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Chapter 6: Problem 143

Using only isobutene and any inorganic reagents synthesize \(2,2,4\) -trimethylpentane.

Short Answer

Expert verified
To synthesize 2,2,4-trimethylpentane from isobutene, follow these steps: 1. Hydrate isobutene with an acid catalyst to produce 2-methyl-2-propanol. 2. Dehydrate 2-methyl-2-propanol using a strong acid, forming 2-methyl-2-butene. 3. Hydrate 2-methyl-2-butene, following Markovnikov's rule, to create 2,3-dimethyl-2-butanol. 4. Replace the hydroxy group in 2,3-dimethyl-2-butanol with a halogen using hydrogen halide, yielding 2,3-dimethyl-2-bromo-butane. 5. Perform dehydrohalogenation with a strong base to form 2,2,4-trimethylpent-2-ene. 6. Catalytically hydrogenate the product using a metal catalyst, resulting in 2,2,4-trimethylpentane.

Step by step solution

01

Hydration of Isobutene

To start with, we'll need to hydrate isobutene (2-methylpropene) to produce 2-methyl-2-propanol. This is essentially just adding a water molecule across the double bond. Hydration is often carried out with an acid catalyst, typically sulfuric acid or phosphoric acid.
02

Acidic Dehydration

The next step is to dehydrate the 2-methyl-2-propanol. This is achieved by heating the alcohol in the presence of a strong acid, such as sulfuric acid. This causes the elimination of a water molecule and formation of a more substituted alkene, 2-methyl-2-butene.
03

Second Hydration

Then, hydrate the 2-methyl-2-butene to get 2,3-dimethyl-2-butanol. Here, we add water across the double bond. This is a delicate process because we want to hydrate the internal carbon of the butene, not the terminal carbon. The major product will be the one where the water adds to the more substituted carbon atom, in accordance with Markovnikov's rule.
04

Halogenation

Next, the hydroxy group in 2,3-dimethyl-2-butanol is replaced with a halogen using a reaction with hydrogen halide (HI or HBr) to give 2,3-dimethyl-2-bromo-butane. This is a substitution reaction where the hydroxy group is replaced by a bromine atom.
05

Dehydrohalogenation

The bromo group in 2,3-dimethyl-2-bromo-butane is next eliminated via dehydrohalogenation to yield 2,2,4-trimethylpent-2-ene. This is achieved by reacting the bromo-butane with a strong base (usually ethanolic KOH).
06

Catalytic Hydrogenation

Finally, the 2,2,4-trimethylpent-2-ene is hydrogenated to provide the target molecule, 2,2,4-trimethylpentane. This involves the geotropic absorption of H2 across the double bond in the presence of a suitable metal catalyst, such as platinum or palladium.

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Most popular questions from this chapter

Compound \(\mathrm{X}\) has the molecular formula \(\mathrm{C}_{4} \mathrm{H}_{8}\). Compound \(\mathrm{Y}\) is obtained when hydrogen bromide is added to \(\mathrm{X}\). Compound Y reacts with AgOH to form a tertiary alcohol. Identify all structures.

Consider the feasibility of a free-radical chain mechanism for hydrogenation of ethylene in the vapor state at \(25^{\circ}\) by the following propagation steps: $$ \begin{aligned} &\mathrm{CH}_{3}-\mathrm{CH}_{2}+\mathrm{H}_{2} \rightarrow \mathrm{CH}_{3}-\mathrm{CH}_{3}+\mathrm{H} \\ &\mathrm{CH}_{2}=\mathrm{CH}_{2}+\mathrm{H} \cdot \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \end{aligned} $$

Describe dehalogenation of vicinal dihalides to obtain an alkene.

Treatment of \(\mathrm{C}_{7} \mathrm{H}_{15} \mathrm{Br}\) with strong base gave an alkene mixture that was shown by careful gas chromatographic analysis and separation to consist of three alkenes, \(\mathrm{C}_{7} \mathrm{H}_{14}\), A, B, and C. Catalytic hydrogenation of each alkene gave 2-methythexane. Reaction of A with \(\mathrm{B}_{2} \mathrm{H}_{6}\) followed by \(\mathrm{H}_{2} \mathrm{O}_{2}\) and \(\mathrm{OH}^{-}\) gave mostly an alcohol, D. Similar reaction of \(\mathrm{B}\) or C gave approximately equal amounts of \(\mathrm{D}\) and an isomeric alcohol \(\mathrm{E}\). What structural assignments can be made for \(\mathrm{A}\) to \(E\) on the basis of these observations? What structural element is left undetermined by these data alone?

Describe the catalytic hydrogenation reaction of alkenes.
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