STEP 1: Place 100 g (1.53 mol) of zinc wool in a
1-litre three-necked flask and amalgamate it.
STEP 2: Fit
the flask with a sealed
stirrer unit, an efficient double surface condenser and a lead-in tube dipping almost to the bottom of the flask
for the introduction of hydrogen chloride gas;
insert an empty wash bottle between the hydrogen chloride generator and the flask.
STEP 3: Introduce through
the condenser
250 ml of concentrated hydrochloric acid and 50 ml of water, set the stirrer in
motion and then add 40 g (0.35 mol) of heptan-4-one.
STEP 4: Pass a slow current of hydrogen chloride
through the mixture; if the reaction becomes too vigorous, the passage of
hydrogen chloride is temporarily stopped.
STEP 5: After 2-3 hours most of the amalgamated zinc will have reacted.
STEP 6: Leave the reaction mixture overnight,
but disconnect the hydrogen chloride
gas supply first.
STEP 7: Remove the stirrer and the condenser from the flask. Arrange for direct steam distillation from the
flask by fitting a stopper into one
neck, a knee tube connected to a downward condenser in the central aperture
and connect the lead-in tube to a source of steam.
STEP 8: Stop the steam distillation when the distillate passes over as a
clear liquid. Separate the upper layer,
wash it twice with distilled water, dry with magnesium sulphate or anhydrous calcium sulphate and distil through a
short fractionating column.
STEP 9: Collect
the fraction, b.p. 97-99 °C (1). The yield of heptane is 26 g (74%).
Notes to keep in mind:
1. The products of most Clemmensen reductions contain
small amounts of unsaturated hydrocarbons. These can be removed by
repeated shaking with 10 per cent of the volume of concentrated sulphuric
acid until the acid is colourless or nearly so; each shaking should be of about 5 minutes
duration. The hydrocarbon is washed with water, 10 per cent sodium carbonate
solution, water (twice), dried with magnesium sulphate or anhydrous calcium
sulphate and finally fractionally distilled over sodium.
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