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e) lysine →cadaverine + CO
2
f) glutamic acid →γ-aminobutyric acid + CO
2
9. Write the equations of a qualitative reaction for cysteine in the presence of
NaOH: a) with lead nitrate and b) with lead acetate.
10. Write the equationsof qualitative reaction for aromatic amino acids
phenylalanine and tyrosine with concentrated nitric acid.
Laboratory work.
Experiment 1. The reaction of glycine with ninhydrin.
Place 4 drops of
1% glycine solution in a test tubeand 2 drops of a 0.1% solution of ninhydrin.
Gently warm the contents of the tubeuntil the appearance of blue-violet color.
Write the reaction equation (see the textbook). What is the practical significance
of this reaction?
Experiment 2. The reaction of glycine with formaldehyde
. Place 5 drops
of 1% glycine solutionin a test tube and add 1 drop of methyl red indicator.
How does the color of the solution change? What is the reaction of the solution
medium? Add an equal volume of formalin to the resulting mixture. Note
the change in solution color. How and why has the reaction of the medium
changed in the test tube? Write the reaction equation (see the textbook). What is
the practical significance of this reaction?
Experiment 3. The reaction of glycine with nitrous acid.
Put 5 drops of 1%
glycine solution into the test tube and equal volume of 5% solution of sodium
nitrite. Add 2 drops of concentrated acetic acid and shake the mixture gently.
What are you observing? Write theequation of reaction (see the textbook).
What is the practical significance of this reaction?
Experiment 4. Formation of the complex copper salt with glycine
. Place
5 drops of 1% glycine solution in a test tube. Add dry copper carbonate (II) at
the tip of the spatula and heat the mixture. The glycine complex with copper
hydroxide is formed. How is the solution colored?
2NH
2
-CH
2
-C
O
OH
+ Cu(OH)
2
Cu
NH
2
CH
2
C
O
O
O
C
CH
2
NH
2
O
+ 2H
2
O
Experiment 5. Xantoprotein reaction to tyrosine.
Place 5 drops of 1%
glycine solution in a test tube and add 3 drops of concentrated HNO
3.
Heat the