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Alcohols

Alcohols. Alcohol. alcohol : a compound that has an –OH group bonded to a carbon (R-OH). CH 3 OH CH 3 CHCH 3 OH. OH. methanol 2-propanol phenol. Alcohols & Water. structural similarity

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Alcohols

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  1. Alcohols

  2. Alcohol • alcohol: a compound that has an –OH group bonded to a carbon (R-OH). CH3OH CH3CHCH3 OH OH methanol 2-propanol phenol

  3. Alcohols & Water • structural similarity • physical property similarity • hydrogen bonding H – O – H CH3 – CH2 – OH bp. 100 °C bp 78.5 °C

  4. Cu catalyst high pressure Some Common Alcohols: Methanol • aka methyl alcohol, wood alcohol • CH3OH • colorless • miscible with water • toxic to humans when ingested or inhaled (causes blindness in low doses ~15 mL for an adult, death in larger amounts 100-250 mL) • it was once prepared by heating wood in the absence of air, but today is made by CO(g) + H2(g) CH3OH(l)

  5. yeast enzymes H2SO4 Ethanol • aka ethyl alcohol, grain alcohol • CH3CH2OH • production by fermentation of grains and sugar known for thousands of years • wine ~13%, beer ~3-5%, distilled liquors 35-90% • fermentation alone yields maximum alcohol concentration of about 14% by volume • distillation gives a higher concentration C6H12O6 2CH3CH2OH + 2CO2 CH2=CH2 + H2O CH3CH2OH

  6. Isopropyl Alcohol • aka rubbing alcohol, 2-propanol • (CH3)2CHOH • solvent for medicines, skin cleanser before injections • much more toxic than ethanol, but less toxic than methanol

  7. Ethylene Glycol • aka 1,2-ethanediol • HOCH2CH2OH • colorless liquid • miscible with water • insoluble in nonpolar solvents • used in antifreeze and as a starting material from making polyester films and fibers • lethal dose for an adult is about 100 mL

  8. Glycerol • aka glycerin, 1,2,3-propanetriol • HOCH2CH(OH)CH2OH • colorless liquid • miscible with water • not toxic • sweet taste • used in cosmetics and tobacco as a moisturizer, candy and prepared foods, plastics manufacture, antifreeze and shock-absorber fluids, and as a solvent.

  9. Naming Alcohols • use the ending “-ol” for the parent compound

  10. OH 1. Name the Parent Compounds • Find the longest chain that has the hydroxyl (-OH) substituent attached. • Name the parent compound by adding the ending “-ol” CH3 OH CH3CHCH2CHCH2CH3 …hexanol cyclopentanol

  11. OH 6 1 2 5 3 4 CH3 2. Number the Carbon Atoms in the Main Chain • Begin at the end nearer the hydroxyl group. (-OH groups take precedence over alkyl groups in determining the direction in which a carbon chain is numbered) • In a cyclic alcohol, begin with the carbon that bears the –OH group and proceed in the direction that gives the other substituents the lowers possible numbers CH3 OH CH3CHCH2CHCH2CH3 6 5 4 3 2 1

  12. 3. Identify the Location of other Substituents. • Indicate the position of the other substituents in the chain by giving the number of the carbon to which it is attached.

  13. OH 6 1 2 5 3 4 CH3 4. Write the Full Name • Place the number for the hydroxyl group location immediately before the parent compound name • list other substituents alphabetically • if 2 or more –OH groups are present, use “-diol”, “-triol”, etc. as appropriate CH3 OH CH3CHCH2CHCH2CH3 6 5 4 3 2 1 5-methyl-3-hexanol 3-methylcyclohexanol

  14. Additional Examples CH3CH2CH2CH2OH 1-butanol OH Cl CH3 CH3CHCH2CHCH2CHCH3 CH3CHCH2CH=CHCH2CHCH3 4-octene-2,7-diol OH OH 4-chloro-6-methyl-2-heptanol

  15. Diols (Glycols) • contain 2 alcohol groups OH HOCH2CH2OH CH3CHCH2OH ethylene glycol propylene glycol 1,2-ethanediol 1,2-propanediol

  16. H3C OH H3C Practice: Name 2-ethyl-1-pentanol CH2OH CH3CH2CHCH2CH2CH3 4,4-dimethylcyclohexanol

  17. OH Practice: Draw • 3-methyl-3-pentanol OH CH3CH2CCH2CH3 CH3 • cyclobutanol

  18. Your Turn • Name: OH CH3CH2CHCH2CH2CH2CH3 • Draw: 3-chloro-1-propanol 3-heptanol HOCH2CH2CH2Cl

  19. Primary, Secondary, & Tertiary Alcohols • Alcohols are classified according to the number of carbon substituents bonded to the carbon with the OH group. H R’ R’ R – C – OH R – C – OH R – C – OH H H R” primary alcohol secondary alcohol tertiary alcohol 1° 2° 3°

  20. Practice • Name the alcohol and classify it as primary, secondary, or tertiary. CH3 CH3CH2CH2C – OH CH3 2-methyl-2-pentanol tertiary alcohol

  21. Properties of Alcohols • strongly affected by hydrogen bonding • recall  hydrogen bonding …..

  22. Water is polar. This means that the electron density is greater on one side of the molecule than the other. d- O H H d+

  23. Hydrogen Bonds • Hydrogen bonding is a loose, long-distance kind of attraction. • Hydrogen bonding is an intermolecular force. (This means it occurs between molecules.) • Occurs in molecules containing O-H, N-H, and F-H bonds (because they are highly polar bonds)

  24. : : : : O O H H H H O H H O O H H H H : : : : : : Hydrogen Bonding hydrogen bond

  25. Practice • Which has the highest boiling point? CH3CH2CH2OH or CH3CH2CH3 CH3CH2CH2OH • Which is most soluble in water? CH3(CH2)10CH2OH or CH3CH2CHCH3 OH CH3CH2CHCH3 OH

  26. General Properties • straight-chain alcohols with up to 12 carbon atoms are liquids • each boils at a higher temperature than the related alkane • alcohols with a small organic portion (like methanol and ethanol) are like water in their solubility behavior • methanol and ethanol are miscible with water and can dissolve small amounts of many salts • methanol and ethanol are also miscible with many organic solvents • alcohols with a larger organic part such as 1-heptanol are more like alkanes and less like water • 1-heptanol is nearly insoluble in water and can’t dissolve salts but does dissolve alkanes • alcohols with two or more –OH groups can form more than one hydrogen bond. Therefore they have higher boiling and more water-soluble than similar alcohols with one –OH group • CH3CH2CH2CH2OH (bp 117 °C, water solubility of 7g/100mL) • HOCH2CH2CH2CH2OH (bp 230 °C and miscible with water)

  27. Physical Properties of Some Alcohols Name Structure mp(C) bp(C) solubility (g/100 mL H2O) methanol CH3OH -94 65 infinite ethanol CH3CH2OH -117 78 infinite 1-propanol CH3(CH2)2OH -127 97 infinite 2-propanol (CH3)2CHOH -90 82 infinite 1-butanol CH3(CH2)3OH -90 117 9 2-butanol CH3CHCH2CH3 -115 100 12.5 ׀ OH 1-pentanol CH3(CH2)3CH2OH -79 138 1-hexanol CH3(CH2)4CH2OH -52 157 0.6 1-dodecanol CH3(CH2)10CH2OH 26 259 insoluble 1-octadecanol CH3(CH2)16CH2OH 59 332 insoluble

  28. Reactions of Alcohols • reaction with metals • dehydration • conversion to alkyl halide • oxidation

  29. increasing reactivity toward metals 1. Reaction with Metals (Group 1A and 2A) • alcohol + metal  metal alkoxide + hydrogen gas • CH3OH + 2Na  2Na+-OCH3 + H2 methanol sodium methoxide • (CH3)2CHOH + 2 K  2K+-OCH(CH3)2 + H2 R3COH < R2CHOH < RCH2OH < CH3OH tertiary secondary primary methyl least most reactive reactive

  30. 2. Dehydration • dehydration: the loss of water from an alcohol to yield an alkene • occurs in presence of strong acid catalyst OH CH3 H CH3CCH3 H2O + C = C CH3 CH3 H tert-butyl alcohol 2-methylpropene H2SO4

  31. Dehydration Cont. • When more than one alkene can result from the dehydration of an alcohol a mixture of products is usually formed. • Rule of thumb: the major product is the one that has the greater number of alkyl groups attached to the double bond carbons OH CH3CH2CHCH3 CH3–CH=CH–CH3 + CH3CH2–CH=CH3 H2SO4 2-butene (80%)1-butene (20%) dehydrationor here? from here

  32. Practice • What will be the major and minor products of: OH H2SO4 CH3CHCHCH3 CH3 H OH H CH3 – C – CH – CH2 CH3 CH3 – C = CH – CH3 CH3 2-methyl-2-butene (major) CH3 – CH – CH = CH2 CH3 3-methyl-1-butene (minor)

  33. Another Example H2SO4 + H2O OH

  34. Your Turn • Write the products of the dehydration reactions of… CH3CH2CH2OH CH3CH=CH2 OH CH3 CH3 CH3CHCH2CHCH3 CH2=CHCH2CHCH3 CH3 CH3CH=CHCHCH3

  35. SOCl2 K2CO3 SOCl2 pyridine 3. Formation of Alkyl Halide • SOCl2 (thionyl chloride) • alcohol + SOCl2 alkyl chloride + SO2 + HCl CH3CH(CH2)5CH3 CH3CH(CH2)5CH3 OH Cl 2-octanol 2-chlorooctane (81%) (CH3CH2)2CHCH2OH (CH3CH2)2CHCH2Cl 2-ethyl-1-butanol 1-chloro-2-ethylbutane (82%)

  36. PBr3 PBr3 OH Br H H • PX3 (phosphorus tribromide/trichloride, etc) 3ROH + PBr3 3RBr + P(OH)3 alcohol phosphorus alkyl phosphorous tribromide bromide acid (CH3)2CHCH2OH (CH3)2CHCH2Br

  37. CH2Br Practice SOCl2, pyridine dimethyl ether (CH3)2C=CHCH2CH2CHCH3 (CH3)2C=CHCH2CH2CHCH3 OH Cl 6-methyl-5-hepten-2-ol 6-chloro-2-methyl-2-heptene cyclopentylmethanol bromomethylcyclopentane CH2OH PBr3

  38. O R – C – H O R – C – OH O R – C – R’ = = = 4. Oxidation • Primary and secondary alcohols are converted into carbonyl-containing compounds when oxidized • carbonyl group C = O • carbonyl containing functional groups include: • aldehyde • carboxylic acid • ketone

  39. Oxidation Cont. • many oxidizing agents can be used (KMnO4, K2Cr2O7, etc) • in organic chemistry oxidation increases the number of C-O bonds and/or decreases the number of C-H bonds • In oxidation of an alcohol, 2 H atoms are removed from the alcohol and are converted into water by the oxidizing agent • one H comes from the –OH group • one H comes from the carbon atom bonded to the –OH group

  40. Primary Alcohol Oxidation Primary alcohols are converted into aldehydes or carboxylic acids OH O O R – C – H R – C – H R – C – OH H primary alcohol aldehyde carboxylic acid O O CH3CH2CH2CH2OH CH3CH2CH2CH CH3CH2CH2C - OH oxidizing agent oxidizing agent = = = = =

  41. oxidizing agent oxidizing agent O OH cyclohexanol cyclohexanone Secondary Alcohol Oxidation • Secondary alcohols are converted into ketones OH O R – C – H R – C – R’ R’ secondary alcohol ketone = =

  42. oxidizing agent Tertiary Alcohols • Tertiary alcohols don’t normally react with oxidizing agents because they don’t have a hydrogen on the carbon atom to which the –OH group is bonded OH R – C – R” no reaction R’ tertiary alcohol

  43. O O CH COH Practice • What is the product of the following oxidation reaction? oxidizing agent CH2OH

  44. O O CH3CH2CH CH3CH2COH O CH3CCH2CH2CH3 OH CHCH3 O CCH3 Your Turn • What products would you expect from oxidation of the following alcohols? CH3CH2CH2OH OH CH3CHCH2CH2CH3 oxidizing agent oxidizing agent oxidizing agent

  45. H3C OH Phenol C6H5OH OH Phenols are usually named with the ending “-phenol” rather than “-benzene” OH Cl o-chlorophenol p-methylphenol

  46. Acidity of Alcohols & Phenols • weakly acidic because of the positively polarized H atom of the OH group • CH3CH2OH CH3CH2O- + H3O+ • methanol and ethanol are about as acidic as water (so little dissociated in water that their aqueous solutions are neutral pH = 7) • the alkoxide ion (RO-), or anion of an alcohol, is as strong a base as OH- • phenols are considerably more acidic than water • phenols react with dilute aqueous NaOH to give water and a salt called sodium phenoxide

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