Chapter 16, Problem 16.85P

Interpretation Introduction

(a)

Interpretation:

The products should be identified by the reaction of benzaldehyde with $H_2,Pd$.

Concept Introduction:

Addition of H₂gas to a multiple bond is known as hydrogenation. In the presence of palladium metal as the catalyst H₂ molecules react with aldehydes and give the respective alcohol of the particular aldehyde.

Answer to Problem 16.85P

Explanation of Solution

When an aldehyde reacts with H₂ gas in the presence of palladium metal resulting product is an alcohol of the initial aldehyde molecule. Palladium metal act as a catalyst to the reaction that provides a surface to bind both the H₂ and carbonyl compound which reduce the activation energy of the reaction.

Hydrogen atoms in the alcohol molecule shown below, which are indicated in red color are the added H during the hydrogenation reaction.

Interpretation Introduction

(b)

Interpretation:

The products should be identified by the reaction of benzaldehyde with $K_{2}C{r}_2{O}_7$.

Concept Introduction:

Addition of an O atom in to a molecule is known as oxidation. The hydrogen atom directly connected to the carbonyl C in an aldehyde will oxidized in the presence of an oxidizing agent such as $K_{2}C{r}_2{O}_7$ and give the respective carboxylic acid of the particular aldehyde.

Oxygen atom in the carboxylicacid molecule shown below, which is indicated in red color is the added O during the oxygenation reaction.

Answer to Problem 16.85P

Explanation of Solution

When an aldehyde reacts with $K_{2}C{r}_2{O}_7$ resulting product is a carboxylic acid of the initial aldehyde molecule. $K_{2}C{r}_2{O}_7$ act as an oxidizing agent. Aldehyde's $C-H$ bond can be converted in to $C-OH$ bond.During the reaction red-orange colored $K_{2}C{r}_2{O}_7$ solid reduced in to a green color $C{r}^{3+}$ ion.

Interpretation Introduction

(c)

Interpretation:

The products should be identified by the reaction of benzaldehyde with $A{g}_{2}O,N{H}_{4}OH$.

Concept Introduction:

Addition of an O atom in to a molecule is known as oxidation. The hydrogen atom directly connected to the carbonyl C in an aldehyde will oxidized in the presence of an oxidizing agent such as ( $A{g}_{2}O$ ) in an aqueous medium of ammonium hydroxide( $N{H}_{4}OH$ ) and give the respective carboxylic acid of the particular aldehyde.

Oxygen atom in the carboxylic acid molecule shown below, which is indicated in red color is the added O during the oxygenation reaction.

Answer to Problem 16.85P

Explanation of Solution

When an aldehyde reacts with $A{g}_{2}O,N{H}_{4}OH$ resulting product is a carboxylic acid of the initial aldehyde molecule. $A{g}_{2}O,N{H}_{4}OH$ act as an oxidizing agent. The hydrogen atom directly connected to the carbonyl C in an aldehyde will oxidized in the presence of an oxidizing agent such as ( $A{g}_{2}O$ ) in an aqueous medium of ammonium hydroxide( $N{H}_{4}OH$ ), this $A{g}_{2}O,N{H}_{4}OH$ known as as Tollens reagent.

Aldehyde's $C-H$ bond can be converted in to $C-OH$ bond. During the reaction Ag+ reduced in to Ag metal, which precipitates out of the reaction mixture as a silver mirror.

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Interpretation Introduction

(d)

Interpretation:

The products should be identified by the reaction of benzaldehyde with $C{H}_{3}OH(2\text{ equivalents), }{H}_2{\text{SO}}_4$.

Concept Introduction:

In the presence of alcohol in the acidic medium, aldehydes undergo addition reactions and give acetal in two steps.

Hydrogen atom and CH₃ groups in the acetal and hemiacetal molecules shown below, which are indicated in red color are the added molecules during the reaction.

Answer to Problem 16.85P

Explanation of Solution

In the presence of alcohol in the acidic medium, aldehydes undergo addition reactions and give acetal in two steps. In the first step aldehydes form hemiacetals and during the second step it converts to an acetal molecule of the respective aldehyde molecule.

Addition of one molecule of alcohol in to an aldehyde forms a hemiacetal, one bond of the $C=O$ is broken and two new single bonds are formed. In the presence of $C{H}_{3}OH\text{, }{H}_2{\text{SO}}_4$ , acyclic hemiacetals react with another alcohol molecule and produce acetals due to the un stability of the acyclic hemiacetal molecule.

Interpretation Introduction

(e)

Interpretation:

The products should be identified by the reaction of benzaldehyde with $C{H}_{3}C{H}_{2}OH(2\text{ equivalents), }{H}_2{\text{SO}}_4$.

Concept Introduction:

In the presence of alcohol in the acidic medium, aldehydes undergo addition reactions and give acetal in two steps.

Hydrogen atom and CH₂CH₃ groups in the acetal and hemiacetal molecules shown below, which are indicated in red color are the added molecules during the reaction.

Answer to Problem 16.85P

Explanation of Solution

In the presence of alcohol in the acidic medium, aldehydes undergo addition reactions and give acetal in two steps. In the first step aldehydes form hemiacetals and during the second step it converts to an acetal molecule of the respective aldehyde molecule.

Addition of one molecule of alcohol in to an aldehyde forms a hemiacetal, one bond of the $C=O$ is broken and two new single bonds are formed. In the presence of $C{H}_{3}C{H}_{2}OH\text{, }{H}_2{\text{SO}}_4$ , acyclic hemiacetals react with another alcohol molecule and produce acetals due to the un stability of the acyclic hemiacetal molecule.

Interpretation Introduction

(f)

Interpretation:

The products should be identified by the reaction of $C_6{H}_{5}CH-{(OC{H}_{2}C{H}_3)}_2$ with ${\text{H}}_2\text{O, }{H}_2{\text{SO}}_4$.

Concept Introduction:

In the presence of water and acid, acetals undergo hydrolysis reaction and produce aldehydes.

OR' groups in the acetal molecule shown below, which are indicated in red color are the molecules which becomes alcohol molecules during the hydrolysis.

Answer to Problem 16.85P

Explanation of Solution

Acetals are stable molecules, but their bonds can cleave by a reaction with water and produce aldehydes.

In the acetal molecule, two bonds of the $C-O$ are broken and $C=O$ formed, each CH₂CH₃group becomes a molecule of alcohol.

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