Standard Operating Procedure: Use and Maintenance of THF Stills (shared with DOH)

Overview

The All researchers who use a solvent still must read these notes. All operations such as solvent top-up, withdrawal, stills start-up and shut-down must be recorded in the log book (kept with the still). A person(s) must be made responsible for turning on the still, topping it up and turning it off at the end of the day. If he/she is unable to carry out this duty then it is that person’s responsibility to ensure that a deputy is nominated. There should always be sieves-dried solvent ready for each still and always a good supply of regenerated molecular sieves. THF is dried by refluxing in a still containing sodium and benzophenone. The characteristic blue/purple colour indicates the solvent is dry and can thus be collected and used. Yellow/orange colours are indicative of wet solvents and mean the solvent is insufficiently dry.

Operation

Topping up.

Only top up stills with sieve pre-dried solvents and when the stills are cold (usually first thing in the morning). Take great care not to mix up the solvents by mistake. Ensure that these are pre-dried for at least 3 days over molecular sieves before using them in the stills. Write on the label of the bottle the date when it was opened and sieves were added. Pre-drying over sieves prolongs the life of the drying agents in the stills and increases the time interval required between regeneration of the stills. The solvent for the stills are NOT to be ‘borrowed’ for use in any other laboratories. If you have topped up a solvent then write in the log book the amount of solvent was added. Be sure that the receivers are properly bedded into the necks of the round bottom flasks and that the Teflon collars fit properly.

Note that ether-type solvents such as THF, diethyl ether, 1,4-dioxane, DME, di-n-butylether, etc. are prone to forming peroxides if left open to air. This presents an explosion risk if the solvent is heated to reflux especially to near-dryness. Always test for peroxides in ethereal solvents if the flask/bottle is quite old (> 2 months). Always test di-n-butyl ether for peroxides before use as it is particularly prone to peroxide formation.

Switching the stills on.

See the diagram below:

  1. Check that all the taps ‘A’ (if present) and ‘C’ are open and that the N2 is flowing through the oil bubbler at the end of the solvent line.
  2. Turn the water supply on.
  3. You MUST NOT turn the stills on yourself. Ask an authorised and experienced user to check all is OK with the set-up. They then switch on the stills. Initial the log book with both names. Do not adjust the power setting on any of the stills or substantially change the nitrogen delivery pressure without prior discussion with the supervisor or nominee.

Collecting solvent.

Close tap ‘B’ and solvent will collect into the reservoir. Do not collect solvent if the volume of solvent in the round-bottom flask is less than 600 ml (for 3000 ml flasks). Enter this in the log book with your name and the date.

Drawing off solvent.

  1. Turn off the power to all of the stills in that particular bank. You do not need to wait a long time for solvents to cool down before drawing off – just check that the reflux level of the solvent drops below the level of the solvent in the still head). The O’Hare THF stills is sharing the same gas feed as the Goicoechea THF stills, before collection of solvents, the GoicoecheaTHF stills MUST BE SWITCHED OFF and COOLED – high pressure from the mercury bubbler combined with boiling solvent present a risk of explosion due to over-pressurising of the setup.
  2. Switch the tap slowly to change the gas flow outlet from an oil bubbler to a mercury bubbler – this ensures high pressure is present within the stills setup so then drawing of solvents from tap D is possible
  3. Open tap ‘D’ and pass cannula through the septum cap but DO NOT immerse the end of the cannula in the solvent; allow the purging of the cannula for a minute and then open the tap of the receiving vessel.
  4. Submerge the end of cannula into solvent andcannula solvent off under positive pressure into the receiving vessel (taking care not to spill solvent on the heating mantle) until a sufficient amount is withdrawn.
  5. Close tap to receiving vessel and withdraw cannula.Take cannula out of stills setup and close ‘D’ and slowlyopen tap to change from mercury bubbler to oil bubbler. Finally, open tap ‘B’.

Starting up again.

You must turn the stills back on yourself. The stills should be checked by an authorised user and then this person should turn the stills back on once they are sure it is safe to do so. Do not turn on the power to a particular still if the level in the round-bottom flask is less than 600 ml (for 3000 ml flasks). This other person signs in the log book for turning the stills back on.

Shutting down.

The stills must NEVER be left on overnight. Turn off the power to all the stills and sign this in the log book.

Date / Name / Signature / Trainer’s name / Trainer’s signature