Many reactions occur in organic chemistry involving aromatics, especially benzene. Benzene is a six ring carbon with three double bonds. Benzene rings can have groups attached to them; for example, if a methyl (CH3) is attached to a benzene ring, the molecule is called Toluene. In a recent organic lab, my partner and I synthesized methyl 3-nitrobenzoate from methyl benzoate.
To start, nitric acid (HNO3) is slowly added to sulfuric acid (H2SO4). This reaction is exothermal so it must be kept in an ice bath. The reaction of acids produces nitrate ion (NO2-) which will attach to the benzene ring. The substituent (molecule) that is attached to a benzene ring determines where and if another group will bond to the ring. The type of substituent determines how reactive the ring will be and is based on the resonance forms that can be formed. The COOCH3 that is on the ring above if not reactive, so it is a meta director. Groups that are reactive will cause ortho and para addition to the ring. Coming from Latin, ortho means “next to”, meta means “after that”, and para means “across”. These prefixes are used to specify where a molecule will attach to a ring based on what group is already on the ring.
The acid mixture is slowly added to the reactant, methyl benzoate. This reaction is extremely exothermic, which means it produces a significant amount of heat energy. For this reason, the acid mixture is added very slowly and the reaction is kept in an ice bath. After the reaction goes to completion, a solid is formed. These crystals are then filtered using vacuum filtration. This gives a crude product, which is recrystallized using methanol as the solvent. After heating and then cooling, this mixture is again filtered which gives the final product. We weighed the product to determine percent yield and found the melting point to determine purity. This lab was very informative and helped explain how to nitrate a benzene ring.