Find the final product

Question: What will be the final product P of the following reaction?

Solution: To find out the final product let us treat the given reactant with the reagent step by step:

First the given reactant is treated with H₃O⁺.

[H₃0]+ is a hydronium cation, also known as hydroxonium. It's an acid according to Bronstend-Lowry theory, about bases and acids, because it can give of a [H]⁺ :

[H₃0] <--> H₂O + H⁺

So when given reactant reacts with H₃O⁺, it gives:

On heating the obtained product losses CO₂

Now the obtained alkene is react with O₃ and H₂O₂.

As a reagent, ozone is used to cleave alkenes. When alkenes are treated with ozone and H₂O₂, they are subjected to “Oxidative workup”, this breaks the carbon-carbon double bond to form carboxylic acid. 

Now this is final product P. 

Dizonium coupling

Diazonium Coupling (Diazo Coupling, Azo Coupling)

An azo coupling is an organic reaction between a diazonium compound and another aromatic compound that produces an azo compound. Nitrogen is used to make a bridge between two benzene rings.

Dizonium compound + Aromatic compound = Azo compound

 

This is basically an electrophilic aromatic substitution reaction. Due to the positive charge on the terminal nitrogen of the -N=N⁺ group, dizonium cation may participate as an electrophile. As a result, two aromatic compounds are coupled by a -N=N- group. This is known as the azo group (diazo group). The corresponding reaction is called diazonium coupling (diazo coupling, azo coupling).

Examples of Coupling Reactions:

1)   Reaction with Phenol

Phenol is dissolved insodium hydroxide solution to give a solution of sodium phenoxide.

When this phenoxide ion reacts with dizonium ion, an azo compound is formed in which two benzene rings are linked by a nitrogen bridge.

2)   Reaction with Phenylamine (aniline)

The reaction of aniline with dizonium salt produced a yellow solid known as aniline yellow.

 

Uses: Azo coupling is the most widely used industrial reaction in the production of dyes, lakes and pigments. 

Limitation:  The electrophilicity of diazonium ions is only relatively weak, as their positive charge is delocalized over the two nitrogen atoms.

The unsubstituted benzenediazonium cation may react only with strongly activated aromatic compounds, such as phenolates and amines, The substitution normally occurs at the para position, except when this position is already occupied, in which case ortho position is favoured. .  

Friedal Crafts Alkyation

Friedal Crafts Alkylation:

This reaction is developed by Charles Friedel and James Crafts in 1877.

In Friedal crafts alkylation, a haloalkane reacts with benzene in the presence of an aluminium halide catalyst, or any other lewis acid catalyst, and produce an alkylbenzene and a hydrogen halide.

 The reactivity and polarity of haloalkane increase as we move up the periodic table. It means:

RF > RCl > RBr > RI

This means that the Lewis acid used as catalyst in Friedel Craft alkylation reaction tend have similar halogen combination. BF₃, SbCl₅, AlCl₃ and AlBr₃ are commonly used Lewis acid in the reaction.

Mechanism of Friedel Crafts alkylation:

1)    In this step, a carbocation is formed which act as a electrophile in the reaction. This activates the haloalkane.

2)    In step two, an electrophillic attacks on benzene which results in multiple resonance forms. The halogen reacts with the intermediate and picks up the hydrogen to eliminate the positive charge.

3)    The last step shows end of the step two and give the final product.

 

Limitations:

There are few limitations of Friedel Crafts alkylation.

·         The reaction works only with benzene or ACTIVATED benzene derivatives. It will not occur if the benzene ring is deactivated.

·         The reaction works only with ALKYL halides (i.e. chlorides, bromides or iodides), but it does not work with VINYL or ARYL halides.

·         Alkylation reactions are prone to carbocation rearrangement.

·         Over alkylation can be a problem since the product is more reactive than the starting material. This can usually be controlled with an excess of the benzene.

·         The Lewis acid catalyst AlCl₃ often complexes to aryl amines making them very unreactive.