Synthesis of Hydrazones-Task 1
Synthesis of Hydrazones-Task 1
Synthesis of Hydrazones-Task 1
(PMMMNMTT)
Department of Chemistry
Savitribai Phule Pune University
Pune
Organic Task I
This experiment is available in the public domain and has been adapted from 45th International Chemistry
Olympiad held in Moscow, Russia in 2013 and is accessed from:
http://www.icho2013.chem.msu.ru/en/problems-solutions/icho-2013-problems
This procedure is standardized in our laboratory with different molecules for this workshop
Teaching Learning Centre Pune Workshop Organic Task I
Synthesis of 2,4-dinitrophenylhydrazones
List of Chemicals
Reagent Quantity Placed in Labeled Safety
Plastic tube 2,4
2,4-Dinitrophenylhydrazine 1g
with screw neck dinitrophenylhydrazine
Plastic tube
Sulfuric acid, concentrated 5 mL H2SO4 concentrated
with screw neck
Aldehyde solution 1 mmol in 4 mL each, Plastic tube Aldehyde 1 and
ethanol 2 bottles with screw neck Aldehyde 2
Plastic tube
NaOH solution 10 mL NaOH 2M
with screw neck
Plastic tube Acetone
Acetone 10 mL
with screw neck
Plastic tube
NaHCO3 solution 10 mL NaHCO3 10%
with screw neck
Ethanol
Ethanol 500 mL
Hazard Symbols
Item Quantity
On every working place
5 mL Plastic tube with screw neck labeled “1” 1
5 mL Plastic tube with screw neck labeled “2” 1
Lab stand 1
50 mL beaker 2
15 mL test tube 4
Spatula 2
500 mL plastic washer bottle 1
10 mL measuring cylinder 1
Filter paper, round 2
Glass rod 1
pH indicator papers (in a zipper-bag) 3
On the tables for the common use
Filter paper, round
Filter paper
Gloves
Balances
Büchner funnel
Filtration flask
Water-jet pump
Scissors
Filter paper
Hydrazones are organic compounds with the general formula, R1R2C=N-NHR3. Reaction of
hydrazine or substituted hydrazines (like 2,4-dinitrophenylhydrazine) with ketones or aldehydes
leads to formation of hydrazones, (imine derivatives). The properties of hydrazones are largely
due to the presence of the >C=N-N< structural unit, which contains two nitrogen atoms that are
nucleophilic in nature. The carbon atom may act as either electrophile or nucleophile according to
the reaction conditions and environment. The C=N bond of dialkyl hydrazones can be hydrolyzed,
oxidized and reduced that gives variety of products. Similarly the N-N bond can be reduced to the
free amine.
These derivatives are highly colored solids, often stable and crystalline. You must have used
formation of hydrazones as a qualitative test for confirming the presence of a carbonyl group. In
fact, the concentration of low molecular weight aldehydes and ketones can be determined by
converting them to their hydrazone derivatives. Hydrazone derivatives have various important
pharmacological activities and are used for synthesis of a wide variety of medicinally active
compounds.
References: i) Reactions, Mechanisms, and Structure, John Wiley & Sons, Milton, Australia, 6th edition, 2007.
ii) http://dx.doi.org/10.1155/2014/761030
In the current task, you will be preparing substituted hydrazone using 2,4-
dinitrophenylhydrazine for the given samples of two substituted benzaldehydes (shown
below). In fact, using the colour and some simple qualitative tests, you will identify the
substituted benzaldehydes given to you
O O
OH
OCH3
Procedure
Preparation of 2,4-dinitrophenylhydrazones
Answer Sheet
1. The structures of the aldehydes are given to you. Draw the structures of the two hydrazones
that will be formed.
Product 1 Product 2
(sample 1) (sample 2)
3 In your opinion, whether the acidic pH of the reaction mixture is a crucial factor which
will affect the yield of the above synthesis? Explain your answer in brief.
a) neutral Yes No
b) basic Yes No
5. If the above synthesis is carried out with p-nitrobenzaldehyde in acidic medium the
rate of formation of product will be:
Characterization
Dissolve a single crystal of each hydrazone in a test tube in 10 mL of acetone and divide
into two parts.
6. a) To I part add 1 drop of saturated NaHCO3 solution and shake the resultant solution
well. Record your observations of the solutions color changes in the box.
b) To the second part of the solution, add 2 drops of NaOH solution and shake the
resultant solution well. Record your observations of the solutions color change in the
box.
7. What structural features of your products explain the color change in the reaction with
NaHCO3? Tick the appropriate box/es.
8. What structural features of your products explain the color change in the reaction with
NaOH? Tick the appropriate box/es.
9. Which of the listed processes is responsible for the color change observed in the
reaction of 2,4-dinitrophenylhydrazones with aqueous NaOH? Tick the appropriate
box.
10. Draw the structures of the main organic species present in each test reaction medium in the
answer box below.
Sample 1
Sample 1
11. Calculations
Mass of aldehyde Molar Mass of aldehye Molar Mass of Hydrazone Mass of hydrazone
Sample 1
Sample 2
12. Calculate the theoretical yield and the percentage yield of the hydrazones
Sample 1
Sample 2