[lrw281]

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?

[Guitarmaniac86]

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. 

[lrw281]

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?

[Guitarmaniac86]

Deprotonation occurs at the H-S bond.

Na₂S.9H₂O dissociates to the following:

Na₂S.9H₂O 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.

[lrw281]

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