* Credit Suisse, Goldman Sachs acting as bookrunners
* About 18 mln shares to be placed at 86.25-88.46 euros
* Covestro shares down in late Frankfurt trade (Adds detail on placement, context)
FRANKFURT/MUNICH, Jan 10 (Reuters) - German drugs and pesticides group Bayer on Wednesday said it was selling more of its stake in chemicals group Covestro, aiming to raise about 1.5 billion euros ($1.8 billion) in an accelerated bookbuilding process.
Bayer has said it wants to fully dispose of its holding in Covestro, which it demerged in 2015, in the medium term. It has raised 4.7 billion euros in four previous placements.
Credit Suisse and Goldman Sachs are acting as joint bookrunners for the overnight placement, which is aimed at institutional investors and marks the fifth time in 10 months that Bayer has moved to sell Covestro stock.
About 18 million shares will be placed at 86.25-88.46 euros apiece for proceeds of 1.55-1.59 billion euros, one of the banks said in a note to investors. Bayer has agreed to a 90-day lockup period.
Based on Covestro's current market value, this would amount to as much as 8.9 percent, which would bring Bayer's direct stake, currently at 24.6 percent, to below 16 percent. The Bayer Pension Trust holds a further 8.9 percent stake.
Covestro shares were 1.9 percent lower in late trading in Frankfurt, while those of Bayer were down 1.3 percent.
$1 = 0.8358 euros Reporting by Christoph Steitz and Alexander Huebner. Editing by Jane Merriman