What is Raschig process and Why halo arenes can not prepared from phenol ?

What is Raschig process ?

This is an example of industrial method for the production of chloro benzene from benzene molecule . 

In Raschig process, the mixture of benzene vapor , air and hydrogen chloride are passed over the heated copper chloride catalyst under 400ᵒC temperature . 

As a result , the expected chloro benzene is obtained .

The Raschig process is a best process for the industrial preparation of chloro benzene  from benzene . 

 

Why halo arenes can not prepared from phenol ?

The  –OH group of aliphatic alcohol  is substituted by the halogen atom easily and forms halo alkane . 

But halo arenes or aryl halide can not prepared from phenol .

Because the substitution of phenolic – OH group by halogen atom is not so easy . 

This is due to the resonance . The lone pair on oxygen atom participate in resonance  with the pi electrons of benzene ring . 

As a result , C – O bond in phenol gains partially double bond character .  

Therefore, the phenolic C – O bond is more stronger than alcoholic C – O bond .   

Generally, the dissociation of more strong  phenolic C – O bond  is not possible .

That is why halo arenes can not prepared from phenol . 

 

Which one is more active between chloro cyclohexane and chloromethyl cyclohexane in SN2 reaction ?

Between chloro methyl cyclo hexane and chloro cyclo hexane, chloro methyl cyclo 

hexane is a primary alkyl halide . We know that primary alkyl halide is very effective towards SN2 reaction . 

Consequently, chloro methyl cyclo hexane is more active than chloro cyclo hexane in SN2 reaction .

Which halogen atom of 1,3-dibromo-3-methyl butane is more active in SN1 reaction ?

The rate of SN1 reaction depends on the stability of the carbo cation  which  is formed the in first step of SN1 reaction. 

Now, if the first bromine atom is eliminated from 1,3-dibromo-3-methyl butane, the carbo cation formed is tertiary .

 But ,if the second bromine atom is eliminated , the carbo-cation formed is primary . 

Since tertiary carbo-cation is more stable than primary one due to hyper conjugation  effect. 

So first halogen atom of 1,3-dibromo-3-methyl butane is more active in SN1 reaction than the second one.  

Compare the ability of 5-bromo cyclopenta-1,3-diene, 3-bromocyclopent-1-ene and 4-bromo-4H-pyran in SN1 reaction .

The rate of SN1 reaction depends on the stability of carbocation produced by the dissociation of alkyl halide .

 Now, on dissociation of 4-bromo-tertahydro-pyran Produced a most stable aromatic hydrocarbon With (4n+2) number of π electrons. 

This carbo cation get stabilized through the resonance.

On the other hand 3-bromocyclopent-1-ene compound produced a less stable carbo cation with respect to carbo cation  is produced from 4-bromo-4H-pyran .

Because ,the number of resonating structure of the former compound  is less than the later compound . 

Consequently, the ability of later compound in SN1 reaction is higher than the former compound.

Now , in case of 5-bromocyclopenta-1,3-diene , on dissociation of this compound , an unstable anti aromatic carbocation with 4n number of π electrons should be obtained . 

But, practically it does not obtained due to very much unstable . 

So from the above discussion it is clear that the 4-bromo-tetra hydro-pyran is more 

effective towards SN1 reaction and the less effective compound towards SN1 reaction is 5-bromo cyclopenta-1,3-diene . 

What is Raschig process ?

Why halo arenes can not prepared from phenol ?

Which one is more active between chloro cyclohexane and chloromethyl cyclohexane in SN2 reaction ?

Which halogen atom of 1,3-dibromo-3-methyl butane is more active in SN1 reaction ?

Compare the ability of 5-bromocyclopenta-1,3-diene, 3-bromocyclopent-1-ene and 4-bromo-4H-pyran in SN1 reaction .

Why benzyl chloride is highly reactive in SN1 reaction ? Click here