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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: vitaly on June 26, 2012, 07:46:09 AM

Title: which reaction goes faster?
Post by: vitaly on June 26, 2012, 07:46:09 AM: which reaction is faster? Br-Ac-C0Cl reacting with NH2-CH2-CH2-CH2-NH2? (Sn2 removing Br- or amide formation removing Cl-)?
Any advice as to how to increase rate of amide bond formation reaction? THanks!
Title: Re: which reaction goes faster?
Post by: discodermolide on June 26, 2012, 08:05:10 AM: Quote from: vitaly on June 26, 2012, 07:46:09 AM
which reaction is faster? Br-Ac-C0Cl reacting with NH2-CH2-CH2-CH2-NH2? (Sn2 removing Br- or amide formation removing Cl-)?
Any advice as to how to increase rate of amide bond formation reaction? THanks!

The acid chloride is the more reactive functional group. I would say that the reaction with a primary amine is very rapid. Want to make it go faster, heat it, make it more concentrated, apply pressure etc.
Title: Re: which reaction goes faster?
Post by: vitaly on June 26, 2012, 08:17:51 AM: I would be grateful for advice regarding which other compound with function (Fn) group Br-Ac-C0-X-Fn group would you recommend for amide bond formation with a primary amine (taking into account that carbonyl group should be preserved and the compound should be commercially available or easy to synthesize). Br will be used to attach the final compound to a big molecule via Sn2 using amino group of the latter.
Title: Re: which reaction goes faster?
Post by: vitaly on June 26, 2012, 09:02:22 AM: Quote from: vitaly on June 26, 2012, 08:17:51 AM
I would be grateful for advice regarding which other compound with function (Fn) group Br-Ac-C0-X-Fn group would you recommend for amide bond formation with a primary amine (taking into account that carbonyl group should be preserved and the compound should be commercially available or easy to synthesize). Br will be used to attach the final compound to a big molecule via Sn2 using amino group of the latter.

came to realize that bromoacetic acid is the best starting compound that can be coupled to a primary amine using a strong coupling reagent...
Thanks for the reply!
Title: Re: which reaction goes faster?
Post by: discodermolide on June 26, 2012, 09:37:41 AM: Quote from: vitaly on June 26, 2012, 09:02:22 AM
Quote from: vitaly on June 26, 2012, 08:17:51 AM
I would be grateful for advice regarding which other compound with function (Fn) group Br-Ac-C0-X-Fn group would you recommend for amide bond formation with a primary amine (taking into account that carbonyl group should be preserved and the compound should be commercially available or easy to synthesize). Br will be used to attach the final compound to a big molecule via Sn2 using amino group of the latter.

came to realize that bromoacetic acid is the best starting compound that can be coupled to a primary amine using a strong coupling reagent...
Thanks for the reply!

Sorry but the acid chloride is the better compound.
Peptide coupling agents are difficult to use and it is hard to remove the reaction products from the coupling reagent products.
Go for the acid chloride every time.
Title: Re: which reaction goes faster?
Post by: BobfromNC on June 26, 2012, 03:33:39 PM: Use bromoacetyl bromide or chloroacetyl bromide if you wish to speed up the acylation, then the SN2 will go at the same rate, giving you more product. This is the classic lidocaine synthesis, if you use the correct SMs. Great for sunburn.
Title: Re: which reaction goes faster?
Post by: curiouscat on July 23, 2012, 06:11:57 PM: Quote from: BobfromNC on June 26, 2012, 03:33:39 PM
This is the classic lidocaine synthesis, if you use the correct SMs. Great for sunburn.

And for toothaches! :)