Alkenes, Reactions

1. Alkenes, Reactions

2. R-H R-X R-OH R-O-R Alkenes Acids Bases Metals Oxidation Reduction Halogens

3. Alkenes, reactions. Addition ionic free radical Reduction Oxidation Substitution

4. Reactions, alkenes: • Addition of hydrogen (reduction). • Addition of halogens. • Addition of hydrogen halides. • Addition of sulfuric acid. • Addition of water (hydration). • Addition of aqueous halogens (halohydrin formation). • 7. Oxymercuration-demercuration.

5. 8. Hydroboration-oxidation. 9. Addition of free radicals. 10. Addition of carbenes. 11. Epoxidation. 12. Hydroxylation. 13. Allylic halogenation 14. Ozonolysis. 15. Vigorous oxidation.

6. Addition of hydrogen (reduction). • | | | | • — C = C — + H2 + Ni, Pt, or Pd  — C — C — • | | • H H • a)Requires catalyst. • #1 synthesis of alkanes • CH3CH=CHCH3 + H2, Ni  CH3CH2CH2CH3 • 2-butene n-butane

7. Alkanes Nomenclature Syntheses 1. addition of hydrogen to an alkene 2. reduction of an alkyl halide a) hydrolysis of a Grignard reagent b) with an active metal and acid 3. Corey-House Synthesis Reactions 1. halogenation 2. combustion (oxidation) 3. pyrolysis (cracking)

8. heat of hydrogenation: CH3CH=CH2 + H2, Pt  CH3CH2CH3 + ~ 30 Kcal/mole ethylene 32.8 propylene 30.1 cis-2-butene 28.6 trans-2-butene 27.6 isobutylene 28.4

9. fats & oils: triglycerides O CH2—O—CCH2CH2CH2CH2CH2CH2CH2CH2CH3 | O CH—O—CCH2CH2CH2CH2CH2CH2CH2CH2CH3 | O CH2—O—CCH2CH2CH2CH2CH2CH2CH3 “saturated” fat

10. O CH2—O—CCH2CH2CH2CH2CH=CH2CH2CH2CH3 | O CH—O—CCH2CH2CH2CH2CH=CH2CH2CH2CH3 | O CH2—O—CCH2CH2CH=CHCH2CH2CH3 Ω - 3 “unsaturated” oil

11. Saturated triglycerides are solids at room temperature and are called “fats”. butter fat, lard, vegetable shortening, beef tallow, etc. Unsaturated triglycerides have lower mp’s than saturated triglycerides. Those that are liquids at room temperature are called “oils”. (All double bonds are cis-.) corn oil, peanut oil, Canola oil, cottonseed oil, etc.

12. polyunsaturated oils + H2, Ni  saturated fats liquid at RT solid at RT oleomargarine butter substitute (dyed yellow) Trans-fatty acids formed in the synthesis of margarine have been implicated in the formation of “bad” cholesterol, hardening of the arteries and heart disease. 

13. 2. Addition of halogens. • | | | | • — C = C — + X2 — C — C — • | | • X X • X2 = Br2 or Cl2 • test for unsaturation with Br2 • CH3CH2CH=CH2 + Br2/CCl4  CH3CH2CHCH2 • Br Br • 1-butene 1,2-dibromobutane

14. Addition of hydrogen halides. • | | | | • — C = C — + HX  — C — C — • | | • H X • HX = HI, HBr, HCl • Markovnikov orientation • CH3CH=CH2 + HI  CH3CHCH3 • I • CH3 CH3 • CH2C=CH2 + HBr  CH3CCH3 • Br

15. Markovnikov’s Rule: In the addition of an acid to an alkene the hydrogen will go to the vinyl carbon that already has the greater number of hydrogens.

16. CH3CH2CH=CH2 + HCl CH3CH2CHCH3 Cl CH3 CH3 CH3CH=CCH3 + HBr CH3CH2CCH3 Br CH3CH=CHCH3 + HI  CH3CH2CHCH3 I

17. An exception to Markovikov’s Rule: CH3CH=CH2 + HBr, peroxides CH3CH2CH2Br CH3 CH3 CH3C=CH2 + HBr, peroxides CH3CHCH2Br “anti-Markovnikov” orientation note: this is only for HBr.

18. Markovnikov doesn’t always correctly predict the product! CH3 CH3 CH2=CHCHCH3 + HI  CH3CH2CCH3 I Rearrangement!

21. why Markovinkov? CH3CH=CH2 + HBr  CH3CHCH2 1o carbocation |   H or? CH3CHCH2 2o carbocation  | more stable H + Br- CH3CHCH3 | Br

22. In ionic electrophilic addition to an alkene, the electrophile always adds to the carbon-carbon double bond so as to form the more stable carbocation.

23. Addition of sulfuric acid. • | | | | • — C = C — + H2SO4 — C — C — • | | • H OSO3H • alkyl hydrogen sulfate • Markovnikov orientation. • CH3CH=CH2 + H2SO4  CH3CHCH3 • O • O-S-O • OH

24. Addition of water. • | | | | • — C = C — + H2O, H+ — C — C — • | | • H OH • a) requires acid • Markovnikov orientation • low yield  • CH3CH2CH=CH2 + H2O, H+  CH3CH2CHCH3 • OH

26. | | H+ | | — C = C — + H2O  — C — C — | | OH H Mechanism for addition of water to an alkene to form an alcohol is the exact reverse of the mechanism (E1) for the dehydration of an alcohol to form an alkene.

29. How do we know that the mechanism isn’t this way? One step, concerted, no carbocation

30. CH3CH=CH2 + Br2 + H2O + NaCl  CH3CHCH2 + CH3CHCH2 + CH3CHCH2 Br Br OH Br Cl Br

31. Some evidence suggests that the intermediate is not a normal carbocation but a “halonium” ion: | | — C — C — Br  The addition of X2 to an alkene is an anti-addition.

32. Addition of halogens + water (halohydrin formation): • | | | | • — C = C — + X2, H2O  — C — C — + HX • | | • OH X • X2 = Br2, Cl2 • Br2 = electrophile • CH3CH=CH2 + Br2(aq.)  CH3CHCH2 + HBr • OH Br

34. 7. Oxymercuration-demercuration. | | | | — C = C — + H2O, Hg(OAc)2 — C — C — + acetic | | acid OH HgOAc | | | | — C — C — + NaBH4 — C — C — | | | | OH HgOAc OHH alcohol

35. oxymercuration-demercuration: • #1 synthesis of alcohols. • Markovnikov orientation. • 100% yields.  • no rearrangements  • CH3CH2CH=CH2 + H2O, Hg(OAc)2; then NaBH4 • CH3CH2CHCH3 • OH

36. With alcohol instead of water: alkoxymercuration-demercuration: | | | | — C =C — + ROH, Hg(TFA)2 — C — C — | | OR HgTFA | | | | — C — C — + NaBH4 — C — C — | | | | OR HgTFA ORH ether

37. alkoxymercuration-demercuration: • #2 synthesis of ethers. • Markovnikov orientation. • 100% yields.  • no rearrangements  • CH3CH=CH2 + CH3CHCH3, Hg(TFA)2; then NaBH4 • OH • CH3CH3 • CH3CH-O-CHCH3 • diisopropyl ether • Avoids the elimination with 2o/3o RX in Williamson Synthesis.

38. Ethers nomenclature syntheses 1. Williamson Synthesis 2. alkoxymercuration-demercuration reactions 1. acid cleavage

39. 8. Hydroboration-oxidation. | | | | — C = C — + (BH3)2 — C — C — | | diboraneH B — | | | | | — C — C — + H2O2, NaOH — C — C — | | | | H B — H OH | alcohol

40. hydroboration-oxidation: • #2 synthesis of alcohols. • Anti-Markovnikov orientation.  • 100% yields.  • no rearrangements  • CH3CH2CH=CH2 + (BH3)2; then H2O2, NaOH  • CH3CH2CH2CH2-OH

41. CH3 CH3C=CH2 + H2O, Hg(OAc)2; then NaBH4 CH3 Markovnikov CH3CCH3 OH CH3 CH3C=CH2 + (BH3)2; then H2O2, NaOH  CH3 anti-Markovnikov CH3CHCH2 OH

42. Alcohols: nomenclature syntheses 1. oxymercuration-demercuration 2. hydroboration-oxidation 3. 4. hydrolysis of a 1o / CH3 alcohol 5. 6. 8.

43. 9. Addition of free radicals. • | | | | • — C = C — + HBr, peroxides  — C — C — • | | • H X • anti-Markovnikov orientation. • free radical addition • HI, HCl + Peroxides • CH3CH=CH2 + HBr, peroxides  CH3CH2CH2-Br

44. Mechanism for free radical addition of HBr: • Initiating steps: • 1) peroxide  2 radical• • 2) radical• + HBr  radical:H + Br• (Br• electrophile) • Propagating steps: • 3) Br• + CH3CH=CH2  CH3CHCH2-Br (2o free radical) • • • 4) CH3CHCH2-Br + HBr  CH3CH2CH2-Br + Br• • • • 3), 4), 3), 4)… • Terminating steps: • Br• + Br•  Br2 • Etc.

45. In a free radical addition to an alkene, the electrophilic free radical adds to the vinyl carbon with the greater number of hydrogens to form the more stable free radical. In the case of HBr/peroxides, the electrophile is the bromine free radical (Br•). CH3CH=CH2 + HBr, peroxides  CH3CH2CH2-Br

46. 10. Addition of carbenes. | | | | — C = C — + CH2CO or CH2N2 , hν — C — C — CH2 •CH2• “carbene” adds across the double bond | | — C = C —   •CH2•

47. | | | | — C = C — + CHCl3, t-BuOK — C— C — CCl2  -HCl •CCl2• dichlorocarbene | | — C = C —   •CCl2•

49. 11. Epoxidation. | | C6H5CO3H | | — C = C — + (peroxybenzoic acid)  — C— C — O epoxide Free radical addition of oxygen diradical. | | — C = C —   •O•