[Moz29386]

Experimental method:

5.2: 1,3,5-Tribromobenzene

Dissolve from the experiment above 10 g of tribromoaniline in 60 cm3 of IMS and
15 cm3 of toluene, in a 250 cm3 conical flask by swirling it on a steam bath. Add, with swirling, 3.5 cm3 of conc. H2SO4 to the warm solution from a burette. Return the flask to the steam bath until the clear solution boils, remove it and add 3.5 g of sodium nitrite in small portions with continuous swirling. The heat of the reaction should cause the solution to boil; add the NaNO2 at such a rate that the reaction does not become too vigorous. Return the flask to the steam bath and continue heating it until gas evolution ceases.

Allow the solution to cool for 10 min., then immerse the flask in an ice-bath. A mixture of tribromobenzene and sodium sulphate should crystallise out. Filter this using a Büchner apparatus, wash with a small amount of cooled IMS and then repeatedly with water (to remove the Na2SO4).  Recrystallise some of your product from aqueous acetic acid (1:4), using decolourising charcoal and a hot filtration. Allow the product at least 10 min. to air dry while on the Büchner filter.  Record the IR spectrum.


There is this is question which asks:  Give reasons (note the plural!)  why the product from 1,3,5trimbromoanline has to be prepared from aniline, rather than by ‘direct’ tribromination of benzene itself.?

It has something to do with the ortho para effect?

Thanks for any assistance!!

[zengjia1029]

Sorry to ask Which compound IMS refers to?

[sHaY]

yup, your on the right track notice that all Br's are meta to each other, what would happen if you try to directly brominate the ring?

[Moz29386]

yup, your on the right track notice that all Br's are meta to each other, what would happen if you try to directly brominate the ring?

Hi Shay thanks for the response

So would that mean we could end up with multiple isomers of tribromoanilline (since the Br can attack any position of the double bonds) instead of the 2,4,6 isomer that we need in this experiment? im not sure.

The only thing I know is the amino group is a strong activating subsituent, the group is introduced to promote reactivity and then removed later to increase the reaction efficiency/speed.

[orgopete]

If you were to nitrate benzene, it would nitrate meta to the first nitro group. If you did the same with bromination of benzene, where would the second bromine go?

[Moz29386]

If you were to nitrate benzene, it would nitrate meta to the first nitro group. If you did the same with bromination of benzene, where would the second bromine go?

??

That didnt help....

[orgopete]

A nitro group is a meta director and bromine is an ortho-para director.