Question

Using your roadmap as a guide, show how to convert 2-methylpentane into 2-me- thylS-pentanote Show all reagents needed and all molecules synthesized along the way. CCC(C)C(O)CC 2-Methylpentane 2-Miethy13-pentanone Reactions in Context

Short answer

Question: Outline the steps and reagents required to convert 2-methylpentane into 2-methyl-3-pentanone. Answer: The conversion of 2-methylpentane into 2-methyl-3-pentanone requires the following steps and reagents: 1. Perform a halogenation reaction using N-bromosuccinimide (NBS) to obtain 2-bromo-2-methylpentane. 2. Convert the alkyl halide into a nitrile using sodium cyanide (NaCN) to get 2-cyano-2-methylpentane. 3. Hydrolyze the nitrile using sodium hydroxide (NaOH) and water to form 2-methyl-3-pentanoic acid. 4. Perform a reduction reaction using Pd/C (palladium on carbon) to obtain the target compound, 2-methyl-3-pentanone.

Step-by-step solution

Identify the target functional group

The target functional group in this case is a ketone (2-methyl-3-pentanone). To form a ketone, we need to oxidize a secondary carbon atom in the 2-methylpentane molecule.

Perform a halogenation reaction

To introduce a reactive site on the molecule, we will perform a halogenation reaction using N-bromosuccinimide (NBS) and a radical initiator like benzoyl peroxide. 2-methylpentane + NBS -> 2-bromo-2-methylpentane

Convert the alkyl halide to a nitrile

Next, we will convert the alkyl halide (2-bromo-2-methylpentane) into a nitrile using sodium cyanide (NaCN). 2-bromo-2-methylpentane + NaCN -> 2-cyano-2-methylpentane

Hydrolyze the nitrile to a carboxylic acid

The nitrile (2-cyano-2-methylpentane) will be hydrolyzed to form a carboxylic acid. This can be achieved by using a strong base like sodium hydroxide (NaOH) and water. 2-cyano-2-methylpentane + NaOH + H2O -> 2-methyl-3-pentanoic acid

Perform a reduction reaction

Finally, we will perform a reduction reaction to convert the carboxylic acid (2-methyl-3-pentanoic acid) into the desired ketone (2-methyl-3-pentanone). This can be achieved using either Pd/C (palladium on carbon) or LAH (lithium aluminum hydride). In this case, we will use Pd/C. 2-methyl-3-pentanoic acid + Pd/C -> 2-methyl-3-pentanone Through these steps and using the mentioned reagents, we have successfully converted 2-methylpentane into 2-methyl-3-pentanone.

Key concepts

Functional Group Conversion

Functional group conversion is a cornerstone technique in organic chemistry, allowing chemists to transform one functional group into another to synthesize a wide variety of compounds. This is achieved through specific reactions that introduce or modify the functional groups within a molecule.

For instance, in the transformation of 2-methylpentane into 2-methyl-3-pentanone, various functional group conversions are necessary. Initially, the molecule 2-methylpentane, which is a hydrocarbon, undergoes conversion to introduce a halogen, later to form a nitrile, and finally to synthesize the desired ketone group. Each step is crucial for the next, creating an interlinked sequence of transformations that guide the molecule from a simple hydrocarbon to a more complex oxygen-containing ketone.

Halogenation Reaction

The halogenation reaction is a fundamental chemical transformation in which a halogen atom, such as bromine or chlorine, is introduced into an organic molecule. This is often used as a stepping stone in multi-step synthesis. Particularly in the given exercise, a bromine atom is added to 2-methylpentane using N-bromosuccinimide (NBS) and a radical initiator like benzoyl peroxide to form 2-bromo-2-methylpentane.

Why NBS and Benzoyl Peroxide?

These specific reagents are chosen to achieve a selective and controlled bromination. NBS is particularly useful for brominating alkyl groups at allylic or benzylic positions, making it the reagent of choice for this conversion. The radical initiator then helps in generating the reactive species that facilitate the addition of bromine to the molecule.

Nitrile Hydrolysis

Nitrile hydrolysis is a chemical process that converts nitrile groups into carboxylic acids or amides, depending on the reaction conditions. In the synthesis of 2-methyl-3-pentanone, 2-cyano-2-methylpentane (a nitrile) is transformed into a carboxylic acid.

This change is brought about by reacting the nitrile with a strong base, such as sodium hydroxide (NaOH), and water. The reaction breaks the triple bond of the nitrile and replaces it with a carboxylic group, making it a crucial stage in the pathway towards synthesizing 2-methyl-3-pentanone from 2-methylpentane. Hydrolysis of a nitrile to a carboxylic acid is not only useful in this particular sequence but is also a valuable reaction for the production of many other pharmaceuticals and fine chemicals.

Reduction Reaction

A reduction reaction in organic chemistry is the process of adding hydrogen to a molecule or removing oxygen from it (or doing both), typically with the aid of a reducing agent. In the context of the exercise, the final step in the synthesis of 2-methyl-3-pentanone involves reducing a carboxylic acid into a ketone.

Using Pd/C, which is palladium on carbon, or LAH (lithium aluminum hydride), the carboxylic acid (2-methyl-3-pentanoic acid) is transformed into the desired ketone. The choice of reducing agent is critical; Pd/C is a heterogeneous catalyst and is often preferred for its ease of handling and its applicability in various reduction reactions, such as the conversion of carboxylic acids to aldehydes or ketones. The ketone product formed is significant as ketones are vital compounds in biochemistry and industry, often serving as solvents, intermediates in pharmaceutical synthesis, and as precursors to other complex molecules.