1. Field of this Invention
This invention relates to a process for the preparation of 3-picoline.
2. Prior Art
Pyridine bases are important intermediates in the chemical industry, for example, for the preparation of nicotinic acid or nicotinamide. Various processes for the preparation of pyridine bases are known.
2-Methyl-5-ethylpyridine is nowadays industrially manufactured by means of a liquid phase process from acetaldehyde or paraldehyde and ammonia in the presence of a large variety of catalysts, for example, ammonium salts. Small amounts of 2-picoline and 4-picoline are formed as by-products.
2-Picoline and 4-picoline are nowadays prepared by gas phase reactions from acetaldehyde and ammonia at a temperature of about 400.degree. C. using fixed-bed or fluidized-bed catalysts based upon aluminum silicate.
For the production of pyridine and of 3-picoline, which is constantly gaining in importance, gas phase reactions are nowadays employed. In such reactions the formation of 2-picoline and 4-picoline is suppressed, in favor of 3-picoline, by adding formaldehyde to the acetaldehyde. These reactions, again, are carried out in a fixed bed or fluidized bed using aluminum silicate as the catalyst at a temperature of about 400.degree. C. Using such processes, yields of 3-picoline in the order of magnitude of at most 40 to 44 percent are achieved. At the same time large amounts of pyridine are formed.
Instead of saturated aldehydes, it is also known that unsaturated aldehydes, for example acrolein or crotonaldehyde, can be used as the starting materials. Such reactions take place in the gas phase at high temperatures; the yields are substantially of the same order as when using saturated aldehydes as the starting material.