Question

\(\mathrm{CH}_{3} \mathrm{CHO}\) converts into ethyl ethanoate when treated with (A) dil. \(\mathrm{NaOH}\) (B) conc. \(\mathrm{NaOH}\) (C) \(\mathrm{Al}\left(\mathrm{OCH}_{2} \mathrm{CH}_{3}\right)_{3}\) (D) \(\mathrm{NaOEt} / \mathrm{EtOH}\)

Short answer

The correct reagent for converting acetaldehyde (CH3CHO) into ethyl ethanoate is (D) NaOEt/EtOH (sodium ethoxide in ethanol). The reaction occurs through a nucleophilic acyl substitution mechanism, with sodium ethoxide acting as the nucleophile. The balanced chemical equation is: \(CH_3CHO + CH_3CH_2ONa \rightarrow CH_3COOCH_2CH_3 + NaOH\)

Step-by-step solution

Identify the reagents and their general reactions

(A) dil. NaOH: This is a dilute solution of sodium hydroxide, which is a weak base. It usually undergoes reactions such as hydrolysis or neutralization. (B) conc. NaOH: This is a concentrated solution of sodium hydroxide, a strong base. It is commonly involved in reactions like saponification and base-catalyzed condensation reactions. (C) Al(OCH2CH3)3: This reagent is aluminum isopropoxide. It is used in various reactions, such as the Meerwein-Ponndorf-Verley (MPV) reduction and the Oppenauer oxidation. (D) NaOEt/EtOH: This reagent is called sodium ethoxide, which is the sodium salt of ethanol (a strong base). It is used in various reactions, such as the Williamson Ether Synthesis and the Claisen Condensation.

Analyze the reaction of acetaldehyde with each reagent

(A) With dil. NaOH, acetaldehyde would react to form a hydrate, which is not ethyl ethanoate, and thus this isn't the correct reagent. (B) With conc. NaOH, acetaldehyde will undergo a Cannizzaro reaction, which will lead to the formation of an alcohol and a carboxylic acid, not an ester. (C) Al(OCH2CH3)3 (aluminum isopropoxide) is not the correct reagent to form an ester. It can be used for MPV reductions or Oppenauer oxidations, but not for ester formation. (D) NaOEt/EtOH (sodium ethoxide in ethanol) is the correct reagent for this reaction. When acetaldehyde reacts with sodium ethoxide, it undergoes a nucleophilic acyl substitution reaction, leading to the formation of an ester.

Write the balanced chemical equation for the reaction of acetaldehyde with sodium ethoxide

The balanced chemical equation for the reaction of acetaldehyde with sodium ethoxide in ethanol is: CH3CHO + CH3CH2ONa → CH3COOCH2CH3 + NaOH In this reaction, sodium ethoxide acts as a nucleophile, attacking the carbonyl carbon of acetaldehyde, and ultimately leads to the ester formation.

Conclusion

The correct option is (D) NaOEt/EtOH (sodium ethoxide in ethanol), as it effectively converts acetaldehyde into ethyl ethanoate through a nucleophilic acyl substitution reaction.

Key concepts

Sodium Ethoxide in Ethanol

When exploring organic chemistry reactions, it's crucial to understand the role of specific reagents. Sodium ethoxide in ethanol, known as NaOEt/EtOH, is one such reagent that plays a pivotal role in synthetic organic chemistry. Sodium ethoxide is essentially the sodium salt of ethanol. It's created when ethanol reacts with sodium metal.

The use of sodium ethoxide in ethanol is particularly interesting because it serves as a strong base and a potent nucleophile. This means it readily donates electron pairs to electron-deficient (or electrophilic) carbon atoms, initiating chemical reactions. NaOEt/EtOH is used in a host of procedures, ranging from the Williamson Ether Synthesis, where it helps form ethers, to the Claisen Condensation, which creates carbon-carbon bonds in the formation of more complex molecules.

In the context of the exercise, sodium ethoxide in ethanol is the key reagent that transforms acetaldehyde into ethyl ethanoate through a mechanism known as nucleophilic acyl substitution, which we will discuss in more detail in the following section.

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction mechanism in organic chemistry. It occurs when a nucleophile, which is a molecule with electrons to spare, attacks an electrophilic carbon atom within a carbonyl group. The carbonyl group is characterized by a carbon atom double-bonded to an oxygen atom, as found in aldehydes, ketones, carboxylic acids, and their derivatives.

The process is stepwise. Initially, the nucleophile attacks the electrophilic carbonyl carbon, creating a tetrahedral intermediate. This intermediate then collapses, re-establishing the double bond and ejecting the weakest leaving group.

In the specific organic chemistry reaction from the exercise, sodium ethoxide acts as the nucleophile, attacking acetaldehyde (an aldehyde with the structure CH3CHO). The product of this nucleophilic attack is ethyl ethanoate, a type of ester. This process transforms a simple aldehyde into a more complex and functionalized compound, showcasing the versatility of acyl substitution reactions in building molecular complexity.

Organic Chemistry Reactions

Organic chemistry is full of varied and intricate reactions that allow chemists to synthesize complex molecules from simpler ones. Understanding these reactions is essential in multiple scientific fields such as pharmaceuticals, materials science, and biochemistry.

Many reactions in organic chemistry involve the creation and breaking of bonds, the movement of electrons, and the interconversion of molecular structures. For instance, we have addition reactions where atoms are added to a double or triple bond; substitution reactions where atoms or groups of atoms are replaced; elimination reactions where atoms are removed to form double or triple bonds; and rearrangement reactions where the skeleton of the molecule is rearranged.

In the context of the exercise improvement advice, providing clear explanations and analogies can help students better understand these concepts. For example, thinking of nucleophilic acyl substitution as a 'molecular dance,' where the nucleophile (sodium ethoxide) cuts in to pair up with the carbonyl carbon of acetaldehyde, only to leave behind a different partner (hydroxide ion), could make this complex reaction more accessible.