Condensed Structural Formula For Propanol

2.5 Reactions of Alcohols

Learning Objectives

1. Requite two major types of reactions of alcohols.
2. Describe the result of the oxidation of a main booze.
3. Describe the event of the oxidation of a secondary alcohol.

Chemical reactions in alcohols occur mainly at the functional group, just some involve hydrogen atoms attached to the OH-bearing carbon atom or to an adjacent carbon atom. Of the three major kinds of alcohol reactions, which are summarized in Figure two.4 "Reactions of Alcohols", ii—dehydration and oxidation—are considered here. The third reaction type—esterification—is covered in Chapter 4 "Carboxylic Acids, Esters", Department 4.8 "Preparation of Esters".

Figure 2.four Reactions of Alcohols

Oxidation and aridity of alcohols are considered here.

Dehydration

Equally noted in Effigy 2.4 "Reactions of Alcohols", an alcohol undergoes dehydration in the presence of a catalyst to form an alkene and h2o. The reaction removes the OH group from the booze carbon atom and a hydrogen cantlet from an adjacent carbon atom in the same molecule:

Under the proper weather condition, it is possible for the aridity to occur between two alcohol molecules. The unabridged OH grouping of ane molecule and simply the hydrogen atom of the OH group of the 2nd molecule are removed. The ii ethyl groups fastened to an oxygen cantlet grade an ether molecule.

(Ethers are discussed in Section 2.4 "Reactions That Course Alcohols".) Thus, depending on conditions, one can fix either alkenes or ethers past the aridity of alcohols.

Annotation

Both aridity and hydration reactions occur continuously in cellular metabolism, with enzymes serving as catalysts and at a temperature of about 37°C. (For more than information about hydration reactions, run into Chapter 1 "Organic Chemistry Review / Hydrocarbons", Section one.fourteen "Chemical Properties of Alkenes".) The following reaction occurs in the Embden–Meyerhof pathway. (For more information well-nigh metabolic reactions, see Chapter 11 "Metabolic Pathways and Energy Production".)

Although the participating compounds are complex, the reaction is the same: elimination of water from the starting material. The idea is that if you know the chemistry of a particular functional group, you know the chemical science of hundreds of dissimilar compounds.

Oxidation

Chief and secondary alcohols are readily oxidized. We saw earlier how methanol and ethanol are oxidized by liver enzymes to form aldehydes. Because a variety of oxidizing agents tin bring near oxidation, nosotros can indicate an oxidizing amanuensis without specifying a particular 1 by writing an equation with the symbol [O] to a higher place the pointer. For example, we write the oxidation of ethanol—a primary booze—to form acetaldehyde—an aldehyde—equally follows:

We shall encounter (in Chapter 3 "Aldehydes, Ketones" Section 3.i "Aldehydes and Ketones: Structure and Names") that aldehydes are even more hands oxidized than alcohols and yield carboxylic acids.

Secondary alcohols are oxidized to ketones. The oxidation of isopropyl alcohol by potassium dichromate (K₂Cr₂O₇) gives acetone, the simplest ketone:

Different aldehydes, ketones are relatively resistant to further oxidation (Affiliate three "Aldehydes, Ketones" Section three.i "Aldehydes and Ketones: Structure and Names"), so no special precautions are required to isolate them equally they form.

Notation that in oxidation of both chief (RCH₂OH) and secondary (R₂CHOH) alcohols, two hydrogen atoms are removed from the alcohol molecule, i from the OH group and other from the carbon cantlet that bears the OH grouping.

Note

These reactions tin can too be carried out in the laboratory with chemical oxidizing agents. One such oxidizing agent is potassium dichromate. The balanced equation (showing merely the species involved in the reaction) in this case is as follows:

Booze oxidation is important in living organisms. Enzyme-controlled oxidation reactions provide the energy cells need to do useful piece of work. One pace in the metabolism of carbohydrates involves the oxidation of the secondary booze group in isocitric acid to a ketone group:

Note that the overall type of reaction is the same as that in the conversion of isopropyl booze to acetone. (For more data on metabolic reactions, see Chapter 11 "Metabolic Pathways and Energy Production".)

Tertiary alcohols (R₃COH) are resistant to oxidation because the carbon cantlet that carries the OH grouping does non accept a hydrogen atom attached but is instead bonded to other carbon atoms. The oxidation reactions we take described involve the formation of a carbon-to-oxygen double bail. Thus, the carbon cantlet bearing the OH group must be able to release ane of its attached atoms to course the double bail. The carbon-to-hydrogen bonding is easily cleaved under oxidative conditions, just carbon-to-carbon bonds are not. Therefore tertiary alcohols are not easily oxidized.

Instance 4

Write an equation for the oxidation of each booze. Use [O] above the arrow to betoken an oxidizing amanuensis. If no reaction occurs, write "no reaction" later on the arrow.

1. CH₃CH₂CH₂CH₂CH₂OH

2. 

3. 

Solution

The first step is to recognize the form of each alcohol every bit primary, secondary, or tertiary.

1. This booze has the OH group on a carbon cantlet that is fastened to only one other carbon atom, so it is a chief alcohol. Oxidation forms first an aldehyde and further oxidation forms a carboxylic acrid.

   

2. This alcohol has the OH grouping on a carbon atom that is fastened to iii other carbon atoms, and then it is a tertiary alcohol. No reaction occurs.

   

3. This alcohol has the OH group on a carbon atom that is fastened to 2 other carbon atoms, then it is a secondary alcohol; oxidation gives a ketone.

   

Skill-Edifice Exercise

Write an equation for the oxidation of each booze. Use [O] to a higher place the arrow to signal an oxidizing agent. If no reaction occurs, write "no reaction" subsequently the arrow.

1. 

2. 

3. 

Concept Review Exercises

1. In a reaction, chemical compound W with the molecular formula C₄H₁₀O is converted to compound X with the formula C₄H_eightO. Is W oxidized, reduced, dehydrated, or none of these? Explain.

2. In a reaction, ii mol of chemical compound Y with the molecular formula C_fourH_xO is converted to 1 mol of compound Z with the formula C₈H_xviiiO. Is Y oxidized, reduced, or neither? Explain.

Answers

1. oxidized; H is removed

2. neither; water is removed

Primal Takeaways

• Alcohols can be dehydrated to form either alkenes (higher temperature, excess acid) or ethers (lower temperature, excess alcohol).
• Primary alcohols are oxidized to form aldehydes.
• Secondary alcohols are oxidized to form ketones.
• 3rd alcohols are not readily oxidized.

Exercises

1. Name the three major types of chemical reactions of alcohols.

two. Why do 3rd alcohols non undergo oxidation? Can a tertiary booze undergo aridity?

three. Draw the structure of the product for each reaction.

a.

b.

iv. Depict the structure of the production for each reaction.

a.

b.\

5. Write an equation for the aridity of 2-propanol to yield each chemical compound type.

a. an alkene

b. an ether

6. Describe the structure of the alkene formed past the aridity of cyclohexanol.

Answers

ane. dehydration, oxidation, and esterification

3.

a.

b.

five.

a.

b.

Condensed Structural Formula For Propanol,

Source: https://guides.hostos.cuny.edu/che120/chapter2

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