1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
Table 4. Saponification trials used for 50 mg each of o-(cyanomethyl) porphyrin 50.
1.
38
solvent(s)/reagent(s) T t Result
5 mL CH2Cl2, 20 mL AcOH, 20 mL
H2SO4, 5 mL H2O
90 °C 15 h
2. 10 mL THF, 5 mL H2SO4, 5 mL H2O 70 °C 12 h
3.
4.
5a.
5b.
6.
10 mL CH2Cl2, 10 mL HBr (5.4 M in
AcOH), 2 mL H2O
10 mL TFA, 2.5 mL H2SO4, 2.5 mL
H2O
20 mL (CH2OH)2, NaHS (5 eq), 1 mL
i-BuNH2, acidic work-up
same as 5a.
15 mL AcOH, 15 mL H2SO4, 5 mL
H2O
60 °C 12 h
75 °C 15 h
rt
55 °C
6 h
12 h
90 °C 96 h
inseparable mixture of carboxylic acid
51 and amide
carboxylic acid 51 (14 %) isolable,
many by-products
inseparable mixture of carboxylic acid
51 and amide
carboxylic acid amide (93 %) only
isolable product
no conversion
no conversion
carboxylic acid 51 (90 %) isolated
besides some minor degradation
products
Those trials showed that the nitrile functionality could only be efficiently attacked by acidic
methods under forced conditions (entries 4. & 6. in Table 4), where stronger acids seemed to
promote the amide formation while weaker ones lead to the desired full hydrolysis. 75 In
most cases, the obtained porphyrin ethanoic acid 51 was pure enough for further
transformations. FC can be performed on silica using e.g. mixtures of toluene and THF as
eluent. 96
3.2.2.1.3 Characterization of 45, 50 & 51
The 1 H NMR spectra show up significantly affected by altering the side chain from -CH2Br
(45) over -CH2CN (50) to -CH2CO2H (51) as not only the chemical shift of the methylene group
change (from 4.25 over 3.23 to 3.24 ppm, respectively) but also the spectral positions and
splitting patterns for the β-pyrrolic and arylic protons. The situations are depicted in Figure
13. For 45, the signals of the two distant pyrrolic units appear as one singlet which is being
shifted upfield in 50 to overlay with the doublet of 2/8 and finally splits into two doublets
even more upfield in 51. The same effect is detectable for the resonances of the phenyl rings
on positions 10, 15 and 20. Besides an equivalent shift to higher field of approx. 0.08 ppm
each, the signals also appear resolved although overlaid in a 1:2 ratio for 45, as two pseudo-
doublets for 50 and finally as two sets of three doublets in 51. This behavior is to be
explained by the more and more pronounced differentiability of the half-space including the
functional group and the other one containing the methyl substituent. This leads to the
appearance of an ABCD spin system for the unfunctionalized phenyl rings in 51 (largest