5.25.2016

Why How does Schweizer's reagent work to dissolve cellulose cotton? Reducing agent

I have tried dissolving cellulose in the past and have not really been successful.  Some protocols call for using frozen sodium hydroxide whereas other protocols call for hot sodium hydroxide.  Some call for the addition of urea.  One thing that looks most promising is alkali plus a reducing agent.  But then there is Schweizer's reagent.  What is this bizzare compound and how does it work so well to dissolve cellulose?  Well it is a copper atom bonded with 4 ammonia molecules, two water molecules, and a couple hydroxides.  



So how and why does this weird wonky molecule work to dissolve cellulose?  Well first of all it has hydroxides which are strong alkali's which is how sodium hydroxide kind of works to dissolve cellulose.  Next it has ammonia.  Ammonia can act as a reducing agent by loosing a proton.  However the other end of the ammonia is bound to a copper ion.  What does this do?  Well it makes the Ammonia more like ammonium, a nitrogen with 4 hydrogens instead of 3.  So the copper ion makes the ammonia an even better proton donor and hence reducing agent. We couldn't achieve the same result by just adding ammonium to the mix, because it would immediately loose its extra proton from the alkaline conditions. The copper helps stabilize an ammonium-like compound even in alkaline conditions.  The water molecules as well, they act like H3O since they have an extra bond with copper so can more easily give a proton as a reducing agent. Again H30 only occurs in acidic conditions so the copper ion makes it possible in alkaline solution.

Well there you have it, that is why this bizarre  reagent works so well at dissolving wood.

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