1.0 VACUUM DISTILLATION
1.1 Distillation under reduced pressure should always be carried out behind adequate to
shields. This applies to both oil pump and water pump systems. Always use a suitable trap
between the pump and the apparatus.
1.2 Evacuate the apparatus and check for leaks before commencing heating. Avoid heating by
direct flame.
1.3 At the end of the distillation allow it to cool before slowly admitting air or nitrogen.
Nitrogen is preferable to air on all capillary bleeds since many organic substances tend to oxidise
at elevated temperatures.
1.4 Use a proprietory all glass capillary fitting. Never use rubber stoppers in distillation
equipment. They tend to soften with heat and may be pulled into the distillation flask.
1.5 Do not use flat-bottomed flasks in vacuum distillation.
1.6 Do not use water cooled condensers if the temperature of the distillate entering the
condenser is above 1600c.
1.7 Some oil pumps discharge an invisible aerosol of oil droplets into the air. It is better to fit
an approved filter or to vent oil pumps in to a fume cupboard to minimise the risk of breathing in
the aerosole.
2.0 Solvent Extraction :-
2.1 Separating funnel – Release the pressure developed on shaking by inverting the funnel with the stopper securely held and opening the tap with care. Point the funnel away from the eyes and the naked flames, or heating mantles.
2.2 Ensure that the condensing system above a Soxhlet extraction unit is adequate to cope with the solvent in use.
2.3 Do not handle volatile, flammable solvents anywhere near an open flame or other source of ignition e.g. electric motor, electric heater.
2.4 Dialkyl ethers and Tetrahydrofuran form peroxide in contact with the air or on exposure to sunlight. They should, therefore, be stored in dark bottles with the air space above the liquid kept to a minimum. Beware of any ether which has been in half filled bottles for several months. (see 2.6 below).
Distillation to near dryness of low boiling aliphatic ethers which contain peroxide can lead to detonation. The presence of peroxide can easily be detected and if they are present they should be destroyed.
1.1 Solvent stripping involving flammable substances should be carried out using a water-bath or electrically heated bath.
1.2 Before opening the closures (caps, bungs etc.) of all solvent bottles and containers, specially those containing low boiling solvents, they should be cooled atleast 200c below their boiling point. Protective eye goggles and gloves must be worn.
2.0 ORGANIC PREPARATIVE REACTIONS :
2.1 Never leave preparatory experiment unattended. Arrange for supervision by another competent person until you return.
2.2 Never increase the size of a preparation without first consulting the Chemist-in-charge.
2.3 Remember that a stirrer which efficiently agitates a 500 ml flask may be useless at the 2 litre scale.
2.4 Ensure that stirring equipment is in good order before starting an experiment. If a stirrer stops, if can lead to over-heating and subsequent boil-over. Do not re-start a stirrer if it has been stopped for any length of time in a heated reaction flask; allow it to cool first.
2.5 Magnetic stirrer hot plates are a useful and convenient means of heating and stirring small scale experiments. It may not be able to cope if at some stage the viscosity increases or a thick precipitate forms.
2.6 A thermostatically controlled silicone oil bath offers both convenience and safety as a means of heating medium sized organic preparations. Stirring should be carried out with an over-head stirring motor.
2.7 Ensure that the size of the reaction flask is adequate enough to allow for possible frothing.
2.8 Condenser capacity should always be in excess of requirements.
2.9 Always make provision for rapid removal of the heating source.
Ensure free access to electrical switches, gas and water taps.
2.10 Never look down into the neck of a flask which is being agitated.
1.1 Isolate all potentially dangerous experiments and conduct preparations involving toxic reactants, by-product and so on, in a fume cupboard (fume hood).
1.2 Limit the size of –
-All first time experiments.
-Experiments involving the alkali metals, inorganic cyanides etc.
-Halogenations, particularly brominations.
-Alkylations.
-Reactions involving fluorine, hydrofluoric acid, boron trifluoride etc
-Reactions involving alkylene oxides.
-Polymerisation reactions which are liable be becomes uncontrollable.
-Nitric acid oxidations.
-Reactions involving the use of hydrogen peroxide at 50 volumes or above.
-Perchloric acid oxidations.
1.3 It is generally bad practice to add active catalysts at elevated temperatures.
1.4 When using a boiling aid, add it to a liquid well below the boiling point and limit the amount added. The boiling aids should preferably be in the form of powder or granules.
Remember that addition of finely divided materials, such as, carbon black, to a nearly boiling liquid can cause frothing over.
1.5 The bench should be kept dry in the vicinity of an experiment involving alkali metals.
