Chapter 22, Problem 19PP

Interpretation Introduction

Interpretation:

The conversion of D-galactose to D-galacturonic acid is to be suggested, by carrying out specific oxidation.

Concept introduction:

舧 A carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1.

舧 ${\text{HNO}}_{\text{3}}$ is an oxidizing agent.

舧 Carbohydrates are oxidized by ${\text{HNO}}_{\text{3}}$ to give aldaric acid as a product.

舧 Aldaric acids are carbohydrates having two carboxylic acids. They are formed due to oxidation reaction of aldoses with dilute ${\text{HNO}}_{\text{3}}$ and their general reaction can be represented as:

舧 The molecules that are nonsuperimposable or not identical with their mirror images are known as chiral molecules.

舧 A pair of two mirror images that are nonidentical is known as enantiomers, which are optically active.

舧 The stereoisomers that are nonsuperimposable on each other and not mirror images of each other are known as diastereomers.

舧 The achiral compounds in which plane of symmetry is present internally and consists of chiral centres are known as meso compounds, but they are optically inactive.

舧 Compounds that have a plane of symmetry tend to exist in meso forms. A meso form arises when the two stereoisomers produce superimposable images, and hence, compounds having meso forms are optically inactive.

舧 The reaction in which there is removal of water molecule is called dehydration reaction. ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is a dehydrating agent.

舧 ${\text{KMnO}}_4$ is a oxidizing agent.

舧 Monosaccharide carbohydrates that have their ${\text{CH}}_{\text{2}}\text{OH}$ placed at the $\text{C}-\text{6}$ atom specifically oxidize to a carbonyl group are called uronic acids. Uronic acid of glucose is called glucuronic acid and that of galactose is called galacturonic acid.

舧 Based on the given information, direct oxidation of an aldose affects its aldehyde group first, converting it to a carboxylic acid. Most oxidizing agents that attack $1^{\text{o}}$ alcohol groups also attack $2^{\text{o}}$ alcohol groups. Hence, the synthesis of a uronic acid from an aldose needs protection of these groups from getting oxidized.