In what part on The Cather in the Rye does Holden just want to die and be alone?
Holden is depressed, so there are several parts of the novel where he makes comments about death and dying. He becomes obsessed with the fact that he thinks he is going to die soon, so that is why he decides to go home for a final visit, to see Phoebe, but avoid his parents. After fleeing Mr. Antolini's house, Holden spends the night in Grand Central Station. Mr. Antolini has freaked him out by first telling him that he is the type of person who may die nobly for a highly unworthy cause, and then stroking Holden's head, leading Holden to think he is making advances.
Holden sends a note to Phoebe and tells her to meet him. While he is waiting for her, he becomes extremely agitated and imagines that every time he tries to cross the street, he will die. He eventually passes out.
A couple of quotes about death are in Chapter 18:
Anyway, I'm sort of glad they've got the atomic bomb invented. If there's ever another war, I'm going to sit right the hell on top of it. I'll volunteer for it, I swear to God I will.
and in Chapter 20:
Boy, when you're dead, they really fix you up. I hope to hell when I do die somebody has sense enough to just dump me in the river or something. Anything except sticking me in a goddam cemetery. People coming and putting a bunch of flowers on your stomach on Sunday, and all that crap. Who wants flowers when you're dead? Nobody.
Read about it here on eNotes.