Download DETECTION OF ALCOHOLS, ALDEHYDES AND KETONES

DETECTION OF ALCOHOLS, ALDEHYDES AND
KETONES
Notice: The tasks carried out in this block do not require precise volume measurements, so you will estimate the
volumes only roughly. Suppose that 1 ml in a test tube corresponds approximately to 1 cm height of the liquid column.
If you do not feel to estimate 1 cm, use ruler or a calibrated test tube (to compare the heights only). It is not necessary to
use pipettes, except it is explicitly required in the procedure.
1) Reaction of ethanol with potassium permanganate
Principle:
The alcohol gets oxidized into acetic acid. The permanganate gets reduced into a manganese(II) salt
leading to a color change. Suggest an equation of this process!
Reagents:
1. potassium permanganate
2. concentrated sulfuric acid
3. ethanol
Procedure:
1. Put about 3 ml (3 cm) of the permanganate solution into a test tube.
2. Add 0.5 ml of concentrated H₂SO₄ using an automatic pipette.
3. Add 1 ml of ethanol (1 cm). Mix and observe the color change.
Conclusion:
2) Reaction of ethanol with potassium dichromate
Principle:
Ethanol gets oxidized by potassium dichromate into acetaldehyde in alkaline environment:
3 CH₃CH₂OH + K₂Cr₂O₇ + 4 H₂SO₄ ⇌ 3 CH₃CHO + K₂SO₄ + Cr₂(SO₄)₃ + 7 H₂O
Reagents:
1. potassium dichromate
2. concentrated sulfuric acid
3. ethanol
Procedure:
1. Put about 3 ml of the dichromate solution into a test tube.
2. Add several drops of concentrated H₂SO₄ .
3. Add 1 ml of ethanol. Mix and observe the color change. (The reaction is not specific to ethanol,
aldehydes react as well.)
Conclusion:
3) Reaction of acetone with Lugol’s solution (iodoform reaction)
Principle:
The Lugol’s solution reacts with acetone according to the following equation:
2 KOH + 2 KI ⇌ KIO + H₂O
CH₃COCH₃ + 3 KIO ⇌ CH₃COCI₃ + 3 KOH
CH₃COCI₃ + KOH ⇌ CH₃COOK + CHI₃ (jodoform)
Reagents:
1. Lugol’s solution (iodine dissolved in a potassium iodide aqueous solution)
2. sodium hydroxide solution
3. acetone
Procedure:
1. Put about 3 ml of the Lugol’s solution into a test tube.
2. Add 1 ml of NaOH soution using an automatic pipette.
3. Add 0.5 ml of acetone. Observe the iodoform formation (whose presence is manifested by its
characteristic smell).
Conclusion:
DETECTION OF KETONE BODIES AND REDUCING
SUGARS
4) Fehling’s test
Principle:
The Fehling’s (as well as Benedict’s) test proves the presence of reducing compounds. It is based on
non‐specific reduction of chelated Cu²⁺ into Cu₂O by citrate or tartrate.
Reagents:
1. Fehling’s solution 1 (solution of copper (II) sulfate)
2. Fehling’s solution 2 (solution of NaOH and sodium‐potassium tartrate)
3. a urine sample and a glucose solution
Procedure:
1. Put about 1 ml of the Fehling’s 1 and 1 ml of the Fehling’s 2 solutions into a test tube, mix and
add 2 ml of the urine sample.
2. Prepare (in the same way) two other test tubes using the remaining two urine samples.
3. Put the test tubes into the boiling water bath for about 5 minutes. Compare the appearance of the
samples. (The reaction is not specific to aldoses, other reducing substances, e. g. aldehydes,
react in this way.)
Conclusion:
5) Lestradet’s specific test for acetone
Principle:
In alkaline environment, acetone forms a colored complex with sodium nitroprusside.
Reagents:
1. Lestradet’s powder reagent (sodium nitroprusside, ammonium sulfate and sodium carbonate)
2. urine sample
Procedure:
Put a small mound (about ¼ of a tea spoon) of the powder reagent on a piece of filtration paper.
Then put several drops of the urine onto it. In the presence of acetone, a purple color develops.
Conclusion:
6) Detection of ketone bodies and glucose in the urine using a diagnostic strip
Principle:
The test for ketone bodies is based on the Legal’s reaction principle. The indication zone contains
an alkaline buffer mixed with sodium nitroprusside, whitch gives a purple colored product by a
reaction with acetoacetic acid or acetone. The product amount is proportional to the ketone bodies
concentration in the urine.
The glucose assay is based on a specific enzyme reaction utilizing the enzymes glucose oxidase
(GOD) and peroxidase (POD). The substrate (D-glucose) gets oxidized by air oxygen (reaction
catalyzed by GOD) into δ-D-gluconolactone. The hydrogen peroxide formed here oxidizes in the
subsequent reaction (catalyzed by POD) a chromogenic system into distinctively colored products.
Procedure:
Immerse the diagnostic strip for about 3 s into the urine sample and compare the resulting color
with the corresponding scale on the original strip’s box (or tube).
Conclusion: