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Why do α-hydroxy ketones give Tollens' test? [duplicate]
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Alan Bloom
Why do α-hydroxy ketones give Tollens' test? [duplicate]
The Tollens' test is done in base, which mediates tautomerization through the enolate:
The misconception that you have is that all alpha-hydroxy ketones can give a positive Tollens' test. Aldehydes give a positive test, and so only alpha-hydroxy ketones that can tautomerize to aldehydes will give a positive Tollen's test. My example above is 1-hydroxy-2-propanone, which isomerizes to 2-hydroxypropanol. Most alpha-hydroxy ketones with names that match the pattern 1-hydroxy-2-alkanone will give a positive Tollens' test.
Benzoin will not give a positive test, since it cannot isomerize to an aldehyde. What does benzoin form upon tautomerization?
The Tollens' test is done in base, which mediates tautomerization through the enolate:
The misconception that you have is that all alpha-hydroxy ketones can give a positive Tollens' test. Aldehydes give a positive test, and so only alpha-hydroxy ketones that can tautomerize to aldehydes will give a positive Tollen's test. My example above is 1-hydroxy-2-propanone, which isomerizes to 2-hydroxypropanol. Most alpha-hydroxy ketones with names that match the pattern 1-hydroxy-2-alkanone will give a positive Tollens' test.
Benzoin will not give a positive test, since it cannot isomerize to an aldehyde. What does benzoin form upon tautomerization?
@BenNorris benzoin in basic medium gets oxidised to benzil through SET(Single Electron Transfer) and in this process converts $\text(Ag)^+$ ions into $\text(Ag)$ solid... So technically it gives tollens' test!More
The Tollens' test is done in base, which mediates tautomerization through the enolate:
The misconception that you have is that all alpha-hydroxy ketones can give a positive Tollens' test. Aldehydes give a positive test, and so only alpha-hydroxy ketones that can tautomerize to aldehydes will give a positive Tollen's test. My example above is 1-hydroxy-2-propanone, which isomerizes to 2-hydroxypropanol. Most alpha-hydroxy ketones with names that match the pattern
1-hydroxy-2-alkanonewill give a positive Tollens' test.Benzoin will not give a positive test, since it cannot isomerize to an aldehyde. What does benzoin form upon tautomerization?
The Tollens' test is done in base, which mediates tautomerization through the enolate:
The misconception that you have is that all alpha-hydroxy ketones can give a positive Tollens' test. Aldehydes give a positive test, and so only alpha-hydroxy ketones that can tautomerize to aldehydes will give a positive Tollen's test. My example above is 1-hydroxy-2-propanone, which isomerizes to 2-hydroxypropanol. Most alpha-hydroxy ketones with names that match the pattern
1-hydroxy-2-alkanonewill give a positive Tollens' test.Benzoin will not give a positive test, since it cannot isomerize to an aldehyde. What does benzoin form upon tautomerization?
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