Tollen's Test, and how OH- turns Aldehydes into Carboxylic Acids

[johnwandering]

I just went through the carbonyls and alcohols section of the BR, and the one thing they seemed to be very keen on was that Ketones and Aldehydes did not have viable leaving groups.

However, in the Tollen's Test
http://www.uni-regensburg.de/Fakult...che_Chemie/Didaktik/Keusch/Grafik/Tollens.gif

They seem to just pop OH-, and the aldehyde Hydrogen just pops right off.


So, OH is efficient at turning Aldehydes into Carboxylic acids?

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[syoung]

OH- can oxidise aldehydes, and other milder oxidizing agents. Strong oxidizing agents would oxidize aldehydes and ketones.

 

[johnwandering]

OH- can oxidise aldehydes, and other milder oxidizing agents. Strong oxidizing agents would oxidize aldehydes and ketones.

Both the EK and the BR both indicate that an Aldehyde needs an oxidizing agent along with OH-.

K2Cr2O7/OH-
KMnO4/OH-

If an MCAT question asks if an Aldehyde can be oxidized with OH- alone, would yes be the correct answer?

 

[chiddler]

Both the EK and the BR both indicate that an Aldehyde needs an oxidizing agent along with OH-.

K2Cr2O7/OH-
KMnO4/OH-

If an MCAT question asks if an Aldehyde can be oxidized with OH- alone, would yes be the correct answer?

No, OH- by itself will not convert aldehyde to a carboxylic acid.

 

[SaintJude]

Wait... so K2Cr2O7/OH- turns an aldehyde into COOH.

And K2Cr2O7/H2SO4 oxidizes alcohols into COOH and ketones ?

 

[chiddler]

wait sorry i misread let me edit. you can tell i'm doing spectacularly well on my VR :-3

 

[chiddler]

Wait... so K2Cr2O7/OH- turns an aldehyde into COOH.

And K2Cr2O7/H2SO4 oxidizes alcohols into COOH and ketones ?

Cr2O7 anything is an oxidizer. I've not seen any conditions where it is not. Also MnO4 and CrO3. PCC is a weak oxidizer so it will not go all the way to carboxylic acid.

To convert an alcohol into a ketone you need that one special reaction that has been brought up occasionally on the forums. It seems that it is required knowledge so be sure to know it. Sorry I don't remember the name i'll have to look it up later!

 

[SaintJude]

To convert an alcohol into a ketone you need that one special reaction that has been brought up occasionally on the forums. It seems that it is required knowledge so be sure to know it. Sorry I don't remember the name i'll have to look it up later!

Lots of rx convert alcohol into a ketone. (any oxidizing agent except Tollens)

Do you mean aldehyde to a ketone? In which case you would use a reducing agent like NaBH4 to reduce the aldehyde to an alcohol and then use an oxidizing agent.

Think you can only move to aldehyde to ketone directly with a grignard reagent.

 

[chiddler]

Lots of rx convert alcohol into a ketone. (any oxidizing agent except Tollens)

Do you mean aldehyde to a ketone? In which case you would use a reducing agent like NaBH4 to reduce the aldehyde to an alcohol and then an oxidizing agent.

Think you can only move to aldehyde to ketone directly with a grignard reagent.

i'm sorry i confused ketone for ester :<

 

[SaintJude]

Oh, Fisher esterification?

Under acidic conditions, Alcohol + COOH = ester