University:
University of Houston
Course:
CHEM 2323 | Organic Chemistry I
Academic year:

2022
Views:

368

Pages:

5
Author:

Carleigh Vargas

I Chapter 11 : Reactions of Alcohols I. Oxidations: oxidation increases# of bonds to 0, N, or halogens or decreases# of bonds to H reduction increases# of bonds to Hor decreases# of bonds to 0, N, or halogens neither oxidation or reduction if HX or H2O is gained or lost 0 0 R-CHs -----► R-CH20H -•--► II II R-C-H 411 R-C-0-H A. Oxidation of 2° alcohols: OH 1 R-CH-R [ox] : [ox] ► 1. chromic acid reagents a. Na2Cr2O7 I H2SO4 I H2O b. CrO3 / H2SO4 I H2O I acetone I 0°C (Jones reagent) 2. KMnO4 3. HNO3 4. pyridinium chlorochromate I CH 2Cl 2 (written as: PCC/CH 2Cl 2 or CrO3 pyridine HCI / CH 2Cl 2) B. Oxidation of 1° alcohols: [ox-b] ► [ox-b] : 1-3 above [ox-a] : PCC ONLY C. Oxidation of 3° alcohols: R I R-C-OH I R [ox] ► Examples: II. Formation and uses of the tosylate ester (converting the OH group to a better leaving group) CN A-OH A-OH TsCI + pyridine ,- R-OTos NaCN acetone ,. .. Ill. Conversion of alcohols to alkyl halides - The BEST methods A. Formation of 3° alkyl halides from 3° alcohols: use hydrohalic acids (HBr, HCI) HCl/ether 0°c ,. - for 1° and 2° alcohols, treatment of alcohol with HX is not the best method of forming alkyl halides - addition of catalyst (Lucas reagent) improves results 3 B. Formation of 1°/ 2° alkyl halides from 1°/ 2° alcohols: 1. Bromides: use PBr3 Br I R-0-H P-Br + I Br 2. Chlorides a. PCI3 or PCI 5 b. SOCl 2 - NOTE: The mechanism given on page 474 (p. 449 of 3rd ed.) occurs only under "special conditions." The more typical mechanism is the following: 0 II R-0-H + s Cl_... 'Cl 3. Iodides: use P/ 12 R-0-H Stereochemistry of Indirect Substitution of ROH: R-0-H iPBr3 TsCI ... I-{ IV. Acid-catalyzed dehydration to alkene (first discussed in Ch. 7) Mechanism: E1 Intermediate: C+ Major product : formed according to Saytzeff's rule (more stable alkene is major product) Example: H I CH3CH2CH-CHrO-H + I H ~ Acid-catalyzed dehydratons of 1° alcohols do NOT give good yields of terminal alkenes. Phosphorous oxychloride (POCl 3) - a good dehydrating agent for 1°, 2°, and 3° alcohols 0 CN II CH3CH2CH2CH2-OH + Cl/ t,CI ► Cl V. Formation of Ethers A. Symmetrical ethers through intermolecular dehydration R-O-H + H-O-R R-O-R + H-O-H Mechanism: H I R-O-H R-O-H + ► H I R-O-R ► + R-O-R R-O-H NOT for unsymmetrical ethers! CH3CH2-O-H + CH3-O-H H2SO').. 140°c B. Williamson Ether Synthesis (symm. or unsymmetrical ethers) alkoxide + alkyl halide ,. ether tNa or K R -O-H order of reactivity of ROH in alkoxide formation : Me> 1° > 2° > 3° 5 Williamson Ether Synthesis continued: + R-O Na CH3 I CH3-O-CH-CH3 ◄◄1--- VI. Ester Formation A. Fischer Esterification (intermolecular dehydraton) - mechanism next semester! H+ O + R-O-H ---I► II ◄ H-O-C-R' ,.. o 11 R-O-C-R' + H-O-H B. Nucleophilic acyl substitution of acid chloride 0 + R-O-H i H 0 I + I Cl 0 II R-O-C-R' + H-CI H 0 I R-O-C-R' ... II CI-C-R' I - - - 1 , ..... . II R-O-C-R' + 0 II CI-C-CH3 ... VII. Unique reactions of 1,2-diols A. Periodic acid cleavage OH OH I I -c-c- I I HI04 .. + O=C / "

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