Question

What are the precautions to be observed when distilling a flammable solvent?

Answer 1

No nekkid flames.........

Explanation:

The distillation apparatus is contained so that the mixture is distilled under a slow bubble of dinitrogen or argon gas (clearly, we don't distil using a closed system, why not?). The apparatus is continually supervized (mind you, were such a system to ignite, the physical heat of the flames would prevent you from coming close to it). Large volumes to be avoided.

Check your distillation setup BEFORE you start the process (this is where a nitrogen bubbler is useful, because if there is a leak or the in the line or a misfit in the glass seals the bubbler won't bubble; sometimes you reseat a glass joint by pushing the seals together, and the bubbler starts going berserk!) The collecting flasks are removed (with respect to distance) somewhat from the distillation flask, and the heat source. Before disassembling the distillation setup AFTER you have finished distillation, you allow the assembly to cool to room temperature.

I could probably think of some more precautions, but despite the best intentions, you cannot make a lab idiot proof, and we always make mistakes thru tiredness or carelessness or ignorance.

And I forgot the TOP priority. Don't WORK ALONE, and don't leave the still unattended. If you boil the still dry while collecting the solvent, you will not be the first klutz to do so (that was me!). Note that there are probably some very experienced chemists in your department who should be willing to look at your setup and offer advice and suggestions. Avail yourself of their experience; it's free and highly useful, tho you might have difficulty in shutting them up! And when you yourself become experienced pass that experience on to the next generation.

Just to add that in many labs these days, where safety is the over-riding priority, chemists who require water-free, oxygen free solvents, often use drying columns, where a solvent is pushed thru a column packed with molecular sieves to remove water, and Q5 catalysts to remove oxygen, and bottled gas, i.e. dinitrogen or argon is used to provide the pressure. The use of compressed gas entails its own particular, and significant safety hazards (and sometimes these are blithely ignored!). Nowadays we seem to be out of the flame and still age........