Hexion Specialty Chemicals Inc. has sued to get out of its $10.6 billion deal to buy Huntsman Corp. claiming the merged company would be insolvent.

When Hexion, which is owned by Apollo Management LP, disclosed the suit after the market closed Wednesday, it confirmed long-running suspicions the deal might fall apart. Huntsman shares had been trading at more than a $7 spread to the $28 per share bid. The deal had an April termination date that was extended to July 4. It could be extended further, to October under some circumstances.