Diaminoazobenzene Research Articles

Ionic liquid mediated synthesis of 4, 4'diamino azo benzene substituted aliphatic polyamides and thermal studies

Ionic liquids act as green solvents, which can replace the usual traditional solvents which pose both environmental and biological hazard. In the present work 4,4'diamino azobenzene has been condensed with various aliphatic diacids such as succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid and Pimelic acid using imidazolium based ionic liquids in the presence of triphenylphosphite(TPP). The resulting azopolyamides have been obtained in high yield with intrinsic viscosity ranging from 0.56 - 0.81 dlg-1. This method is compared with modified Higashi’s method. The thermodynamic parameters like G, H and S are calculated by approximate methods such as Freeman & Carroll, Coats & Red fern, Doyle and Murray and White. The resulting polyamides prepared using green condition show increased thermal stability when compared to polyamides prepared by modified Higashi’s method.

Evaluation of Corrosion Inhibition Efficiency of Aluminum Alloy 2024 by Diaminostilbene and Azobenzene Schiff Bases in 1 M Hydrochloric Acid

The Schiff base compounds N,N ′ -bis(salicylidine)-4,4 ′ –diaminostilbene(SDS) and N,N ′ -bis(salicylidine)-4,4 ′ -diamino azobenzene(SDA) were synthesized, and their molecular structure was determined by FT-IR and 1H NMR. The corrosion inhibitions of Schiff base compounds on aluminum alloy 2024 in 1 M hydrochloric acid were evaluated by potentiodynamic polarization, impedance techniques, weight loss method, and scanning electron microscopic technique. The potentiodynamic polarization (PDP) studies revealed that SDS and SDA compounds acted predominantly as cathodic inhibitors. The electrochemical impedance spectroscopic (EIS) parameters confirmed the adsorption of SDS and SDA molecules over the surface of aluminum alloy 2024 alloy by forming an inhibitive layer. The weight loss studies showed that the inhibition efficiency of these compounds increases directly with concentration and decreases with an increase in solution temperature and immersion time. The thermodynamic parameters were calculated to investigate the mechanism of corrosion inhibition. The SDA was found to be more effective than SDS and followed the Langmuir adsorption isotherm model. The scanning electron microscopy (SEM) results revealed that the deterioration of the alloy surface is minimal in the presence of an inhibitor. Both Schiff base molecules exhibited superior corrosion inhibition for aluminum alloy 2024 alloy in HCl medium.

Z-E isomerization of azobenzene based amphiphilic poly(urethane-urea)s: Influence on the dynamic mechanical properties and the effect of the self-assembly in solution on the isomerization kinetics

Azobenzene containing polymers have been used in the development of materials and devices responsive to light, devices for optical storage information, with shape-changing and shape-memory capacities, surface-relief grating, holograms, etc. Poly(urethane-urea)s (PUU) based on a hydrophilic polyethylene glycol (PEG-PUU), on a hydrophobic polycaprolactone diol (PCL-PUU) polyols, and on an equimolar mixture of them (PEG/PCL-PUU), 4,4′-diphenylmethane diisocyanate and 4,4′-diaminoazobenzene (DAAB), as a chain extender, were synthesized by a two-step route. PUU were characterized with respect to their chemical structure, molar masses, thermal and dynamic mechanical properties, and spectroscopic properties. The kinetics of the photo- and thermal-induced isomerization were studied in DMF solutions. The isomerization rate constant was two orders of magnitude higher for DAAB compared with PUU in DMF solution, except for PEG/PCL-PUU, for which the rate constant was half the value observed for DAAB. The amphiphilic nature of the PUU resulted in aggregates in DMF and, therefore, the azo isomerization for PEG-PUU and PCL-PUU occurred in a solid-state-like environment. On the other hand, PEG/PCL-PUU presented unimers and aggregates in DMF and the isomerization of azo groups in free PUU chains was faster. The PUU were semicrystalline and thermo-mechanically stable up 150 °C due to the hydrogen bonding involving urea, urethane and ester groups. The aggregates size in DMF solution, as well as the dynamic mechanical properties of the PUU, were sensitive to photo- and thermo-induced isomerization.

Plasmon-driven catalysis of adsorbed p-nitroaniline (PNA) by surface-enhanced Raman scattering (SERS): Platinum versus silver

The adsorption of p-nitroaniline (PNA) on Pt nanoparticles, both in the absence (in aqueous solution) and in the presence of oxygen (in air environment), is studied by SERS for the first time. Differences between the plasmon-driven catalysis of adsorbed PNA on Pt and Ag nanoparticles have been found. In the presence of oxygen, the oxidative coupling of the NH2 group in PNA to yield dinitroazobenzene (DNAB) occurs on both Pt and Ag nanoparticles. However, in the absence of oxygen, PNA behaves clearly differently on Ag than on Pt. Thus, whereas diaminoazobenzene (DAAB) is catalytically produced on Ag nanoparticles by plasmon-driven reduction reactions of the NO2 group, on Pt nanoparticles this reaction does not fully take place as indicated by the presence of NO2 groups on the surface of the nanoparticles. A mechanism for this distinctive behavior is tentatively proposed in which water acts as a sacrificial agent, being reduced to hydrogen by hot electrons coming from the Pt surface, while the hot holes on Pt are proposed to attach to an occupied molecular state of adsorbed PNA. The overall photocatalytic reaction of adsorbed PNA on Pt nanoparticles, in an O2 free solution, would actually be consistent with a dehydrogenation process of water.

Observation of Olefin/Paraffin Selectivity in Azo Compound and Its Application into a Metal-Organic Framework.

Olefin/paraffin separation is an important and challenging issue because the two molecules have similar physicochemical properties. Although a couple of olefin adsorbents have been developed by introducing inorganic nanoparticles into metal-organic frameworks (MOFs), there has been no study on the development of an olefin adsorbent by introducing a certain organic functional group into a MOF. In this study, we posited that azo compounds could offer olefin/paraffin selectivity. We have revealed using first-principles calculations that the simplest aromatic azo compound (azobenzene, Azob) has an unusual propylene/propane selectivity due to special electrostatic interactions between Azob and propylene molecules. On the basis of this interesting discovery, we have synthesized a novel propylene adsorbent, MIL-101(Cr)_DAA, by grafting 4,4'-diaminoazobenzene (DAA) into open metal sites in a mesoporous MIL-101(Cr). Remarkably, MIL-101(Cr)_DAA exhibited enhanced propylene/propane selectivity as well as considerably higher propylene heat of adsorption compared to pristine MIL-101(Cr) while maintaining the high working capacity of MIL-101(Cr). This clearly indicates that azo compounds when introduced into MOFs can provide propylene selectivity. Moreover, MIL-101(Cr)_DAA showed good C3H6/C3H8 separation and easy regeneration performances from packed-bed breakthrough experiments and retained its propylene adsorption capacity even after exposure to air for 12 h. As far as we know, this is the first study that improves the olefin selectivity of MOF by postsynthetically introducing an organic functional group.

Plasmon-Driven Diazo Coupling Reactions of p-Nitroaniline via −NH2 or −NO2 in Atmosphere Environment

Plasmon-driven diazo coupling reaction of p-nitroaniline (PNA), containing both an amine group (−NH2) and a nitro group (−NO2), in ambient atmosphere environments remains unknown in experiments, on both metal nanoparticles and graphene-mediated metal nanostructures. Using the surface-enhanced Raman scattering (SERS) technique, we presented the surface coupling reactions of PNA under atmospheric environment, adsorbed on the Ag nanoparticle (AgNP) arrays, graphene-coated Ag nanoparticle (G/AgNPs) hybrids, and graphene-covered Ag nanowire (G/AgNW) composites, respectively. It was found that PNAs were converted into 4,4′-diaminoazobenzene (DAAB) through a selective reduction reaction, rather than oxidized into 4,4′-dinitroazobenzene (DNAB). These results may be useful for understanding the reaction mechanism for plasmon-driven chemical reactions of the molecules containing both amine groups and nitro groups under ambient conditions.

Selective plasmon-driven catalysis for para-nitroaniline in aqueous environments.

The plasmon-driven oxidation of amine (−NH2) groups and the reduction of nitro (−NO2) groups on a nanostructured metal surface in an aqueous environment have been reported experimentally and theoretically. The question of which process occurs first in the aqueous environment is an interesting question in the field of plasmon-related photochemistry. Para-nitroaniline (PNA), with both nitro (−NO2) and amine (−NH2) groups, is the best candidate for studying the priority of the plasmon-driven oxidation and the reduction reactions in an aqueous environment. Using surface-enhanced Raman scattering (SERS) spectroscopy, our experimental results and theoretical simulations reveal that PNA is selectively catalyzed to 4,4′-diaminoazobenzene (DAAB) through the plasmon-assisted dimerization of the nitro (−NO2) group into an azo group in an aqueous environment. This indicates that the plasmon-driven reduction of the nitro (−NO2) group clearly occurs before the oxidation of the amine (−NH2) group in an aqueous environment. The plasmon-driven reduction of PNA to DAAB is a selective surface catalytic reduced reaction in aqueous environment.

A plasmon-driven selective surface catalytic reaction revealed by surface-enhanced Raman scattering in an electrochemical environment

Plasmonic catalytic reactions of molecules with single amine or nitro groups have been investigated in recent years. However, plasmonic catalysis of molecules with multiple amine and/or nitro groups is still unknown. In this paper, plasmon-driven catalytic reactions of 4,4'-dinitroazobenzene (DNAB), 4,4'-diaminoazobenzene (DAAB) and 4-nitro-4'-aminoazobenzene (NAAB) are investigated using electrochemical surface-enhanced Raman scattering (SERS) spectroscopy. The results reveal that a plasmon-driven reduction reaction occurred for DNAB and NAAB in which the NO2 group was reduced to NH2, while the plasmon-driven oxidation reaction of NH2 did not occur. This result demonstrates that plasmon-driven reduction reactions are much easier than plasmon-driven oxidization reactions in electrochemical environments. The molecular resonance may also play an important role in plasmon-driven catalytic reactions. These findings provide us with a deeper understanding of plasmon-driven catalytic reactions.

Investigation of solid state imidization reactions of the vapour deposited azo-polyimide thin films by FTIR spectroscopy

In this paper solid state imidization reactions of azo-polyimide thin films prepared at different temperatures have been investigated by FTIR spectroscopy. The starting precursors DAAB (4,4′-diaminoazobenzene) and PMDA (pyromellitic dianhydride) were vacuum deposited as thin films. It was estimated that the necessity of the following thermal treatment 1h at 300°C are appropriate conditions for imidization of the initial PMDA–DAAB mix to Azo-PI (azo-polyimide) film. The parameters have been selected experimentally (temperatures, deposition rates, mode of substrates, etc.), for the vapour deposition of the precursors in view to prepare layers with a high imidization degree, reproducible composition and structure, which determined the film properties. Due to their magnetic anisotropy and cis–trans–cis isomerization cycle the azo-polymer films are promising material for application in optics, optoelectronics, sensors, etc. For this reason a study of the kinetics of solid state imidization reactions at different temperatures is carried out. It is identified and discussed that the imide III band intensity at 1363–1381cm−1 characterizing imide ring is different at three temperatures.

Construction and Characterization of Molecular Nonwoven Fabrics Consisting of Cross-Linked Poly(γ-methyl-l-glutamate)

Molecular nonwoven fabrics in the form of ultrathin layer-by-layer (LbL) helical polymer films with covalent cross-linking were assembled on substrates by an alternate ester-amide exchange reaction between poly(γ-methyl L-glutamate) (PMLG) and cross-linking agent ethylene diamine or 4,4'-diamino azobenzene. The regular growth of helical monolayers without excessive adsorption and the formation of amide bonds were confirmed by ultraviolet-visible (UV-vis) spectrophotometry, quartz crystal microbalance (QCM), ellipsometry, and infrared reflection-absorption spectroscopy (IR-RAS) measurements. Nanostructures with high uniformity and ultrathin films with few defects formed by helical rod segments of PMLG were characterized by atomic force microscopy (AFM) and Kelvin probe force microscopy (KFM).

Kinetics and thermodynamics of isothermal curing reaction of epoxy‐4, 4′‐diaminoazobenzene reinforced with nanosilica and nanoclay particles

AbstractThe kinetics of the cure reaction for a system of bisphenol‐A epoxy resin (DGEBA), with 4, 4′‐diaminoazobenzene (DAAB), reinforced with nanosilica (NS), and nanoclay (NC) by means of isothermal technique of differential scanning calorimetry were studied. The Kamal autocatalytic‐like kinetic model was used to estimate the reaction orders (m, n), rate constants (k1, k2), and also active energies (Ea) and pre‐exponential factors (A) of the curing reaction. However, the existence of NS and NC with hydroxyl groups in the structure improves the cure reaction and influence the rate of reaction and therefore kinetics parameters. The Ea of cure reaction of DGEBA/DAAB system showed a decrease when nanoparticles were present and therefore the rate of the reaction was increased. Using the rate constants from the kinetic analysis and transition state theory, thermodynamic parameters such as enthalpy (ΔH#), entropy (ΔS#), and Gibbs free energy (ΔG#) changes were also calculated. The thermodynamic functions were shown to be very sensitive parameters for evaluation of the cure reaction. POLYM. COMPOS., 31:1442–1448, 2010. © 2009 Society of Plastics Engineers

Curing studies of epoxy resin by 4,4′‐diaminoazobenzene as curing agent reinforced with nanosilica and nanoclay particles along with impact resistance and thermal evaluation

AbstractThe effects of nanosilica (NS) and nanoclay (NC) particles as catalyst on the mechanism and kinetic parameters of cure reaction of DGEBA/4,4′‐diaminoazobenzene (DAAB) systems were studied. The kinetics parameters were obtained from nonisothermal differential scanning calorimeter data using the Kissinger, Ozawa, and isoconversional equations. The exothermic peak was shifted toward lower temperatures in DGEBA/DAAB/nanoparticle (NP) systems with increasing amount of the NP. However, the existence of NS and NC particles with hydroxyl groups in the structure in the mixture of DGEBA/DAAB catalyzes the cure reaction and increases the rate constant. The activation energy of cure reaction of DGEBA/DAAB systems, obtained from three methods, was in good agreement and showed a decrease when NPs were present in the mixture. The morphology of nanocomposite and dispersion of NPs in the composites was also observed using scanning electron microscopy. The impact resistance and thermogravimetric analysis of cured epoxy systems were also reported. POLYM. COMPOS., 31:1465–1473, 2010. © 2009 Society of Plastics Engineers

Improvement in photo-alignment efficiency of azobenzene-containing polyimide films

We have investigated the photo-induced in-plane anisotropy of the films of two different polyimides (PIs) containing azobenzene in the backbone structure (Azo-PIs), which were synthesized from the same diamine, 4, 4′-diaminoazobenzene (DAAB), and two different dianhydrides, pyromellitic dianhydride (PMDA) or oxydiphthalic anhydride (ODPA). Under the same photo-alignment condition, the in-plane anisotropy of the ODPA–DAAB PI film was significantly larger than that of the PMDA–DAAB PI film. This result shows that the photo-alignment efficiency of the former is higher than that of the latter; i.e. the photo-alignment efficiency of Azo-PI can be improved by changing the backbone structure. We believe that the observed enhancement in the photo-alignment efficiency is attributed to a lowering of the polymer chain rigidity, which is caused by introducing an ether linkage with free rotation around non-parallel bonds into the dianhydride part.

Medium effect on deprotonation equilibrium of HA-type acid-indicators in aqueous NaNO3 solutions- a model aquo-ionic system

The saturated solubility and the indicator constant of four newly synthesized HA-type azo-dye acid indicators, have been determined in NaNO 3 aquo-ionic model solvent system. The relative dissociation equilibrium of HA is found to be a function of transfer Gibb's energy of all the involved species in equilibrium for each indicator, although it is mainly dictated by that of conjugate anion A-. The greater stability of the oxo anion A- of 2-carboxy-2',4'-diaminoazo benzene with respect to other indicators due to increasing interaction with the solvated Na + ions with increased NaNO 3 concentration, differentiates it from others.

Syntheses of 2-carboxy-2', 4' -diamino azo benzene and 2-nitro-2' -hydroxy-4'methyl azo benzene and their use as acid-base indicators

The present paper describes the studies on acid-base characteristics of two synthesized novel azo-dyes. The isosbestic points and apparent pK In values of them have been determined spectrophotometrically. These dyes can be used as pH indicators for estimation of strength of the mixtures of acids, bases and salts. The parameters measuring the performance of indicators have been also evaluated with the help of UV-visible and IR-spectroscopy and conductivity measurements and comparison of our indicators have been also made with some known indicators like methyl orange and phenolphthalein. The study shows better performance of our synthesized indicators, particularly for titration of dilute solutions.

Application of 2-carboxy-2',4' -diamino azo benzene dye in jute dyeing

In the present study 2-carboxy-2',4'-diamino azo benzene dye is synthesized by diazo coupling of anthranilic acid with m-phenylenediamine which has been applied on jute fabric under three different dying condition like neutral, alkaline and acidic pH using conventional jute dying process at boil. Considering the colour yield and washing fastness property, dyeing of jute fabric in acidic condition is found to exhibit best results.

Cure kinetics of epoxy resin and aromatic diamines

AbstractThe kinetics of curing reaction of a diglycidyl ether of a bisphenol‐A based epoxy (DGEBA) with 4,4′‐diaminostillbene (DAS) and 4,4′‐diaminoazobenzene (DAAB) as curing agents are studied by differential scanning calorimetery (DSC) using the isothermal technique. The experimental data show that the cure reaction is autocatalytic in nature, and all kinetic parameters of the curing reaction are determined using a semiempirical equation. The reaction of DGEBA with DAS is faster than that with DAAB under the same conditions and the activation energies of both systems are higher than those reported for other aromatic diamines. With increasing isothermal temperature and concentration of curing agents the rate constants are increased by the increasing of probability collisions between epoxide and primary amine groups while the activation energies remain constant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1049–1056, 2004

Incorporation of a photochromic hinge in a rodlike polypeptide and its influence on dielectric and optical properties

AbstractA hinged, photoresponsive polypeptide (PAzP) was prepared and the effect of the photochromic hinge on the dielectric and photoisomerization behavior of the polymer in solution was probed. Polymerization of N‐carboxyanhydride of γ‐benzyl‐L‐glutamate was carried out with two different bifunctional photochromic amine initiators: di[(mercaptoethylamine)‐methylpropanamide]azobenzene (DMMPAB) and diaminoazobenzene (DAAB). Careful structural comparison of the polymers revealed that the basicity of the initiator plays a key role in determining the shape and structure of the polymer. Specifically, the use of a novel initiator DMMPAB prepared by the addition of flexible aliphatic amine substituents onto DAAB resulted in a hinged polymer (PAzP1), in which a single photochromic hinge was located within the polymer chain (Mw ∼ 36 kDa). In contrast, direct initiation with DAAB resulted in a polymer (PAzP2) in which the photochromic moiety was preferentially near the terminus of the polymer chain (Mw ∼ 21 kDa) and the polymer possessed a significant degree of asymmetry. Dielectric spectroscopy revealed that, in spite of a higher molecular weight, PAzP1 had a lower rotational relaxation time (2.72 μs) in solution than that of PAzP2 (4.41 μs). The residual dipole moment for the hinged PAzP1 was also smaller than that observed for PAzP2. The hinged polypeptide PAzP1 prepared from DMMPAB showed uniform photoisomerization between cis and trans states. However, the presence of flexible aliphatic amine substituents on DMMPAB caused the rate of isomerization of PAzP1 to be similar to the initiator DMMPAB. Optical characterization revealed that heterogeneity in the structure of PAzP2 was manifested as nonuniform rates of photoisomerization and thermal relaxation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2759–2773, 2001

Determination of hemoglobin in plasma and serum by linear-sweep polarography

A new method for the determination of hemoglobin (Hb) is described. It is based on the amplification of the Hb enzyme-catalyzed reaction between O-phenyldiamine (OPD) and H2O2 and polarographic measurement of the enzyme-generated product 2,2′-diaminoazobenzene (DAA). A linear calibration plot has been obtained within the range of 1∼20 μg/ml (r = 0.987) Hb. The assay is performed on the microtitre plate to avoid the influence of serum protein and to obtain good reproducibility. The method is practical, reliable and convenient, and has been applied to determine Hb in plasma and serum.

An Improved Elisa for the Determination of Thyroglobulin with Differential Pulse Voltammetry

Abstract An improved ELISA for the determination of Thyroglobulin(TG) in human serum with differential pulse voltammetry(DPV) has been developed. The enzymatic product 2,2′-diaminoazobenzene(DAA), produced from horseradish peroxidase(HRP) catalyzing the oxidation of H2O2 with orthophenylene diamine(OPD), yielded a sensitive differential pulse voltammetric response at - 0.18V(Vs Ag/AgCL) in pH2.0 0.2mol/L phosphate-0.1mol/L citrate buffer at a gold electrode. The small three-electrode system was directly inserted in the well of an ELISA plate for detection. The detection limit for TG was 3.8 ng/mL, which was about four times lower than that obtained by measuring the absorbance of DAA.