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Published byJosephine Preston Modified over 9 years ago
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AlcoholsR-O-H Classification CH 3, 1 o, 2 o, 3 o Nomenclature: Common names: “alkyl alcohol” IUPAC: parent = longest continuous carbon chain containing the –OH group. alkane drop -e, add –ol prefix locant for –OH (lower number for OH)
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CH 3 CH 3 CH 3 CHCH 2 CHCH 3 CH 3 CCH 3 OH OH 4-methyl-2-pentanoltert-butyl alcohol 2-methyl-2-propanol 2 o 3 o CH 3 HO-CHCH 2 CH 3 CH 3 CH 2 CH 2 -OH sec-butyl alcoholn-propyl alcohol 2-butanol 1-propanol 2 o 1 o
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Physical properties of alcohols: polar + hydrogen bonding relatively higher mp/bp water insoluble! (except for alcohols of three carbons or less) CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 -OH hydrophobic hydrophilic
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Oldest known organic synthesis: “fermentation” Sugar + yeast ethyl alcohol + CO 2 Grape juice => “wine” Barley => “beer” Honey => “mead” Rice => “sake” ~5-11% ethanol
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Distillation of fermented beverages to produce “distilled spirits” with a greater percentage of ethyl alcohol (bp 78.3 o C). Ethyl alcohol forms a binary azeotrope with water: 95% ethanol + 5% water (bp 78.15 o C) Diluted with water => “vodka” 40% ethyl alcohol in water. “proof”: when aqueous alcohol is placed on a sample of gunpowder and ignited, the gunpowder will burn at a minimum concentration of 50% alcohol. This is called “100-proof”. (proof = 2 * alcohol percent)
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Add oil of juniper => gin Add peat smoke => scotch Age in a burned barrel => whiskey Add peppermint => schnapps Etc. Ethyl alcohol is a poison. LD 50 = ~10g/Kg orally in mice. Nausea, vomiting, flushing, mental excitement or depression, drowsiness, impaired perception, loss of coordination, stupor, coma, death may occur. (intoxication)
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Alcohols, synthesis: 1. 2. 3. 4. Hydrolysis of alkyl halides (CH 3 or 1 o ) 5. 6. 7. 8.
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NR some NR 1 o /2 o NR R-H R-X R-OH Acids Bases Active metals Oxidation Reduction Halogens
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Alcohols, reactions: R-|-OH 1.With HX 2.With PX 3 3.(later) RO-|-H 4.As acids 5.Ester formation 6.Oxidation
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1. Reaction of alcohols with HX: (#1 synthesis of RX) R-OH + HX R-X + H 2 O a) HX: HI > HBr > HCl b) ROH: 3 o > 2 o > CH 3 > 1 o c) May be acid catalyzed d) Rearrangements are possible except with most 1 o alcohols.
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CH 3 CH 2 CH 2 CH 2 -OH + NaBr, H 2 SO 4, heat CH 3 CH 2 CH 2 CH 2 -Br n-butyl alcohol n-butyl bromide 1-butanol 1-bromobutane CH 3 CH 3 CH 3 C-OH + HCl CH 3 C-Cl (room temperature) CH 3 CH 3 tert-butyl alcoholtert-butyl chloride 2-methyl-2-propanol2-chloro-2-methylpropane CH 3 CH 2 -OH + HI, H +, heat CH 3 CH 2 -I ethyl alcohol ethyl iodide ethanol iodoethane
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Mechanism? CH 3 -OH and most 1 o alcohols react with HX via S N 2 mechanism 3 o and 2 o react with HX via S N 1 mechanism Both mechanisms include an additional, first step, protonation of the alcohol oxygen: R-OH + H + R-OH 2 + “oxonium ion”
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Whenever an oxygen containing compound is placed into an acidic solution, the oxygen will be protonated, forming an oxonium ion.
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Mechanism for reaction of an alcohol with HX: CH 3 OH or 1 o alcohols:
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Mechanism for reaction of an alcohol with HX: 2 o or 3 o alcohols:
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May be catalyzed by acid. S N 2 rate = k [ ROH 2 + ] [ X - ] S N 1 rate = k [ ROH 2 + ] Acid protonates the -OH, converting it into a better leaving group (H 2 O), increasing the concentration of the oxonium ion, and increasing the rate of the reaction.
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Rearrangements are possible (except with most 1 o alcohols): CH 3 CH 3 CH 3 CHCHCH 3 + HBr CH 3 CCH 2 CH 3 OH Br Br - CH 3 CH 3 [1,2-H] CH 3 CH 3 CHCHCH 3 CH 3 CHCHCH 3 CH 3 CCH 2 CH 3 OH 2 + + + 2 o carbocation 3 o carbocation
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Most 1 o ? If large steric requirement… CH 3 CH 3 CH 3 CCH 2 -OH + HBr CH 3 CCH 2 CH 3 CH 3 Br neopentyl alcohol 2-bromo-2-methylbutane CH 3 CH 3 CH 3 CH 3 CCH 2 -OH 2 + CH 3 CCH 2 + CH 3 CCH 2 CH 3 CH 3 CH 3 + 1 o carbocation 3 o carbocation [1,2-CH 3 ]
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2.With PX 3 ROH + PX 3 RX a)PX 3 = PCl 3, PBr 3, P + I 2 b)No rearrangements c)ROH: CH 3 > 1 o > 2 o CH 3 CH 3 CH 3 CCH 2 -OH + PBr 3 CH 3 CCH 2 -Br CH 3 CH 3 neopentyl alcohol 2,2-dimethyl-1-bromopropane
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3.Dehydration (later)
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4)As acids. a)With active metals: ROH + Na RONa + ½ H 2 b)With bases: ROH + NaOH NR! CH 4 < NH 3 < ROH < H 2 O < HF
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CH 3 CH 2 OH + NaOH H 2 O + CH 3 CH 2 ONa WA WB SA SB CH 3 CH 2 OH + CH 3 MgBr CH 4 + MgBr(OCH 2 CH 3 ) SA SB WA WB CH 3 OH + NaNH 2 NH 3 + CH 3 ONa SA SB WA WB
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5.Ester formation. CH 3 CH 2 -OH + CH 3 CO 2 H, H + CH 3 CO 2 CH 2 CH 3 + H 2 O CH 3 CH 2 -OH + CH 3 COCl CH 3 CO 2 CH 2 CH 3 + HCl CH 3 -OH + CH 3 SO 2 Cl CH 3 SO 3 CH 3 + HCl Esters are alkyl “salts” of acids.
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oxidation states of carbon - oxidation CH 4 CH 3 OH CH 2 O HCO 2 H CO 2 -4 -2 0 +2 +4 reduction -
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6.Oxidation Oxidizing agents: KMnO 4, K 2 Cr 2 O 7, CrO 3, NaOCl, etc. Primary alcohols: CH 3 CH 2 CH 2 -OH + KMnO 4, etc. CH 3 CH 2 CO 2 H carboxylic acid Secondary alcohols: OH O CH 3 CH 2 CHCH 3 + K 2 Cr 2 O 7, etc. CH 3 CH 2 CCH 3 ketone Teriary alcohols: no reaction.
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Primary alcohols can also be oxidized to aldehydes: CH 3 CH 2 CH 2 -OH + C 5 H 5 NHCrO 3 Cl CH 3 CH 2 CHO pyridinium chlorochromate aldehyde or CH 3 CH 2 CH 2 -OH + K 2 Cr 2 O 7, special conditions
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Alcohols, synthesis: 1. 2. 3. 4. Hydrolysis of alkyl halides (CH 3 or 1 o ) 5. 6. 7. 8.
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Alcohols, reactions: R-|-OH 1.With HX 2.With PX 3 3.(later) RO-|-H 4.As acids 5.Ester formation 6.Oxidation
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