Rеaction of Alcohols – Equations, Examples, Uses

Alcohols are a class of organic compounds characterized by the presence of a hydroxyl (-OH) functional group attached to a carbon atom. Alcohols undergo various reactions such as oxidation, reduction, esterification , dehydration, substitution reaction to yield various compounds which are of important use.

In this article, we’re going to look into the reactions of alcohols along with their chemical equations and understand their applications for various uses.

What is Alcohols in Chemistry?

In chemistry, alcohols are group of organic compounds which has presence of hydroxyl (-OH) functional group attached to carbon atom. They are commonly represented as R-OH.

Classification of Alcohols

Alcohols are classified based on the number of carbon atoms directly bonded to the carbon bearing the hydroxyl group:

• Primary Alcohols: 1 carbon atom is directly attached to the hydroxyl-bearing carbon atom.
• Secondary Alcohols: 2 carbons are bonded directly to the carbon that carries the hydroxyl group.
• Tertiary alcohols: 3 carbons are connected directly to the carbon with –OH.

Common Reactions of Alcohols

Alcohols exhibit various reactions, including oxidation, dehydration, and esterification, among others.

Oxidation of Alcohols

Oxidation of Alcohol gives Aldehyde or ketone as product depending upon the type of alcohols. The oxidation reaction for different types of alcohols is given below:

Primary Alcohols Oxidation

Primary alcohols when oxidized, the hydroxyl group (—OH) is changed to an aldehyde (RCHO), after adding an oxygen atom ([O]) in this case water (H₂O) is produced. Afterward, the aldehyde itself oxidizes further by another oxygen atom ([O]) to give carboxylic acid (RCOOH).

ROH + [O] → RCHO + H₂O

RCHO + [O] → RCOOH

Secondary Alcohol Oxidation

In the case of secondary alcohols, it is a chemical change of hydroxyl (-OH) group into a ketone (RCOR) by an oxygen atom ([O]) and water (H2O), is formed as byproduct.

ROH +[ O] → RCOR + H₂O

Tertiary Alcohols Oxidation

Tertiary alcohols do not undergo oxidation reactions under mild conditions.

Dehydration Reaction of Alcohol

Dehydration reactions are one of the methods to remove a hydrogen molecule from an alcohol molecule through which the alkene is formed. This process normally uses acid catalysts such as sulfuric acid when it is being carried out. The hydrogen atoms of the hydroxyl (-OH) groups of the alcohol molecules participate inside the reaction through joining with hydroxyl group from a neighboring alcohol molecules to form a water molecule, leaving in the back of a carbonyl (-C=O) linkage between the carbon atoms of the authentic alcohol molecule.

ROH → R =H(Alkene) + H₂O

The result of dehydration of different types of alcohol is mentioned below:

• Primary alcohols: Primary alcohols undergo dehydration to form primary alkenes.
• Secondary alcohols: Secondary alcohols undergo dehydration to form secondary alkenes.
• Tertiary alcohols: Tertiary alcohols can undergo dehydration to form tertiary alkenes, but they may also undergo rearrangement reactions due to the stability of the carbocation intermediate

Esterification Reactions

When alcohol reacts with carboxylic acids in the presence of an acidic catalyst, it is called esterification · In an esterification reaction, an ester is obtained as a product and water. Hydroxyl group (-OH) of an alcohol in some cases is functionalized with a carboxyl group (RCOOH).

ROH + RCOOH → (Acid Catalyst) RCOOR + H₂O

Acid-Catalyzed Reactions of Alcohols

Acid-catalyzed reactions of alcohols involve the use of an acid catalyst to facilitate various chemical transformations of alcohol molecules.

Dehydration of Alcohols to Alkenes

Acid-catalyzed dehydration of alcohols leads to the removal of a water molecule to form an alkene. This reaction is typically carried out using a strong acid catalyst, such as sulfuric acid (H₂SO₄) or phosphoric acid (H₃PO₄)

ROH → R=H(Alkene) + H₂O

Conversion of Alcohols to Alkyl Halides

Hydrogen halides (HCl, HBr, HI) or thionyl chloride (SOCl₂) in the presence of a typical Lewis acid catalyst such as zinc chloride (ZnCl₂) react with alcohols to form alkyl halides. This transformation is an important step in organic synthesis as it helps to create alkyl halides- important intermediates for many reactions including nucleophilic substitution and elimination.

ROH + HX → RX + H₂O

Alcohols in Organic Synthesis

Alcohols are active and focused reagents within organic synthesis introduced in numerous reactions to generate complicated chemicals. They are routinely used to reduce double bonds, introduce functional groups or alter existing ones by Grignard reactions, reduction reactions, and other transformations, respectively.

Use of Alcohols in Grignard Reactions

Alcohols are usually used as starting materials for the synthesis of the Grignard reagents. They are organo-magnesium compounds, which are the most reactive analogs of conventional organometallic reagents. Grignard reagents are found to add nucleophilicity to larger number of electrophiles, including carbonyl compounds, derive from ketones, aldehydes, etc. Such type of mechanism for the syntheses of carbon-carbon bonds are useful for building new compounds and to be used within the framework of organic chemistry.

RMgX + ROH → ROR + MgOHX

Alcohol Reduction Reactions

Reduction of alcohols can lead to the formation of alkanes or other reduced products, depending on the reducing agent used.

Reduction of Alcohols to Alkanes

Here, alcohols are reduced to alkanes by hydrogen gas under the circumstances involving suitable catalysts such as platinum (Pt), palladium (Pd), or nickel (Ni). The role of hydrogen gas (H₂), which is the reducing agent, is to reduce the metal ions into metallic form. The process more often happens under high temperature and pressure.

CH₃CH₂OH + H₂ → CH₃CH₃ + H₂O

Reduction of Alcohols to Alkenes

Alcohols, too, can be converted into alkenes under specific set of conditions. A common technique employs reagents like concentrated sulphuric acid (H₂SO₄) and heat. This reaction is known as dehydration, where a molecule of water is removed from the alcohol molecule, and the alkene is formed as the product.

CH₃CH₂OH → CH₂ = CH₂ + H₂O

Special Cases and Reactions of Phenols

Phenols are the group of alcohol in which benzene group (-C₆H₅OH) attached to the -OH group. Unlike aliphatic alcohols with linear structures, phenols have unique structural features that give them distinctive chemical properties. Here are some notable reactions and characteristics of phenols, illustrated with chemical equations.

Electrophilic Aromatic Substitution (EAS) of Phenol

In phenol, an electrophile (a molecule or ion that seeks electrons) reacts with the aromatic ring, replacing a hydrogen atom with the electrophile. This happens because the aromatic ring in phenol has many electrons, which makes it attractive to electrophiles. This reaction is known as electrophilic aromatic substitution. For example, consider the reaction of phenol with bromine (Br2) in the presence of a Lewis acid catalyst (FeBr3):

C₆H₅OH + Br₂ → C₆H₅B + HBr

Nitration of Phenols

Phenolic compounds are capable of present process nitration reactions wherein the hydroxyl institution of the phenolic compound is changed by using manner of the nitro group (-NO₂). This reaction is done with a mixture of nitric acid (HNO₃) and sulfuric acid (H₂SO₄) acting as a catalyst.

C₆H₅OH + HNO₃ → C₆H₄(NO₂)OH + H₂O

Phenol Oxidation Reactions

Phenols go through oxidation reactions that result in the manufacturing of quinones, that are cyclic compounds containing two carbonyl organizations. Typically, this chemical transformation is done the use of sturdy oxidizing agents like chromic acid (H2CrO4) or Potassium permanganate (KMnO4).

2C₆H₅OH + O₂ → C₆H₄(O)₂ + H₂O

Uses of Alcohol Reactions

The reactions of alcohols find extensive applications in organic synthesis, pharmaceuticals, perfumes, and various industrial processes.

• Pharmaceutical Synthesis: Alcohol reactions are a must for manufacturing drugs in the pharmaceutical industry.
• Solvent Production: Ethanol and methanol, which might be constructed from alcohol reactions, are commonly used as cleaning agents in industries.
• Biofuel Generation: Moreover, via alcohol reactions, bio fuels inclusive of biodiesel and bio ethanol had been made to decrease over-reliance on fossil fuels.
• Organic Compound Synthesis: Some of the natural compounds that alcohol reactions form consist of esters, aldehydes, ketones among others wished for various purposes.
• Flavor and Fragrance Manufacturing: Also, this process is employed by alcohol reactions in producing fragrances used in food additives and perfumes.

Conclusion

In conclusion, Alcohols are super important in chemistry because they can do lots of different reactions. These reactions help make all kinds of important stuff we use every day, like medicine and materials. Understanding how alcohols react is really important for figuring out how to make things in a more sustainable way

Sample Questions on Alcohol Reactions

Q1. What is the product obtained when 1-butanol is treated with concentrated sulfuric acid at high temperatures?

1-butanol undergoes dehydration in the presence of concentrated sulfuric acid at high temperatures to form 1-butene.

Q2. What is the product obtained when ethanol is oxidized with acidified potassium dichromate (K₂Cr₂O₇) under reflux conditions?

Ethanol is oxidized to form acetic acid when treated with acidified potassium dichromate under reflux conditions.

Q3. Which of the following alcohols will not undergo oxidation with Jones reagent (chromic acid)?

• Methanol
• Ethanol
• 2-propanol
• 2-methyl-2-propanol

The correct answer is 2-methyl-2-propanol. It will not undergo oxidation with Jones reagent due to steric hindrance.

Q4. When benzyl alcohol is treated with Lucas reagent (concentrated HCl and ZnCl₂), which of the following is formed?

• Benzene
• Benzaldehyde
• Benzyl chloride
• Benzoic acid

The correct answer is c) Benzyl chloride. Benzyl alcohol undergoes substitution reaction with Lucas reagent to form benzyl chloride.

Q5. Which of the following alcohols is most easily dehydrated to form an alkene?

• 1-butanol
• 2-butanol
• 2-methyl-2-propanol
• 1-pentanol

The correct answer is b) 2-butanol. It undergoes dehydration most readily due to the stability of the resulting alkene.

Q6. What is the product obtained when phenol is treated with bromine water?

Phenol undergoes electrophilic aromatic substitution reaction with bromine water to form 2,4,6-tribromophenol as the major product.

Q7. What is the product obtained when 2-propanol undergoes oxidation using Jones reagent (chromic acid)?

• Acetone
• Propanal
• Propionic acid
• Isopropyl chloride

Propanal

Q8. Which of the following alcohols can undergo dehydration most readily?

• 1-butanol
• 2-butanol
• 2-methyl-2-propanol
• 1-pentanol

2-methyl-2-propanol

Q9. When benzyl alcohol is treated with Lucas reagent (concentrated HCl and ZnCl₂), what is the formed product?

• Benzene
• Benzaldehyde
• Benzyl chloride
• Benzoic acid

Benzyl chloride

Q10. What is the primary product formed when ethanol reacts with thionyl chloride (SOCl₂)?

• Ethyl chloride
• Ethyl bromide
• Ethyl iodide
• Ethyl sulfate

Ethyl chloride

Rеaction of Alcohols Practice Questions

Q1. What is the primary product formed when 3-methyl-2-butanol undergoes dehydration?

• 2-Methyl-2-butene
• 3-Methyl-1-butene
• 2-Methyl-1-butene
• 3-Methyl-2-butene

Q2. Which of the following reagents is commonly used in the oxidation of alcohols to aldehydes?

• PCC (Pyridinium chlorochromate)
• NaBH₄ (Sodium borohydride)
• H₂SO₄ (Sulfuric acid)
• KMnO₄ (Potassium permanganate)

Q3. What is the major product obtained when 2-propanol reacts with concentrated hydrochloric acid (HCl) in the presence of zinc chloride (ZnCl₂)?

• Isopropyl chloride
• Acetone
• Propene
• Isopropyl bromide

Q4. Which of the following alcohols is most likely to undergo an esterification reaction with acetic acid?

• 1-butanol
• 2-butanol
• 3-methyl-2-butanol
• 2-methyl-2-propanol

Reaction of Alcohol FAQs

What is the product of oxidation of alcohols?

Alcohols get oxidized to give aldehyde, ketone and carboxylic acids

What are the key characteristics of alcohols?

The key characteristics of alcohols include presence of hydroxyl group, ability to form hydrogen bond, undergo various chemical reactions, including oxidation, dehydration, substitution, esterification, and reduction.

How do alcohols react with Grignard Reagent?

Alcohols can react with Grignard reagents (alkyl magnesium halides) to form magnesium alkoxides.

What are some common applications of alcohol reactions in industry?

Alcohol reactions find applications in pharmaceuticals, perfumes, flavorings, and as solvents in various industrial processes. They are also crucial in organic synthesis for the production of complex molecules.

What is the difference between primary, secondary, and tertiary alcohols?

The difference between different alcohols is mentioned below:

• Primary Alcohols: -OH group attached to a carbon atom bonded to only one carbon atom.
• Sеcondary Alcohols: -OH group attached to a carbon atom bonded to two other carbon atoms.
• Tеrtiary Alcohols: -OH group bonded to a carbon atom connected to three other carbon atoms.

How do you distinguish between primary, secondary, and tertiary alcohols?

Lucas reagent (concentrated HCl and ZnCl₂) is used to distinguish between alcohols based on their mechanism of action. The third alcohol readily forms an alkyl chloride, the second alcohol reacts after a delay, and the first alcohol shows no immediate reaction