ALCOHOLS & ETHERS part 1 ROHAZITA BAHARI

1. ALCOHOLS & ETHERSpart 1ROHAZITA BAHARI

2. Physical Properties of Alcohols • The most important physical property is their polarity • Both the C-O bond and the O-H bond are polar covalent bonds • Thus alcohols are polar molecules • They also have the ability to hydrogen bond. • These factors lead to higher B.P’s, M.P’s. etc

3. Physical Properties of Alcohols • Because of increase London forces (van der Waals forces) between larger molecules, the B.P. of all types of compounds, including alcohols, increase as molecular weight increases • Alcohols are much more soluble in H2O due to their H-bonding capacity. • As MW increases, the water solubility of alcohols decreases • This is because the hydrocarbon portion of the molecule dominates.

4. Reactions of Alcohols • Acidity of Alcohols Alcohols are considerably weaker acids than carboxylic acids, but can lose their hydrogen in an acid-base reaction.

5. Methanol • Methanol was once prepared by the destructive distillation of wood. • Wood alcohol. • Toxic, causes blindness in low doses (15 mL). • Routinely used as a solvent and starting material. • Methanol used by the chemical industry is prepared by the catalytic reduction of carbon monoxide. Cu/ZnO/Al2O3 CO + 2 H2 CH3OH 250°C

6. Ethanol • Prepared by the fermentation of grains and sugars. • Grain alcohol. • Used in alcoholic beverages. • The largest single use of ethanol is as a motor fuel and fuel additive (replaces MTBE). • 5 billion gallons are prepared (primarily from corn) annually in the U.S. for fuel uses. • Ethanol used by the chemical industry is prepared by the acid-catalyzed hydration of ethylene. H3PO4 H2C=CH2 + H2O CH3CH2OH 250°C

7. Neutral methyl group The Polar -OH Group • The physical properties of the alcohols are strongly influenced by the polar -OH group. Negatively polarized oxygen Positively polarized hydrogen Methanol

8. Compound MW (g/mol) BP (°C) CH3CH2CH2CH3 CH3CH2Cl CH3CH2CH2OH Boiling Points • The polar -OH group allows hydrogen bonding to take place in alcohols. These strong intermolecular forces result in higher than expected boiling points. + + - - - + + + - - 58 -0.5 65 12.5 60 97

9. Ethers • Alcohols and ethers are organic derivatives of water where one or both H atoms are replaced by R groups. H-O-H  R-O-H  R-O-R’ Alcohol Ether Water

10. Ethers • Structure- functional group is a Oxygen bonded to 2 carbons • Simplest ether is dimethyl ether

11. Nomenclature of Ethers • The common naming system is used for simple ethers: • List the alkyl groups bonded to the oxygen in alphabetical order, followed by the work “ether”.

12. Ether Nomenclature diethyl ether ethyl methyl ether cyclohexyl methyl ether cyclooctyl ethyl ether

13. Crown Ethers • Large rings consisting repeating (-OCH2CH2-) or similar units • Named as x-crown-y • x is the total number of atoms in the ring • y is the number of oxygen atoms • 18-crown-6 ether: 18-membered ring containing 6 oxygens atoms • Central cavity is electronegative and attracts cations

14. 18-Crown-6

15. Uses of Crown Ethers • Complexes between crown ethers and ionic salts are soluble in nonpolar organic solvents • Creates reagents that are free of water that have useful properties • Inorganic salts dissolve in organic solvents leaving the anion unassociated, enhancing reactivity

16. Physical Properties of Ethers • Ethers are polar compounds • The oxygen has a partial minus charge, the carbons bonded to the oxygen have a partial positive charge • Ether have very weak intermolecular forces which results in low boiling points

17. Electrostatic Potential Map Negatively polarized oxygen Neutral ethyl group Neutral ethyl group Diethyl ether The Ethers Ethers lack the polar -OH group and therefore do not have hydrogenbonding.

18. Reactions of Ethers • Like alkanes, they are resistant to most chemical reactions • Therefore, they are ideal to use as solvents

19. H2SO4 2 CH3CH2OH CH3CH2OCH2CH3 + H2O Diethyl Ether • Was once widely used as an anesthetic. • Highly flammable. • Presently used as a solvent. • Prepared by the sulfuric acid-catalyzed dehydration of ethanol.

20. MW (g/mol) BP (°C) Compound CH3CH2OH CH3OCH3 CH3CH2CH2CH2OH CH3CH2OCH2CH3 Boiling Points Ethers have weak intermolecular forces, which results in low boiling points. Low molecular weight ethers are highlyvolatile. 46 78.5 46 -25 74 117.2 74 34.5

21. Hydrogen-Bonding? Compound Polarity BP Reactive? Uses ROH ROR’ Alcohols & Ethers Alcohols and ethers have very different chemical and physical properties. This is due to the polar -OH group that’s present in alcohols but absent in ethers. starting materials polar yes high yes non-polar no low no solvents

22. OXIDATION REDUCTION Oxidation and Reduction Carboxylic Acid Aldehyde / Ketone Alcohol Alkane Oxidation: Increase C-O bondsReduction: Increase C-H bonds

23. Common Reducing Agents Sodium borohydride (NaBH4) is a mild reducing agent. 1º alcohol aldehyde 2º alcohol ketone

24. Common Reducing Agents Lithium aluminum hydride (LiAlH4) is a strong reducing agent. carboxylic acid 1º alcohol

25. Predict the Products

26. Common Oxidizing Agents Pyridinium chlorochromate (PCC) (C5H6NCrO3Cl) is a mild oxidizing agent. aldehyde 1º alcohol ketone 2º alcohol

27. Common Oxidizing Agents Chromium trioxide (CrO3) and sodium dichromate (Na2Cr2O7) are strong oxidizing agents. carboxylic acid 1º alcohol ketone 2º alcohol

28. Predict the Products

29. The Williamson Ether Synthesis 2 ROH + 2 M  2 ROM + H2 alcohol M = Na, K SN2 RO- + R’X  ROR’ + X- alkoxide alkyl halide ether R can be 1º, 2º, 3º, or cycloalkyl. R’ should be methyl or 1º.

30. Synthesis of Diethyl Ether via the Williamson Synthesis Diethyl ether is a symmetrical ether. 2 CH3CH2OH + 2 Na  2 CH3CH2ONa + H2 ethanol sodium ethoxide SN2 CH3CH2O- + CH3CH2I  CH3CH2OCH2CH3 + I- ethoxide ion ethyl iodide diethyl ether

31. Synthesis of tert-Butyl Methyl Ether via the Williamson Synthesis tert-Butyl methyl ether is an asymmetrical ether. SN2 + This is the better route nucleophile tert-butyl methyl ether E2 + + base 2-methylpropene