Question

When ethyl bromide and n-propyl bromide is allowed to react with sodium, in ether, they form: (a) Mixture of four alkanes (b) Mixture of three alkanes (c) Mixture of two alkanes (d) Single alkane

Short answer

The reaction results in a mixture of three alkanes.

Step-by-step solution

Understand the Reaction

This is a classic example of a Wurtz reaction, where alkyl halides react with sodium metal under ether conditions to form higher alkanes.

Identify Reactants

The reacting alkyl halides are ethyl bromide ( C_2H_5Br ) and n-propyl bromide ( C_3H_7Br ).

Determine Possible Alkanes

Combine different pairs of alkyl groups (either ethyl or propyl): - Ethyl + Ethyl = Butane ( C_4H_{10} ) - Ethyl + Propyl = Pentane ( C_5H_{12} ) - Propyl + Propyl = Hexane ( C_6H_{14} )

Count the Alkane Mixtures

The possible alkanes produced are butane, pentane, and hexane, making a total of three distinct alkanes.

Key concepts

Alkyl Halides

Alkyl halides are organic compounds that contain a halogen atom bonded to an alkyl group. The most common halogens found in these compounds are chlorine, bromine, and iodine. In the exercise, ethyl bromide (\(C_2H_5Br\)) and n-propyl bromide (\(C_3H_7Br\)) are used as reactants. These compounds are integral to the Wurtz reaction because halogens, being highly reactive, facilitate the bonding between alkyl chains.
When halogens exit as leaving groups, they allow for the formation of new carbon-carbon bonds by the coupling of alkyl radicals. This transformation is crucial since alkyl halides serve as the starting materials in producing longer chain hydrocarbons. They act as both a source of halogen and alkyl group. To understand their role, remember that the carbon-halogen bond is typically polarized, with the carbon carrying a partial positive charge. This makes the carbon susceptible to nucleophilic attack, a key step in the Wurtz reaction.

Sodium Metal

Sodium metal is a reactive alkali metal that plays a crucial role in the Wurtz reaction. It acts as a reducing agent, engaging in single-electron transfer processes that facilitate the creation of carbon-carbon bonds between alkyl groups. When sodium metal is introduced to the solution containing alkyl halides, it provides electrons that help replace the halogen atoms with alkyl radicals.
This process begins with sodium metal donating an electron to the alkyl halide, forming a radical anion. This is followed by the release of halogen and the formation of two alkyl radicals, which subsequently couple to form a new alkane. The reactivity of sodium is paramount here, as its ability to donate electrons makes it an effective catalyst in these coupling processes.

• Sodium reacts intensely with alkyl halides.
• It facilitates the removal of halogen atoms.
• Helps form new carbon-carbon bonds.
  

Ether Solvent

Ether serves as the solvent for the Wurtz reaction and provides an ideal environment for the reaction to proceed. Its role is not as reactive as sodium metal or alkyl halides, but it is crucial in maintaining a controlled reaction environment. Ethers are chosen because they are generally inert, meaning they do not participate in or interfere with the chemical reactions they are facilitating.
Their ability to dissolve a wide range of compounds, coupled with relatively low reactivity, makes ethers excellent solvents in many organic reactions. They help stabilize the reactive intermediates, such as the radical species involved in Wurtz reaction.

• Nonpolar nature of ether prevents unwanted side reactions.
• Facilitates the necessary interactions between reagents.
• Volatility of ether permits easy removal after reaction completion.
  

Higher Alkanes

Higher alkanes are the target products of the Wurtz reaction. In the context of the given problem, the reaction between ethyl bromide and n-propyl bromide, in the presence of sodium and ether, results in the formation of longer carbon chains. These longer chains result from coupling reactions facilitated by the process.
In the example, three higher alkanes are possible: - Butane (\(C_4H_{10}\)), - Pentane (\(C_5H_{12}\)), and - Hexane (\(C_6H_{14}\)). Higher alkanes are saturated hydrocarbons, meaning they contain only single bonds between the carbon atoms. As such, they tend to be more stable than their unsaturated counterparts. These alkanes often serve as fuels or intermediates in various industrial applications. Their relatively inert nature makes them less reactive, which is beneficial for storage and transport.
By understanding the products of the Wurtz reaction, one recognizes the ability to synthesize higher alkanes from simpler starting materials, which is a cornerstone in organic synthesis.