Question

Identify each of the following glucose derivatives: (a) \(\mathrm{A}+4 \mathrm{HIO}_{4} \rightarrow 3 \mathrm{HCOOH}+\mathrm{HCHO}+\mathrm{OHC}-\mathrm{COOH}\) (b) \(\mathrm{B}+5 \mathrm{HIO}_{4} \rightarrow 4 \mathrm{HCOOH}+2 \mathrm{HCHO}\) (c) \(\mathrm{C}+3 \mathrm{HIO}_{4} \rightarrow 2 \mathrm{HCOOH}+2 \mathrm{OHC}-\mathrm{COOH}\) (d) \(\mathrm{D}+4 \mathrm{HIO}_{4} \rightarrow 4 \mathrm{HCOOH}+\mathrm{OHC}-\mathrm{COOH}\)

Short answer

The glucose derivatives for each reaction are: (a) Glucaric acid, (b) Glucoheptose, (c) Gluconic acid, and (d) Glucaric acid.

Step-by-step solution

(a) Identify glucose derivative A

In this reaction, we have: \(A + 4 \ HIO_4 \rightarrow 3 \ HCOOH + HCHO + OHC-COOH\) Since 4 molecules of HIO4 are used, there must be 4 vicinal diols in the glucose derivative A. Also, out of 4 cleavages, 1 results in a carboxylic acid. The resulting glucose derivative A is Glucaric acid.

(b) Identify glucose derivative B

In this reaction, we have: \(B + 5 \ HIO_4 \rightarrow 4 \ HCOOH + 2 \ HCHO\) Since 5 molecules of HIO4 are used, there must be 5 vicinal diols in the glucose derivative B. Out of 5 cleavages, none of them result in a carboxylic acid. The resulting glucose derivative B is Glucoheptose.

(c) Identify glucose derivative C

In this reaction, we have: \(C + 3 \ HIO_4 \rightarrow 2 \ HCOOH + 2 \ OHC-COOH\) Since 3 molecules of HIO4 are used, there must be 3 vicinal diols in the glucose derivative C. Out of 3 cleavages, 2 of them result in carboxylic acids. The resulting glucose derivative C is Gluconic acid.

(d) Identify glucose derivative D

In this reaction, we have: \(D + 4 \ HIO_4 \rightarrow 4 \ HCOOH + OHC-COOH\) Since 4 molecules of HIO4 are used, there must be 4 vicinal diols in the glucose derivative D. Out of 4 cleavages, 1 of them results in a carboxylic acid. The resulting glucose derivative D is Glucaric acid.

Key concepts

Periodate Oxidation

Periodate oxidation is a chemical process used by organic chemists to cleave vicinal diols – compounds in which two hydroxyl (OH) groups are adjacent to each other on a carbon chain. During this reaction, periodic acid (HIO_4) acts as an oxidizing agent, effectively cutting the carbon-carbon bond between the two hydroxyl groups.

When applied to carbohydrates, periodate oxidation serves as a powerful tool for structure elucidation. It allows chemists to determine the presence of vicinal diols by observing the break down into smaller fragments. Different carbohydrates yield specific fragments upon periodate oxidation, which can be further analyzed to identify the original molecule. For example, the reaction often results in the formation of formic acid (HCOOH) and formaldehyde (HCHO), alongside other possible products such as carboxylic acids.

Vicinal Diols

Vicinal diols are organic compounds that feature two hydroxyl groups on adjacent carbon atoms within a molecule. They play a crucial role in carbohydrate chemistry, as sugars often contain vicinal diol functional groups.

These groups are the key targets in periodate oxidation reactions. The presence of vicinal diols within a sugar molecule can be indicative of specific structural elements, which in turn affect reactivity and the types of products formed during such reactions. This feature of sugars becomes particularly important when trying to identify glucose derivatives, as the pattern and number of vicinal diol groups will inform the outcome of periodate oxidation and the subsequent identification process.

Glucaric Acid

Glucaric acid, also known as saccharic acid, is one of the glucose derivatives that can be identified through periodate oxidation. It is characterized by the presence of carboxyl groups (COOH) at both ends of the molecule. As a dicarboxylic acid derivative of glucose, it possesses several vicinal diol groups which are susceptible to oxidation.

In the context of the exercise, the production of three molecules of formic acid and one molecule each of formaldehyde and OHC-COOH indicates the presence of glucaric acid, as the specific pattern of oxidation matches its diol group arrangement.

Glucoheptose

Glucoheptose is a seven-carbon monosaccharide, an extended version of glucose with an additional -CH2OH group, making it a heptose rather than a hexose like glucose. During periodate oxidation, glucoheptose reveals its structure by not forming any carboxylic acid as a product, just formic acid and formaldehyde.

This outcome suggests an arrangement of vicinal diols without interruption by non-diol groups, which is consistent with glucoheptose structure where the chain is elongated but maintains the necessary diol arrangement to be completely cleaved by HIO_4 without resulting in the formation of carboxylic acids.

Gluconic Acid

Gluconic acid is a glucose derivative where the aldehyde group at the end of the glucose molecule is oxidized to a carboxyl group. It is significant in biochemistry and food industry as a mild organic acid. When subjected to periodate oxidation, gluconic acid is cleaved to produce two molecules of formic acid and two molecules of OHC-COOH, providing insight into its structure.

During the oxidation process, the vicinal diol groups in gluconic acid react with periodate to form the products indicative of a glucose structure containing a carboxylic group resulting from the initial oxidation of its aldehyde group.