Paul wrote this letter approximate a year after 1 Corinthians (inferred from 2 Corinthians 12:14, 13:1-2). It most likely was written after a visit to Corinth. Paul was now in Macedonia, which is to the north of Ephesus. The date this letter was written is approximately A.D. 55.
Encountering the New Testament, Walter A. Elwell / Robert W. Yarbrough, 1998, Baker Books, page 293
A Survey of the New Testament, Third Edition, Robert H. Gundry, 1994, A Survey of the New Testament, Third Edition, Robert H. Gundry, 1994, Zondervan, page 370