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Chapter 19: Problem 438

In the manufacturing of methyl isobutyl ketone (MIBK), large quantities of acetone are used. Propose a reasonable mechanism of synthesis for MIBK.

Short Answer

Expert verified
In the synthesis of methyl isobutyl ketone (MIBK) from acetone, a series of reactions take place: aldol condensation of acetone forms diacetone alcohol, which then undergoes dehydration to form mesityl oxide. Mesityl oxide reacts with another acetone molecule through an aldol condensation to form phorone. Finally, phorone is reduced to MIBK using a metal-based catalyst such as palladium or platinum.

Step by step solution

01

Formation of an aldol product from acetone

In the first step, acetone undergoes an aldol condensation reaction to form a new carbon-carbon bond by reacting with another molecule of acetone. This reaction involves the enolate ion (formed by the deprotonation of the alpha carbon next to the carbonyl group) attacking the carbonyl carbon of another acetone molecule, followed by the subsequent loss of water. The resulting aldol product is diacetone alcohol (\(CH_3C(O)CH_2C(O)CH_3CH_3\)).
02

Dehydration of diacetone alcohol

In the second step, the aldol product, diacetone alcohol, undergoes a dehydration reaction to form mesityl oxide. The reaction involves the elimination of water from the diacetone alcohol molecule, usually with the aid of an acid catalyst. The dehydration reaction leads to the formation of a double bond between the alpha and beta carbons (\(CH_3C(O)CH=C(O)CH_3\)).
03

Repeated aldol condensation

Mesityl oxide formed in the previous step can undergo a second aldol condensation with another molecule of acetone. The enolate ion generated from the mesityl oxide reacts with the carbonyl carbon of an acetone molecule, followed by the loss of water, which results in the formation of phorone (\(CH_3C(O)C(CH_3)C(O)CH=C(O)CH_3\)).
04

Reduction of phorone to MIBK

In the final step, the phorone molecule undergoes a reduction reaction to form methyl isobutyl ketone (MIBK). The reduction process involves the addition of hydrogen to the double bond between the alpha and beta carbons in the presence of a catalyst, usually a metal-based catalyst such as palladium or platinum. The final product is MIBK (\(CH_3COCH(CH_3)_2\)). In summary, the synthesis of methyl isobutyl ketone (MIBK) from acetone can be achieved through a series of aldol condensation reactions, dehydration, and reduction. The reaction mechanism proceeds through the formation of diacetone alcohol, mesityl oxide, and phorone before finally obtaining the desired MIBK product.

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Most popular questions from this chapter

Compound \(\mathrm{K}, \mathrm{C}_{5} \mathrm{H}_{10}\) decolored a solution of \(\mathrm{Br}_{2}\) in carbon tetrachloride. When \(\mathrm{K}\) was dissolved in cold, concentrated sulfuric acid and then heated with water, L resulted. L, \(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}\), reacted with chromic acid \(\mathrm{H}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) to give \(\mathrm{M}\), \(\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}\). Both \(\mathrm{L}\) and \(\mathrm{M}\) gave positive iodoform tests. The reaction mixture of the iodoform test also produced isobutyric acid \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCOOH}\). Determine the structure of \(\mathrm{K}, \mathrm{L}\), and \(\mathrm{M}\).

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