Picoline

The picoline or methylpyridines form a group of substances of organic compounds belonging to the heterocyclic compounds in chemistry (more precisely, heteroaromatic) counts. They consist of a pyridine ring which is substituted with a methyl group. Due to their different arrangement of three structural isomers arise. They are quite similar in their properties to the pyridine and can this where it does not depend on the exact molecular structure, easy to replace, for example, as a solvent. Otherwise, they serve in many ways as synthetic building blocks for pharmaceutical and agricultural chemical products and dye manufacture.

History

The 2- picoline was first isolated in 1846 by T. Anderson from coal tar. The term picoline is made up of latin pix ( unlucky ) and oleum together (oil).

Representation

At present, 2 -picoline is produced mainly on two synthetic routes: by condensation of acetaldehyde, formaldehyde and ammonia, and by cyclization of nitriles and acetylene ( Bönnemann cyclization ). An example is the reaction of acetaldehyde and ammonia:

Approx. 8000 tonnes were produced worldwide in 1989.

3-methylpyridine is produced industrially by reaction of acrolein with ammonia:

A more efficient way is based on acrolein, propionaldehyde and ammonia:

Approx. 9,000 tonnes were produced worldwide in 1989.

Properties

The picoline are colorless liquids with a pyridinartigen odor. They are miscible with water, ethanol and diethyl ether. The 4- picoline, which has the highest symmetry, has the highest melting point.

Since in the 2 -, the methylene groups are arranged in direct conjugation with the electron-attracting nitrogen atom, and 4- picoline, the methyl groups in these two isomers can be relatively easily deprotonated by a strong base such as lithium diisopropylamide or butyllithium, and then further derivatized.

Use

Picoline are used as intermediates for the preparation of other chemical compounds. May be prepared from 2- picoline, 2- vinylpyridine, and the agricultural chemical nitrapyrin. 3-picoline is, for example, as a starting material for the synthesis of chlorpyrifos and niacin, 4- picoline, the production of the anti-tuberculosis drug isoniazid.

By oxidation, for example by means of potassium permanganate ( KMnO4 ) is formed from 2-picoline, the picolinic acid, nicotinic acid from 3-picoline and 4 -picoline, the isonicotinic acid.