Molecular sieve abstract
The present invention provides an improved process for synthesis
of porphyrin compounds of the general formula 1 1 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 the synthesis of a tetraaryl porphyrin of the
formula 1 3said 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.
2. A process as claimed in claim 1 wherein the zeolite molecular
sieve catalyst used is in alkali ion form, ammonium ion form or
proton form.
3. A process as claimed in claim 2 wherein the alkali ion is selected
from sodium and postassium.
4. A process as claimed in claim 1 wherein the zeolite molecular
sieve catalyst is selected from the group consisting of MCM-41
A1-MCM-41 HY, SAPO-5 ZSM 5 and HZSM-5 (30).
5. A process as claimed in claim 1 wherein 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.
6. A process as claimed in claim 5 wherein the aromatic aldehyde
used is selected from the group consisting of benzaldehyde, o/m/p-methoxy
ben zaldehyde, 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 to aldehyde
molar ratio is 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 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.
9. A process as claimed in claim 1 wherein the time period of heating
is in the range of 3 minutes to 30 minutes.
10. A process as claimed in claim 1 wherein the yield of the compound
of formula 1 is 23.5%.
Molecular sieve description
FIELD OF INVENTION
[0001] 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.
[0002] 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
[0003] 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.
[0004] 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%.
[0005] 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.
[0006] 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
773K in air.
OBJECTS OF THE INVENTION
[0007] The main object of the present invention is to provide a
selective, solvent free, eco-friendly, economical process for synthesis
of tetraaryl porphyrines.
[0008] 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
[0009] Accordingly the present invention provides a process for
the synthesis of a tetraaryl porphyrin of the formula 1 2
[0010] 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.
[0011] In one embodiment of the invention, the zeolite molecular
sieve catalyst used is in alkali ion form, ammonium ion form or
proton form.
[0012] In a further embodiment of the invention, the alkali ion
is selected from sodium and postassium.
[0013] 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).
[0014] 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.
[0015] 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.
[0016] In a further embodiment of the invention, the pyrrole to
aldehyde molar ratio is in the range of 1:1 to 1:4.
[0017] 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.
[0018] In another embodiment of the invention, the yield of the
compound of formula 1 is 23.5%.
DETAILED DESCRIPTION OF THE INVENTION
[0019] 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.
[0020] 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.
[0021] 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.
[0022] In the reaction an equimolar ratio of pyrrole and benzaldehyde
were dissolved in a suitable solvent (chloroform/dichloromethane)
for thorough mixing and then the solvent 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.
[0023] 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.
[0024] 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.
[0025] 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
[0026] Mesoporous molecular sieve MCM-41 was synthesized according
to C. T. Kresge et al, Nature 359 (1992) 710 as follows.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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
[0032] 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. |