Trifluoroacetic Acid Hydroxylamine System as Organocatalyst Reagent in a One-Pot Salt Free Process for the Synthesis of Caprolactam and Amides of Industrial Interest

Catalysis Letters - In this work we studied the reactivity of the Trifluoroacetic acid hydroxylamine system in the one step salt free synthesis of amides from ketones. A particular regards was paid...     

Effectiveness of crystalline admixtures and lime/cement coated granules in engineered self-healing capacity of lime mortars

Recently, the use of lime mortars in the restoration of historic buildings has found a renewed interest because they can guarantee the required mechanical, chemical and physical compatibility with the existing substrate. Spontaneous occurrence of self-healing phenomena in lime-based mortars is well known; the possibility of engineering the self-healing capacity, through tailored additions, is therefore of the utmost interest with the aim of enhancing the durability of the building masonry restoration works. This work proposes a system for the evaluation of the self-healing capacity with reference to traditional and advanced lime mortars. The autogenous healing capacity of a reference lime mortar has been first of all evaluated. Then, the possibility of engineering the aforementioned capacity has also assessed, through both commercial crystalline admixtures and tailored encapsulated additives. These should work according to a twofold mechanism: first, the coated granules envelope a core of lime mortar with purpose of making it inert during the hardening phase. Secondly, once the coated granules rupture upon cracking and damage of the mortar, the reactive binder is released and undergoes a delayed hardening, which is responsible of the healing phenomena. The results show that the mortar is able to heal micro-cracks; moreover, the addition of the crystalline admixture enhances this capacity. The different kinds of employed coated granules were also able to induce a sensible self-healing, but they decrease the instantaneous compressive strength.     

Selective hydrogenation of benzene to cyclohexene using a suspended Ru catalyst in a mechanically agitated tetraphase reactor

The reactivity on unsupported Ru based catalyst in benzene selective hydrogenation to cyclohexene has been studied. The reaction has been carried out in a tetraphase slurry reactor at 423 K, at 5 MPa, in the presence of two liquid phases: benzene and an aqueous solution of ZnSO₄ 0.6 mol l⁻¹. A detailed study of the influence of the transport phenomena on the reactivity of the catalyst has been carried out. No correlation has been found between the characteristic numbers of Weeler–Weisz and of Carberry mass transport at external liquid/solid interface or into the catalyst pores for both benzene and hydrogen and the selectivity of the catalyst. The main features of the catalysts are the strong dependence between the catalysts preparation procedure and their activity and selectivity. In particular the influence of the alkaline or the earth alkaline hydroxide, employed in the precipitation of the Ru precursor, on the selectivity, has been studied. Hydrogen chemisorption measurements indicate that the amount of weakly adsorbed hydrogen depends on the nature of the base employed in the precipitation step.     

Through wafer via holes manufacturing by variable isotropy Deep RIE process for RF applications

This paper reports a method on the manufacturing of through silicon wafer via holes with tapered walls by Deep Reactive Ion Etching using the opportunity to change the isotropy in the DRIE equipments during processing. By using consecutively anisotropic and isotropic etching steps it is possible to enlarge the dimension of via holes on one side of the wafer, while on the other side dimension is set by the initial etching window. The optimized process was used to obtain via’s with a good control over the walls angles for two etching windows sizes (100 and 20?μm respectively) on 300?μm thick silicon wafers. After process optimization, a deviation smaller than 10% of the manufactured via holes across the wafers was observed for the designed walls angles of 11.3° and 21.8°. Barrier and seed layers were deposited in via’s performed by Physical Vapor Deposition techniques with a very good coverage of the walls. Finally, gold electroplating was used to fill the narrow part of via’s.     

On the acidity of liquid and solid acid catalysts. Part 2. A thermodynamic and kinetic study for acid-catalysed nitrations

Solid acids prepared by adding sulfuric acid on silica gel have been used as catalysts in the nitration of nitrobenzenes and their properties have been tested by kinetic studies at 25°C. Nitration rates in concentrated aqueous solutions of sulfuric acid were also analysed and the catalytic efficiencies of sulfuric acid in liquid and solid phase were compared by using kinetic data of analogous compounds. The results show that the solid acid samples exhibit nitrating properties very similar to those observed in concentrated aqueous solutions of sulfuric acid (range of 90 wt%). The relationship between nitration rates and effective concentration of electrophilic species [NO ₂ ⁺ ], determined by studying the protonation–dehydration equilibrium of nitric acid in strong acids (HNO₃ + H⁺ ⇌ H₂O + NO ₂ ⁺ ), was tested to better understand the acidity properties of medium. This revised version was published online in November 2006 with corrections to the Cover Date.     

Selective hydrogenation of benzene to cyclohexene catalyzed by Ru supported catalysts: Influence of the alkali promoters on kinetics, selectivity and yield

The selective hydrogenation of benzene to cyclohexene in the presence of Ru supported catalysts has been investigated in a tetraphase slurry reactor at 423 K, at 5 MPa of pressure, in the presence of two liquid phases: benzene and an aqueous solution of ZnSO₄ (0.6 mol l⁻¹). A study of the influence of the transport phenomena on the reactivity of the catalyst has been carried out. But no correlation between Carberry and Wheeler–Weisz numbers and the selectivity of the catalysts has been found. The main features of the catalysts are the strong dependence between the catalysts preparation procedure and their activity and selectivity. The best results have been observed with Ru/ZrO₂ catalysts. The influence of the bases employed in the precipitation of the catalysts precursor has also been investigated. KOH is the most effective, yield of 41% and initial selectivity of 80% of cyclohexene has been observed.     

On the acidity of liquid and solid acid catalysts: Part 1. A thermodynamic point of view

The protonation equilibria of weak bases (B) in solid acids (HClO₄/SiO₂, CF₃SO₃H/SiO₂, H₂SO₄/SiO₂) were studied by UV spectroscopy and the results were compared to those obtained for analogous compounds in concentrated aqueous solutions of strong acids (HClO₄, CF₃SO₃H, H₂SO₄). The behaviour of B in liquid (L) and solid (S) phase was analysed by titration curves, log[BH⁺]/[B] ratios and thermodynamic pK _BH+ values. It has been shown that the proton transfer process acid → base (i.e., from (H+A^-)_(L,S) to (BH+A^-)_(L,S)} can be described by the relationship observed between the activity coefficient terms that are to be taken into account for acid–base equilibria occurring in nonideal systems ( – log(f _B f _B+/f _BH+)_(L,S)= -n _BA log(f _A–f _H+/f _HA)_(L,S)) and can be estimated by the n _BA values. Two “activity coefficient functions” (i.e., Mc(B) = – log(f _B f _B+/f _BH+)and Mc(s) = – log(f _A–f _H+/f _HA)) were used to describe, respectively, the equilibria of B and the equilibria of the acids in concentrated aqueous solutions and the meaning of terms “activity coefficient function” and “protonating ability of an acid” were discussed. The difference between “acidity functions”, determined for solutes (Ac(i)) and solvents (Ac(s)) in aqueous acids, and the H_x acidity functions, the latter developed for solutes in analogous media by the Hammett procedure, was also shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-performance PIN photodiodes on TMAH thinned silicon wafers

The electro-optical characteristics of PIN photodiodes fabricated on high-resistivity silicon substrates locally thinned by bulk micromachining techniques are discussed. Experimental results and numerical simulations demonstrate that devices fabricated by the proposed approach have leakage current, quantum efficiency and speed performance comparable to the best commercially available Si PIN photodiodes, with the additional advantage of possible back-side illumination, making them suitable for the implementation of two-dimensional arrays having a read-out electronic chip connected to the front-side.     

On the acidity of liquid and solid acid catalysts. Part 3. Esterification of benzoic and mesitoic acids

Methyl esters of benzoic and mesitoic acid have been prepared with high yields (>98 wt%) from the corresponding carboxylic acids + methanol in aprotic solvents over samples of H₂SO₄/SiO₂ at 60°C. The results show a high catalytic efficiency of the solids but also suggest an acid strength comparable to that observed in concentrated aqueous H₂SO₄ (range >90 wt%) when the acid requirements for the esterification of analogous compounds in aqueous acid solutions are taken into account. Indeed, different reacting species, i.e., ArC(OH) ₂ ⁺ from benzoic acid and 2,4,6‐triMe‐ArC=O⁺ from mesitoic acid are involved in the esterification, but the mesitoyl cation can be formed and esterified in the acidity ranges between 92 and 98 wt% H₂SO₄. This revised version was published online in July 2006 with corrections to the Cover Date.