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Topic: Disodium sulfide and ethyl acrylate  (Read 2527 times)

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Offline lrw281

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Disodium sulfide and ethyl acrylate
« on: November 08, 2014, 01:20:18 PM »
Q: draw an arrow pushing mechanism for this reaction. In what way does the hard/soft principle of reactivity operate here?

I'm really unsure of the mechanism and just have the double bond attaching to the sulphur and then the electrons in the sulphur/sodium bond moving on to the sodium.
I'm having trouble finding anything about 'hard/soft principle of reactivity' but assume it's the same as the hard/soft acid/base concept?

Offline Guitarmaniac86

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Re: Disodium sulfide and ethyl acrylate
« Reply #1 on: November 09, 2014, 02:32:40 AM »
Sodium disulfide in solution forms HS- (if using the nonahydrate form) which is a soft nucleophile. Think about the orbital energy of the sulphur lone pair and why does this make it a soft nucleophile?

Look up Michael addition to see how this reaction works. 
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Offline lrw281

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Re: Disodium sulfide and ethyl acrylate
« Reply #2 on: November 14, 2014, 10:17:40 AM »
Ah okay thanks, so sulphur's lone pair is easily accessible it's a soft nucleophile. I'm still a bit confused on the mechanism though, I can't really see how it's a Michael addition. Which hydrogen would the base take off in the first step?

Offline Guitarmaniac86

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Re: Disodium sulfide and ethyl acrylate
« Reply #3 on: November 14, 2014, 11:25:03 AM »
Deprotonation occurs at the H-S bond.

Na2S.9H2O dissociates to the following:

Na2S.9H2O ::equil:: NaSH + NaOH + 8H2O

The sodium hydroxide will deprotonate the S-H bond forming the sulfur nucleophile which attacks the ethyl acrylate to form the product shown in your original post. Drawing the mechanism will show how it is a Michael type addition, I use the name for all 1,4 addition reactions and in this context I am probably wrong to use it to describe the process.
Don't believe atoms, they make up everything!

Offline lrw281

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Re: Disodium sulfide and ethyl acrylate
« Reply #4 on: November 18, 2014, 10:14:15 AM »
Oh I see now, thank you. Except this is Na2S and Ethanol so would that make EtO- Na+ and HS? And then the EtO- deprotonates the HS? Or is the question assuming that I'll know what you've written out? Thanks again

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