Question

Outline a method of synthesizing \(\alpha\) -phenylethyl tert-buty1 ether from styrene and tert-butyl alcohol. Any inorganic reagents may be employed.

Short answer

To synthesize α-phenylethyl tert-butyl ether from styrene and tert-butyl alcohol, follow these steps: 1. Deprotonate tert-butyl alcohol with sodium hydride (NaH) to form the tert-butoxide ion: \[ tert\text{-}butyl\,alcohol + NaH \rightarrow tert\text{-}butoxide\,Na+ + H_2 \] 2. React styrene with N-bromosuccinimide (NBS) for benzylic bromination to produce α-phenylethyl bromide: \[ styrene + NBS \rightarrow \alpha\text{-}phenylethyl\,bromide \] 3. Perform Williamson Ether Synthesis by reacting the tert-butoxide ion with α-phenylethyl bromide, resulting in the desired ether product and a by-product: \[ tert\text{-}butoxide\,Na+ + \alpha\text{-}phenylethyl\,bromide \rightarrow \alpha\text{-}phenylethyl\,tert\text{-}butyl\,ether + NaBr \]

Step-by-step solution

Formation of tert-butoxide ion from tert-butyl alcohol

To form the tert-butoxide ion from tert-butyl alcohol, we need to deprotonate the alcohol with a strong base, such as sodium hydride (NaH). The reaction takes place as follows: \[ tert\text{-}butyl\,alcohol + NaH \rightarrow tert\text{-}butoxide\,Na+ + H_2 \] This generates the sodium salt of the tert-butoxide ion.

Formation of alkyl halide from styrene

To prepare an alkyl halide from styrene, we need to react it with a suitable halogenation reagent. In this case, we can use N-bromosuccinimide (NBS) as the halogenating agent. The reaction proceeds via radical bromination of the styrene molecule at the benzylic position, generating the desired benzyl bromide. The process can be written as: \[ styrene + NBS \rightarrow \alpha\text{-}phenylethyl\,bromide \]

Williamson Ether Synthesis for the final product formation

With the tert-butoxide ion and the α-phenylethyl bromide in hand, we can now proceed to perform Williamson Ether Synthesis to form the desired ether product. This involves the nucleophilic attack of the alkoxide ion on the alkyl halide, leading to the formation of the ether product and a by-product. The reaction can be represented as: \[ tert\text{-}butoxide\,Na+ + \alpha\text{-}phenylethyl\,bromide \rightarrow \alpha\text{-}phenylethyl\,tert\text{-}butyl\,ether + NaBr \] This reaction yields the desired product, α-phenylethyl tert-butyl ether.

Key concepts

Williamson Ether Synthesis

The Williamson Ether Synthesis is a powerful method in organic chemistry for the formation of ethers. It combines an alkoxide ion with an alkyl halide to form an ether. This process is a classic example of an S\(_N\)2 reaction, where the alkoxide ion acts as a nucleophile. It seeks out and attacks an electrophilic carbon atom in the alkyl halide, displacing a leaving group, usually a halogen.

In the synthesis of \(\alpha\)-phenylethyl tert-butyl ether, the tert-butoxide ion serves as the nucleophile. It attacks the benzylic carbon of \(\alpha\)-phenylethyl bromide. The displacement of the bromine atom results in the formation of the ether. This method is widely used as it allows for the formation of a wide variety of ether products by simply changing the alkoxide or alkyl halide substrate involved.

Alkyl Halides

Alkyl halides are organic compounds where a halogen (such as chlorine, bromine, or iodine) is bonded to an alkyl group. They are crucial intermediates in many chemical reactions, including nucleophilic substitution and elimination reactions. Their reactivity is mainly due to the presence of the polar carbon-halogen bond, which makes the carbon atom electrophilic; susceptible to attack by nucleophiles.

In our synthesis, the \(\alpha\)-phenylethyl bromide serves as the alkyl halide. It is formed through radical bromination of styrene. In the Williamson Ether Synthesis, this bromide acts as the substrate that the tert-butoxide ion attacks, facilitating the creation of the desired ether.

Radical Bromination

Radical bromination is a method of introducing a bromine atom into an organic compound by free radical mechanisms. This reaction typically involves radicals, which are highly reactive atoms or groups of atoms with unpaired electrons. The process commonly uses N-bromosuccinimide (NBS), especially for allylic or benzylic hydrogen abstraction.

For the creation of \(\alpha\)-phenylethyl bromide, styrene undergoes radical bromination at the benzylic position to install a bromine atom. This specific positioning is due to the stability of the benzylic radical that forms during the reaction. These reactions are typically selective and an important tool for chemists to functionalize molecules in a controlled manner.

Tert-butoxide Ion

The tert-butoxide ion is an anion derived from tert-butyl alcohol, and is denoted as \( (CH_3)_3CO^- \) or simply \( t-BuO^- \). It is a strong, bulky base and a powerful nucleophile. Its strength as a nucleophile is particularly useful in reactions like the Williamson Ether Synthesis, where it attacks alkyl halides to form ethers.

To generate the tert-butoxide ion for our synthesis, tert-butyl alcohol is treated with a strong base, like sodium hydride (NaH). This deprotonates the alcohol, resulting in the formation of the tert-butoxide ion, which is then a key reactant in forming \(\alpha\)-phenylethyl tert-butyl ether.

Deprotonation

Deprotonation is the removal of a proton (H\(^+\)) from a molecule, resulting in the formation of an anion. It is a fundamental step in many chemical syntheses. In the context of forming the tert-butoxide ion, deprotonation involves removing a hydrogen ion from tert-butyl alcohol using a strong base like sodium hydride.

The reaction can be visualized as \( (CH_3)_3COH + NaH \rightarrow (CH_3)_3CO^-Na^+ + H_2 \). Here, the hydrogen gas \( H_2 \) is released, and the tert-butoxide ion \( (CH_3)_3CO^- \) is generated. This step is crucial for preparing the reactive species needed for later stages of the ether synthesis, illustrating the interconnectedness of these fundamental reactions in synthetic chemistry.