Question

Write an equation for the formation of the free amine from butylammonium chloride by reaction with aqueous \(\mathrm{OH}^{-}\).

Short answer

\(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_3\mathrm{Cl} + \mathrm{OH}^- \rightarrow \mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2 + \mathrm{H}_2\mathrm{O} + \mathrm{Cl}^-\)

Step-by-step solution

Identify the reactants

The reaction involves butylammonium chloride and hydroxide ions (\(\mathrm{OH}^{-}\)). Butylammonium chloride has the chemical formula \(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_3\mathrm{Cl}\).

Determine the products

The hydroxide ion (\(\mathrm{OH}^{-}\)) will react with butylammonium chloride to produce the free amine, butylamine (\(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2\)), along with water (\(\mathrm{H}_2\mathrm{O}\)) and chloride ion (\(\mathrm{Cl}^−\)).

Write the chemical equation

Combine the reactants and products into a chemical equation: \[\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_3\mathrm{Cl} + \mathrm{OH}^- \rightarrow \mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2 + \mathrm{H}_2\mathrm{O} + \mathrm{Cl}^-\].

Confirm conservation of mass and charge

Ensure that the number of each type of atom is the same on both sides of the equation and that the charges are balanced. Both conditions are satisfied in the equation presented.

Key concepts

Chemical Equations

Chemical equations provide a simple way to describe chemical reactions using symbols and formulas. They detail the reactants—substances that start a reaction—on the left side, and the products—substances formed by the reaction—on the right. Using an arrow (\(\rightarrow\)) indicates the direction of the reaction. In our original exercise, butylammonium chloride reacts with hydroxide ions to produce butylamine, water, and chloride ions.
Balancing a chemical equation is crucial. It ensures the Law of Conservation of Mass is upheld, meaning no atoms are lost or gained. Every element must have an equal number on both sides of the equation. Additionally, charges should balance. For the presented equation, this means checking that the overall charge on both sides is the same. In our given equation, we have \(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_3\mathrm{Cl} + \mathrm{OH}^- \rightarrow \mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2 + \mathrm{H}_2\mathrm{O} + \mathrm{Cl}^-\).
It's balanced: each element appears equally on either side and the charges net to zero for both reactants and products.

Amines

Amines are important organic compounds derived from ammonia (\(\mathrm{NH}_3\)), where one or more hydrogen atoms are replaced by alkyl or aryl groups. They are categorized based on the number of carbon-containing groups that replace hydrogen atoms in ammonia:

• Primary amines, where one hydrogen atom is replaced by an organic group.
• Secondary amines, where two hydrogen atoms are replaced.
• Tertiary amines, where all three hydrogen atoms are replaced.

In the mentioned exercise, we start with butylammonium chloride, which contains a butyl group attached to an ammonium ion. Upon reaction with \(\mathrm{OH}^-\), a hydrogen ion is removed, producing butylamine (\(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2\)), a primary amine. Amines have distinct properties due to the presence of a nitrogen atom with a lone pair of electrons, making them polar and often basic.
In practical chemistry and biological systems, amines play critical roles in forming amino acids and neurotransmitters. Their reactivity and functionality allow them to participate in diverse reactions.

Reaction Mechanisms

Reaction mechanisms clarify how a chemical reaction occurs at a molecular level. They describe the step-by-step sequence of elementary reactions that lead to product formation. Understanding these mechanisms provides insight into how bonds break and form, which intermediates are created, and how different conditions affect the reaction rate.
For the given exercise, the transformation of butylammonium chloride to butylamine involves an acid-base reaction. Here, the hydroxide ion (\(\mathrm{OH}^-\)) acts as a base and removes a proton (\(\mathrm{H}^+\)) from butylammonium.The mechanism can be understood as:

• The \(\mathrm{OH}^-\) ion approaches the \(\mathrm{NH}_3^+\) part of the molecule.
• It forms a bond with a hydrogen ion, removing it from the molecule, forming water.
• This forms the neutral amine, butylamine (\(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2\)) along with \(\mathrm{H}_2\mathrm{O}\) and an isolated chloride ion (\(\mathrm{Cl}^-\)).

Such acid-base mechanisms are common in organic chemistry, demonstrating how basic conditions can deprotonate amines to liberate the free amine form.