Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

ADIPIC ALDEHYDE FROM CYCLOHEXENE 385
per hour are passed through and the ozone content is 5 per cent by
volume the cyclohexene (0-2 mole) is saturated in five hours.
The student is strongly recommended to determine iodometrically
the amount of ozone delivered in a fixed time and to regulate the strength
of the current of oxygen with a gas meter. The determination should be
made before the experiment is begun about ten minutes after the current
in the ozoniser has been switched on.
Since over-ozonisation must be in any case avoided, attach a
second wash bottle containing acid potassium iodide solution to the
outlet tube of the first before the calculated time has elapsed. If no
ground glass joint 1 is available, use a long bored cork stopper which
has been dipped in molten paraffin wax.
The end of the ozonisation is recognised by sudden extensive
separation of iodine.
Hydrogenate the clear mobile solution of the ozonide (still cold)
by means of 0-5 g. of palladium on a carrier (see p. 378). Moderate
the rapid uptake of hydrogen immediately after hydrogenation is
begun by cooling the bulb in ice water. Finally allow the action to
run to completion whilst the spontaneous evolution of heat continues.
After about one hour and uptake of three quarters of the calculated
amount of hydrogen the hydrogenation ceases. Less hydrogen is
consumed if the cooling during ozonisation has been insufficient or if
over-ozonisation has occurred.
Remove the catalyst by filtration at the pump, distil the solvent
using a receiver for fractional distillation and collect the adipic aldehyde
by distillation in a vacuum from a small flask fitted with a
column. Yield 12-14 g. Pure adipic aldehyde boils at 92°-94°/12
mm., solidifies in an ice-salt freezing mixture and then melts at - 8°
to - 7°. Keep it in a sealed tube under nitrogen or CO2 in order to
protect it from auto-oxidation.
When dealing with ozonides always wear goggles, since ozonides,
in particular amongst compounds of low molecular weight, are often
explosive. Benzene triozonide, for example, is very dangerous.
Suitable solvents for the ozonisation of organic substances are :
hexane, chloroform, carbon tetrachloride, ethyl chloride, glacial
acetic acid, and ethyl acetate.
Many ozonides are difficultly soluble in the hydrocarbons and
chloro-compounds and consequently separate during the ozonisation.
1 For rendering joints gas-tight when working with ozone use not fat but syrupy
phosphorus pentoxide or graphite.
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