General, Auxiliary-Enabled Photoinduced Pd-Catalyzed Remote Desaturation of Aliphatic Alcohols.

A general, efficient, and site-selective visible light-induced Pd-catalyzed remote desaturation of aliphatic alcohols into valuable allylic, homoallylic, and bis-homoallylic alcohols has been developed. This transformation operates via a hybrid Pd-radical mechanism, which synergistically combines the favorable features of radical approaches, such as a facile remote C-H HAT step, with that of transition-metal-catalyzed chemistry (selective ß-hydrogen elimination step). This allows achieving superior degrees of regioselectivity and yields in the desaturation of alcohols compared to those obtained by the state-of-the-art desaturation methods. The HAT at unactivated C(sp3)-H sites is enabled by the easily installable/removable Si-auxiliaries. Formation of the key hybrid alkyl Pd-radical intermediates is efficiently induced by visible light from alkyl iodides and Pd(0) complexes. Notably, this method requires no exogenous photosensitizers or external oxidants.

Attenuated UV Radiation Alters Volatile Profile in Cabernet Sauvignon Grapes under Field Conditions.

This study aimed to explore the effect of attenuated UV radiation around grape clusters on the volatile profile of Cabernet Sauvignon grapes (Vitis vinifera L. cv.) under field conditions. Grape bunches were wrapped with two types of polyester films that cut off 89% (film A) and 99% (film B) invisible sunlight of less than 380 nm wavelength, respectively. Solar UV radiation reaching the grape berry surface was largely attenuated, and an increase in the concentrations of amino acid-derived benzenoid volatiles and fatty acid-derived esters was observed in the ripening grapes. Meanwhile, the attenuated UV radiation significantly reduced the concentrations of fatty acid-derived aldehydes and alcohols and isoprenoid-derived norisoprenoids. No significant impact was observed for terpenes. In most case, these positive or negative effects were stage-dependent. Reducing UV radiation from the onset of veraison to grape harvest, compared to the other stages, caused a larger alteration in the grape volatile profile. Partial Least Square Discriminant Analysis (PLS-DA) revealed that (E)-2-hexenal, 4-methyl benzaldehyde, 2-butoxyethyl acetate, (E)-2-heptenal, styrene, α-phenylethanol, and (Z)-3-hexen-1-ol acetate were affected most significantly by the attenuated UV radiation.

Volatile organic compounds characterized from grapevine (Vitis vinifera L. cv. Malbec) berries increase at pre-harvest and in response to UV-B radiation.

Ultraviolet-B solar radiation (UV-B) is an environmental signal with biological effects in plant tissues. Recent investigations have assigned a protective role of volatile organic compounds (VOCs) in plant tissues submitted to biotic and abiotic stresses. This study investigated VOCs in berries at three developmental stages (veraison, pre-harvest and harvest) of Vitis vinifera L. cv. Malbec exposed (or not) to UV-B both, in in vitro and field experiments. By Head Space-Solid Phase Micro Extraction-Gas Chromatography-Electron Impact Mass Spectrometry (HS-SPME-GC-EIMS) analysis, 10 VOCs were identified at all developmental stages: four monoterpenes, three aldehydes, two alcohols and one ketone. Monoterpenes increased at pre-harvest and in response to UV-B in both, in vitro and field conditions. UV-B also augmented levels of some aldehydes, alcohols and ketones. These results along with others from the literature suggest that UV-B induce grape berries to produce VOCs (mainly monoterpenes) that protect the tissues from UV-B itself and other abiotic and biotic stresses, and could affect the wine flavor. Higher emission of monoterpenes was observed in the field experiments as compared in vitro, suggesting the UV-B/PAR ratio is not a signal in itself.

Photooxidation of alcohols by a porphyrin/quinone/TEMPO system.

Photooxidation of alcohols to the corresponding aldehydes with a porphyrin/quinone/TEMPO (TEMPO=2,2,6,6-tetramethyl-1-piperidinyloxy free radical) system is described. This photoreaction is a combination of a photoinduced electron transfer from the porphyrin to the quinone and a TEMPO-catalyzed oxidation of alcohols triggered by one electron oxidation. The rates of oxidation were in the order of benzylic approximately allylic>primary>>secondary, which is consistent with the intermediacy of the oxoammonium cation derived from TEMPO. Examination of the initial rates suggested that the reaction proceeded via the triplet excited state of the zinc porphyrin. The dependence of initial rates on the oxidation potentials of the porphyrin showed a characteristic bell shape, which is caused by two competitive factors, the efficiency of photoinduced electron transfer and the equilibrium of electron exchange between the porphyrin cation radical and TEMPO. The potential significance of this reaction in photosynthetic model chemistry is briefly discussed.

Identification of the degradation pathways of alkanolamines with TiO2 photocatalysis.

The present study deals with the photocatalytic degradation of the alkanolamine, 2-dimethylamino-2-methyl-1-propanol (DMAMP), in the presence of TiO(2) particles and UV-A (lambda=365 nm) radiation. The obtained results show complete oxidation of DMAMP after 20h, and a little over 90% of DMAMP was mineralization after 64-h of treatment. The effects of the solution pH, catalyst loading, and anions on the photocatalytic degradation of DMAMP were investigated, as well as the reaction intermediates that were formed during treatment. To the best of our knowledge, this is the first time that reports the degradation pathways of DMAMP. A number of intermediates were identified by GC/MS techniques during the treatment of DMAMP, following three tentative degradation routes. The first one is based on the oxidation of the primary alcohol group leading to the formation of corresponding aldehyde and carboxylic acid. The second route is based on the rupture of the N-C bond to form 2-methylpropanal and acetone. The last degradation route is based on the cyclization of the beta-amino alcohol group to form the oxazolidine derivatives.

Synthesis and characterization of thiochromone S,S-dioxides as new photolabile protecting groups.

3-Arylthiochromone derivatives were synthesized as new photolabile protecting groups, in which the photoreactivity was switchable based on oxidation of the sulfur atom (sulfide and sulfone); the protected substrates , released the corresponding alcohols, amines or carbonxylic acids almost quantitatively under UV-light in neutral condition and the photoproduct showed high fluorescence intensity.

Acceleration of arylzinc formation and its enantioselective addition to aldehydes by microwave irradiation and aziridine-2-methanol catalysts.

The formation and 2-amino alcohol catalyzed addition of arylzinc reagents from and with boronic acids, respectively, is drastically accelerated to a few minutes under microwave irradiation without loss of enantioselectivity (up to 98% ee). Of the amino acid derived catalysts tested, the conformationally restricted bulky substituted aziridine-2-methanols derived from serine show the best overall performance in the formation of diarylmethanols.

Mechanistic analysis of the photocycloaddition of silyl-tethered alkenes.

The photochemistry of substituted cinnamyloxy silanes has been examined in both cyclohexane and acetonitrile solvents. Alkene isomerization occurs in addition to cycloaddition. Fluorescence quantum yields and excited singlet state lifetimes have been determined for each compound. We have used the information in order to better understand the regio- and stereoselectivity of photocycloaddition between silyl-tethered cinnamyl groups. This study allows us to conclude that the 2 + 2 photocycloaddition between alkenes is not a Woodward-Hoffmann orbital symmetry controlled event. The most consistent explanation for the excellent regio- and stereoselectivity is that the photocycloaddition is conformationally controlled.

Electron-induced chemistry of alcohols.

We studied dissociative electron attachment to a series of compounds with one or two hydroxyl groups. For the monoalcohols we found, apart from the known fragmentations in the 6-12 eV range proceeding via Feshbach resonances, also new weaker processes at lower energies, around 3 eV. They have a steep onset at the dissociation threshold and show a dramatic D/H isotope effect. We assigned them as proceeding via shape resonances with temporary occupation of sigma orbitals. These low energy fragmentations become much stronger in the larger molecules and the strongest DEA process in the compounds with two hydroxyl groups, which thus represent an intermediate case between the behavior of small alcohols and the sugar ribose which was discovered to have strong DEA fragmentations near zero electron energy [S. Ptasinska, S. Denifl, P. Scheier and T. D. Märk, J. Chem. Phys., 2004, 120, 8505]. Above 6 eV, in the Feshbach resonance regime, the dominant process is a fast loss of a hydrogen atom from the hydroxyl group. In some cases the resulting (M- 1)(-) anion (loss of hydrogen atom) is sufficiently energy-rich to further dissociate by loss of stable, closed shell molecules like H(2) or ethene. The fast primary process is state- and site selective in several cases, the negative ion states with a hole in the n(O) orbital losing the OH hydrogen, those with a hole in the sigma(C-H) orbitals the alkyl hydrogen.

Probing the effects of microwave irradiation on enzyme-catalysed organic transformations: the case of lipase-catalysed transesterification reactions.

The lipase-catalysed transesterification reaction of methyl acetoacetate in toluene as a solvent has been studied using carefully controlled conditions. Results suggest that microwave heating does not have a noticeable effect on reaction rate or product conversion.

Aerobic oxidation of benzyl- and allylic alcohols under visible light irradiation of a fluorescent lamp in the presence of catalytic iodine.

Benzyl alcohols and allylic alcohols were found to be oxidized to the corresponding aldehydes in the presence of a catalytic amount of iodine under irradiation of a fluorescent lamp.

Identification and quantification of aerosol polar oxygenated compounds bearing carboxylic or hydroxyl groups. 2. Organic tracer compounds from monoterpenes.

In this study, a comparison is made of polar organic compounds found in the field with those produced in secondary organic aerosol from laboratory irradiations of natural hydrocarbons and oxides of nitrogen (NOx). The field samples comprised atmospheric particulate matter (PM2.5) collected at Research Triangle Park (RTP), NC, during the summer of 2003, and the laboratory samples originated from the photooxidation of the following monoterpenes: alpha-pinene, beta-pinene, and d-limonene. To determine the structural characteristics of the polar compounds, the filter samples were solvent extracted and derivatized using a technique based on single and multistep derivatizations. The resulting compound derivatives were analyzed by GC-MS in the methane-Cl and El modes. In addition to previously reported biogenic oxidation products (pinic acid, pinonic acid, norpinic acid, nopinone, and pinonaldehyde), seven multifunctional organic compounds were found in both field and laboratory samples. These compounds, which are proposed as possible atmospheric tracers for secondary organic aerosol from monoterpenes, were consistent with the following identifications: 3-isopropyl pentanedioic acid; 3-acetyl pentanedioic acid; 3-carboxy heptanedioic acid; 3-acetyl hexanedioic acid; 2-isopropyl-1,2-dihydroxybutanol; 4-isopropyl-2,4-dihydroxyhexanol; and 3-(2-hydroxy-ethyl)-2,2-dimethyl-cyclobutane carboxylic acid. Initial attempts have been made to quantify the concentrations of these tracer compounds on the basis of surrogate compound calibrations. The occurrence of these compounds in both laboratory and field measurements suggests that secondary organic aerosol originating from biogenic hydrocarbons are contributing to the regional aerosol burden in the southeastern United States. Several of these compounds also appear to contribute to the global aerosol burden in that they have also been identified in Europe and Brazil.

Photorelease of alcohols from 2-nitrobenzyl ethers proceeds via hemiacetals and may be further retarded by buffers intercepting the primary aci-nitro intermediates.

The mechanism for the photoinduced release of glycolic acid from its 2-nitrobenzyl ether was reinvestigated. The pH-dependent rate constants of the thermal reactions initiated by irradiation are similar to those reported previously for 2-nitrobenzyl methyl ether. A hemiacetal intermediate that limits the release rate of glycolic acid at pH values

Analysis of concentration characteristics in ultrasonic atomization by droplet diameter distribution.

The droplet diameter distribution and concentration characteristics in ultrasonic atomization were experimentally studied. The samples were aqueous solutions of methanol, ethanol and 1-propanol. The diameter distribution of atomized droplets showed the normal distribution, and the median diameter and standard deviation were expressed by means of the ultrasonic condition and the liquid properties. The concentration characteristic in ultrasonic atomization was analyzed by using the model of shell and core to the atomized droplet, where the former and latter consist of solute and solution, respectively. The value, which was surface solute amount in droplet multiplied by the molecular volume, increased with increasing solute molar fraction in bulk liquid and was independent of alcohol kinds. The rate of accompanying liquid and the solute molar fraction in accompanied liquid were estimated from the diameter distribution and the surface solute amount in droplet.

Dehydration reaction of hydroxenin monoacetate in carbon tetrachloride and an aliphatic alcohol under ultrasound irradiation.

A new method for the preparation of an E/Z mixture of vitamin A acetate from hydroxenin monoacetate is described. This two-step reaction was studied by changing the reaction parameters (reaction temperature, ultrasound power, and reaction time) and the alcohol used. This approach consists of the dehydration reaction of hydroxenin monoacetate under ultrasound irradiation in CCl4 and an aliphatic alcohol under an inert atmosphere. The formation of small amounts of HCl from CCl4 and an aliphatic alcohol under ultrasound irradiation is followed by the dehydration reaction of hydroxenin monoacetate. An E/Z mixture of vitamin A acetate was obtained resulting in the desired pentaenes. Some ethers derivatives were also formed as by-products, isolated and characterized. Study of the reaction mechanism is also reported here.

Structure of copper(II) dithiocarbamate mixed-ligand complexes and their photoreactivities in alcohols.

The composition of the co-ordination sphere of Cu(II) dithiocarbamate mixed-ligand complexes Cu(Et2)dtc)X (X = Cl-, Br-) and Cu(Et2)dtc)(+)...Y- (Y- = ClO4-, NO3-) is studied from the combined analysis of spectrophotometric and EPR data. The results obtained about CT-photolysis of the complexes in EtOH and i-PrOH are compared with our previous data of photolysis in chloromethane/ROH solutions. Reaction mechanism and the role of alcohol are discussed on the ground of electronic and EPR spectra and quantum yield results.

Mineralization of organic micropollutants (homologous alcohols and phenols) in water by vacuum-UV-oxidation (H2O-VUV) with an incoherent xenon-excimer lamp at 172 nm.

Twenty different organic micropollutants (for example C1-C8 homologous alcohols and some phenols) in aqueous solution were subjected to vacuum-UV-oxidation (H2O-VUV) within a xenon-excimer flow-through photoreactor. The incoherent xenon-excimer lamp used exhibited an emission maximum at 172 nm. At this wavelength water is efficiently photolyzed with formation of hydrogen atoms and of highly oxidative hydroxyl radicals. The short lived hydroxyl radicals initiate a series of complex interrelated radical reactions that lead finally to the mineralization of the organic material dissolved in water. The efficiency of the total organic carbon (TOC) diminution is dependent on the nature of the organic substrate treated. For example, in the series of homologous alcohols the substrate methanol is mineralized faster than 1-octanol by a factor of 2.7 under identical conditions of VUV treatment and with similar initial TOC content of the water ranging between 40 and 50 ppm.

E.s.r. of spin-trapped radicals in aqueous solutions of deuterated amino acids and alcohols.

Selectively deuterated compounds can be utilized in spin-trapping to obtain conclusive evidence for the structures of the trapped radicals. Radicals formed from DL-alanine-2-d1, DL-alanine-3, 3, 3-d3, DL-alanine-d4, glycine-d5, isopropyl-2-d1 alcohol, isopropyl-d7 alcohol and t-butyl-d9 alcohol were studied. The hydrogen abstraction, deamination and decarboxylation radicals generated from deuterated alanines were investigated by spin-trapping using t-nitrosobutane. Since nitroxides of the type XYZC-CH2-N(O)-tBu which contain an asymmetric centre next to the CH2 group exhibit unequal beta-proton splittings and temperature-dependent line width alternations, the effects of temperature on the e.s.r. spectra were studied. By these methods the structures of the trapped radicals were verified and the hyperfine coupling constants could be assigned without ambiguity. In gamma-irradiated polycrystalline amino acids, the observed deuterium exchange can be conveniently surveyed by dissolution in aqueous solutions containing t-nitrosobutane.