tupence_hapeny
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Metallo-5,10,15,20-tetraphenylporphyrin synthesis (MW)
The synthesis of porphyrin’s via brand new techniques (which appear to have been disclosed only in September 2006):
http://www.u-bourgogne.fr/jpp/base_article/index.php?to=to_b...
Porphyrins are sciences latest attempt to recreate nature, and are structurally similar to chlorophyll and the structures of mammalian blood (Iron
containing porphyrins are called hemes, one of which is hemoglobin). The purpose behind doing so appears to have been at least twofold, to allow for
greater effectiveness in drug delivery and to recreate the in-vitro effects of blood upon a variety of compounds.
http://en.wikipedia.org/wiki/Porphyrin
The simplest synthesis of the porphyrin complexes is that of 5,10,15,20-tetraphenylporphyrin (TPP), which synthesis consists of simply heating a
mixture of benzaldehyde and pyrrole, absorbed on silica, in a microwave for about 10 minutes:
http://greenchem.uoregon.edu/Pages/Overview.php?WhereFrom=Re...
An alternative synthesis is to bring pyrrole and benzaldehyde into contact with each other in the gas-phase:
http://greenchem.uoregon.edu/Pages/Overview.php?WhereFrom=Re...
While a higher yielding (30%) synthesis uses xylene as a solvent and microwave heating:
http://web.chemistrymag.org/cji/2001/039044le.htm
This should be compared to the RSC Supplement (2 pages, attached in PDF format), which operates under argon, uses propionic acid as a solvent (as did
the original TPP synthesis).
The TPP is purified by column chromatography, and apparently is the first compound through the coloumn when eluted with ethylacetate and hexane,
however, this can be checked by UV.
The exciting aspect of these papers is that not only do they provide amateur chemists with the opportunity to reach the previously considered to be
unreachable porphyrin complexes, but they also provide details on how to metallate the pophyrin complex:
http://greenchem.uoregon.edu/Pages/Overview.php?WhereFrom=Re...
[NB If someone can get that first article it provides details on the metallation of the porphyrin(s) with 4 metals, hopefully including iron,
manganese and/or cobalt].
The metallo-porphyrin complexes are used for a variety of reactions, although, it would appear that the books are not shut at this time, they are
still being written.
However, one interesting use of metalloporphyrins is the epoxidation of styrene (and other alkenes) with hypochlorite/peroxide. In fact one
metalloporphyrin (Manganese-5,10,15,20-tetraphenylporphyrin acetate) has become the very first reagent which can transform styrene to its epoxide in
100% yields (using iodosylbenzene).
Other porphyrin utilizing reactions may be achieved, they are even used as PTC’s.
tup
PS I am sorry to have to start yet another topic, I did UTFSE however I found nothing more than general discussion on the porphyrins (apart from some
discussion of Copper Phthalocyanine synthesis - however that is a different molecule althogether).
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Nicodem
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Not particularly on topic…but the synthesis of copper phthalocyanine from phthalanhydride, urea and CuCl2 used to be a common practical excercise
for students. Phthalocyanine is similar to porphyrin in that it is ring condensed with benzene rings and with imine instad of methine bridges. It can be used as
a metal ligand just like any porphyrin. You can find the experimental in some old schoolbooks for practice or probably in one of the old issues of the
Journal of Chemical Education or sources like that. I always wandered why here this practice is not used for eductional purposes anymore
since it must be quite a colorful reaction, but I guess it is considered too simple since it uses no laboratory skills of value except for vacuum
filtration.
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tupence_hapeny
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Here is an interesting use of iron-tetra(substituted)phenylporphyrins, namely as a catalyst for transfer hydrogenation of ketones & aldehdyes
using either 2-propanol or HCOOH/Et3N. I realize that the synthesis of catalysts (particularly clean, green catalysts) is of little interest on this
board, just thought that I would share it.....
Stephan Enthaler, Giulia Erre, Man Kin Tse, Kathrin Junge and Matthias Beller, 'Biomimetic transfer hydrogenation of ketones with iron porphyrin
catalysts', Tetrahedron Letters, Volume 47, Issue 46, 13 November 2006, Pages 8095-8099
[Edited on 19-5-2007 by tupence_hapeny]
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Eclectic
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I think catalyst preps and green chem. applications are great.
Should they be in Organic Chemisty, Technochemistry, or maybe a new group?
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tupence_hapeny
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Good point, however, the substrate (the porphyrin) is organic - thus they were put here for the moment. Seriously, I think they should all go
somewhere together.
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tupence_hapeny
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Here is another use for Fe(TPP), with H2O2 it epoxidises natural propenylbenzenes (the best performance is with isosafrole - 98% epoxide)
Here too is the article which the authors of the first article cite with regard to the preparation of the Fe(TPP)Cl.
It's nice when a catalyst is useful for multiple reactions
tup
[Edited on 26-5-2007 by tupence_hapeny]
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