Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

408 SUBSTITUTED PYRROLES
CC CC2-Hg HgC.C
II II II II
HC CH , H3C.C CH
COOH,
NH NH
3 : 4-Methylethylpyrrole Haemopyrrole carboxylic acid
H3C.C C.CH2.CH2 H3C.C C.CH2.CH2
|| || COOH, || || COOH.
HC C.CHg H3C.C C.CHg
\ / V
NH NH
Cryptopyrrole carboxylic acid Phyllopyrrole carboxylic acid
All these degradation products have also been obtained synthetically,
chiefly by H. Fischer. On oxidation, haemin yields derivatives of
maleic imide (W. Kuster) corresponding to the fact that pyrrole itself
can be oxidised to this substance.
CH—CH CH=CH
II II I I
CH CH —>- CO CO.
NH NH
Thus the imide of methylethylmaleic acid (I) corresponds to the
pyrroles, and the so-called haematinic acid (II) to the carboxylic acids
formulated above:
H3C.C==C.C2H5
H3C.C=C.CH2.CH2.COOH
I OC CO , II OC CO
NH NH
As will be seen later, C—C bonds of substituents in the a-position
are broken on hydrogenation and so the various pyrrole units are set free.
The porphyrins are pigments of this group, which have been freed
from iron ; they are closely related to haemin, and iron in complex
union can be reintroduced into them. Similar porphyrins are also
derived from chlorophyll.
Two natural porphyrins, uroporphyrin C40H38O16N4 and coproporphyrin
C36H38O8N4, have acquired great importance in connection with
the question of constitution. These substances tyere first isolated by
Hans Fischer from the urine and faeces of a patient sufEering from deranged
porphyrin metabolism; they are also formed in traces during
normal metabolism. Uroporphyrin is an octa-, coproporphyrin a tetracarboxylic
acid. Both are converted by thermal decarboxylation into
the oxygen-free aetioporphyrin C32H38N4, a substance which Willstatter
had obtained from haemin.
With the synthesis of haemin (H. Fischer, 1929) our knowledge of the