formedKetoneTake some iodine in potassium iodide solution; add sodium hydroxide until it is
pale yellow. Add a few drops of compound and shake.A yellow precipitate (iodoform) slowly
forms.Primary/secondary alcoholsAdd a small amount of Phosphorus Pentachloride to the
compound in a fume cupboard.Steamy fumes of HCl gas are observed, these can be tested with
damp litmus paper to confirm acidic gas.
After testing the compound with these diagnostic tests, the unknown compounds
functional group can be determined.
Preparing a derivative and finding its melting point:
The first stage of preparing a derivative is filtration under reduced pressure:
Mixing a small amount of the substance with 2,4-dinitrophenylhydrazine and then adding 20 ml
of ethanol, after heating the mixture in a water bath until limpid, the substance was filtered
through the Buchner funnel.
To isolate a solid product from a liquid, suction filtration using a Buchner funnel is an
effective method.
A small amount of cold solvent should be used to wet the filter paper prior to filtration,
and to remove any solid remains from the reaction flask.
The second stage is recrystallisation, to purify the solid product. Dissolve the solid in the
minimum volume of hot solvent (the original compound), Quickly filter the hot solution using
preheated filter funnel and fluted filter paper. Collect the filtrate and allow to cool and the solid
to recrystallise. Use suction filtration (Buchner funnel) to collect the solid. Wash the solid with a
small amount of cold solvent, finally dry the solid product. To prepare a derivative of the
compound.
To determine the melting point of the solid, melting point apparatus should be used;
The sample is placed in a capillary tube, and the temperature increased slowly until it
melts.
Determining the boiling point of the original compound:
Boiling points can be used for identification purposes. Boiling points are most commonly
measured in the process of distillation.
The boiling point can be determined by setting up apparatus shown below:
When bubbles begin to flow in a steady stream from the capillary tube the substance
should then be left to cool, observe until the bubbles begin to be drawn back up the capillary
tube this point is the boiling temperature of the substance.
Safety issues:
Fume cupboards should be used for all reactions involving toxic, irritant or carcinogenic
chemicals.
No naked flames should be used with flammable chemicals.
The use of gloves is required when dealing with corrosive or irritant chemicals such as
concentrated acids.
How to determine the compound.
The unknown compound can be identified by its functional group and boiling
temperature which can be referenced in a data book for identification purposes.
Results.
The unknown organic compound named substance D, gave a positive result for a
carbonyl group, and a negative result for an aldehyde, and a positive result for a Ketone, the
organic substance was therefore a Ketone.
After preparing the derivative 2,4-dinitrophenylhydrazone, the solid was heated it
melted at 117oC, making the melting point of the derivative 117oC.
The Original organic compound D, had a boiling point of 80oC.
Using these results, the unknown organic compound D was compared to information in
a Data book, the boiling point of the compound and the melting point of its derivative matched
that of the organic substance, a ketone, 2-Butanone.
Conclusions:
Functional group-- Positive result for ketone
Boiling point-- 80oC
Melting point of Derivative-- 117oC
Organic chemical D-- 2-Butanone
