The boiling point is the temperature at which a liquid turns into a gas. The boiling point of a substance depends on the strength of the intermolecular forces in the substance.

N-methylmorpholine is a cyclic tertiary amine. It has a boiling point of 115-116 °C at 750 mmHg. This is because the molecules of N-methylmorpholine are held together by strong hydrogen bonds. The hydrogen bonds between N-methylmorpholine molecules are strong enough to prevent the molecules from escaping into the gas phase until the temperature rises to 115-116 °C.