Pyridine-N-oxide

Pyridine 1-oxide

White, technically brown solid

Fixed

62-54 ° C

90-92 ° C ( 0.13 Pa)

4.25 D

Attention

Template: Infobox chemical / molecular formula search available

Pyridine- N-oxide is an organic compound consisting of a pyridine ring is oxidized at the nitrogen atom.

In general, all of the pyridine derivatives are referred to as an oxygen atom on the ring nitrogen as a pyridine N- oxide, pyridine -1-oxide wherein the parent compound.

Representation

The compound can be prepared by the reaction of pyridine with peroxycarboxylic acids. The peroxycarboxylic acids can here be made ​​of the underlying acid and hydrogen peroxide in situ. The reaction is similar to the mechanistically Prileschajew reaction. A further oxidizing agent for the preparation of pyridine -N-oxide is, for example Caro's acid.

Use

Electrophilic aromatic substitution reactions of pyridine proceed with good selectivity in the 3-position on what is due to the electronic structure of the pyridine ring. The carbon atoms in position 3 has the highest electron density of all carbon atoms in the ring, which is why preferably substituted at this position. However, the oxidized nitrogen atom in N-oxide causes the increase of the electron density in the ring and the reverse of the electronic structure of the ring. The carbon atoms in 2 - and 4-position, thus having the highest electron density as opposed to pyridine. This leads to a reversal of the selectivity and electrophilic substitutions are preferably the 2 - and 4-substituted products obtained. For this reason, pyridine -N-oxide is an important starting compound for the synthesis of 2 - or 4- substituted pyridines (for example, 4- nitropyridine - N-oxide), which are not accessible by nucleophilic aromatic substitution.

Reactions

After substitution of the nitrogen atom can be reduced mostly smooth, wherein the substituted pyridine derivative is obtained. Suitable reducing agents are generally trivalent phosphorus compounds or divalent sulfur compounds that are readily oxidized. As a convenient reagent triphenylphosphine is frequently used, which is oxidized to triphenylphosphine oxide. Furthermore, samarium ( II) iodide, tin (II ) chloride or chromium (II ) chloride is used at room temperature for deoxygenation of pyridine- N-oxide. Reduction by means of ammonium formate in the presence of palladium on charcoal resulting in the deoxygenation of the nitrogen, while the hydrogenation of the pyridine ring, so that the piperidine derivative is obtained.