The following mechanism for acyl chloride hydrolysis was given by my professor :


However I do not understand why in the second step, oxygen has a partially negative charge, should it not gain a positive charge as it is bonded to three atoms, furthermore shouldn't the $\text{O}-\text{H}$ bond breaking homolytically form a $\text{H}^-$ ion and not a proton?

Should the arrow be reversed in the second step?

  • 1
    $\begingroup$ Do not confuse real charge with formal charge. $\endgroup$
    – Zhe
    Apr 15, 2021 at 3:10

1 Answer 1


This reaction is mostly ignored in basic organic texts and the mechanism you give is straight out of Wikipedia with some modification. I am sure some serious study exists some where but not on the web. Please bear with me because I can't[or just don't know how to] do drawings. The first step is probably as written and is most likely slow because it involves charge separations. You are right there is a + charge on the O of water. [btw there is no homolysis involved, that generates radicals, and there is no reasonable path to generate hydride ions] The second step seems to require the participation of a base this may be loosely described as an E2 reaction where a proton is removed from the protonated O atom by another water molecule and the developing negative charge on the other oxygen expels the chloride ion. This mechanism[if plausible] requires enough water for active solvation. This mechanism possibly explains the success of the Schotten-Bauman method where base is added to the reaction as a "catalyst" [tho it is consumed]. If water is limited the base may be the attached chlorine and references do state that dry reactions evolve HCl gas. These are my thoughts on the reaction; library research is in order.


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