Question

The compound pentaerythritol, \(\mathrm{C}\left(\mathrm{CH}_{2} \mathrm{OH}\right)_{4}\), used in making explosives, is obtained from the reaction of acetaldehyde and formaldehyde in the presence of calcium hydroxide. Outline the probable steps in this synthesis.

Short answer

The probable steps in the synthesis of pentaerythritol from acetaldehyde and formaldehyde in the presence of calcium hydroxide are: 1. Nucleophilic attack: Acetaldehyde reacts with formaldehyde, forming an intermediate species. 2. Deprotonation: Calcium hydroxide deprotonates the hydroxyl group of the intermediate species. 3. Reduction: The intermediate species are reduced, forming a compound containing a \(\mathrm{C}\left(\mathrm{CH}_{2}\mathrm{OH}\right)_{2}\) moiety. 4. Reaction with more formaldehyde: This compound reacts with additional molecules of formaldehyde, forming a larger intermediate species with multiple \(\mathrm{C}\mathrm{H}_{2}\mathrm{OH}\) groups. 5. Formation of pentaerythritol: The intermediate species undergoes intramolecular cyclization, forming the final pentaerythritol product (\(\mathrm{C}\left(\mathrm{CH}_{2}\mathrm{OH}\right)_{4}\)).

Step-by-step solution

Identify the reactants and products

In this synthesis, the reactants are acetaldehyde (\(\mathrm{C}\mathrm{H}_{3}\mathrm{C}\mathrm{H}\mathrm{O}\)) and formaldehyde (\(\mathrm{H}\mathrm{C}\mathrm{H}\mathrm{O}\)), and the product is pentaerythritol (\(\mathrm{C}\left(\mathrm{CH}_{2}\mathrm{OH}\right)_{4}\)). Calcium hydroxide (\(\mathrm{Ca}\left(\mathrm{OH}\right)_{2}\)) is used as a catalyst.

Determine the key functional groups

The key functional groups involved in this synthesis are the carbonyl groups (\(\mathrm{C}=\mathrm{O}\)) present in both acetaldehyde and formaldehyde, along with the hydroxyl groups (\(\mathrm{O}\mathrm{H}\)) present in pentaerythritol. These groups will be participating in the reaction.

Consider possible reaction mechanisms

One possible mechanism for this synthesis is the nucleophilic attack of formaldehyde by the carbonyl oxygen of acetaldehyde, followed by the reduction of the product to form pentaerythritol. The presence of calcium hydroxide can facilitate these steps by acting as a base to deprotonate the hydroxyl groups in the intermediate species, promoting the nucleophilic attack and reduction.

Outline the synthesis steps

1. Nucleophilic attack: Acetaldehyde reacts with formaldehyde through nucleophilic attack by acetaldehyde's carbonyl oxygen on the carbonyl carbon of formaldehyde, forming an intermediate species. 2. Deprotonation: Calcium hydroxide deprotonates the hydroxyl group of the intermediate species, making the oxygen more nucleophilic and ready for the next step. 3. Reduction: The intermediate species are reduced, forming new \(\mathrm{C}-\mathrm{O}\) and \(\mathrm{C}-\mathrm{H}\) bonds. The resulting compound contains a \(\mathrm{C}\left(\mathrm{CH}_{2}\mathrm{OH}\right)_{2}\) moiety. 4. Reaction with more formaldehyde: The reaction product from step 3 reacts with additional molecules of formaldehyde through nucleophilic attack, forming a larger intermediate species containing multiple \(\mathrm{C}\mathrm{H}_{2}\mathrm{OH}\) groups, connected to a central carbon atom. 5. Formation of pentaerythritol: The above-mentioned intermediate species undergoes intramolecular cyclization, forming the final pentaerythritol product (\(\mathrm{C}\left(\mathrm{CH}_{2}\mathrm{OH}\right)_{4}\)). These steps outline the probable synthesis of pentaerythritol from acetaldehyde and formaldehyde in the presence of calcium hydroxide. Keep in mind that other mechanisms and pathways could also be possible, but this represents a plausible mechanism based on the given information.

Key concepts

Nucleophilic Attack

Understanding the mechanism of nucleophilic attack is crucial when studying organic reactions. A nucleofile, often a molecule with a lone pair of electrons, seeks out a positive center, typically the carbon in a carbonyl functional group. In the synthesis of pentaerythritol, the nucleophile is the oxygen of the acetaldehyde's carbonyl group initiating a nucleophilic attack on the carbon of formaldehyde's carbonyl group.

This key step initiates the reaction process, leading to the formation of an intermediate complex. During this step, the electron-rich oxygen donates a pair of electrons towards the electron-deficient carbonyl carbon, creating a covalent bond. This is the cornerstone of the synthesis of pentaerythritol and an essential organic reaction mechanism.

Carbonyl Functional Group

A carbonyl functional group, marked by the presence of a carbon-oxygen double bond \( \mathrm{C}=\mathrm{O} \), is highly reactive due to the polarity of this bond.

The carbon, being electrophilic, attracts nucleophiles and is consequently a common site for chemical reactions. Acetaldehyde and formaldehyde, both utilized in the synthesis of pentaerythritol, contain this reactive carbonyl group which is the target for nucleophilic attack, setting the stage for the subsequent steps in the reaction.

Hydroxyl Functional Group

The hydroxyl functional group, \( \mathrm{OH} \), comprises an oxygen bound to a hydrogen atom and is highly characteristic of alcohols. In pentaerythritol, each of the four carbon atoms is connected to an \( \mathrm{OH} \) group.

These \( \mathrm{OH} \) groups give the molecule unique properties, such as increased solubility in water and other polar solvents, and also make it reactive towards the deprotonation that occurs in the presence of a base, like calcium hydroxide. This deprotonation assists steps in organic synthesis, aiding in the nucleophilic attack by stabilizing the intermediate species through the creation of an alkoxide.

Calcium Hydroxide Catalysis

Calcium hydroxide \(\mathrm{Ca}\left(\mathrm{OH}\right)_{2}\) acts as a catalyst in the synthesis of pentaerythritol. The role of a catalyst is to lower the activation energy for a reaction, thereby making the reaction more efficient.

In this process, calcium hydroxide facilitates the nucleophilic attack by deprotonating the hydroxyl groups, which is crucial for the overall reaction sequence. Its basic nature allows it to accept protons and increases the nucleophilic character of the oxygen atoms in the reactant molecules.

Organic Synthesis Steps

Organic synthesis follows a series of steps or stages to transform simple molecules into more complex compounds. Each step in the synthesis of pentaerythritol — from the nucleophilic attack to the intermediate formation and eventual production of the final compound — demonstrates the intricacies of organic synthesis.

It involves specific sequences of chemical reactions, often requiring catalysts, to create the desired bonds, functional groups, and ultimately, the target molecular structure. The steps in the synthesis of pentaerythritol illustrate the planning and execution of multi-step organic synthesis, embodying the elegant choreography of chemical transformations.