Dow Chemical and DuPont are expected to announce a merger by Thursday, in a deal that would be one of the biggest in the best-ever year for mergers and acquisitions.

Sources told CNBC that a potential tie-up between the storied chemicals behemoths would be structured as a merger of equals.

The expected deal, which was first reported by The Wall Street Journal on Tuesday night, would likely be followed by a breakup of the combined entity, with separate businesses created to house the agricultural, materials services and specialty products operations.

Dow and DuPont have market capitalizations of almost $59 billion each.