARY OF THE INVENTION
Accordingly the present invention provides a process for the synthesis
of a tetraaryl porphyrin of the formula 1 ##STR2##
said process comprising reacting the corresponding pyrrole and
aldehyde in a solvent free system under microwave radiation in the
presence of a zeolite molecular sieve catalyst to obtain the compound
of formula 1.
In one embodiment of the invention, the zeolite molecular sieve
catalyst used is in alkali ion form, ammonium ion form or proton
form.
In a further embodiment of the invention, the alkali ion is selected
from sodium and postassium.
In another embodiment of the invention, the zeolite molecular sieve
catalyst is selected from the group consisting of MCM-41 Al-MCM-41
HY, SAPO-5 ZSM 5 and HZSM-5 (30).
In another embodiment of the invention, the aromatic aldehyde is
of the general formula RPhCHO wherein R in the ortho, meta and para
positions is selected from the group consisting of methoxy, N, N,
dimethyl, hydroxy and nitro.
In a further embodiment of the invention, the aromatic aldehyde
used is selected from the group consisting of benzaldehyde, o/m/p-methoxy
benzaldehyde, o/m/p-methyl benzaldehyde, o/m/p-nitro benzaldehyde,
m/p-hydroxy benzaldehyde, N,N, dimethyl benzaldehyde, 345 tri
methoxy benzaldehyde.
In a further embodiment of the invention, the pyrrole to aldehyde
molar ratio is in the range of 1:1 to 1:4.
In yet another embodiment of the invention, the catalyst is regenerated
by burning out the carbon deposited thereon by passing air through
the catalyst layer at a temperature in the range of 450.degree.
C. to 550.degree. C.
In another embodiment of the invention, the yield of the compound
of formula 1 is 23.5%.
DETAILED DESCRIPTION OF THE INVENTION
Tetraphenyl porphyrines by reacting pyrroles with aromatic aldehyde
under microwave irradiation in presence of a catalyst, wherein the
catalyst is a commercially available or as synthesized catalyst.
The aromatic aldehydes used in the present invention includes benzaldehyde,
o/m/p-methoxy benzaldehyde, o/m/p-methyl benzaldehyde, o/m/p-nitro
benzaldehyde, m/p-hydroxy benzaldehyde, N,N, dimethyl benzaldehyde,
345 tri methoxy benzaldehyde to produce corresponding substituted
tetraphenyl porphyrins.
Zeolites used in the present invention are commercially available,
and can also be prepared by methods known in the art. The zeolite
used in the present invention may be any of an alkali ion form such
as sodium, potassium or the like, ammonium ion form and proton form.
The alkali ion, however, is not preferably because it lowers the
catalytic activity if it remains in the catalyst finally. The microwave
power varied from low to high power and the time of heating also
varied from 3 minutes to 25 minutes. The catalyst weight can be
varied in this reaction from 0.1 g to 1 g and the pyrrole to aldehyde
molar ratio can be varied from 1:1 to 1:4.
In the reaction an equimolar ratio of pyrrole and benzaldehyde
were dissolved in a suitable solvent (chloroform/dichloromethane)
for thorough mixing and then the sovent was evaporated. To this,
the pre-calcined and dried (200.degree. C., 3 h) MCM-41 catalyst
was added to and after mixing thoroughly with a glass rod, is subjected
to microwave irradiation for 15 minutes with 2 minutes intervals.
Then after the reaction, (20.times.5) ml chloroform solvent was
added to extract the organic compound and then the catalyst is subjected
soxhlet extraction with chloroform. Then porphyrin was seperated
by columun chromatography over neutral alumina with hexane as eluent
(DCM :Hexane). The quantification was alos done by HPLC and compared
with the isolate yields and are characterised by Mass and UV-VIS.
Along with the cyclized product, tetraphenyl porphyrin, minor amounts
of linear chain condensed products of pyrrole and aldehyde were
compounds are also formed.
In place of MCM-41 catalyst when HY was used, a small amount of
porphyrin is formed, whereas HZSM-5 (30) yields major amount of
porphyrin which may be due to surface reaction. The reaction was
compared with SAPO-5 and also with silica alumina catalyst and low
conversions and selectivities of the porphyrin molecules under microwave
irradiation were observed.
The regeneration of the catalyst is easily effected according to
any conventional method. For example the carbon deposited on the
catalyst can be burned out by passing air through the catalyst layer
at a temperature of 450.degree. C. to 550.degree. C.
By using the catalyst of the present invention, as shown, for example,
in Example 1 the yield of tetraphenyl porphyrin 23.5%. The yields
being shown are as the value calculated based on the conversion
of pyrrole. The present invention is described below in more detail
referring to Examples, to which the present invention is not limited.
By replacing the benzaldehyde with substituted benzaldehydes corresponding
tetra substituted porphyrins were formed, which were characterised
by UV-VIS spectroscopy.
EXAMPLE 1
Mesoporous molecular sieve MCM-41 was synthesized according to
C. T. Kresge et al, Nature 359 (1992) 710 as follows.
Solution A was prepared by mixing 0.38 g of NaOH, 20 ml of water,
0.76 g of Aluminium isoproxide and heated till a clear solution
was obtained. After this 9.8 ml of Tetra ethyl ammonium hydroxide
was added while cooling the mixture.
Solution B was prepared by mixing 11.6 ml (9.6 g) of 50wt % ludox
silica in 50 ml of distilled water the mixture was kept under vigorous
stirring until a clear solution formed.
Solution A was added to Solution B under vigorous stirring and
kept for stirring for one hour, after that 10.55 g of Hexadecyl
trimethyl ammonium bromide (HDTMABr). The pH was adjusted to 10.5.
A stainless steel autoclave having 0.6 liters of volume was charged
with the above solution. The autoclave was sealed and heated to
100.degree. C. Hydrothermal synthesis was effected under this condition
while continuing stirring for 20 hours. In this period, the inner
pressure of the autoclave was 5 to 6 kg/cm.sup.2.
After completion of the reaction, the reaction mixture was cooled
to room temperature and the product was separated by filtration.
After repetition of washing and filtration until the concentration
of Br.sup.- ion in the filtrate became 1 ppm or below, the product
was dried at 110.degree. C. for 16 hours and then calcined in air
at 500.degree. C. for 12 hours to elute the surfactant and obtain
white crystals of Na form Al-MCM-41. As a result of the measurement
of X-ray diffraction, the crystals had a diffraction pattern coincident
with that of MCM-41 reported in Nature 1992 by Breck et al.
EXAMPLE 2
In a test tube, 1 ml of pyrrole and corresponding volume of benzaldehyde
(1:1 Molar) are dissolved in chloroform solvent and then the solvent
was evaporated. To this, pre-calcined and dried 0.5 g MCM-41 catalyst
was added, and after thorough mixing with a glass rod, subjected
to microwave irradiation at a power of 2450 MHz for 15 minutes with
2 minutes intervals. After the reaction, the catalyst was thoroughly
washed (20.times.5 ml) with solvent and subjected to soxhlet extraction
with chloroform. Porphyrin was separated by column chromatography
using neutral alumina and hexane as eluent. The quantification was
also done by HPLC and confirmed by isolated yields. Further the
products were further confirmed by Uv-Visible spectroscopy and Mass
spectroscopy. Average yields of the products found 23.5% of tetraphenyl
porphyrin when pyrrole reacted with benzaldehyde over Al-MCM-41.
ADVANTAGES OF THE INVENTION
The present invention provides an improved process that comprises
environmentally clean technology with low wastage, easy separable
and reusability of the catalyst. The catalysts used in this process
are easily separable by the simple filtration. This process provides
an eco-friendly method with higher selectivity. A method provides
a selective heterogeneous catalyst with longer life. |