Mass transfer from a highly soluble single cylinder in parallel flow

This work deals with the study of mass transfer rates from single cylinders of oxalic, succinic and boric acids placed in parallel flowing water stream. Due to high dissolution rates of acids, the surface area of the cylinder is continually changing with time and cannot be assumed constant. The hydrodynamic regimes through which mass transfer takes place from a cylinder are divided into three regions: (i) transfer from the bottom surface of the cylinder; (ii) transfer from the lateral surface; and (iii) transfer from the top surface. In the present work, appropriate correlations have been obtained experimentally for each of these cases, together with the overall mass transfer. The predictive equations proposed herein enable calculation of the overall mass transfer coefficient in a new application with an acceptable level of accuracy.     

One step synthesis of highly crystalline and high coercive cobalt-ferrite nanocrystals

Highly crystalline and almost monodisperse spinel cobalt-ferrite nanocrystals are synthesized in a one step process, which has very high coercivity at 10 K and exhibits superparamagnetic behaviour at 300 K.     

Pyrimidotetrathiafulvalenes. 3.* synthesis and properties of cation-radical salts,cation-radical betaines,and complexes of dimethyl[2,4-dioxo(1H,3H)pyrimido]tetrathiafulvalene and its N-alkyl substituted derivatives with iodine

The reaction of dimethyl[2,4-dioxo(1H,3H) pynmido]tetrathiafulvalene and its N-alkyl derivatives with iodine leads to the formation of complexes with various numbers of iodine atoms. Depending on the conditions, the betaine of the cation-radical of dimethyl[2, 4-dioxo(1 H, 3H)pyrimidojtetrathiafulvalene or a complex of the latter with dimethy1[2,4-dioxo(1H,3H)pyrimidoltetrathiafulvalene is formed by the oxidation of the pyrimidotetrathiafulvalene. The cation-radical perchlorates are formed on carrying out the oxidation of dimethyl[2,4-dioxo(1H,3H)pyrimidojtetrathiafulvalene and its N-methyl derivatives in the presence of perchloric acid. The preparation of the cation-radical salts is usually linked with the reaction of the cation-radical betaine with acids.For part 2 see [1].     

Photoinduced electron transfer between triplet erythrosin dianion and highly charged ionic quenchers

Abstract  

The lifetime of the lowest triplet state of the dianion erythrosin B depends on its concentration because of self-quenching. The self-quenching rate constants vary with the solution viscosity at room temperature. Dextrose was used to change the viscosity of aqueous solutions in the range 1 ≤ η ≤ 5.31 cP. Photoinduced electron transfer reactions between the triplet state of the erythrosin dianion and the highly charged ionic quenchers K₄[Fe(CN)₆] and K₄[Mo(CN)₈] were investigated in aqueous borate buffer solutions at pH 9.2 using flash photolysis. Electron transfer rates vary from 3.0 × 10⁸ to 1.4 × 10⁸ M⁻¹ s⁻¹ depending on viscosity.     

Soluble cycloannulated tetroxa[8]circulane derivatives: synthesis, optical and electrochemical properties, and generation of their robust cation-radical salts

Syntheses of soluble bicycloalkane-annulated tetraoxa[8]circulane derivatives via Lewis acid-catalyzed tetramerization of readily available cycloannulated benzoquinons is described. The ready availability of the soluble circulane derivatives allows the evaluation of their optical and electrochemical properties. These circulanes form stable (isolable) cation-radical salts upon 1-electron oxidation using antimony pentachloride and various aromatic oxidants.     

Design and asymmetric synthesis of chiral diaryliodonium salts

The application of chiral hypervalent iodine reagents in asymmetric synthesis is highly desirable, as the reagents are metal-free, environmentally benign and employed under mild conditions. Three chiral diaryliodonium salts have been designed to provide chemoselectivity and asymmetric induction in asymmetric α-phenylation of carbonyl compounds. The synthetic routes to the selected targets are detailed herein, together with a structural investigation into the diastereoselectivity of the alkylation process.     

A practical one-pot synthesis of soluble hexa-peri-hexabenzocoronene and isolation of its cation-radical salt

A simple and practical synthesis of soluble hexa-peri-hexabenzocoronene (HBC) from readily available hexaphenylbenzene (HPB) is described. In this simple procedure, the substitution of the free para positions of the propeller-shaped HPB with tert-butyl groups and the oxidative cyclodehydrogenation to planar HBC is achieved in a one-pot reaction using ferric chloride both as a Lewis acid catalyst and as an oxidant in excellent yields. The ready availability of HBC allows the isolation of its pure cation-radical salt using a variety of chemical oxidants such as antimony pentachloride and triethyloxonium and nitrosonium hexachloroantimonate salts.     

Electrophoretic mobility of a highly charged colloidal particle in a solution of general electrolytes.

For a highly charged particle in an electrolyte solution, counterions are condensed very near the particle surface. The electrochemical potential of counterions accumulated near the particle surface is thus not affected by the applied electric field, so that the condensed counterions do not contribute to the particle electrophoretic mobility. In the present paper we derive an expression for the electrophoretic mobility mu(infinity) of a highly charged spherical particle of radius a and zeta potential zeta in the limit of very high zeta in a solution of general electrolytes with large ka (where k is the Debye-Hückel parameter) on the basis of our previous theory for the case of symmetrical electrolytes (H. Ohshima, J. Colloid Interface Sci. 263 (2003) 337). It is shown that zeta can formally be expressed as the sum of two components: the co-ion component, zetaco-ion, and the counterion component, zetacounterion (where zeta = zetaco-ion + zetacounterion) and that the limiting electrophoretic mobility mu(infinity) is given by mu(infinity) = epsilonr epsilon0 zetaco-ion(infinity)/eta + 0(1/ka), where zetaco-ion(infinity) is the high zeta-limiting form of zetaco-ion, epsilonr and eta are, respectively, the relative permittivity and viscosity of the solution, and epsilon0 is the permittivity of a vacuum. That is, the particle behaves as if its zeta potential were zetaco-ion(infinity), independent of zeta. For the case of a positively charged particle in an aqueous electrolyte solution at 25 degrees C, the value of zetaco-ion(infinity) is 35.6 mV for 1-1 electrolytes, 46.0 mV for 2-1 electrolytes, and 12.2 mV for 1-2 electrolytes. It is also found that the magnitude of mu(infinity) increases as the valence of co-ions increases, whereas the magnitude of mu(infinity) decreases as the valence of counterions increases.     

A single step synthesis of 6-aminophenanthridines from anilines and 2-chlorobenzonitriles

Biologically active 6-aminophenanthridines were prepared in a single step procedure: Metal amides in liquid ammonia promoted the condensation of anilines with 2-chloro-benzonitriles. 6-Aminophenanthridines were isolated in moderate yield.     

Carbocations in action. Design, synthesis, and evaluation of a highly acid-sensitive naphthalene-based backbone amide linker for solid-phase synthesis

The design, synthesis, and properties of an extremely acid-labile backbone amide linker based on a regiospecifically substituted tetraalkoxy naphthaldehyde core are presented. This handle enables cleavage of peptide backbone amides (secondary amides) off a solid support using as little as 0.5% TFA in CH2Cl2. This proceeds without cleavage of tert-butyl ethers and tert-butyl esters. The design is based on a DFT study that predicted the most stabile alkoxy-substituted methyl naphthyl carbocation. [structure: see text]     

Electrochemical recognition of charged species using quaternary ammonium binaphthyl salts.

The effects of ionic analytes on the electrochemical properties of quaternary ammonium binaphthyl salts are described in this work. The stability of the binaphthyl radicals and hence the reversibility of the electrochemical response are discussed in terms of molecular structure. The ability of azacrown derivatised binaphthyl salts to act as amperometric receptors is ascribed to the strain imparted in the cyclic ammonium ring when Li+ ions complex with them. It is also shown that the redox properties of quaternary ammonium binaphthyl salts are pH dependent in aqueous solutions, but that reversible redox properties can be observed in extremely basic solutions. The effect of anions binding to the quaternary ammonium cation can be seen in the redox properties of the binaphthyl moiety and the use of a chiral binding site for enantiomeric recognition is also demonstrated.     

"Click to chelate": synthesis and installation of metal chelates into biomolecules in a single step

Click chemistry has been employed for the assembly of novel and efficient triazole-based multidentate chelating systems while simultaneously attaching them to molecules of biological interest. The "click-to-chelate" approach offers a powerful new tool for the modification of (bio)molecules with metal chelators for potential diagnostic and therapeutic applications.     

Reactions of hexamethylditin with alkylmercury salts I. Stoichiometry and rate step

Hexamethylditin in methanol solution reacts rapidly with mercuric chloride to yield mercury and trimethyltin chloride. With alkylmercuric salts the reaction is complex, yielding tetraalkyltin and/or dialkylmercury, depending upon the reactivity of the alkylmercuric salt. An electrophilic substitution mechanism involving trimethylstannyl mercurials as transient intermediates is suggested. The reaction of hexaalkylditin with diarylmercury is suggested to follow a homolyric pathway.     

Pot, atom and step economic (PASE) synthesis of highly functionalized piperidines: a five-component condensation

The diastereoselective pot, atom and step economic (PASE) synthesis of highly functionalized piperidines has been realized. The procedure simply involves mixing methyl acetoacetate, 2 equiv of aldehyde and 2 equiv of aniline together in the presence of InCl₃. In most cases the piperidine precipitates out of solution.     

Design and synthesis of highly reactive photopolymerizable epoxy monomers

The synthesis of a series of novel cationically photopolymerizable epoxide monomers bearing benzyl, allyl, and propargyl acetal and ether groups that can stabilize free radicals was carried out. These monomers display enhanced reactivity in cationic photopolymerization in the presence of certain onium salt photoinitiators. Specifically, this article describes schemes for the synthesis of cycloaliphatic epoxy monomers bearing free‐radical stabilizing groups. During UV irradiation of an onium salt cationic photoinitiator, the aryl radicals that are generated abstract labile protons present in such monomers to generate the corresponding carbon‐centered radicals. Subsequently, these radicals can interact with the onium salt by a redox mechanism to induce the decomposition of these salts. The overall result is that additional cationic species are generated by this mechanism that increase the rate and extent of the cationic ring‐opening polymerization of the epoxide monomer. An investigation of the photopolymerizations of the monomers prepared during this work was carried out using Fourier transform real‐time infrared spectroscopy, and conclusions were drawn with respect to the relationship between their structures and reactivity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2385–2395, 2001     

Asymmetric epoxidation of cis-alkenes mediated by iminium salts: highly enantioselective synthesis of levcromakalim

[reaction: see text] A range of cis-substituted olefins has been epoxidized with a new dihydroisoquinolinium salt catalyst, using tetraphenylphosphonium monoperoxysulfate as the stoichiometric oxidant, giving ee's of up to 97%. The reaction has been used as the key step in an enantioselective synthesis of the antihypertensive agent levcromakalim.