Drug Intermediates

The nitrogen atom on pyridine features a basic lone pair of electrons. Because this lone pair is not delocalized into the aromatic pi-system, pyridine is basic with chemical properties similar to tertiary amines. The pka of the conjugate acid is 5. 21. Pyridine is protonated by reaction with acids and forms a positively charged aromatic polyatomic ion called pyridinium cation. The bond lengths and bond angles in pyridine and the pyridinium ion are almost identical^[1] because protonation does not disrupt the aromatic pi system. In addition, the pyridinium cation is isoelectronic with benzene.

The nitrogen atom on pyridine features a basic lone pair of electrons. Because this lone pair is not delocalized into the aromatic pi-system, pyridine is basic with chemical properties similar to tertiary amines. The pKa of the conjugate acid is 5.21. Pyridine is protonated by reaction with acids and forms a positively charged aromatic polyatomic ion called pyridinium cation. The bond lengths and bond angles in pyridine and the pyridinium ion are almost identical^[1] because protonation does not disrupt the aromatic pi system. In addition, the pyridinium cation is isoelectronic with benzene.

The Cornforth reagent (pyridinium dichromate; PDC), is the complex of chromium(VI) oxide with aqueous pyridine, with the chemical formula (C₅H₅NH)₂Cr₂O₇. Like pyridinium chlorochromate (PCC), it is used as an oxidising agent to convert alcohols to aldehydes and ketones. Compared with PCC, PDC presents the advantage of being less acidic

Pyridinium chlorochromate is a reddish orange solid reagent used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. Pyridinium chlorochromate, or PCC, will not fully oxidize the alcohol to the carboxylic acid as does the Jones reagent.

The rate constants and the kinetic parameters of the reaction of phenacyl bromide with mono and disubstituted anilines in ethanol have been determined. The substituent effects on the free energy of activation have been found to be additive. HAMMETT equation for multiple substitution was applied to correlate reactivity with structural parameters.