CAUTION: All preparations and reactions with hydrogen peroxide
and organic peroxyacids must be conducted behind a safety screen, because these
reactions sometimes proceed with violence.
- In a 50Q-ml three-necked flask, equipped with a mechanical stirrer, a thermometer and a dropping funnel, place 300 ml (6 mol) of 88-90 per cent formic acid and add 70 ml (0.62 mol) of 30 per cent hydrogen peroxide.
- Then introduce slowly 41 g (51 ml, 0.5 mol) of freshly distilled cyclohexene over a period of 20-30 minutes; maintain the temperature of the reaction mixture between 40 and 45 °C by cooling with an ice bath and controlling the rate of addition.
- Keep the reaction mixture at 40 °C for 1 hour after all the cyclohexene has been added and then allow to stand overnight at room temperature.
- Remove most of the formic acid and water by distillation from a water bath under reduced pressure (rotary evaporator).
- Add an ice-cold solution of 40 g (1 mol) of sodium hydroxide in 75 ml of water in small portions to the residual mixture of the diol and its formate; take care that the temperature does not rise above 45 °C.
- Warm the alkaline solution to 45 °C and add an equal volume (c. 200 ml) of ethyl acetate.
- Extract thoroughly, separate the lower layer and extract at 45 °C six times with equal volumes of ethyl acetate. Combine the ethyl acetate extracts (total volume about 1 litre), distil off the solvent using a rotary evaporator until the residual volume is about 150 ml and solid commences to crystallise.
- Cool to 0°C and separate the crude product (c. 4.5 g) by suction filtration.
- Concentrate the mother-liquor to 30-40 ml, when more solid crystallises (c. 8g).
- Cool and filter the mixture as before.
- Distil the combined crude products under reduced pressure from an oil bath and using an air condenser; the pure frans-cyclohexane- 1,2 -diol passes over at 128-132°C/15mmHg (or at 120-124 °C/4mmHg) and solidifies immediately, m.p. 102-103 °C. The yield is 40 g (69%).
- It may be recrystallised from acetone or from ethyl acetate.
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