CHAPTER 17 ALDEHYDES AND KETONES NUCLEOPHILIC ADD|TONT○ THE CARB○ NYL GROUP SOLUTIONS TO TEXT PROBLEMS 17.1 (b) The longest continuous chain in glutaraldehyde has five carbons and terminates in aldehyde functions at both ends. Pentanedial is an acceptable IUPAC name for this compound CCHCH CHCH Pentanedial (glutaraldehyde) (c) The three-carbon parent chain has a double bond between C-2 and C-3 and a phenyl sub stituent at C-3 CH CHECHCH 3-Phen (d) Vanillin can be named as a derivative of benzaldehyde. Remember to cite the remaining sub- stituents in alphabetical order. HO 4-Hydroxy-3-methoxybenzaldehyde 426 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
CHAPTER 17 ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP SOLUTIONS TO TEXT PROBLEMS 17.1 (b) The longest continuous chain in glutaraldehyde has five carbons and terminates in aldehyde functions at both ends. Pentanedial is an acceptable IUPAC name for this compound. (c) The three-carbon parent chain has a double bond between C-2 and C-3 and a phenyl substituent at C-3. (d) Vanillin can be named as a derivative of benzaldehyde. Remember to cite the remaining substituents in alphabetical order. HO CH O CH3O 4-Hydroxy-3-methoxybenzaldehyde (vanillin) 3-Phenyl-2-propenal (cinnamaldehyde) C6H5CH CHCH O 2 1 3 Pentanedial (glutaraldehyde) HCCH2CH2CH2CH O O 1 23 4 5 426 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP 427 17.2 (b) First write the structure from the name given. Ethyl isopropyl ketone has an ethyl group and an isopropyl group bonded to a carbonyl group CH.CCHCH H3 Ethyl isopropyl ketone may be alternatively named 2-methyl-3-pentanone Its longest contin uous chain has five carbons. The carbonyl carbon is C-3 irrespective of the direction in which the chain is numbered, and so we choose the direction that gives the lower number to the sition that bears the methyl group (c) Methyl 2, 2-dimethylpropyl ketone has a methyl group and a 2, 2-dimethylpropyl g bonded to a carbonyl group o CH CH. CCHCCH The longest continuous chain has five carbons, and the carbonyl carbon is C-2. Thus, methyl 2, 2-dimethylpropyl ketone may also be named 4, 4-dimethyl-2-pentanone (d) The structure corresponding to allyl methyl ketone is O CH,CH=CH, Because the carbonyl group is given the lowest possible number in the chain, the substitutive name is 4-penten-2-one not 1-penten-4-o1 17.3 No Lithium aluminum hydride is the only reagent we have discussed that is capable of reducing carboxylic acids(Section 15.3) 17. 4 The target molecule, 2-butanone, contains four carbon atoms. The problem states that all of the car bons originate in acetic acid, which has two carbon atoms. This suggests the following disconnections H CHa CCH,CH3 CH; CHCH,CH CHCH CHCH The necessary aldehyde(acetaldehyde) is prepared from acetic acid by reduction followed by on CH- COH 1.LiAIH. CH, CH2OH 2.H,O CH3CH Acetic acid Ethanol Ethylmagnesium bromide may be obtained from acetic acid by the following sequence CHCHOH HBr or CH CHBI CHCHMgBr Ethanol Ethyl bromide Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP 427 17.2 (b) First write the structure from the name given. Ethyl isopropyl ketone has an ethyl group and an isopropyl group bonded to a carbonyl group. Ethyl isopropyl ketone may be alternatively named 2-methyl-3-pentanone. Its longest continuous chain has five carbons. The carbonyl carbon is C-3 irrespective of the direction in which the chain is numbered, and so we choose the direction that gives the lower number to the position that bears the methyl group. (c) Methyl 2,2-dimethylpropyl ketone has a methyl group and a 2,2-dimethylpropyl group bonded to a carbonyl group. The longest continuous chain has five carbons, and the carbonyl carbon is C-2. Thus, methyl 2,2-dimethylpropyl ketone may also be named 4,4-dimethyl-2-pentanone. (d) The structure corresponding to allyl methyl ketone is Because the carbonyl group is given the lowest possible number in the chain, the substitutive name is 4-penten-2-one not 1-penten-4-one. 17.3 No. Lithium aluminum hydride is the only reagent we have discussed that is capable of reducing carboxylic acids (Section 15.3). 17.4 The target molecule, 2-butanone, contains four carbon atoms. The problem states that all of the carbons originate in acetic acid, which has two carbon atoms. This suggests the following disconnections: The necessary aldehyde (acetaldehyde) is prepared from acetic acid by reduction followed by oxidation in an anhydrous medium. Ethylmagnesium bromide may be obtained from acetic acid by the following sequence: CH3CH2OH Ethanol (Prepared as previously) CH3CH2Br Ethyl bromide CH3CH2MgBr Ethylmagnesium bromide HBr or PBr3 Mg diethyl ether CH3CO2H Acetic acid CH3CH2OH Ethanol CH3CH O Acetaldehyde 1. LiAlH4 2. H2O PDC CH2Cl2 CH3CHCH2CH3 OH CH3CCH2CH3 O O CH3CH CH2CH3 2-Butanone CH3CCH2CH CH2 O CH3CCH2CCH3 CH3 O CH3 CH3CH2CCHCH3 O CH3 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
428 ALDEHY DES AND KETONES: NUCLEOPHI ON TO THE CARBONYL GROUP The preparation of 2-butanone is completed as follows I diethyl ether K, Cr,O, CH,CH+ CH, CH, MgBl CH3 CHCH,CH CHaCCH,CH Acetaldehvde 2-Butanol 2-Butanone bromide 17.5 Chloral is trichloroethanal, CCl3 CH. Chloral hydrate is the addition product of chloral and water. ClCCH Chloral hydrate 17.6 Methacrylonitrile is formed by the dehydration of acetone cyanohydrin, and thus has the structure shown H+ heat CH3CCH,.) Acetone cyanohydrin 17. The overall reaction is CBH_CH 2CH3 CH,OH Benzaldehyde Water HCI is a strong acid and, when dissolved in ethanol, transfers a proton to ethanol to give ethylox onium ion. Thus, we can represent the acid catalyst as the conjugate acid of ethanol The first three steps correspond to acid-catalyzed addition of ethanol to the carbonyl group eld a hemiacetal Step 1: CH, CH3 ChS CH+ H-O CHCH + 0: CHCH CHCH CHCH + O C6HSCH-O: Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
428 ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP The preparation of 2-butanone is completed as follows: 17.5 Chloral is trichloroethanal, . Chloral hydrate is the addition product of chloral and water. 17.6 Methacrylonitrile is formed by the dehydration of acetone cyanohydrin, and thus has the structure shown. 17.7 The overall reaction is HCl is a strong acid and, when dissolved in ethanol, transfers a proton to ethanol to give ethyloxonium ion. Thus, we can represent the acid catalyst as the conjugate acid of ethanol. The first three steps correspond to acid-catalyzed addition of ethanol to the carbonyl group to yield a hemiacetal. Step 1: Step 2: C6H5CH O C6H5CH OH CH2CH3 H O H CH2CH3 H O CH2CH3 H C6H5CH O O H C6H5CH CH2CH3 H H O O Ethanol 2CH3CH2OH Benzaldehyde diethyl acetal C6H5(OCH2CH3)2 Water H2O Benzaldehyde C6H5CH O HCl Acetone Methacrylonitrile cyanohydrin CH3CCH3 OH CN H, heat (H2O) CH3C CH2 CN Chloral hydrate Cl3CCH OH OH CCl3CH O CH3CH2MgBr Ethylmagnesium bromide Acetaldehyde CH3CH O 2-Butanone CH3CCH2CH3 O 2-Butanol CH3CHCH2CH3 OH 1. diethyl ether 2. H3O K2Cr2O7 H2SO4, H2O Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP 429 Step 3: CHCH CHCH CH CH C6HSCH-O CH CH-OCH CH +H-O Hemiacetal Formation of the hemiacetal is followed by loss of water to give a carbocation Step 4: CHCH H.CH CHC-OCH. CH, t HO C6HC—9CH2CH3+:O3 H C6HSCH-OCH,CH C6HSCH-OCH, CH3+ H-O-H The next two steps describe the capture of the carbocation by ethanol to give the acetal CHCH C6HCH-ΩCH2CH3+:O C6HSCH--OCH,CH H CH3CH2 H CHCH CHCH CH CH-OCH,CH +iO C6HCH—9CH2CH3+H-O3 :OCH2CH3 CHCH H Acetal 17. 8(b) 1, 3-Propanediol forms acetals that contain a six-membered 1, 3-dioxane ring C6HSCH HOCH,CHaCH,OH CsHs H Benzaldehyde 1, 3-Propanediol 2-Phenyl-1, 3-dioxane Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
Step 3: Formation of the hemiacetal is followed by loss of water to give a carbocation. Step 4: Step 5: The next two steps describe the capture of the carbocation by ethanol to give the acetal: Step 6: Step 7: 17.8 (b) 1,3-Propanediol forms acetals that contain a six-membered 1,3-dioxane ring. H C6H5 H 2-Phenyl-1,3-dioxane HOCH2CH2CH2OH 1,3-Propanediol C6H5CH O Benzaldehyde O O H O CH2CH3 C6H5CH OCH2CH3 OCH2CH3 Acetal C6H5CH OCH2CH3 O CH3CH2 H O CH2CH3 H H C6H5CH OCH2CH3 O CH3CH2 H C6H5CH OCH2CH3 O CH2CH3 H C6H5CH OCH2CH3 H H O C6H5CH H H O OCH2CH3 C6H5C HOH O H CH2CH3 OCH2CH3 H O H H CH2CH3 C6H5C HO H OCH2CH3 C6H5CH OH O CH2CH3 O H CH2CH3 H Hemiacetal C6H5CH OH H O H CH2CH3 OCH2CH3 ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP 429 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
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