Wrong: Beaucoup des
Right: Beaucoup de
Explanation: Beaucoup des is not always wrong - just most of the time. Like other adverbs of quantity, beaucoup is nearly always followed by de, with no article:
- J'ai beaucoup de temps (I have a lot of time)
Tu as beaucoup d'amis (You have many friends)
C'est un détail de peu d'importance (It's a minor detail, a detail of little importance)
etc
- J'ai acheté une chemise dont beaucoup des boutons s'étaient détachés
(I bought a shirt that a lot of the buttons had come off of)
I'm talking about the specific buttons on this particular shirt
Beaucoup des idées de Jean-Luc sont intéressantes
(A lot of Jean-Luc's ideas are interesting)
I'm not referring to ideas in general, but rather the specific ideas that Jean-Luc has
Related lessons: Adverbs of quantity | Definite article | De vs du, de la, des

