Nitration of Benzene Mechanism Electrophilic Aromatic Substitution Reactions

in this video we're going to focus on the mechanism for the nitration of benzene so here's benzene and we're going to react it with two reagents two strong acids in this case nitric acid mixed with sulfuric acid and in its reaction we're going to replace hydrogen atom with an electrophile in this case no2 and because we replace hydrogen with an electrophile this is called an electrophilic aromatic substitution reaction and the product of this reaction is called nitro benzene now let's focus on the mechanism for this reaction the first thing we need to do is we need to generate the electrophile that's going to react with the benzene ring so let's begin by drawing nitric acid channel three and so the nitrogen atom is attached to three oxygen atoms one of the oxygen atoms has the hydrogen atom attached to it the other oxygen atom has three lone pairs and negative charge this one has two now the nitrogen atom in the middle has positive formal charge and so nitric acid is going to react with sulfuric acid which looks like this and the purpose of sulfuric acid is to help nitric acid generate the electrophile and so what's going to happen is protonation is going to occur right now the group is bad leaving group but once we add hydrogen atom to it we can convert it into good leaving group and so this step is reversible so we're going to put double arrow and so now we have an oh2 group with positive charge and one lone pair and we're going to use this oxygen atom to expel water and so this will generate the nitronium ion which looks like this and so we have positive charge on the nitrogen atom that is positive formal charge and we also have water as side product so this is the electrophile that we're going to react the benzene ring with so now let's start with benzene it has three double bonds and let's react it with the nitronium ion so the benzene ring is going to attack the no2 group and one of the pi bonds will break it really doesn't matter which one we break because they're the same and so here are the two hydrogen atoms that we have and now the benzene ring is attached to nitrogen atom which still has double bond with an oxygen atom and another single bond with another oxygen atom so this oxygen has two lone which both of these had two to begin with and the other oxygen atom has three lone pairs and negative charge whereas the nitrogen atom whenever it has four bonds has positive formal charge we also have positive charge on the benzene ring now the next step is to get rid of the carbocation and regenerate the aromatic ring and so we need to use base to do that now what can we use as the base in this example in the last step in the production of the no2 ion we generated water so we could use water as base we could also use the bisulfate ion or we could use the solvent so we could use any one of these as base so therefore i'm going to use generic base for this step so the base is going to take the proton the carbon hydrogen bond will break regenerating the aromatic ring and so now we have nitrobenzene so you could see that the net effect is that we replaced hydrogen atom with an electrophile and so that's the mechanism for the nitration of benzene to produce nitrobenzene you