Henry Rzepa's Blog

In the preceding post, I looked at a computed mechanism for the hydrolysis of a ketal by water. Of course, pure water consists of three potential catalysts, water itself or [H₂O], and the products of autoionisation, [OH^–] and [H₃O⁺]. The latter are in much smaller concentration, equivalent to a penalty of ~11.9 kcal/mol on any free energy barrier. Here I take a look at these ion-catalysed routes to see if that penalty can be overcome.

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The previous post was about an insecticide and made a point that the persistence of both insecticides and herbicides is an important aspect of their environmental properties. Water hydrolysis will degrade them, a typical residency time being in the order of a few days. I noted in passing a dioxepin-based herbicide[cite]10.1039/P29890001265[/cite] which contains a ketal motif and which in water can hydrolise to a ketone and alcohol. The reverse (acid catalysed) formation of a ketal is a staple of the taught organic chemistry curriculum. Here as a prelude to looking at the hydrolysis of that dioxepin, I take a look at a possible computational mechanism for the hydrolysis of 2,2-dimethoxypropane using pure water, without the help of acid or base.

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