For Daniel Neff of Wachtell, Lipton, Rosen & Katz, Wednesday's announcement that client Airgas Inc. will be acquired by France's Air Liquide S.A. for $10.3 billion brings more than the usual satisfaction. Five years earlier, Airgas, Neff and his team at Wachtell were in the midst of one of the longest and most tenacious corporate battles of the century—fending off a hostile takeover attempt by Air Products and Chemicals Inc. that dragged on for 16 months.

Airgas and Wachtell prevailed, with the Delaware Court of Chancery issuing an important ruling validating Airgas' poison pill defense, and Air Products walking away empty-handed. Air Liquide's all-cash offer of $143 a share is 75 percent higher than the final price that Air Products offered in December 2010 (though, as Bloomberg's Tara Lachapelle points out, the S&P 500 has risen 92 percent in that time). Airgas is the largest U.S. supplier of industrial gases used in welding and health care.

“We view this as a total vindication of the law and the outcome from four years ago,” said Neff, who is taking the lead for Airgas in the Air Liquide transaction. He notes that the earlier battle with Air Products, represented by Cravath, Swaine & Moore, was the most challenging of his career.