Sigma-Aldrich, headquartered in St Louis in the US, is already the world's largest supplier of biochemicals and organic chemicals to research laboratories, clocking up sales of $2.7 billion last year.

Merck has not shied away from splashy takeovers in the past. In 2015, the company agreed to buy US lab equipment supplier Sigma-Aldrich for $17 billion, its biggest-ever deal. In 2019, Merck ...