Introduction Synthesis of Porphyrins

Porphyrin an intruduction:

==>Porphyrins are macro-cyclic molecules.
==>They are highly Florasent molecules. 
==>they are formed in the process of condensation of pyrrole with aldehydes in presence
of acid,followed by tretment of oxidizing agent like DDQ.
==>They have applications in medicinal chemistry also. 

SYNTHESIS:
Porphyrin is a macro organic molecule result of condensation of pyrrole(4eq) and aldehydes (4eq), in presence of lewis acid like BF3. Generally BF3 exists as BF3.Et2O adduct.
DDQ(2,3-dichloro-5,6-dicyanobenzoquinone) used as oxidizing agent(dehydrogenation).

Generally we can varii the groups are brought at meso position by using different aldehydes in condensation.
If we used benzaldehyde we get phenyl groups at meso position.
If we use tolaldehyde we get tolyl groups at meso position.

Here H+ is BF3,
DDQ used as dehydrogenation agent.

MECHANISM INVOLVED:





(porphyrin 1*)

1. Let the alde hyde used in condensation is para 'X' benzaldehyde , then,
if,
X=CH3-, aldehyde is p-tolaldehyde, porphyin will be H2TTP(TETRA TOLYL PORPHYRIN)
X=H-,aldehyde is benzaldehyde,porphyin will be H2TPP(TETRA PHENYL PORPHYRIN)

synthesis of mono substituted porphyrins:

Take 3 eq of one type of aldehyde and 1 eq of other type aldehyde and condensate with 4 eq of pyrrole, then you are going to get 5 types of products, separate them by column chrometography, then you can isolete one porphyrin having the aldehyde residue in 3:1 ratio(that is product will have 3 'X=R', 1X=Y in the above porphyrin1*) .

the structure will be as follow,

This product will be obtained by condensation of p-tolaldehyde and p-X aldehyde(where X can be any group).


For example if we have taken 3 eq tolaldehyde, 1eq p-nitro benzaldehyde the we get 5 products.
1.H2TTP( that is product will have 4X=CH3, in the above porphyrin1*)
2.Mono Nitro H2TTP( that is product will have 3 'X=CH3', 1X=NO2 in the above porphyrin1*)
3.DI Nitro H2TTP( that is product will have 2 'X=CH3', 2=NO2 in the above porphyrin1*)
4.Tri Nitro H2TTP( that is product will have 1 'X=CH3', 3=NO2 in the above porphyrin1*)
5.Tetra Nitro H2TTP( that is product will have 4X=NO2 in the above porphyrin1*)

SEPARATION OF PORPHYRINS BASING ON POLARITY(COLUMN CHROMATOGRAPHY):
We can separate them by column chromatography, basing on polarities.
polarity of above porphyrins increases with increase in nitro groups.
Here we are running column with mixture of pet ether(nonpolar) and DCM(polar).
so as percentage of DCM increases polarity of eluting solvent increases and polar porphyrin starts coming.

so H2TTP comes out first,
mono nitro H2TTP next,
di nitro H2TTP next,
tri nitro H2TTP next,
tetra nitro H2TTP comes last through silica gel column.
We can find out separating sovent mixture by TLC(Thin Layer Chromatography)


ANYONE HAVING DOUBTS REGARDING ABOVE TOPICS MAIL ; pavan@chem.iitb.ac.in