Acetone : Ketone

Acetone

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Lab Preparation of Acetone –

It is prepared in laboratory  by heating Anhydrous Calcium acetate.

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Method-

Fused calcium acetate mixed with little iron fillings is taken in a retort, fitted with water condenser & a receiver. Iron fillings help in the uniform distribution of heat.

The retort is heated slowly,when acetone distills over & collected in the receiver. The distillate is shaken with saturated solution of sodium bisulphite then colourless  crystals of  acetone sodium bisulphite are formed which on treatment with sodium carbonate gives acetone.

The aqueous solution of acetone is dried over Anhy.CaCl2 & redistilled to obtain pure acetone. The fraction is collected between 55 to 570C.( Its boiling point is 560C)

(CH3)2C=O [impure] + NaHSO₃—->( CH3 )2C(OH) SO₃Na [Acetone Sodium bisulphite  compound]

( CH3 )2C(OH) SO₃Na + Na2CO3 ——>  (CH3)2C=O [pure] + NaHCO3 + Na2SO3

General methods of preparation:
1) By oxidation of Alcohols:

Secondary alcohol  on oxidation with K2Cr2O7 + H2SO4  forms  ketone.

2) By catalytic dehydrogenation of Alcohols:

On passing the vapors of secondary alcohol over Cu at 300 o C, ketone is formed.

3)  From Acetic  acid –

 By passing vapours of  acetic acid over heated MnO catalyst at 300⁰C, acetone  is formed.

CH3COOH + CH3COOH ——>CH3COCH3 + CO₂ + H₂O

4) By hydrolysis of gem-dihalides-

By the hydrolysis of isopropylidene dichloride with aq. KOH , acetone is formed.

(CH3)2CCl2 +2KOH (aq.)——–> (CH3)2C(OH)2 [unstable compd] —–>CH3COCH3 +H2O

5) By the ozonolysis of Alkenes

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6) From Grignard reagent-

When  Methyl cyanide ( Alkyl cyanide ) reacts with methyl magnesium iodide then addition compd is formed which on hydrolysis gives acetone.

CH3CN + CH3MgI ——> (CH3)2C=NMgI [addition compd] ——> (CH3)2C=O +NH3 + Mg(OH)I

Test –

1. Iodoform test-  Acetone gives yellow ppt. of  iodoform when heated  with I2 & NaOH solution or ammonia.(Ethyl alcohol also give  yellow ppt. of  iodoform when heated  with I2 & NaOH solution but not with ammonia)
2.  It gives red colour with sodium nitroprusside & sodium hydroxide solution.
3. It does not react with Schiff’s reagent, tollen’s reagent, fehling solution.

Uses –

1. As a solvent for cellulose acetate , cellulose nitrate, celluloid resins etc.
2. As a nail polish remover
3. In the preparation of chloroform , iodoform , chloretone etc.

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