chem3331-bean-10 - . CHAPTER 10: Structure and Synthesis of...

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Unformatted text preview: . CHAPTER 10: Structure and Synthesis of Alcohols (omit: 10-12) Nomenclature: 1. Longest chain containg the OH is the parent chain. Chain is numbered to give OH the lowest possible #. Suffix is "ol." CH3 CHQOH | I CH3CH-CHQCH-CHQCH3 2. Alcohols have priority over alkenes and alkynes. OH CH3 | | CH2=CH-CH2-CH-OH 3. In cyclic alcohols, OH is always on carbon # 1. CH3 : OH CH3 4. When the OH group cannot be incorporated into the parent chain, it is named as a "hydroxy" substituent. OH :: (IDH CHg-CH-CH3 5. Alcohols with two OH groups are named as diols. Add "diol" to the alkane/alkene/alkyne name. OH on C|3H3 CHZCHaCH-CHQ-CH-OH OH 6. In phenols, the OH group is always on carbon # 1. OOH QM OOH Br CH3 PHYSICAL PROPERTIES OF R-O-H Boiling Point: CH3CHQCH3 CH3-O-CH3 CH3CH20H HOCH2CH20H Solubility: OH /\/OH vs /\/\/ CHEMICAL PROPERTIES: ACIDITY/BASICITY - can serve as weak acid or weak base As a Base: 0 R _.q_ H + H — X _’ As an Acid: . e .9 R + Na 0 H —.’ Structure vs Acidity: F | CHacHQO — H VS F— (‘3-CH2O --H F ?“3 CH30H20 — H vs CH3 — (‘3-0 —H CH3 Acidity of Phenols: 0H ('2') OH OH OQN Nio— vs Q OH NaOH —> SYNTHESIS OF ALCOHOLS I. From Alkyl Halides: Ch. 6 heat R—X + —OH —> R—O—H OR R—X + H-OH —> R—O—H II. From Alkenes: Ch. 8 A. Hydration (acid catalyzed) B. Oxymercuration/Demercuration C. Hydroboration D. Epoxidation followed by acidic hydrolysis E. Hydroxylation III. From Acetylide Anion and Carbonyl Compound: Ch. 9 Go FR R—CEC: Na + C=O the—fur» R/ H3O IV. Organometallic Reagents + Carbonyl Compounds ——> R-OH A. Preparation of Reagents 1 . Grignard Reagent ether R—X + Mg ———~> R—MQX 2. Organolithium Reagent . pentaneor _ _ R—X + 2L1 -—-——> R—LI + LIX hexane Examples: CHSCHQ — Br fit'eman H __ ’ M CHSCH —C\ —fi—>et er Br B. Mechanism of Grignard Reaction (mechanism of organolithium reaction is similar) 0 OH 0 + H ether l H-OH2 l C R— X __..__> _ _ _C _R C. Grignard Reactions (RLi reactions are similar) H 1. with formaldehyde: R—Mg X + \C=o Em, / 2. H30" H F"\ 2. with aldehydes: R—Mg X + (3:0 1. t r / 2. H3O+ H “"\ 3. with ketones: R—Mg x + 0:0 1_ t r / 2. H30+ RI Examples: H30 \ CHQCHQ'MQBI' + / 2. H3O+ H [H H3C\ CHSCH =C\ + C=O ' MgBr / 2. H3O+ H30 4. with esters or acid halides: CI R—ng + ‘C=O tether R/ 2. H30+ Example of RMgX + acid chloride or ester: 0 || MgBr C\ 0/ 0/ OCH3 ether + ———> O 5. with ethylene oxide: R—Mg X + 1. ether , Example: 0 1 h CHs—CH—MgBr + _;Mr_, 3 D. Limitations on Grignard / Organolithium reactions: Use caution when selecting the halide compound that forms the Grignard or organolithium reagent and the carbonyl compound. Observe the followmg rules. 1. NO ACIDIC HYDROGENSI! ( NO -OH, -NH, -SH, -C02H or -CEC-H) Examples: OH éH2_ CHTBr Mg/ether ll R—MgX + R—C—O—H ———> 2. NO functional groups that react with Grignard/ organolithium reagents (besides the intended carbonyl component): . O N O O No- u H II II /C\ /C\ / S\ / \ CEN Notice the general structural feature: a multiple bond in which one atom is strongly partial + Examples: 0 II CH3—C —CHZCHQCHQCHzBr m 0 O H n 1. ether CH3—Mg Br + CHa—C—CHQCHz—C-H 2. H30+ 3. Dubious and Worthwhile Uses of a Side Reaction: M/th R—X if; 3-ng _"'2_O, M/th R—x i3» R—ng $9? SYNTHESIS INTERLUDE: rHs CH30H2—C—OH I CHQCHQCHa A Slightly Related Reaction of an Organolithium Reagent: The Corey-House Reaction: forms a new carbon-carbon bond a multiple step synthesis: 1. R-X + 2 Li fl R-Li + LiX 2. 2 R-Li + Cul fl RgCuLi + Lil 3. RgCuLi + R'-X —> R-R' + RCU + V. Synthesis of Alcohols: Reduction of a Carbonyl The "organic" definitions of oxidation and reduction: oxidation - reduction - A. Hydride Reductions O OH O OH ll [H] I ll [H] I R-C—H ———>~ R-C—H 2 R-C—R ———>- R-O—R H H O OH O OH ll [H] I H [H] l 3. R—C-OH—> R—C—H + H20 4. R—C-OR'—-> R—c—H + R'OH H H (I? [H] (le 5 R—C-m ———>’ R-O—H + HCI H Reducing agents: NaBH4 - the milder choice; usually chosen for aldehydes and ketones - may use H20 or alcohol as solvents - very slow reduction of esters; will not reduce acid chlorides or carboxylic acids LiAlH4 - more reactive than NaBH4 - reduces aldehydes, ketones, esters, acid halides and carboxylic acids - CAUTION: reacts violently with H20 and alcohols! Must use ethers as solvents. Mechanism: 0 O OH H H—AlH Li+ H-6H I R—C—H “3+ Fl—Cl2-H _L’ “‘9‘” ' H H O O o 0 ll _ ‘+ l - I _ R—C—OR'wLI—l» n—c—H ——> 3.344 W, R—C—H Ha]? I OR' H I R'OH + R—C-H Examples: 0 || NaBH4 a" CchHg— C — CH3 W 0 ll 1.LiA|H4 b. CchHQ—C‘OCH(CH3)2 B. Catalytic Hydrogenation of Aldehydes and Ketones: \ C / \ / \ / C=O II o - catalytic reduction of carbonyl is slower than reduction of double bond - Raney Ni is best catalyst Examples: 0 || 2 a. 0 || H2 b. CchHQ—C—CHQCH= CH2 NaBH4/EtOH ...
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chem3331-bean-10 - . CHAPTER 10: Structure and Synthesis of...

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