Lucia Emanuele

Photochemical degradation of crude oil: Comparison between direct irradiation, photocatalysis, and photocatalysis on zeolite.

Direct irradiation for 100h of crude oil from Basilicata (Southern Italy) gave in the case of linear and branched alkanes a reduction of 9 and 5%, respectively. On the contrary, cyclic alkanes decreased for 54% while aromatic hydrocarbons showed a reduction of 37%. These results are in agreement with a prevalent electron transfer mechanism. Photocatalysis (100h) gave extensive degradation of crude oil: linear alkanes were degraded for 98.66%, branched alkanes were reduced for 97.31%, cyclic alkanes for 96.04%, while aromatic compounds and alkenes were reduced for 99.54 and 98.38%, respectively. These results are in agreement with a prevalent hydrogen abstraction mechanism. When photocatalysis is performed in the presence of zeolite linear alkanes were degraded for 79.85%, branched alkanes were reduced for 45.38%, cyclic alkanes for 58.10%, while aromatic compounds were reduced for 91.85%. In this case, an increase of the relative amount of alkenes (42.05%) was observed.

On the stereoselectivity of the Paternò-Büchi reaction between carbonyl compounds and 2-furylmethanol derivatives. The case of aliphatic aldehydes and ketones

Abstract The Paterno–Buchi reaction between 2-furylmethanol derivatives and aliphatic aldehydes and ketones induced by irradiation through Vycor at 8°C shows high regioselectivity but no stereoselectivity. This behaviour can be rationalised by assuming that this type of compound reacts through both singlet and triplet excited states. Ab initio calculations are in agreement with the formation of the 1,4-biradical. The more stable biradical accounts for the observed regioselectivity. The lack of stereoselectivity was discussed on the basis of two hypotheses. The allylic strain proposed by Adam does not account for the observed results. On the contrary, hydrogen bond interaction between (triplet excited) carbonyl oxygen and hydroxy group is able to describe the observed behaviour.

The Paterno-Buchi Reaction on Furan Derivatives

The Paterno-Buchi reaction on furan derivatives is reviewed. The photochemical reaction of furan derivatives in the reaction with carbonyl compounds gives the corresponding monoadduct with high regio- and stereoselectivity. When the reaction is carried out in benzene, a large amount of the diadduct can be obtained. The exo stereoselectivity at C-6 was explained assuming the presence of a secondary orbital effect on spin orbit coupling. Regio- and stereoselectivity of the reaction of carbonyl compounds with 2, 3-dihydrofuran is described. Applications of the reaction to the synthesis of 2- and 3-furylmethanol derivatives is reported. The synthesis of asteltoxin, avenaciolide, and oxetanocin is also reported. Asymmetric reactions on chiral glyoxylate is reported. The low diastereoselectivity of the reaction with chiral ketones and aldehydes is discussed. Finally, the high diastereoselectivity observed in the reaction with 2-furylmethanol derivatives is reported.

On the origin of “Goût de Lumiere” in champagne

The flavour of champagne before and after UV irradiation was analysed by using SPME (solid phase microextraction). Fourteen components in the flavour were detected; some significant modifications in the composition of the flavour were observed: 1-propanol and 1-hexanol contents did not change during the irradiation, the amount of 2-methylpropanol increased, while 2,6-di-t-butylphenol disappeared after the irradiation. Furthermore, the presence of esters in the wine after the irradiation was completely modified. Ethyl acetate, ethyl butanoate, ethyl 2-hydroxypropanoate, 3-methyl-1-butanol acetate, ethyl hexanoate, and ethyl octanoate reduced their presence in the wine; ethyl decanoate disappeared in the flavour after the irradiation. In order to verify if riboflavin is responsible for the observed modifications in flavour composition, the irradiation of ethyl hexanoate in the presence of riboflavin in ethanol water with a 125 W mercury arc through Pyrex was carried out showing 9% decomposition of the ester.

The stereoselectivity of the Paternò–Büchi reaction between tertiary 2-furylmethanol derivatives and aromatic carbonyl compounds: on the nature of the hydroxy directing effect

The photochemical reaction of 1-(2-furyl)-1-phenylethanol with benzaldehyde gave a mixture of regioisomeric products. The adduct obtained on the more hindered side of the molecule was obtained with complete diastereoselectivity. The same substrate with benzophenone gave only one product with a diastereoisomeric excess of 48%. The reaction of 2-(2-furyl)-3,3-dimethylbutan-2-ol with benzaldehyde and benzophenone gave the corresponding adducts on the more hindered side of the molecule with diastereoisomeric excesses of 42 and 71%, respectively. These results, and also those obtained using 2-furylphenylmethanol with benzophenone and acetone (complete diastereoselectivity and absence of diastereoselectivity, respectively), were explained assuming the attack of the excited carbonyl compound on the same side as the hydroxy group, through the formation of a hydrogen bond or of a complex. This type of attack gave the biradical intermediate in preferential conformations. The relative energies of these conformers account for the observed diastereoselectivity.

Stereoselectivity in the Paterno-Buchi Reaction on Chiral Allylic Alcohols, for A Discussion of the Hydroxy Directing Effect

The stereoselectivity of the photochemical reaction between acetophenone and 2, 2, 5-trimethyl-4-hexen-3-ol was explained on the basis of a DFT study. Conformational analysis of the starting material showed that two conformations were the most stable ones. Assuming that the attack of the excited carbonyl group occurred on the same side of the hydroxy group (due to hydrogen bond or to the formation of a complex), the possible conformations of the biradical intermediate was examined. Only the precursors of the threo stereoisomer was obtained in agreement with experimental results.

Photochemical dimerisation of 2-vinylfuran and 2-vinylthiophene derivatives bearing electron-withdrawing groups

Abstract The photochemical dimerisation of 1,3-diheteroaryl-2-propen-1-one derivatives gave a mixture of dimers in agreement with the hypothesis that the reaction is under frontier orbitals control and preferential formation of only the more stable isomers. On the contrary, the reaction of 2-heteroaryl-nitroethylene derivatives were not observed to give cyclobutane dimers but only coupling products with the loss of one nitro group. This behaviour is in agreement with the nature of the HOMO–LUMO orbitals which do not allow the superimposition of the reagents. This result allows to formulate the hypothesis that the photochemical dimerisation of 1-heteroaryl-2-EWG-ethylenes must occur as a concerted reaction. Finally, 2-heteroaryl-1,1-dicyanoethylene derivatives gave the corresponding dimers. Also in this case, we obtained only the head-to-head dimer and the more stable one.

FT–ICR–MS analysis of lignin

Fourier transform ion cyclotron resonance mass spectrometry (FT–ICR–MS) of a steam-exploded lignin from wheat straw showed that fragments with a mass higher than 4534 Da cannot be obtained. Furthermore, FT–ICR–MS showed that lignin is not a completely random polymer, but shows some regularity with a difference of 44.026 m/z (C2H4O) between the peaks. The distribution of Kendrick mass defect in the function of Kendrick nominal masses showed the same behaviour. FT–ICR–MS analysis of bagasse lignin (Granit) showed that the largest value of mass found was 4347 Da. The peaks show regularities with a difference of 44.026 m/z between the peaks. The organosolv lignin showed that the polymer with the largest mass value was 3699 Da in FT–ICR–MS. The analysis of the peaks did not show regularity; however, the Kendrick diagram for this lignin showed the same slope as in the other samples, in agreement with the C2H4O regular difference between peaks.

Reactivity of rimsulfuron in newly formed inclusion combinations by using cyclodextrin and zeolite

Extending our investigations on environment protection by agrochemicals diffusion and accumulation, newly formed inclusion combinations of rimsulfuron into zeolite-NaY (Z-NaY) and β-cyclodextrin (β-CD) were studied and compared. The reactivity of the included herbicide under UV-irradiation and in the dark was assessed. Many guest/host ratios were tested: the best results were found using 3 g (6.953 mmol) of rimsulfuron per kilogram of zeolite, with 80% inclusion success (5.562 mmol kg−1), and a 1: 2 molar ratio, 190 g of rimsulfuron per kilogram of β-CD with 58% inclusion success. The herbicide Z-NaY-combined underwent rapid and effective (halflive 2–7 h) degradation either catalytically or photochemically, giving rise to different identified by-products. On the contrary, β-CD was able to protect rimsulfuron totally both in the dark and under 24-h direct UV irradiation. On the basis of the obtained results, a different utilization of the two inclusion materials has been suggested.

Novel imazethapyr detoxification applying advanced oxidation processes

Different degradation methods have been applied to assess the suitability of advanced oxidation process (AOPs) to promote mineralization of imazethapyr [(RS)-5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid], a widely used imidazolinone class herbicide, the persistence of which has been demonstrated in surface and ground waters destined to human uses. Independent of the oxidation process assessed, the decomposition of imazethapyr always followed a pseudo-first order kinetic. The direct UV-irradiation (UV) of the herbicide as well as its oxidation with ozone (O3), and hydrogen peroxide tied to UV-irradiation (H2O2/UV) were sufficiently slow to permit the identification of intermediate products, the formation pathway of which has been proposed. Ozonation joined to UV-irradiation (O3/UV), ozonation joined to titanium dioxide photo-catalysis (TiO2/UV+O3), sole photo-catalysis (TiO2/UV), and photo-catalysis reinforced with hydrogen peroxide-oxidation (TiO2/UV+H2O2) were characterized by a faster degradation and rapid formation of a lot of small molecules, which were quickly degraded to complete mineralization. The most effective oxidation methods were those using titanium dioxide photo-catalysis enhanced either by ozonation or hydrogen peroxide. Most of all, these last processes were useful to avoid the development of dangerous by-products.