A novel synthetic strategy to develop second‐order nonlinear optical polysilanes for potential photorefractive effects

A novel strategy to develop polysilanes functionalized with a high density of nonlinear optical chromophores has been explored. Thus a polysilane with phenyl and N,N‐dialkylsubstituted aniline as pendant groups was synthesized under standard conditions for the Wurtz reductive coupling, and the post azo coupling of p‐nitrobenzenediazonium fluoroborate towards the aniline groups afforded a dispersed red (DR) chromophore‐functionalized polysilane (P2). The poled film of P2 reveals a resonant d₃₃ value of 19 pm/V by second harmonic generation (SHG) measurements.     

Diazo Reactions with Unsaturated Compounds: VI. Reaction of 1-(p-Nitrophenylsulfonyl)buta-1,3-diene with Arenediazonium Chlorides

1-(p-Nitrophenylsulfonyl)buta-1,3-diene reacts with arenediazonium chlorides in aqueous acetone in the presence of catalytic amounts of CuCl₂·2H₂O to form 1-(p-nitrophenylsulfonyl)-4-aryl-3-chloro-1-bu- tenes. In the presence of SO₂, 1-(p-nitrophenylsulfonyl)buta-1,3-diene does not react with arenediazonium chlorides.     

Diazo Reactions with Unsaturated Compounds: VII. Vinyl p-Methylphenyl and Vinyl p-Nitrophenyl Ethers in the Meerwein Reaction

Vinyl p-methylphenyl ether in aqueous acetone at pH 3-4 in the presence of catalytic amounts of copper(II) chloride reacts with arenediazonium chlorides to form arylacetaldehydes. Vinyl p-nitrophenyl ether under the same conditions fails to react with arenediazonium chlorides.     

Polarographic Detection of Arenediazonium Ions. Optimization of the Method and Application for Investigating Dediazoniation Mechanisms

The use of differential pulse polarography (DPP) at the dropping mercury electrode (DME) to detect and to investigate the mechanisms for decomposition of arenediazonium ions, ArN₂⁺, under different experimental conditions is discussed. The effect of a number of experimental and instrumental parameters on the polarographic peaks of a model arenediazonium ion was explored and representative applications to investigate their reaction mechanisms are given. The composite data shows that DPP provides an alternative, relatively cheap, technique to monitor ArN₂⁺ decomposition in, for example, opaque systems where, for obvious reasons, spectroscopic detection does not work; meanwhile in homogeneous systems, DPP complements the results obtained by employing spectroscopic or chromatographic techniques. In addition, a variety of valuable mechanistic information such as detection of transient intermediates or estimation of the binding constants of aryl radicals with macromolecular systems, that otherwise cannot be easily obtained, is readily available by using DPP.     

Effects of Micellar Aggregates on the Kinetics and Mechanism of the Reaction between 4‐Nitrobenzenediazonium Ions and Some Amino Acids

We have explored the kinetics and mechanism of the reaction between 4‐nitrobenzenediazonium ions (4NBD), and the hydrophilic amino acids (AA) glycine and serine in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by means of UV/VIS spectroscopy. The observed rate constants k_obs were obtained by monitoring the disappearance of 4NBD with time at a suitable wavelength under pseudo‐first‐order conditions. In aqueous acid (buffer‐controlled) solution, in the absence of SDS, the dependence of k_obs on [AA] was obtained from the linear relationship found between the experimental rate constant and [AA]. At a fixed amino acid concentration, k_obs values show an inverse dependence on acidity in the range of pH 5–6, suggesting that the reaction takes place through the nonprotonated amino group of the amino acid. All kinetic evidence is consistent with an irreversible bimolecular reaction with k=2390±16 and 376±7 M ^?1 s^?1 for glycine and serine, respectively. Addition of SDS inhibits the reaction because of the micellar‐induced separation of reactants originated by the electrical barrier imposed by the SDS micelles; k_obs values are depressed by factors of 10 (glycine) and 6 (serine) on going from [SDS]=0 up to [SDS]=0.05M . The hypothesis of a micellar‐induced separation of the reactants was confirmed by ¹H‐NMR spectroscopy, which was employed to investigate the location of 4NBD in the micellar aggregate: the results showed that the aromatic ring of the arenediazonium ion is predominantly located in the vicinity of the C(β) atom of the surfactant chain, and hence the reactive ? N group is located in the Stern layer of the micellar aggregate. The kinetic results can be quantitatively interpreted in terms of the pseudophase kinetic model, allowing estimations of the association constant of 4NBD to the SDS micelles.     

Electroanalytical Oxidation of p‐Coumaric Acid

Abstract

The mechanism of the electrochemical oxidation of p‐coumaric acid on a glassy carbon electrode was investigated using cyclic, differential pulse, and square wave voltammetry at different pHs. The oxidation of p‐coumaric acid is irreversible over the whole pH range. After successive scans, the p‐coumaric acid oxidation product deposits on the electrode surface, forming a polymeric film that undergoes reversible oxidation at a lower potential than p‐coumaric acid. This polymeric film increases in thickness with the number of scans, covering the electrode surface, and impeding the diffusion of the p‐coumaric acid and its oxidation on the electrode. The oxidation of p‐coumaric acid is pH dependent up until values close to the pK_a. For pHs higher than pK_a, the p‐coumaric acid oxidation process is pH independent. An electroanalytical determination procedure of p‐coumaric in pH 8.7 0.2 M ammonium buffer was developed, and a detection limit, LOD=83 nM, and the limit of quantification, LOQ=250 nM, were obtained.     

Electrochemical Investigation of Na‐Salt of 2‐Methyl‐3‐(4‐nitrophenyl)acrylate on Glassy Carbon Electrode

The electrochemical behavior of Na‐salt of 2‐methyl‐3‐(4‐nitrophenyl)acrylate (NPA) and its reduction product was studied by cyclic (CV), differential pulse(DPV) and square wave voltammetry (SWV) using a glassy carbon electrode (GCE). The results revealed that NPA is irreversibly reduced leading to the formation of a reduction product (P_NPA). For pH<9.0 the peak potential was linearly dependent on pH. For pH>9.0 the peak potential was pH‐independent and the value of pK_b≈9.0 was determined. The adsorbed P_NPA exhibited reversible redox reaction. The reduction of P_NPA was pH dependent. To ensure that the electrochemical behavior of NPA is due to the reducible moiety, NO₂, closely related compounds to NPA were also studied, and a redox mechanism was proposed for NPA.     

A Convenient Dediazoniation of Arenediazonium Tetrafluoroborates: Triethylamine Effects on Competitive Ionic and Radical Dediazoniation

Triethylamine was very efficient in the dediazoniation of arenediazonium salt. The major product depended on the comparative molar ratio (r) of triethylamine to benzenediazonium salt. When r<0.5, anisole (ionic product) was a major, while benzene (radical product) was a major when r>1.     

Solvolysis of o‐methylbenzenediazonium tetrafluoroborate in acidic methanol‐water mixtures. Further evidence for nucleophilic attack on a solvent separated aryl cation

Rate constants for dediazoniation product formation and arenediazonium ion loss and product yields of solvolysis of o‐methylbenzenediazonium tetrafluoroborate in acidic methanol‐water mixtures at T = 35°C are reported. Observed rate constants for diazonium ion loss and product formation are the same, increasing about 45% ongoing from water to methanol, and are not affected by added electrolytes like HCl, NaCl, and CuCl₂. Only three dediazoniation products are detected, o‐cresol, o‐chlorotoluene, and o‐anisole. All data are consistent with a rate‐determining step formation of an aryl cation that reacts immediately with available nucleophiles. The selectivity of the reaction toward nucleophiles, S, which can be defined by: is low and essentially constant upon changing solvent composition, suggesting that the nucleophilic attack takes place on a solvent separated aryl cation. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 531–538, 1999     

Direct Electroanalysis of p‐Nitrophenol (PNP) in Estuarine and Surface Waters by a High Sensitive Type C/p‐NiTSPc Coating Carbon Fiber Microelectrode (CFME)

We report for the first time on the elaboration of a remarkable sensitivity type C/p‐NiTSPc carbon fiber microelectrode (CFME) for p‐nitrophenol (PNP) pollutant. We observed the best performances using square wave voltammetry (SWV) technique in the place of differential pulse voltammetry (DPV). Also the combination of p‐NiTSPc optimized cycles of electrodeposition and accumulation time, helped us to increase remarkably the sensor slope (320 times) and the limit of detection (LOD) (1000 times), with a final LOD of 0.1 µg/L, the current regulatory limit for drinkable waters. Furthermore the recoveries of the standards added are close to 100 % indicating that the method has some suitability. The proposed voltammetric procedure might be applied for organophosphorus pesticides and their by‐products with a remarkable sensing in natural polluted waters.     

Copper‐Catalyzed Arylation of Nitrogen Heterocycles from Anilines under Ligand‐Free Conditions

The arylation of pyrazole and derivatives can be achieved by coupling arenediazonium species (formed in situ from anilines) by using a catalytic system that employs low‐toxicity and inexpensive copper metal under very mild and ligand‐free conditions (T=20 °C). From other nitrogen heterocycles, the presence of an additive (NBu₄I) significantly improves the efficiency of the catalytic system. These results represent the first examples of C?N bond formation from arenediazonium species.     

Electrochemical Reduction of 1,2-Di（p-tolylimino）ethane and 1,2-Di（2,4-dimethylphenylimino）ethane in Dimethylformamide

1,2-Di（p-tolylimino）ethane （Ⅰ） and 1,2-Di（2,4-dimethylphenylimino）ethane （Ⅱ） were synthesized and their electrochemical behavior investigated in dimethylformamide using classical voltammetry, differential pulse voltammetry, cyclic voltammetry, chronoamperometry, controlled potential electrolysis and coulometry. Both bis-Schiff base ligands examined show a cathodic irreversible peak which corresponds to one-electron reduction of the substrate to form anion radical. According to the fact obtained from cyclic voltammetry, that the current function （ip/v^1/2） is a decreasing function of the scan rate, it can be concluded that there is a following coupling chemical reaction （EC mechanism）. Thus, the most probable mechanism of electroreduction of both ligands is the coupling of two radicals to form a dimer.     

Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine on the Tetrabromo‐p‐Benzoquinone Modified Carbon Paste Electrode

The electrochemical properties of hydrazine studied at the surface of a carbon paste electrode spiked with p‐bromanil (tetrabromo‐p‐benzoquinone) using cyclic voltammetry (CV), double potential‐step chronoamperometry and differential pulse voltammetry (DPV) in aqueous media. The results show this quinone derivative modified carbon paste electrode, can catalyze the hydrazine oxidation in an aqueous buffered solution. It has been found that under the optimum conditions (pH 10.00), the oxidation of hydrazine at the surface of this carbon paste modified electrode occurs at a potential of about 550 mV less positive than that of a bar carbon paste electrode. The electrocatalytic oxidation peak current of hydrazine showed a linear dependent on the hydrazine concentrations and linear analytical curves were obtained in the ranges of 6.00×10^?5 M–8.00×10^?3 M and 7.00×10^?6 M–8.00×10^?4 M of hydrazine concentration with CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 3.6×10^?5 M and 5.2×10^?6 M by CV and DPV methods. This method was also used for the determination of hydrazine in the real sample (waste water of the Mazandaran wood and paper factory) by standard addition method.     

Dediazoniation of 1-naphthalenediazonium tetrafluoroborate in aqueous acid and in micellar solutions

We have measured the rates and product yields of dediazoniation of 1-naphthalenediazonium (1ND) tetrafluoroborate in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by employing a combination of UV–vis spectroscopy and high-performance liquid chromatography (HPLC) measurements. Kinetic data were obtained by a derivatization procedure with product yields were determined by HPLC. HPLC chromatograms show that in aqueous acid and in micellar solutions only one dediazoniation product is formed in significant quantities, 1-naphthol (NOH), and the observed rate constants (k_obs) are the same when 1ND loss is monitored spectrometrically and when NOH formation is monitored by HPLC. Activation parameters were obtained both in the presence and absence of SDS micellar aggregates. In both the systems, the enthalpies of activation are high and the entropies of activation are positive. The enthalpy of activation in the absence of SDS is very similar to that in the presence of SDS micelles, but the entropy of activation is lower by a factor of 4. As a consequence, SDS micelles speed up the thermal decomposition of 1ND and increase k_obs by a factor of 1.5 when [SDS] = 0.02 M. In contrast, results obtained in the presence of complexing systems such as crown ethers and polyethers show significant stabilization of the parent arenediazonium ions. Kinetic and HPLC data are consistent with the heterolytic D_N + A_N mechanism that involves the rate-determining fragmentation of the arenediazonium ion into a very reactive phenyl cation that reacts competitively with available nucleophiles. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 301–309, 2008     

Electrochemical Oxidation of Sulfasalazine at a Glassy Carbon Electrode

Sulfasalazine (SSZ) is a pharmaceutical compound used for the treatment of rheumatoid arthritis. The electrochemical oxidation of SSZ at a glassy carbon electrode was studied by cyclic, differential pulse and square wave voltammetry in a wide pH range. For electrolytes with pH<11.0, the oxidation is an irreversible, diffusion‐control, pH‐dependent process that involves the transfer of one electron and one proton from the hydroxyl group of the salicylic moiety. For pH>11.0 the oxidation is pH‐independent, and a pK_a≈11 was determined. The formation of a quinone‐like oxidation product that undergoes two electrons and two protons reversible redox reaction was observed. Also, UV‐vis spectra of SSZ were recorded as a function of supporting electrolytes pH. An electrochemical oxidation mechanism was proposed.     

Study of a Catalytic Mechanism in Additive Differential Pulse Techniques

The new electrochemical double pulse technique, known as additive differential normal pulse voltammetry (ADNPV) when there is no restriction on the duration of both pulses, and additive differential pulse voltammetry (ADPV) when t₂?t₁, has been applied to a pseudo‐first‐order catalytic mechanism. The expressions obtained here are applicable to planar and spherical electrodes, of any radius. This is of great interest since the size of the electrode plays an important role in the preponderating of diffusive and kinetics processes. The signal obtained with this technique presents the same morphological characteristics as the triple pulse technique, double differential pulse voltammetry (DDPV) and is more advantageous than DDPV and than the double pulse one, differential pulse voltammetry (DPV).     

Diazo reactions with unsaturated compounds: XIII. Reactions of p-(buta-1,3-dien-1-ylsulfonyl)benzenesulfonamide with arenediazonium chlorides, 1-aryl-3,3-dimethyltriaz-1-enes, and arenediazonium tetrachlorocuprates(II)

p-(Buta-1,3-dien-1-ylsulfonyl)benzenesulfonamide reacted with arenediazonium chlorides, 1-aryl-3,3-dimethyltriaz-1-enes, and arenediazonium tetrachlorocuprates(II) in aqueous acetone in the presence of copper(II) chloride to give the corresponding p-(4-aryl-3-chlorobut-1-en-1-ylsulfonyl)benzenesulfonamides.     

Application of Polymer‐Modified Hanging Mercury Drop Electrode in the Indirect Determination of Certain β‐Lactam Antibiotics by Differential Pulse,Ion‐Exchange Voltammetry

A selective and sensitive polymer‐modified electrode was developed for β‐lactam antibiotics (cefaclor, amoxycillin and ampicillin) present in formulated and blood plasma samples for the quantitative analysis in aqueous environment. The detection was made using an ion‐exchange voltammetric technique, in differential pulse mode, on poly(N‐chloranil N,N,N′,N′‐tetramethylethylene diammonium dichloride)‐modified hanging mercury drop electrode of a three‐electrode system (PAR Model 303A) attached with a Polarographic Analyzer/Stripping Voltammeter (PAR Model 264A). Antibiotics, which are electroinactive compounds, were essentially converted to their electroactive oxazolone analogues through acid treatment under drastic conditions (0.1 mol L^?1 HCl, ～85 °C, 2 h). These analytes in the form of their respective oxazolones were indirectly analyzed by oxazolone entrapment in the polymeric film through ion‐exchange process at modified electrode surface (accumulation potential ?0.20 V (vs. Ag/AgCl), accumulation time 120 s, pH 7.4, KH₂PO₄‐NaOH buffer (ionic strength 0.1 mol L^?1), scan rate 10 mV s^?1, pulse amplitude 25 mV). The limit of detection of cefaclor‐derived oxazolone was found to be 2.12 nmol L^?1 (0.82 ppb, S/N 3, RSD 3.21%) in terms of cefaclor (a representative β‐lactam) concentration.     

Electrocatalytic Determination of Vitamin C Using Calixarene Modified Carbon Paste Electrodes

Effect of in situ complexation of some ions with variable valencies, like Co(II), Ni(II), Mn(II), Cu(II) and Pb(II) on the the electrooxidation of Vitamin C (L ‐ascorbic acid) was studied by cyclic voltammetry using carbon paste electrodes modified with p‐tert‐butylcalix[4]arene and p‐tert‐butylcalix[6]arene in perchloric acid, acetic acid and ammonium acetate media. Pb(II) was found to bind strongly with p‐tert‐butylcalix[4]arene in acetate medium, resulting in its being retained at the electrode surface and catalyzing the oxidation of ascorbic acid. The overpotential was reduced by about 200 mV with an increase in the peak currents. Linearity was observed over the range of 0.07–400 ppm with a detection limit of 30 ppb by differential pulse voltammetry. Interferences of some common substances like sugars and amino acids were studied and the modified electrode was used for the determination of vitamin C in commercial samples.     

Electrochemical Sensor for Sensitive Determination of Ga(III) Ion Based on β‐Cyclodextrin Incorporated Multi‐walled Carbon Nanotubes and Imprinted Sol‐gel Composite Film

A novel sensor for detection of trace gallium ion [Ga(III)] was created by stepwise modification of a gold electrode with β‐cyclodextrin (β‐CD)/multi‐walled carbon nanotubes (MWCNTs) and an ion imprinted polymer (IIP). The sensor surface morphology was characterized by scanning electron microscopy. The electrochemical performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The sensor displayed excellent selectivity towards the target Ga(III) ion. Meanwhile, the introduced MWCNTs displayed noticeable catalytic activity, and β‐CD demonstrated significant enrichment capacity. A linear calibration curve was obtained covering the concentration range from 5.0×10^?8 to 1.0×10^?4 mol·L^?1, with a detection limit of 7.6×10^?9 mol·L^?1. The proposed sensor was successfully applied to detect Ga(III) in real urine samples.