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Cornforth Reagent
The pyridinium dichromate (PDC) or Cornforth reagent is a pyridinium salt of dichromate with the chemical formula 5H5NHsub>2 r2O7 This compound is named after the Australian-British chemist Sir John Warcup Cornforth (b. 1917) who introduced it in 1962. The Cornforth reagent is a strong oxidizing agent which can convert primary and secondary alcohols to aldehydes and ketones respectively. In its chemical structure and functions it is closely related to other compounds made from hexavalent chromium oxide, such as pyridinium chlorochromate and Collins reagent. Because of their toxicity, these reagents are rarely used nowadays. Synthesis and properties The Cornforth reagent is prepared by slow addition of a concentrated aqueous solution of chromium trioxide to pyridine. The reaction may cause explosion, which is avoided by thoroughly dissolving the trioxide in water and cooling the solution by ice. The product is filtered, washed with acetone and dried, yielding an orange powder. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyridinium
Pyridinium refers to the cation . It is the conjugate acid of pyridine. Many related cations are known involving substituted pyridines, e.g. picolines, lutidines, collidines. They are prepared by treating pyridine with acids. As pyridine is often used as an organic base in chemical reactions, pyridinium salts are produced in many acid-base reactions. Its Salt (chemistry), salts are often insoluble in the organic solvent, so Precipitation (chemistry), precipitation of the pyridinium leaving group complex is an indication of the progress of the reaction. Pyridinium cations are aromatic, as determined through Hückel's rule. They are isoelectronic with benzene. ''N''-Alkylpyridinium cations When the acidic proton is replaced by alkyl, the compounds are called ''N''-alkylpyridinium. A simple representative is Methylpyridinium, ''N''-methylpyridinium ([C5H5NCH3]+). These pyridinium intermediates have been used as electrophiles in synthetic organic chemistry to build dearomatized ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Suspension (chemistry)
In chemistry, a suspension is a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation. The particles may be visible to the naked eye, usually must be larger than one micrometer, and will eventually settle, although the mixture is only classified as a suspension when and while the particles have not settled out. Properties A suspension is a heterogeneous mixture in which the solute particles do not dissolve, but get suspended throughout the bulk of the solvent, left floating around freely in the medium. The internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation, with the use of certain excipients or suspending agents. An example of a suspension would be sand in water. The suspended particles are visible under a microscope and will settle over time if left undisturbed. This distinguishes a suspension from a colloid, in which the colloid particles are smaller and do not settle. Colloids a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
