Sh. S. Akhmetzyanov

Formation of mono-, bi-, and polyradicals upon reduction of poly(arylenesulfophthalides) by metallic lithium

The reduction of poly(biphenylenesulfophthalide) (1), poly(fluorenylenesulfophthalide) (2), and poly(terphenylenesulfophthalide) (3) by metallic lithium in DMSO was studied using UV-visible and ESR spectroscopies. The reduction of compounds 1 and 2 affords blue diamagnetic color centers with absorption bands at 568 and 350 nm (shoulder) for 1 and at 576 and 360 nm (shoulder) for 2. The color centers were attributed to quinoid structures of the Chichibabins hydrocarbon type, being biradicals in the ground singlet state. The spectra of compounds 1 and 2 also exhibit weak absorption bands at ∼420 nm, which are assigned to monoradicals of the triarylmethyl type. The reduction of compound 3, for which the formation of quinoid structures is energetically unfavorable, leads to polyradicals of the triarylmethyl type with a high content (∼100%) of unpaired electrons in the main polymer chain. These radicals are characterized by absorption bands at 430 nm (allowed transition) and 638 nm (forbidden transition). The paramagnetic centers in all polymers under study give singlet lines with g = 2.0028 and ΔH ∼ 10 Oe in the ESR spectra. The color centers and radicals of the triarylmethyl type observed for the poly(arylenesulfophthalides) under study are assumed to be formed upon the dissociative electron transfer from lithium to the sulfophthalide cycles of the polymeric molecules. The PM3 calculations show a high electron affinity of the sulfophthalide cycle and a higher propensity of the fluorenyl bridge to form quinoid structures than that of the biphenyl bridge.

Formation of color centers and paramagnetic species by alkaline hydrolysis of polydiphenylenesulfophthalide

Blue color centers (CC) (an intense absorption band (AB) at 566 nm and a weaker AB at 350 nm) and paramagnetic species (PMS) that give an ESR singlet withg=2.0028 and δH=10 Oe are formed by the treatment of a DMSO solution of polydiphenylenesulfophthalide with an excess of LiOH. The formation of blue CC is accompanied by a decrease in the intensity of the absorption band of the phenyl groups of the polymer at 270 nm. The blue CC were attributed to quinoid structures like the Chichibabin hydrocarbon. The long-wave absorption at 650–800 nm was assigned to the regions of quinoid-benzoid conjugation. The color centers and PMS were also observed when the polymer was hydrolyzed in cyclohexanone; however, in this case, the reaction was accompanied by polymer aggregation. The electronic spectrum of the Chichibabin hydrocarbon was calculated by the PM3 method. The identity of CC formed by alkaline hydrolysis and appearing in the polymer—aniline—cyclohexanone system was shown. The absence of “quinoid” CC for polyterphenyl sulfophthalide was explained by the energetically unfavorable singlet state for structures similar to the Müller hydrocarbon.

IR spectroscopic manifestations of hydration of poly(diphenyl sulfophthalide) during its storage

IR spectroscopy measurements show that films of poly(diphenyl sulfophthalide) (PDSP), a cardo polymer, interact with atmospheric moisture during storage at room conditions. A total of 15 absorption bands were isolated in spectra of PDSP hydrated during storage, which belong to sorbed water and hydrolysis products. A number of absorption bands (within 1500–1800 cm−1 and 980–1100 cm−1) were obtained by subtracting the spectrum of the film after heating from that of the initial hydrated film. At least six individual bands in the region of the O-H bond stretching vibration were isolated by decomposing a broad complex band (3700–2000 cm−1) into Gaussian components. The isolated bands were tentatively assigned based on the available literature data and quantum-chemical calculations of the characteristics of a number of complexes of a diphenyl sulfophthalide model compound with water molecules. The IR spectra and energies of the hydrogen bonds formed were calculated at the B3LYP/6-311G(d, p) level. In particular, the absorption bands at 1010 and 1079 cm−1 were assigned to the symmetric stretching vibrations of the S=O bonds in the −SO3− anion, the 1062-cm−1 absorption band, to ν(C-OH), and the absorption bands at 3646, 3586, and 3475 cm−1, to complexes of water with sulfophthalide cycles of the polymer. After a long storage, PDSP largely transforms into a polymeric oxonium salt, and its spectrum becomes similar to that of a polymeric salt prepared by alkaline hydrolysis. A general mechanism of the interaction of PDSP with water is proposed, according to which the hydrolysis of the sulfophthalide cycles (SPC) by sorbed water yields new hydrophilic groups, sulfoacid, and hydroxyl groups. A further sorption of water by the sulfoacid results in its ionization and the formation of various hydroxonium forms. Sorption and hydrolysis are reversible processes: water is desorbed and the SPC is recovered when the polymer is heated to 100–150°C, as can be judged from an increase in the intensity of the S=O bond vibrations of the sulfophthalide cycle at 1352 and 1192 cm−1. The possibility of using strongly hydrated PDSP for manufacturing proton-conducting membranes is discussed.

Sulfophthalide cycle cleavage and formation of fluorenyl structures upon poly(diphenylene sulfophthalide) thermolysis

Thermolysis of poly(diphenylene sulfophthalide) (PDSP) in the temperature range from 100 to 500 °C was studied by IR and UV-Vis spectroscopy and thermogravimetric analysis. A series of absorption bands in the IR spectrum of PDSP were assigned on the basis of the theoretical calculations of the IR spectrum of diphenyl sulfophthalide used as a model compound, in particular, νas(S=O) = 1352 cm−1, νs(S=O) = 1196 cm−1, ν(C-O) ∼ 920 cm−1, ν(S-O) = 824 cm−1, and δ(SO2) = 576 cm−1. The sulfophthalide cycle (SPC) in PDSP decomposes at the thermolysis temperatures in a range of 260–400 °C. An analysis of the IR spectra of the thermolyzate and the quantum chemical calculations of the IR spectra of the model compounds confirmed the predominant formation of fluorenyl structures in the thermolyzed polymer. The changes in the UV-Vis spectra observed upon the thermolysis of thin films of PDSP (the hypsochromic shift of the long-wavelength absorption band from 271 to 263 nm and the appearance a shoulder at ∼310 nm) and the results of TD-DFT calculations of the UV-Vis spectra of the model compounds are consistent with the hypothesis about the formation of fluorenyl structures. The general scheme of PDSP thermolysis at 260–400 °C was proposed in which the major process is the formation of fluorenyl fragments in macromolecules of the polymer due to the intramolecular ring closure in biradicals formed by the SPC cleavage.

Formation of triphenylmethyl radicals upon alkaline hydrolysis of diphenyl sulfophthalide

Triphenylmethyl radicals (TPMR) with ano-positioned sulfonate group are generated by alkaline hydrolysis of diphenyl sulfophthalide in DMSO. Electronic and ESR spectra of these radicals are characterized. It is suggested that the radicals result from one-electron transfer reactions. Triarylmethyl radicals are also formed in alkaline hydrolysis of polyarylenesulfophthalides.

COLOR REACTIONS OF POLYARYLENESULFOPHTHALIDES IN ANILINE-CYCLOHEXANONE MIXTURES IN AIR

Slow color reactions occur when some polyarylenesulfophthalides are dissolved in an aniline—cyclohexanone mixture; these reactions involve generation of triarylmethyl type radicals that were characterized by ESR and UV spectroscopy.

Formation of triphenylmethyl radicals in the thermolysis of polydiphenylenesulfophthalide and polytriphenylcarbinol

Triphenylmethyl radicals are formed in the thermolysis of polytriphenylcarbinol and polydiphenylenesulfophthalide, which give rise to ESR singlets with poorly resolved hyperfine structure and two bands in the electronic absorption spectra.

Radical products of thermal decomposition of polydiphenylenesulfophthalide

The investigation of the vacuum thermal decomposition of polydiphenylenesulfophthalide at 100–530 °C showed that there are at least four main types of paramagnetic species (PMSs). The ESR spectrum of type I PMSs (120–250 °C) has a signal (g = 2.0028; ΔH ∼1 mT) with a poorly resolved hyperfine structure (HFS) and an even number of lines. The electronic spectrum of these particles shows an absorption band at ∼410 nm. These particles were assigned to “low-temperature” triarylmethyl-type radicals (TAMTR), which are apparently generated from dioxothioxanthene defect structures of the polymer. Type II PMSs (250–360 °C) give a smooth symmetrical ESR singlet (g = 2.0028; ΔH ∼1 mT) and two absorption bands in the electronic spectrum at ∼410 nm (strong band) and ∼710 nm (weak band). Based on the results of calculations of electronic spectra for a series of model structures at the TD-DFT B3LYP/6-311G(d,p) level of theory, these PMSs were assigned to “high-temperature” TAMTR, which have a fluorenyl structure and are formed through the opening of the sulfophthalide ring. The maximum concentration of TAMTR II (∼1020 spin g−1) is achieved at 320 °C. At T > 320 °C, type II radicals decay and type III radicals are generated. The latter are condensed aromatic species presumably having a phenalene structure. In the temperature range of 350–450 °C, the ESR line width and shape remain mainly unchanged, which attests to the retention of the dominant structure of the radicals. An increase in the thermal decomposition temperature to ∼450 °C or above leads to a decrease in the ESR line width and a change in its shape from the Gaussian to Lorentzian type. This fact is an evidence of type IV paramagnetic species corresponding to even higher condensed aromatic structures.

On thermal stability of polydiphenylenesulfophthalide lithium salt

Thermolysis of polytriarylcarbinol (PTAC-Li) (lithium salt of polydiphenylenesulfophthalide (PDSP)) was studied in the temperature range from 100 to 500 °С by thermogravimetric analysis (TG) and IR and electronic spectroscopy to check the available data on the higher thermal stability of PDSP salts over the initial polymer. The mass losses detected by the TG method in the polymer salt at 80—150 and 240—350 °С are mainly caused by the desorption of weakly and strongly bound water. According to the calculations in the B3LYP/6-311+G(d,p) approximation, the С—ОН and C—SO3-Li+ bonds are weakest in the carbinol model for PTAC-Li (D(C—O) ~ D(C—S) ~ 72 kcal mol–1). The thermolysis of PDSP is accompanied by SO2 evolution, whereas hydroxy and sulfo groups detached from PTAC-Li macromolecules remain in the thermolyzate. Phenol fragments and an inorganic phase, the final form of which is lithium sulfate, are formed in this process. An analysis of the IR and UV spectra of the thermolyzates of PTAC-Li and PDSP confirmed that fluorenyl fragments are predominantly formed upon the thermolysis of these polymers. The data obtained do not confirm a higher stability of PTAC-Li compared to that of PDSP.

Some chemical reactions in the polydiphenylenesulfophthalide—aniline—cyclohexanone system

Two main reactions were observed in the polydiphenylenesulfophthalide—aniline—cyclohexanone ternary system by13C NMR and IR spectroscopy: (1) condensation of aniline and cyclohexanone to give the corresponding anil; (2) opening of the sulfophthalide ring in the polymer under the action of aniline. Both reactions also take place in the corresponding binary mixtures, and they should be taken into account in studies of the color and paramagnetic centers in this ternary system.