Question

Classify each amine reaction as acid–base or condensation and list its products. a. \(\mathrm{CH}_{3} \mathrm{NHCH}_{3}+\mathrm{HCl} \longrightarrow\) b. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH} \longrightarrow\) c. \(\mathrm{CH}_{3} \mathrm{NH}_{2}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow\)

Short answer

The reaction in (a) is acid-base with the product \(\mathrm{CH}_3\mathrm{NH}_2\mathrm{CH}_3^+\mathrm{Cl}^-\). The reaction in (b) is condensation resulting in \(\mathrm{CH}_3\mathrm{CH}_2\mathrm{NHCOCH}_2\mathrm{CH}_3\) and H2O. The reaction in (c) is acid-base, yielding \(\mathrm{CH}_3\mathrm{NH}_3^+\) and \(\mathrm{HSO}_4^-\) or \(\mathrm{SO}_4^{2-}\).

Step-by-step solution

Classify the Reaction in (a)

To classify the reaction of \(\mathrm{CH}_3\mathrm{NHCH}_3\) with \(\mathrm{HCl}\), we need to identify if the reaction involves proton transfer or the formation of a new compound through the combination of two molecules. \(\mathrm{HCl}\) is an acid and will likely donate a proton (H+) to the amine group (NH), which is a base. Thus, this reaction is an acid-base reaction where the amine will be protonated.

Identify the Products of Reaction (a)

The amine \(\mathrm{CH}_3\mathrm{NHCH}_3\) will accept a proton to form a charged ammonium species. The product will be an ammonium chloride salt, \(\mathrm{CH}_3\mathrm{NH}_2\mathrm{CH}_3^+\mathrm{Cl}^-\). This occurs because the nitrogen atom in the amine has a lone pair that can bond with the hydrogen from hydrochloric acid.

Classify the Reaction in (b)

The reaction of \(\mathrm{CH}_3\mathrm{CH}_2\mathrm{NH}_2\) with \(\mathrm{CH}_3\mathrm{CH}_2\mathrm{COOH}\) involves the amine group reacting with a carboxylic acid. This type of reaction typically forms an amide linkage with the release of water, which classifies it as a condensation reaction, specifically amidation.

Identify the Products of Reaction (b)

When the amine group reacts with the carboxylic acid, the nitrogen will attack the carbonyl carbon of the acid, releasing a water molecule and forming an amide bond. The product will be an amide, \(\mathrm{CH}_3\mathrm{CH}_2\mathrm{NHCOCH}_2\mathrm{CH}_3\), along with water (H2O) as a byproduct.

Classify the Reaction in (c)

The reaction of \(\mathrm{CH}_3\mathrm{NH}_2\) with \(\mathrm{H}_2\mathrm{SO}_4\) involves the basic amine reacting with the acidic sulfuric acid, indicating it is likely another acid-base reaction. The amine will accept a proton from \(\mathrm{H}_2\mathrm{SO}_4\).

Identify the Products of Reaction (c)

The nitrogen in the amine will take a proton from the sulfuric acid, leading to the formation of an ammonium ion and the sulfate ion as products. The resulting compounds are \(\mathrm{CH}_3\mathrm{NH}_3^+\) and \(\mathrm{HSO}_4^-\), with the potential for a second protonation leading to \(\mathrm{CH}_3\mathrm{NH}_3^+\) and \(\mathrm{SO}_4^{2-}\) if enough amine is present.

Key concepts

Acid-Base Reactions with Amines

Understanding acid-base reactions with amines is crucial for grasping fundamental organic chemistry. An amine is a compound that features a nitrogen atom with a lone pair of electrons, making it a base capable of accepting a proton (H+). An acid, such as HCl, donates this proton, and when it reacts with an amine, a proton transfer occurs, creating an ammonium salt. For example, when dimethylamine (CH3NHCH3) reacts with hydrochloric acid (HCl), the nitrogen’s lone pair accepts a proton, forming dimethylammonium chloride (CH3NH2CH3^+Cl^-).
This kind of reaction is essential in the biological functioning of amino acids and proteins, and in industrial processes like the production of pharmaceuticals. In essence, acid-base reactions are proton transfer processes that result in new ionic compounds.

Condensation Reactions Involving Amines

Condensation reactions are another vital process involving amines, especially in the formation of larger molecules through the bonding of smaller ones while eliminating a small molecule like water or alcohol. In the case of amines, they often engage in condensation with carboxylic acids to form amides. For example, when ethylamine (CH3CH2NH2) reacts with acetic acid (CH3COOH), they undergo a condensation reaction to produce an amide [CH3CH2NHCOC2H5] and water.

Such reactions are not only central to the synthesis of complex organic molecules but are also fundamental to biochemistry, as they are key to the formation of proteins from amino acids.

Proton Transfer Mechanism in Amine Reactions

The mechanism of proton transfer in amine reactions is an essential concept that hinges on the idea of acid-base interaction. When an amine (a base) encounters an acid, it readily accepts a proton due to the electron-rich nitrogen. This is evident in the reaction where methylamine (CH3NH2) and sulfuric acid (H2SO4) combine. The amine seizes a proton from the acid, forming an ammonium sulfate salt.
Proton transfer reactions are omnipresent in chemical and biological systems, affecting pH levels and playing a significant role in enzyme catalysis and energy transfer within cells.

Amide Formation from Amine Condensation

The formation of amides via amine condensation is a specific type of reaction where an amine and a carboxylic acid or ester combine, releasing water and forming an amide bond. This bond formation is central to organic synthesis and peptide bond formation in biology. For instance, the reaction between ethylamine and acetic acid produces acetamide and water.

The underpinning principle is the nucleophilic attack of the amine on the carbonyl carbon of the acid or ester, hence forming the amide linkage. This process is vital for creating polymers, pharmaceuticals, and is the foundational reaction in the construction of proteins from amino acids in living organisms.