Acetone 2,4-Dinitrophenylhydrazone khxckjzbcbc xxkxxblixbckaxzbikzdc ,mzx clkadbckasb xkal ckla PDF

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Description

Organic Section, CHEM-2101P

Preparation of Acetone 2,4-Dinitrophenylhydrazone Reaction involved: NH

NH2

CH3

NO2

O

NO 2 H N

H3C

H+

+

N

+

CH3

H3C

H2O

NO2 N O2

Acetone

2,4-DNPH

Acetone 2,4-Dinitrophenylhydrazone

Mechanism: H O

O H+ CH3

H3C

CH3

H3C

Protonation of oxygen to make the carbonyl carbon more electrophilic.

H

H O

+

Slow step H3C

CH3

H2N

NO 2

O

O 2N H3C

Intramolecular proton transfer

N

H3C

NO 2

NH

H N H

H NO2

H

H

NO2

O H3C H3C

H N N

NO2

CH3 H N

H2O H3C

H N O2

N

CH3 H

NO2 H N

+

H3C

N

H NO2

N O2

Theory: 2,4-Dinitrophenylhydrazones are prepared by the reaction of a carbonyl compound with 2,4-dinitrophenylhydrazine as a reagent. The reagent is prepared in slightly acidic medium. So, pH is maintained throughout the reaction. The reagent unlike other ammonia derivatives is less basic due to the presence of two electron withdrawing nitro groups. Hence, it is a stable reagent and does not get easily oxidized by air. One advantage of using 2,4-dinitrophenylhydrazine is that the compounds (hydrazones) prepared are of high molecular weight, which leads to decrease in solubility in most of the solvents. Hence, isolation and recrystallization is feasible as compared to other ammonia derivatives. 2,4-Dinitrophenylhydrazine reagent is also known as Brady€s reagent. Chemicals required: 1) Acetone (0.5 mL; 0.3955 g; 6.8 mmol) (d = m/v & n = m/M) 2) 2,4-Dinitrophenylhydrazine reagent (1.35 g; 6.8 mmol) 3) Conc. HCl (07 mL) 4) Methanol (60 mL)

1

Organic Section, CHEM-2101P

Procedure: Step I: Brady€s reagent for this experiment was prepared by dissolving 2,4dinitrophenylhydrazine (1.35 g; 6.8 mmol) in 7.0 mL of concentrated HCl and 60 mL of methanol in a beaker. The mixture was shaken with a glass rod and if the solution was not clear, it was filtered off to get a clear solution of Brady€s reagent. Note:- Preferably take 1.4 g (7.0 mmol) 2,4-dinitrophenylhydrazine in this experiment to avoid a minute loss during filtration. Step II: In another beaker 0.5 mL (6.8 mmol) of acetone were taken and whole quantity of above prepared Brady€s reagent was added slowly with shaking. The contents of the beaker were warmed on a water bath for five minutes and allowed to cool at room temperature for 5-10 minutes. The contents were then cooled in an ice water bath to get orange-colored precipitates of acetone 2,4-dinitrophenylhydrazone. The precipitates of the product were filtered and dried to record the experimental yield. A part of the crude product was recrystallized with ethanol and melting point was determined, which was found to be 126-128 oC. Calculations: Molar mass of acetone = 58 g(Limiting reagent hereby) Molar mass of 2,4-dinitrophenylhydrazine = 198 g Molar mass of acetone 2,4-dinitrophenylhydrazone = 238 g

.:

From chemical equation: One mole of acetone gives = one mole of product (acetone 2,4-dinitrophenylhydrazone) 58 g of acetone give = 238 g of product (hydrazone) 01 g of acetone gives = 238/58 g of product (hydrazone) 0.3955 g of acetone give

% Yield =

2...