Grammatically speaking, number 1 is incorrect. That is called a "split infinitive" because you have put a word between "to" and the verb. With this rule in mind, number 2 is the right way to go, especially in formal, written English. That said, this very old rule is based on Old English trying to mimic Latin, which was more influential at the time, so some people feel it serves no useful purpose and ignore it. Also, in spoken English you will hear number 1 very frequently.