Question

Q is When glucose is treated with \(\mathrm{CH}_{3} \mathrm{OH}\) and \(\mathrm{HCl}\), it gives two isomer of methyl glycosides. One of the isomer consumes \(\mathrm{x}\) mole of \(\mathrm{HIO}_{4}\) and it gives one mole of HCOOH but no formaldehyde is obtained.

Short answer

The two isomers of methyl glycosides formed when glucose is treated with CH3OH and HCl are α-D-methylglucoside and β-D-methylglucoside. The isomer reacting with HIO4 to give one mole of HCOOH without any formaldehyde production is α-D-methylglucoside, which has a vicinal diol group that can be cleaved by the strong oxidizing agent.

Step-by-step solution

Identify the reactions involved

First, we need to identify that glucose is being treated with CH3OH and HCl. This process is known as methylation of glucose, and will give rise to methyl glycosides. Furthermore, it is given that one of the isomer reacts with HIO4. HIO4 is a strong oxidizing agent, which reacts with the glycoside isomers to cleave them into smaller molecules.

Structure of Glucose

Glucose is a monosaccharide, with the chemical structure \(C_6H_{12}O_6\). When written in its cyclic form, it is found in two anomeric forms: α-D-glucopyranose and β-D-glucopyranose. Both of these contain a hemiacetal functional group, which will be involved in the formation of methyl glycosides.

Formation of Methyl Glycosides

When glucose is treated with CH3OH and HCl, the hemiacetal group reacts, resulting in the formation of two isomers of methyl glycosides. The isomers formed are α-D-methylglucoside and β-D-methylglucoside, which are the anomeric forms of methyl glucosides.

Reaction of One Isomer with HIO4

It is given that one of the isomers reacts with x moles of HIO4, without producing any formaldehyde. Since formaldehyde is produced when an aldehyde is oxidized, we can conclude that the isomer reacting with HIO4 does not have any aldehyde groups. The α-D-methylglucoside and β-D-methylglucoside isomers only differ in the configuration at the anomeric carbon. Both isomers have an anomeric carbon linked to an OCH3 group, and no aldehydes groups are present. Therefore, both isomers will react with HIO4. In order to produce HCOOH, the initial glycoside must have a vicinal diol group. Only α-D-methylglucoside fits this criterion.

Reaction of α-D-methylglucoside with HIO4

When α-D-methylglucoside reacts with HIO4, the vicinal diol group is cleaved, producing one mole of HCOOH and a molecule which contains one less carbon atom. The number of moles of HIO4 consumed (x) in this reaction will depend on the number of cleavages carried out.

Determining the Structures of the Methyl Glycoside Isomers

Based on our analysis, the two isomers of methyl glycosides formed when glucose is treated with CH3OH and HCl are α-D-methylglucoside and β-D-methylglucoside. The isomer reacting with HIO4 to give one mole of HCOOH without any formaldehyde is α-D-methylglucoside.

Key concepts

Monosaccharides

Monosaccharides are the simplest form of carbohydrates and are often referred to as simple sugars. These molecules are the basic building blocks of more complex carbohydrates such as disaccharides and polysaccharides. A common monosaccharide that plays a central role in biochemistry is glucose, often called 'blood sugar' because of its importance in providing energy to the body.

Glucose has the molecular formula \(C_6H_{12}O_6\) and exists primarily in two cyclic forms when in solution: the six-membered ring glucopyranose, and the five-membered ring glucofuranose. Glucose is a perfect example to show how monosaccharides can have structural variability. The two cyclic forms of glucose, alpha (α) and beta (β), differ in the orientation of the hydroxyl (\(OH\)) group on the first carbon, referred to as the 'anomeric' carbon. This subtle variation leads to different properties and reactivity, which is a key concept in understanding the formation of methyl glycosides.

Methylglucoside Isomers

In our exercise context, glucose undergoes methylation to form methylglucoside isomers. Methylation involves the addition of a methyl group (\(CH_3\)) to a molecule. For glucose, which contains a reactive hemiacetal group, treatment with methyl alcohol (\(CH_3OH\)) and hydrochloric acid (\(HCl\)) leads to the formation of methylated derivatives. This reaction replaces the hydrogen atom of the hydroxyl group that is part of the hemiacetal at the anomeric carbon, thus forming two isomers: α-D-methylglucoside and β-D-methylglucoside.

The α and β forms differ at the anomeric carbon similar to their parent sugars. However, both α-D-methylglucoside and β-D-methylglucoside lack an aldehyde group but have an ether link at the anomeric carbon. This structural detail is important for understanding their reactivity, especially when it comes to oxidation reactions. The fact that they do not contain aldehyde groups excludes the possibility of forming formaldehyde upon oxidation.

Oxidation Reactions

Oxidation reactions involve the loss of electrons from a molecule, often with the involvement of an oxidizing agent. In the context of carbohydrates, oxidation reactions can break down sugar molecules or convert certain functional groups to more oxidized states, such as converting alcohols to carbonyl compounds (aldehydes and ketones).

Periodic acid (\(HIO_4\)) is a strong oxidizing agent used in the oxidation of sugars. It is particularly adept at cleaving vicinal diols, which are pairs of hydroxyl groups on adjacent carbon atoms. When one of the methyl glucoside isomers reacts with periodic acid without producing formaldehyde, it suggests that there are no free aldehyde groups in that isomer to be oxidized, as this molecule has been converted into a methyl ether upon methylation. For α-D-methylglucoside, the oxidation reaction with \(HIO_4\) cleaves the vicinal diol group in the glycoside, producing formic acid (\(HCOOH\)) and reducing the carbon chain by one. This specificity to oxidation reactions links back to the structure of the isomers where only the α-D-methylglucoside has that specific vicinal diol necessary for the reaction with \(HIO_4\) to produce formic acid exclusively.