Determination of total safranal by in situ acid hydrolysis in supercritical fluid media: Application to the quality control of commercial saffron

A procedure allowing hydrolysis reactions to be conducted in a dynamic supercritical-CO₂ medium was developed for quantifying total safranal (viz. free safranal present in the sample + safranal resulting from picrocrocin hydrolysis), which are the main component of the essential oil and responsible for the characteristic aroma of saffron. The proposed method allows total safranal amounts over the ranges 0.05-1.5 mg mL⁻¹ to be determined. The standard deviation achieved was 2%. This method was applied to the determination of safranal in natural saffron samples. The results obtained were compared with the “safranal value” total index, which is widely used as a quality measure of saffron products. The comparison revealed that the proposed method provides useful information not contained in the safranal value, based on the fact that, some samples with a high “safranal index” contain low concentrations of safranal. The proposed method is very useful for quality control in commercial saffron samples.     

Novel and Efficient One Pot Condensation Reactions between Ketones and Aromatic Alcohols in the Presence of CrO3 Producing α,β‐Unsaturated Carbonyl Compounds

We report a new, effective and simple method for preparing α,β‐unsaturated carbonyl compounds by reacting ketones and aromatic alcohols at 56°C in the presence of CrO₃ (CrO₃ acts as an oxidant and also a catalyst) for around 10 h. The condensation reactions occurred effectively among a wide combination of ketones and alcohols. The procedure is simple and the yields can be high up to 98%. And a probable mechanism is proposed.     

Behaviour of Ti electrode in the amperometric determination of high concentrations of strong oxidising species

The study of the capabilities of an unusual electrode material, namely, Ti, is presented: the amperometric determination of species showing responses that, on different materials, cannot be often profitably exploited, is proposed. H₂O₂ and HClO are successfully analysed, even at high concentrations. In similar conditions, which are quite common in industrial environments, these strong oxidising species are determined by time-consuming, off- or at-line, and multistep procedures. A complex real matrix, such as an industrial detergent, containing high H₂O₂ concentrations, has been taken as a meaningful study case to check the effectiveness of the electrode system and procedure proposed.     

Solar heat storage using chemical reactions

As an alternative to storage of sensible heat in liquids or solids or as latent heat of fusion, heat storage by means of reversible chemical reactions is under investigation. By this method, a chemical is separated into two components by heating and heat absorption, following which the components are stored in separate vessels and are recombined to generate heat when it is needed. The attractiveness of this concept of heat storage is not only higher energy density, but the capability to store energy as long as desired at ambient temperature, the option of transporting the chemicals to generate heat at another location, and the high temperatures characteristic of some of the reactions which result in high efficiency when the stored heat is used to generate electricity. Many reactions have been proposed and analyzed. Experimental work is in progress on inorganic hydroxide/oxide reactions, the decomposition of ammoniated salts, sulfur trioxide decomposition, ammonium sulfate decomposition, and others. The problems to be solved and potential applications are illustrated by the results of work in progress on Mg(OH)₂ and Ca(OH)₂ decomposition.     

Investigating the Active Oxidants Involved in Cytochrome P450 Catalyzed Sulfoxidation Reactions

Cytochrome P450 (CYP) heme-thiolate monooxygenases catalyze the hydroxylation of the C−H bonds of organic molecules. This reaction is initiated by a ferryl-oxo heme radical cation (Cpd I). These enzymes can also catalyze sulfoxidation reactions and the ferric-hydroperoxy complex (Cpd 0) and the Fe(III)-H₂O₂ complex have been proposed as alternative oxidants for this transformation. To investigate this, the oxidation of 4-alkylthiobenzoic acids and 4-methoxybenzoic acid by the CYP199A4 enzyme from Rhodopseudomonas palustris HaA2 was compared using both monooxygenase and peroxygenase pathways. By examining mutants at the mechanistically important, conserved acid alcohol-pair (D251N, T252A and T252E) the relative amounts of the reactive intermediates that would form in these reactions were disturbed. Substrate binding and X-ray crystal structures helped to understand changes in the activity and enabled an attempt to evaluate whether multiple oxidants can participate in these reactions. In peroxygenase reactions the T252E mutant had higher activity towards sulfoxidation than O-demethylation but in the monooxygenase reactions with the WT enzyme the activity of both reactions was similar. The peroxygenase activity of the T252A mutant was greater for sulfoxidation reactions than the WT enzyme, which is the reverse of the activity changes observed for O-demethylation. The monooxygenase activity and coupling efficiency of sulfoxidation and oxidative demethylation were reduced by similar degrees with the T252A mutant. These observations infer that while Cpd I is required for O-dealkylation, another oxidant may contribute to sulfoxidation. Based on the activity of the CYP199A4 mutants it is proposed that this is the Fe(III)-H₂O₂ complex which would be more abundant in the peroxide-driven reactions.     

Analysis of electronically nonadiabatic chemical reactions: An information theoretic approach

A practical procedure for the determination of branching ratios for reactions which lead to either excited or electronically ground state products is outlined. The method is applied to four reactions which could (on energetic grounds) produce an electronically excited iodine atom. No case of a complete inversion is found, but one reaction (F + HI) is predicted to yield a statistical, (one half), I^*(²P_1/2) to I(²P_3/2) ratio.     

Orbital correspondence analysis in maximum symmetry: Formulation and conceptual framework

A recently proposed method for the analysis of the course of chemical reactions, based on the maximal use of available symmetry, is formulated as a set of procedural rules. The application of these rules is illustrated with a simple prototype reaction: CH₂+C₂H₄ fcyclo-C₃H₆. They are then derived, using the formalism of time-dependent perturbation theory within the Born-Oppenheimer approximation, thus bringing out the method's underlying assumptions and its relation to the widely used Woodward-Hoffmann procedure.     

Electron transfer reactions between the superoxide ion and quinones

The electron transfer reactions of the superoxide ion with benzoquinone, trimethylbenzoquinone, and menadione in dimethylformamide were studied. A procedure of the determination of the relative rate constants of these reactions was developed; the reaction of O? ₂ with butyl bromide was chosen as a standard one. The relative rate constants measured at 20,°, 35°, and 50°C were slightly dependent on the quinone structure. The relationship between the free energy ΔF*of the electron transfer reactions and the standard free energy ΔF^o was discussed. This relationship is proposed as ΔF* = αΔF^o + β, where the proportionality coefficient α is equal to 0.04–0.11 for exothermal reactions and to 0.90–0.96 for endothermal reactions.     

Synthesis of Triazenes with Nitrous Oxide

Triazenes are valuable compounds in organic chemistry and numerous applications have been reported. Furthermore, triazenes have been investigated extensively as potential antitumor drugs. Here, we describe a new method for the synthesis of triazenes. The procedure involves a reagent which is rarely used in synthetic organic chemistry: nitrous oxide (N₂O, “laughing gas”). Nitrous oxide mediates the coupling of lithium amides and organomagnesium compounds while serving as a nitrogen donor. Despite the very inert character of nitrous oxide, the reactions can be performed in solution under mild conditions. A key advantage of the new procedure is the ability to access triazenes with alkynyl and alkenyl substituents. These compounds are difficult to prepare by conventional methods because the required starting materials are unstable. Some of the new alkynyltriazenes were found to display high cytotoxicity in in vitro tests on ovarian and breast cancer cell lines.     

Monitoring of the formation of binuclear ruthenium carbonyl complexes during reactions by means of high performance liquid chromatography

Reversed-phase high performance liquid chromatography has been used to monitor the reactions of Ru₃(CO)₁₂ with 1,4-diazabutadiene (DAB) and of Ru₂(CO)₆ (DAB) with DAB. The kinetic data show that the formation of an intermediate in the former reaction is the rate determining step, which is first order in Ru₃(CO)₁₂ as well as in DAB. The reactivity depends strongly on the type of substituent on DAB. Exchange of free and coordinated ligands (isopropyl DAB and tert-butyl DAB) is demonstrated in the reaction of Ru₂(CO)₆ (DAB) with DAB. A reversible reaction is proposed to account for this exchange.     

One‐Pot,Three‐Component Synthesis of 1‐(2‐Hydroxyethyl)‐1H‐1,2,3‐triazole Derivatives by Copper‐Catalyzed 1,3‐Dipolar Cycloaddition of 2‐Azido Alcohols and Terminal Alkynes under Mild Conditions in Water

A safe, efficient, and improved procedure for the regioselective synthesis of 1‐(2‐hydroxyethyl)‐1H‐1,2,3‐triazole derivatives under ambient conditions is described. Terminal alkynes reacted with oxiranes and NaN₃ in the presence of a copper(I) catalyst, which is prepared by in situ reduction of the copper(II) complex 4 with ascorbic acid, in H₂O. The regioselective reactions exclusively gave the corresponding 1,4‐disubstituted 1H‐1,2,3‐triazoles in good to excellent yields. This procedure avoids the handling of organic azides as they are generated in situ, making this already powerful click process even more user‐friendly and safe. The remarkable features of this protocol are high yields, very short reaction times, a cleaner reaction profile in an environmentally benign solvent (H₂O), its straightforwardness, and the use of nontoxic catalysts. Furthermore, the catalyst could be recovered and recycled by simple filtration of the reaction mixture and reused for ten consecutive trials without significant loss of catalytic activity. No metal‐complex leaching was observed after the consecutive catalytic reactions.     

Immobilization of palladium nanoparticles on ionic liquid-triethylammonium chloride functionalized magnetic nanoparticles: As a magnetically separable,stable and recyclable catalyst for Suzuki-Miyaura cross-coupling reactions

A facile procedure was applied to successfully synthesize novel Pd nanoparticles immobilized on triethanolamine-functionalized magnetic nanoparticles [Fe₃O₄/IL/Pd]. Diverse characterizations (HR-TEM, XRD, FT-IR, TGA, EDX, FE-SEM, ICP, XPS and VSM) were carried out to identify intrinsic traits of the nanoparticles. At room temperature, Fe₃O₄/IL/Pd demonstrated high catalytic activity toward Suzuki-Miyaura cross-coupling reactions in aqueous solution. Based on the results, Fe₃O₄/IL/Pd acted as zwitterionic IL-type heterogeneous catalyst, which could be separated from the reaction mixture, conveniently. Moreover, it exhibited excellent recyclability for at least eight cycles without considerable loss of its activity.     

Catalyst-free SiO2 sonogels

The sol-gel process has been used extensively to produce a great variety of glasses and ceramics using tetraetoxisilane (TEOS) as precursor of the SiO₂ matrix. The majority of synthetic approaches have been focused on the alkoxide-alcohol-water system. In all cases the alkoxide reactions occur through an acid and/or basic catalyzed hydrolysis condensation process. The sonication of acidified water/TEOS has been used as an alternative method to stimulate the hydrolysis of the alkoxide and avoid the use of ethanol as common solvent. These so-called sonogels have been extensively studied, and interesting new properties have been well established. In this work the occurrence of a reaction between neutral water and TEOS activated by high intensity ultrasonic irradiation is evidenced. As a result of this reaction high purity SiO₂ gels are obtained. An ad-hoc experimental setup was used which allows control of the reaction atmosphere during the sonication step, as well as recording of the pH and temperature of the system. The sonication scheme consisted of successive irradiation and short silent periods. A reaction scheme is proposed based on the formation and recombination of radicals during the ultrasonic irradiation step, which results mainly in the formation of a poly-hydroxylated Si species, while the poly-condensation reactions occur after the irradiation step. The high purity SiO₂ sonogels obtained are of interest due to their potential applications as supports for non-linear optical materials, catalytic active phases or in drug delivery.     

Stability of selenium and its speciation analysis in water using automatic system separation and HR-ICP-MS measurement

A simple and convenient method has been developed for the pre-concentration and separation of inorganic selenium species from environmental water samples using anion exchange chromatographic column combined with high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) measurement. ⁷⁵Se(IV) and ⁷⁵Se(VI) were prepared and used as tracers during the experiments. The volatility of selenium during solution evaporation was investigated to establish a reliable water samples pretreatment procedure. The parameters which affect the uptake of Se(IV) and Se(VI) on Dowex1 × 8 resin was optimized and the procedure for Se(IV) and Se(VI) separation was proposed. Both Se(IV) and Se(VI) are retained on the column in natural or alkaline solution with high distribution coefficient. The successive gradient elution of pre-concentrated species of selenium with HNO₃ solution allows to differentiate between them. Se(IV) and Se(VI) finally were eluted with 0.05 mol/L HNO₃ and 5.0 mol/L HNO₃, respectively. The proposed method has been successfully verified using the certified reference materials (CRMs) of real water samples, and spiked recoveries for real samples were 98%-104% with 5% relative standard deviations (RSDs). The developed procedure is proved to be reliable and can be used for the rapid determination of selenium species in environmental water samples.     

Theoretical study of X + H2 → XH + H and reverse reactions (X = F,Cl, Br,I) using a new empirical potential energy surface

A method for constructing empirical potential surfaces is proposed which is based on the BSBL (bond-strength-bond-length) treatment originally developed to predict kinetic parameters for atom transfer reactions. Quasiclassical trajectory results for X + H₂ → HX + H (X = F, Cl, Br, I) and the reverse reactions were used to demonstrate the utility of the new PES for the study of the dynamics and kinetics of metathesis reactions.     

Molecular iodine: An efficient catalyst for the one-pot synthesis of primary 1-aminophosphonates

A new and convenient procedure has been developed for the one-pot synthesis of different types of primary 1- aminophosphonates from aldehydes/ketones, HMDS and diethyl phosphite using I₂ as an inexpensive, non-toxic, non-metallic and readily available catalyst. These reactions proceeded under solvent-free conditions and produced the desired products in high yields.     

α-aminoazoles in the Synthesis of heterocycles: V. Synthesis of azolo[1,5-a]pyrimidines from 2-ethoxyvinyl trifluoromethyl ketones and 2,2-diethoxyvinyl trifluoromethyl ketone

A procedure was proposed for the synthesis of 7-trifluoromethylazolo[1,5-a]pyrimidines by reactions of 2-ethoxyvinyl trifluoromethyl ketones and 2,2-diethoxyvinyl trifluoromethyl ketone with 5(3)-aminoazoles. The reactions occurred under mild conditions, and the products were formed with high yield and regioselectivity.     

Palladium-Catalyzed Arylation of Sulfones

A procedure was developed for monoarylation of sulfones with aryl halides in the presence of palladium complexes. Optimal reaction conditions were found, and the scope of application of the proposed procedure was determined. The arylation occurs only with those sulfones which are relatively strong CH acids; the corresponding monoarylated sulfones are formed in moderate to high yields. The arylation of carbanions derived from the sulfones and some other CH acids requires the presence of an additional equivalent of base. The presence of the latter is also necessary in stoichiometric reactions of carbanions with the palladium complex CF3C6H4Pd(PPh3)2Br; no reaction occurs in the absence of a base. A new mechanism of arylation was proposed, where the key stage is deprotonation of palladium intermediate ArPdL2CHXY which activates the reductive elimination stage.     

Template-free sol–gel synthesis of high surface area mesoporous silica based catalysts for esterification of di-carboxylic acids

High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/sol–gel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m²/g) mesoporous (pore size 67 Å and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis sol–gel synthesis procedure. The catalysts showed very high acidity as determined by NH₃-TPD with the presence of Lewis as well as Brønsted acidity. These catalysts showed very high catalytic activity for esterification; a typical acid catalyzed organic transformation of various mono- and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost.     

Superacid catalyzed ring-opening reactions involving 2-oxazolines and the role of superelectrophilic intermediates

A variety of 2-oxazolines are found to react with arenes in superacidic triflic acid, CF₃SO₃H. It is proposed that the 2-oxazolines are protonated twice in triflic acid and the resulting intermediates undergo ring-opening reactions to produce reactive, dicationic species. These superelectrophiles are capable of reacting with benzene and o-dichlorobenzene in high yields by Friedel-Crafts type reactions.