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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: xshadow on August 14, 2020, 08:52:39 AM

Title: Conjugated aldehyde(enal) + water/amine
Post by: xshadow on August 14, 2020, 08:52:39 AM
Hi

I've seen that H2O or RNH2 usually give conjugated addition with ester/amide/ketone,in a michael addition


But if I have an acyl chloride group or an aldehydic group what should I get when I add water or an amine?

A  direct addition
Or a conjugated addition?

I.e.:
Acyl chloride α-β insaturated + RNH2 ---> direct addition
Enone +RNH2 --> conjugated addition

Enal + RNH2 --->  direct or conjugated addition ??

Thanks
Title: Re: Conjugated aldehyde(enal) + water/amine
Post by: hollytara on August 14, 2020, 11:15:27 AM
Check the literature, but....   

I think usually the acyl chloride will make an amide by substitution rather than doing a Michael addition.  You can get acryloyl chloride and make acrylamides for polymerization.

The aldehyde is trickier.  If you just add a normal amine, the imine formation is reversible so Michael addition might be favored.  If you use hydroxylamine, you can definitely make oximes of acrolein and methacrolein.  I would expect other stable imine structures (hydrazones, etc) are also favored. 
Title: Re: Conjugated aldehyde(enal) + water/amine
Post by: zyu2ranger on August 17, 2020, 09:10:06 AM
Water and ammonia/amines are "soft" nucleophiles that will add to an enone in a 1,4-fashion.

If you have a carboxylic acid derivative (i.e. acid chloride or acid anhydride), you may have competition between the carbonyl carbon (2 position) and the C=C double bond (4 position).

I would presume that the carbonyl carbon is more reactive because:
- the EWG nature of the C-Cl (poor 2p-3p orbital overlap) and C-O (extensive delocalization over the π system) bonds via inductive effects and, to a lesser extent, resonance effects
- the relative energies of the LUMO (C-O π* vs. C-C π*) and the energy of the HOMO on the nucleophile
- the thermodynamics of breaking that C-Cl and C-O bond and forming the C-Nu bond as opposed to breaking the C=C bond and forming both a C-C and C-Nu bond will probably favor the carbonyl carbon reacting, though I don't have exact numbers in front of me

Does this help?


Quote from: xshadow on August 14, 2020, 08:52:39 AM
Hi

I've seen that H2O or RNH2 usually give conjugated addition with ester/amide/ketone,in a michael addition


But if I have an acyl chloride group or an aldehydic group what should I get when I add water or an amine?

A  direct addition
Or a conjugated addition?

I.e.:
Acyl chloride α-β insaturated + RNH2 ---> direct addition
Enone +RNH2 --> conjugated addition

Enal + RNH2 --->  direct or conjugated addition ??

Thanks