Properties of organosoluble aromatic polyimides from 3′-trifluoromethyl-3,4′-oxydianiline

A colorless fluorinated diamine, 3′-trifluoromethyl-3,4′-oxydianiline (3′-CF₃-3,4′-ODA) (II) was prepared through the nucleophilic substitution reaction of 3-nitrophenol and 2-chloro-5-nitrobenzotrifluoride by catalytic reduction with hydrazine and Pd/C. A series of Polyimides V were synthesized from the diamine II with various aromatic dianhydrides III_a-f via thermal and chemical imidization. These polyimides had inherent viscosities ranging from 0.88 to 1.12 dl/g. A comparison of V, VI to analogous polyimides VII, VIII. VI, VII and VIII was based on 3′4-ODA, 3-CF₃-4,4′-ODA, 4,4′-ODA, respectively. In terms of the color of PI revealed that the color intensity of phenoxy-containing amine of the meta-structure and the para-structure with the CF₃ group would fell off color intensity. The color intensity of the four polyimide series was lessened in the following order: V>VII>VI>VIII. The solubility of V is better than VI, VII and VII. The polyimide V films had a tensile strength ranging from 124 to 147 MPa, elongation at break from 9 to 65%, and initial modulus from 2.3 to 2.8 GPa. The glass transition temperature of polymers was recorded at 234-313 °C. They had 10% weight loss at a temperature above 515 °C and left more than 50% residue even at 800 °C in nitrogen. Compared with polyimides VI, V showed the lower dielectric constants of 2.80-3.50 (40 MHz), and moisture absorptions in the range of 0.44-1.02 wt%.     

Synthesis of 1,9-bis[glycidyloxypropyl]penta(1′H,1′H,2′H,2′H-perfluoroalkylmethylsiloxane)s and copolymerization with piperazine

A series of 1,9-bis[glycidyloxypropyl]pentasiloxanes (IV-VI) were prepared by the platinum catalyzed hydrosilylation of 1,9-dihydridodecamethylpentasiloxane (I), 1,9-dihydrido-3,5,7-tris(3′,3′,3′-trifluoropropyl)heptamethylpentasiloxane (II), and 1,9-dihydrido-3,5,7-tris(1′H,1′H,2′H,2′H-perfluorooctyl)heptamethylpentasiloxane (III) with allyl glycidyl ether. Subsequently, IV-VI were copolymerized with piperazine to form high molecular weight copoly(carbosiloxane)s (VII-IX). The structures of the 1,9-bis[glycidyloxypropyl]penta-siloxanes (IV-VI) and copoly(carbosiloxane)s (VII-IX) were determined by ¹H, ¹³C, ²⁹Si, and ¹⁹F NMR as well as IR spectroscopy. The molecular weight distributions (M_w/M_n) of VII-IX have been characterized by gel permeation chromatography and their thermal properties measured by differential scanning calorimetry and thermal gravimetric analysis.     

Synthesis and properties of chiral helical polymers based on optically active polybinaphthyls

The chiral polymer P-1 was synthesized by the polymerization of (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bisoctoxy-1,1′-binaphthyl (R-M-1) with 5,5′-divinyl-2,2′-bipyridine (M-1)via Pd-catalyzed Heck reaction. P-2 and P-2′ were prepared by Wittig-Horner reaction of (R)-6,6′-dibutyl-2,2′-bisoctoxy-1,1′-binaphthyl-3,3′-dicarbaldehyde (R-M-2) with 5,5′-bis (diethylphosphonomethyl)-2,2′-bipyridine (M-2) in the presence of EtONa or NaH, respectively. P-3 was synthesized by Wittig-Horner reaction of (R)-6,6′-di(4-trifluoromethylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl-3,3′-dicarbaldehyde (R-M-3) with M-2 using NaH as a base. The four polymers have strong blue-green fluorescence due to the extended π-electronic structure between the chiral model compounds (R)-6,6′-dibutyl-/di(4-trifluoromethylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl (R-1 or R-2) and the conjugated linker 2,2′-bipyridyl group via vinylene bridge. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. Based on the great differences of specific rotation values and CD spectra, P-1 and P-2 may adopt a zigzag chain configuration, while P-2′ and P-3 may adopt a helical configuration. The responsive optical properties of the two chiral helical polymers P-2′ and P-3 on transition metal ions were investigated by fluorescence, UV-vis and CD spectra. The results show that Ag⁺ and Ni²⁺ lead to nearly complete fluorescence quenching of P-2′ and P-3, Cu²⁺ and Fe²⁺ can cause obvious fluorescence quenching, but Zn²⁺ and Cd²⁺ can only produce slight fluorescence quenching. Ag⁺, Ni²⁺, Cu²⁺ and Fe²⁺ can also lead to the obvious changes of UV-vis spectra of P-2′ and P-3. On the contrary, Zn²⁺ and Cd²⁺ cause little changes. Most importantly, the CD intensities and wavelengths of the chiral helical polymers P-2′ and P-3 exhibit the pronounced changes upon addition of Ag⁺ and Ni²⁺.     

Synthesis and property of 9,9′-spirobifluorene-containing aromatic polyesters as optical polymers with high refractive index and low birefringence

C₂-Symmetric 9,9′-spirobifluorene-containing polyesters (PEs) were synthesized by polycondensation of 2,2′-dihydroxy-9,9′-spirobifluorene (1) with bis(acyl chloride)s (2) at 230 °C in diphenylether. The molecular weights of PEs 3a-3f were sufficiently high (M_w 13,400-41,600). PEs displayed high thermal stability. The glass transition temperatures (T_g) estimated by differential scanning calorimetry analysis appeared in a range 177-352 °C depending on the spacer structure, while the 5% decomposition temperatures (T_d5) measured by thermogravimetric analysis were over 416 °C both under nitrogen atmosphere and in air. PEs showed good solubility in typical organic solvents such as CHCl₃ and THF easily to afford the tough, transparent, and flexible cast films. The transmittance of the polymer films reached over 90% in the wavelength range from ca. 410-900 nm. In addition, PEs exhibited higher refractive index rather than that of commercially available 9,9-diarylfluorene-containing PE, in addition to very low degree of birefringence presumably due to the C₂-symmetric structure.     

Colorless polyimides from 2,3,3′,4′-biphenyltetracarboxylic dianhydride (α-BPDA) and various aromatic bis(ether amine)s bearing pendent trifluoromethyl groups

A series of organosoluble and light-colored polyimides (III) was prepared from 2,3,3′,4′-biphenyltetracarboxylic dianhydride (α-BPDA) with various fluorinated aromatic bis(ether amine)s via two-step method with thermal or chemical imidization of poly(amic acid)s yielded polyimides. The III series had inherent viscosity of 0.74-1.01 dl/g and showed excellent solubility in a variety of organic solvents. They were soluble in the amide polar solvent, ether-type solvent, and chlorinated solvent. These polyimide films also showed a high optical transparency and less color intensity, with an ultraviolet-visible absorption edge of 369-382 nm and low b^* values (a yellowness index) of 5.0-11.7. Glass-transition temperature of the III series was recorded at 244-319 °C and higher than the isomeric polyimides V series. Compared with the nonfluorinated polyimides IV, the III series showed lighter-colored and lower dielectric constants and moisture absorptions. The good tensile properties and excellent thermal properties of the III series were also observed.     

Polybinaphthyls incorporating chiral 2,2′-binaphthyl and isoquinoline moieties by Sonogashira reaction

Polymers P-1, P-2, P-3, P-4 and P-5 were synthesized by the polymerization of 5,8-bis(ethynyl)isoquinoline (M-1) with (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-2), (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-2), (R)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-3), (S)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-3), and rac-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl (M-4) under Sonogashira reaction, respectively. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. CD spectra of polymers P-1 and P-2, P-3 and P-4 are almost identical except that they gave opposite signals at each wavelength. The long wavelength CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and the helical backbone in the polymer chain. All five polymers have strong blue-green fluorescence due to the efficient energy migration from the extended π-electronic structure of the repeating unit of the polymers to the chiral binaphthyl core and are expected to provide understanding of structure-property relationships of the chiral conjugated polymers.     

Polybinaphthyls incorporating chiral (R) or (S)-2,2′-binaphthyland oxadiazole moieties by Stille reaction

Chiral polymers P-1 and P-2 were prepared by the polymerization of (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-1) and (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-1) with 2,5-bis[(4-tributylstannyl)phenyl]-1,3,4-oxadiazole (M-2) via Pd(PPh₃)₄ catalyzed Stille coupling reaction. 1,3,4-Oxadiazole unit not only has high electron affinity, high thermal and oxidative stability, but also serves as a good chromophore. Polymers have strong blue fluorescence due to the efficient energy migration from the extended π-electronic structure of the polymers to the chiral binaphthyl core and can be expected to have potential application in the materials of fluorescent sensors. Circular dichroism (CD) spectra of polymers P-1 and P-2 are almost identical except that they gave opposite signals at each wavelength. The long wavelengths CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and a high rigidity of the polymer backbone.     

A facile galvanostatic method for the synthesis of quinoxalinediones

Electrochemical oxidation of catechols (1a-d) has been studied in the presence of N,N-dimethylethylendiamine (3) as a nucleophile in aqueous solutions, using cyclic voltammetry, constant-current coulometry and controlled-potential coulometry. The results indicate that the quinones derived from catechols (2a-d) participate in Michael addition reactions with N,N′-dimethylethylendiamine (3) via the ECECE mechanism to form the corresponding quinoxalinedione derivatives (6a-c).     

Synthesis and characterization of donor-acceptor type 4,4′-bis(2,1,3-benzothiadiazole)-based copolymers

A series of novel donor-acceptor type polymers based on 4,4′-bis(2,1,3-benzothiadiazole) were synthesized and characterized. Two soluble regioregular tail-to-tail and head-to-head coupled polymers, poly[7,7′-bis(3-octyl-2-thienyl)-4,4′-bis(2,1,3-benzothiadiazole)] poly[3TBB3T], and poly[7,7′-bis(4-octyl-2-thienyl)-4,4′-bis(2,1,3-benzothiadiazole)] poly[4TBB4T] were synthesized by FeCl₃-mediated oxidative polymerization. To further decrease the band gap of the polymers, vinylene spacers were incorporated into the polymer backbone by Stille coupling of the corresponding monomers and (E)-1,2-bis(tributylstannyl)ethene. A crystal structure of a monomer analog shows near planar arrangement of the aromatic units in the solid state. The optical properties of the monomers and polymers were investigated by steady-state absorption and photoluminescence spectroscopy. Cyclic voltammetry measurements indicate that the polymers could be employed as acceptor materials in polymer-polymer bulk heterojunction solar cells due to their low LUMO energy of about −4.0 eV. A maximum photovoltaic power conversion efficiency of about 0.3% was observed for a 1:1 blend of regioregular poly(3-hexylthiophene) (rr-P3HT) and poly[4TBB4T] and the origin of the moderate efficiency is discussed by interpreting the device current-voltage characteristics, external quantum efficiency and incident light intensity dependence of the power conversion efficiency.     

Redox and catalytic properties of new polypyrrole modified electrodes functionalized by [Ru(bpea)(bpy)H2O] complexes; bpea=N,N′-bis(2-pyridylmethyl)ethylamine, bpy=2,2′-bipyridine

New ruthenium(II) complexes containing one or two pyrrole-functionalized polypyridylic ligands have been prepared in order to study their electrochemical behaviour in heterogeneous phase, after anodic polymerization from CH₂Cl₂ solution on an electrode surface. Complexes containing one pyrrole unit have general formula [Ru(bpea-pyr)(bpy)(L)]²⁺ (bpea-pyr=N-[3-bis(2-pyridylmethyl)aminopropyl]pyrrole, bpy=2,2′-bipyridine, L=Cl, complex 3, or L=H₂O, complex 1), whereas compounds having two pyrrole units correspond to [Ru(bpea-pyr)(bpy-pyr)(L)]²⁺ (bpy-pyr=4-methyl-4′-pyrrolylbutyl-2,2′-bipyridine, L=Cl, complex 4, or L=H₂O, complex 2). Upon oxidative polymerization, all complexes form highly stable polypyrrolic films on a graphite disk electrode surface. An electrode modified with complex 2 polypyrrole coating film, C/poly-2, has been tested as heterogeneous catalyst for the oxidation of benzyl alcohol, showing a remarkably high efficiency and notably improving the results obtained with analogous complexes in homogeneous phase.     

Synthesis of polystyrene microgel with glucose as hydrophilic segment via controlled free-radical polymerization

4-Vinylbenzyl glucoside peracetate (1) was copolymerized with divinylbenzene (DVB) using 1-phenyl-1-(2′,2′,6′,6′-tetramethyl-1′-piperidinyloxy)ethane (2) as an initiator in m-xylene at 138 °C for 20 h ([DVB]/[2]=28; [DVB]=0.62 mol L⁻¹). The copolymerizations were performed using the mole fraction of 1 in the total feed of 1 and DVB (F₁: [1]/[1]+[DVB]) ranging from 0.11 to 0.38 that produced the polystyrene (PSt) microgel with acetyl glucose, 3, in 46-53% yields. Dynamic laser light scattering (DLS) measurements showed that 3 was stably suspended in toluene as particles with average diameters (d's) ranging from 12 to 22 nm. A static laser light scattering (SLS) measurement gave the average molar mass, M_w,SLS, of 3 that ranged from 9.69×10⁴ to 6.96×10⁵. The numbers of the 1, 2, and DVB units in 3 (N₁, N₂, and N_DVB, respectively) were from 111 to 238, from 17 to 208, and from 350 to 4510, respectively. The deacetylation of 3 was achieved by treatment with sodium methoxide in dry 1,4-dioxane to produce the PSt microgel with glucose as the hydrophilic segment, 4. The solubilities of 4 in toluene, CHCl₃, THF, 1,4-dioxane, pyridine, DMF, DMSO, and H₂O, and the mixture of H₂O and 1,4-dioxane were examined, indicating that a hydrophilic property had been effectively introduced into 4.     

Co(salen)/SBA-15 catalysed oxidation of a β-O-4 phenolic dimer under microwave irradiation

The microwave-assisted oxidative degradation of a lignin model phenolic dimer [1-(4-hydroxy-3-methoxyphenoxy)-2-(2-methoxyphenoxy)-propane-1,3-diol, 1] catalysed by Co(salen)/SBA-15 is reported. The investigated model compound 1 was prepared through a multistep synthesis and characterized by ¹H,¹³C NMR, and GC–MS studies. The catalyst was prepared by immobilizing [N,N′-bis(salicylidene)ethane-1,2-diaminato]Cobalt(II), Co(salen) complex onto the periodic mesopore channels of siliceous SBA-15. The activity of the Co(salen)/SBA-15 was investigated in the oxidation of 1 in the presence of hydrogen peroxide as oxidant, both under microwave irradiation and conventional heating. The phenolic dimer was selectively oxidized to 2-methoxy phenol with very high TON under microwave activation conditions. Comparatively, reactions run under conventional heating led to oligomerisation of the dimer and resulted in a mixture of products.     

A highly selective and sensitive fluorescence chemosensor based on optically active polybinaphthyls for Hg

The chiral polymer was synthesized by the polymerization of 4,7-diethynylbenzo[2,1,3]-thiadiazole (M-1) with (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bis(diethylaminoethoxy)-1,1′-binaphthyl (R-M-1) via Pd-catalyzed Sonogashira reaction. The chiral polymer has orange fluorescence due to the extended π-electronic structure between binaphthyl unit and benzo[2,1,3]thiadiazole (BT) group via ethynyl bridge. The responsive optical properties of the polymer on various metal ions were investigated by fluorescence spectra. The fluorescence of the chiral polymer can produce the pronounced enhancement as high as 1.8-fold upon addition of 1:2 molar ratio of Hg²⁺. Compared with other cations, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Zn²⁺, Mn²⁺ and Fe³⁺, Hg²⁺ can produce the pronounced fluorescence response of the polymer. The result indicates this kind of chiral polybinaphthyls incorporating diethylamino and benzo[2,1,3]thiadiazole (BT) moieties as receptors exhibits highly sensitive and selective behavior for Hg²⁺ detection.     

An effective multipurpose building block for 3D electropolymerisation: 2,2′-Bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene

Novel thiophene-based oligomer, 2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene (TX), was designed and synthesized, and its electrochemical and spectral properties characterised. TX was readily polymerised electrochemically to form well organized conducting homopolymer films on various solid electrode substrates. Moreover, it was successfully used for deposition by electropolymerisation of electrochemically active thin films of co-polymers with three different monomers of functionalised bis(2,2′-bithienyl)methane derivatives. It appeared that TX was an effective crosslinker and 3D promoter in these electropolymerisations involving co-monomers intrinsically showing limited aptitude for the electropolymerisation or forming polymer films of low conductivity. This attractive TX ability stems from combination of its (i) high conjugation efficiency in each of the two planar moieties, (ii) intrinsic 3D structure on account of the presence of the central node, and (iii) intrinsic regioselectivity in electropolymerisation on account of the positions of the two available free α-thiophene sites.     

An argon laser induced polymerization photoinitiated by both mono- and bichromophoric hemicyanine dye-borate salt ion pairs. The synthesis, spectroscopic, electrochemical and kinetic studies

A series of homodimeric hemicyanine dyes based on (p-dimethylaminostyryl)benzothiazolium, (p-dimethylaminostyryl)benzoxazolium, (p-dimethylaminostyryl)-2,3,3-trimethyl-3H-indolium residues were synthesized. Several photoredox pairs containing mono- and bichromophoric hemicyanine dyes, possessing benzothiazole, benzoxazole or indolinium group linked by 5 or 10 methylene groups have been evaluated as novel photoinitiators for free radical polymerization induced with the argon-ion laser visible emission. In tested photoredox pairs, hemicyanine dye acts as an electron acceptor and it is coupled with borate anion which is an electron donor. The photochemistry of the series of bichromophoric hemicyanine borates: 1,5-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)benzothiazolium]pentane, 1,10-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)benzothiazolium]decane (S5, S10), 1,5-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)benzoxazolium]pentane, 1,10-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)benzoxazolium]decane (O5, O10) and 1,5-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)-3,3,3′,3′-tetramethyl-3H-indolium]pentane, 1,10-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)-3,3,3′,3′-tetramethyl-3H-indolium]decane (I5, I10) was compared to the photochemistry of structurally related monochromophoric hemicyanine borates (S1, O1, I1).     

A highly selective fluorescent sensor for Hg based on the water-soluble poly(p-phenyleneethynylene)

The conjugated polymer P-1 could be synthesized by the polymerization of 4,7-diethynyl-benzo[2,1,3]thiadiazole (M-1) and 1,4-bis[3′-(N,N-diethylamino)-1′-oxapropyl]-2,5-diiodobenzene (M-2) via Pd-catalyzed Sonogashira reaction. The water-soluble conjugated polyelectrolyte P-2 could be obtained by the reaction of P-1 with ethyl bromide. Both P-1 and P-2 can emit orange fluorescence. The responsive optical properties of P-1 and P-2 on Hg²⁺ were investigated by fluorescence spectra. Hg²⁺ can lead to nearly complete fluorescence quenching of P-1. On the contrary, Hg²⁺ can show the most pronounced fluorescence enhancement response of P-2 in aqueous solution without interference from those coexistent ions, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Zn²⁺. The results also exhibit that this kind of water-soluble conjugated polyelectrolyte can be used as a highly sensitive and selective fluorescence sensor for Hg²⁺ detection in water.     

Synthesis and electrochromic properties of aromatic polyimides bearing pendent triphenylamine units

A series of aromatic polyimides with pendent triphenylamine group were synthesized from equimolar mixtures of 4,4′-oxydianiline (ODA) and 4-(3,5-diaminobenzamido)triphenylamine (4), 4-(3,5-diaminobenzamido)-4′,4″-di-tert-butyltriphenylamine (t-Bu-4) or 4-(3,5-diaminobenzamido)-4′,4″-dimethoxytriphenylamine (MeO-4) with two aromatic tetracarboxylic dianhydrides (DSDA or 6FDA) via a conventional two-step procedure that included a ring-opening polyaddition to give poly(amic acid)s, followed by chemical imidization. These polyimides exhibited good solubility in polar organic solvents and could be solution-cast into flexible and strong films. They showed excellent thermal stability, with T_g values in the range of 284–309 °C. The polyimides derived from diamines t-Bu-4 and MeO-4 exhibited reversible electrochemical oxidation, accompanied by strong color changes with high contrast ratio and electrochromic stability. For the polyimides derived from diamine 4, the coupling reaction between the triphenylamine radical cations occurred during the oxidative process forming a tetraphenylbenzidine structure, which resulted in an additional oxidation state and color change together with enhanced near-IR absorption at fully oxidized state.     

Thermal behavior of 1,4-bis(4-trimellitimido-2-trifluoromethyl phenoxy)benzene (DIDA) solvated with polar organic solvents and properties of DIDA-based poly(amide-imide)s

Fluorinated diimide-dicarboxylic acid (DIDA, Code: IV), 1,4-bis(4-trimellitimido-2-trifluoromethylphenoxy) benzene, synthesized by reacting 1,4-bis(4-amino-2-trifluoromethyl phenoxy)benzene (I) with trimellitic anhydride in polar solvents (PSv), was found to crystallize easily in amide-type solvents, such as N-methyl-2-pyrrolidinone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), or 1,3-dimethyl-2-imidazolidinone (DMI) media, to form a series of stable crystalline solvates (III_(NMP), III_(DMAc), III_DMF), III_(DMI)) containing a certain quantity of crystalline solvent. The solvates III_(PSv) were characterized and proven by DSC, TGA, and X-ray analysis. The decomposition point temperature (T_d) was different with the type of polar solvents in III_(PSv). Elemental analysis and NMR showed that most of the III_(PSv) were formed from IV and polar solvents in the ratio of 1:2, and the solvation processes were found to be reversible. Furthermore, a series of soluble fluorinated poly(amide-imide)s (VI_a-h) were synthesized from reacting either the NMP-solvates III_(NMP) or dry/non-solvates IV with an equivalent amount of diamines by direct polycondensation using triphenyl phosphate and pyridine as condensing agents. Thermal and mechanical properties of the fluorinated VI_a-h were measured, and compared with counterparts of non-fluorinated PAI's (Code: VI′s). In comparison, the fluorinated VI_a-h poly(amide-imide)s exhibited better solubility, tensile, and thermal properties than the non-fluorinated VI′s.     

Paired electrochemical synthesis of new organosulfone derivatives

Electrochemical oxidation of “cathodically generated 4-aminocatechol (2)” has been studied in the presence of 4-toluenesulfinic acid (4a) and benzenesulfinic acid (4b) as nucleophiles in aqueous solutions, using cyclic voltammetry and controlled-potential coulometry. The results indicate that the o-benzoquinone derived from 4-aminocatechol (2) participates in Michael addition reaction with 4a or 4b to form the corresponding new organosulfone derivatives (5a and 5b). In this work we have proposed a mechanism for the electrode process. A Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ redox mediator was used for the anodic oxidation of 4-aminocatechol (2) to the corresponding o-quinone 3. The indirect electrochemical process consists of a multi-step such as (a) cathodic reduction of 4-nitrocatechol (1) to 4-aminocatechol (2), (b) chemical oxidation of 4-aminocatechol (2) to 4-aminoquinone (3) with the resulting Fe(CN)₆³⁻, (c) the chemical reaction of 4-aminoquinone (3) with 4-toluenesulfinic acid (4a) or benzenesulfinic acid (4b), and (d) the anodic regeneration of Fe(CN)₆³⁻. The paired electrochemical synthesis of organosulfone derivatives (5a and 5b) has been successfully performed in an one-pot process at carbon rod electrode as a working and platinum as a counter electrode in an undivided cell.