Over the last week, a hundred or so people crammed into a law firm’s offices high in the General Motors Building on Fifth Avenue, drafting plans to merge Dow Chemical and DuPont.

Yet all the work of those bankers and lawyers in combining two industrial titans, with a shared history of more than three centuries, will ultimately go toward a much bigger goal: breaking up the newly united chemical company.

As Dow and DuPont formally announced their merger, the two companies made clear that they intend to separate into three companies, a path expected to be littered with complex deals, thousands of job cuts and months of government scrutiny.