Journal won't allow PhD student to be corresponding author
It is an extremely weird policy, and I never heard of any journal having a policy like this one.

I couldn't find a "general rule governing corresponding authors" that would apply to all the journals of the American Chemical Society.

In 2012, the editor on chief of ACS Nano wrote, in an editorial called "Who Are Corresponding Authors?",


  In order to be accessible to those requesting information or materials, the corresponding authors must be stable in their positions and locatable. Unless students or postdocs have long-term positions, it is typically not appropriate for these authors to be corresponding authors, even if they serve the function of submitting the manuscript. (There are occasional exceptions, such as where the senior author has passed away.)


Cf. https://pubs.acs.org/doi/pdfplus/10.1021/nn301566x

Their policy (that doesn't say anything about having or not a diploma) seems really strict, and, in my opinion, outdated, but it answers your question


  What is the point of making someone corresponding author who doesn't have as much insights as I have?


Well, their idea (at least according to this editor) is that it is better to have a correspondent, even not aware of all the details of the publication, that no correspondent, because the "student without long-term position" left without leaving an address.