Question

How would you synthesize the following esters? a. \(n\) -octylacetate b.

Short answer

To synthesize n-octyl acetate, ethyl salicylate, and phenyl butyrate, perform the following esterification reactions: a. n-Octyl acetate: \(CH_3COOH + C_8H_{17}OH \rightarrow CH_3COOC_{8}H_{17} + H_2O\), using Fischer esterification with acetic acid and n-octanol. b. Ethyl salicylate: \(C_7H_6O_3 + C_2H_{5}OH \rightarrow C_9H_8O_3 + H_2O\), using Fischer esterification with salicylic acid and ethanol. c. Phenyl butyrate: \(C_4H_8O_2 + C_6H_{5}OH \rightarrow C_{10}H_{12}O_2 + H_2O\), using Steglich esterification with butyric acid, phenol, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine.

Step-by-step solution

Synthesizing n-octyl acetate

To synthesize n-octyl acetate, we must first identify the carboxylic acid and alcohol necessary for the reaction. The ester can be broken down to an acetic acid (CH3COOH) and n-octanol (C8H17OH). \( CH_3COOH + C_8H_{17}OH \rightarrow CH_3COOC_{8}H_{17} + H_2O \) A commonly used method is the Fischer esterification. This reaction can be performed using acetic acid and n-octanol in the presence of a catalytic amount of concentrated sulfuric acid.

Synthesizing ethyl salicylate

To synthesize ethyl salicylate, we need to first identify the carboxylic acid and alcohol required for the reaction. This ester can be broken down into salicylic acid (C7H6O3) and ethanol (C2H5OH). \( C_7H_6O_3 + C_2H_{5}OH \rightarrow C_9H_8O_3 + H_2O \) Again, the Fischer esterification can be used to synthesize ethyl salicylate. This reaction can be performed using salicylic acid and ethanol in the presence of a catalytic amount of concentrated sulfuric acid.

Synthesizing phenyl butyrate

To synthesize phenyl butyrate, we have to first identify the carboxylic acid and alcohol necessary for the reaction. This ester can be broken down into butyric acid (C4H8O2) and phenol (C6H5OH). \( C_4H_8O_2 + C_6H_{5}OH \rightarrow C_{10}H_{12}O_2 + H_2O \) In this case, we can use the Steglich esterification, which uses a coupling reagent such as N,N'-dicyclohexylcarbodiimide (DCC) and a catalytic amount of 4-dimethylaminopyridine (DMAP), to synthesize phenyl butyrate. This reaction can be performed using butyric acid and phenol in the presence of DCC and DMAP.

Key concepts

Fischer Esterification

Fischer Esterification is a widely used method to synthesize esters from carboxylic acids and alcohols. This process involves a reversible reaction. Here, a carboxylic acid like acetic acid reacts with an alcohol such as n-octanol in the presence of an acid catalyst. A common catalyst used is concentrated sulfuric acid.

The reaction proceeds by protonation of the carboxylic acid's carbonyl oxygen, increasing its electrophilicity. The alcohol then nucleophilically attacks this carbon, leading to an intermediate that eventually forms the ester and releases water.

• The process is reversible, and equilibrium lies slightly towards the ester product.
• To shift the equilibrium towards ester formation, excess alcohol or removal of water can be used.
• Fischer esterification is influenced by factors such as reactant concentration, temperature, and catalyst presence.

Understanding this mechanism helps to effectively synthesize esters such as n-octyl acetate using Fischer esterification.

Carboxylic Acids

Carboxylic Acids are organic compounds characterized by having at least one carboxyl group (-COOH). They are crucial reactants in ester synthesis, as shown in exercises involving esters like ethyl salicylate.

The carboxyl group contains a carbonyl (C=O) and a hydroxyl (O-H) group. It's highly polar, making carboxylic acids generally more reactive in nucleophilic substitutions.

Some properties of carboxylic acids include:

• They are typically weak acids, being partially ionized in water.
• Have higher boiling points than alcohols, ketones, or aldehydes of similar molecular weight due to hydrogen bonding.
• Act as proton donors and participate in acid-base reactions.

Carboxylic acids are used in a variety of syntheses, playing a key role as reactants in processes like Fischer esterification, where they donate part of their structure to form esters.

Alcohols

Alcohols are organic compounds with one or more hydroxyl (-OH) groups attached to a carbon atom. In ester synthesis, alcohols react with carboxylic acids to form esters. For instance, ethanol interacts with salicylic acid to produce ethyl salicylate via Fischer esterification.

Alcohols show distinctive properties due to their hydroxyl group, such as:

• Ability to form hydrogen bonds, which influences their boiling and melting points.
• Serving as nucleophiles in many chemical reactions, including esterification.
• Variability in their structural classification, being primary, secondary, or tertiary depending on the carbon atom bearing the hydroxyl group and the adjacent carbon chains.

Understanding these attributes of alcohols enhances their application in organic synthesis, enabling effective use in creating a range of esters through reactions with carboxylic acids.

Steglich Esterification

Steglich Esterification is an alternative method for synthesizing esters, particularly from sterically hindered carboxylic acids and phenols. This process employs a coupling reagent such as N,N'-dicyclohexylcarbodiimide (DCC) and a catalytic amount of 4-dimethylaminopyridine (DMAP).

Unlike Fischer esterification, this method does not require strong acid conditions and is often favored for sensitive substrates. It works by activating the carboxylic acid into an active ester using DCC, which then reacts with the alcohol to form the ester product.

• This reaction is typically mild and can be performed at room temperature.
• It minimizes by-products, making it a cleaner method with fewer purification steps.
• Especially useful in synthesizing esters that are difficult to make through more traditional methods.

With its distinct mechanistic pathway, Steglich esterification is an efficient and versatile approach for creating esters, as illustrated in the synthesis of phenyl butyrate from butyric acid and phenol.