Species transformation and structure variation of fulvic acid during ozonation

The species transformation and structure variation of fulvic acid (FA) during ozonation were investi- gated in this study. The molecular weight (MW) distribution, the species of intermediate products and the variation of polar functional groups were studied by ultrafiltration, gas chromatography/mass spectrometry (GC/MS) and titration analyses respectively. The average MW of FA decreased signifi- cantly during ozonation. The amount of polar functional groups (carboxylic and phenolic (ph-OH) groups) per unit DOC (mol/kg C) increased with increasing ozonation time. Furthermore, GC/MS ex- periments demonstrated the formation of polar species (e.g., hexadecanoic acid, benzoic acid and oc- tadecanoic alcohol) and less-polar species (e.g., aliphatic hydrocarbons and butanedioic acid, bis(2-methylpropyl) ester). Electron spin resonance (ESR) measurements proved the presence of ·OH radicals in the ozonation system. Based on our experimental results, it appears that the oxidations by ozone molecule and ·OH radicals were responsible for the transformation of organics (FA and its oxi- dation products) during ozonation. These two oxidants showed significant influence on organics transformation and exhibited different mechanisms contributing to these processes.     

The oxidative destruction of lignin in the ozonation of wood

The oxidative destruction of lignin in the ozonation of aspen wood was studied. The kinetic curves of ozone consumption for samples with different contents of water were obtained. The consumption of ozone increased as the content of water grew. The second derivatives of the UV absorption spectra of lignin were obtained to show that the principal direction of lignin transformations under the action of ozone was the destruction of its aromatic constituents with the formation of carboxyl- and carbonyl-containing compounds. Measurements of the UV diffuse reflectance and EPR spectra of wood showed that the ozonation of wood caused the destruction of lignin quinoid structures. Part of lignin remained unchanged under the action of ozone. A key role in the destruction of wood lignin was played by ozone dissolved in water. Varying the content of water in wood samples allows various lignin transformation products to be obtained through ozonation.     

基于ReaxFF力场的对硝基苯酚臭氧氧化分子动力学模拟

本文采用基于ReaxFF反应力场的分子动力学方法(ReaxFF MD),利用自主研发的国际首个基于GPU加速的ReaxFF MD程序系统GMD-Reax和独特的化学反应分析工具VARx MD,探索臭氧氧化对硝基苯酚的反应机理。通过模拟考察了300 K恒温条件下臭氧氧化水中对硝基苯酚的行为,获得了酚结构开环、CO_2生成、主要自由基(·OH、·O_2、·O)及团簇型自由基的数量演变趋势,并可定性描述六元环开环和CO_2生成均遵循伪一级反应动力学规律。反应机理分析表明酚类分子在水溶液中被臭氧氧化的路径主要经过攫氢、六元环开环、碳链的氧化分解三个阶段,也揭示了自由基和团簇型自由基在臭氧降解对硝基苯酚时所发挥的重要作用。本工作是应用ReaxFF MD分子模拟方法对常温水环境下臭氧降解酚类污染物反应机理研究的一个尝试,可为深入认识该机理及相关的实验、理论研究提供一定的参考。     

Ozone reaction with 2,4-dinitrotoluene in acetic acid solution

2,4-Dinitrotoluene reacts with ozone along two concurrent pathways: at the aromatic ring yielding stable against ozonolysis hydroperoxide, and at the methyl group with retention of the aromatic structure. The relative amount of products undergoing oxidation at the aromatic ring and at the methyl group depends on the ozonation conditions, especially on the process temperature.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 11, 2004, pp. 1678–1680.Original Russian Text Copyright © 2004 by Andreev, G. Galstyan, A. Galstyan.     

Synthesis of new penicillin derivatives as drug-like molecules for biological screening

Chemical modification of penicillin β-lactam ring was made.Six thiazolidine amides were produced through N4-C7 β-lactam ring opening of penicillin V methyl ester with various aliphatic,aromatic,and heterocyclic primary amines.Five 8-hydroxypenillic acid derivatives with side chains of methyl,propyl,benzyl,and diethylaminoethyl groups were yielded via β-lactam ring rearrangement from6-aminopenicillanic acid(6-APA).Parallel synthetic methods were used for the alkylation of8-hydroxypenillic acid and β-lactam ring opening of penicillin V methyl ester.The biological activities of the compounds were evaluated.     

Ion trap tandem mass spectrometry study of dexamethasone transformation products on light activated TiO2 surface

The photocatalytic transformation of dexamethasone and the formation of its intermediate compounds have been studied using titanium dioxide as a photocatalyst. The degradation of dexamethasone occurs easily through the formation of several hydroxy derivatives whose characterization has been made by HPLC/MS/MS. Even if both oxidative and reductive processes can be operating, only oxidative products have been identified in air saturated aqueous suspensions. A pattern of reaction pathways accounting for the observed intermediates is proposed. The obtained experimental evidence may be rationalized postulating the existence of a double initial mechanism. A single oxidation step resulting from the attack by one ·OH radical leading to the formation of five hydroxy-derivatives and a concomitant attack involving two ·OH radicals leading to the hydroxylation of the quinoid moiety of the molecule.     

Improvement of the wetting and absorption properties of lignocellulosic fibers by means of gas phase ozonation

Gas phase ozonation was done on sheets made from chemical thermomechanical pulp in order to improve the wetting properties of the lignocellulosic fibers. The degree of modification was varied by letting the reaction continue for different lengths of time, ranging from 1 to 60 min. Changes in the chemistry of the fibers after ozone exposure were investigated using Fourier transform infrared (FT-IR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). The evolution of a carbonyl signal and the decrease of aromatic absorption over time was observed with FT-IR spectroscopy. The carbonyl peak grew in intensity as the reaction continued throughout the whole range of treatment times. The ESCA showed that carbonyl and carboxyl functionalities were introduced after 10 min of ozone exposure and that the intensity of the peak from the aliphatic and aromatic carbons decreased. However, an ozone treatment longer than 15 min did not affect the chemical surface composition, as analyzed by ESCA. The single-fiber contact angle with water, measured using a Cahn balance, decreased with extended ozonation. Measuring the time required for the sheet to absorb a water droplet with a high speed camera showed that even a very short ozone exposure (1 min) dramatically affected the absorption behavior. The rate of absorption dramatically increased after as little as 1 min of ozone exposure. This improvement in absorption rate was most likely due to the formation of low molecular weight degradation products, acting as wetting agents, created during the ozonation.     

Transformations of 5,6,7,8-tetrafluoro-2-ethoxycarbonylchromone under the action of primary amines

5,6,7,8-Tetrafluoro-2-ethoxycarbonylchromone in aprotic polar solutions formed by nucleophilic aromatic ipso-substitution 7-alkyl(aryl)amino-5,6,8-trifluorochromones. This transformation in ethanol depended on the reactivity of the acting amine: with stronger nucleophiles, aliphatic amines, an opening of the γ-pyrone ring occurred, with aromatic amines 7-monosubstituted chromones were the main products, and the open-chain esters formed in lesser amount.     

Kinetics and mechanism of the reactions of ozone with guaiacol,veratrol, and veratrol derivatives

The kinetics of the reactions of ozone with compounds modeling structural lignin fragments, viz., phenol, guaiacol, veratrol, veratric aldehyde, and veratric alcohol, was studied. The reaction rate constants were calculated using the mass transfer model for the chemical reaction based on the film theory. The rate constants of the reactions of ozone with compounds of the veratryl series were calculated by the Hammett equation. The major ozonation products of the studied compounds were determined by HPLC. The ozonation mechanism was proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 276–281, February, 2008.     

Identification of microbial inhibitory functional groups in corn stover hydrolysate by carbon-13 nuclear magnetic resonance spectroscopy

Dilute-acid biomass hydrolysates contain biomass degradation products that are inhibitory to cell growth and fermentation. Overliming with Ca(OH)₂ has been found to be one of the most effective methods for detoxifying the dilute-acid hydrolysate for ethanol production. However, the mechanism of overliming is not well understood. Carbon-13 nuclear magnetic resonance (¹³C-NMR) spectroscopy was used to elucidate the functional groups involved in the overliming reaction. The ¹³C-NMR spectra showed that the major functional groups removed during the overliming process were aliphatic and aromatic acids or esters, and other aromatic and aliphatic compounds. Ketone and aldehyde functionalities were not detected in the spectra. This is the first time that ¹³C-NMR has been used to elucidate the overliming reaction.     

Characterization and identification of cleavage products of 3‐glycosyl‐5‐substituted‐2‐isoxazoline

We report herein the synthesis of new synthons obtained by reductive opening of 3‐glycosyl‐5‐substituted‐2‐isoxazolines. Different cleavage products have been obtained depending on the substituents (aliphatic or aromatic) in position five of the heterocycle ring. The new compounds are characterized physically and spectroscopically.     

烯丙基溴化钐与羰基化合物反应合成高烯丙基醇

高烯丙基醇是有机合成中的一类非常重要的中间体,以烯丙基金属试剂与羰基化合物加成反应为其主要合成方法,常用的金属烯丙基化合物有烯丙基锂(镁、锌、硼、铟、硅、锡、钛)等.由于烯丙基的Grignard试剂制备过程中常伴随着大量的烯丙基偶联反应,所以用烯丙基的Grignard试剂来合.     

Enhanced degradation of 2,4-dinitrotoluene by ozonation in the presence of manganese(II) and oxalic acid

Manganese catalytic ozonation of 2,4-dinitrotoluene (DNT) in the presence of oxalic acid was studied. The addition of manganese ion (Mn²⁺) or oxalic acid alone in ozonation process did not enhance DNT degradation, but the addition of Mn²⁺ coupled with oxalic acid accelerated degradation of DNT. The DNT degradation efficiency was influenced by carbonate in the catalytic ozonation process. Kinetics study showed that Mn²⁺ catalytic ozonation significantly promoted the decomposition of ozone. Experimental results of electron spin resonance (ESR) demonstrated that addition of Mn²⁺ and oxalic acid produced much hydroxyl radicals in catalytic ozonation system than that in single ozonation system. These results suggested that catalytic ozonation followed hydroxyl radical-type mechanism. Mn²⁺ promoted decomposition of ozone to produce hydroxyl radical and it was oxidized into manganese oxide. Manganese oxide was reduced into Mn²⁺ by oxalic acid, which is the key step of catalytic process. Based on above results, a cycle catalytic mechanism of Mn²⁺ was proposed. Intermediates were determined by HPLC and GC–MS, and they mainly included aromatic organics and aliphatic carboxylic acids.     

Reactions of 2,3-Dioxopyrrolo[2,1-<Emphasis Type="Italic">a</Emphasis>]isoquinolines with Active N-Nucleophiles

It is shown that 2,3-dioxopyrrolo[2,1-a]isoquinolines react readily with aliphatic diamines and hydroxyamine with opening of the dioxopyrrole ring and formation of the corresponding bisenaminoketoamides and hydroxamic acids. Reaction with the thiosemicarbazide and hydrazides of aromatic acids proceeds without opening of the pyrrole ring at the ketone carbonyl. Derivatives of hexahydropyridazine are formed when compounds with carboxyethyl groups at position 1 react with hydrazine. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, 1383–1387, September, 2005.     

Ion trap tandem mass spectrometry study of dexamethasone transformation products on light activated TiO2 surface

The photocatalytic transformation of dexamethasone and the formation of its intermediate compounds have been studied using titanium dioxide as a photocatalyst. The degradation of dexamethasone occurs easily through the formation of several hydroxy derivatives whose characterization has been made by HPLC/MS/MS. Even if both oxidative and reductive processes can be operating, only oxidative products have been identified in air saturated aqueous suspensions. A pattern of reaction pathways accounting for the observed intermediates is proposed. The obtained experimental evidence may be rationalized postulating the existence of a double initial mechanism. A single oxidation step resulting from the attack by one ·OH radical leading to the formation of five hydroxy-derivatives and a concomitant attack involving two ·OH radicals leading to the hydroxylation of the quinoid moiety of the molecule.     

Identification of transformation products from β‐blocking agents formed in wetland microcosms using LC‐Q‐ToF

Identification of degradation products from trace organic compounds, which may retain the biological activity of the parent compound, is an important step in understanding the long‐term effects of these compounds on the environment. Constructed wetlands have been successfully utilized to remove contaminants from wastewater effluent, including pharmacologically active compounds. However, relatively little is known about the transformation products formed during wetland treatment. In this study, three different wetland microcosm treatments were used to determine the biotransformation products of the β‐adrenoreceptor antagonists atenolol, metoprolol and propranolol. LC/ESI‐Q‐ToF run in the MS^E and MS/MS modes was used to identify and characterize the degradation products through the accurate masses of precursor and product ions. The results were compared with those of a reference standard when available. Several compounds not previously described as biotransformation products produced in wetlands were identified, including propranolol‐O‐sulfate, 1‐naphthol and the human metabolite N‐deaminated metoprolol. Transformation pathways were significantly affected by microcosm conditions and differed between compounds, despite the compounds' structural similarities. Altogether, a diverse range of transformation products in wetland microcosms were identified and elucidated using high resolving MS. This work shows that transformation products are not always easily predicted, nor formed via the same pathways even for structurally similar compounds. Copyright © 2016 John Wiley & Sons, Ltd.     

Transcyclization of benzoxazoles

The reaction of benzoxazoles with aromatic and aliphatic acids, which gives transcyclization products — 2-substituted benzoxazoles — was studied. The reaction of 2-hydroxyacetanilide with aliphatic acids gives a mixture of 2-substituted benzoxazoles. Under similar conditions, 2-methylbenzothiazole, 2-alkyl-²-oxazolines, and 2-alkyl-²-thiazolines do not undergo transcyclization, but ring opening is observed in the latter two cases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1480–1482, November, 1972.     

Atmospheric Pressure Plasma Pretreatment of Sugarcane Bagasse: The Influence of Moisture in the Ozonation Process

Sugarcane bagasse samples were pretreated with ozone via atmospheric O₂ pressure plasma. A delignification efficiency of approximately 80 % was observed within 6 h of treatment. Some hemicelluloses were removed, and the cellulose was not affected by ozonolysis. The quantity of moisture in the bagasse had a large influence on delignification and saccharification after ozonation pretreatment of the bagasse, where 50 % moisture content was found to be best for delignification (65 % of the cellulose was converted into glucose). Optical absorption spectroscopy was applied to determine ozone concentrations in real time. The ozone consumption as a function of the delignification process revealed two main reaction phases, as the ozone molecules cleave the strong carbon–carbon bonds of aromatic rings more slowly than the weak carbon–carbon bonds of aliphatic chains.     

Combined Analytical Study on Chemical Transformations and Detoxification of Model Phenolic Pollutants during Various Advanced Oxidation Treatment Processes

Advanced oxidation processes (AOPs) have been introduced to deal with different types of water pollution. They cause effective chemical destruction of pollutants, yet leading to a mixture of transformation by-products, rather than complete mineralization. Therefore, the aim of our study was to understand complex degradation processes induced by different AOPs from chemical and ecotoxicological point of view. Phenol, 2,4-dichlorophenol, and pentachlorophenol were used as model pollutants since they are still common industrial chemicals and thus encountered in the aquatic environment. A comprehensive study of efficiency of several AOPs was undertaken by using instrumental analyses along with ecotoxicological assessment. Four approaches were compared: ozonation, photocatalytic oxidation with immobilized nitrogen-doped TiO₂ thin films, the sequence of both, as well as electrooxidation on boron-doped diamond (BDD) and mixed metal oxide (MMO) anodes. The monitored parameters were: removal of target phenols, dechlorination, transformation products, and ecotoxicological impact. Therefore, HPLC–DAD, GC–MS, UHPLC–MS/MS, ion chromatography, and 48 h inhibition tests on Daphnia magna were applied. In addition, pH and total organic carbon (TOC) were measured. Results show that ozonation provides by far the most suitable pattern of degradation accompanied by rapid detoxification. In contrast, photocatalysis was found to be slow and mild, marked by the accumulation of aromatic products. Preozonation reinforces the photocatalytic process. Regarding the electrooxidations, BDD is more effective than MMO, while the degradation pattern and transformation products formed depend on supporting electrolyte.