Naphthalenesulfonic Acids Research Articles

Mechanism of unactivated peroxymonosulfate-induced degradation of amino-G acid: Kinetics and transformation pathway

Amino-G acid (7-amino-1,3-naphthalenedisulfonic acid), a pollutant produced during textile preparation and in dyeing industries, is discarded in wastewater and causes ecological problems. In this study, amino-G acid (50.0 μM) could be completely removed by unactivated peroxymonosulfate (PMS) (1.0 mM) within 240 min, and the reaction kinetics exhibited strong pH dependence. A species-specific parallel reaction describes this pH dependence well, and the species-specific reaction rate constants of [amino-G acid]2− and [amino-G acid]− with HSO5− were calculated to be 0.0826 ± 0.0019 and 000122 ± 0.0027 M−1 s−1. The reactivity of the six naphthalene sulfonic acids and unactivated PMS varied according to the structure, and the amino group in naphthalene sulfonic acid, a typical electron-donating group, was more vulnerable to attack by unactivated PMS, which was further confirmed by the density functional theory results. The high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS) spectral analysis results indicated that naphthalene sulfonic acid was first oxidized to hydroxylamine products and then further oxidized to nitroso compounds, which exhibited more ecological toxicity. However, as the reaction processing, the toxicity of the product gradually decreased. Our results provide new insights into the in-situ oxidation of unactivated PMS.

STABILIZATION OF WATER-COAL COMPO­SITE FUELS USING CARBON MICRO-NANO­MATERIALS AND AMINO ALCOHOLS

The study investigated the potential of stabilizing composite water-coal fuel (CWCF) by adding carbon micro-nanomaterials obtained through the plasma-chemical conversion of organics-containing wastewater and amino alcohols. The study focused on systems based on anthracite with a solid phase concentration of 62%. Two amino alcohols, 2-amino-­2-methyl-1-propanol (AMP) and 2-amino-­2-ethyl-1,3-propanediol (AEPD) were used at concentrations of 0.25%, 0.5%, 1%, and 2.5% by weight of CWCF.
 The low stability and heterogeneity of coal particle distribution in organic liquids cause an increase in the viscosity of dispersed systems in combined systems. To regulate the rheological properties and stabilize the CWCF, chemicals such as dispersants, plasticizers, and stabili­zers are added. The CWCF 's properties can be improved by using additives such as sodium, calcium, and magnesium lignosulfonates, and naphthalene sulfonic acids. However, these reagents may not provide the desired properties of coal slurries in organomineral environments. Therefore, substitutes for these pro­ducts need to be found.
 Amino alcohols are commonly used as dispersants and stabilizers, especially in the production of water-based paints. They are low in cost, low in toxicity, and serve as anti-corrosive agents and pH stabilizers without causing excessive foaming. To strengthen the spatial structure, reactive particles such as carbon micro- and nanomaterials (CNM) can be introduced into the CWCF. Unlike polyelectrolytes and surfactants, CNM particles can have a varying number of active centers depending on the method of formation. By varying the properties of CNMs, it is possible to increase the number of contact centers and form a spatial grid without increasing the concentration of surfactants and polyelectrolytes. This is because contact interactions are activated during grinding, forming a new surface with energy-saturated active centers. As a result, the concentration of the system can be increased, and the calorific value of the fuel can be increased as well. However, the presence of an organic component can render mechanochemical activation ineffective by shielding active sites with large organic molecules. Therefore, identifying the most effective stabilizer reagents and deve­loping technology for their introduction into the dispersed system is a crucial and intricate problem in obtaining CWCF
 The study revealed that the ξ potential of anthracite particles is 40–45 mV in the pre­sence of amino alcohols. Sedimentation stabi­lity in the presence of highly dispersed carbon additives increases from 5–6 to 10–14 days, i.e., almost twice. The introduction of highly dispersed carbon leads to an increase in the effective viscosity of the systems and can be recommended for controlling the fluidity of the CWCF. The technical and operational requirements are best met by the CWCF containing 0.25% AMR and 1% highly dispersed carbon.

Characteristics and Behavior of Different Catalysts Used for Water Decontamination in Photooxidation and Ozonation Processes

The objective of this study was to summarize the results obtained in a wide research project carried out for more than 15 years on the catalytic activity of different catalysts (activated carbon, metal–carbon xerogels/aerogels, iron-doped silica xerogels, ruthenium metal complexes, reduced graphene oxide-metal oxide composites, and zeolites) in the photooxidation (by using UV or solar radiation) and ozonation of water pollutants, including herbicides, naphthalenesulfonic acids, sodium para-chlorobenzoate, nitroimidazoles, tetracyclines, parabens, sulfamethazine, sodium diatrizoate, cytarabine, and surfactants. All catalysts were synthesized and then texturally, chemically, and electronically characterized using numerous experimental techniques, including N2 and CO2 adsorption, mercury porosimetry, thermogravimetric analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV–vis spectroscopy, photoluminescence analysis, and transmission electron microscopy. The behavior of these materials as photocatalysts and ozonation catalysts was related to their characteristics, and the catalytic mechanisms in these advanced oxidation processes were explored. Investigations were conducted into the effects on pollutant degradation, total organic carbon reduction, and water toxicity of operational variables and the presence of different chemical species in ultrapure, surface, ground, and wastewaters. Finally, a review is provided of the most recent and relevant published studies on photocatalysis and catalyzed ozonation in water treatments using similar catalysts to those examined in our project.

The effect of a plasticizer based on polymethylene naphthalene sulfonic acids on the structure of a magnesian stone

The article presents the results of a study devoted to identifying the effect of a plasticizer based on polymethylene naphthalene sulfonic acids on the structure of a magnesian stone. It is known that the strength characteristics of magnesian stone samples modified with various amounts of such additive have different strength, provided that the water/cement ratio does not change. This study allows to identify the relationship between strength characteristics and structural features of magnesia stone modified by additive, as well as the effect on the dosage of this additive on the formation of the main structural minerals of magnesia stone. Study of the samples structure, the electron-scanning microscopy method and an X-ray microanalyzer were used. According to the results of the study, it was found that the presence and amount of a plasticizer based on polymethylene naphthalene sulfonic acids promotes the various formation and distribution of the main structural phases of magnesia stone. The optimal amount of additive allows to get the most amorphized structure of magnesium pentaoxyhydrochloride, providing it with the highest strength characteristics.

Correlation of the effectiveness of dispersing agents with different liquefaction mechanisms

Effective borehole sealing depends on many properties of the cement slurry. The rheological parameters are the most important. Designing the cement slurry with the required values of plastic viscosity, yield point or consistency coefficient contributes to the efficient performance of the cementing procedure and allows for effective filling of the cemented space outside the tubing. In order to adjust rheological parameters to technological requirements, dispersants are used. The operation of these plasticizers or superplasticizers is related to their chemical structure, which determines their liquefaction mechanism. Therefore, in order to properly select a fluidizing agent, it is beneficial to become familiar with its mechanism of operation, thanks to which it will be possible to use the optimal amounts for a given cement slurry recipe. The publication discusses the effectiveness of dispersing agents depending on their liquefaction mechanism. The research work carried out consisted in the modification of the cement slurry with the use of sodium salts of polycondensates of naphthalene sulfonic acids and a polymer dispersant based on carboxylates. Amounts of dispersant ranging from 0.05% (bwoc) to 1.0% (bwoc) were used. The rheological parameters described by means of five rheological models, i.e. Newton, Bingham, Ostwald de Waele, Casson and Herschele-Bulkley, were tested for the cement slurries. The main goal of the work presented in the article was to conduct a correlation analysis of the change in rheological parameters of slurries modified with dispersants belonging to different groups depending on their liquefaction mechanism. Thanks to this, it was possible to indicate the effectiveness of the dispersing additives depending on the amount of the fluid used belonging to a specific group. The work carried out is helpful in determining the optimal amount of dispersing agent depending on its type (mechanism of action).

Bioaccumulation of sediment-associated dinonylnaphthalene sulfonates in the freshwater mussel Lampsilis siliquoidea and oligochaete Tubifex tubifex

Naphthalene sulfonic acids (NSAs) are used primarily as additives in a wide range of industrial products (e.g., rubber materials, coatings, sealants, fuels, paints). Based on modeled physicochemical properties, NSAs would likely partition into sediments or the tissues of biota in an aquatic system. This study examined the potential for three NSAs, dinonylnaphthalene disulfonic acid (DNDS), barium dinonylnaphthalene sulfonate (BaDNS), and calcium dinonylnaphthalene sulfonate (CaDNS), to accumulate in the tissue of a freshwater mussel (Lampsilis siliquoidea) and oligochaete worm (Tubifex tubifex). The ability of L. siliquoidea to depurate accumulated chemical was also assessed. Mussels were exposed via sand spiked with CaDNS for 25 d, and then transferred to clean water where their ability to depurate the chemical over an additional 28 d was monitored. Worms were exposed to each of the three NSAs via spiked sediment for 28 d. NSA concentrations were measured separately in gill, foot, and remaining soft tissues (viscera) for mussels and in whole body tissue samples of worms. For L. siliquoidea, the largest concentration of CaDNS was measured in the gill tissue; once removed from CaDNS exposure, mussels were able to depurate up to 87% of the CaDNS from their tissues in 28 days. The biota-sediment accumulation factors (28-d BSAFs) for T. tubifex were 2.8–5.2, 0.53–0.76, and 0.83–1.11 for DNDS, BaDNS, and CaDNS, respectively. For mussel gill and viscera, BCFK values were 14.07 and 16.39, respectively. When BAFKs were calculated using the concentration of CaDNS in sand, they were 1.11 and 1.29 for mussel gill and viscera, respectively. These values are much lower than what would be necessary to classify this chemical as bioaccumulative; however, the BSAFs for DNDS in T. tubifex indicated a potential biomagnification concern if this compound were to occur in the aquatic environment.

The influence of organic carbon on the toxicity of sediment-associated dinonylnaphthalene sulfonic acids to the benthic invertebrates Tubifex tubifex and Hyalella azteca

Naphthalene sulfonic acids (NSAs) are used extensively in industrial applications as dispersants in dyes, rubbers, and pesticides, and as anti-corrosive agents in coatings, gels, and sealants. This study examined the toxicity of three NSA congeners, barium dinonylnaphthalene sulfonate (BaDNS), calcium dinonylnaphthalene sulfonate (CaDNS), and dinonylnaphthalene disulfonic acid (DNDS), to two benthic species, Tubifex tubifex and Hyalella azteca. Two substrates with different levels of organic carbon (sediment [2%] and sand [0%]) were used in toxicity tests. Juvenile production was the most sensitive endpoint for T. tubifex: the 28-d EC50s were <18.2, 22.2, and 64.0 μg/g dw in sand and 281.3, 361.6, and 218.9 μg/g dw in sediment for BaDNS, CaDNS, and DNDS, respectively. The 28-d LC50s for H. azteca were similar among compounds: 115.3, 82.1, and 49.0 μg/g dry weight (dw) in sand, and 627.3, 757.9, and >188.5 μg/g dw in sediment, for BaDNS, CaDNS, and DNDS, respectively. However, when LC50s were estimated based on concentrations of NSAs measured in overlying water (which can be an important route of exposure for H. azteca), BaDNS and CaDNS were 3–4 orders of magnitude more toxic than DNDS. The NSAs examined were >3-fold more toxic when present in substrates with no organic carbon (e.g., sand) for all H. azteca endpoints where LC/EC50s could be calculated and for sublethal endpoints for T. tubifex. The organic carbon content of the sediment appears to have acted as a sink and reduced NSA toxicity by decreasing bioavailability. Environmental sediment samples were collected from 12 river sites across southern Ontario. The maximum concentration of CaDNS observed in sediment collected from this region was 2.8 μg/g dw in sediment with 2% organic carbon; 100-fold lower than the lowest EC10 in the current study.

Sub-lethal effects of calcium dinonylnaphthalenesulfonate on Western clawed frog embryos

Naphthalene sulfonic acids (NSAs) are used as additives in lubricants, dyes, and greases and commonly act as surfactants in many industrial processes. The calcium salt of dinonyl NSA (calcium dinonylnaphthalenesulfonate; CaDNS) is listed among thousands of chemicals identified as priorities for assessment by the Government of Canada's Chemical Management Plan due to the limited toxicity data. The purpose of this study was two-fold: 1) to establish the toxicity of CaDNS to Western clawed frog (Silurana tropicalis) embryos and 2) to assess the sub-lethal effects and mechanisms of toxicity of CaDNS in amphibians through targeted gene expression and metabolite analyses. Frog embryos were exposed to water overlying sand spiked with a range of concentrations of CaDNS (17–1393 μg/g) over a 72-h period. Results indicated significantly higher mortality and presence of malformations in frog larvae exposed to over 672 μg/g CaDNS in the sand (14 ng/mL CaDNS in the water) compared to control treatments. An overall decrease in the glutathione redox cycle was observed, including decreases in relative mRNA levels of enzymes (glutathione S-transferase (gst), glutathione reductase (gsr), glutathione peroxidase (gpx)) and decreases in the glutathione (GSH) and glutathione disulfide (GSSG) metabolite concentrations. In addition, transcript levels of genes involved in antioxidant capacity and essential amino acid metabolites decreased significantly in embryos exposed to low levels of CaDNS. This is the first study to assess the toxicity of NSAs in amphibians, contributing important data to aid in the assessment of NSAs.

Synthesis, Characterization and Dyeing Assessment of Novel Acid Dyes on Wool Fabric IV

We report synthesis and performance evaluation of a series of novel acid dyes based on diazotized substituted aryl amines and employing substituted naphthalene sulfonic acids as coupling component. The synthesized dyes were thoroughly characterized using UV-visible, IR, 1HNMR spectroscopy, elemental analysis and negative MALDI-TOF mass spectrometric analysis. The effectiveness of these dyes was evaluated by applying them on wool fabric using a standard exhaust dyeing procedure. The results for washing, light, perspiration and rubbing fastness of the dyed fabric demonstrate excellent fixation, binding strength and fastness properties which indicate that they are suitable for industrial wool dyeing operations.

Evaluation of the Concentration Polymethylene Naphthalene Sulfonates in Concrete

A procedure is developed for the determination of technical polymethylene naphthalene sulfonates (TPNS) in concrete by HPLC. The presence of 9.8–18.8% of a fraction with a low adsorption activity in TPNS is detected. A correlation is found between the initial slump of the concrete mix cone and the refined amount of oligomers of polymethylene naphthalene sulfonic acids with n ≥ 11, contained in TPNS.

Effective Removal of Naphthalenesulfonic Acid from Water Using Functionalized Metal–Organic Frameworks

Effective removal of toxic 1,5-naphthalenedisulfonic acid (NDS) and 2-naphthalenesulfonic acid (NSA) from contaminated water still faces a challenge to date. Herein, porous MIL-101, MIL-101-NH2, and MIL-101-SO3H were systematically studied for their adsorption performances toward these toxic molecules. Upon the introduction of −NH2 groups, H-bond interaction and electrostatic interaction were enhanced, and accordingly MIL-101-NH2 can exhibit more excellent adsorption capacity (NDS, 188.1 mg g–1; NSA, 285.0 mg g–1) compared to MIL-101-SO3H, MIL-101, and some other common adsorbents. Further study indicates that MIL-101-NH2 can be easily regenerated even after three adsorption processes. This work demonstrates that MIL-101-NH2 may have large potential in naphthalenesulfonic acids removal and rational selection of organic functional groups may be critical in construction of adsorbents.

Adsorptive removal of naphthalenesulfonic acids using wild almond shell activated carbon from aqueous solution

Activated carbon was prepared from wild almond shells using phosphoric acid as an activating agent. The BET surface area and the pore volume were found to be 1133.25 m2/g and 1.41 cm3/g, respectively. Batch adsorption of two naphthalene dye intermediates, H‐ and γ‐acid was carried out using prepared activated carbon. The maximum adsorption capacities were found to be 911 and 809.4 mg/g, respectively, at 65°C. Freundlich isotherm fitted well the equilibrium data, indicating favorable adsorption of both the acids. Adsorption was controlled by the external mass transfer and intraparticle diffusion. Thermodynamic analysis showed that the adsorption was physical, spontaneous, and endothermic in nature. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 38–44, 2017

Electrochemical synthesis, characterisation and comparative study of new conducting polymers from amino-substituted naphthalene sulfonic acids

Conducting polymers have been synthesised electrochemically from 4-amino-3-hydroxynaphthalene-1-sulfonic acid (4A3HN1SA), 4-aminonaphthalene-1-sulfonic acid (4AN1SA) and 7-amino-4-hydroxynaphthalene-2-sulfonic acid (7A4HN2SA) on glassy carbon electrodes. The influence of the positive potential limit on the potential cycling polymerisation of 4A3HN1SA was studied, and a sufficiently high potential limit allowed better film growth. Under similar polymerisation conditions, the three monomers showed different radical formation potentials and different voltammetric peak profiles. The effects of scan rate and solution pH on the electrochemical properties of the polymers were investigated, in the range between 10 and 200 mV s−1, all the modified electrodes showing a surface-confined electrode process. In the pH range from 2.0 to 9.0, the anodic peak potentials decreased linearly with increasing pH for all the three modified electrodes. The modified electrodes were characterised by electrochemical impedance spectroscopy in pH 4.0 and 7.0 buffer solutions. The results showed a more porous poly(7A4HN2SA) film, which is less affected by pH change than the other two films. Scanning electron microscopy of the polymer films also showed significant differences in their morphologies.

Relationship of mineralization of amino naphthalene sulfonic acids by Fenton oxidation and frontier molecular orbital energies

Six amino naphthalene sulfonic acids including mono-, di- and tri-sulfonic acid compounds were studied to find the relationship between the reactivity of this kind of compounds in Fenton oxidation process and energies of the frontier molecular orbital. It was found that the initial rates of TOC reduction and oxalic acid production correlated strongly to the frontier molecular orbital energies and can be estimated by EHOMO and the absolute electronegativity (χ). The cleavage of –SO3H and –NH2 groups to produce SO42− and NH4+ species was dependent on the electron density distribution on the –SO3H moiety and the α-carbon atom connecting the –NH2 moiety. The electron withdrawing effect of the –SO3H groups influenced the mineralization of naphthalene sulfonic acids significantly. The naphthalene sulfonic acid with more –SO3H groups was more recalcitrant to the Fenton oxidation.

The enhancement of fluorescence quantum yields of anilino naphthalene sulfonic acids by inclusion of various cyclodextrins and cucurbit[7]uril

The association constants (K) for the inclusion complexation of four kinds of cyclodextrins (CDs (β- and γ-), 2,6-di-O-methylated β-CD, and 2,3,6-tri-O-methylated β-CD) and cucurbit[7]uril (CB[7]) with 1,8- and 2,6-anilinonaphthalene sulfonic acids (ANSs) were determined from fluorescence spectra enhanced by inclusion. Various CDs and CB[7] form stable 1:1 inclusion complexes with 1,8- and 2,6-ANSs: K=80–11700M−1 for 2,6-ANS and 50–195M−1 for 1,8-ANS. The high stability of the inclusion complexes of 2,6-ANS with CB[7] and 2,6-di-O-methylated β-CD is shown. Further, we determined the fluorescence quantum yields (Φ values) for the inclusion complexes of ANSs by using a fluorescence spectrophotometer equipped with a half-moon unit. The Φ values of 1,8- and 2,6-ANSs were largely enhanced by the inclusion of methylated β-CDs and did not correlate with the degree of stability (K) of the inclusion complexes. We characterized the structures of the inclusion complexes by 2D ROESY-NMR measurements. In addition, the microenvironmental polarity inside the hydrophobic CD and CB[7] cavities was evaluated using the fluorescence probe 2,6-ANS. Based on the emission mechanism and the aspect of inclusion in a hydrophobic cavity, we have suggested that the microenvironmental polarity and viscosity for the excited state of ANS plays an important role for the Φ values of inclusion complexes.

Synthesis and Characterization of Sulfonated Polyanilines and Application in Construction of a Diazinon Biosensor

A series of sulfonated polyaniline/derivatized polyaniline nanocomposites was chemically synthesized in the presence of anthracene and naphthalene sulfonic acids. UV-vis and FTIR results indicated the emergence of new bands at 420 and 700 nm and 1100 cm−1 in their spectra, respectively, meaning the dopant/polymer intercalations involved electronic interactions between dopant/polymer sub-lattices. The electroactive composites displayed moderately fast electrode kinetics. A composite-based biosensor for hydrogen peroxide reached a steady state current of 9.2 and 5.3 µA, and when fine-tuned for diazinon detection gave % inhibitions to be 41 and 81% for the polyaniline and poly-o-methoxyaniline biosensors, respectively.

H 2O 2/UV-C treatment of the commercially important aryl sulfonates H-, K-, J-acid and Para base: Assessment of photodegradation kinetics and products

H 2O 2/UV-C treatment of four commercially important aryl sulfonates (naphthalene sulfonic acids H-acid, K-acid, J-acid and benzene sulfonic acid Para base) in aqueous solutions was investigated. Photodegradation kinetics was followed in terms of changes brought about in the parent compound concentration via high performance liquid chromatography, as well as abatement of the collective environmental parameters COD and TOC. The efficiency of H 2O 2/UV-C treatment was also evaluated by determining H 2O 2 consumption rates throughout the reactions whereas the formation of intermediates (photodegradation products) was traced by means of mass spectrometry. Our experimental findings indicated that especially trisulfonated K-acid was not very prone to photochemical degradation, closely followed by the other studied aryl sulfonates. The highest abatement rates (treatment efficiencies and reaction kinetics) were obtained for the relatively simpler structured Para base. Mass spectrometric analysis revealed that the early stages of H 2O 2/UV-C treatment followed a OH-addition mechanism as mainly hydroxylated photodegradation products were qualitatively identified.

Photooxidation of naphthalenesulfonic acids: Comparison between processes based on O 3, O 3/activated carbon and UV/H 2O 2

The aim of the present study was to analyze and compare the efficacy of UV photodegradation with that of different advanced oxidation processes (O 3, UV/H 2O 2, O 3/activated carbon) in the degradation of naphthalenesulfonic acids from aqueous solution and to investigate the kinetics and the mechanism involved in these processes. Results obtained showed that photodegradation with UV radiation (254 nm) of 1-naphthalenesulfonic, 1,5-naphthalendisulfonic and 1,3,6-naphthalentrisulfonic acids is not effective. Presence of duroquinone and 4-carboxybenzophenone during UV irradiation (308–410 nm) of the naphthalenesulfonic acids increased the photodegradation rate. Addition of H 2O 2 during irradiation of naphthalenesulfonic acids accelerated their elimination, due to the generation of OH radicals in the medium. Comparison between UV photodegradation 254 nm and the advanced oxidation processes (O 3, O 3/activated carbon and UV/H 2O 2) showed the low-efficacy of the former in the degradation of these compounds from aqueous medium. Thus, among the systems studied, those based on the use of UV/H 2O 2 and O 3/activated carbon were the most effective in the oxidation of these contaminants from the medium. This is because of the high-reactivity of naphthalenesulfonic acids with the OH radicals generated by these two systems. This was confirmed by the values of the reaction rate constant of OH radicals with these compounds k OH, obtained by competitive kinetics (5.7 × 10 9 M −1 s −1, 5.2 × 10 9 M −1 s −1 and 3.7 × 10 9 M −1 s −1 for NS, NDS and NTS, respectively).

Decomposition of Aqueous Naphthalene-1,5-Disulfonic Acid by Means of Oxidation Processes

Three different Advanced Oxidation Processes (ozonation at pH 7.5, electron beam irradiation and a combination ozonation/electron beam irradiation) have been applied to study decomposition of aqueous naphthalene-1,5-disulfonic acid (1,5-NDSA) with regard to mineralization and formation of biodegradable intermediates. Formation of biodegradable intermediates could not be indicated for any of the processes used; single electron beam irradiation treatment was the most efficient process for mineralization of organic carbon contained in aqueous 1,5-NDSA. Applied to a real wastewater effluent from a mixed municipal/industrial wastewater, electron beam irradiation with a radiation dose of 2 kGy was sufficient to reduce the concentrations of all naphthalene sulfonic acids and some of the alkylphenol ethoxylates also contained in that water by about 2 orders of magnitude.

An analysis of the photo-reactivity of monoazo reactive dyes derived from H-acid and related naphthalene sulfonic acids using the PM5 method

The reactivities ( k 0) of 10 reactive azo dyes derived from H-acid (eight) and related naphthalene sulfonic acids (two) on cellulose films toward singlet oxygen ( 1O 2) were determined by exposing the dyed films immersed in aerobic Rose Bengal solution to a carbon arc. The k 0 values were analyzed in terms of frontier orbital theory using the semiempirical molecular orbital PM5 method, and were confirmed to correlate to the electrophilic frontier density, f r ( E ) , at the double bonds with high electron density in HOMO for the predominant tautomers of the dyes on cellulose. The azo–hydrazone tautomerism of the dyes examined was analyzed by calculating the standard heat of formation in the gas phase and water using the PM5 method. The modes of reaction between the azo dyes and 1O 2 were the ene and/or the [2 + 2] cycloaddition reaction. The reactivities were expressed as the sum of f r ( E ) at the corresponding double bonds. The plots of log k 0 against the sum of f r ( E ) for all of the dyes examined yielded a close correlation line, and this was considered to be the molecular descriptor of the reactivity of aromatics against 1O 2.