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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Aznhmonglor on March 08, 2009, 09:29:36 PM

Title: Trace Acid
Post by: Aznhmonglor on March 08, 2009, 09:29:36 PM: Can anyone explain to me what is a trace acid or take a look at this problem? Not sure what it wants.

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Title: Re: Trace Acid
Post by: nj_bartel on March 08, 2009, 09:34:15 PM: I'd assume it just means very dilute.
Title: Re: Trace Acid
Post by: Aznhmonglor on March 08, 2009, 09:36:18 PM: Protonate the double bond Oxygen then?
Title: Re: Trace Acid
Post by: alexofordummies on March 08, 2009, 09:44:40 PM: That's what I'd do, but the major product may just end up being your reactant anyway?
Title: Re: Trace Acid
Post by: Aznhmonglor on March 08, 2009, 09:52:07 PM: This question is confusing.
Title: Re: Trace Acid
Post by: nj_bartel on March 08, 2009, 11:08:20 PM: Any nucleophilic sites you see that could attack a protonated carbonyl?
Title: Re: Trace Acid
Post by: James Newby on March 09, 2009, 04:11:25 AM: Trace is just a different word for catalytic amount
Title: Re: Trace Acid
Post by: cundi on March 09, 2009, 09:31:17 AM: Trace means very small amount, which can not be determined exactly.
Title: Re: Trace Acid
Post by: Aznhmonglor on March 09, 2009, 11:28:21 AM: What would small amounts of acid do to my reactant?
Title: Re: Trace Acid
Post by: Aznhmonglor on March 09, 2009, 06:41:16 PM: Can anybody help? I tried this and still couldn't get it right, I thought the OH would form a bond with the Carbonyl group to form a ring but was wrong.

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Title: Re: Trace Acid
Post by: nj_bartel on March 09, 2009, 06:47:30 PM: You're right, but something has to happen to the carbonyl - you aren't displacing a proton/hydrogen.
Title: Re: Trace Acid
Post by: Aznhmonglor on March 09, 2009, 06:50:00 PM: would the carbonyl group turn into an alcohol? double bond O turns into OH?

Something like this?

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Title: Re: Trace Acid
Post by: Aznhmonglor on March 09, 2009, 08:39:04 PM: Can anybody still help me on this? Its bothering me so bad. I know what trace acid is now. It works the same way as any acid would but with this reactant, I dont know where to start. Maybe the double bond O is protonated to form this:

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After that can the two OH groups come together to form a cyclic compound?
Title: Re: Trace Acid
Post by: Aznhmonglor on March 09, 2009, 08:53:41 PM: Okay that didnt work out. This was incorrect.

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Any ideas?
Title: Re: Trace Acid
Post by: nj_bartel on March 09, 2009, 11:26:16 PM: Quote from: Aznhmonglor on March 09, 2009, 06:50:00 PM
would the carbonyl group turn into an alcohol? double bond O turns into OH?

Something like this?

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That would be my answer. Do you know why?
Title: Re: Trace Acid
Post by: cundi on March 10, 2009, 09:41:51 AM: I think that all of you are mistaked in the answer.

Dehydratation, isomerization = a,b-insaturated aldehyde
Title: Re: Trace Acid
Post by: lutesium on March 10, 2009, 04:47:53 PM: Might he be just a purification process??? It can't be dehydration reaction cuz the acid is too dilute!!! It might be a hydration reaction or maybe a rearrangement reaction which seems unlikely!!! I'd still say him to be a purification reaction!!!

Lutesium...
Title: Re: Trace Acid
Post by: James Newby on March 10, 2009, 05:33:41 PM: My two cents:

The aldehyde is by far the most reactive group here so would get protonated before the alcohol. The alcohol is tethered to the cyclic ring and one of its lone pair of electrons will be sat right next to an activated aldehyde. The ring would snap shut as 5 membered cyclic hemiacetals are stable (wiki hemiacetals).
Title: Re: Trace Acid
Post by: nj_bartel on March 10, 2009, 05:47:35 PM: Quote from: lutesium on March 10, 2009, 04:47:53 PM
Might he be just a purification process??? It can't be dehydration reaction cuz the acid is too dilute!!! It might be a hydration reaction or maybe a rearrangement reaction which seems unlikely!!! I'd still say him to be a purification reaction!!!

Lutesium...

It never said the acid was in water.
Title: Re: Trace Acid
Post by: lutesium on March 12, 2009, 04:29:10 PM: Quote from: nj_bartel on March 10, 2009, 05:47:35 PM
Quote from: lutesium on March 10, 2009, 04:47:53 PM
Might he be just a purification process??? It can't be dehydration reaction cuz the acid is too dilute!!! It might be a hydration reaction or maybe a rearrangement reaction which seems unlikely!!! I'd still say him to be a purification reaction!!!

Lutesium...

It never said the acid was in water.
Ok but I really don't see a reaction in here that'd occur with trace amount of acid here!!! Dehydrative cyclization (to the BenzoPentanone) with the phenolic -OH group being eliminated which is so unlikely!!!

Lutesium...
Title: Re: Trace Acid
Post by: James Newby on March 12, 2009, 04:54:28 PM: trace acid catalyses the ring closing reaction, ill give the mechanism as well:

Can you see how the acid is acting as a catalyst?
Title: Re: Trace Acid
Post by: lutesium on March 13, 2009, 10:37:23 AM: Ok that's possible but with trace amounts of substrate!!! If the substrate is 1kg / lt trace amounts of acid won't do anything if this reaction is desired long reflux times must also be considered!!!

Lutesium...
Title: Re: Trace Acid
Post by: sjb on March 13, 2009, 10:47:02 AM: Quote from: lutesium on March 12, 2009, 04:29:10 PM
Ok but I really don't see a reaction in here that'd occur with trace amount of acid here!!! Dehydrative cyclization (to the BenzoPentanone) with the phenolic -OH group being eliminated which is so unlikely!!!

What phenolic -OH? All I can see is regular old aliphatic hydroxyl groups....

S
Title: Re: Trace Acid
Post by: lutesium on March 13, 2009, 11:04:05 AM: Ok ok I didn't pay attention to the molecule!!! Of course he is not a phenolic -OH he is just an aliphatic -OH...

Lutesium...