Question

Using your roadmap as a guide, show how to convert 3-hexyne into propanal. All of the carbon atoms of the target molecule must be derived from the starting material as efficiently as possible. Show all intermediate molecules synthesized along the way.

Short answer

Answer: 3-hexyne can be converted into propanal through an ozonolysis reaction, which involves reacting 3-hexyne with ozone (O3) and a reducing agent such as zinc (Zn) to cleave the triple bond and form two carbonyl groups. The intermediate molecules formed in the process are 1,2,4-trioxolane, and the final products are propanal and acetone.

Step-by-step solution

Analyze the molecules

First, let's analyze the starting material and target molecule. 3-hexyne is an alkyne with six carbon atoms and a triple bond between the third and fourth carbon atoms. The molecular formula of 3-hexyne is C6H10. Propanal is an aldehyde with three carbon atoms and a double bond between the first carbon and an oxygen (C=O). The molecular formula of propanal is C3H6O. From this analysis, we can see that we need to reduce the number of carbon atoms from six to three and introduce an oxygen atom to form the aldehyde functional group.

Ozonolysis reaction

To efficiently cleave the triple bond and reduce the number of carbon atoms, we can perform an ozonolysis reaction on 3-hexyne. In a typical ozonolysis reaction, the triple bond is cleaved by reacting with ozone (O3), followed by the addition of a reducing agent, such as zinc, to complete the cleavage of the alkyne and form two carbonyl groups. 3-hexyne + O3 + Zn → propanal + acetone

Determine intermediate molecules

Now that we have established the reaction sequence, we need to identify the intermediate molecules formed along the way. The ozonolysis reaction proceeds through the formation of an ozonide intermediate. First, the 3-hexyne molecule reacts with ozone to form the ozonide intermediate: 3-hexyne + O3 → [1,2,4-Trioxolane] In the second step, the ozonide intermediate is reduced by the reducing agent, zinc, to produce the final products, propanal and acetone: [1,2,4-Trioxolane] + Zn → propanal + acetone

Final transformation

In conclusion, 3-hexyne can be efficiently converted into propanal through the ozonolysis reaction, involving the formation of an ozonide intermediate. The final products of this reaction are propanal and acetone, with all carbon atoms in propanal being derived from the starting material, 3-hexyne.

Key concepts

Ozonolysis Reaction

When it comes to organic chemistry, one pivotal reaction to change the structure of alkenes and alkynes is the ozonolysis reaction. This process entails the cleaving of carbon-carbon double or triple bonds using ozone (O₃), a powerful oxidizing agent. It's particularly useful for dissecting larger molecules into smaller ones and introducing oxygen into the resulting fragments.

During ozonolysis, ozone first reacts to form an unstable ozonide intermediate. This reaction is fascinating as it takes something as static as a triple bond and transforms it into two new bonds with oxygen. The typical reaction sequence for alkynes, like 3-hexyne, involves the addition of ozone, resulting in the formation of the ozonide: \( R-C\equiv C-R' + O_3 → R-C(=O)-O-O-C(=O)-R' \)

Then, a reducing agent (frequently zinc or dimethyl sulfide) is introduced, which converts the ozonide into carbonyl compounds. For instance, when zinc is used, it splits the ozonide into two parts and typically leads to aldehydes or ketones depending on the placement of the original double or triple bond. When applied correctly, ozonolysis is a highly efficient step for molecular deconstruction in synthetic chemistry.

3-Hexyne Conversion

3-Hexyne conversion via ozonolysis is an elegant example of utilizing chemical processes to reshape a molecule. 3-Hexyne is a six-carbon compound with a distinguishing triple bond between the third and fourth carbon atoms. The molecular goal here is to transform it into a simpler molecule, such as propanal, which only has three carbons.

In this context, the ozonolysis of 3-hexyne cleaves the molecule at the triple bond, forming two distinct fragments. Let's visually break down what happens during this chemical performance: \( 3-Hexyne \xrightarrow[\text{Ozonolysis}]{O_3, Zn} propanal + acetone \)

It's like cutting a paper in two: the alkyne's triple bond reacts with ozone, we split the molecule, and then a little chemical assist from our friend zinc helps us to pull apart the two sections. The carbon atoms redistribute to form propanal and another molecule, acetone. The charm lies in the simplicity—through a single major reaction, we're significantly altering the complexity of the starting molecule.

Propanal Synthesis

The synthesis of propanal from 3-hexyne is a transformative process that showcases the precision with which chemists can construct desired molecules from more complex starting materials. Propanal is an aldehyde consisting of a three-carbon chain, with its formula being C₃H₆O.

Its creation involves strategically cutting the six-carbon chain of 3-hexyne right down the middle. Once the ozonolysis of 3-hexyne is performed, we're left with two three-carbon fragments. Zinc plays a crucial role here by sweeping in to complete the reaction, allowing the ozonide to break down into the target aldehyde—propanal—and a byproduct, acetone.

In chemistry language, the equation looks like this: \( [1,2,4-Trioxolane]+ Zn → propanal + acetone \)

This reaction is highly tactical, harnessing the power of ozone to cleave and oxidize a molecule in a way that sets the stage for the creation of a specific desired product. Propanal synthesis through ozonolysis is not only efficient but also preserves the number of carbon atoms from the original alkyne, reflecting the clever orchestration of molecular manipulation in synthetic chemistry.