Question

what are some of the possible impurities in the preparation of tetraphenylporphyrin and how does the purification scheme remove most of them in synthesizing tetraphenylporphyrin and cu(TPP) lab.

Answer 1

Preparation of Tetraphenylporphyrin from benzaldehyde and pyrrole , four molecules of each is required for the synthesis, the condensation of this benzaldehyde and pyrrole leads TPP, The possible impurities are, dimerised product of pyrrole itself. this dimerisation can be overcome by heating to reflux temp. which reduces the possiblity of pyrrole dimerisation.

catalyst required to be weak acid propanoic acid, if strong acid used it will dimerise the two pyrrole molecules. this propanoc acid at the end required to be seprated from product, which is insoluble in product and washed out with methanol otherwise it will gives purple colour to the product.

another impurity is formation of quaternary salt, which can be overcome by subsequent deprotonation of pyrrole,

another impurity is meso tetraphenylchlorin formed by reduction of TPP, AND CAN BE SEPRATED BY USING,

COLOUMN CHROMATOGRAPHY, meso tetrahydrochlorin is less polar and can be easily removed from Cu TPP by non poalr mobile phase.

so these are some of the possible impurities formed and also scheme has set to remove that impurities from product or taken care of it can not be formed as discussed above.