Sciencemadness Discussion Board

Is an extremely rapid reaction a good thing, if it doesn't yield too many products?

CrimpJiggler - 30-3-2014 at 06:16

My professor (the one coordinating my 4th research project) wants me to keep all my work within the college for now so I can't get into details, but basically I found two reagents which react so readily that just mixing them together (one of them is a liquid), then adding a bit of weak base (NaCO3) instantly turns the powder red. I need to do more tests to make sure its not some kinda solvatochromism (I doubt its that since the liquid reagent was added in a 1:1 ratio so there was a very small volume of it, nowhere near enough to dissolve the solids) or halochromism but I suspect that its a reaction behind the colour change. Lets say it is the expected reaction that occured, is this good that it rapidly reacts at room temperature like that, or will this be a problem for regioselectivity (i.e. I don't want to end up with a load of different products and isomers).

I specifically chose a bulky reagent to control the regiochemistry, and I've seen in the literature a similar reagent used on the same starting material, and it produced a single disubstituted isomer, but that reaction required heat and wasn't that fast. A stronger base was used too. The product I'm expecting from this reaction is a new one that hasn't been characterised yet, and this class of compound is used as a starting material for an important reaction. I'm hoping this is a good observation I made, because so far I haven't obtained any interesting data and since I'm new to research, have been struggling to obtain info that is worth recording. I record everything, but I often later learn that my methodology wasn't that good, and allowed for too many variables. I'm learning at a rapid pace, but its frustrating not getting any interesting data, so it would be pretty cool if this easy, rapid reaction turns out to be something useful for industry. The mild conditions make it environmentally friendly, so thats a plus. I haven't felt any heat come from the flasks, so its not very exothermic which is another plus, safety wise.

[Edited on 30-3-2014 by CrimpJiggler]

Chemosynthesis - 30-3-2014 at 06:39

I don't think there is a way to answer your question without more information, which I completely understand your inability to divulge. If you consider thermodynamic versus kinetic control of reactions with only two products, the amount of byproduct can vary as major and minor products change proportions. If the major product at one temperature suddenly becomes the minor product at a second temperature, it really is a matter of which product was desired by the chemist that determines is purity increased or decreased.

In your instance, perhaps a quick, cheap TLC would be useful without necessitating running a column? That might give you a qualitative idea of purity, confirm a reaction has occurred, and allow you to subsequently compare with a chilled or heated reaction.

CrimpJiggler - 30-3-2014 at 11:42

Yeah its frustrating that I can't get into more detail. Good point about thermodynamic control, maybe this red compound is more of an intermediate than a product. Didn't have time to run a TLC or IR on the reaction mixture, only had time to setup the reaction and let it stir for the weekend. I have no experience with columning yet, so nows a good time to start since I have some strongly colored compounds.