Efficient Synthetic Approach to Substituted Benzo[b]furans and Benzo[b]thiophenes by Iodine‐Promoted Cyclization of Enaminones

An efficient synthetic approach to the substituted benzo[b]furan and benzo[b]thiophene scaffolds by iodine‐mediated cyclization of the corresponding enaminones is described. This protocol was applied to a large series of these latter precursors to afford the respective benzoheterocycles substituted at the C‐2 position by a carbonyl group functionality. A study of the factors that control this process reveals that the reactivity depends on the presence of electron‐donor groups in the aryl ring of the aryloxycarbonylic and arylthiocarbonylic moieties.     

A fast,efficient and automated method to extract vessels from fundus images

Abstract  

We present a fast, efficient, and automatic method for extracting vessels from retinal images. The proposed method is based on the second local entropy and on the gray-level co-occurrence matrix (GLCM). The algorithm is designed to have flexibility in the definition of the blood vessel contours. Using information from the GLCM, a statistic feature is calculated to act as a threshold value. The performance of the proposed approach was evaluated in terms of its sensitivity, specificity, and accuracy. The results obtained for these metrics were 0.9648, 0.9480, and 0.9759, respectively. These results show the high performance and accuracy that the proposed method offers. Another aspect evaluated in this method is the elapsed time to carry out the segmentation. The average time required by the proposed method is 3 s for images of size 565 × 584 pixels. To assess the ability and speed of the proposed method, the experimental results are compared with those obtained using other existing methods.     

LMC-complexity and various chaotic regimes

A variant of the statistical complexity originally advanced by López-Ruiz et al. [R. López-Ruiz, H.L. Mancini, X. Calbet, Phys. Lett. A 209 (1995) 321], is here used in conjunction with Fisher's information measure so as to explore fine details of chaotic dynamics. As a main result we can easily distinguish between (i) periodicity and chaos or (ii) between distinct chaotic dynamics belonging to different attractors.     

Adsorption mode of the chiral modifier cinchonidine on Au(1 1 1)

The adsorption of the chiral modifier cinchonidine on Au(l 1 1) in UHV has been studied by means of TPD, LEED and XPS. In the monolayer the molecule is bound via nitrogen lone pair electrons of its quinoline part rather than via the π-system of this aromatic moiety. Intact molecular desorption is only observed for the multilayers. Decomposition in the first monolayer upon heating occurs above 400 K, indicating a stronger interaction in the monolayer. No long-range ordered structures were observed via LEED. Long-time exposure leads to rearrangement and further stabilization of the first molecular monolayer. Quinoline is bound to gold via the nitrogen lone pair as well. The binding energy of 9.6 kcal/mol is characteristic for physisorption.     

Unraveling the surface reactions during liquid-phase oxidation of benzyl alcohol on Pd/Al2O3: an in situ ATR-IR study

The palladium-catalyzed liquid-phase reaction of benzyl alcohol to benzaldehyde was investigated in the presence and absence of oxygen by attenuated total reflection infrared (ATR-IR) spectroscopy. The 5 wt % Pd/Al2O3 catalyst was fixed in a flow-through ATR-IR cell serving as a continuous-flow reactor. The reaction conditions (cyclohexane solvent, 323 K, 1 bar) were set in the range commonly applied in the heterogeneous catalytic aerobic oxidation of alcohols. The in situ ATR-IR study of the solid-liquid interface revealed a complex reaction network, including dehydrogenation of benzyl alcohol to benzaldehyde, decarbonylation of benzaldehyde, oxidation of hydrogen and CO on Pd, and formation of benzoic acid catalyzed by both Pd and Al2O3. Continuous formation of CO and its oxidative removal by air resulted in significant steady-state CO coverage of Pd during oxidation of benzyl alcohol. Unexpectedly, benzoic acid formed already in the early stage of the reaction and adsorbed strongly (irreversibly) on the basic sites of Al2O3 and thus remained undetectable in the effluent. This observation questions the reliability of product distributions conventionally determined from the liquid phase. The occurrence of the hydrogenolysis of the C-O bond of benzyl alcohol and formation of toluene indicates that Pd was present in a reduced state (Pd0) even in the presence of oxygen, in agreement with the dehydrogenation mechanism of alcohol oxidation.     

Supercritical carbon dioxide: an inert solvent for catalytic hydrogenation?

Various surface species originating from the reaction between CO2 and H2 over Al2O3-supported Pt, Pd, Rh, and Ru model catalysts were investigated by attenuated total reflection infrared (ATR-IR) spectroscopy under high-pressure conditions. Two different spectroscopic cells were used: a variable-volume view cell equipped with ATR-crystal and transmission IR windows (batch reactor) and a continuous-flow cell also equipped with a reflection element for ATR-IR spectroscopy. The study corroborated that CO formation from dense CO2 in the presence of hydrogen occurs over all Pt-group metals commonly used in heterogeneous catalytic hydrogenations in supercritical CO2 (scCO2). In the batch reactor cell, formation of CO was detected on all metals at 50 and 90 degrees C, with the highest rate on Pt. Additional surface species were observed on Pt/Al2O3 at 150 bar under static conditions. It seems that further reaction of CO with hydrogen is facilitated by the higher surface concentration at higher pressure. In the continuous-flow cell, CO coverage on Pt/Al2O3 was less prominent than that in the batch reactor cell. A transient experiment in the continuous-flow cell additionally revealed CO formation on Pt/Al2O3 at 120 bar after switching the feed from a H2-ethane to a H2-CO2 mixture. The in situ ATR-IR measurements indicate that CO formation in CO2-H2 mixtures is normally a minor side reaction during hydrogenation reactions on Pt-group metal catalysts, and dense ("supercritical") CO2 may be considered as a relatively "inert" solvent in many practical applications. However, blocking of specific sites on the metal surface by CO and consecutive products can affect structure sensitive hydrogenation reactions and may be at the origin of unexpected shifts in the product distribution.