Aim:synthesis of p-bromonitrobenzene through nitration of bromobenze.
Nitration reaction consist of nitro group being added to benzene substituted molecule and is an aromatic electrophilic substitution reaction.In this reaction nitronium ion acts as an electrophile attacking benzene ring to remove one hydrogen atom and substitute nitro group.
Mixture of concentrated nitric acid and concentrated sulfuric acid produced heat and it was yellow in color this was due to Sulfuric acid being strong enough to protonate nitric acid.The mixture gives an equilibrium of the ions and the acid in the following way :
2H2SO4 + HNO3 ? 2HSO4- + NO2+ + H3O+
When the bromobenzene was added the solution turned yellow with heat produced.It was then cooled down by cold ice-water bath.The mixture was heated for about thirty minutes and was not allowed to exceed 60oC so as to avoid evaporation of the reaction mixture.Fifteen minutes after the mixture was heated small yellow precipitates formed.The mixture was then added to cold water and a water-insoluble yellow-oily nitrobromobenzene formed.Filtration of the crude nitrobromobenzene seperated it and formed crystals which were then collected and transfered to an erlenmayer flask.The crystals were added with 95% ethyl alcohol and heated for the crude to dissolve.It was then cooled and filtered with ice cold alcohol to form pure p-nitrobromobenze crystals, washes and mother liquors were collected into the filter flask.After the crystals dried melting point and the weight was determined.
The overall reaction took place in the following way:
Mass recorded = 1,55g
Melting point 128oC-132oC
In the reaction for the nitration of bromobenzene the aromatic ring undergoes substitution rather than addition because of the ring’s stability by resonance.Expected products are the major(p-nitrobromobenze) and minor(o-nitrobromobrenze) but in this reaction a major product was formed this is observed from the melting point.
The compounds were extracted weighed and all melting points were found.Errors could have occurred during separation and filtration due to those solids left out.