Effects of temperature and physical state on heterogeneous oxidation of oleic acid droplets with ozone

The heterogeneous reactions of pure micrometer-sized oleic acid droplets with ozone were studied as a function of temperature and physical state. Oxidation reactions were monitored using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FT-IR) and UV-vis spectrometry. Variations in droplet morphology due to the extent of oxidation were monitored using an optical microscope. Oleic acid droplets were maintained in either solid or liquid state at 9.0 °C. The physical state of the aerosol was determined from the IR absorbance spectra. Oxidation of solid state oleic acid with ozone at 9.0 °C was rapidly converted to the liquid state, which was most likely due to the presence of oxidation products on the surface of the droplets. The fast melting process that resulted from exposure of solid-phase droplets to ozone produced an oxidation rate similar to that for liquid-phase droplets exposed to ozone at the same temperature. Analysis of the carboxylic IR absorbance ratio for esters vs carboxylic acids indicates that the larger ester C═O-to-carboxylic acid C═O ratios at higher temperature appeared to correspond to the production of α-acyloxyalkyl hydroperoxide oligomers and polymers. The wide variation in product yields will result in vastly different physical properties of aerosol particles under different ambient environmental conditions.     

Static SIMS studies of carboxylic acids on gold and aluminium–magnesium alloy surfaces

Static secondary ion mass spectrometry was used to study the surface reactions and lateral distributions of fatty carboxylic acid molecules on sputter‐deposited gold and aluminium surfaces, as well as commercial aluminium–magnesium alloy surfaces, cleaned using UV/ozone. Films were prepared by spin coating dilute solutions of stearic acid and lauric acid onto the above surfaces. These carboxylic acids were shown to react with the oxide formed on the aluminium and aluminum–magnesium alloy substrates to produce a deprotonated acid anion, stabilized by the formation of a magnesium soap on the aluminium–magnesium alloy surface. Secondary ion imaging of stearic acid films revealed the formation of C‐type crystals. Copyright © 2003 John Wiley & Sons, Ltd.     

Catalytic Enantioselective Methylene C(sp3)−H Amidation of 8‐Alkylquinolines Using a Cp*RhIII/Chiral Carboxylic Acid System

Catalytic enantioselective directed methylene C(sp³)?H amidation reactions of 8‐alkylquinolines using a Cp*Rh^III/chiral carboxylic acid (CCA) hybrid catalytic system are described. A binaphthyl‐based chiral carboxylic acid efficiently differentiates between the enantiotopic methylene C?H bonds, which leads to the formation of C?N bonds with good enantioselectivity.     

The effect of humidity on the ozonolysis of unsaturated compounds in aerosol particles

Atmospheric aerosol particles are important in many atmospheric processes such as: light scattering, light absorption, and cloud formation. Oxidation reactions continuously change the chemical composition of aerosol particles, especially the organic mass component, which is often the dominant fraction. These ageing processes are poorly understood but are known to significantly affect the cloud formation potential of aerosol particles. In this study we investigate the effect of humidity and ozone on the chemical composition of two model organic aerosol systems: oleic acid and arachidonic acid. These two acids are also compared to maleic acid an aerosol system we have previously studied using the same techniques. The role of relative humidity in the oxidation scheme of the three carboxylic acids is very compound specific. Relative humidity was observed to have a major influence on the oxidation scheme of maleic acid and arachidonic acid, whereas no dependence was observed for the oxidation of oleic acid. In both, maleic acid and arachidonic acid, an evaporation of volatile oxidation products could only be observed when the particle was exposed to high relative humidities. The particle phase has a strong effect on the particle processing and the effect of water on the oxidation processes. Oleic acid is liquid under all conditions at room temperature (dry or elevated humidity, pure or oxidized particle). Thus ozone can easily diffuse into the bulk of the particle irrespective of the oxidation conditions. In addition, water does not influence the oxidation reactions of oleic acid particles, which is partly explained by the structure of oxidation intermediates. The low water solubility of oleic acid and its ozonolysis products limits the effect of water. This is very different for maleic and arachidonic acid, which change their phase from liquid to solid upon oxidation or upon changes in humidity. In a solid particle the reactions of ozone and water with the organic particle are restricted to the particle surface and hence different regimes of reactivity are dictated by particle phase. The potential relevance of these three model systems to mimic ambient atmospheric processes is discussed.     

The catalytic ozonization of model lignin compounds in the presence of Fe(III) ions

The ozonization of several model lignin compounds (guaiacol, 2,6-dimethoxyphenol, phenol, and vanillin) was studied in acid media in the presence of iron(III) ions. It was found that Fe³⁺ did not influence the initial rate of the reactions between model phenols and ozone but accelerated the oxidation of intermediate ozonolysis products. The metal concentration dependences of the total ozone consumption and effective rate constants of catalytic reaction stages were determined. Data on reactions in the presence of oxalic acid as a competing chelate ligand showed that complex formation with Fe³⁺ was the principal factor that accelerated the ozonolysis of model phenols at the stage of the oxidation of carboxylic dibasic acids and C₂ aldehydes formed as intermediate products.     

Oxidation of oleic acid and oleic acid/sodium chloride(aq) mixture droplets with ozone: changes of hygroscopicity and role of secondary reactions

The heterogeneous reactions of oleic acid (OL) and oleic-acid/sodium-chloride(aq) (OL/NaCl(aq)) mixture droplets with ozone are studied at two relative humidities (RH). The reactions were monitored concomitantly using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FT-IR) for the organic species and UV-vis spectrometry for the ozone concentration in order to investigate reaction rate discrepancies reported in literature as well as the oxidation mechanism. The less volatile products were identified and resolved by a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS). This led to identification of 13 organic molecules (up to 45 carbons). Identified products were predominantly composed by nananoic acid and azelaic acid. Our results suggest that the propagation reaction is possibly initiated by a secondary reaction such as the stabilized Criegee intermediates reacting with oleic acid. For hygroscopic properties, the ATR-IR spectra at high RH (87 +/- 5%) showed that the hydrophobic oleic acid droplets can take up water slightly when exposed to ozone. For internally mixed OL/NaCl(aq) droplets, the hygroscopic properties of the droplets upon ozone exposure were found to be complex; hygroscopic properties or the growth factors of the droplets are altered as the oxidation products of oleic acid exist concurrently with NaCl(aq). Furthermore, the concentration of ozone was monitored to examine the kinetics of the oxidation reaction. The integrated ozone profile recorded by UV-vis spectrometry showed the consumed ozone represents only 30 +/- 2% of total oleic acid and hence confirmed the existence of secondary reactions. A kinetic model was used to simulate an ozone temporal profile that could only be described if the secondary reactions were included. The discrepancy of ozone uptake coefficients according to the OL and ozone measurements as well as their atmospheric implications are herein discussed.     

Heterogeneous reactions of linoleic acid and linolenic acid particles with ozone: reaction pathways and changes in particle mass, hygroscopicity, and morphology

In this study, an electrodynamic balance (EDB) and a single particle Raman spectroscopic system were used to investigate the heterogeneous reactions of linoleic acid and linolenic acid with ozone under ambient temperatures (22-24 degrees C) and dry conditions (RH<5%). Raman characterizations provide evidence that ozone-induced autoxidation, in addition to direct ozonolysis, is a plausible pathway in the reactions between ozone and linoleic acid and linolenic acid particles. Furthermore, the significance of this specific oxidation pathway depends on the ozone concentrations used in the experiment. A low ozone concentration (approximately 200-250 ppb) with a longer exposure period (20 h) favors autoxidation but an extremely high ozone concentration (approximately 10 ppm) favors ozonolysis and forces most unsaturated fatty acids to react with ozone in a relatively short period of time. In the low ozone concentration experiments, the mass of the ozone-processed linoleic acid and linolenic acid particles increased by about 2-3% and 10-13%, respectively. In addition, the mass ratios (particle mass at RH approximately 85% to particle mass at RH<5%) of the ozone-processed linoleic acid and linolenic acid particles increased by about 2-3% and 3-4%, respectively. The morphology of the pure and ozone-processed linoleic acid and linolenic acid particles are compared, based on imagining and their light scattering patterns.     

The ozonization of model lignin compounds in aqueous solutions catalyzed by Mn(II) ions

The influence of Mn(II) ions on the rate of the reaction between ozone and model lignin compounds, guaiacol and veratrole, was studied. The catalyst did not influence the rate of the destruction of the aromatic ring and intermediate ozonolysis products, compounds with conjugated double bonds, in acid media but substantially increased the rate of oxidation of saturated carboxylic acids, ketoacids, and aldehydes. Ozone consumption then increased from 2 to 5 moles per mole of the transformed substrate. A mechanism of the catalytic action of Mn(II) in reactions between ozone and the compounds studied was suggested.     

Influence of organic coatings on pyrene ozonolysis at the air-aqueous interface

Glancing angle laser-induced fluorescence was used to investigate the effects of organic monolayer coatings on the ozonation kinetics of pyrene at the air-aqueous interface. Fluorescence spectra show that both 1-octanol and octanoic acid coatings give rise to similar decreased polarity at the interface relative to the uncoated surface and show a similar propensity of pyrene to partition to the interface. Ozonation kinetics follow a Langmuir-Hinshelwood mechanism, indicating a surface reaction. At high ozone concentrations, a monolayer coating of 1-octanol enhances the rate relative to the uncoated surface and a coating of octanoic acid decreases the rate. Pyrene fluorescence is most efficiently quenched by ozone in the presence of a 1-octanol coating, followed by the uncoated surface, and least efficiently quenched by ozone in the presence of octanoic acid. In agreement with earlier work, a significant photoenhancement of the ozonation is observed at the uncoated surface; however, no enhancement is observed with monolayer coatings of either organic. Quantum chemical calculations indicate a reasonable binding of ozone by the carboxylic acid group (in both its dissociated and undissociated forms). We suggest that the inhibition of the water surface reaction by a monolayer of octanoic acid is due to the sequestration of ozone by the carboxylic acid group.     

二氧化碳作为羧化试剂用于羧酸及其衍生物的合成(英文)

二氧化碳是储量丰富、廉价易得且可再生的C1资源,将其催化转化成高附加值精细化学品的研究已经引起了人们的广泛关注.目前,虽然二氧化碳用作初始原料的反应已经工业化的很少,但过去几十年中仍有二十多个具有实际应用前景的二氧化碳参与的新反应被发现,其中以二氧化碳作为羧化试剂合成各种羧酸及其衍生物的反应为突出代表.本文综述了过渡金属催化合成羧酸及其衍生物的二氧化碳与多种碳亲核试剂、碳氢键以及碳碳多重键化合物的反应,并总结了无过渡金属参与或有机小分子催化条件下将二氧化碳转化成羧酸及其衍生物的反应.     

Decomposition processes of an organic monolayer formed on Si(111) via a silicon-carbon bond induced by exposure to UV irradiation or ozone

The decomposition processes of an organic monolayer, which was formed on Si(111) via a Si-C covalent bond, induced by exposure to UV light irradiation or ozone, were investigated using attenuated total reflectance Fourier transform infrared spectroscopy. Exposure to both ozone and UV light resulted in a reduction of the intensities of the IR peaks corresponding to CH stretching vibration and bending scissors and the appearance of peaks corresponding to CO stretching and COH in-plane bending. The latter peaks initially increased, reached a maximum, and then decreased, indicating that the monolayer was decomposed through the formation of intermediates such as aldehyde and carboxylic acid. The monolayer was also decomposed by exposure only to UV light or ozone but more slowly as the time dependencies of the CH peaks showed. While the peaks corresponding to the CO stretching and the COH in-plane bending behaved similarly under the condition of exposure to ozone, they were not observed during decomposition induced by UV irradiation. These results show that, while the monolayer was decomposed through the formation of oxidized intermediates such as aldehyde and carboxylic acid under the condition of exposure to ozone, the decomposition of the monolayer under the condition of UV irradiation proceeded via cleavage of Si-C bonds by photogenerated electrons or holes without such oxidized intermediates. An increase of gauche defects as the decomposition proceeded was demonstrated by sum frequency generation spectroscopy.     

To probe the origin of activation effect of carboxylic acid and (+)-NLE in tridentated titanium catalyst systems

The activation effect of carboxylic acid and positive nonlinear effect ((+)-NLE) in tridentated titanium catalyst systems for hetero Diels-Alder reaction and aldol-type reactions has been first elucidated on the basis of X-ray crystal structural analysis of homochiral (pseudo-octahedral coordination geometry with C2 symmetry) and heterochiral (pseudo-octahedral coordination geometry with C1 symmetry) titanium complexes and the observation of their different reactivities with carboxylic acid additive.     

硅磷酸铝分子筛催化羧酸的酯化反应研究

用新型硅磷酸铝分子筛和改性的硅磷酸铝分子筛催化脂肪族羧酸与脂肪族醇的酯化反应，以正戊酸分别与正丙醇、正丁醇、正戊醇和正辛醇以及正辛醇分别与乙酸、丙酸、正丁酸、正戊酸和正己酸的酯化反应作为探针实验进行了系统研究，实验结果显示，改性的硅磷酸铝分子筛比不改性的硅磷酸铝分子筛具有更高的酯化催化活性，实验发现，反应物的结构对酯化反应产生了显著的影响，文章揭示了新型硅磷酸铝分子筛和改性的硅磷酸铝分子筛对于羧酸的直接酯化反应的系列规律性。     

Distal γ‐C(sp3)−H Olefination of Ketone Derivatives and Free Carboxylic Acids

Reported herein is the distal γ‐C(sp³)?H olefination of ketone derivatives and free carboxylic acids. Fine tuning of a previously reported imino‐acid directing group and using the ligand combination of a mono‐N‐protected amino acid (MPAA) and an electron‐deficient 2‐pyridone were critical for the γ‐C(sp³)?H olefination of ketone substrates. In addition, MPAAs enabled the γ‐C(sp³)?H olefination of free carboxylic acids to form diverse six‐membered lactones. Besides alkyl carboxylic acids, benzylic C(sp³)?H bonds also could be functionalized to form 3,4‐dihydroisocoumarin structures in a single step from 2‐methyl benzoic acid derivatives. The utility of these protocols was demonstrated in large scale reactions and diversification of the γ‐C(sp³)?H olefinated products.     

Catalytic oxidative degradation of polyethylene crystals

Linear polyethylene crystals have been degraded with oxygen in the presence of a catalyst composed of cobaltous and bromide ions at temperatures between 60 and 130°. The number of carbonyl groups introduced into polyethylene increases as the oxidation temperature is raised. Infra-red spectroscopy and molecular weight evidence suggests that ketone groups are formed by a non-chain scission reaction, whereas aldehyde and carboxylic acid groups result from chain scission reactions. Molecular weight distributions of the degradation products show that reactions occur selectively in the amorphous regions at the crystal surfaces, when oxidations are performed below 110°. At higher temperatures, the chains are degraded randomly. The carbonyl groups introduced into polyethylene were oxidized to carboxylic acid groups with concentrated (～ 70 per cent) nitric acid. The results demonstrate that this two-stage process yields a polydisperse long-chain linear paraffin with carboxylic acid end-groups, when the catalytic oxidations are performed between 115 and 130°.     

Photoinduced Copper-Catalyzed Asymmetric Decarboxylative Alkynylation with Terminal Alkynes

We describe a photoinduced copper-catalyzed asymmetric radical decarboxylative alkynylation of bench-stable N-hydroxyphthalimide(NHP)-type esters of racemic alkyl carboxylic acids with terminal alkynes, which provides a flexible platform for the construction of chiral C(sp³)−C(sp) bonds. Critical to the success of this process are not only the use of the copper catalyst as a dual photo- and cross-coupling catalyst but also tuning of the NHP-type esters to inhibit the facile homodimerization of the alkyl radical and terminal alkyne, respectively. Owing to the use of stable and easily available NHP-type esters, the reaction features a broader substrate scope compared with reactions using the alkyl halide counterparts, covering (hetero)benzyl-, allyl-, and aminocarbonyl-substituted carboxylic acid derivatives, and (hetero)aryl and alkyl as well as silyl alkynes, thus providing a vital complementary approach to the previously reported method.     

Highly selective enzymatic kinetic resolution of primary amines at 80 degrees C: a comparative study of carboxylic acids and their ethyl esters as acyl donors

Optimization of the kinetic resolution of 2-amino-4-phenyl-butane was achieved at 80 degrees C using CAL-B-catalyzed aminolysis of carboxylic acids and their ethyl esters. The reactions carried out with long chain esters and the corresponding acids as acyl donors proceeded with remarkably high enantioselectivity. The use of carboxylic acids as acylating agents led to a marked acceleration of the reaction rate compared to their ester counterparts. Lauric acid led to enantiomeric excesses superior to 99.5% for both the remaining amine and the corresponding lauramide at 50% conversion (reached in 3 h). These optimized conditions were applied to the resolution of a series of aliphatic and benzylic amines.     

Access to β‐Lactams by Enantioselective Palladium(0)‐Catalyzed C(sp3)H Alkylation

β‐Lactams are very important structural motifs because of their broad biological activities as well as their propensity to engage in ring‐opening reactions. Transition‐metal‐catalyzed C? H functionalizations have emerged as strategy enabling yet uncommon highly efficient disconnections. In contrast to the significant progress of Pd⁰‐catalyzed C? H functionalization for aryl–aryl couplings, related reactions involving the formation of saturated C(sp³)? C(sp³) bonds are elusive. Reported here is an asymmetric C? H functionalization approach to β‐lactams using readily accessible chloroacetamide substrates. Important aspects of this transformation are challenging C(sp³)? C(sp³) and strain‐building reductive eliminations to for the four‐membered ring. In general, the β‐lactams are formed in excellent yields and enantioselectivities using a bulky taddol phosphoramidite ligand in combination with adamantyl carboxylic acid as cocatalyst.     

Access to β‐Lactams by Enantioselective Palladium(0)‐Catalyzed C(sp3)?H Alkylation

β‐Lactams are very important structural motifs because of their broad biological activities as well as their propensity to engage in ring‐opening reactions. Transition‐metal‐catalyzed C H functionalizations have emerged as strategy enabling yet uncommon highly efficient disconnections. In contrast to the significant progress of Pd⁰‐catalyzed C H functionalization for aryl–aryl couplings, related reactions involving the formation of saturated C(sp³) C(sp³) bonds are elusive. Reported here is an asymmetric C H functionalization approach to β‐lactams using readily accessible chloroacetamide substrates. Important aspects of this transformation are challenging C(sp³) C(sp³) and strain‐building reductive eliminations to for the four‐membered ring. In general, the β‐lactams are formed in excellent yields and enantioselectivities using a bulky taddol phosphoramidite ligand in combination with adamantyl carboxylic acid as cocatalyst.     

Synthesis of telechelic oligostyrenes by the ozonoloysis of poly(styrene-stat-butadiene): Protection of styrene units against ozone attack by the use of Di-N-alkyl amides as sacrificial ozone scavengers

Polystyrene and a poly(styrene-stat-butadiene) have been reacted with ozone in various solvents to establish the conditions necessary for the production, from the latter, of telechelic oligostyrenes having high and controllable end group functionalities. Polymeric ozonides produced by ozonolysis of poly(styrene-stat-butadiene)s, on workup with sodium borohydride or zinc/acetic acid, give dihydroxy- or dialdehyde-ended oligostyrenes, respectively. Workup with borane gives oligomers with a mixture of hydroxy and aldehyde end groups. Oxidative workup with selenium dioxide/hydrogen peroxide yields carboxylic acid-ended oligostyrenes. Workup with polymer-supported reducing or oxidizing agents was less successful. It is shown that side reactions associated with the synthesis of telechelic oligostyrenes by the ozonolysis route, i.e., attack at the α position and possibly also on the phenyl rings of the styrene units, can be minimized by the use of N-dialkyl amides, particularly dimethylacetamide, as sacrificial ozone scavengers. © 1996 John Wiley & Sons, Inc.