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Propose a mechanism for the acid-catalyzed hydrolysis of cyclohexanone dimethyl acetal.

Short Answer

Expert verified

Dilute aqueous acid can be used for the hydrolysis of cyclohexanone dimethyl acetal. The mechanism is shown below.

Step by step solution

01

Acetals

The compound in whichtwo alkoxy groups are attached with the same carbon atom is termed as acetal. Aldehyde and ketones react with alcohols to form hemiacetal and acetal. The reaction occurs in the presence of acids.

02

Mechanism of the reaction

The acid-catalyzed hydrolysis of cyclohexanone dimethyl acetal occurs in five steps. In the first step, the protonation of acetal occurs. In the second step, the lone pair present on the second oxygen atom shifts beween the carbon and oxygen and removal of methanol occurs. In the third step, water molecules attack the carbonyl carbon and pi-bond electrons move to the oxygen atom.

In the fourth step, the transfer of proton and the removal of methanol molecule occurs. In the last step, the deprotonation takes place and cyclohexanone is obtained as the major product.

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Most popular questions from this chapter

Predict the products formed when cyclopentanone reacts with the following reagents.

(a) CH3NH2 , H+

(b) excess CH3OH , H+

(c) hydroxylamine and weak acid

(d) ethylene glycol and p-toluenesulfuric acid

(e) phenylhydrazine and weak acid

(f) PhMgBr and then mild H3O+

(g) Tollens reagent

(h) sodium acetlylide, then H3O+

(i) hydrazine, then hot. fused KOH

(j) Ph3P=CH2

(k) sodium cyanide

(l) acidic hydrolysis of the product from (k)

In the mechanism for acetal hydrolysis shown, the ring oxygen atom was protonated first, the ring was cleaved, and then the methoxy group was lost. The mechanism could also be written to show the methoxy oxygen protonating and cleaving first, followed by ring cleavage. Draw the alternative mechanism.

(a) Simple aminoacetals hydrolyze quickly and easily in dilute acid. Propose a mechanism for hydrolysis of the following aminoacetal:

(b) The nucleosides that make up DNA have heterocyclic rings linked to deoxyribose by an aminoacetal functional group. Point out the aminoacetal linkages in deoxycytidine and deoxyadenosine.

(c) The stability of our genetic code depends on the stability of DNA. We are fortunate that the aminoacetal linkages of DNA are not easily cleaved. Show why your mechanism for part (a) does not work so well with deoxycytidine and deoxyadenosine.

Show how you would accomplish the following synthetic conversions by adding an organolithium reagent to an acid.

Show how you would accomplish the following syntheses efficiently and in good yield. You may use any necessary reagents.

(a)acetaldehyde→lacticacid,CH3CH(OH)COOH

(b)

(c)

(d)

(e)

(f)

(g)

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