The reason that an argon environment is used to conduct reactions using a Lewis acid is due to the fact that Lewis acids are often unstable in air and/or in the presence of water. Lewis acids are electron acceptors and molecules like water which has a number of lone-pair electrons on the oxygen atom are able to easily donate electrons thereby reacting with the Lewis acid. Using an argon atmosphere ensures that no water or other potential electron donors are present.

Argon is an inert gas. An argon atmosphere is used to protect chemicals that are sensitive to oxygen and water. In many cases,nitrogen gas can also be used as an inert atmosphere. Most Lewis acids are sensitive to water. Because of the lone electron pairs on the oxygen atom in a water molecule, water can act as a Lewis base and react with some Lewis acids. In other cases, water can hydrolyze the Lewis acid. For example, the lewis acid PC_l5 reacts with water to form POC_{l3 and 2 HCl (hydrogen chloride gas). However, some Lewis acids have been discovered that can be used in reactions with water as the solvent. This is quite useful because water is much more environmentally friendly than organic solvents.}