How would one favor the formation of p-TsCl over o-TsCl in the chlorosuflonation of toluene? [closed]








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I found an old synthesis of $\ce{o-TsCl}$ that purportedly gives a yield of $85\%$ [here](https://www.prepchem.com/synthesis-of-2-toluenesulfonyl-chloride/) and was wondering how, still using chlorosulfonic acid, I could favor the formation of $\ce{p-TsCl}$ instead.




Chlorosulphonation using $\ce{ClSO3H}$ is an irreversible, electrophilic aromatic substitution reaction.


In the book [Chlorosulfonic Acid](https://books.google.co.in/books?id=roI_CwMEcHMC&lpg=PA35&dq=chlorosulfonic%20acid%2C%20chlorosulfonation%20by&pg=PA36#v=onepage&q=chlorosulfonic%20acid,%20chlorosulfonation%20by&f=false), On taking Toluene as the aromatic substrate, it is seen to yield two products -


* $para$-tosylchloride i.e. the **thermodynamic** product (because it is devoid of the steric hindrance offered by the methyl group)
* $ortho$-tosylchloride i.e. the **kinetic** product (because of more activated ortho position due to proximity with methyl $(+I)$ group, which is favourable for the electrophile to attack on despite facing steric hindrance)


At low temperatures like $0-5°C$, the kinetic product is favoured and thus the ortho-isomer is formed. This reaction is exploited in the manufacture of the non-fattening sweetener $Saccharin$.


At higher temperatures like $75-80°C$, the thermodynamic product is favoured i.e. the para-isomer.


According to [Chlorosulfonic Acid](https://books.google.co.in/books?id=roI_CwMEcHMC&lpg=PA35&dq=chlorosulfonic%20acid%2C%20chlorosulfonation%20by&pg=PA36#v=onepage&q=chlorosulfonic%20acid,%20chlorosulfonation%20by&f=false), The yield of para-tosyl chloride can be increased by 


* heating, or
* addition of ammonium chloride or other catalysts


[![enter image description here](https://i.stack.imgur.com/1tCOC.png)](https://i.stack.imgur.com/1tCOC.png)


However, Clayden instead goes on to suggest on Pages 486 and 566, that the preference of ortho-isomer in chlorosulphonation and para-isomer in sulphonation is due to the fact that the latter is **reversible** unlike the former.



> 
> If the reaction is irreversible (as in chlorosulphonation), the alpha-product is usually formed. (with respect to naphthalene, here analogous to ortho position on toluene)
> 
> 
> Sulphonation at low temperatures give the alpha-product by kinetic control and sulphonation at high temperatures gives the beta-product (corresponding to para-position on toluene) by thermodynamic control. The beta product is formed more slowly but it is more stable as there is less steric hindrance.... (as the case in toluene)
> 
> 
> 


...which suggests that chlorosulphonation may not be temperature-dependent at all and shall always yield the ortho-isomer, which I am a bit doubtful about. (help needed)


However, the thermodynamic-kinetic explanation seems very satisfactory to me.


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