It’s hard to explain… I hope I made a little sense…

“Alexis de Tocqueville was a nineteenth century French philosopher whose classic work “Democracy in American” was based on observations during a tour of the United States.”

You will notice the above has a better flow and has the same meaning but less wordy. Are you sure the name of his classic work was “…American” rather than “…America”?

However, should you choose to use the original sentence, be sure to use “who” rather than “whom.”

I hope this helps you.

You don’t need appositive starting with Alexis De Tocqueville French is a capital letter, again you don’t need appositive for democracy