Stereoselective synthesis of C12–C21 common fragment of thermolides 1–5

A highly stereoselective synthesis of C12–C21 common fragment of thermolides 1–5 has been described. The salient features of the synthesis are the utilization of desymmetrization protocol, Barton-McCombie reaction, Brown’s asymmetric allylation and Wacker oxidation.     

Determination of uranium by displacement of labelled zinc from Zn:PAN

A radiochemical method, based on the displacement of labelled zinc from Zn:PAN /1-/2-Pyridylazo/-2-Naphthol/ complex for the determination of uranium has been developed. 40–160 g of uranium U/VI/ in pH 7 ammonia buffer can be determined. the effect of diverse ions on the displacement reaction has also been studied.     

Titration of antimony(III) with cerium(IV) sulphate and diphenylamine and its derivatives as reversible indicators

Diphenylamine, barium diphenylamine sulphonate, N-phenylanthranilic acid and 2-nitrodiphenylamine have been investigated as reversible indicators for the titration of antimony(III) with cerium(IV) sulphate in 0.5–2 M sulphuric acid medium. Diphenylamine is the most satisfactory in titrations of antimony(III) in chloride-free solutions, e.g. of potassium antimonyl tartrate. Even low chloride concentrations affect the indicator action of N-phenyl-anthranilic acid or 2-nitrodiphenylamine, but diphenylamine is satisfactory in 1 M hydrochloric acid media. Iodine catalyst is necessary to accelerate the reduction of the oxidized indicator by antimony(III). The indicator colour change is vivid and the colour of the oxidized indicator is stable. Titrations of antimony(III) in mixtures with iron(II) and arsenic(III) are also considered.     

Volumetric estimation of potassium permanganate and potassium dichromate in mixtures with oxalic acid

1. A simple method has now been developed for the volumetric estimation of potassium permanganate and potassium dichromate in mixtures The method consists in taking an aliquot volume of the mixture in an Erlenmeyer flask, adding sufficient quantities of sulphuric acid and manganous sulphate (catalyst) and titrating with a standard solution of sodium oxalate or oxalic acid run in from the burette, until the colour changes from orange-red to yellow. The oxalic acid run ingives a measure of the permanganate present in the mixture Then the mixture in the flask is titrated with a standard solution of Mohr's salt using diphenylbenzidine as indicator. The volume of Fe⁺² solution run in the second stage gives a measure of the dichromate present in the original mixture. 2. The reverse titration does not give accurate results, because it is affected by the induced reaction between oxalic acid and dichromate which is induced by the reaction between oxalic acid and permanganate during the first stage of the reaction. This induced reaction has been studied in some detail.     

PMR Spectra of Piperidine Involved in the Formation of Charge Transfer Complexes with 1,4-Benzoquinones

The proton magnetic resonance spectra of piperidine involved in the formation of charge transfer complexes with 1,4-benzoquinones, in chloroform, have been presented and discussed.     

Use of tetravalent manganese in solutions of sulfuric acid as an oxidant for the direct titration of nitrite

Conditions have been worked out for the direct titration of nitrite with manganese(IV) sulfate using ferroin as indicator. The method is suitable for the estimation of 8–60 mg of sodium nitrite with a standard deviation of 0.04, in an acidity range of 0.3 to 0.6 M. The special feature of this method lies in the reagent's association with acid and its relatively higher redox potential.     

Elementary and Good Group Gradings of Incidence Algebras over Partially-Ordered Sets with Cross-Cuts

Let G be a group, X a locally-finite partially-ordered set, and F a field. We provide an algorithmic method for finding all good G-gradings of the incidence algebra I(X,F) when X has a cross-cut of length one or two. In these cases, we show that the good gradings are determined by a “freeness” property. It is shown that the number of good gradings of the incidence algebra I(X,F), when X has a cross-cut of length one or two, depends only on the size of G and not on its structure, but this is no longer true when the shortest cross-cut of X has length greater than two. If X has a cross-cut of length one, then every good grading of I(X,F) is an elementary grading, but, when the shortest cross-cut of X has length greater than one, there may exist good gradings of I(X,F) that are not elementary gradings. Finally, we establish bounds on the number of good gradings of I(X,F) for any finite partially-ordered set X.     

Syntheses of the four stereoisomers of Phytophthora mating hormone α2 and a concise synthesis of mating hormone α1

Four stereoisomers of Phytophthora mating hormone α2 were synthesized using both enantiomers of citronellol as starting materials. The absolute configuration of the natural product was determined to be 7S,11R,15R by oospore-inducing assays of the synthetic isomers. A concise synthetic procedure of α1 was also established using a common synthetic intermediate of α2.     

Synthesis and antimicrobial activity of pyrrolyl/pyrazolyl arylaminosulfonylmethyl 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and 1,2,4-triazoles

A new class of pyrrolyl/pyrazolyl arylaminosulfonylmethyl 1,3,4-oxadiazoles, 1,3,4-thiadiazoles, and 1,2,4-triazoles were prepared and tested for antimicrobial activity. Amongst the tested compounds, 5c displayed high antimicrobial activity.