Question

I had carried out a reaction with PhHgCl and a sodium thiocyanate complex. It produced crystals, but they were really fragile and flaky, so to try and improve the product, a lecturer of mine suggested to add a bulky compound to the mixture such as tetraethylammonium chloride. Adding this did seem to improve my product and my yield, but I am unsure of why. What about adding tetraethylammonium chloride allowed for my results to be better and why do you think my lecturer suggested to add something bulky to the reaction?

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Thanks :)

Answer 1

This technique is called as PTC (Phase Transfer Catalyst). Here tetraethylammonium chloride is PTC (It is water soluble). We know that PhHgCl is soluble in organic layer & sodium thiocyanate is soluble in water. To make reaction success there should be fruitful Collision between reactants. To do this we will introduce PTC and it reacts with sodium thiocyanate and forms tetraethylammonium thiocyanate, which goes into organic layer and reacts with PhHgCl and forms your complex PhHgSCN. Now this process repeats again and again until reaction completes. So PTC shuttles between aqueous & organic layer and makes reaction much more easier, consequently we get higher yields of products.

A pictorial representation can be seen as