Hello!
I am currently considering the usage of BF3 etherate in a reaction, but in contrast to the complex' components the BF3 etherate has a boiling point of 120 °C. A current synthesis protocol just mentions to evaporate the solvent after performing the reaction. Caused by the high boiling point I would assume very harsh conditions in a rotavap, like 60 °C and 50 mbar.
This does not seem really safe to me, in case that complex could also revert back into BF3 and diethyl ether?
Also the compound gives off heavy fumes, which may indicate that traces of BF3 are released. Therefore I would assume any fumes entering the vacuum pump may cause heavy corrosion effects.
Therefore my question is, how to handle BF3 etherate after a finished reaction?
Wikipedia states it will hydrolyze to HF, so just a quick hydrolysis does not seem like a safe way of destroying it.
I would not recommend heating this mixture to +60°C in a rotary evaporator. The main idea of evaporation in such a system - or should I say, reduced temperature boiling, under vacuum, is that you do not need high heat for delicate samples or those which are more reactive.
If you have a high quality system, then the vacuum pump should be membrane sytem (diaphragm) with PTFE or similar membranes and other parts in the vapour path, so the pump shuold be OK. Be aware of where the vacuum pump exhaust goes ... the right answer here is into the fume extratcion system, and not into the lab! Also, ensure that you try and capture the majority of the vapours in the cold trap, for ether, then I would suggest the dry ice / acetone cold finger style, unless you have a refrigerated chiller supplying coolant to the traditional water cooled style of condenser. I suspect, that most of the ether will evaporate first, as you say, it is highly volatile. At 50mbar the boililng point is -30°C, at 200mbar it is -4°C therefore you will understand the requirement for a below zero solvent condenser. Given the properties of ether, then reduce the vacuum slowly over time, a gradient from about 700mbar where ether boils at +25°C. The water bath for heating the sample can be just above ambient, say +25°C to start. If the BF3 is more diffiuclt to evaporate, then the temperature can be increased [I cannot find a delta H vap for BF3 with a quick search, so cannot say how much energy it needs to boil, however I suspect, that given it's natural state is gaseous then it will boil easily, with little heat input.].
For all the systems we design, if using highly flammable solvents like ether, then the strong recommendation is to purge the O2 from the system before you start, this may help with any breakdown of BF3 also, but I am not experienced in the physical chemistry of BF3
I hope this helps.
Regards
Rob
Hello Rob,
thanks for your answer. Indeed there should be a decent chemical resistance of the pump's membrane and also all the papers I found just mention to "concentrate the mixture".
Still, this is not exactly an ether evaporation problem, as my initially asked question whether that BF3 etherate would decompose and form BF3 and diethyl ether cannot be answered by me. Therefore a possible decomposition was just an assumption and if not happening, then the BF3 etherate will still remain as this complex compound, which has a BP of 120 °C, so no ether and no gaseous BF3 will be formed. Therefore I was mentioning these harsh rotavap conditions, as even water needs to 50 mbar and 60 °C in our setups to be removed.
So I'm basically curious about a person who really has worked with exact BF3 etherate (also labelled as BF3*diethylether) and can confirm this substance is indeed compatible with rotavap solvent removal.
Best regards!
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