Question

Show how one could synthesize-and resolve methylethylallylamine oxide from allylamine, with the knowledge that amine oxides are somewhat basic substances having \(\mathrm{K}_{\mathrm{B}}\) values at about \(10^{-11}\).

Short answer

To synthesize methylethylallylamine oxide from allylamine, perform two reactions: 1. Alkylation: React allylamine with methyl iodide (CH3I) and sodium ethoxide (NaOEt) under anhydrous conditions and an inert solvent, such as THF or DCM, at low temperature. The reaction is: \( H_2C=CH-CH_2NH_2 + CH_3I + NaOEt \rightarrow CH_3CH_2NHCH_2CH=CH_2 + NaI + H_2O \). 2. Oxidation: React methylethylallylamine with hydrogen peroxide (H2O2) and a weak base like sodium bicarbonate (NaHCO3) to maintain the pH. The reaction is: \( CH_3CH_2NHCH_2CH=CH_2 + H_2O_2 \rightarrow CH_3CH_2N(CH_2CH=CH_2)O + H_2O \). Amine oxides are somewhat basic (\(\mathrm{K}_{\mathrm{B}}\) values around \(10^{-11}\)), but their basicity is weaker than that of the corresponding amines due to the partial positive charge on the nitrogen atom.

Step-by-step solution

Identify the chemical structures of allylamine and methylethylallylamine oxide

First, we need to determine the chemical structures of both compounds: - Allylamine (\( H_2C=CH-CH_2NH_2 \)) is an organic compound with a double bond between the first and second carbons and an amine group on the third carbon. - Methylethylallylamine oxide (\( CH_3CH_2NHCH_2CH=CH_2 \)) has a methyl group (CH3) and ethyl group (CH2CH3) attached to the nitrogen atom and is an oxide.

Determine the difference between the two structures

The main difference between the two structures is that allylamine (\(H_2C=CH-CH_2NH_2\)) contains only an amine group, while methylethylallylamine oxide (\( CH_3CH_2NHCH_2CH=CH_2\)) has an amine group with a methyl group and an ethyl group attached to the nitrogen atom.

Find a suitable reaction to convert allylamine into methylethylallylamine oxide

To convert allylamine into methylethylallylamine oxide, we need to perform two reactions: 1. Alkylation: The first reaction is the alkylation of allylamine, in which we add both a methyl group and an ethyl group to the nitrogen atom. Following are the reagents and conditions required for this reaction: - Allylamine - Methyl iodide (CH3I) and sodium ethoxide (NaOEt) as alkylating agents - Anhydrous conditions and an inert solvent, such as THF or DCM - Low temperature to control the extent of alkylation The reaction will be as follows: \( H_2C=CH-CH_2NH_2 + CH_3I + NaOEt \rightarrow CH_3CH_2NHCH_2CH=CH_2 + NaI + H_2O \) 2. Oxidation: The second reaction is the oxidation of the amine to form the amine oxide: - Methylethylallylamine as the substrate - Hydrogen peroxide (H2O2) as an oxidizing agent - A weak base such as sodium bicarbonate (NaHCO3) to maintain the pH of the reaction mixture The reaction will be as follows: \( CH_3CH_2NHCH_2CH=CH_2 + H_2O_2 \rightarrow CH_3CH_2N(CH_2CH=CH_2)O + H_2O \)

Discuss the basicity of amine oxides and their \(\mathrm{K}_{\mathrm{B}}\) values

Amine oxides are somewhat basic substances, with \(\mathrm{K}_{\mathrm{B}}\) values around \(10^{-11}\). The basicity of amine oxides arises from the lone pair of electrons on the nitrogen atom, which can act as a Lewis base and accept a proton (H+) from an acid, forming a conjugate acid. However, since amine oxides have a partial positive charge on the nitrogen atom due to the oxygen atom's higher electronegativity, their basicity is weaker than that of the corresponding amines.

Key concepts

Allylamine

Allylamine is a fundamental compound in organic chemistry, easily recognized by its formula,\( H_2C=CH-CH_2NH_2 \). It consists of a simple structure with a carbon-carbon double bond and a primary amine group. The presence of the double bond gives allylamine its unique reactivity.
Allylamine is an unsaturated amine with a flexible molecular structure, allowing it to undergo various chemical transformations. These characteristics make it an excellent starting material for syntheses aiming to introduce new functional groups.
In the transformation to methylethylallylamine oxide, allylamine serves as the base molecule. This conversion involves a series of chemical reactions including alkylation and oxidation, transforming it into a more complex amine oxide.

Alkylation Chemistry

Alkylation is a crucial step in turning allylamine into methylethylallylamine. This reaction introduces alkyl groups to the nitrogen atom, increasing the compound's complexity and potential functionality. Two particular alkylating agents are used here: methyl iodide and sodium ethoxide. These agents benchmark their roles by attaching a methyl group and an ethyl group to the nitrogen.
Conditions are meticulously controlled during the alkylation process. An inert solvent, such as THF (tetrahydrofuran), is employed alongside anhydrous conditions to ensure the reaction proceeds without unwanted side reactions. In addition, low temperatures help manage the extent of alkylation, preventing over or multiple alkylations, which could lead to a mixture of products.
This well-crafted alkylation step is vital because it not only expands the functionality of the original allylamine but also sets the stage for subsequent oxidation reactions needed to form the final methylethylallylamine oxide.

Oxidation Reactions

In the final step of synthesizing methylethylallylamine oxide from allylamine, an oxidation reaction occurs. After alkylation, oxidation converts the amine into its corresponding oxide. This transformation introduces an oxygen atom into the compound, leading to the creation of an amine oxide. Hydrogen peroxide (\(H_2O_2\)) is used as the oxidizing agent in this conversion.
The oxidation process often requires the presence of a mild base like sodium bicarbonate (\(NaHCO_3\)), to maintain a favorable pH throughout the reaction. The environment necessary for oxidation must be controlled to avoid degradation of the product.
Amine oxides obtained through this method possess interesting chemical properties. They have lower basicity compared to their parent amines due to the oxygen's electronegativity. This property is reflected in their basicity constant \(K_B\), which has a much lower value around \(10^{-11}\), indicative of their weaker ability to accept protons compared to primary amines.