Question

The following compounds are commercially available for use as water-soluble solvents. How could each be made? (a) ${\mathrm{CH}}_3{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$ Carbitol (b) ${\mathrm{C}}_6{\mathrm{H}}_5-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$ Phenyl carbitol (c) $\mathrm{HO}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$ Diethylene gloycol (d) $\mathrm{HO}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$ Triethylene glycol

Short answer

In summary, the compounds can be synthesized as follows: 1. Carbitol: By using Williamson ether synthesis- Prepare ethoxide ion (from ethanol and NaH) and react it with 2-chloroethyl ethyl ether. 2. Phenyl carbitol: By using Williamson ether synthesis- Prepare phenoxide ion (from phenol and NaH) and react it with 2-chloroethyl ethyl ether. 3. Diethylene glycol: Dehydrate ethylene glycol to form ethylene oxide, then open the ring with the nucleophilic addition of ethylene glycol. 4. Triethylene glycol: Start with the synthesis of Diethylene glycol, obtain ethylene oxide, and open the ring with the nucleophilic addition of Diethylene glycol.

Step-by-step solution

1. Synthesize Carbitol (#$a$#)

To synthesize Carbitol: ${\mathrm{CH}}_3{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$, we can use the Williamson ether synthesis, which involves the reaction of an alkoxide ion with an alkyl halide. In this case: 1. Prepare ethoxide ion from ethanol (${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}$) and a strong base like sodium hydride ($\mathrm{NaH}$). 2. React the ethoxide ion with 2-chloroethyl ethyl ether (${\mathrm{CH}}_3{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{Cl}$) to form Carbitol.

2. Synthesize Phenyl carbitol (#$b$#)

To synthesize Phenyl carbitol: ${\mathrm{C}}_6{\mathrm{H}}_5-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$, we can also use the Williamson ether synthesis. In this case: 1. Prepare phenoxide ion from phenol (${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{OH}$) and a strong base like sodium hydride ($\mathrm{NaH}$). 2. React the phenoxide ion with 2-chloroethyl ethyl ether (${\mathrm{CH}}_3{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{Cl}$) to form Phenyl carbitol.

3. Synthesize Diethylene glycol (#$c$#)

To synthesize Diethylene glycol: $\mathrm{HO}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$, we can follow these steps: 1. Start with the dehydration of ethylene glycol ($\mathrm{HO}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$), which produces ethylene oxide (${\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}$). 2. Open the ethylene oxide ring with the nucleophilic addition of ethylene glycol to form Diethylene glycol.

4. Synthesize Triethylene glycol (#$d$#)

To synthesize Triethylene glycol: $\mathrm{HO}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$, we can follow these steps: 1. Start with the synthesis of Diethylene glycol (see step 3) and obtain ethylene oxide (${\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}$) and Diethylene glycol ($\mathrm{HO}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2-\mathrm{OH}$). 2. Open the ethylene oxide ring with the nucleophilic addition of Diethylene glycol to form Triethylene glycol.

Key concepts

Williamson Ether Synthesis

Williamson Ether Synthesis is a classic method in organic chemistry, useful for forming ethers. It involves the reaction between an alcohol-derived alkoxide ion and an alkyl halide. This reaction is widely used due to its simplicity and efficiency.

Here's how it works:

• Alkoxide Ion Formation: An alcohol reacts with a strong base, often sodium hydride (NaH), to form an alkoxide ion. This ion is particularly reactive due to its negative charge.
• Nucleophilic Attack: The alkoxide ion acts as a nucleophile and attacks the electrophilic carbon of an alkyl halide, such as chloroethane, leading to the formation of an ether bond.
• Product Formation: The resultant compound is a stable ether, often characterized by its relatively low reactivity and ability to serve in various applications, including solvents and chemical intermediates.

Williamson Ether Synthesis is an essential tool for synthesizing complex molecules, thanks to its versatility and straightforward protocol.

Ethylene Glycol

Ethylene Glycol is a simple diol and one of the most important compounds in both industrial and automotive applications. It has two hydroxyl (-OH) groups, making it a versatile building block in organic synthesis.

This compound can be synthesized and manipulated through various reactions, including dehydration and nucleophilic addition:

• Dehydration: When heated, ethylene glycol can be dehydrated to form ethylene oxide, an important intermediate in chemical synthesis.
• Nucleophilic Addition: Ethylene oxide can then react with nucleophiles, such as the additional ethylene glycol, to create longer-chain glycols like diethylene glycol.

Ethylene Glycol also prevents the formation of large crystals in solutions, making it extremely useful as an antifreeze agent in cooling systems.

Nucleophilic Addition

Nucleophilic Addition is a key mechanism in organic reactions whereby a nucleophile forms a bond with an electrophilic center in a molecule. This process is fundamental in building complex organic structures.

Here are some details about this reaction:

• Electrophile Characteristics: Electrophiles are partially positively charged species that are attractive targets for nucleophiles. Common examples include carbon atoms in polarized bonds such as C=O or C-Br.
• Role of Nucleophiles: Nucleophiles, such as alkoxide ions, are rich in electrons and donate a pair of electrons to form new covalent bonds.
• Applications: This type of addition is not only crucial in forming alcohols but also important in building complex polyols and polymers.

Nucleophilic addition occurs widely across different organic synthesis reactions, transforming simple molecules into ones with increased functionality.

Alkoxide Ion

Alkoxide Ions are pivotal intermediates in many organic reactions. These ions are formed by the deprotonation of an alcohol using a strong base, resulting in a negatively charged oxygen atom attached to an alkyl chain.

Here are some insights on how these ions work:

• Formation: Reacting an alcohol with a strong base like sodium hydride generates an alkoxide ion, which is more reactive than the alcohol itself.
• Reactivity: As strong nucleophiles, alkoxide ions readily attack electrophiles, such as in Williamson Ether Synthesis.
• Chemical Versatility: Alkoxide ions can participate in a myriad of reactions, making them vital tools for chemists to manipulate organic molecules.

Understanding alkoxide ions helps in predicting and controlling the outcomes of several synthetic routes in organic chemistry.

Strong Base Chemistry

Strong Base Chemistry is an integral part of organic synthesis, especially in the context of forming and utilizing reactive intermediates like alkoxide ions. Strong bases such as sodium hydride (NaH) are essential for deprotonating weakly acidic compounds like alcohols.

Here's why strong bases are crucial:

• Deprotonation Capability: Strong bases effectively remove protons from alcohols, generating reactive species such as alkoxide ions.
• Facilitating Reactions: These generated ions can then participate in various organic transformations, including nucleophilic substitutions and additions.
• Key Examples: NaH and potassium tert-butoxide are common examples of strong bases used in labs to facilitate synthesis activities.

Mastering strong base chemistry offers a strategic advantage in developing robust and efficient synthetic methodologies.