AS Chemistry

1. AS Chemistry Alcohols

2. Learning Objectives • Candidates should be able to: • recall the chemistry of alcohols, as exemplified by ethanol, including their oxidation to carbonyl compounds and carboxylic acids. • classify hydroxy compounds into primary, secondary and tertiary alcohols. • suggest characteristic distinguishing reactions, e.g. mild oxidation.

3. Starter activity Complete task 1 on your worksheet.

4. Production of alcohol

5. Classes of alcohols

6. Oxidation of alcohols Primary alcohols Secondaryalcohols

7. Oxidation of alcohols Primary alcohol  aldehyde  carboxylic acid e.g. ethanol ethanal ethanoic acid Secondary alcohol  ketone  no reaction e.g. propan-2-ol propanone Tertiary alcohol  no reaction

8. Oxidising agent Cr2O72- Cr3+ Orange  Green

9. Heating under reflux Prevents evaporation of aldehyde

10. AS Chemistry Physical properties and general chemistry

11. Learning Objectives • Candidates should be able to: • recall the chemistry of alcohols, exemplified by ethanol: • combustion • substitution to give halogenoalkanes • reaction with sodium • dehydration to alkenes

12. Starter activity Complete task 1 on your worksheet.

13. Physical properties – boiling point

14. Physical properties – boiling point • The boiling point of an alcohol is always much higher than that of an alkane with similar Mr. • This is due to hydrogen bonding between the alcohol molecules. • In alkanes the only intermolecular forces are vdW.

15. Physical properties – solubility The small alcohols are completely soluble in water.

16. Physical properties – solubility In both pure water and pure ethanol the main intermolecular forces are hydrogen bonds. In order to mix them together you must supply energy to break these bonds.

17. Physical properties – solubility • Fortunately, alcohols can form hydrogen bonds with water: • H – OH • R - OH

18. Physical properties – solubility This bond-making process releases energy which more or less compensates for the energy input. N.B. an alcohol only has one + H atom, unlike water which has 2.

19. Physical properties – solubility The hydrocarbon chains in an alcohol cannot form hydrogen bonds. As the chains get longer they force their way between water molecules preventing them from hydrogen bonding. Too little energy is released from bond-making to compensate for that used in bond-breaking.

20. Physical properties – boiling point • The boiling point of an alcohol is always much higher than that of an alkane with similar Mr. • This is due to hydrogen bonding between the alcohol molecules. • In alkanes the only intermolecular forces are vdW.

21. General chemistry – combustion Ethanol can be used as a fuel, mainly as a biofuelalternative to gasoline. Because it is easy to manufacture and process and can be made from renewable resources such as sugar cane and corn, it is an increasingly common alternative to gasoline in some parts of the world, e.g. Brazil. Anhydrous ethanol (ethanol with less than 1% water) can be blended with gasoline in varying quantities and most gasoline engines will operate well with mixtures of 10% ethanol (E10).

22. General Chemistry - electron density map Ethanol – CH3CH2OH Chemistry can involve breaking the C-O bond and the O-H bond.

23. General chemistry – reaction with Sodium 2Na + 2HO-H  2NaOH + H2 2Na + 2RO-H  2NaOR + H2 NaOR is more usually written as RONa or RO- Na+ 2Na + 2CH3CH2OH  2CH3CH2O-Na+ + H2 sodium ethanol sodium ethoxide hydrogen

24. General chemistry – substitution to form halogenoalkanes Consider the reaction below: CH3CH2Br + OH- CH3CH2OH + Br- You should remember that this hydrolysis reaction occurs quite readily in a warm, aqueous solution. The reverse reaction is more difficult, -OH is not a good leaving group. Presence of H+ required to form water, a much better leaving group.

25. General equation The general reaction looks like this: ROH + HX  RX + H2O

26. Replacing –OH by bromine Rather than using hydrobromic acid, you usually treat the alcohol with a mixture of sodium or potassium bromide and concentrated sulphuric acid. This produces hydrogen bromide in situ which reacts with the alcohol. The mixture is warmed to distil off the bromoalkane (see page 338 of your textbook).

27. Replacing –OH by iodine Iodoalkanes can be made by two different methods. In the first method the alcohol is reacted with a mixture of sodium or potassium iodide and concentrated phosphoric(V) acid, H3PO4, and the iodoalkane is distilled off.

28. Replacing –OH by iodine In the second method the iodoalkanecan be made by warming the alcohol with a mixture of red phosphorus and iodine: This then reacts with the alcohol to give the corresponding halogenoalkane which can be distilled off.

29. Replacing –OH by chlorine Chloroalkanes are more easilymade by the secondroute: you can react an alcohol with phosphorus(III) chloride, PCl3, phosphorus(V) chloride, PCl5, or sulphur dichloride oxide (thionyl chloride, SOCl2). • CH3CH2OH + PCl5 CH3CH2Cl + HCl + POCl3 • CH3CH2OH + SOCl2 CH3CH2Cl + HCl + SO2

30. Elimination (when a small molecule is removed from a larger molecule – converts a single bond to a double bond) C2H5OH(g) CH2=CH2(g) + H2O(g)

31. AS Chemistry Aldehydes and Ketones

32. Learning Objectives • Candidates should be able to: • describe the reduction of aldehydes and ketones e.g. using NaBH4. • describe the mechanism of the nucleophilic addition reactions of hydrogen cyanide with aldehydes and ketones. • describe the use of 2,4-dinitrophenylhydrazine (2,4-DNPH) to detect the presence of carbonyl compounds. • deduce the nature (aldehyde or ketone) of an unknown carbonyl compound from the result of simple tests (i.e. Fehling’s or Tollens’ reagents; ease of oxidation). • describe the formation of carboxylic acids from nitriles.

33. Starter activity Can you write balanced equations for the synthesis of chloro-, bromo- and iodoethane from ethanol? Give the names of the reagents and the reaction conditions.

34. Aldehyde or Ketone

35. Tollen’s reagent

36. Aldehyde or Ketone Using Fehling's solution

37. Fehling’s reagent

38. Reduction of aldehydes and ketones – H2 butanone  butan-2-ol prop-2-enal  propan-1-ol

39. Reduction of aldehydes and ketones – NaBH4 ethanal ethanol propanone propan-2-ol

40. Reduction of aldehydes and ketones – NaBH4 prop-2-enal prop-2-en-1-ol

41. Formation of hydroxynitriles (or cyanohydrins)

42. Reactions of nitriles Hydrolysis Reduction

43. Aldehyde or ketone? 2,4-DNPH Test:Add a solution of 2,4-dinitrophenylhydrazine (2,4-DNPH). Result:a deep yellow or orange precipitate

44. AS Chemistry Carboxylic acids

45. Learning Objectives • Candidates should be able to: • describe the reactions of carboxylic acids in the formation of salts.

46. Starter activity – can you complete task 1? methanoic acid 2-methylbutanoic acid hexanedioic acid

47. Acidity of the carboxylic acids Reaction with metals

48. Neutralisation reactions Reaction with alkalis CH3COOH(aq) + NaOH(aq) CH3COO-Na+(aq) + H2O(l) Reaction with carbonates 2H+(aq) + CO32-(aq)/(s) H2O(l) + CO2(g) Reaction with hydrogencarbonates H+(aq) + HCO3-(aq)/(s) H2O(l) + CO2(g)

49. AS Chemistry Esters

50. Learning Objectives • Candidates should be able to: • describe the formation of esters from carboxylic acids using ethyl ethanoate as an example. • Describe the acid and base hydrolysis of esters. • State the commercial use of esters, e.g. solvents, perfumes, flavourings.