I'm looking to reflux a 250 mL of ethylene glycol solution. Would an Allihn condenser be suitable; if so what length?
Ethylene glycol was a boiling point of 193 °C using any water cooled condenser will crack. Use a air cooled condenser. It is just a glass rod. The length of tube depends on how much you want to condense and how quickly you want it to come over. Remember visible condensation should always take place in the condenser. If it goes further down the tube then some hot vapours will be lost to atmosphere if your system is open. If under vacuume the ethylene glycol will boil at a lower temperature but you should use a cold trap at minus 40 °C or below to catch vapours which come over. Remember liquid ethylene glycol is toxic and the vapours are more dangerous check the MSDS. I suggest that you should work with a closed system in a fume cupboard for this job or you might never see your grandchildren. Good luck.