Evaluation of the quality of colour changes of complexometric indicators in the titration of copper (II) with EDTA by tristimulus colorimetry

The quality of colour changes of the indicators hematoxylin, 4(2-pyridylazo)resorcinol (PAR), xylenol orange, pyrocatechol violet, chromazurolS and eriochrome cyanineR in the complexometric titration of copper(II) with ethylenediaminetetraacetic acid (EDTA) were studied with the help of tristimulus colorimetry, utilising a comparative study of the parameters SCD (specific colour discrimination), CIE La^*b^* 1976 and LABHNU 1977. Hematoxylin was found to be the best indicator among those studied. A screened indicator, viz. PAR + malachite green (52), was developed to enhance the quality of colour transition at the end-point and the accuracy of the titrimetric determination.     

A facile synthesis of steroidal D-ring fused pyrazolo[1,5-a]pyrimidines

A facile method for the synthesis of steroidal D-ring fused pyrazolo[1,5-a]pyrimidines through a microwave mediated reaction between steroidal β-bromovinyl aldehydes and pyrazoloamines using palladium(II) catalyst has been described.     

A facile synthesis of benzo[b][1,4]thiazepine derivatives by palladium acetate catalyzed reaction

The preparation of steroid/nonsteroid fused benzo[b][1,4]thiazepines and 2-arylsubstituted benzo[b][1,4]thiazepines is described from Pd(OAc)₂ catalyzed reaction of steroidal/nonsteroidal β-halovinyl aldehydes and 2-aminothiophenols in DMF under heating condition.     

Microwave-assisted novel and efficient one-pot synthesis of fused steroidal and non-steroidal isothiazoles

An efficient microwave promoted one-pot synthesis of steroidal and non-steroidal isothiazole derivatives from corresponding β-bromo-α,β-unsaturated aldehydes has been described using a sodium thiocyanate-urea system. The β-bromo-α,β-unsaturated aldehydes derivatives are efficiently synthesized from corresponding cyclic ketones using Vilsmeir formylation reaction. The synthetic protocol is also applied for the synthesis of antifungal brassilexin.     

Spectrophotometric determination of drugs in pharmaceutical formulations withN-bromosuccinimide and celestine blue

Simple, sensitive and selective methods are proposed for the spectrophotometric determination of drugs, viz., tetracycline HCl, nifurtimox, ethionamide, propranolol HCl and isonicotinic acid hydrazide, based on their reactivity withN-bromosuccinimide (NBS). The method involves the addition of excess NBS of known concentration in the presence of 0.25M HCl and the unreacted NBS is determined by the measurement of the decrease in the absorbance of the dye celestine blue (_max 540 nm), which was found to be the most suitable of several dyes tested. This method was applied for the determination of drug contents in pharamaceutical formulations and enabled the determination of the drugs in microgram quantities (0.2 to 5 g/ml). Standard deviations were typically 0.5mg per dose (RSD 0.1–1.0%). No interferences were observed from excipients and the validity of the method was tested against reference method. Recoveries were 99.8–101.1%.     

Screening and specification of colour changes of nitritometric indicators

The specification of colour changes of nitritometric indicators, viz., cresyl fast violet acetate, amethyst violet, safranine O, neutral red, methylene violet, neutral violet, phenosafranine, brilliant cresyl blue and lissamine blue BF, in the titration of sulphanilamide has been carried out with the help of tristimulus colorimetry. Apart from the determination of true colour co-ordinates and complementary colour co-ordinates, the quantitative parameters specific colour discrimination (SCD), total colour difference (E*) values of CIE La^*b^*, CIE Lu^*v^* and LAB HNU colour spaces together with the standard deviation of colour matching (S) were also evaluated for all the indicators at different concentrations ratios of nitrite and sulphanilamide, for a quantitative measure of quality of colour change. The quality of colour change of many of the studied indicators is further improved by screening with appropriate inert colorants to obtain a colour transition between complementary colours through colourlessness at the equivalence point.     

A facile one-pot synthesis of 7-substituted pyrazolo[1,5-a]pyrimidines by base induced three-component reaction

The preparation of steroid/nonsteroid fused 7-substituted pyrazolo[1,5-a]pyrimidines is described by a one-pot reaction of steroidal/nonsteroidal ketones, aromatic aldehydes and 3-amino-1H-pyrazoles/5-amino-1H-pyrazoles in the presence of potassium tert-butoxide in good yield under reflux condition in ethanol.     

A facile method for the synthesis of steroidal and nonsteroidal 5-methyl pyrazolo[1,5-a]pyrimidines

The steroidal and nonsteroidal 5-methyl pyrazolo[1,5-a]pyrimidines were synthesized by the reaction of steroidal/nonsteroidal α,β-unsaturated ketones and 3-amino-1H-pyrazoles/5-amino-1H-pyrazoles in the presence of KO^tBu in ethanol under reflux condition.