Question

When methyl phosphate is heated in acid solution, it reacts with water: $$ \mathrm{CH}_{3} \mathrm{OPO}_{3} \mathrm{H}_{2}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{CH}_{3} \mathrm{OH}+\mathrm{H}_{3} \mathrm{PO}_{4} $$ If the reaction is carried out in water enriched with \({ }^{18} \mathrm{O}\), the oxygen- 18 isotope is found in the phosphoric acid product but not in the methanol. What does this tell us about the bond-breaking scheme in the reaction?

Short answer

The bond-breaking scheme of the reaction suggests that the Oxygen-Phosphorus bond is formed from the oxygen atom in the water molecule. The Oxygen-Carbon bond in the methyl phosphate is not broken in this reaction process, hence the Oxygen-18 isotope, initially in water, is not observed in methanol but is observed in phosphoric Acid.

Step-by-step solution

Understand the Plaintext Chemical equation

The provided chemical equation is: \(CH_{3}OPO_{3}H_{2} + H_{2}O \rightarrow CH_{3}OH + H_{3}PO_{4}\). This indicates that methyl phosphate in solution with water produces methanol and phosphoric acid.

Note the involvement of Oxygen-18 isotope

The reaction is carried out in water which is enriched with Oxygen-18. However, after the reaction, this specific isotope is only found in the phosphoric acid product and not in the methanol.

Interpret the placement of Oxygen-18 isotope

The absence of the Oxygen-18 isotope in methanol means the oxygen atom in methanol must be derived from the original methyl phosphate molecule. Therefore, the Oxygen-18 isotope from the water molecule must be present in the phosphoric acid product. This gives us information how oxygen atoms are relocated during the reaction.

Determine the bond-breaking scheme

Based on the above steps, it can be concluded that the Oxygen-18 isotope, which is incorporated into the phosphoric acid, comes from the water molecule. This implies that the Oxygen-Hydrogen bond in water is broken and the Oxygen-Phosphorus bond is formed during the reaction. Therefore, the Oxygen-Carbon bond in methyl phosphate is not broken in the reaction process, supporting why Oxygen-18 isotope is not observed in methanol.

Key concepts

Isotope Labeling

Isotope labeling is a technique that helps scientists track atoms through a chemical reaction. In this process, certain atoms like oxygen, nitrogen, or carbon are replaced by their isotopes. An isotope is a form of an element with the same number of protons but a different number of neutrons, giving it a different mass.
For example, Oxygen-18 is a heavier version of the common oxygen-16 isotope. By using isotope labeling, like incorporating Oxygen-18 into water, researchers can trace how a specific atom moves during a chemical transformation.
This method is crucial for understanding complex reaction mechanisms, as it reveals which bonds are formed or broken based on where the labeled isotope ends up in the reaction products. Through this technique, you gain insight into the pathway and efficiency of the reaction, making it a valuable tool in chemistry and biochemistry.

Bond-Breaking Scheme

A bond-breaking scheme outlines how chemical bonds between atoms are altered during a reaction. This concept is essential in understanding reaction mechanisms, as it explains the transformation of reactants into products.
During a reaction, understanding which bonds are broken and formed can tell us a lot about how atoms are rearranged. For instance, in the reaction between methyl phosphate and water, it's critical to pinpoint which specific bonds in both reactants are disrupted and reformed. In this case, the bonds in water, specifically one involving an oxygen-hydrogen pair, need to break to incorporate into the phosphoric acid product.
A practical way to confirm this understanding is by using isotope labeling. If a labeled hydrogen or oxygen atom ends up in a specific product, it indicates that the bond involving this atom was broken and reformed. Therefore, applying bond-breaking schemes alongside isotope labeling enhances the understanding of reaction paths and energy changes.

Oxygen-18 Isotope

The Oxygen-18 isotope plays a pivotal role in deciphering reaction mechanisms. It serves as a tracer that helps scientists track the movement of oxygen atoms during chemical reactions. Distinct from the regular oxygen-16, Oxygen-18 has two more neutrons, making it heavier and distinguishable in experiments.
When used in reactions, such as the formation of methanol and phosphoric acid from methyl phosphate and water, Oxygen-18 helps determine which bonds are dynamic. The result that it's found in phosphoric acid but not in methanol tells us a story. It confirms that the oxygen in methanol was originally part of the methyl phosphate, while the labeled oxygen from water is incorporated into phosphoric acid.
Thus, the presence and absence of Oxygen-18 in different products allow researchers to map bond formations and breaks, offering deep insight into the reaction's mechanism. This isotope, due to its unique properties, serves as a significant tool in understanding and verifying chemical reactions.