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CHEM 2331H
T.Andrew Taton

Chapter 10 Book Notes Structure and Synthesis of Alcohols 10.1) Introduction • Alcohols: organic compounds containing hydroxyl group (-OH) • Many ways to synthesize them, -OH group can be converted into other functional groups alcohols = versatile 10.2) Structure and Classification of Alcohols • Alcohol has similar structure to water o one has H, while other has alkyl group o both have sp hybridized O, but C-O-H bond angle = 108.9, H-O-H angle = 104.5 b/c methyl group = more bulky, counteracts angle compression from O’s nonbonding electrons o O-H bond lengths = similar size but C-O bond = longer (b/c C has larger covalent radius than H) • Can classify each alcohol according to type of carbinol C: the one bonded to -OH o primary alcohol: -OH bonded to primary C o secondary alcohol: -OH bonded secondary C o tertiary alcohol: -OH bonded in tertiary C o each reacts a bit differently • Phenols: hydroxyl group bonded to aromatic (benzene) ring; some characteristics similar to alcohols, others similar to aromatic rings 10.3) Nomenclature ofAlcohols and Phenols • 10.3A) IUPAC Names (“Alkanol” Names) o Name must have –ol suffix and # to tell where hydroxyl group is; rules:  1) Name largest C chain that contains –OH group; drop –e from alkane name and replace w/ -ol root name  2) # C chain, start nearest to –OH group, and then use corresponding # for C that contains –OH group (-OH group has priority over double and triple bonds)  3) Name all substituents and give their #s (same as how you do for alkane/ene) o ex: 1-bromo-3,3-dimethylbutan-2-ol o cyclic alcohols have cyclo- prefix, -OH group is assumed to be on 1 C st o for alkenes/ynes, use –ol suffix after alkene/yne name  alcohol functional group has priority over double/triple bonds has lowest # (put before –ol suffix)  # for double/triple bonds used to be before entire name, but now before – en/-yn suffix o generally, highest priority functional group = main group; rest = substituents o hydroxyl substituent: -OH group on structure w/ higher priority functional group or if structure’s too difficult to name as simple alcohol • 10.3B) Common Names of Alcohols o common name of alcohol = common name of alkyl group + word alcohol  picture alcohol as water molecule and alkyl group replaces one of the H’s  If too complex structure, use IUPAC name • 10.3C) Names of Diols o Diols/glycols: has 2 –OH groups  named like other alcohols, except has diol suffix and has 2 #s to tell where = -OH groups  glycol = 1,2-diol or vicinal diol (2 –OH groups = on adjacent C’s) • synthesized by hydroxylation of alkenes w/ peroxides, osmium tetroxide, or potassium permanganate • named for alkene from which it’s synthesized (ex: ethane-1,2-diol) o Usually use IUPAC names for glycols/diols, but common names are well accepted too • 10.3D) Names of Phenols o ortho (1,2-distributed), meta (1,3-distributed), para (1,4-distributed) used in names when has benzene ring o cresols: methylphenols; but names of benzenediols = based on their historical uses & sources rather than their structure 10.4) Physical Properties of Alcohols • Most common alcohols (up to 11/12 C’s) = liquids @ room T o methanol & ethanol = free-flowing, volatile, characteristic fruity odors o higher alcohols (butanols-decanols) = somewhat viscous, some highly branched isomers = solids @ room T, heavier but still fruity odors o propan-1ol and propan-2-diol = in middle, barely noticeable viscosity, characteristic odor associated w/ physician office • 10.4A) Boiling Points ofAlcohols o Mostly deal w/ liquid alcohols, but surprising that lower-molecular-weight alcohols = liquids  ex: ethyl alcohol and propane have similar molecular weights, but significantly different boiling points  ethanol molecules = more strongly attracted to each other than propane molecules  hydrogen bonding and dipole-dipole interactions o Hydrogen bonding = major IMF high boiling pt for ethanol  hydroxyl H = strongly polarized by bond to O  H bond w/ lone electron pair from O of another alcohol molecule  ethers have 2 alkyl groups bonded to O  no H bonding  weaker IMF than typical covalent bond, but stronger than dipole-dipole  dipole-dipole: polarized /C-O bonds and H-O bonds and nonbonding electrons  strong dipole moment; positive and negative ends and line up  H bonding contributes more and makes bonding stronger • 10.4B) Solubility Properties ofAlcohols o water and alcohols have similar properties b/c have hydroxyl groups  H bond  miscible: alcohols form H bonds w/ water; soluble in any proportions  alcohols = better solvents than hydrocarbons for polar substances  hydrophilic: water loving; affinity for water and other polar substances; significant amt ionic compounds (ex: NaCl) dissolve in some lower alcohols; alcohol’s hydroxyl group  hydrophobic: water hating; alkyl group acts like alkane: disrupts H bonding and dipole-dipole attractions of polar solvent • alkyl group makes alcohol less hydrophilic, but makes it more soluble/miscible in nonpolar organic solvents o as alkyl group becomes larger, water solubility ↓  if 1,2,or 3 C alkyl group  miscible w/ water  some isomers of 4 C alkyl group not miscible w/ water, tert-butyl group (compact sphere) = miscible  each hydroxyl/other H bonding group can carry about 4 C’s in water  ex: hexan-1-ol is only slightly soluble, but hexane-1,6-diol = miscible  ex: phenol = soluble b/c compact shape and particularly strong H bonding w/ phenolic –OH groups and water 10.5) Commercially ImportantAlcohols • 10.5A) Methanol (Methyl alcohol) o aka wood alcohol b/c originally produced by destructive distillation of wood chips in absence of air  during Prohibition (1919-1933), anything called alcohol used for mixing drinks  methanol = more toxic than ethanol blindness and death o now, most methanol synthesized by catalytic rxn of CO w/ H (together called synthesis gas) @ high T and P in large, complicated industrial reactors  make synthesis gas by partially burning coal in presence of water (need to carefully regulate amt water correct ratio of CO and H) o one of most common industrial solvents  cheap  relatively less toxic compared to halogenated solvents  dissolves variety of polar and nonpolar substances  starting material for variety of methyl ethers, methyl esters, and other compounds used in plastics, medicines, fuels, and solvents o good fuel for internal combustion engines  1965-2006: all cars @ Indianapolis 500 used methanol-fueled engines  crash in 1964  bad fire  switched from gasoline to methanol (less flammable)  water’s effective in methanol fires b/c mixes w/ and dilutes methanol  advantages of methanol: high octane rating, low pollutant emissions, lower flammability  disadvantages: lower energy content (smaller ΔH of combustion per gram) requires 1.7 g methanol to produce same energy as 1 g gasoline, hard on rings, seals, and plastic fuel-system parts (b/c good solvent); tends to burn w/ no visible flame dangerous methanol fires can go undetected • 10.5B) Ethanol o rotton fruit consumed intoxicating effect ethanol discovered  intentional fermentation of fruit juices primitive wine could be stored in sealed container w/o danger of decomposition and = safe, unpolluted drinking water source o Ethanol produced by fermenting sugars & starches from different sources  aka grain alcohol b/c ferment from grain (corn, wheat, rye)  cook grain, then add sprouted barley (called malt), convert starches simple sugars  then add brewer’s yeast, then incubate soln so yeast cells convert simple sugars (ex: glucose) ethanol and carbon dioxide o From fermentation, only get 12-15% alcohol in sol’n b/c yeast cells can’t survive higher concentrations  can distill to get 40-50% (80 to 100 “proof”) for hard liquors  can’t distill ethanol-water sol’n to above 95% ethanol b/c boils @ lower T than pure ethanol/water (called minimum-boiling azeotrope) o Can use 95% alcohol if traces of water don’t affect rxn  If need absolute alcohol (100%), then 95% azeotrope passed through dehydrating agent like CaO, which removes 5% water o Since World War II, most industrial alcohol synthesized directly by catalized high-T, high-P gas phase rxn of water w/ ethylene  catalyst = 2 O5, tungsten oxide, or various specially treated clays o Ethanol (like methanol) = good solvent, low toxicity, cheap to produce  but liquor tax makes ethanol relatively expensive  can use untaxed ethanol, but needs extensive record-keeping and buying special liscence  denatured alcohol: ethanol w/ impurities undrinkable; untaxed, but impurities (methanol, methyl isobutyl ketone, aviation gasoline, etc) makes it unsuitable for lot of lab use o good motor fuel (like methanol), similar advantages and disadvantages  race cars in Indianapolis 500 used ethanol as primary fuel since 2006  carburetor must be adjusted (for richer mixture) and fitted w/ alcohol- resistant seals if want to run it on pure ethanol  can use 10% sol’n (10% ethanol in gasoline) well w/o any adjustment o ethanol half as toxic as methanol  fatal dose = 100 mL methanol and 200 mL ethanol, but smaller doses damage optic nerve, still harmful  less toxic compared to benzene and chloroform (truly hazardous) but still harmful • 10.5C) Propan-2-ol (2-propanol, isopropyl alcohol) o made by catalytic hydration of propylene o used as rubbing alcohol b/c has less drying effect on skin, not regulated and taxed by government o as toxic as methanol orally, but doesn’t pass through skin as easily as methanol 10.6) Acidity ofAlcohols and Phenols • hydroxyl proton of alcohol = weakly acidic strong base can remove hydroxyl proton alkoxide ion o alcohols can be from as acidic as water to much less acidic o acid dissociation constant K deained by eqbm - +  R-O-H + H O+2R-O - H O 3  K a [H O 3[RO]/[ROH]; pK = -logaK ) a • 10.6A) Effects onAcidity o acidity ↓ as substitution on alkyl group ↑ b/c more highly substituted alkyl group inhibits alkoxide ion solvation alkoxide ion = less stable eqbm towards left o substitution by electron-withdrawing halogen atom  better acidity b/c stabilizes ion • 10.6B) Formation of Sodium and PotassiumAlkoxides o alkoxide ions = strong nucleophiles and bases  when needed for synthesis, formed by reacting sodium/potassium metal w/ the alcohol (redox rxn, metal’s oxidized, H reduced to H ga2)  H bubbles out of sol’n, leaving Na/K salt of alkoxide ion  more acidic alcohols (ex: methanol and ethanol) react fast w/ Na sodium methoxide/ethoxide  secondary alcohols (ex: propan-2-ol) react more slowly w/ Na, so K used b/c more reactive, faster rxn o some alcohols react slowly w/ Na and K use NaH in tetrahydrofuran (THF) sol’n forms alkoxide even w/ difficult compounds • 10.6C) Acidity of Phenols o phenol actually = 100 million times more acidic than cyclohexanol even if similar structures o cyclohexanol = typical secondary alcohol, typical acid dissociation constant for alcohol  phenoxide ion = more stable than typical alkoxide ion b/c negative charge delocalized over O and 3 C’s of ring o still lot of negative charge on O b/c most electronegative, but b/c still spread over 4 atoms more stable ion  rxn of phenol and NaOH = exothermic, eqbm on right o phenoxide ions prepared by adding phenol to aqueous NaOH sol’n or KOH, don’t need to use Na/K metal  phenol once called carbolic acid b/c neutralizes common bases 10.7) Synthesis of Alcohols: Introduction and Review • Alcohols can be directly synthesized from variety of other functional groups o alkyl halides  a
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