Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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formic acid : HCOOH
thionyl chloride : OSCl2
Class:
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elem=C
organic
Summary:
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Formic acid does not form an acid chloride with thionylchloride, but it
decomposes. Normally, the following reaction occurs:
RCOOH + SOCl2 --> RCOCl + SO2 + HCl
When R = H (formic acid), then decomposition occurs and carbon monoxide is
formed.
Description:
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Take a few drops of concentrated formic acid (> 90%) and add a few drops of
thionyl chloride: The two liquids can be mixed completely, no visible reaction
occurs after a short transient, in which some bubbles of gas are formed.
Heat the liquid for a while at 50 C in a warm water bath, while keeping the
test tube LOOSELY stoppered: Slowly, the amount of liquid decreases and a
colorless gas mix is formed. Fumes of HCl can be observed which escape from the
test tube when it is loosely stoppered.
Put the loosely stoppered test tube under water and turn it upside down and
remove the stopper: The water fairly quickly moves into the test tube and only
a third or so of the volume of gas remains, the rest dissolves in the water.
Stopper the test tube again and take it out of the water. Remove the stopper
and immediately keep a flame near the open test tube: A blue flame appears,
which flashes somewhat into the test tube. This blue flame is due to burning
CO.
Most likely, the following reaction occurs:
HCOOH + SOCl2 --> [HCOCl] + SO2 + HCl --> HCl + CO + SO2 + HCl
The HCl and SO2 dissolve in water, the CO does not. The CO can be ingited and
burns with blue flame.