An Efficient and Selective Solid State Oxidation of Thiols to Disulfides with Quinolinium Fluorochromate on Silica Gel

Various kinds of aliphatic (cyclic and acyclic), aromatic, and heterocyclic thiols are converted into the corresponding disulfides by quinolinium fluorochromate (QFC) on silica-gel in excellent yields. Selective oxidation of thiols in the presence of sulfides is also achieved under solid phase conditions.     

A Novel Spectrophotometric Method for the Determination of Zolmitriptan in Pharmaceutical Formulations

A simple, rapid, cost effective and extraction‐free spectrophotometric method has been developed for the determination of zolmitriptan in pharmaceutical raw and dosage forms. The method is based on the charge‐transfer reaction of zolmitriptan in acetonitrile medium with 0.2% 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone to form a colored product peaking at 555 nm. Beer's law is obeyed in the concentration range 10‐250 μg mL^?1 with molar absorptivity of 1.7 × 10³ L mole^?1 cm^?1. The effects of variables such as reagent concentration, time of reaction, color stability and interferences have been investigated to optimize the procedure. The results have been validated analytically and statistically. The proposed method has been successfully applied for the determination of zolmitriptan in pharmaceutical formulations. Results indicate that the method is accurate, precise and reproducible (relative standard deviation < 2%).     

Reactions of a stable silylene with halocarbons

An unusual product formation is observed for the insertion reaction of the thermally stable silylene Si[(NCH(2)Bu(t))(2)C(6)H(4)-1,2][abbrev. as Si(NN)] into the carbon-halogen bond of alkyl or aryl halides RHal (Hal=Cl, Br). In general, depending on the halogen, the reaction either results in a disilane of type (NN)Si(Hal)-(R)Si(NN) for Hal=Cl or a mixture of disilane and the monosilane (NN)Si(R)(Hal) for Hal=Br. The results are put into context to previously suggested mechanisms. The disilane (NN)Si(Hal)-(R)Si(NN)(Hal=Cl or Br) is thermally labile and mild thermolysis yields the corresponding monosilane (NN)Si(R)(Hal) and silylene 1. Additionally, strong evidence is presented for a radical pathway for the reaction of 1 and RHal.     

Investigation of enhanced HgBr(B 2Σ+−X 2Σ+) laser emission due to collisions of Xe ions and HgBr2

Electronic excitation of Hg and the HgBr radical has been observed during collisions of HgBr₂ with Xe⁺ ions at different laboratory kinetic energies. Emission cross-sections of the most intense band of the HgBr(B ²⁺, v=0–X ²⁺, v=22) transition at 502 nm have been measured at different energies of the projectile ions.     

Synthesis and mesomorphic properties of 7-acyloxy-3-(4-acyloxyphenyl)-4H-1-benzopyran-4-one

A new homologous series of 7-acyloxy-3-(4-acyloxyphenyl)-4H-1-benzopyran-4-ones was synthesized and characterized by elemental analysis and spectroscopic techniques along with thermal behaviour study using differential scanning calorimetry. Texture observation was performed under the polarizing optical microscope from which the derivatives were found to exhibit different molecular organizations as exemplified by various mesophases. Whilst the compounds containing butanoyloxy and hexanoyloxy groups behave as nematogens, the other compounds with heptanoyloxy and longer side chains show a SmC phase. The octadecanoyloxy derivative was the only member showing a monotropic SmC phase. The difference in phase behaviour is discussed based on the molecular structure and the presence of a lateral dipole which can be associated with the intermolecular interaction within the mesophase.