[curiouscat]

I was confused about the setup described in a protocol:

"The following protocol describes a condensation polymerization through a reaction between equimolar amounts of maleic acid, and 1,4-butanediol using a strong acid as catalyst. The polymerization will be performed in a five-neck glass reactor setup equipped with an electrical heater, a mechanical stirrer, a nitrogen gas inlet, a thermometer, a water trap, and a condenser."

What's a water trap in this context, and where exactly does it attach to? Also, do they just bubble N2 through one of the necks and let it escape through the condenser? I'm assuming that's for keeping an inert atm.

[Archer]

It's a Dean-Stark, it goes between the reactor and the condenser.

what solvent are you using?

[Archer]

Sorry about the brevity of my last post, I am in the middle of some frustrating chemistry.

If you are using a solvent with a lower density than water then you fit a normal Dean-Stark on the apparatus (for azeotropic distillation), attach a condenser as normal to the top of the Dean-Stark.

For the nitrogen, you need to purge the system first (with N₂), then you have a nitrogen bubbler attached to the top of the condenser. If you simply pass nitrogen through your experiment from one intlet to another you will eventually run it dry, even with a condenser.

If you are using a solvent with a higher density than water (DCM, chloroform etc. these still form water azeotropes) it is the same set up but you need a Clavenger apparatus. This is fairly unusual in chemical reactions but I have used them before.

[curiouscat]

Thanks @archer!

Actually, I've no solvent but I'm trying to adapt this protocol. Let me explain. I have a reaction between a neat organic and aq. acid (90 C with reflux; atmospheric pressure) and I suspect the organic degrades by exposure to air. To test this I was planning how to carry this out under N2.

I'm guessing I won't need the Dean-Stark based on what you said. Just have to figure the part about a nitrogen bubbler. Funny this protocol didn't mention the bubbler at all.

I'm thinking adding a N2 purge to one neck, then attach condensor to another with bubbler tacked on. Thoughts?

PS. You'd fill bubbler with oil? Water? Either?

[Archer]

The bubbler is filled with mineral oil. I tend to use a fairly heavy oil.

The idea of the bubbler is that it maintains an N₂ atmosphere. No air can get in and as it is slightly pressurised (one or two bubbles per second maximum) then fluctulations in the internal pressure from heating / cooling don't allow for air to get sucked back in.

 Funny this protocol didn't mention the bubbler at all.

This was standard aparatus in my lab if you didn't have an inert gas manifold. The inlet would be to purge so is a good idea.

Actually, I've no solvent but I'm trying to adapt this protocol. Let me explain. I have a reaction between a neat organic and aq. acid (90 C with reflux; atmospheric pressure) and I suspect the organic degrades by exposure to air. To test this I was planning how to carry this out under N2.

Your making a polyester, the equlibrium is between the acid + alcohol  ester + water, if you don't remove the water then this may keep the equilibrium favouring your starting materials.