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to yellow-red. In begin the copper complex is destroyed to form copper (I) hy-
droxide yellow:
O H
C
(CHOH)
2
CH-O
CH-O
HOCH
2
CH
2
OH
O-CH
O-CH
(CHOH)
2
C
H O
Cu
H
H
+ 3OH -
CH
2
OH
CH-OH
CH-OH
(CHOH)
2
C
OH O
+ CuOH
2
Then, the copper (I) hydroxide decomposes to form a red-orange color Cu
2
O:
2CuOH → Cu
2
O + H
2
O
This reaction is called a Trommer probe and is used to open glucose in the urine.
Experiment 3. Discovery of glucose by an alkaline solution of copper glycerate
(Guineas reagent).
Place a drop of 0.2 N CuSO
4
solution in the test tube and 2 drops
of 2N NaOH solution. Add a drop of glycerin and mixto the resulting precipitate of
copper (II) hydroxide. What happens to the sediment? Add 1 drop of 0.5% glucose
solution to the resulting solution, and add a few drops of water so that the height of
the liquid layer is 18–20 mm. Shake the solution thoroughly. Heat to the boil only
the top of the solution (the bottom should remain cold for control). Do not shake the
test tube. Pay attention to what happens at the top of the solution.
Alkaline solution of copper glycerate is used for the clinical determination
of glucose in urine called the reagent Guinness. Reaction’s equation:
H
H
Cu
CH
2
OH
O-CH
O-CH
2
CH
2
OH
CH-O
CH
2
-O
O=C-H
(CHOH)
4
CH
2
OH
+
t
CH
2
OH
(CHOH)
4
O=C-OH
CH
2
OH
CHOH
CH
2
OH
Cu
2
O
+
+
+ 2H
2
O
2
4
Experiment 4. Selivanov's reaction to fructose.
Put a grain of dry
resorcinol into the test tube and add 2 drops of concentrated hydrochloric acid.
Add 2 drops of fructose solution and heat until the boiling point. The liquid
becomes gradually red. A non-stable compound, hydroxymethylfurfural, is
formed in the reaction:
O
HO
CH
2
OH
OH
OH
HOH
2
C
-3H
2
O
O
C=O
H
HOH
2
C