Question

The final major product \(\mathrm{Q}\) in the following reaction is \(+\mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{NH}_{2} \longrightarrow \mathrm{P} \stackrel{\left(\mathrm{NH}_{4}\right)_{2} \mathrm{~S}}{\longrightarrow} \mathrm{Q}\)

Short answer

The final major product Q in the reaction is \(\mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{SH}\), which is also known as 2-aminoethyl hydrogen sulfide or 2-mercaptoethylamine.

Step-by-step solution

Determine the reactants

The given reactants are: 1. \(\mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{NH}_{2}\): This is 1,2-diaminoethane, also known as ethylenediamine. 2. \(\left(\mathrm{NH}_{4}\right)_{2}\mathrm{S}\): This is ammonium sulfide.

Identify the main functional groups

We have the following main functional groups in the given reactants: 1. Ethylenediamine has two amine groups, \(\mathrm{NH}_{2}\), connected by an ethylene (or \(\mathrm{CH}_{2}-\mathrm{CH}_{2}\)) group. 2. Ammonium sulfide is composed of two ammonium (\(\mathrm{NH}_{4}^{+}\)) cations and one sulfide (\(\mathrm{S}^{2-}\)) anion.

Predict the intermediate product P

Since ammonia (\(\mathrm{NH}_{3}\)) acts as a mild reducing agent, and considering the ammonium sulfide is used in the reaction, this reaction likely involves the formation of hydrogen sulfide (H2S) as an intermediate, which will then reduce the ethylenediamine.

Determine the final product, Q

Considering the intermediate formation of hydrogen sulfide, we can now write down the two steps in this reaction: Step 1: Ethylenediamine reacts with ammonium sulfide: \\ $\mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{NH}_{2} +\\ \left(\mathrm{NH}_{4}\right)_{2}\mathrm{S} \longrightarrow \mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{NH}_{3^{+}-S^{-}}$ Step 2: Reduction of \(\mathrm{NH}_{3^{+}-S^{-}}\) by hydrogen sulfide (H2S): \\ \(\mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{NH}_{3^{+}-S^{-}} + \mathrm{H}_{2}\mathrm{S} \longrightarrow \mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{SH} + \mathrm{NH}_{4}^{+}\) So, the final major product Q is: \(\mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{SH}\), which is also known as 2-aminoethyl hydrogen sulfide or 2-mercaptoethylamine.

Key concepts

Amines and Their Reactions

Amines are a crucial class of organic compounds characterized by a nitrogen atom attached to one or more alkyl or aryl groups. They can be classified as primary, secondary, or tertiary amines, depending on the number of organic groups connected to the nitrogen atom. In the given reaction, ethylenediamine (\(\mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{NH}_{2}\)) is our compound of interest, and it is a primary amine due to having two amine groups bonded to an ethylene chain.
Amines often participate in reactions due to their basic nature. They can act as nucleophiles and partake in several types of reactions, including formation of amides, reductive amination, and reactions with acyl chlorides. In the exercise, ethylenediamine serves as the substrate that reacts with ammonium sulfide. Understanding amines' reactivity is crucial to predicting the outcome of such reactions.
Ammonia or derivatives like ethylenediamine can also function as reducing agents, which introduces complexity to the possible reaction pathways. In the solution, we observe that amines engage with sulfur to eventually form a C-S bond, highlighting their versatility in organic synthesis.

Sulfide Compounds

Sulfides are compounds consisting of sulfur bonded to one or more elements. Organic sulfides are a subset where sulfur is bonded to carbon. In the reaction from the exercise, gain of sulfur into the ethylenediamine backbone is facilitated by ammonium sulfide (\((\mathrm{NH}_{4})_{2}\mathrm{S}\)).
Sulfides can participate in a wide variety of reactions due to their ability to donate sulfur atoms. The \(\mathrm{S}^{2-}\) ion in ammonium sulfide easily reacts with electrophilic centers, making it valuable for introducing sulfur into organic molecules. This property is essential in synthesizing sulfide compounds where the sulfur is on an organic chain.
In this particular scenario, the sulfide ion plays a role in converting the diamine into an amine-sulfide compound. The reaction mechanism involves the transfer of sulfur to form an organic sulfide, exemplified by the end product known as 2-aminoethyl hydrogen sulfide or 2-mercaptoethylamine.

Intermediate Steps in Reactions

Organic reactions often proceed through a series of intermediate steps before reaching the final product. Understanding these steps unlocks the mechanism of how reactants transform into products.
In this exercise, we see that hydrogen sulfide (\(\mathrm{H}_2\mathrm{S}\)) likely forms as an intermediate, acting to reduce and rearrange the components into the desired products. Intermediates can be short-lived species holding a pivotal role in ensuring the reaction progresses in the intended direction.
The intermediate in this particular reaction assists in generating a sulfur bridge between ethylenediamine chains, transforming it into an organic sulfide. This procedure involves critical steps where sulfur initially binds and modifies the nitrogen ends to form a C-S bond. Understanding intermediates helps in predicting outcomes and troubleshooting reactions by revealing hidden pathways often overlooked in single-step analyses.