Methylamine was an organic compound commonly used in the manufacture of methamphetamine. In gaseous form, it was toxic to humans and could potentially be used as a weapon.
After Roman failed to pay off his debt to Mishka, Mishka's enforcers Alik and Sasho visited Roman's brother Petro and coerced him into stealing a container of methylamine from the port where he worked. Petro turned to his friend "Borys" - actually Jack Bauer - for help, and Jack formed a plan to hijack the shipment before it arrived at the docks to be shipped out. When a nearby CIA station discovered the incident and obtained footage of Jack driving the truck, the station chief ordered his subordinates to focus on finding him, and told them Bauer likely meant to use the methylamine as a weapon. (Underground #1)