Process for preparing 2-methyl-3,5-dialkylpyridines by dealkylation with sulfur

DETAILED DESCRIPTION I claim: 1.
A process for dealkylating the 2- position on a trisubstituted pyridine derivative having the formula ##STR3## where R.
sub.
1 is a straight chain alkyl group from about C.
sub.
2 -C.
sub.
5 and where R.
sub.
2 and R.
sub.
3 are alkyl, aryl or aralkyl groups up to about C.
sub.
10, comprising the step of reacting said pyridine derivative under heat with sulfur.
2.
The process of claim 1 wherein R.
sub.
1 is an ethyl group and R.
sub.
2 and R.
sub.
3 are methyl groups.
3.
The process of claim 1 wherein said reacting is under reflux at a temperature of at least about 150.
degree.
C.
4.
The process of claim 3 wherein said reacting is with excess sulfur at a mole ratio of at least about 3:1 of sulfur to said trisubstituted pyridine precursor.
5.
The process of claim 4 wherein said reacting is for a period of about 4-30 hours.
6.
The process of claim 5 comprising the additional step of using an H.
sub.
2 S absorption system to trap H.
sub.
2 S gas evolved during said reacting.
7.
A process for preparing 2,3,5-trimethylpyridine comprising the steps of initially preparing 2-ethyl-3,5-dimethylpyridine by the Chichibabin reaction of propionaldehyde and ammonia, followed by heating said 2-ethyl-3,5-dimethylpyridine at reflux with excess sulfur.




Description:
BACKGROUND OF THE INVENTION This invention relates generally to the field of pyridine chemistry, and, more particularly to an improved process for preparing 2-methyl-3,5-dialkylpyridine derivatives.
Pyridine, with its characteristic aromatic ring structure, is the parent to a large number of substituted homologues and derivatives having uses in valuable industrial, pharmaceutical and agricultural chemicals.
One such derivative is 2,3,5-trimethylpyridine, which is also known by the name 2,3,5-collidine.
For example, the compound 2,3,5-trimethylpyridine has recently proven valuable as a key intermediate for the synthesis of a highly-substituted pyridine derivative known as omeprazole, which has been accorded much medical and commercial interest because it and a family of related compounds have been found useful as gastric secretion inhibitors for treating ulcers and related diseases