Highly selective deblocking of propargyl carbonates in the presence of propargyl carbamates with tetrathiomolybdate

Propargyloxycarbonyl chloride, 1, has been used to protect the hydroxyl and amino functionalities of amino alcohols and aminophenols in one pot using triethylamine or pyridine as a base. The increased reactivity of benzyltriethylammonium tetrathiomolybdate, 2, toward propargyl carbonates over propargyl carbamates is studied in detail and has been exploited further to develop an orthogonal protection strategy for the hydroxyl and amino functionalities. For example, 2-amino-1-butanol, 6a, was treated with 1 to get the N,O-diPoc compound 7a in 90% yield, which when treated with 1.1 equiv of 2 at room temperature removes the Poc group attached to oxygen while leaving the one attached to nitrogen intact to yield compound 8a in 85% yield. This particular observation offers a new protecting strategy where an amine and an alcohol group can be protected simultaneously in one pot, and in a later synthetic step, if the alcohol group has to be deprotected selectively, it can be achieved with 1 equiv of 2.     

Conformational studies of 3,4-dideoxy furanoid sugar amino acid containing analogs of the receptor binding inhibitor of vasoactive intestinal peptide

Conformational analysis of vasoactive intestinal peptide (VIP) receptor binding inhibitor Leu¹-Met²-Tyr³-Pro⁴-Thr⁵-Tyr⁶-Leu⁷-Lys⁸1 by various NMR techniques and constrained molecular dynamics (MD) simulation studies revealed that the molecule had a turn structure involving its Tyr³-Pro⁴-Thr⁵-Tyr⁶ moiety with intramolecular hydrogen bond between Tyr⁶NH→Tyr³CO. In order to mimic the structure of 1, peptidomimetic analogs 2-4 were synthesized using conformationally constrained scaffolds of 3,4-dideoxy furanoid sugar amino acids (2S,5R)-ddSaa1 5 and its enantiomer (2R,5S)-ddSaa2 6. All these analogs displayed well defined three-dimensional structures akin to that found in 1. Peptides 2 and 3, which differed only in the sugar amino acid stereochemistry, show propensity of structures with identical intramolecular hydrogen bonds between ThrNH→MetCO. A similar structure with a hydrogen bond between TyrNH→MetCO was observed in 4.     

Rapid spectrophotometric determination of phenothiazines with molybdophosphoric acid

A simple and rapid spectrophotometric method for the determination of six phenothiazines can be based on the formation of a coloured compound between molybdophosphoric acid and phenothiazines. The i.r. and e.s.r. spectra of the coloured compounds showed that molybdophosphoric acid oxidizes phenothiazines to a radical cation with which it then forms a coloured compound. The proposed method is employed for the determination of phenothiazines in pharmaceutical preparations. Calibration graphs are linear over ranges of about 100–2000 μg of the phenothiazine.     

Micellar effect of sodium dodecyl sulfate on the reactions between iron(II) and p-benzoquinone, and iron(III) and hydroquinone

The micellar effet of sodium dodecyl sulfate (SDS) on the initial stages of the reaction between (1) Fe(II) and p-benzoquinone, and (2) Fe(III) and hydroquinone have been investigated. In the former case acceleration was observed, the rate-[surfactant] profile showing a maximum. SDS has an inhibitory effect on the latter reaction. Kinetic analysis has been carried out using Berezin's approach.

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() 1) Fe(II) 2) Fe(III) . - . . , .

     

Chlorpromazine hydrochloride as a new redox indicator in vanadametry

Chlorpromazine hydrochloride is proposed as an indicator in the vanadametric titration of iron(II) and molybdenum(V). It gives a sharp, reversible colour change from green to violet at the equivalence point. It has advantages over the diphenylamine class of indicators. Its redox and transition potentials are reported.     

Extraction of Am(III) from different acid media by di-2-ethyl hexyl phosphoric acid containing phosphorous pentoxide

The extraction of Am(III) from nitric, hydrochloric, oxalic, phosphoric and hydrofluoric acids was studied using 0.4F di-2-ethyl hexyl phosphoric acid (HDEHP) containing 0.1M phosphorous pentoxide (P₂O₅) in dodecane/xylene. The extraction with pure 0.4F HDEHP was found to be negligible from all the media studied. However, the presence of a small amount of P₂O₅ in it increased the extraction substantially. The distribution ratios of Am(III) obtained for HDEHP - P₂O₅ mixture 3M nitric acid containing different concentrations of oxalic acid/phosphoric acid/hydrofluoric acid are in the order of 200-250. The same for 3M hydrochloric acid is very high (800). These distribution ratios are sufficiently high for the quantitative extraction of Am(III) from all the acid media studied. Different reagents such as ammonium oxalate, sodium oxalate, oxalic acid, hydrofluoric acid, sodium carbonate and potassium sulphate were explored for the back extraction of Am(III) from 0.4F HDEHP + 0.1M P₂O₅ in dodecane/xylene. Of these, 0.35M ammonium oxalate and 1M sodium carbonate were found to be most suitable. The back extraction of Am(III) was also attempted with water and 1M H₂SO₄, HNO₃, HClO₄ and HCl solutions after allowing the extracted organics to degrade on its own. It was found that more than 90% of Am could be back extracted with these acids. Using this method more than 90% of Am(III) was recovered from nitric acid solutions containing calcium and fluoride ions.     

Spectrophotometric determination of vanadium(V) and its application to vanadium steel containing chromium,molybdenum, manganese,and nickel

Promethazine hydrochloride forms a red colored species with vanadium(V) in 6.0–7.5 M phosphoric acid. A 16-fold molar excess of the reagent is necessary for full development of color intensity. Beer's law is valid over the concentration range of 0.1–7.0 ppm. The optimum concentration range as evaluated by Ringbom's method is 0.5–7.0 ppm. The sensitivity of the reaction is 0.005 μg cm^?2 and the molar absorptivity is 9.60 × 10³ liter mol^?1 cm^?1 at 517 nm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions were reported. Vanadium in vanadium steel containing chromium, molybdenum, manganese, and nickel was determined.     

Hydrogenation and hydrogenolysis of furfural and furfuryl alcohol catalyzed by ruthenium(II) bis(diimine) complexes

The catalytic activity of ruthenium(II) bis(diimine) complexes cis‐[Ru(6,6′‐Cl₂bpy)₂(OH₂)₂](Z)₂ ( 1 , Z = CF₃SO₃; 2 , Z = (3,5‐(CF₃)₂C₆H₃)₄B, i.e. BArF) and cis‐[Ru(4,4′‐Cl₂bpy)₂(OH₂)₂](Z)₂ ( 3 , Z = CF₃SO₃; 4 , Z = BArF) for the hydrogenation and/or the hydrogenolysis of furfural (FFR) and furfuryl alcohol (FFA) was investigated. The molecular structures of cis‐[Ru(4,4′‐Cl₂bpy)₂(CH₃CN)₂](CF₃SO₃)₂ ( 3 ′) and dimeric cis‐[(Ru(4,4′‐Cl₂bpy)₂Cl)₂](BArF)₂ ( 5 ) were characterized by X‐ray crystallography. The structures are consistent with the anticipated reduction in steric hindrance about the ruthenium centers in comparison with corresponding complexes containing 6,6′‐Cl₂bpy ligands. While compounds 1 , 2 , 3 , 4 are all active and highly selective catalysts for the hydrogenation of FFR to FFA under modest reaction conditions, 3 and 4 showed decreased activity. This is best explained in terms of reduced Lewis acidity of the Ru²⁺ centers and reduced steric hindrance about the metal centers of catalysts 3 and 4 . cis‐[Ru(6,6′‐Cl₂bpy)₂(OH₂)₂](BArF)₂ ( 2 ) also displayed high catalytic efficiency for the hydrogenation of FFA to tetrahydrofurfuryl alcohol. Presumably, this is because coordination of C═C bonds of FFA to the ruthenium center is poorly inhibited by non‐coordinating BArF counterions. Interestingly, cis‐[Ru(6,6′‐Cl₂bpy)₂(OH₂)₂](CF₃SO₃)₂ ( 1 ) showed some catalytic activity in ethanol for the hydrogenolysis of FFA to 2‐methylfuran, albeit with fairly modest selectivity. Nonetheless, these results indicate that ruthenium(II) bis(diimine) complexes need to be further explored as catalysts for the hydrogenolysis of C―O bonds of FFR, FFA, and related compounds. Copyright © 2012 John Wiley & Sons, Ltd.     

On the Uniform Nonsingularity Property for Linear Transformations on Euclidean Jordan Algebras

In a recent paper, Chua and Yi introduced the so-called uniform nonsingularity property for a nonlinear transformation on a Euclidean Jordan algebra and showed that it implies the global uniqueness property in the context of symmetric cone complementarity problems. In a related paper, Chua, Lin, and Yi raise the question of converse. In this paper, we show that, for linear transformations, the uniform nonsingularity property is inherited by principal subtransformations and, on simple algebras, it is invariant under the action of cone automorphisms. Based on these results, we answer the question of Chua, Lin, and Yi in the negative.