The reaction of butylamine (CH₃CH₂CH₂CH₂NH₂) with hydrochloric acid (HCl) is a simple acid-base reaction. Butylamine acts as a base, accepting a proton (H⁺) from the acid. This results in the formation of butylammonium chloride salt.

Here's the equation:

CH₃CH₂CH₂CH₂NH₂ + HCl → CH₃CH₂CH₂CH₂NH₃⁺Cl⁻

* CH₃CH₂CH₂CH₂NH₂ represents butylamine

* HCl represents hydrochloric acid

* CH₃CH₂CH₂CH₂NH₃⁺Cl⁻ represents butylammonium chloride (the salt formed)

Explanation:

* The lone pair of electrons on the nitrogen atom of butylamine accepts a proton (H⁺) from HCl.

* This creates a positively charged butylammonium ion (CH₃CH₂CH₂CH₂NH₃⁺).

* The chloride ion (Cl⁻) from HCl remains as a counterion, forming the salt.

Important Note: This reaction is an example of a neutralization reaction, as a base and an acid react to form a salt and water. However, since butylamine is a weak base, the resulting solution will be slightly acidic.