Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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potassium bromide : KBr
bleach : NaClO
acetic acid : CH3COOH
ethanol : CH3CH2OH
methanol : CH3OH
Class:
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elem=C,Cl,Br
organic
Summary:
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Hypochlorite ion forms esters very easily with alcohols. The esters simply are formed from aqueous
solutions. The methyl ester is a colorless gas, which gives extremely powerful explosions when
ignited. The ethyl ester is a very volatile yellow/green oil, which burns with a WHOOSH sound and
which is quite unstable (it easily decomposes). The t-butyl ester is quite stable and can be kept
around for a somewhat longer time. This burns quickly with a sooty flame.
Description:
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Preparation of ethyl hypochlorite:
- Take 4 ml of bleach with appr. 13% active chlorine. Put this in test tube A.
- Take 1 ml of acetic acid (80%) and put this in test tube B.
- Take 0.5 ml of ethanol (96%, denatured with 1% MEK) and add this to test tube B.
Swirl the contents of test tube B.
- Pour the contents of test tube B in test tube A. Do this not at once, but add in 4 steps.
After each time swirl the test tube to mix the solutions.
A yellow oil separates and remains floating on the aqueous layer. The layer only has a thickness
of 3 mm or so. The yellow oil is very volatile and quickly disappears (in 10 minutes or so, all
of it is gone). The oil has a strong and pungent smell, not very pleasant.
Using a glass pasteur pipette, take some of the oil and put on a watch glass. Immediately keep a
small flame near the oil. The oil catches fire very easily and burns explosively violently with a
WHOOSH sound. If you wait too long with igniting the oil, then nothing is left, it evaporates very easily.
The experiment was carried out at 15 C, the test tube A cooled under a running tap with water of appr. 15 C
as well. No excessive heat was observed.
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The same experiment was repeated with tert-butyl alcohol instead of ethyl alcohol. Now appr. 1 ml of t-butyl
alcohol was mixed with 1 ml of acetic acid (80%) and this mix was added to 7 ml of 13% bleach. Now, a layer
of more than 5 mm of oily yellow liquid was obtained. This liquid is much less volatile. Some of this liquid
was put on the watch glass and ignited. It can be lighted very easily and burns fiercely with a sooty flame.
The smell of the soot is the same as that when chlorinated alkanes are burnt.
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The same experiment also was repeated with methanol instead of ethyl alcohol. Now appr. 0.5 ml of methanol was
taken and this was mixed with appr. 0.75 ml of acetic acid. This mix was added to appr. 4 ml of 13% bleach. No
layer of oil is formed, on shaking a colorless gas escapes from the liquid and while doing so, it produces a
strong bubbling noise. The liquid was shaken until no more gas was produced anymore. This gas was ignited by
keeping a flame in front of the test tube. A special thick-walled test tube was used for this experiment!!
When the gas is ignited, a remarkably powerful explosion occurs. Only the gas in the test tube explodes, the
liquid does not change. The sound was thundering loud.
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Take appr. 1 gram of KBr and dissolve this in 7 ml of water. To this, add appr. 0.25 ml of t-butyl hypochlorite.
As soon as that liquid comes in contact with the solution of KBr, it turns orange. The liquid becomes more dense
and starts to float around in the liquid. On shaking the test tube, the liquid turns red. Red oily drops are
formed, which partially sink to the bottom while others move up to the surface. The red drops most likely are
either t-butyl hypobromite, or t-butyl hypochlorite, contaminated with Br2. However, no Br2-vapor, nor any smell
of Br2 could be observed.
Some of the red drops were collected in a pasteur pipette and transferred to a watch glass and ignited. These
drops burn much more violently than t-butyl hypochlorite, the burn is nearly explosive. There is no soot and the
flame is not orange, but a weak flash occurs with a pale color (hard to observe, the effect only lasts for a
very short time). I think that I made some (impure) t-butyl hypobromite.
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Remark: The experiment with methanol is quite risky. Do not scale up this experiment, an explosion of 100 ml of
the gas mix most likely will result in serious damage. Even with just 20 ml in a test tube, the explosion is so
strong that there is a good chance of shattering the test tube. In this experiment a thick-walled tube was used
and the tube in turn was wrapped in a towel.
A final remark: It is important to mix acetic acid with an alcohol and add this mix to the solution of NaOCl.
If you add the 80% acetic acid to the NaOCl first, then you get a cloud of Cl2 and the liquid which remains has
lost most of its active chlorine and is not useful anymore.