No, this is not possible. This is due to the fact that commands cannot detect things like chat. If you want to detect chat, you could use Bukkit. There are many Bukkit plugins that allow you to detect players entering commands into chat and processing them. An example will be [here][1]. The good part about Bukkit is that vanilla, non-modded clients can connect without any problems. However, bukkit was taken down due to a [DMCA request][2]. An alternertive would be making your own plugin with [Canarymod][3], which has similar functionality as Bukkit. Do note that it it is not as popular.

  [1]: http://dev.bukkit.org/bukkit-plugins/easy-warp/
  [2]: https://github.com/github/dmca/blob/master/2014/2014-09-05-CraftBukkit.md
  [3]: http://canarymod.net/releases