Question

What reagents can be used to prepare the ester \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) ?

Short answer

The reagents that can be used to prepare the ester \(CH_{3}CH_{2}CH_{2}CO_{2}CH_{2}CH_{3}\) are propionic acid (\CH_{3}CH_{2}COOH) and ethanol (\CH_{3}CH_{2}OH), with an acid catalyst.

Step-by-step solution

Identify the Carboxylic Acid

First, find the carboxylic acid that can be used to produce this ester. Recognize that the carboxylic acid always contributes the R-COO part of the ester structure. In this case, the R group is propyl \(-CH_{2}CH_{2}CH_{3}\), so the carboxylic acid needed is propionic acid \(\CH_{3}CH_{2}COOH\)

Identify the Alcohol

Next, find the alcohol that can be used to produce this ester. The alcohol always contributes the R' part of the ester structure. In this case, the R' group is ethyl \(-CH_{2}CH_{3}\), so the alcohol needed is ethanol \(\CH_{3}CH_{2}OH\)

Verify and Conclude

Finally, confirm that combining propionic acid and ethanol through esterification reaction can indeed produce the given ester molecule \(CH_{3}CH_{2}CH_{2}CO_{2}CH_{2}CH_{3}\). There are also additional reagents needed for the reaction such as an acid catalyst. \(\CH_{3}CH_{2}COOH + \CH_{3}CH_{2}OH \rightarrow CH_{3}CH_{2}CH_{2}CO_{2}CH_{2}CH_{3} + H_{2}O\)

Key concepts

Carboxylic Acid

Carboxylic acids are organic compounds characterized by the presence of a carboxyl group, which is denoted as \( -COOH \). This group comprises a carbonyl (

• C=O) and
• a hydroxyl (-OH) group

attached to the same carbon atom. Carboxylic acids are weak acids, which means they partially dissociate in water to produce hydrogen ions.

In organic synthesis, carboxylic acids often act as precursor molecules for various chemical reactions, including esterification. Their ability to donate a proton (H^+) and to stabilize the resulting carboxylate ion due to resonance makes them key participants in reactions.

When considering the structure R-COOH, the R part is the hydrocarbon chain. For example, propionic acid, used in the esterification exercise, has the formula \( CH_3CH_2COOH \), where the R group is propyl (-CH_2CH_2CH_3). This R group determines the type of ester that the acid will form when it reacts with an alcohol. Thus, understanding the structure and behavior of carboxylic acids is vital in predicting and controlling the outcomes of their reactions.

Ethanol

Ethanol is a simple alcohol, commonly known as ethyl alcohol, with the chemical formula \( C_{2}H_{5}OH \). It consists of an ethyl group (-CH_2CH_3) attached to a hydroxyl group (-OH). As an alcohol, ethanol is characterized by the presence of this hydroxyl group, which makes it polar and capable of forming hydrogen bonds.

This property gives ethanol its key roles in chemical reactions, especially esterification. Alcohols react with carboxylic acids to form esters and water, with ethanol serving as the alcohol component.

In the reaction scheme discussed in the exercise, ethanol contributes the ethyl group (-CH_2CH_3) to the final ester product. This donor role is crucial as it complements the structure of the ester being synthesized, differentiating it by the R' component of the ester chain.

Besides its roles in chemistry, ethanol is widely used, ranging from serving as a household solvent to being a key ingredient in alcoholic beverages. Its versatility and prevalence in reactions like esterification stem from its balanced combination of polarity and reactivity.

Reaction Mechanism

Understanding the reaction mechanism of esterification is essential to mastering organic chemistry. Esterification is a chemical reaction that forms an ester, typically through the reaction of an alcohol and a carboxylic acid in the presence of an acid catalyst.

The process starts with the protonation of the carbonyl oxygen of the carboxylic acid by the acid catalyst, increasing the electrophilicity of the carbonyl carbon. This step makes the carbonyl carbon more susceptible to a nucleophilic attack.

• The alcohol then acts as the nucleophile, attacking the electron-deficient carbon, forming a tetrahedral intermediate.
• This intermediate undergoes a rearrangement, resolving into an ester and water through the elimination of a water molecule.

The presence of an acid catalyst, such as sulfuric acid ( H_2SO_4), speeds up the reaction. It provides protons required for initiating and stabilizing the reaction intermediates.

Esterification is a reversible process; thus, to drive the reaction towards ester formation, excess alcohol or removal of water is often employed. This mechanism allows us to understand how different conditions and components affect the formation of esters, enabling the efficient synthesis of the desired ester product.