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Tollen's test is an old oxidation reaction in which the oxidizing agent is a complex cation, diamminesilver(I), (NH3)2Ag+, and the reducing agent is probably the anion of an aldehyde hydrate, which for formaldehyde could be written as HOCH2-O(-). The mechanism is probably not known; a literature search I just performed turned up no immediately useful hits. Historically, the two front-runners for the likely mechanism are single-electron-transfer (SET) and hydride abstraction by diaminosilver(I). These two processes turn up in most oxidation mechanisms involving an electron-rich CH bond (as the one in the aldehyde hydrate) and an electron-poor metal cation. SET involves direct transfer of an electron from the molecular orbital closely tied to the C-H bond about to be broken, to the silver ion. Hydride abstraction involves a favorable collision between the silver ion and the aldehyde hydrate in which H- (the hydride ion) is transferred to the silver, leaving HOCH(+)-O(-) behind, which is essentially just a resonance structure for formic acid, HOCHO. The fate of the newly formed silver-hydride bond is almost certainly the release of a hydronium ion, leaving behind a neutral silver ion. The mechanism would have to explain why benzaldehyde reacts almost instantly, while sugars and branched-chain aldhydes react slowly, for example, as well as why siilver carbonate, Ag2CO3, supported on celite oxidizes alcohols to aldehydes and stops (J. Org. Chem, 1974, vol 39, p. 523), but Tollen's test conditions oxidize aldehydes (not alcohols) to acids, among other experimental observations.
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Why fructose gives positive tollen reagent test?
Only aldehydes give a positive Tollens test. However, under the strongly basic conditions of the test, alpha-hydroxy ketones can isomerize to aldehydes, so they will also give a positive Tollens test. Fructose is an alpha-hydroxy ketone.
Why pyrrole-2-aldehyde does not respond to tollens reagent?
Pyrrole-2-aldehyde does not respond to Tollens reagent because it is not a reducing sugar. Tollens reagent (silver nitrate) is used to test for the presence of aldehyde groups, which are commonly found in reducing sugars. Reducing sugars contain aldehyde groups and are capable of donating electrons to Tollens reagent, forming a silver mirror on the test tube wall. Pyrrole-2-aldehyde does not contain aldehyde groups, and therefore is not a reducing sugar. As a result, it does not react with Tollens reagent.
Is vanillin positive in tollens test?
No.While vanillin is an aldehyde, which should react with Tollens' reagent to precipitate silver metal, vanillin does not "pass" Tollens' test. Tollens' reagent is very basic (sodium or potassium hydroxide). Vanillin has a phenolic hydrogen (OH bonded to a phenyl ring) which is slightly acidic. Vanillin will react first with the excess hydroxide ions in solution to form a phenoxide salt, which will not participate in the silver-precipitating reaction.
explain using sample equation, the application of benedicts tollens and fehlings test in hospital?
wrt
What substances give a positive tollens test?
When adding the aldehyde or ketone to Tollens' reagent, the test tube is put in a warm water bath. If the reactant under test is an aldehyde, Tollens' test results in a silver mirror. If the reactant is a ketone, it will not react because a ketone cannot be oxidized easily. A ketone has no available hydrogen atom on the carbonyl carbon that can be oxidized - unlike an aldehyde, which has this hydrogen atom.
Is fructose gives positive test with tollens reagent?
no negative
Does the tollens test deal with alkenes?
No, the Tollen's Silver Mirror Test only confirms the presence of aldehydes.
How is a positive tollens test recognised?
A silverish ppt. Called "silver mirror"
Why fructose gives positive tollen reagent test?
Only aldehydes give a positive Tollens test. However, under the strongly basic conditions of the test, alpha-hydroxy ketones can isomerize to aldehydes, so they will also give a positive Tollens test. Fructose is an alpha-hydroxy ketone.
Why pyrrole-2-aldehyde does not respond to tollens reagent?
Pyrrole-2-aldehyde does not respond to Tollens reagent because it is not a reducing sugar. Tollens reagent (silver nitrate) is used to test for the presence of aldehyde groups, which are commonly found in reducing sugars. Reducing sugars contain aldehyde groups and are capable of donating electrons to Tollens reagent, forming a silver mirror on the test tube wall. Pyrrole-2-aldehyde does not contain aldehyde groups, and therefore is not a reducing sugar. As a result, it does not react with Tollens reagent.
What is the Formula for oxidation product formed from formaldehyde in the Tollens test?
It is Formic acid or its anion.
Is vanillin positive in tollens test?
No.While vanillin is an aldehyde, which should react with Tollens' reagent to precipitate silver metal, vanillin does not "pass" Tollens' test. Tollens' reagent is very basic (sodium or potassium hydroxide). Vanillin has a phenolic hydrogen (OH bonded to a phenyl ring) which is slightly acidic. Vanillin will react first with the excess hydroxide ions in solution to form a phenoxide salt, which will not participate in the silver-precipitating reaction.
What is the principles of tollen's test?
The principle of Tollens' test is to distinguish between aldehydes and ketones. It involves the reduction of silver ions to silver metal in the presence of aldehydes, which results in the formation of a silver mirror on the inner surface of the test tube. Ketones do not give a positive Tollens' test because they do not undergo this reaction with silver ions.
explain using sample equation, the application of benedicts tollens and fehlings test in hospital?
wrt
What is the mechanism of formaline test?
What is the mechanism of formaline test
What substances give a positive tollens test?
When adding the aldehyde or ketone to Tollens' reagent, the test tube is put in a warm water bath. If the reactant under test is an aldehyde, Tollens' test results in a silver mirror. If the reactant is a ketone, it will not react because a ketone cannot be oxidized easily. A ketone has no available hydrogen atom on the carbonyl carbon that can be oxidized - unlike an aldehyde, which has this hydrogen atom.
what is the outcome of tollens reagent reacting with methanal, ethanol and propanone?
The outcome of the Tollens reagent reacting with methanal (formaldehyde), ethanol (ethyl alcohol), and propanone (acetone) is the formation of metallic silver (Ag) in the case of methanal, while ethanol and propanone do not show a significant reaction with Tollens reagent. Tollens reagent is used as a chemical test to distinguish between aldehydes and ketones, where aldehydes react to produce a silver mirror, while ketones do not react.
