Question

Meso tartaric acid cannot be obtained by reaction: (A) Fumaric acid \(+\mathrm{HCO}_{3} \mathrm{H}\) (B) Maleic acid \(+\mathrm{OsO}_{4}\) (C) Fumaric acid \(+\mathrm{OsO}_{4}\) (D) Maleic acid + dil. \(\mathrm{KMnO}_{4}\)

Short answer

Meso tartaric acid cannot be obtained by reaction (C) Fumaric acid + \(\mathrm{OsO}_{4}\) because the syn addition of two hydroxyl groups (-OH) to the trans isomer of butenedioic acid (Fumaric acid) does not result in the formation of meso tartaric acid.

Step-by-step solution

Reaction A: Fumaric acid + HCO3H

Fumaric acid (C4H4O4) is a trans isomer of butenedioic acid. In this reaction, addition of hydrochloric acid (HCO3H) is a hydration reaction. It will add one water molecule to the double bond present in fumaric acid. However, the resulting product will not be meso tartaric acid because the positions of the hydroxyl (-OH) and carboxyl groups (-COOH) are different from those in meso tartaric acid.

Reaction B: Maleic acid + OsO4

Maleic acid (C4H4O4) is a cis isomer of butenedioic acid. OsO4 (osmium tetroxide) is a reagent used in the dihydroxylation of alkenes. The reaction will add two hydroxyl groups (-OH) in a syn addition to the double bond present in maleic acid, which will form meso tartaric acid. This reaction can produce meso tartaric acid, so it is not the correct answer.

Reaction C: Fumaric acid + OsO4

Fumaric acid (C4H4O4) is a trans isomer of butenedioic acid. OsO4 (osmium tetroxide) is a reagent used in the dihydroxylation of alkenes. The reaction will add two hydroxyl groups (-OH) in a syn addition to the double bond found in fumaric acid. As a result, the product formed will not be meso tartaric acid. Therefore, this reaction cannot produce meso tartaric acid.

Reaction D: Maleic acid + dil. KMnO4

Maleic acid (C4H4O4) is a cis isomer of butenedioic acid. KMnO4 (potassium permanganate) is a strong oxidizing agent, which causes oxidative cleavage of alkenes. In this reaction, KMnO4 will oxidize the double bond in maleic acid. However, the reaction will not generate meso tartaric acid, but instead dicarboxylic acid. This is not the correct answer because the reaction can produce meso tartaric acid. Based on the analyses of each reaction, we can conclude that the answer is: (C) Fumaric acid + \(\mathrm{OsO}_{4}\)

Key concepts

Cis-Trans Isomerism

Cis-trans isomerism is a type of stereoisomerism where the relative orientations of functional groups within a molecule differ. Let's use fumaric acid and maleic acid as examples. Both have the same molecular formula, but they differ in the arrangement of their respective functional groups around a double bond.

Maleic acid is the cis isomer; its carboxyl (-COOH) groups are on the same side of the double bond. On the other hand, fumaric acid, the trans isomer, has its carboxyl groups on opposite sides. This difference in arrangement leads to distinct chemical properties and reactivities between the two.

In synthesis and reactions, these differences play a crucial role. For example, the reaction between OsO₄ and maleic acid leads to meso tartaric acid, whereas with fumaric acid, the same reagent does not yield the meso form. This highlights the importance of cis-trans isomerism in determining the outcome of chemical reactions.

Dihydroxylation

Dihydroxylation is the process of adding two hydroxyl groups (-OH) to a substrate, typically an alkene. This reaction is significant in organic chemistry for converting alkenes into diols (two alcohol functional groups).

OsO₄, or osmium tetroxide, is a common reagent used in this process, known for inducing a syn addition. This means the two hydroxyl groups are added to the same side of the double bond. In the case of maleic acid, OsO₄ helps to create a diol that has the same stereochemistry on both carbons, leading to meso tartaric acid.

Syn addition is crucial in producing particular stereoisomers. For maleic acid, it results in a single stereoisomer: meso tartaric acid, due to its symmetrical structure. This reaction's stereochemical outcome contrasts with that of fumaric acid, which does not result in a meso compound when treated similarly.

Hydration Reaction

Hydration reactions involve the addition of water to a molecule. They are fundamental in organic transformations, often converting alkenes or alkynes into alcohols. In our example, fumaric acid undergoes such a reaction, transforming its double bond through the addition of water (in the form of H and OH) to produce an alcohol.

However, trans isomers like fumaric acid challenge formation routes due to their steric configurations. Even when subjected to hydration, the outcome is not meso tartaric acid but rather a different diol configuration. This instance demonstrates that not all hydration reactions lead to identical products, especially in molecules exhibiting stereoisomerism.

The reaction conditions and reagent choices can manipulate the specific hydration outcomes of compounds, highlighting the importance of understanding the surrounding chemical environment in these processes.

Oxidative Cleavage

Oxidative cleavage is a powerful reaction that breaks down alkenes into smaller units using oxidation. This reaction alters the carbon-carbon double bond into carbonyl or carboxyl groups, depending on the conditions.

Potassium permanganate ( KMnO₄ ) is a frequently used reagent for this purpose. It is particularly potent and can lead to the complete oxidation of alkene substrates like maleic acid. Instead of yielding meso tartaric acid, KMnO₄ with maleic acid leads to the formation of smaller, oxidized products such as dicarboxylic acids.

This reaction showcases how oxidative cleavage can change the structure of molecules significantly. It emphasizes the need to choose reagents wisely based on the desired chemical transformation and target structure.

Reagents in Organic Chemistry

Reagents are the chemical substances added to interact with other compounds to create reactions. In the context of organic chemistry, they are essential tools for guiding the path of chemical transformations.

Several key reagents help achieve specific transformations. Osmium tetroxide (OsO₄) is prominent in dihydroxylation reactions, creating syn-addition outcomes and impacting the stereochemistry of products. Potassium permanganate ( KMnO₄ ) is another versatile reagent, often used for both dihydroxylation and oxidative cleavage, depending on its concentration and the reaction conditions.

When selecting reagents, considering the reaction mechanism, potential by-products, and final product stereochemistry is paramount. Understanding the role and effect of each reagent helps predict and control the outcome of organic synthesis, crucial for efficiently achieving desired chemical structures like meso tartaric acid.