Supramolecular regioselectivity of meso-phenylporphyrin sulfonation. Synthesis of 5,10,15-tris(4’-sulfophenyl)porphine Текст научной статьи по специальности «Химические науки»

Порфирины

Porphyrins

iVJaKporaTepoLii/JKj-JbJ

Статья

Paper

http://macroheterocycles.isuct.ru

DOI: 10.6060/mhc170833s

Supramolecular Regioselectivity of meso-Phenylporphyrin Sulfonation. Synthesis of 5r10r15-Tris(4r-sulfophenyl)porphine

Vladimir B. Sheinin,a@ Dmitriy A. Ivanov,a and Oscar I. Koifmanab

Dedicated to Academician Aslan Yusupovich Tsivadze on the occasion of his Birthday

aG.A. Krestov Institute of Solution Chemistry of Russian Academy of Sciences, 153045 Ivanovo, Russia bIvanovo State University of Chemistry and Technology, 153000 Ivanovo, Russia Corresponding author E-mail: [email protected]

The results of the prognostic computer synthesis of meso-phenylporphyrins H2P(Ph)n sulfo derivatives, which demonstrate the supramolecular nature of the porphyrins sulfonation regioselectivity in concentrated sulfuric acid and oleum, are presented. By means of DFT calculation it has been shown that regioselectivity of meso-phenylporphyrins sulfonation is due to host-guest complex formation of the diprotonated porphyrin platform with two hydrosulfate anions, [Hp2+(Ph) J(HSO4)2. The guest anions control the reactivity of Hp2+(Ph)n. First, they activate Hf2+(Ph)n for elec-trophilic substitution by partial negative charge transfer to the diprotonated porphyrin. Second, the guest anions are the cause of a total charges redistribution on the carbon atoms of Hp2+ and the phenyl rings, thereby providing the regioselectivity of Hp2+(Ph)n sulfonation. The data from prognostic stage calculations and method of organic synthesis were used to obtain the new 5,10,15-tris(4'-sulfophenyl)porphine. The obtained results are comprehensive and applicable to other SEAr reactions of porphyrins.

Keywords: meso-Phenylporphyrins, protonation, host-guest complexes, electrophilic substitution, supramolecular regioselectivity, sulfonation, sulfophenyl porphyrins.

Супрамолекулярная региоселективность сульфирования мезо-фенилпорфиринов. Синтез 5г10Д5-трис(4'-сульфофенил) порфина

В. Б. Шейнин,^ Д. А. Иванов^ О. И. Койфман^

аИнститут химии растворов им. Г.А. Крестова РАН, 153045 Иваново, Россия

ъИвановский государственный химико-технологический университет, 153000 Иваново, Россия

@Е-таИ: [email protected]

Приведены результаты прогностического компьютерного синтеза сульфопроизводных мезо-фенилпорфири-нов Н2Р(РИ)п, которые демонстрируют супрамолекулярную природу региоселективности сульфирования пор-фиринов в концентрированной серной кислоте и в олеуме. Методом DFT показано, что региоселективность сульфирования мезо-фенилпорфиринов обусловлена образованием комплексов [Нр2+(Р^ ](^04)2 типа «хозяин-гость» дипротонированной порфириновой платформы с двумя гидросульфатными анионами. Анионы-«гости» контролируют реакционную способность Нр2+(РЬ)п. Во-первых, они активируют Нр2+(Р^4 к электрофильному замещению путем частичного переноса отрицательного заряда на дипротонированный порфирин. Во-вторых, анионы-«гости» являются причиной тотального перераспределения зарядов на атомах углерода Нр2+ и фениль-ных колец, обеспечивая тем самым региоселективность сульфирования Нр2+(Р^п .Прогностический этап и органический синтез были использованы для получения нового 5,10,15-трис(4'-сульфофенил)порфина. Полученные результаты имеют общий характер и могут быть распространены на другие SEAr реакции порфиринов.

Ключевые слова: мезо-Фенилпорфирины, протонирование, комплексы «хозяин-гость», электрофильное замещение, супрамолекулярная региоселективность, сульфирование, сульфофенилпорфирины.

Introduction

Sulfonated derivatives of meso-phenylporphyrins generally are obtained by direct sulfonation in concentrated sulfuric acid (CSA), using the original Menotti procedure for 5,10,15,20-tetraphenylporphyrin (H2P(Ph)4),[1] or its variations. The only sulfonated derivatives currently described are these of 5,15-diphenylporphyrins (H2P(Ph)2) and H2P(Ph)P-10]

Figure 1. Nucleophilic centers in HP(Ph)2 and HjP(Ph)4 molecules.

There are a total of 28 nucleophilic centers (NCs) in the molecule of H2P(Ph)4, considering the porphyrin platform as well as all phenyl rings (Figure 1). However, when H2P(Ph)4 reacts with CSA, only 4'-sulfophenyl-derivatives are formed (Figure 2).

The fractional yields of H2P(Ph)4 4'-sulfophenyl-derivatives depend on the reaction conditions (Table S1). It should be noted that no yield optimizations have been reported in the literature. The use of CSA allows to introduce only four sulfo groups into H2P(Ph)4. The product of its

exhaustive sulfonation with CSA - 5,10,15,20-tetrakis(4'-sulfophenyl)porphine (H2P(PhSO3H)4) is the major product at 100 X if the reaction time does not exceed 4 h. Lower temperatures and/or shorter reaction times results in greater fractional yields of lower sulfonated derivatives. Further sulfonation of H2P(PhSO3H)4 is possible only in oleum. Treatment of H2P(Ph)4 with fuming sulfuric acid (2 h at ambient temperature) results in cross-linking of the adjacent respective 2 and 2'-positions of the porphyrin platform and a phenyl ring and affords a sulfone compound (Figure 2).[9]

Compared to H2P(Ph)4, the molecule of H2P(Ph)2 contains more reaction centers in the porphyrin platform, namely at 2, 8, 10, 12, 18, and 20 positions. One could expect H2P(Ph)2 to have a greater variety of sulfonated derivatives. In 1998 R. Rubires et al. performed sulfonation of H2P(Ph)2 in CSA for 3 h at 100 X and obtained 5,15-6/s(4'-sulfophe-nyl)porphine (H2P(PhSO3H)2) as the only product.[6] Later, H. Garcia-Ortega and J.M. Ribo[10] sulfonated H2P(Ph)2 in 96 % sulfuric acid at 0 °C, ambient temperature, 50, 80, and 100 °C, as well as in slightly dilute (90 % and 81 %) sulfuric acid. A thorough HPLC monitoring of the product yields was carried out.

The authors determined that sulfonation of H2P(Ph)2 in CSA occurs in positions 4' and 2 (Figure 3). All possible products are formed. Addition of water and using higher porphyrin concentrations decrease the overall yield but do not influence the regioselectivity. When an anhydrous medium (30 % oleum - methanol, 9:1) is used, sulfonation of H2P(Ph)2 proceeds via a different pathway and results in the formation of 10,20-sulfo-5,15-bis(4'-sulfophenyl)porphine.

In this communication we report computed predictions for sulfonation of H2P(Ph)4 and 5,10,15-tris(4'-sulfophenyl) porphine (H2P(Ph)3), which demonstrate a supramolecular influence on the regioselectivity of the reaction in concentrated sulfuric acid and in oleum. In addition, a preliminary

Figure 2. Products of HjP(Ph)4 sulfonation in concentrated sulfuric acid and of HjP(PhSO3H)4 sulfonation in oleum (sulfone). 488 Макрогетероциmbl /Macroheterocycles 2017 70(4-5) 487-495

H03S

(8%)

Ho3s

(8%)

SO3H

SO3H \

SO3H

(15%) SO3H

HO3S

SO3H

(30%)

SO3H

\

HO3S

SO3H

HO3S

SO3H

SO3H

Figure 3. Products of intermediate (upper row) and exhaustive (middle row) sulfonation of HjP(Ph)2 in 96 % sulfuric acid and in a 30 % oleum - methanol mixture (9:1) (lower row).[10] Optimized yields are given in brackets.

prognostic stage and organic synthesis were used to obtain a novel 5,10,15-tris(4'-sulfophenyl)porphine.

Experimental

All solvents and other chemicals were obtained from commercial sources and used as received without further purification. 5,10,15-triphenylporphine and 5,10,15,20-tetraphenylporphine were purchased from PorphyChem. A fiber-optic spectrofluorim-eter Avantes AvaSpec-2048-2 was used to obtain spectral data. A Bruker Avance III 500 instrument was used for 1H NMR spectra (500.17 MHz operating frequency for 1H at 294 K). Mass spectra were obtained on a MALDI-TOF Shimadzu Biotech AXIMA Confidence mass-spectrometer. Geometry optimization was performed at the B3LYP/3-21G(d,p) level of density functional theory using Gaussian software package.1111

5,10,15-Tris(4-sulfophenyl)porphine triple ammonium salt. A mixture of 100 mg (1.86 10-4 mol) H2P(Ph)3 and 3 mL concentrated sulfuric acid was sealed in a glass tube and subjected to sonica-tion for 1.5 h at 50 °C. The tube was then heated in a boiling water bath for 6 h. The contents of the tube was cooled, poured onto ice and neutralized with concentrated aqueous ammonia. The obtained solution was evaporated to dryness on a water bath, the crude product was extracted with ethanol. The solvent was distilled off and the residue subjected to chromatographic purification on alumina (Brockmann grade II), eluting with ammonia-saturated butanol. The purified product was extracted with a minimal amount of water, the aqueous solution separated by decantation. An equal volume of butanol was then added and the mixture evaporated to dryness on a water bath. Anhydrous ammonia salt HjP(PhSO3NH4)3 was obtained as the only product with a 69 % (127.3 mg) yield. 1H[ NMR (500 MHz, [D6]DMSO) H2P(PhSO3-)[ 5 ppm: 10.60 (s, 1H, 20-H); 9.65 (d, 2H, 3J=4.6 Hz, 2,18-H); 9.01 (d, 2H, 3J=4.6 Hz, 3,17-H); 8.89 (m, 7,8,12,13-H); 8.22 (m, 6H, 2',6'-H); 8.05 (m, 6H, 3',5'-H); -3.16 (br.s, 2H, 21,23-H). MS (MALDI-TOF, MeOH), C[8H26N4O9S3 (H2P(PhSO3H)[): calculated m/z 778.82; found 778.95

The Supporting Information is available free of charge on the www.macroheterocycles.isuct.ru website at DOI 10.6060/ mhc170833s.

Results and Discussion

DFT study of meso-phenylporphyrin sulfonation regioselectiviy in sulfuric acid

Reaction regioselectivity and pathways of meso-phenylporphyrin sulfonation were analysed using DFT/ B3LYP/3-21G(d,p) theory level calculated charges of NCs (kinetic control) and total formation energies of sulfonated derivatives El (thermodynamic control), based on four postulates:

1. The driving force of meso-phenylporphyrins dissolution in sulphuric acid is the formation of supramolecu-lar complexes of doubly protonated porphyrinic platform H4P2+ which is an anion receptor[12-15] with two hydrosulfate anions (1).

H"2P(Ph)n(solid)+2H2SO4 ^ [H4P2+(Ph)n](HSO4-)2(Sol-n) (1)

2. Porphyrinic sulfoacids are non-electrolytes in CSA.[16]

3. Sulfonation of meso-phenylporphyrins in CSA proceeds via the SEAr mechanism and is reversible due to acidic hydrolysis of the formed sulfoacids with residual water (2). The yields of sulfonation products are determined by the charges of nucleophilic centers (5j- and 52-) and the relative thermodynamic stability (AEj) of competing isomers. If the reaction is carried out in oleum, it is irreversible.

iC — H + H3SO4+ :/

w-

IC— SO3H + H30+

(2)

4. When CSA is used as the reaction medium, NCs with 5j- > -0.108 are active. This value corresponds to the maximal charge of NC in nitrobenzene, which does

HF(Ph)4

^P^Ph^

BC* isomer of [^P^Pty^HSO;),

planar 1,3-alternate

* guest anions are localized in the vicinity of pyrrole rings B and C

A "double roost" complex

Figure 4. Optimized molecular geometry of HjP(Ph)4, H4P2+(Ph)4, and [Н4Р2+(Ph)4](HSO4■)2. Numbers denote the values of Sr for NCs that are active in CSA. For the two latter compounds, orthogonal phenyl rings are not shown for clarity.

not react with CSA. Nucleophilic centers with 5j- < -0.108 undergo sulfonation in oleum.

Regioselectivity of 5,10,15,20-tetraphenylporphine sulfonation

We initially performed regioselectivity DFT modelling for H2P(Ph)4 which has the simplest molecular structure with no NCs in weso-positions of the porphyrinic platform (Figure 4).

The process of H2P(Ph)4 dissolution in CSA (1) can be divided into two steps: double protonation of the porphyrin platform with the formation of an H4P2+(Ph)4 anionic receptor, followed by the formation of dihydrosulfate host-guest complex (3).

H2P(Ph)4+2H2SO4 S H4P2+(Ph)4+2HSO; S

S [H4P2+(Ph)4](HSO;)2 (3)

The starting molecule of H2P(Ph)4 has active NCs in 7, 8, 17, 18 positions of the main conjugation circuit of H2P and in 4' positions of the phenyl rings. Double protonation of H2P(Ph)4 leads H4P2+(Ph)4 to be completely inert in CSA due to a dramatic fall of 5j- charges on all NCs of the formed dication. Diprotonated H4P2+ platform is an elastic 1,3-alternate with two pairs of opposite NH groups that are hydrogen bond donors. This, together with a circuit-delocalized positive charge, leading to the formation of twin bidentate coordina-

tion sites, pre-organized for a synergetic hydrogen and electrostatic bonding with contacting atoms of guest anions. An axial complex of the "double roost" type is formed as the result.[12] The H4P2+(Ph)4 receptor possesses high complementarity towards the contacting atoms of HSO4- anions. The mean value of hydrogen bond angles in [H4P2+(Ph)4](HSO4-)2 complex is 174.30, which is close to the ideal value of 180°. Guest anions exhibit a strong and determining influence on the reactivity of H4P2+(Ph)4. First, they activate H4P2+(Ph)4 for electrophilic substitution by transferring a total of -0.733 unit charge to the macrocycle. The 5j- charges of NCs in 4' positions of phenyl rings of [H4P2+(Ph)4](HSO4-)2 are -0.111, that is equal to the value for benzene, which easily undergoes sulfonation in CSA even at 40 °C with a 90 % yield. Second, guest anions cause a total charge redistribution on carbon atoms of H4P2+ which provides supramolecular-driv-en regioselectivity of sulfonation of H4P2+(Ph)4 in its dihy-drosulfate complex. Meanwhile, positions 4' remain the only active NCs of the complexes during all stages of sulfonation in CSA, which is in complete accord with experimental data (Figure 5, Table P1).

All the formed 4'-sulfoacids H4P2+(Ph)4 afford dihydrosulfate complexes, which can exist in different isomeric forms with different positions of the two guest anions, namely AB, BC, CD, and AD types. The letter notation shows near which pyrrole rings the guest anions are localized (Figure 4). The isomeric complexes have different thermodynamic stability (Figure P1). Only the most stable isomers are shown

Figure 5. Prognostic scheme of sulfonation of H2P(Ph)4 in sulfuric acid and oleum, including DFT calculated data. Numbers denote the Sj-values of the nucleophilic centers related to sulfonation. Numbers in brackets denote the S2- values of the nucleophilic centers related to acidic hydrolysis.

in Figure 5, as intramolecular rearrangements of the isomers occur more rapidly than intermolecular sulfonation reaction steps. All 4'-position NCs are equal and independent until [H4P2+(PhSO3H)3(Ph)](HSO4-)2 is formed. The most stable isomer AB [HP2+(PhSO3H)3(Ph)](HSO4% does not react

of the active phenyl ring's NC is lowered to -0.110. In practice, the above data should manifest in a quick build-up of AB isomer of [H4P2+(PhSO3H)3(Ph)](HSO4-)2 followed by its slow sulfonation into [H4P2+(PhSO3H)4](HSO4-)2. A paper by J. Winkelman et al.[2] describes a slowdown

with CSA, because it contains no NCs with -5,-> -0.108. In effect for the step of [H4P2+(PhSO3H)3(Ph)](HSO4-)2 forma-

order to perform further sulfonation, an energy-demanding AB^AD rearrangement is required. Moreover, the 5j- value

tion. The authors subjected H2P(Ph)4 to sulfonation is CSA at ambient temperature for 36 h and obtained a mixture

10 15 20 time (min)

25 30

100 90

so

70

)

Ь 60

Ф

^ 50

(0 о

£ 40 о

e

н 30

2o 10 o

10 15 20 time (min)

25 30

Figure 6. On the left - relative yields of products of H2P(Ph)4 sulfonation in CSA at 100 °С. On the right - results of mathematical modelling of stepwise H2P(Ph)4 sulfonation with a kinetic constants ratio of 1:(0.1;0.06;0.00014). The numerals correspond to the amount of sulfo-groups.

0

0

5

5

of di-, tri-, and tetrasulfoacids with the respective yields of 19.6 %, 76.0 %, and 3.9 %. When we performed sulfonation of H2P(Ph)4 in CSA at 100 oC (using the procedure of C.A. Busby et al.),[5] we confirmed our DFT calculations data (Figure 6). Under such conditions, a mixture of mono- and disulfonated products is already formed after a 5 min heating of the reaction mixture (preliminary thoroughly ground in a mortar). After a 15 min period, most of the porphyrin was converted into the tri-sulfoacid, which then undergoes a relatively slow conversion into the final tetrasulfoacid. The tri-acid H2P(PhSO3H)3(Ph) was isolated with a 60 % yield when the reaction was interrupted after a 15 min period. The result is in accord with the mathematical model of H2P(Ph)4 sulfonation, the kinetic constants ratio is 1:(0.1;0.06 ;0.00014).

Sulfonation of meso-phenylporhyrins in CSA is reversible due to acidic hydrolysis of the formed sulfoacids (3), which leads to lowered yields.[10] The values of 52- charges for all 4'-sulfoderivatives of [H4P2+(Ph)2](HSO4-)2 and [H4P2+(Ph)4](HSO4-)2 are in the range of -0.390 - -0.393, which is almost equal to the value of -0.393 for benzenesul-foacid. Such 52- values correspond to low hydrolysis rates, thus, the fractional yields of the products of exhaustive sulfonation of H2P(Ph)4 and H2P(Ph)2 in CSA are always the highest (Table P1). The experimental data shown in Figure 5 also demonstrate that sulfonation steps should be the same for H2P(Ph)4 in sulfuric acid and in oleum, until [H4P2+(PhSO3H)4](HSO4-)2 is formed, which can be subjected to further sulfonation with oleum into a sulfone.[9]

Using DFT calculations to predict the results of 5,10,15-triphenylporphine sulfonation

The prognostic scheme of H2P(Ph)3 dissolution and sul-fonation in CSA, including the calculated data, is shown in Figure 7.

A distinctive parameter of H2P(Ph)3 is a relatively high 5j- charge (-0.150) on C-20 atom, which is significantly higher than the charges of other NCs of this molecule and H2P(Ph)4. The charge value for C-20 remains elevated on all steps of dissolution and sulfonation of H2P(Ph)3. The dihydrosulfate complex [H4P2+(Ph)3](HSO4-)2, which is formed as the result of dissolution of H2P(Ph)3 in sulfuric acid, has three isomers: AB, BC, and AD (Figure P2). The most stable isomer BC exhibits a transfer of -0.742 charge from guest anions onto the macrocycle and an averaged > N-H--O-SO3H- hydrogen bond angle of 173.6°. The guest anions direct the electrophilic attack to position 20 of the porphyrin platform and positions 4' of the phenyl rings on all steps of [H4P2+(Ph)3](HSO4-)2 sulfonation. These competing NCs have different reactivity which is determined by a combination of kinetic activity parameters (5j-, 52-) and relative thermodynamic stability of the isomeric sulfoacids (A£1). Position 20 has significantly higher values of 5f (-0.132--0.135) and S2- (-0.492 - -0.474) charges compared to the corresponding values of positions 4': 5j-(-0.110 - -0.111) and S2- (-0.392 - -0.393). Thus, position 20 exhibits greater kinetic activity in both the direct sulfonation reaction and the reverse acidic hydrolysis reaction (2). Furthermore, the isomeric 20-sulfoacids possess lower thermo-dynamic stability compared to the 4'-sulfoacids. At substan-

tially high hydrolysis rates of 20-sulfoacids, the corresponding 4'-sulfoacids should be the major products of H2P(Ph)3 sulfonation in CSA. Analysis of the calculated data shows that 5j- , 52-, and AEj parameters of these two competing NCs depend on the number of meso-phenyl substituents connected to the porphyrinic platform. Therefore, sulfonation of positions 20 and 4' in [H4P2+(Ph)3](HSO4-)2 should proceed in CSA and oleum in a similar way it does for [H4P2+(Ph)2](HSO4-)2 and [H4P2+(Ph)4](HSO4-)2. High hydrolysis rates of porphyrinic meso-sulfoacids were reported by H. Garcia-Ortega and J.M. Ribo,[10] the authors demonstrated that vacant meso-positions in H2P(Ph)2 indeed undergo sulfonation only in oleum, while in CSA only 4'-sulfoacids are formed. We conclude that for 52- > -0.474 hydrolysis completely suppresses sulfonation of vacant meso-positions in phenylporphyrins and the final product, if the reaction of H2P(Ph)3 is carried out in CSA is only H3P(PhSO3H)3. If oleum is used as the reaction medium, only direct sulfonation reaction dominates, which leads to a very rapid sulfonation of position 20 of the por-phyrinic platform followed by a subsequent sulfonation of 4' positions of three phenyl rings.

The prognostic capabilities of scheme shown in Figure 7 was demonstrated in this work by a synthesis of a novel water-soluble 5,10,15-tris(4-sulfophenyl)porphine, which was isolated as the only product of H2P(Ph)3 sulfonation in CSA.

Synthesis of 5,10,15-tris(4-sulfophenyl)porphine triple ammonium salt

A modified procedure of C.A. Busby et al.[5] was used to carry out sulfonation, purification and isolation of H2P(Ph)3 (see Experimental). was obtained as the only product with a 69 % (127.3 mg) yield. 'H NMR spectrum of the sulfonated product is presented in Figure 8. In [D6]DMSO, which is a polar and basic solvent (e=46.68; DNSbCl5=29.8), the ammonium salt of porphyrin sulfoacid dissociates with the formation of H2P(PhSO3-)3 trianion, which is not prone to aggregation in concentrated solutions used for NMR studies. This was further proved by recording an electronic absorption spectrum of a thin film of the solution on the inner surface of the NMR tube and a spectrum of the same solution diluted to about 10-4 M (Figure P3).

MS spectrum of H2P(PhSO3H)3 is shown in Figure 9. Under spectrum registration conditions the salt H2P(PhSO3NH4)3 loses ammonia and transforms into tri-sulfonic acid H2P(PhSO3H)3 with corresponding signal of main product. Two supplementary signals (m/z: 800.96 and 816.88) correspond to impurities of monosodium (+22.01) and monopotassium (+37.93) salts, which were obtained as a result of H2P(PhSO3H)3 interaction with glass vessel.

Optical spectroscopy

A H2P(PhSO3-)3 trianion is formed when H2P(PhSO3NH4)3 is dissolved in water. The absorption and fluorescence spectra of an aqueous p^-neutral solution of H2P(PhSO3-)3 are shown with key parameters in Figure 10. Aqueous solutions of H2P(PhSO3-)3, diluted to about 10-4 M and below, obey the Beer law A=elC with a linearity coefficient not less than 0.999 (Figure 11).

CONCENTRATED SULFURIC ACID

_KHSO4-)2

-0.111 HOjSt;

(-0.393)

J2*(HSO/):

_|2*(Hso4b

J2*(HSO,-)2

_KHSO,-)2

(-0.392) (-0.392)

_Кнзо,"Ь

_|2*(HSO,-)j

SO,H HO,s<; (-0.361) (-0.—л

J2*(HS04-)2

h" J2*(HS04"h

Figure 7. A prognostic scheme of H2P(Ph)3 sulfonation in sulfuric acid and oleum, including the DFT calculated data. Numbers denote the values of Sj- for the nucleophilic centers of sulfonation. Numbers in brackets denote the values of S2- for the nucleophilic centers of acidic hydrolysis.

A(s) -3.16

A(s) 1IS6&

JI

Bf(d)

[¿«I

so3-

-3.1 -3.2 fl (Mfl)

k(m) F(m)

¡8.22 8.08

\\

o3s

y*/ 21

3—2 1

3=7

; 1 \ J

N=V

HN 1'

l-NH

2—3

//

S<h

y

-N

V

■1 .L

T"

___J v_

T

TH

_y y U

-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-1-'-r

10.6 10.5 10.4 10.3 10.2 10.1 10.0 9.9 9.8 9.7 9.6 9.5 9.4 9.3 9.2 9.1 9.0 8.9 8.8 8.7 8.6 8.5 8.4 8.3 8.2 8.1 8.0

fl (Mfl)

Figure 8. 1H NMR spectrum of H2P(PhSO")3 solution in [D6]DMSO.

Figure 9. MALDI-TOF spectrum of H2P(PhSO3H)3 (without using matrix).

Wavelenght (nm) Concentration of porphyrin xio5 M

Figure 10. Optical spectra of H2P(PhSO3-)3 aqueous solutions at 25 °C and pH=7. Absorption (solid curve) Xmax nm (lge): 407 (5.418), 510 (3.897), 545 (3.494), 573 (3.508),m628 (3.186). Fluorescence (dot-dash curve), X , nm: 637, 694.

v '' max' '

Figure 11. Compliance with Beer law in aqueous solutions of HjP(PhSO3-)3 at 25 °C.

Conclusion

Regioselectivity of meso-phenylporphyrin sulfonation is supramolecular-directed. Understanding of the mechanism of this phenomenon allows the use of modern computational chemistry methods to explain the already accumulated experimental material on the synthesis of the corresponding sulfo-derivatives and for the purposeful preparation of 10,15-tr/s(4'-sulfophenyl)porphine. Since this regi-oselectivity is due to the properties of the diprotonated porphyrin platform anion complexes, this approach can be extended to other numerous electrophilic substitution reactions of porphyrins in acidic media (for example, nitration in the NaNO2 - CF3COOH system).[17]

Acknowledgements. Financial support by Russian Science Foundation (Project No. 14-23-00204-P). We thank the Centre for joint use of scientific equipment "The upper Volga region centre of physico-chemical research". The authors are grateful to Dr. Viktor V Aleksandriiskii and Dr. Alexander V. Zavialov for their help.

References

1. Menotti A.R. Doctoral Dissertation. Columbus: The Ohio State University, 1941.

2. Winkelman J., Slater G., Grossman J. Cancer Research 1967, 27(1), 2060-2064.

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Received 26.08.2017 Revised 09.10.2017 Accepted 14.10.2017