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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Rutherford on January 27, 2013, 10:32:30 AM

Title: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: Rutherford on January 27, 2013, 10:32:30 AM
What is the reaction of formaldehyde with acetylene (when the hydrogens get substituted) based on? I mean, how is it called and what is it based on (mechanism)?

When a lactone reacts with NH3, is an amide or an amide and an amino-acid (in less quantity) made?
Title: Re: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: discodermolide on January 27, 2013, 10:36:42 AM
I presume you mean the deprotonation of the acetylene hydrogens? If so I suppose it's an aldol reaction.
The lactone opens to give a an amide.
Title: Re: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: Rutherford on January 27, 2013, 10:42:26 AM
Quote from: discodermolide on January 27, 2013, 10:36:42 AM
I presume you mean the deprotonation of the acetylene hydrogens?
The problem is I don't know what to mean. I only got a reaction of C2H2 and HCHO where the product is OH-CH2C≡CCH2-OH. What is the mechanism?

For the second one, I thought so either but in a problem I was solving, the product was an amino-acid. Could it be (at least in traces)?
Title: Re: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: discodermolide on January 27, 2013, 10:57:50 AM
The acetylene protons are abstracted by a strong base which attacks the C=O carbon atom to give the aldol.
No amino acid is formed, you get the amide. Draw it out, a lactone the carbonyl of which is attacked by NH3 it opens the ring to give an amide and an alkyl chain with an OH at the end.
Title: Re: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: Rutherford on January 27, 2013, 12:14:51 PM
How are these protons so acidic? Does it work for other alkynes or alkenes?

I thought that no amino acid can be formed too, but in the answer of a problem it was the product, so I guess that it is a mistake then.
Title: Re: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: discodermolide on January 27, 2013, 12:18:56 PM
I can't remember the pka of the acetylene protons. You need a base like sodium amide, or LDA to remove them. It will work for any terminal acetylene, but it does not work for alkenes.
Title: Re: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: Rutherford on January 27, 2013, 02:07:39 PM
I guess it's something similar with the production of acetilides (only there is substitution and here addition). Thanks for helping me with this.
Title: Re: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: discodermolide on January 27, 2013, 02:48:49 PM
Quote from: Raderford on January 27, 2013, 02:07:39 PM
I guess it's something similar with the production of acetilides (only there is substitution and here addition). Thanks for helping me with this.

Look at scheme 6 in this paper by Evans
http://chemistry.williams.edu/files/TSmith8.pdf (http://chemistry.williams.edu/files/TSmith8.pdf)

It shows alkylations and acylations of acetylene anions. It may be a bit complex for you but ask me questions if you need to.

Title: Re: 2 quick q. Acetylene+Formaldehyde and Lactone amonolysis
Post by: Rutherford on January 28, 2013, 09:00:16 AM
Seems complex, but I could recognize where the reaction happens.

I read in a book that the protons in acetylene are acidic because of the triple bond and sp hybridized C atoms. Why is this so?
The triple bond is shorter than the single and double, so distance between the C atoms is reduced (they are closer to each other). Does this mean that the C-H bond gets stretched? If so, why?