34
Ethanal and its tetramer
Ethanal
Extremely
flammable
Harmful
Acetaldehyde
CH3CHO
R12: Extremely flammable. R40: Limited evidence of a carcinogenic effect.
Category 3 carcinogen. R36/37: Irritating to eyes and respiratory system.
Dangerous with: SULFURIC(VI) ACID AND OTHER ACIDS. Violent polymerisation
reactions may occur.
SILVER NITRATE(V) SOLUTION. Explosive products are formed.
-3
WEL (mg m ): 37 (LTEL), 92 (STEL). Flash point: -38 °C.
F
H
Store: FL
Ethanal has been known to spontaneously boil away
during storage and on opening. It should only be
opened in a fume cupboard. Cool in an ice bath before
opening the bottle. Ethanal oxidises to ethanoic acid
during storage.
Ethanal tetramer
Harmful
Store: FS
Disposal: W7
3
W7:
Add 10 cm to 1 litre of water before pouring
down a foul-water drain.
Metaldehyde
R10: Flammable. R20/22: Harmful by inhalation and if swallowed.
Hexamethylene is possibly a safer solid fuel.
(CH3CHO)4
H
Disposal: W1, W6
W6:
Burn it in a fume cupboard.
For emergencies, see Hazcard E as well as more detailed information which may be on this Hazcard.
© CLEAPSS 2007
34
Ethanal and its tetramer
Activity
User
Control measures
Metaldehyde
fuel
Y9
Wear eye protection.
Reducing
copper(II) ions
Y9
Wear eye protection.
Test-tube
reactions of
aldehydes
Y12
Wear eye protection.
Addition of sulfur
dioxide
Y12
Wear eye protection.
Use a fume cupboard.
Condensation
reactions
Polymerisation
Y12
Wear eye protection.
Wear disposable nitrile gloves.
Wear goggles for all these
procedures.
Use a fume cupboard.
Wear disposable nitrile gloves.
Y12
Model risk assessments
Experimental points
Pupils should be supplied with what they will use and not allowed
access to a larger supply. If used with a model steam engine, only the
teacher should use it. Hexamethylene is possibly a safer solid fuel.
Ethanal reduces Fehling’s solution (see Recipe Card 25) when placed
in boiling water. Benedict’s solution does not work as well. However,
Sandell’s solution works in hot water and should be considered as a
safer alternative. See Hazcard 27C.
Investigations can be carried out on a small scale using 3 or 4 drops of
3
ethanal with 1 cm of acidified potassium dichromate(VI) or potassium
manganate(VII) solutions (see Recipe Cards 53 & 56). Warming should
be carried out in a beaker of hot water. However, because of the ease
of air oxidation of ethanal and loss by evaporation, consider using
propanal as an alternative. Silver mirror test: See Hazcard 87.
Prepare saturated sodium hydrogensulfite solution by passing sulfur
dioxide through saturated sodium metabisulfite solution. Use 3-5 drops
3
of ethanal to 2 cm of the saturated solution, apply a stopper and shake
carefully. Leave for 1-2 hours. Benzaldehyde produces more reliable
results.
See Hazcard 30. Benzaldehyde and propanal produce more reliable
results.
Trimer: The reaction is highly exothermic. Cool 10 drops of ethanal in
ice/salt mixture before 1 drop of concentrated sulfuric(VI) acid is added.
Stir carefully.
Metaldehyde (Tetramer): Dry hydrogen chloride gas is passed
3
3
through 1 cm of ethanal dissolved in 2 cm of ethoxyethane.
-3
3
Resin: Add 5 mol dm sodium hydroxide solution dropwise to 1 cm of
ethanal until the brown resin forms.
For emergencies, see Hazcard E as well as more detailed information which may be on this Hazcard.
© CLEAPSS 2007