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Oxy-and Aminopyridines

The three oxy-pyridines are subject to tautomerism involving hydrogen interchange between oxygen and nitrogen, but again with a significant difference between a- and 7- on the one hand and /3-isomers on the other. [Pg.88]

Under all normal conditions, a- and 7-isomers exist almost entirely in the carbonyl tautomeric form, and are accordingly known as pyridones the hydroxy tautomers are detected in significant amounts only in very dilute solutions in non-polar solvents like petrol, or in the gas phase where, for the a-isomer, 2-hydroxypyridine is actually the dominant tautomer by 2.5 1. The polarised pyridone form is favoured by solvation. 3-Hydroxypyridine exists in equilibrium with a corresponding zwitterionic tautomer, the exact ratio depending on solvent. [Pg.89]

All three aminopyridines exist in the amino form the a- and 7-isomers are polarised in a sense opposite to that in the pyridones. [Pg.89]

3-Hydroxypyridine protonates on nitrogen, with a typical pyridine pATa of 5.2 the pyridones however are much less basic, and both, like amides, protonate on oxygen.2,6-Dimethyl-4-pyridones produce isolable 4-hydroxypyridinium bromides on reaction with t-butyl bromide. [Pg.89]

An apparent exception to this pattern is the reaction of 4-pyridone with acid chlorides producing A-acyl derivatives. l-Acetyl-4-pyridone subsequently equilibrates in solution affording a mixture with 4-acetoxypyridine.  [Pg.89]

3-Hydroxypyridine exists in equilibrium with a corresponding zwitterionic tautomer, the exact ratio depending on solvent. [Pg.89]


See other pages where Oxy-and Aminopyridines is mentioned: [Pg.88]    [Pg.89]    [Pg.89]    [Pg.91]    [Pg.93]    [Pg.88]    [Pg.89]    [Pg.89]    [Pg.91]    [Pg.93]    [Pg.190]    [Pg.361]    [Pg.227]   


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2-Aminopyridine

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