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The 13
th
Symposium on Analytical and Environmental Problems, Szeged, 25 September 2006
88
ANALYSIS OF SOME DERIVATIVES OF
TETRAPHENYLPORPHYRIN BY FT-IR AND MASS
SPECTROMETRY
Gheorghe Fagadar-Cosma
a
, Valentin Badea,
a
Dana Vlascici,
b
Eugenia Fagadar-Cosma,
c
Monika Simon
a
a
"Politehnica" University, Chemistry department, 2 T. Lalescu Street, 300223-Timisoara,
Romania, e-mail: gfagadar@yahoo.com
b
West University of Timisoara, Faculty of Chemistry – Biology – Geography,
Inorganic Chemistry Department, 16 Pestalozzi Street, Timişoara, Romania
c
Roumanian Academy - Institute of Chemistry Timişoara, 24 M. Viteazul Ave,
300223-Timisoara, Romania
ABSTRACT
The present paper offers data about the FT-IR and mass spectrometry characterization of
some symmetrical meso-tetrakis-phenylporphyrins bearing different substituents in the para -
phenylic position. A comparison between the mass fragmentations of the compounds revealed
that each of the mass spectra presents the peaks corresponding to molecular ion and also for
double charged ion.
INTRODUCTION
The para substituted meso-tetrakis-phenylporphyrins were obtained by modified Adler
synthesis [1-3] as figured in reaction equation 1:
NN
H
N
N
H
R
R
R
R
R
CH O
N
H
H
5
C
2
-CO-O-CO-C
2
H
5
+
4
H
+
/
4
(1)
Where R= H (compound 1); CH
3
(compound 2); OCH
3
(compound 3).
The porphyrin macrocycle is usually characterized by plan geometrical structure which in
some cases can change into nonplanar conformation. This nonplanarity can be usually
realized by three different ways: by metallation, by the presence of bulky groups in meso
position or by the protonation of internal nitrogen atoms which are not possessing hydrogen
atoms. In this respect, the meso-tetraphenyl substituted porphyrins can be consider as
belonging to S
4
symmetry group because the S
4
and C
2
rotation axis is the z-axis and the
reflection plane for the S
4
operation is the xy-plane [4].
Some reliable electron-impact (EI) spectra were achieved during the present study for some
porphyrins and are fully discussed. The mass spectra of all the investigated porphyrins,
namely: meso-tetraphenylporphyrine (1), meso-tetrakis(p-tolyl)porphyrine (2) and 5,10,15,20-
tetrakis(p-methoxyphenyl)-21H,23H-porphyrine (3) are characterized by the presence of the
The 13
th
Symposium on Analytical and Environmental Problems, Szeged, 25 September 2006
89
molecular ion followed by different specific fragmentation and by the peak corresponding to
the double charged ion.
RESULTS
Comparing the data registered in the mass spectra of the analyzed porphyrins: meso-
tetraphenylporphyrine (Table 1), meso-tetrakis(p-tolyl)porphyrine (Table 2) and 5,10,15,20-
tetrakis(p-methoxyphenyl)-21H,23H-porphyrine (Table 3), it can be put into evidence the
presence of the molecular ion (M]
+.
) at m/e values of: 614(1), 670(2) and 734(3).
Besides the molecular ion, an identical m/e= 307 fragment, corresponding to the double
charged ion of the meso-tetraphenylporphyrin molecule is appearing in each spectrum.
Other common splitting of all analyzed compounds are those in which fragments having the
following m/e values were obtained. This are m/e: 91, 77; 76; 75, and they are corresponding
to fragments of the following types: C
7
H
7+
(stabilized tropilium ion, because of the
delocalized charge over the all seventh carbon atoms of the cycle) and phenylic ions: C
6
H
5+
,
C
6
H
4+
, C
6
H
3+
very usually find in mass spectra of the compounds possessing aromatic groups.
By comparison of spectrum of (1) with spectrum of (2), it can be revealed the losing of the
fourth methyl radicals from the para positions of the benzene rings (tolyl structure) of the
compound 2, generating a new fragment identical in mass (m/e= 614) with that of the phenyl
unsubstituted porphyrin (meso-tetraphenylporphyrin).
The compound possessing oxygen in its molecule, namely: and 5,10,15,20-tetrakis(p-
methoxyphenyl)-21H,23H-porphyrine (2) can be commonly characterized by the loss of water
molecules and by the appearance of remarkable abundant (23%-55%) carbonylium fragments.
Organic groups belonging to the phenolic ethers [5] type are known to generate fragments
m/e= 93, which by loosing of a CO molecule transforms into more stable conjugated
cyclopentadienilium ion m/e=65, situation that is present, as expected, in mass spectrum of
compound 3. These two peaks are characterized by relatively large abundance, around the
value of 20%. Instable fragments m/e= 93 have been formed by loosing CH
3.
groups from
CH
3
O-C
6
H
4
- structure (m/e= 108) which is abundantly (31.16%) present in mass spectrum.
The assignments of the fragments from the mass spectra
[5,6] of the analyzed compounds are
given in Tables 1-3.
The FT-IR spectra present the most important expected bands. The absorptions at 3319 and
3424 cm
-1
are attributed to stretching and bending vibrations of N-H and that near 1000 cm
-1
belongs to C-N, respectively, which are the characteristic absorptions of porphyrin free base.
The bands in the range 1500 - 1600 cm
-1
are due to stretching vibration of C = C in the
benzene aromatic ring. The main bands were asigned as follows:
FT
-
IR(KBr)
-
Compound 1: 418, 514, 659, 700(γ C-H
Ph
), 730, 748, 799(γ C-H
Pirol
), 965,
981(δ C-H
Pirol
), 1002(ν C-N
Pirol
), 1074(δ C-H
Ph
), 1157, 1179(δ C-H
Ph
), 1223, 1351, 1442(ν
C=N), 1474, 1559, 1597(ν C=C
Ph
), 3059, 3319 (ν N-H)
FT-IR(KBr)- Compound 3: cm
-1
: 752 (γ C-H
Ph
), 801 (γ C-H
Pyrrol
), 1001(ν C-N
Pirol
), 1032 (ν
C-O-C), 1096 and 1176 (δ C-H
Pyrrol
), 1248((ν C-O-C), 1352 (ν C-N), 1464 (ν C=N), 1488 (ν
C=C
Pyrrol
), 1512 (ν C=C
Ph
), 1544 and 1608 (ν C=C
Pyrrol
), 3424 (ν N-H).
MATERIALS and METHODS
A 212 Varian Finnigan Mat mass spectrometer was used. The EI ion source conditions were:
electron energy 54 eV, temperature up to 300 °C, mass range: 30- 818. The probes were
introduced as solids. FT-IR spectrum were registred on a JASCO 430 apparatus as KBr
pellets.
The 13
th
Symposium on Analytical and Environmental Problems, Szeged, 25 September 2006
90
General method of synthesis for the p-substituted- meso- tetraphenylporphyrins (1-3.
The syntheses were done by adapting the literature data [1-3].
RESULTS
Table 1: Mass fragmentation of meso-tetraphenylporphyrine
m/e Relatively
abundance, %
Ionic specie
615 72.04 M+1]
+.
614 100 C
44
H
30
N
4
]
+.
613 8.09 M-1]
+.
537 13.63 C
38
H
25
N
4
]
+.
By loosing of C
6
H
5.
522 40.70 C
38
H
24
N
3
]
+.
By loosing of NH
343 8.99 C
25
H
15
N
2
]
+.
By loosing of C
8
H
7
N
.
307 23.28 C
44
H
30
N
4
]
2+
Double charged ion of meso-tetraphenylporphyrine
280 15.76 C
20
H
12
N
2
]
+.
By loosing of C
2
H
3.
241 8.60 C
17
H
9
N
2
]
+.
By loosing of C
3
H
3.
, specific elimination of aromatics
or heterocycles
91 7.53 C
7
H
7+.
Tropilium cation- radical
77 7.21 C
6
H
5+
Table 2: Mass fragmentation of meso-tetrakis(p-tolyl)porphyrine
m/e Relatively
abundance, %
Ionic specie
670 100 C
48
H
38
N
4
]
+.
Molecular ion
614 14.26 C
44
H
30
N
4
]
+.
Four methylic radicals linked to phenyl are
eliminated (as two ethane molecules), generating radical ion
identical with meso-tetraphenylporphyrine
335 15.26 C
48
H
38
N
4
]
2+.
Double charged ion of meso-tetratolylporphyrin
307 4.05 C
44
H
30
N
4
]
2+
Double charged ion of meso-tetraphenylporphyrine
168 2.18 C
24
H
20
N
2
]
2+.
The rest corresponding to the double charged ion
formed by splitting into half the meso-tetratolylporphyrine
119 1.06 C
8
H
9
N]
+.
Resulted from combination of phenylic and ethenic
fragments.
91 1.74 C
7
H
7+.
Tropilium radical
Table 3: Mass fragmentation of 5,10,15,20-tetrakis(p-methoxyphenyl)-21H,23H-porphyrine
m/e Relatively
abundance, %
Ionic specie
734 1.09 C
48
H
38
N
4
O
4
]
+.
Molecular ion
732 5.45 C
48
H
36
N
4
O
4
]
+.
Two protons linked by internal pyrrolic nitrogen
are eliminated from m/e= 734.
307 24.91 C
44
H
30
N
4
]
2+
Double charged ion of meso-tetraphenylporphyrine
280 16.96 C
20
H
12
N
2
]
+.
By loosing of C
2
H
3.
229 7.05 C
16
H
9
N
2
]
+.
By loosing of C
4
H
3.
specific to aromatics
130 9.55
N
H
CH
2
+
Specific to nitrogen heterocycles
The 13
th
Symposium on Analytical and Environmental Problems, Szeged, 25 September 2006
91
121 100
CH
2
CH
3
O
+
108 31.16 CH
3
O-C
6
H
4+
Phenolic ether type group.
107 19.02
C
H
2
OH
+
94 23.57
N
H
C O
+
93 12.32 C
6
H
5
O
+.
Conjugated ion, specific for phenolic ethers
fragmentations
80 40.45
N
H
CH
2
]
+
77 28.48 C
6
H
5+
76 48.39 C
6
H
4+
65 7.86 C
5
H
5+.
Cyclopentadienylium ion, stabilized by conjugation,
resulted from m/e= 93 by CO loss
42 20.27 C
3
H
6+
39 7.41 C
3
H
3+
Specific to aromatics and heterocycles
CONCLUSIONS
■
Some symmetrical meso-tetrakis-phenylporphyrins bearing different substituents in the
para - phenylic position were compared regarding the mass fragmentations and each of the
mass spectra presents the peaks corresponding to molecular ion and also for double
charged ion.
■
The FT-IR spectra present the most important expected bands. The absorptions at 3319 and
3424 cm
-1
are attributed to stretching and bending vibrations of N-H and that near 1000
cm
-1
belongs to C-N, respectively, which are the characteristic absorptions of porphyrin
free base.
LIST OF REFERENCES
[1] Fagadar-Cosma E., Vlascici D., Fagadar-Cosma G., Spiridon-Bizerea O., Chiriac A.
(2004). The study of the electrochemical behaviour of metalo-porphyrins with Co(II) and
Co(Ill). Nitrite-selective electrode based on [5,10,15,20-tetraphenyl-21H,23H-porphyrinato-
N21, N22, N23, N24]Co(III)chloride. Rev. Chim. (Bucharest). 55, p. 882-885.
[2] Adler A.D., Longo F.R., Goldmacher, J., Assour J., Korsakoff L. (1967). A simplified
synthesis for meso-tetraphenylporphine. J. Org. Chem. 32, p. 476-487.
[3] Vlascici D., Fagadar-Cosma E., Spiridon-Bizerea O., Pascariu A., Chiriac A. (2005). The
characterization of the membrane material of a tiocyanate-selective electrode based on
rhodium(III) [5,10,15,20-tetraphenyl-21H, 23H-porphyrinato-N21,N22,N23,N24] chloride.
Rev. Chim. (Bucharest). 56, p. 224-228.
[4] Shriver D. F., Atkins P. W., Langford C. H. (1994). Inorganic Chemistry. Second Edition,
Oxford University Press p. 116-117.
[5] Balaban A. T., Banciu M., Pogany I. (1983). Aplicatii ale metodelor fizice in chimia
organica. Editura Stiintifica si Enciclopedica, Bucuresti p. 63-94.
[6] McLafferty F. W., Turecek, F. (1993). Interpretation of Mass Spectra. 4th Edition,
University Science Books, Mill Valley, CA
