Ch.17 Alcohols and Phenols C An alcohol A phenol An enol
- Me: wood alcohol: made from wood - industrial preparation of methanol: C + 2 2 400 o C Zinc oxide/chromia C 3 - Ethanol: fermentation of grains and sugars - industrial preparation of ethanol: 2 C C 2 + 2 250 o C 3 P 4 C 3 C 2
- Phenols t-bu t-bu C 2 C 3 Phenol C 3 BT antioxidant food additive Methyl salicylate Urushiols ( = different C 15 alkyl and alkenyl chains) allergenic constituents of poison oak and poison ivy
17.1 Nomenclature Alcohols C C C A primary alcohol (1 o ) A secondary alcohol (2 o ) A tertiary alcohol (3 o )
step 1. select the longest carbon chain containing the group ; -e to -ol step 2. numbering: begin at the end nearer the step 3. list alphabetically 1 2 2-Methyl-2-pentanol cis-1,4-cyclohexanediol 1 2 3-Phenyl-2-butanol
common names; tert-butyl alcohol (2-Methyl-2-propanol) Ethtylene glycol (1,2-Ethanediol) Glycerol (1,2,3-Propanetriol) Benzyl alcohol (Phenylmethalol) Allyl alcohol (2-Propen-1-ol)
Phenols: name as aromatic compounds, -phenol N 2 3 C p-methylphenol 2 N 2,4-Dinitrophenol
17.2 Properties of Alcohols and Phenols: ydrogen Bonding alcohols, phenols, ethers are 2 derivatives 3 C 109 o 3 C C 3 112 o ydrogen bonding: numbering: begin at the end nearer the δ + δ δ δ δ + δ + -bonding: 5-10 kcal/mol - alcohols, phenols: high b.p., - bonding must be destroyed to boil
Boiling points: alcohols > chloroalkanes > alkanes (with same molecular weight)
17.3 Properties of Alcohols and Phenols : Acidty and Basicity - weak acid, weak base X an oxonium ion X - Alkoxide ion ( - ), phenoxide ion (Ph - ) + + - + + Y Y
Alcohols are weakly acidic Phenols are much more acidic: resonance stabilization of phenoxide ion Alcohol Phenol t-bu Et 2 C 3 CF 3 C 2 p-aminophenol p-methoxyphenol p-methylphenol Phenol p-chlorophenol p-bromophenol p-nitrophenol 2,4,6-Trinitrophenol pk a 18.00 16.00 15.74 15.54 12.43 10.46 10.21 10.17 9.89 9.38 9.35 7.15 0.60 stronger acid
- The effects of alkyl substituents on alcohol acidity ; primarily solvation effects of alkoxide ion (easily solvated ions by water are more stable, therefore, more acidic) ; less hindered ions are easily solvated, hindered ions are less solvated and less stabilized C - pk a = 15.54 sterically accessible; less hindered and more easily solvated C C C C - pk a = 18.00 sterically less accessible; more hindered and less easily solvated
Inductive effects; ; electron withdrawing substituents stabilize alkoxide ions 3 C F 3 C 3 C C - F 3 C C - 3 C F 3 C pk a = 18 pk a = 5.4
- alcohols are unreactive to weak bases such as amine, bicarbonate ion - react to only a limited extent with Na and Na - react with alkali metals 2 C 3 + 2 Na 2 C 3 Na + 2 2 t-bu + 2 K 2 t-buk + 2 Potassium tert-butoxide - alkoxides are frequently used as reagent bases
- react with strong bases such as Na, NaN 2, MgX, Li C 3 + Na C 3 Na + 2 + NaN 2 Na + N 3 + C 3 MgBr MgBr + C 4
- phenols are deprotonated by aq.na ; phenols are soluble in dilute aq.na solution + Na Na + 2 Sodium phenoxide resonance stabilization of phenoxide ion
substituent effects of phenols EWG EDG more acidic less acidic resonance stabilization of p-nitro phenoxide ion; N N N N N N
17.4 Preparation of Alcohols: A eview ' ' C X '
ydration of alkene: 2 g(ac) 2 C 3 gac NaB 4 C 3 C 3 B 3 C 3 - C 3 B 2
Dihydroxylation of alkene: C 3 s 4 Pyridine 3 C s NaS 3 2 C 3 C 3 C 3 3 + C 3
17.5 Alcohols from eduction of Carbonyl Compounds ydride reduction: [ - ] C C [ - ] is a generalized reducing agent [ - ] = NaB 4, LiAl 4
eduction of Aldehydes and Ketones [ - ] C aldehyde C primary alcohol C ketone [ - ] C secondary alcohol
eduction of Aldehydes 1. NaB 4 Et 2. 3 + 2. 3 + B- 4 Na + eduction of Ketones 1. NaB 4 Et 2. 3 +
eduction with LiAl 4 ; much more reactive, reacts violently with water 1. LiAl 4 ether 2. 3 + 1. - 2. 3 +
eduction of Esters and Carboxylic Acids: need strong hydride reagent ; LiAl 4 ; NaB 4 reduces esters very slowly and cannot reduce carboxylic acid at all [ - ] C ' or C C ester acid primary alcohol
1. LiAl 4 ether 2. 3 + C 3 1. LiAl 4 ether 2. 3 + + C 3
17.6 Alcohols from eaction of Carbonyl Compounds with Grignard eagents Grignard reagent: -X + Mg -Mg-X = 1 o, 2 o, 3 o alkyl, aryl, alkenyl X = Cl, Br, I + MgX MgX 3 + + MgX
Alcohol synthesis MgBr 1. C 2 2. 3 + C 1. PhMgBr 2. 3 + 1. PhMgBr 2. 3 + Ph
Me 1. excess PhMgBr 2. 3 + 2
Carboxylic acid: no addition reaction 'MgBr -MgX acid salt + '-
Limitations of Grignard reagents: good nucleophile, strong base Grignard reagents can't be prepared from an organohalide that has other reactive functional groups in the same molecule. - acidic protons are deprotonated - electrophilic functional groups react Br Molecule FG acidic groups FG = -, -N, -S, -C electrohilic groups FG = -C, C, CN 2, CN, N 2, S 2...
17.7 Some eactions of Alcohols C - reactions C- reactions
Dehydration: 3 o alcohol, strong acidic condition C 3 cat. 2 S 4 2 50 o C C 3 2 S 4, 2 + major
eactivity of dehydration: C C C reactivity
S N 1 reaction: C 3 cat. 2 S 4 2 50 o C C 3 3 C C 3 2
Dehydration under mild, basic condition C 3 PCl 3 Pyridine 0 o C C 3 Cl P Cl Cl PCl 2 N
Conversion of Alcohols into Alkyl alides 3 o alcohols: S N 1 C 3 Cl C 3 Cl Cl C 3 C 3 Cl -
1 o and 2 o alcohols: SCl 2, PBr 3 by S N 2 reaction C 2 SCl 2 C 2 S Cl + Cl S N 2 Cl - C 2 Cl + S 2 + Cl PBr 3 S N 2 3 C 2 C 2 P(') 2 + 3 Br 3 C 2 Br Br - + P() 3
Conversion of Alcohols into Tosylates Activation of C- bond C 2 p-tols 2 Cl Pyridine C 2 S Tol + Cl-Pyridine p-tscl or p-tols 2 Cl 3 C S Cl
Et - Et PBr 3 Br (+)-1-Phenyl-2-propanol p-tscl pyridine Ts Et - Et
17.8 xidation of Alcohols oxidation C reduction C C [] C [] C primary alcohol aldehyde carboxylic acid
C [] C secondary alcohol ketone C [] N reaction tertiary alcohol
Cr 3, 2 Cr 2 7, Na 2 Cr 2 7 Pyridinium chlorochromate (PCC): Cr 3 + pyridine + Cl C 2 PCC C 2 Cl 2 C C 2 Cr 3 C 3 + PCC C 2 Cl 2 or Na 2 Cr 2 7 2, C 3 C
Mechanism: chromate intermediate, E2 C Cr Cr(VI) C Cr C Cr base E2 Cr + Cr(IV) C
17.9 Protection of Alcohols Mg Br ether MgBr acidic proton not formed Protecting group: Br P Br Mg ether P MgBr
Trimethylsilyl (TMS) ether: Et 3 N, ClSi(C 3 ) 3 C 3 + 3 CSi Cl C 3 Et 3 N Si + Et 3 N-Cl TMS TMSCl SiMe 3 TMS Et 3 N
Silyl ether can be formed with tertiary Si-Cl: S N 2 at tertiary center - silicon is 3rd -row atom, larger than C, form longer Si-C bond - sterically less hindered C 3 C 3 Cl C C 3 C 3 Cl Si C 3 C 3 silicon is less hindered C-C bond length: 154 pm C-Si bond length: 195 pm
Deprotection of TMS ether: labile to acid and F - (strong F-Si bond) SiMe 3 3 + or F - + (C 3 ) 3 Si
TMS-protected alcohol in Grignard reaction Br (C 3 ) 4 SiCl Et 3 N TMS Br Mg ether TMS MgBr 1. C 2. 3 + TMS F - or 3 +
17.10 Preparation and Uses of Phenols Used as: raw material for picric acid (2,4,6-trinitrophenl), Bakelite resin, adhesives for binding plywood Dow process: chlorobenzene + Na at high temperature Synthesis of phenol from cumene: produce phenol and acetone 3 C C 3 2 3 C C 3 3 + heat + 3 C C 3
adical mechanism 3 C C 3 3 C C 3 3 + 3 C C 3 2 2 2 + 3 C C 3
Synthesis of phenols from sulfonic acid S 3 S 3 2 S 4 C 3 1. Na 300 o C C 3 2. 3 + C 3 72%
other use of phenol Cl Cl C 2 C Cl Cl Cl Cl Cl Cl Pentachlorophenol wood presertive Cl 2,4-Dichlorophenoxyacetic acid 2,4-D (herbicide) Cl Cl Cl Cl exachlorophene antiseptic t-bu t-bu t-bu + t-bu C 3 C 3 BT antioxidant food additive C 3 BA C 3
17.11 eactions of Phenols Electrophilic Aromatic Substitution eactions Br 2, FeBr 3 N 3, 2 S 4 Br S 3, 2 S 4 N 2 S 3
Alcohol-like reactions of phenols: no dehydration, no reaction with Cl, 2 S 4 N 2 K 2 C 3 acetone n-bubr n-bu N 2
xidation of Phenols -Na 2 Cr 2 7, Fremy's salt [potassium nitrosodisulfonate, (KS 3 ) 2 N)] - quinones are reduced to hydroquinone by NaB 4 or SnCl 2. (KS 3 ) 2 N 2 SnCl 2 Fremy's salt Benzoquinone ydroquinone - hydroquinone is used as photographic developer: reduces Ag + on film to metallic silver
Ubiquinone: coenzyme Q biological oxidizing agent Me C 3 Me n Ubiquinones (n = 1-10) NAD + + + reduced form Me Me C 3 Me Me C 3 + NAD + oxidized form Me Me C 3 1 + 2 2 Me Me C 3 + 2
17.12 Spectroscopy of Alcohols and Phenols I Spectroscopy - stretching C- stretching 3600 cm -1 3300-3400 cm -1 1050 cm -1 - non hydrogen bonded alcohol - hydrogen bonded alcohol
NM Spectroscopy 1 NM 13 C NM C--() - C- - 3.5-4.5 ppm - no coupling with nearby C- - 50-80 ppm
- proton signal: unpredictable chemical shift, often not observed C A C + A no coupling Deuterium exchange: - proton signal disappears rapidly C D 2 C D + D
MS Spectrometry Alchols: fragment in two pathways alpha (α) cleavage 2 C C C + C 2 dehydration C C C C + 2
Chemistry @ Work Ethyl Alcohol: Chemical, Drug, and Poison Fermentation: alcoholic beverage C 6 12 6 A carbohydrate Yeast 2 Et + 2 C 2 ydration of ethylene: industrial production 2 C C 2 + 2 acid catalyst Et
Chemistry @ Work Ethyl Alcohol: Chemical, Drug, and Poison Metabolism C 3 C 2 C 3 C C 3 C Acetaldehyde toxic Acetic acid - test of blood alcohol concentration: oxidation test with K 2 Cr 2 7
Problem Sets Chapter 17 26, 31, 36, 44, 52, 57, 64