Polymerization of aromatic nuclei. XIX. Polymerization of thiophene by aluminum chloride

Thiophene was polymerized in high yield on exposure to aluminum chloride in solvent under mild conditions. Experimental evidence [IR, NMR, UV, and mass spectra, elemental analyses, reductive desulfurization, and comparison with the literature trimer of thiophene (prepared with phosphoric acid)] suggests the following structure: From gel permeation chromatography an average weight of 1290 was obtained, which corresponded to the presence of 15 rings; the highest-molecular-weight chains contained about 192 rings. Mechanistically, participation of cationic intermediates is proposed. Apparently chain extension can occur by various routes, including participation of neutral oligomer molecules.     

Polychlorination of thiophene. A reinvestigation

Some old controversies in the literature with regard to the structures of trichlorothiophenes have been elucidated. In the course of these studies, we found that the best method for the preparation of 2,3,5-trichlorothiophene is the direct chlorination of thiophene in the presence of catalytic amounts of ferric chloride. If 2,5-dichlorothiophene is available 2,3,5-trichlorothiophene can also be obtained in good yields through chlorination with thionyl chloride and sulfuryl chloride, using aluminum trichloride as catalyst.     

Polymerization of aromatic nuclei. XIV. Polymerization of toluene with aluminum chloride–cupric chloride

The polymerization of toluene with aluminum chloride and cupric chloride was performed in carbon disulfide and in a neat system. The solvent reaction produced an insoluble, light-brown product which did not melt below 350°C. In the neat system, polymerization was much more vigorous, yielding a dark, purple-brown solid with mp ～250°C and molecular weight of 634. Infrared, NMR, and ultraviolet spectroscopy, along with elemental analysis and oxidative degradation, indicated that the backbone chain contains o-polyphenylene units with the methyl group situated in the 4-position. Some p-polyphenylene structures may also be present. Evidence for small amounts of benzyl and polynuclear moieties was obtained. The mechanistic aspects are discussed. Our principal conclusions concerning oligomer structure are in disagreement with those of Kuwata.     

Polymerization of aromatic nuclei. VIII. Molecular weight control in benzene polymerization

The molecular weight of p-polyphenyl prepared from benzene—aluminum chloride—cupric chloride, was affected by solvent, concentration, and temperature. Relative molecular weights were measured by polymer solubility in chloroform, and positions of the infrared para band and ultraviolet reflectance λ_max. The order of effectiveness of the solvents in reducing molecular weight was: o-C₆H₄Cl₂ > 1,2,4-C₆H₃Cl₃ > SnCl₄ ～ CS₂ > [C₆H₆]. Degradative oxidation revealed that o-dichlorobenzene solvent was incorporated as an endgroup to only a minor extent. In general, the molecular weight of p-polyphenyl decreased with increasing temperature and with decreasing concentration. The theoretical aspects are treated.     

Polymerization of aromatic nuclei. XII. Oligomerization of halobenzenes by aluminum chloride-cupric chloride

Polymerization of chloro- and fluorobenzene by aluminum chloride-cupric chloride produced highly colored oligomers. Chlorobenzene reacted under the standard conditions, i.e., 6/1/0.5 (molar ratio) of aromatic/catalyst/oxidant at 60°C. for 1 hr., to give a red solid in 14% yield. Evidence concerning the structure was obtained from elemental analyses, infrared and ultraviolet spectra, dechlorination, oxidation, solubility, molecular weight, and color. The data indicate that the backbone chain consists of an o-polyphenyl structure with chlorine atoms situated at the 4-positions. Polynuclear regions presumably comprise part of the structure. Molecular weight data pointed to an average of 10–12 units per chain. The coupled product from fluorobenzene was very similar to the chlorobenzene oligomer in most respects. In contrast to the chlorobenzene case, there was evidence of propagation occurring to some extent by attack ortho to the fluorine. Bromobenzene produced brominated p-polyphenyl apparently by disproportionation to benzene which then functioned as the monomer. An oxidative cationic mechanism (σ polymerization) is proposed for the nuclear coupling.     

Polymerization of aromatic nuclei. XVII. Catalytic hydrogenation of poly(p-phenylene)

Hydrogenation of poly(p-phenylene) (I) in cyclohexane at high temperature and pressure with rhodium catalyst gave, in low yield, oligomers of 1,4-cyclohexylene(II) in the range of 2–16 cyclohexyl units per chain. Apparently only the low molecular weight fraction in I is reduced because of extreme insolubility. II, which appears to be a novel class, was characterized by molecular weight, ¹H-NMR, ¹³C-NMR, and infrared spectra, gas chromatography, and microanalyses. Dicyclohexyl and perhydro-p-sexiphenyl served as model compounds for comparison in characterization of II.     

A reinvestigation of alloxan-like compounds derived from uric acid

The structures of two isomeric intermediate in the oxidative conversion of uric acid ($\text{1}$) to alloxan ($\text{5}$) are revised and the compounds shown to be uric acid glycol ($\text{3}$) and 5-hydroxy-pseudouric acid ($\text{4}$), respectively.     

Polymerization of aromatic nuclei. XV. Polymerization of 2,5-di- and 2,3,5-trichlorothiophenes with aluminum chloride–cupric chloride

2,5-Dichlorothiophene was polymerized to a solid in 93% yield on treatment with aluminum chloride–cupric chloride in carbon disulfide under mild conditions. The product is believed to be poly-5-chloro-2,3-thienylene on the basis of elemental analysis and infrared and NMR spectral data. Hydrogen chloride was collected in 90% of the theoretical amount. Dimer- and tetramer-type fractions were isolated from the polymer. 2,3,5-Trichlorothiophene underwent an analogous transformation in trichlorobenzene at 90–100°C. Polythienylenes coupled through the 2,3-positions have not been reported previously. The net effect of the reaction is nuclear coupling by dehydrohalogenation. We believe that the mechanism involves cationic polymerization accompanied by loss of hydrogen chloride. 2-Chlorothiophene and thiophene gave products of complex make-up.     

Polymerization of aromatic nuclei. X. Polymerization of benzene to p-polyphenyl oligomers by nitrogen dioxide—aluminum chloride

Benzene was polymerized to p-polyphenyl oligomers by nitrogen dioxide–aluminum chloride. Polymer production was favored by AlCl₃:NO₂ ratios of at least 2, long reaction times, and higher temperatures. Evidence for the polymer structure was obtained from elemental analyses, oxidative degradation, solubility, molecular weight, functional group tests, low molecular weight products, and infrared and ultraviolet spectra. The chains contained small amounts of chloro, amino, hydroxyl, and carboxyl substituents. Molecular weight data on the benzene-soluble portion (40–71%) revealed an average of 4–6 phenylene units per chain. Under altered conditions nitrobenzene could be obtained as the major product, indicating the sensitivity of the system to changes in reaction variables. With nitrobenzene as oxidant, a similar type of polymer resulted. The theoretical aspects are discussed.     

Effect of addition of trifluoroacetic acid on the photophysical properties and photoreactions of aromatic imides

The UV and IR spectra of N-methyl-1,8-naphthalimide in benzene showed a two-step consecutive complexation (hydrogen bond formation) with trifluoroacetic acid (TFA). The equilibrium constant K₁ for the first complexation in benzene was determined from the UV spectrum to be 48 M⁻¹. The fluorescence intensities of the imide in benzene were found to be remarkably enhanced by the addition of TFA. Furthermore, photochemical cyclobutane formation of the imide with styrene in benzene was enhanced by the addition of TFA. Enhancement of the fluorescence intensity and the photoreaction of the imide by complexation with TFA was explained by a decrease of the efficiency of the intersystem crossing from ¹(ππ^∗) to ³(nπ^∗), that results from an increase in the energy of the ³(nπ^∗) level due to the complexation.     

Polymerization of aromatic nuclei. XXVII. ESR studies on polymers and oligomers from reaction of benzenoid and naphthalene monomers with lewis acid catalyst–oxidant systems

Chlorobenzene and toluene were polymerized with aluminum chloride–cupric chloride to produce materials that consist mainly of poly(o-phenylene) structures. These species exhibited radical cation concentrations comparable to that of poly(p-phenylene). Polymerization of naphthalene and 1-chloronaphthalene with aluminum chloride–cupric chloride or ferric chloride–water also resulted in products with high radical cation concentrations. Polynuclear structures may be responsible for the paramagnetic character; alternatively, p-quinoidal moieties may be present in naphthalenes. The depth of color in the samples is directly related to the concentration of radical cations.     

Polymerization of aromatic nuclei. XVIII. Polymerization of benzene to poly-p-phenylene by aluminum chloride–air–water

Although the reaction of benzene with aluminum chloride has been quite thoroughly examined by prior investigators, the present report is the first one on formation of poly-p-phenylene in this system. Optimum conditions, which gave low yields, involved 7 days at 49–51deg;C. The presence of oxygen (oxidant) and presumably water (cocatalyst) was necessary in order for polymerization to occur. Physical and chemical properties, e.g., behavior toward Br₂ and H₂O₂–CH₃CO₂H, indicate that the polymer structure is slightly different from that of the material from C₆H₆–AlCl₃–CuCl₂. The polymer from C₆H₆–AlCl₃ may possess a lower molecular weight and exhibits a greater degree of structural irregularity in the form of dihydrobenzene, p-quinoid, or polynuclear regions. In the chemical studies, various compounds were used as models (tetrahydroquaterphenyl, triphenylene, and lower p-polyphenyls).     

Efficient epimerization of pyrene and other aromatic C-nucleosides with trifluoroacetic acid in dichloromethane

Trifluoroacetic acid has been found to be an efficient and non-oxidative catalyst for the epimerization of pyrene and other C-nucleosides in dichloromethane at ambient temperature. Aspects of the epimerization mechanism are also elucidated.     

Polymerization of aromatic nuclei. XXV. ESR and chemical studies on the radical cation nature of poly(p-phenylene)

The radical cation nature of poly(p-phenylene) (PPP) was examined by electron spin resonance (ESR) and chemical means. ESR studies revealed a radical concentration of 1.0 × 10²¹ spins/g for the crude polymer. Workup with aqueous acid decreased the value to 1.5 × 10¹⁸ spins/g. Reactions of the polymer with certain nucleophiles followed the half-regeneration mechanism, whereas with others, electron transfer mainly occurred. The origin of halogen in the polymer was found to arise from reaction of the radical cation with the oxidant, and not with halide during workup. Oxidation of PPP with various species increased the concentration of radical cations.     

A reinvestigation of the bamberger-ham phenazine. Synthesis: A limitation

The Bamberger-Ham condensation of 4-substituted nitrosobenzenes in concentrated sulfuric acid reported as a method of synthesis for phenazine N-oxides has been found to be limited to electron donating substituents. Methyl 4-nitrosobenzoale has been found to react under these conditions to give dimethyl 2-nitrodiphenylamine-4, 5-diearboxylate ( 2 ). Compounds of unknown structure previously reported to arise from acid treatment of 4-bromo- and 4-chloronilrosobenzene have been shown to be 4, 5-dibromo-2-nitrosophenylamine ( 10 ) and the analogous dichloro compound. Treatment under stronger acidic conditions (oleum) converted 10 but not 2 into the corresponding phenazine N-oxide. Mechanistic implications are discussed.