Shutdown xfce with a keystroke?

[ezzetabi]

I'd like adding a keystroke that shutdown my xfce returning to my 
virtual console that started X.

I tried adding to Setting->Window Manager->Keyboard the following 
command, but it does not work.
terminal "--command=kill -2 `pidof X`"

A terminal appears and disappears quickly and nothing happens. If I 
execute the same command from a terminal it works...
What I am doing wrong?

thanks