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|Title:||Process for the manufacture of 1-hydroxy-2-pyridones|
|Abstract:||New 1-hydroxy-2-pyridones of the general formula ##SPC1## In which R.sub.1 is alkyl of 1 to 17 carbon atoms, cycloalkyl of 5 to 8 carbon atoms, cyclohexylalkyl or phenalkyl both having 1 to 3 carbon atoms in the alkylene chain or .alpha.-furyl, all of which may be substituted by halogen, and R.sub.2 to R.sub.4 are hydrogen or lower alkyl, or two adjacent substituents together form a trimethylene or tetramethylene chain, and in which R.sub.1 to R.sub.4 together contain at least 2 carbon atoms, are prepared by contacting unsaturated .delta.-keto esters or mixtures thereof with hydroxylamine and subjecting the products to cyclization.|
|Inventor(s):||Lohaus; Gerhard (Kelkheim, Taunus, DT), Dittmar; Walter (Hofheim, Taunus, DT)|
|Assignee:||Hoechst Aktiengesellschaft (Frankfurt am Main, DT)|
|Filing Date:||Aug 30, 1974|
|Claims:||1. The method of making a 1-hydroxy-2-pyridone of the formula ##SPC4## |
wherein R.sub.1 is alkyl having 1 to 17 carbon atoms, cycloalkyl having 5 to 8 carbon atoms, .alpha.-furyl, or cyclohexylalkyl or phenylalkyl each having 1 to 3 carbon atoms in the alkyl portion thereof, all of which may be substituted by halogen; R.sub.2 to R.sub.4 are hydrogen or lower alkyl, or two adjacent substituents taken together form a trimethylene or tetramethylene chain; and R.sub.1 to R.sub.4 all together contain at least two carbon atoms, which method comprises reacting, at a temperature from 0.degree.to 150.degree.C., at least one unsaturated .delta.-keto ester of the formula ##EQU3## or defined ##EQU4## wherein R.sub.1 to R.sub.4 are as earlier defined and R.sub.5 is lower alkyl, with hydroxylamine or an acid addition salt thereof.
2. The method as in claim 1 wherein the reaction occurs in the additional presence of an acid.
3. The method as in claim 2 wherein said acid is a mineral acid.
4. The method as in claim 2 wherein said acid is a lower fatty acid.
5. The method as in claim 1 wherein said reaction occurs in the additional presence of a buffer initially establishing a pH of about 5 to 8.
6. The method as in claim 5 wherein, after the establishment of a pH of about 3 to 4 in the reaction mixture by the production of acid during the formation of an intermediate oxime ester product, said oxime ester intermediate is subsequently cyclized by reducing pH to a value below about 3 to 4.
7. The method as in claim 5 wherein, after the establishment of a pH of about 3 to 4 in the reaction mixture by the production of acid during the formation of an intermediate oxime ester product, said oxime ester intermediate is subsequently cyclized by increasing pH to a value above about 9.5 to 10.
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