Difference Between Alcohol and Carboxylic Acid

Main Difference – Alcohol vs Carboxylic Acid

Alcohols and carboxylic acids are organic compounds. They are composed of C, H and O atoms in different combinations. Both these compounds are acidic compounds. They have special groups of atoms that are called functional groups. The difference between alcohol and carboxylic acid can be identified by the presence of these functional groups. Since they are different compounds, they show different physical and chemical properties as discussed in this article. There are many applications of alcohols and carboxylic acids in the laboratory and in the industry. The main difference between alcohol and carboxylic acid is that the functional group present in alcohol is a hydroxyl group (-OH) whereas the functional group in carboxylic acid is carboxyl group (-COOH).

Key Areas Covered

1. What is an Alcohol
      – Definition, Different Forms with Examples, Properties, and Reactions
2. What is a Carboxylic Acid
      – Definition, Different Forms with Examples, Properties, and Reactions
3. What are the Similarities Between Alcohol and Carboxylic Acid
      – Outline of Common Features
4. What is the Difference Between Alcohol and Carboxylic Acid
      – Comparison of Key Differences

Key Terms: Alcohol, Carboxyl Group, Carboxylic Acid, Hydrogen Bonding, Hydroxyl Group, Polarity

What is an Alcohol

Alcohol is an organic compound composed of one or more hydroxyl groups (-OH). Alcohols are molecules made out of C, H and O atoms which are arranged in an alkyl group and hydroxyl groups. The hydroxyl group is attached to one carbon atom of the alkyl group.

Alcohols can be synthesized through different methods. Moreover, alcohol act as either the starting molecule or the intermediate for the synthesis of other organic compounds. Some beverages contain alcohols as a major or minor component. Sometimes alcohols can be used as solvents for purification of compounds out of impure mixtures.

When considering the structure of alcohols, there are three major types of alcohol structures. The structures and some examples of each structure are given below.

Primary Alcohols

Primary alcohols are composed of a hydroxyl group that is attached to a carbon atom of the alkyl group which is attached to only one alkyl group.

Ex: Ethanol is composed of a hydroxyl group that is attached to a carbon atom.

Figure 1: A primary alcohol – Ethanol.

Secondary Alcohol

Secondary alcohol is composed of a carbon atom that is attached to a hydroxyl group and two other alkyl groups.

Ex: 2-butanol is a secondary alcohol.

Figure 2: A general structure of secondary alcohol. Here “R” groups indicate alkyl groups.

Tertiary Alcohol

A tertiary alcohol is composed of a carbon atom that is bonded to a hydroxyl group and with three alkyl groups.

Ex: 2,2-methylbutanol

Figure 3: General structure of tertiary alcohol.

Although the presence of –OH group cause acidity, alcohols are weak acids. These –OH groups cause the hydrogen bonding in alcohols. There are hydrogen bonds between the oxygen atom of –OH group of one alcohol and hydrogen atom of another alcohol. These hydrogen bonds cause alcohols to have higher boiling points. However, the boiling point of alcohols increases with the number of carbon atoms present in an alcohol. In addition, alcohols are completely soluble in water. This is also because the alcohol molecules can form hydrogen bonds with water molecules.

Alcohols can be synthesized by hydration of alkenes, by reduction of aldehydes, ketones, acids, and esters. One of the major chemical reaction associated with alcohols is the substitution of H atom in –OH group with electrophiles such as Sodium (Na). Here, if H is substituted with an alkyl group, it gives an ether as the end product. Likewise, there are a number of reactions that alcohols can undergo such as elimination reactions, nucleophilic substitutions, etc.

What is a Carboxylic Acid

A carboxylic acid is an organic compound composed of a carboxyl group (-COOH). The chemical formula of carboxylic acid can be given as R-COOH where “R” indicates an alkyl group. The presence of a carboxyl group indicates a molecule as a carboxylic acid.

As given by its name, a carboxylic acid is an acid. They are found in many food such as vinegar, citrus and in medicine, etc. The simplest carboxylic acid is HCOOH; this is called formic acid in common. When the R group is substituted with a methyl group (-CH₃), it gives acetic acid.

Carboxylic acids are polar molecules due to the presence of carboxyl group. Therefore, it is well dissolved in polar solvents. Moreover, carboxylic acids are soluble in water due to their ability to form hydrogen bonds. Carboxylic acids can have two hydrogen bonds between two carboxylic acids, forming a dimer of carboxylic acids. This is called “self-association”.

Figure 4: A Dimer of Carboxylic Acid

Carboxylic acids have higher boiling points since the formation of dimers give them an extra stability. The acidity of carboxylic acids arise as the H in carboxylic acid can be released as a proton. This proton-releasing causes the pH of the system to be increased, indicating an acidic behavior. 

Carboxylic acids can be synthesized by treating CO₂ with Grignard reagent. Carboxylic acids can easily be reacted with a metal forming metal-carboxylate and hydrogen gas. The reaction between a carboxylic acid and a metal hydroxide can also produce the metal-carboxylate. Another important reaction is the reaction between a carboxylic acid and ammonia.

Similarities Between Alcohol and Carboxylic Acid

• Alcohols and carboxylic acids are organic compounds.
• Both compounds show acidic properties.
• Both are composed of C, H and O atoms.
• Both alcohols and carboxylic acids are polar compounds.
• Both molecules are able to form hydrogen bonds.

Difference Between Alcohol and Carboxylic Acid

Definition

Alcohol: An alcohol is an organic compound composed of one (or more) hydroxyl group (-OH).

Carboxylic Acid: A carboxylic acid is an organic compound composed of a carboxyl group (-COOH).

Number of Oxygen Atoms

Alcohol: Alcohols have one oxygen atom per one functional group.

Carboxylic Acid: Carboxylic acids have two oxygen atoms per one functional group.

Functional Groups

Alcohol: Alcohols have –OH as a functional group.

Carboxylic Acid: Carboxylic acids have –COOH as a functional group.

Boiling Points

Alcohol: Alcohols have a lower boiling point than corresponding carboxylic acids.

Carboxylic Acid: Carboxylic acids have higher boiling points than corresponding alcohols.

Dimer Formation

Alcohol: Alcohols cannot form dimers.

Carboxylic Acid: Carboxylic acids can form dimers.

Acidity

Alcohol: Alcohols are weak acids.

Carboxylic Acid: Carboxylic acids are more acidic than corresponding alcohol.

Conclusion

Alcohols and carboxylic acids are organic compounds. Although both of them are made of C, H and O atoms, they are different in their structures and properties. The main difference between an alcohol and a carboxylic acid is that the functional group present in alcohol is a hydroxyl group (-OH) whereas the functional group in carboxylic acid is carboxyl group (-COOH).

References:

1. “Alcohol.” Encyclopædia Britannica, Encyclopædia Britannica, inc., Available here. Accessed 18 Aug. 2017.
2. “Structure and Classification of Alcohols.” Chemistry LibreTexts, Libretexts, 21 July 2016, Available here. Accessed 18 Aug. 2017.

Image Courtesy:

1. “Ethanol flat structure” By Cacycle – Own work (Public Domain) via Commons Wikimedia
2. “Sec. Alcohol Structural Formulae V.1” By Jü – Own work (Public Domain) via Commons Wikimedia
3. “Tert. Alcohol Structural Formulae V.1” By Jü – Own work (Public Domain) via Commons Wikimedia
4. “Carboxylic Acids Hydrogen Bonds V.1” By Jü – Own work (CC0) via Commons Wikimedia