Question

How can diethyl sulfide \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{SC}_{2} \mathrm{H}_{5}\right)\) be prepared from a Grignard reagent?=

Short answer

Use ethyl halide to form a Grignard reagent, react it with sulfur, and then quench the intermediate to make diethyl sulfide.

Step-by-step solution

Understanding Grignard Reagents

Grignard reagents are organomagnesium compounds used to form carbon-carbon bonds. Typically, a Grignard reagent has the form:\[ \text{R-Mg-X} \]where \( \text{R} \) is an organic group and \( \text{X} \) is a halogen.

Preparing the Grignard Reagent

To form a Grignard reagent for diethyl sulfide synthesis, we first need an ethyl halide, \( \text{C}_2\text{H}_5\text{X} \). We react it with magnesium in anhydrous ether to form \( \text{C}_2\text{H}_5\text{MgX} \).

Reacting the Grignard Reagent with Sulfur

The formed Grignard reagent \( \text{C}_2\text{H}_5\text{MgX} \) is then reacted with elemental sulfur (\( \text{S} \)) to form the magnesium thioalkoxide intermediate \( \text{C}_2\text{H}_5\text{MgS} \text{C}_2\text{H}_5 \).

Quenching the Reaction

The intermediate \( \text{C}_2\text{H}_5\text{MgS} \text{C}_2\text{H}_5 \) can be quenched with water or dilute acid to yield diethyl sulfide \( \text{C}_2\text{H}_5\text{SC}_2\text{H}_5 \) by eliminating the magnesium ion.

Key concepts

Organomagnesium Compounds

Grignard reagents are fascinating organomagnesium compounds that play a crucial role in organic chemistry. These reagents consist of an organic group, often represented as \( \text{R} \), bonded with magnesium and a halogen. The general formula for a Grignard reagent is \( \text{R-Mg-X} \), where \( \text{X} \) can be any halogen, such as chlorine or bromine.
Grignard reagents are known for their high reactivity, especially towards various electrophiles. This makes them extremely useful for synthesizing a wide range of chemical structures.
One of the most pivotal roles of Grignard reagents is their ability to form carbon-carbon bonds, which are essential in constructing larger organic molecules.

Carbon-Carbon Bond Formation

The formation of carbon-carbon bonds is a fundamental step in organic synthesis. Grignard reagents excel in this area thanks to their reactivity. When a Grignard reagent approaches a molecule with a carbon atom that carries a positive partial charge, known as an electrophile, it can attach itself to this carbon, creating a new carbon-carbon bond.
This ability is invaluable in organic chemistry, as it provides a straightforward method to construct complex molecules from simpler ones. The versatility of Grignard reagents also means they can be used to introduce various functional groups into a molecule, depending on the nature of the organic group (\( \text{R} \)) attached to the magnesium in the reagent.

Ethyl Halide Preparation

To create a Grignard reagent necessary for the synthesis of diethyl sulfide, the preparation of an ethyl halide is required. Ethyl halides are simple compounds where an ethyl group (\( \text{C}_2\text{H}_5 \)) is bonded to a halogen atom.
The halogen can be chlorine, bromine, or iodine, depending on the desired reactivity and conditions. These halides are typically synthesized by reacting ethylene with the appropriate halogen acid, like hydrochloric acid or hydrobromic acid.
Once the ethyl halide \( \text{C}_2\text{H}_5\text{X} \) is obtained, it serves as a starting material to react with magnesium metal. The magnesium replaces the halogen to form the corresponding Grignard reagent in anhydrous ether.

Magnesium Thioalkoxide

Magnesium thioalkoxides are intermediates in the synthesis of organosulfur compounds using Grignard reagents. When the Grignard reagent \( \text{C}_2\text{H}_5\text{MgX} \) reacts with elemental sulfur, a thioalkoxide intermediate is formed: \( \text{C}_2\text{H}_5\text{MgS}\text{C}_2\text{H}_5 \).
This reaction is crucial as it introduces sulfur into the compound, opening the pathway for the creation of various sulfur-containing molecules. The sulfur atom bonds with the two ethyl groups from two separate molecules of the reaction mixture, forming a bridge with magnesium bound to it.
Magnesium thioalkoxides are key due to their ability to undergo further transformations, especially when quenched with water, leading to the final sulfide products.

Synthesis of Diethyl Sulfide

The synthesis of diethyl sulfide involves several straightforward but important steps. After forming the magnesium thioalkoxide intermediate, the final goal is to obtain pure diethyl sulfide \( \text{C}_2\text{H}_5\text{SC}_2\text{H}_5 \).
The magnesium ion in the thioalkoxide is typically removed by quenching the reaction mixture. This process involves adding water or a dilute acid, which reacts with the magnesium ion, leading to its removal and the liberation of the diethyl sulfide.
Quenching is an essential step as it helps eliminate any unwanted side reactions, ensuring the purity of the diethyl sulfide produced. This easy method makes diethyl sulfide a readily accessible and useful compound in various applications.