[CHM]

Hi, I tried to make a reaction: R-Cl + ROH to form R-O-R, in th aceton and K2CO3 IN nitrogen atmospher and reflux for 24h with stierr.
when I come back next day aceton evaporated. how I can keep aceton in the flask by reflux for 24 h.

[Mitch]

You attached a chilled condenser to your setup right?

[Dan]

Assuming you did attatch the condenser (securely), here are two possible causes:

1. You heated it too hard. Before leaving the reaction unattended make sure your oil bath has been on a constant setting for at least half an hour and check with a thermometer so you can be sure your oil bath has stopped warming up, and check that that no vapours are escaping (you can see the vapours condensing in the condenser, make sure this is occuring no more than half way up the condenser, just to be sure). The temperature dial on oil baths is rarely reliable, so you need to make sure it has reached a constant appropriate temperature before you leave the lab.

2. Loss of water pressure. Make sure the water flow in your condenser is fast, because the water pressure in the plumbing system will probably be subject to fluctuations - this has happened to me before with the same result you experienced, I came back after lunch once, flow had dropped considerably and the ether was gone!

Just make sure you double check it all before you leave and it should be fine. I've refluxed reactions in acetone overnight a fair few times now without problems.

[Ψ×Ψ]

is a longer condenser available?

[CHM]

thanks every body. but my problem is when th N2 gas flow, it taks the acetone vapour outside from the condenser,and i make the reaction on a watr bath at 53 C, and i use long condenser.
whn i dont use N2, aceton keep to 24h, but my expermint should be under N2 flow?

[russellm72]

It has nothing to do with your nitrogen flow unless you have it going like a steam train!!!

Are you doing it in a 1 necked flask or multimecked? If multinecked make sure your septa are in good condition or if you have stoppers apply a light film of grease.

Use a double jacket condensor and just have a small trickle of water going through. You should have no problem what so ever with acetone even DCM proves no problem if you set it up right. Ever thought of replacing your constant flow of nitrogen by attaching a baloon through a septa on top of your condensor?

Make sure the level of oil is just below the level of liquid in your reaction and that a gentle reflux is evident before you leave it overnight. Don't immerse the whole flask in the oil or stir too vigourously.

R.

[movies]

Are you actually passing N₂ through the headspace of the reaction, or are you just keeping it under a slight positive pressure of N₂?  You don't need to flow the gas over through the headspace for this reaction!

[Ψ×Ψ]

By the way, I'm sure you know this already, but make sure you have the water going in through the bottom inlet of the condenser and out through the top.