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Topic: Fehling's test and benzaldehyde  (Read 15172 times)

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fc3stud

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Fehling's test and benzaldehyde
« on: February 21, 2006, 12:43:57 PM »
We recently received a revised copy of the results for a paper practical examination from the board suggestion that performing Fehling's test on benzaldehyde would give a negative result.  An aberration, or is there any truth in this?
Thanks
Andrew  ???
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Offline Alberto_Kravina

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Re:Fehling's test and benzaldehyde
« Reply #1 on: February 21, 2006, 12:55:55 PM »
I don't think that it would give a negative result. If it does, try to use Tollens-reagent
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Offline movies

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Re:Fehling's test and benzaldehyde
« Reply #2 on: February 21, 2006, 03:45:23 PM »
What are the conditions for Fehling's test?
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Offline Albert

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Re:Fehling's test and benzaldehyde
« Reply #3 on: February 21, 2006, 04:02:19 PM »
It's an oxidation of aldehydes to carboxylic acids with Cu2+, which is reduced to Cu2O. The test is carried out in presence of NaOH, tartrate and water.
I don't know anything about the pH, thus, I thought about a possible Cannizzaro reaction.
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Offline AWK

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Re:Fehling's test and benzaldehyde
« Reply #4 on: February 22, 2006, 02:30:56 AM »
Fehling test is destined for reducing sugars (alpha hydroxyaldehydes). Positive test gives also fructose because in the conditions of reaction it isomerises to glucose. Moreover, positive tests give also  aliphatic aldehydes, but not aromatic ones (they can undergo A Cannizarro reaction under strong alcaline condisions)
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Offline Alberto_Kravina

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Re:Fehling's test and benzaldehyde
« Reply #5 on: February 22, 2006, 11:21:55 AM »
I tried the Fehling test with benzaldehyde and it worked. It also worked with tollens' reagent and nylandres' reagent :)
« Last Edit: February 22, 2006, 11:22:16 AM by Alberto_Kravina »
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