Chapter 21, Problem 31P

a)

Interpretation Introduction

Interpretation:

The product obtained when D-galactose reacts with nitric acid is to be stated.

Concept Introduction:

D-galactose is a monosaccharide molecule and it is sweet in taste as glucose.  It is C-$4$ epimer of glucose.

Epimers are pair of stereoisoisomers which differ in configuration at one stereogenic center.  In D-galactose molecule one terminal aldehydic and one terminal alcoholic group is present.

Nitric acid has the chemical formula ${\text{HNO}}_3$ and behaves as a good oxidizing agent. It oxidizes both the terminal functional groups in the acidic group.

Answer to Problem 31P

The product obtained when D-galactose reacts with nitric acid is given below,

Figure 1

Explanation of Solution

The product obtained when D-galactose reacts with nitric acid is as follows,

Figure 1

${\text{HNO}}_3$ oxidizes D-galactose to D-galactaric acid.

b)

Interpretation Introduction

Interpretation:

The product obtained when D-galactose reacts with ${\text{Ag}}^{+},{\text{NH}}_3,{\text{OH}}^{-}$ is to be stated.

Concept Introduction:

D-galactose is a monosaccharide molecule and it is sweet in taste as glucose. It is C-$4$ epimer of glucose.

Epimers are pair of stereoisoisomers which differ in configuration at one stereogenic center.  In D-galactose molecule one terminal aldehydic and one terminal alcoholic group is present.  The given ions ${\text{Ag}}^{+},{\text{NH}}_3,{\text{OH}}^{-}$ are the reactants and gives diamine silver complex.  This complex reacts with D-galactose.  It gives D-galactonic acid.

Answer to Problem 31P

The product obtained when D-galactose reacts with ${\text{Ag}}^{+},{\text{NH}}_3,{\text{OH}}^{-}$ is given below in Figure 2.

Figure 2

Explanation of Solution

The product obtained when D-galactose reacts with ${\text{Ag}}^{+},{\text{NH}}_3,{\text{OH}}^{-}$ is as follows,

Figure 2

The given ions ${\text{Ag}}^{+},{\text{NH}}_3,{\text{OH}}^{-}$ are the reactants and gives diamine silver complex. This complex reacts with D-galactose.  It gives D-galactonic acid.

c)

Interpretation Introduction

Interpretation:

The product obtained when D-galactose reacts with ${\text{NaBH}}_{\text{4}}$, followed by ${\text{H}}_{\text{3}}{\text{O}}^{+}$ is to be stated.

Concept Introduction:

D-galactose is a monosaccharide molecule and it is sweet in taste as glucose.  It is C-$4$ epimer of glucose.

Epimers are pair of stereoisoisomers which differ in configuration at one stereogenic center.  In D-galactose molecule one terminal aldehydic and one terminal alcoholic group is present.  ${\text{NaBH}}_{\text{4}}$ is a good reducing agent.  It reduces aldehydic group to the alcoholic group in the presence of ${\text{H}}_{\text{3}}{\text{O}}^{+}$.

Answer to Problem 31P

The product obtained when D-galactose reacts with ${\text{NaBH}}_{\text{4}}$, followed by ${\text{H}}_{\text{3}}{\text{O}}^{+}$ is given in Figure 3.

Figure 3

Explanation of Solution

The product obtained when D-galactose reacts with ${\text{NaBH}}_{\text{4}}$, followed by ${\text{H}}_{\text{3}}{\text{O}}^{+}$ is as follows,

Figure 3

The product obtained when D-galactose reacts with ${\text{NaBH}}_{\text{4}}$, followed by hydrolysis in acidic medium is D-galacitol.

d)

Interpretation Introduction

Interpretation:

The product obtained when D-galactose reacts with excess ${\text{CH}}_3\text{I}$ and ${\text{Ag}}_2\text{O}$ is to be stated.

Concept Introduction:

D-galactose is a monosaccharide molecule and it is sweet in taste as glucose. It is C-$4$ epimer of glucose.  Epimers are pair of stereoisoisomers which differ in configuration at one stereogenic center.  In D-galactose molecule one terminal aldehydic and one terminal alcoholic group is present.

Answer to Problem 31P

The product obtained when D-galactose reacts with excess ${\text{CH}}_3\text{I}$ and ${\text{Ag}}_2\text{O}$ is given in Figure 4.

Figure 4

Explanation of Solution

The product obtained when D-galactose reacts with excess ${\text{CH}}_3\text{I}$ and ${\text{Ag}}_2\text{O}$ is as follows,

Figure 4

e)

Interpretation Introduction

Interpretation:

The product obtained when D-galactose reacts with ${\text{Br}}_2$ in water is to be stated.

Concept Introduction:

D-galactose is a monosaccharide molecule and it is sweet in taste as glucose.  It is C-$4$ epimer of glucose.  Epimers are pair of stereoisoisomers which differ in configuration at one stereogenic center.  In D-galactose molecule one terminal aldehydic and one terminal alcoholic group is present.

Answer to Problem 31P

The product obtained when D-galactose reacts with ${\text{Br}}_2$ in water is given in Figure 5.

Figure 5

Explanation of Solution

The product obtained when D-galactose reacts with ${\text{Br}}_2$ in water is as follows,

Figure 5

f)

Interpretation Introduction

Interpretation:

The product obtained when D-galactose reacts with ethanol $\text{+HCl}$ is to be stated.

Concept Introduction:

D-galactose is a monosaccharide molecule and it is sweet in taste as glucose.  It is C-$4$ epimer of glucose.  Epimers are pair of stereoisoisomers which differ in configuration at one stereogenic center.  In D-galactose molecule one terminal aldehydic and one terminal alcoholic group is present.

Answer to Problem 31P

The product obtained when D-galactose reacts with ethanol $\text{+HCl}$ is given in Figure 6.

Figure 6

Explanation of Solution

The product obtained when D-galactose reacts with ethanol $\text{+HCl}$ is as follows,

Figure 6

g)

Interpretation Introduction

Interpretation:

The products obtained when D-galactose reacts with the given reactants are to be stated.

Concept Introduction:

D-galactose is a monosaccharide molecule and it is sweet in taste as glucose.  It is C-$4$ epimer of glucose.  Epimers are pair of stereoisoisomers which differ in configuration at one stereogenic center.  In D-galactose molecule one terminal aldehydic and one terminal alcoholic group is present.

Answer to Problem 31P

The products obtained when D-galactose reacts with the given reactants are shown in figure 7.

Figure 7

Explanation of Solution

The given reactants are hydroxylamine/trace acid, acetic anhydride/heat and ${\text{OH}}^{\text{-}}{\text{/H}}_{\text{2}}\text{O}$. All these reactants are used in a sequence and it is shown as,

Figure 7

In the above reaction D-galactose first reacts with hydroxylamine in the presence of an acid, a compound of oxime is formed.  Then it reacts with acetic anhydride with heat gives nitrile compound.  Now, nitrile compound undergoes a reaction with base a compound D-Lyxose is formed.