I am currently working on an undergraduate experiment to form a cyclic acetal. We were asked to use p-toluenesulfonic acid as a catalyst rather than sulfuric acid. This seems to be common practice when forming an acetal, but the reasons given are not satisfactory to me.

Being a solid, it is more easy to handle, I can understand that. But another reason given is that it is less dehydrating than sulfuric acid. In the formation of acetals, water is being formed as a product, thus dehydrating effects of the acid would be productive. In this case, it would not make a difference since I am using a water separator, but still I am wondering why dehydrating effects of the acid are not desired.

Is there any other reason I am missing? If so, I would also be happy about literature references.

  • 2
    $\begingroup$ pTsOH is better soluble in organic solvents than sulfuric acid, and not as strong dehydrating than sulfuric acid. Do you recall sulfuric acid's action on sugar example? Thus it is better to have some pTsOH well dissolved in the reaction mixture remove the water by Dean-Stark distillation. See if your school has access to Paquette's enyclopedia (there is an online-version, too [campus license?]) and continue from there. $\endgroup$
    – Buttonwood
    Jul 7, 2021 at 20:35


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