Mechanism of ethene hydration

Given above is the mechanism that I drew but my textbook puts it a bit differently. It says that the ethene is dissovled in the concentrated $\ce{H2SO4}$ to form ethyl hydrogen sulphate $\ce{CH3-CH2OSO3H}$ which when diluted with water reacts to form ethanol and the acid $$\ce{CH3CH2OSO3H + H-OH -> CH3CH2OH + H2SO4}$$ So which mechanism is true?

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    $\begingroup$ I think that the first mechanism occurs when a solution of sulphuric acid in water is reacted with ethene. The second mechanism occurs if you first add conc. H2SO4 to ethene, and then add water. I am not fully sure, though. I will answer if I get a reference to back my claim. $\endgroup$
    – S R Maiti
    Dec 3, 2017 at 9:09

1 Answer 1


At first I thought your mechanism was very comprehensive but upon closer inspection I think it has some flaws because in this reaction conc. sulphuric acid is used as a catalyst and it must be regenerated at the end and in the above mechanism only ethanol is generated.

mechanism of H2SO4 addition

This must be the mechanism shown in your book.

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    $\begingroup$ Hmm, yes but no but yes but no … $\endgroup$
    – Jan
    Oct 25, 2019 at 8:07
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    $\begingroup$ The sulphuric acid is indeed regenerated in the proposed mechanism, no? $\endgroup$
    – Yoda
    Apr 3, 2020 at 18:46

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