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Aer heating at 120 ꢁC for 60 minutes, the solution was cooled produced TPyP in 11% yield, and TPyP can be separated from IL
to room temperature, diluted with distilled water (50 mL) and a only by ltration. In other words, this nding suggests that
precipitate was formed. The solution was ltered, and the cake using [HC4im][X] ILs can purify TPyP easier than with the
on the funnel was washed with distilled water. However, further traditional Adler method using propionic acid. In addition,
purication procedures were not carried out because only a [HC4im][CF3CO2] could be reused at least 3 times without any
trace of porphyrin formation was observed by TLC.
loss of catalytic activity.
General procedure for porphyrins, (2), (3), (4), (5) in propionic
acid
Abbreviations
These compounds were prepared using almost the same
procedure with only minor differences. In the case of (2), pyrrole
(0.155 mL, 2.2 mmol) and 4-tolualdehyde (0.264 mL, 2.2 mmol)
were added to the propionic acid (8.0 mL) and reuxed for 60
minutes, the solution was cooled to room temperature, diluted
with distilled water (50 mL) and a precipitate was formed. The
solution was ltered, and the cake on the funnel was washed
with hot distilled water. Further, the precipitate was dried in
vacuo to produce 77.8 mg of TPP (0.116 mmol, 21%).
[HC4im]
[CF3SO3]
[HC4im][ClO4]
[HC4im][Cl]
[HC4im]
1-Butylimidazolium
triuoromethanesulfonate
1-Butylimidazolium perchlorate
1-Butylimidazolium chloride
1-Butylimidazolium triuoroacetate
[CF3CO2]
[HC4im][BF4]
1-Butylimidazolium tetrauoroborate
General procedure for 5,10,15,20-tetra(4-pyridyl)-21H,23H-
porphyine, TPyP, (6) in acidic ionic liquids
Acknowledgements
This research was supported by JSPS, Grant-in-Aid for Young
Scientists (B) (25810109, 2013), and by the Electric Technology
Research Foundation of Chugoku.
TPyP was prepared in the 5 species of acidic ionic liquids
([HC4im][X]; X ¼ CF3SO3ꢀ, ClO4ꢀ, Clꢀ, CF3CO2ꢀ, and BF4ꢀ). In
the case of [HC4im][CF3CO2], pyrrole (0.19 mL, 2.8 mmol) and 4-
pyridinecarboxaldehyde (0.263 mL, 2.8 mmol) were added to
[HC4im][CF3CO2] (10 mL) at 120 ꢁC. Aer heating at 120 ꢁC for
60 minutes, the solution was cooled to room temperature,
diluted with distilled water (50 mL) and a precipitate formed.
The solution was ltered, and the cake on the lter funnel was
washed with distilled water. The precipitate was diluted with a
minimum amount of chloroform and puried by column
chromatography on silica gel (MeOH/CHCl3). The purple crys-
tals were dried in vacuo to produce 48 mg of TPyP (6) (0.077
mmol, 11%). 1H NMR (400 MHz, CDCl3–TMS): d ¼ 9.07 (d, 8H,
pyridyl-meta), 8.87 (s, 8H, b-pyrrole), 8.16 (d, 8H, pyridyl-ortho),
2.92 (s, 2H, NH).
Notes and references
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Procedure for 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyine
(TPyP, 6) in propionic acid
Pyrrole (0.19 mL, 2.8 mmol) and 4-pyridinecarboxaldehyde
(0.263 mL, 2.8 mmol) were added to propionic acid (10 mL) and
reuxed for 60 minutes, the solution was cooled to room
temperature. Aer the oligomer component was ltered off,
propionic acid was removed by distillation under reduced
pressure to give a dark residue. The residue was puried by
column chromatography on silica gel (MeOH/CHCl3). The
purple crystals were dried in vacuo to produce 61 mg of TPyP (6)
(0.098 mmol, 14%).
Conclusions
We have shown that the relationship between the anion struc-
ture of [HC4im][X] and its acidity plays an important role in
porphyrin preparation using the Adler method. The general
TPyP preparation in propionic acid needs a troublesome solvent
removal process, whereas the reaction in [HC4im][CF3CO2]
8 (a) T. Welton, Chem. Rev., 1999, 99, 2071; (b) P. Wasserscheid
and W. Keim, Angew. Chem., Int. Ed., 2000, 39, 3772; (c)
R. Sheldon, Chem. Commun., 2001, 2399; (d) J. Dupont,
R. F. de Souza and P. A. Z. Suqrez, Chem. Rev., 2002, 102,
3667.
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RSC Adv., 2014, 4, 26777–26782 | 26781