430 ALDEHY DES AND KETONES: NUCLEOPHI ON TO THE CARBONYL GROUP (c) The cyclic acetal derived from isobutyl methyl ketone and ethylene glycol bears an isobutyl group and a methyl group at C-2 of a 1, 3-dioxolane ring. (CH;),CHCH, CCH3 HOCH, CH,OH (CH3), CHCH, CH Isobutyl methyl ketone 2-1sobutyl-2-methyl-1, 3-dioxolan (d) Because the starting diol is 2, 2-dimethyl-1, 3-propanediol, the cyclic acetal is six-membered and bears two methyl substituents at C-5 in addition to isobutyl and methyl groups at C-2. HaC CH (CH),CHCH,CCH3 HOCH,CCH,OH H3 (CH),CHCHA Isobutyl methyl ketone 2, 2-Dimethyl-1,3- 2-lsobutyl-2, 5. 5-trimethyl propanediol 1.3-dioxane 17.9 The overall reaction is CHSCH(OCH,CH),+H,O= CH_CH 2CH, CH,OH Benzaldehyde diethyl acetal Water Benzaldehyde Ethanol The mechanism of acetal hydrolysis is the reverse of acetal formation. The first four steps convert the acetal to the hemiacetal CHCH CHCH-OCH.CH +HCo C6HSCH-OCH, CH3+: O OCHCH H:CH2 CHCH C6HSCH-OCH, CH3 C6HSCH-OCH, CH3+ : O CHCH H Step 3: H C6HSCH-OCH, CH3+ CHCH—QCH2CH3 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website(c) The cyclic acetal derived from isobutyl methyl ketone and ethylene glycol bears an isobutyl group and a methyl group at C-2 of a 1,3-dioxolane ring. (d) Because the starting diol is 2,2-dimethyl-1,3-propanediol, the cyclic acetal is six-membered and bears two methyl substituents at C-5 in addition to isobutyl and methyl groups at C-2. 17.9 The overall reaction is The mechanism of acetal hydrolysis is the reverse of acetal formation. The first four steps convert the acetal to the hemiacetal. Step 1: Step 2: Step 3: C6H5CH OCH2CH3 H H O C6H5CH OCH2CH3 O H H O H CH2CH3 C6H5CH OCH2CH3 C6H5CH OCH2CH3 O CH3CH2 H C6H5CH O H CH2CH3 OCH2CH3 OCH2CH3 H O H CH2CH3 C6H5CH OCH2CH3 O CH3CH2 H C6H5CH(OCH2CH3)2 Benzaldehyde diethyl acetal H2O Water C6H5CH O Benzaldehyde 2CH3CH2OH Ethanol HCl H (CH3)2CHCH2CCH3 O Isobutyl methyl ketone HOCH2CCH2OH CH3 CH3 2,2-Dimethyl-1,3- propanediol 2-Isobutyl-2,5,5-trimethyl- 1,3-dioxane CH3 (CH3)2CHCH2 H3C CH3 O O Ethylene glycol HOCH2CH2OH H Isobutyl methyl ketone (CH3)2CHCH2CCH3 O 2-Isobutyl-2-methyl-1,3-dioxolane (CH3)2CHCH2 O O CH3 430 ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website