Experiment O04 Preparation of Aniline

Chemicals:Nitrobenzene (4 cm3),

granulated tin (10 g),

conc. hydrochloric acid (35 cm3),

approx. 30% aqueous NaOH solution (50 cm3),

ether (15 cm3),

sodium hydroxide pellets (5 g),

litmus paper (blue and red)

potassium hydroxide pellets (5 g). (for second practical session)

Apparatus:10 cm3 measuring cylinder,

25 cm3 measuring cylinder,

250 cm3 round-bottomed flask,

1000 cm3water-bath,

Liebig water condenser,

screw-cap adaptor,

rubber tubing adaptor,

separating funnel,

2×150 cm3 beakers,

100 cm3 conical flask and stopper,

50 cm3 round-bottomed flask,

100 cm3 round-bottomed flask,

air condenser,

thermometer pocket,

250 oC thermometer,

Bunsen burner, tripod and gauze.

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Experiment O04 Preparation of Aniline

Procedure:

a. Reduction of nitrobenzene

Place 4 cm3 of nitrobenzene and 10 g of tin in a 250 cm3round-bottomed flask fitted with a reflux condenser.Add excess concentrated hydrochloric acid, by addingit to the flask a few cm3 at a time, until a total of24 cm3 has been added. It is most convenient to pourthe acid down the condenser, and it is advisable to shakethe flask between each addition. When all the acid hasbeen added heat the reaction mixture on a water-bath for15 minutes.


Reflux

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Experiment O04 Preparation of Aniline

b. Steam distillation

Cool the flask and add sodium hydroxide solution until the solution is strongly alkaline. The hydroxide of tin, which is precipitated first, should be dissolved (about50 cm3 of 30% sodium hydroxide solution should be sufficient)


Set up the apparatus for steam distillation and proceed until oily droplets of aniline are no longer visible inthe distillate coming over.

Steam distillation

c. Ether extraction

Add concentrated hydrochloric acid to the distillate, until the solution is acidic (about 3 or 4 cm3 of acid should be needed) and, when cool, transfer the solutionto the separating funnel. Extract with two separate 5 cm3portions of ether. After shaking the separating funnel, invert the funnel and open the tap to release the ether vapour. Discard the ether layer in each case (run it into the ether residues bottle).

Transfer the aqueous layer to a beaker and add sodiumhydroxide pellets, one at a time, until the solution isalkaline.

Shake this alkaline solution, in a separating funnel, with 5 cm3 portions of ether. Retain the ether layerfrom this separation. (First practical session finished)

Dry the ethereal extract, by standing it over 5gpotassium hydroxide pellets, in a stoppered flask until the next practical session.

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Experiment O04 Preparation of Aniline

d. Ether distillation and distillation of aniline

Heat a water bath to about 70 oC and, after extinguishingall flames, decant the ethereal solution into a 50 cm3round-bottomed flask fitted with a screw-cap adaptor andwater condenser. Heat the flask in the water bath untilno more ether distils.

Replace the water condenser by an air condenser, fit a thermometer pocket and 250 oC thermometer to the screw-capadaptor and heat the flask over a gauze using a Bunsenburner. Collect the fraction which distils between 180 oCand 185oC and record the yield.


Ether distillation


Distillation of aniline

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Experiment O04 Preparation of Aniline

Name:

Seat No.:

Date:

Yield of aniline =

Grade:

Questions:

1. Why must the solution be made alkaline before steam distillation? (Procedure b)

2. Why is the reaction mixture cooled before the additionof sodium hydroxide in part b. (Procedure b)

3. Why is hydrochloric acid added to the distillate beforethe first ether extraction and why is this etherealsolution discarded? (Procedure c)

4. Why is sodium hydroxide added before the second etherextraction and why is this ethereal solution retained?(Procedure c)

5. Why are two separate 5 cm3 portions of ether used in Procedure c, rather than one 10 cm3 portion?

6. Why is potassium hydroxide used for drying aniline, ratherthan the cheaper calcium chloride?

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