Alkenes, Reactions.ppt

1、Alkenes, Reactions,Acids Bases Metals Oxidation Reduction Halogens,R-H R-X R-OH R-O-R Alkenes,Alkenes, reactions.Additionionicfree radicalReductionOxidationSubstitution,Reactions, alkenes: Addition of hydrogen (reduction). Addition of halogens. Addition of hydrogen halides. Addition of sulfuric acid

2、. Addition of water (hydration). Addition of aqueous halogens (halohydrin formation). Dimerization. Alkylation.,Oxymercuration-demercuration. Hydroboration-oxidation. Addition of free radicals. Polymerization. Addition of carbenes. Epoxidation. Hydroxylation. Allylic halogenation Ozonolysis. Vigorou

3、s oxidation.,Addition of hydrogen (reduction).| | | | C = C + H2 + Ni, Pt, or Pd C C | |H H a) Requires catalyst. #1 synthesis of alkanesCH3CH=CHCH3 + H2, Ni CH3CH2CH2CH32-butene n-butane,AlkanesNomenclatureSyntheses1. addition of hydrogen to an alkene2. reduction of an alkyl halidea) hydrolysis of

4、a Grignard reagentb) with an active metal and acid3. Corey-House SynthesisReactions1. halogenation2. combustion (oxidation)3. pyrolysis (cracking),heat of hydrogenation:CH3CH=CH2 + H2, Pt CH3CH2CH3 + 30 Kcal/moleethylene 32.8 propylene 30.1 cis-2-butene 28.6 trans-2-butene 27.6 isobutylene 28.4,fats

5、 & oils: triglyceridesO CH2OCCH2CH2CH2CH2CH2CH2CH2CH2CH3| OCHOCCH2CH2CH2CH2CH2CH2CH2CH2CH3| O CH2OCCH2CH2CH2CH2CH2CH2CH3“saturated” fat,O CH2OCCH2CH2CH2CH2CH=CH2CH2CH2CH3| OCHOCCH2CH2CH2CH2CH=CH2CH2CH2CH3| O CH2OCCH2CH2CH=CHCH2CH2CH3 - 3 “unsaturated” oil,Saturated triglycerides are solids at room t

6、emperature and are called “fats”. butter fat, lard, vegetable shortening, beef tallow, etc.Unsaturated triglycerides have lower mps 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 oi

7、l, etc.,polyunsaturated oils + H2, Ni saturated fatsliquid at RT solid at RToleomargarinebutter 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. ,2) Addition of halog

8、ens.| | | | C = C + X2 C C | |X XX2 = Br2 or Cl2 test for unsaturation with Br2CH3CH2CH=CH2 + Br2/CCl4 CH3CH2CHCH2Br Br1-butene 1,2-dibromobutane,Addition of hydrogen halides.| | | | C = C + HX C C | |H X HX = HI, HBr, HCl Markovnikov orientationCH3CH=CH2 + HI CH3CHCH3ICH3 CH3CH2C=CH2 + HBr CH3CCH3B

9、r,Markovnikovs Rule: In der Hinzufgung einer Sure zu einem alkene wird der Wasserstoff zum Vinylkohlenstoff gehen, der schon den greren Anzahl Wasserstoffe hat. 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.,Regla de

10、 Markovnikov: En la adicin inica de un cido al doble enlace de un alqueno, el hidrgeno de aqul se une al tomo de carbono que ya tiene el mayor nmero de hidrgenos.“Al que tiene, le ser dado.” “El que tiene, recibir.”,Dans laddition dun acide un alcne lhydrogne ira au carbone de vinyle qui a dj le nom

11、bre plus grand de hydrogne. . 酸付加水素行既水素大数。 , () .,CH3CH2CH=CH2 + HCl CH3CH2CHCH3ClCH3 CH3 CH3CH=CCH3 + HBr CH3CH2CCH3BrCH3CH=CHCH3 + HI CH3CH2CHCH3I,An exception to Markovikovs Rule:CH3CH=CH2 + HBr, peroxides CH3CH2CH2BrCH3 CH3 CH3C=CH2 + HBr, peroxides CH3CHCH2Br“anti-Markovnikov” orientationnote:

12、this is only for HBr.,Markovnikov doesnt always correctly predict the product!CH3 CH3 CH2=CHCHCH3 + HI CH3CH2CCH3 IRearrangement!,why Markovinkov?CH3CH=CH2 + HBr CH3CHCH2 1o carbocation | Hor? CH3CHCH2 2o carbocation | more stableH+ Br- CH3CHCH3|Br,In ionic electrophilic addition to an alkene, the e

13、lectrophile always adds to the carbon-carbon double bond so as to form the more stable carbocation.,Addition of sulfuric acid.| | | | C = C + H2SO4 C C | |H OSO3Halkyl hydrogen sulfate Markovnikov orientation.CH3CH=CH2 + H2SO4 CH3CHCH3OO-S-OOH,Addition of water.| | | | C = C + H2O, H+ C C | |H OH a)

14、 requires acid Markovnikov orientation low yield CH3CH2CH=CH2 + H2O, H+ CH3CH2CHCH3OH,| | H+ | | C = C + H2O C C | |OH HMechanism 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.,How do we know that

15、the mechanism isnt this way?One step, concerted, no carbocation,CH3CH=CH2 + Br2 + H2O + NaCl CH3CHCH2 + CH3CHCH2 + CH3CHCH2Br Br OH Br Cl Br,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.,A

16、ddition of halogens + water (halohydrin formation):| | | | C = C + X2, H2O C C + HX | |OH XX2 = Br2, Cl2 Br2 = electrophileCH3CH=CH2 + Br2(aq.) CH3CHCH2 + HBrOH Br,Dimerization:CH3 CH3 CH3 CH3C=CH2 + H2SO4, 80oC CH3C-CH=CCH3CH3+CH3 CH3 CH3C-CH2C=CH2CH3,carbocation as electrophile,Alkylation:CH3 CH3

17、CH3C=CH2 + CH3CHCH3 + HF, 0oC CH3 CH3CH3C-CH2CHCH3CH32,2,4-trimethylpentane( “isooctane” )Used to increase gasoline yield from petroleum and to improve fuel performance.,intermolecular hydride (H:-) transfer,Internal combustion engine (four-stroke).Also called an Otto engine.,1. Intake stroke: air/f

18、uel mixture is drawn into the cylinder.,2. Compression stroke: air/fuel mixture is compressed.,Ignition of air/fuel mixture by spark at approximately 0o top dead center.,3. Power stroke: expanding gases push piston down driving crank shaft around.,4. Exhaust stroke: CO2 + H2O are pushed out of the c

19、ylinder.,Compression is the key to building a more powerful four-stroke engine. The more the air/fuel mixture is compressed prior to ignition, the more efficient is the conversion of heat energy into mechanical motion. Increasing the compression ratio = More powerful engine. Lighter engine (greater

20、power to weight ratio). Greater fuel economy.,But, compression of the air/fuel mixture above a certain point causes “knocking”. PV = nRTT P If, during compression of an air/fuel mixture, the temperature goes high enough, the mixture may explode prematurely.,A knocking sound is produced by an interna

21、l combustion engine when fuel ignites spontaneously and prematurely (pre-ignition) during the compression cycle in an engines combustion chamber. Consequently, the piston will be forced down when it should be traveling upwards on its compression stroke. At best, knocking reduces the performance of t

22、he engine; at worst, it can damage the engines moving parts. ,Fuel for four-stroke internal combustion engines:Gasoline ( historically a waste product from the production of kerosene ).Gasoline is a complex mixture of hydrocarbons distilled from petroleum. It is mixed with air to form an explosive m

23、ixture.Gasoline + (xs) O2, spark CO2 + H2O + heat,The fuel limits how high the compression ratio can be before the engine knocks.CH3CH2CH2CH2CH2CH2CH3 knocks like crazy atn-heptane low compression.CH3 CH3 CH3CCH2CHCH3 resists knockingCH32,2,4-trimethylpentane( “isooctane” ),Octane rating: a measure

24、of the resistance of a fuel to knock in an internal combustion engine at high compression ratios. Determined by comparing the fuel to mixtures of: n-heptane (octane number = 0) and 2,2,4-trimethylpentane (octane number = 100) in a test engine.,Tetraethyl lead, (CH3CH2)4Pb, was discovered to increase

25、 the octane rating of gasoline. Lead is extremely toxic, especially in small children where exposure leads to nerve damage. All gasoline in the US is now “lead free”.Tetraethyl lead has been replaced by “alkylates” and catalytically reformed hydrocarbons.,Compression vs. Octane Number5:1 72 6:1 817:

26、1 878:1 92 9:1 96 10:1 10011:1 10412:1 108,Use the octane rating recommended by your car maker! Using a higher octane gasoline only puts more of your money into the fuel companys pockets.,Oxymercuration-demercuration.| | | | C = C + H2O, Hg(OAc)2 C C + acetic| | acidOH HgOAc| | | | C C + NaBH4 C C |

27、 | | |OH HgOAc OH Halcohol,oxymercuration-demercuration: #1 synthesis of alcohols. Markovnikov orientation. 100% yields. no rearrangements CH3CH2CH=CH2 + H2O, Hg(OAc)2; then NaBH4 CH3CH2CHCH3OH,With alcohol instead of water:alkoxymercuration-demercuration:| | | | C =C + ROH, Hg(TFA)2 C C | |OR HgTFA

28、| | | | C C + NaBH4 C C | | | |OR HgTFA OR Hether,alkoxymercuration-demercuration: #2 synthesis of ethers. Markovnikov orientation. 100% yields. no rearrangements CH3CH=CH2 + CH3CHCH3, Hg(TFA)2; then NaBH4 OHCH3 CH3CH3CH-O-CHCH3 diisopropyl ether Avoids the elimination with 2o/3o RX in Williamson Sy

29、nthesis.,Ethersnomenclaturesyntheses1. Williamson Synthesis2. alkoxymercuration-demercurationreactions1. acid cleavage,Hydroboration-oxidation.| | | | C = C + (BH3)2 C C | | diborane H B | | | | | C C + H2O2, NaOH C C | | | |H B H OH|alcohol,hydroboration-oxidation: #2 synthesis of alcohols. Anti-Ma

30、rkovnikov orientation. 100% yields. no rearrangements CH3CH2CH=CH2 + (BH3)2; then H2O2, NaOH CH3CH2CH2CH2-OH,CH3 CH3C=CH2 + H2O, Hg(OAc)2; then NaBH4 CH3Markovnikov CH3CCH3OHCH3 CH3C=CH2 + (BH3)2; then H2O2, NaOH CH3anti-Markovnikov CH3CHCH2OH,Alcohols:nomenclaturesyntheses1. oxymercuration-demercur

31、ation2. hydroboration-oxidation3.4. hydrolysis of a 1o / CH3 alcohol5.6.8.,Addition of free radicals.| | | | C = C + HBr, peroxides C C | |H Xanti-Markovnikov orientation. free radical additionCH3CH=CH2 + HBr, peroxides CH3CH2CH2-Br,Mechanism for free radical addition of HBr: Initiating steps: 1) pe

32、roxide 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.,In a free radical addition to an alkene, the electrophilic free radical adds

33、 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,Polymerization.CH2=CH2 + heat, pressure -(CH2CH2)-n n = 10,000+polyethylene CH3CH=CH2

34、 polymerization -(CH2CH)-n CH3polypropyleneCH2=CHCl poly -(CH2CH)-nClpolyvinyl chloride (PVC),Plastics: man-made polymers that at some time in their manufacture are soft and pliable.Thermoplastics: plastics that soften when heated.Free radical polymerization.| | | | | | R + C = C R C C + C = C | |,A

35、ddition of carbenes.| | | | C = C + CH2CO or CH2N2 , h C C CH2CH2 “carbene” adds across thedouble bond| | C = C CH2,| | | | C = C + CHCl3, t-BuOK C C CCl2 -HClCCl2 dichlorocarbene| | C = C CCl2,14. Epoxidation.| | C6H5CO3H | | C = C + (peroxybenzoic acid) C C Oepoxide Free radical addition of oxygen

36、 diradical.| | C = C O,15. Hydroxylation. (mild oxidation)| | | | C = C + KMnO4 C C syn| |OH OHOH| | | | C = C + HCO3H C C antiperoxyformic acid | |OHglycol,CH3CH=CHCH3 + KMnO4 CH3CH-CHCH3OH OH2,3-butanedioltest for unsaturation purple KMnO4 brown MnO2CH2=CH2 + KMnO4 CH2CH2OH OHethylene glycol“anti-

37、freeze”,Allylic halogenation.| | | | | | C = C C + X2, heat C = C C + HX| |H allyl XCH2=CHCH3 + Br2, 350oC CH2=CHCH2Br + HBra) X2 = Cl2 or Br2 b) or N-bromosuccinimide (NBS),CH2=CHCH3 + Br2 CH2CHCH3Br Br additionCH2=CHCH3 + Br2, heat CH2=CHCH2-Br + HBrallylic substitution,Ozonolysis.| | | | C = C +

38、O3; then Zn, H2O C = O + O = C used for identification of alkenesCH3 CH3CH2CH=CCH3 + O3; then Zn, H2O CH3CH3CH2CH=O + O=CCH3,Vigorous oxidation.=CH2 + KMnO4, heat CO2=CHR + KMnO4, heat RCOOH carboxylic acid=CR2 + KMnO4, heat O=CR2 ketone,CH3CH2CH2CH=CH2 + KMnO4, heat CH3CH2CH2COOH + CO2CH3 CH3 CH3C=

39、CHCH3 + KMnO4, heat CH3C=O + HOOCCH3,CH3CH=CHCH3 + KMnO4 CH3CHCHCH3OHOH mild oxidation glycolCH3CH=CHCH3 + hot KMnO4 2 CH3COOHvigorous oxidation,Reactions, alkenes: Addition of hydrogen Addition of halogens Addition of hydrogen halides Addition of sulfuric acid Addition of water/acid Addition of hal

40、ogens & water (halohydrin formation) Dimerization Alkylation,Oxymercuration-demercuration Hydroboration-oxidation Addition of free radicals Polymerization Addition of carbenes Epoxidation Hydroxylation Allylic halogenation Ozonolysis Vigorous oxidation,CH3 CH3 CH3C=CH2 + H2, Pt CH3CHCH3 isobutyleneC

41、H3 “ + Br2/CCl4 CH3C-CH2Br BrCH3“ + HBr CH3CCH3BrCH3“ + H2SO4 CH3CCH3OSO3H,CH3 CH3 CH3C=CH2 + H2O, H+ CH3CCH3 isobutylene OHCH3 “ + Br2(aq.) CH3C-CH2BrOHCH3 CH3 CH3 CH3C=CH2 + H2SO4, 80oC CH3C-CH=CCH3(dimeriz.) CH3CH3 CH3 + CH3C-CH2C=CH2CH3,CH3 CH3 CH3C=CH2 + CH3CHCH3 + HF, 0oC CH3 CH3CH3C-CH2CHCH3C

42、H3CH3 CH3 CH3C=CH2 + H2O,Hg(OAc)2; then NaBH4 CH3CCH3OHCH3 “ + (BH3)2; then H2O2, OH- CH3CHCH2OH,CH3 CH3 CH3C=CH2 + HBr, peroxides CH3CHCH2 isobutylene BrCH3 “ + polym. -(CH2C)-nCH3 CH3“ + CH2CO, hv CH3CCH2CH2CH3“ + PBA CH3CCH2O,CH3 CH3 CH3C=CH2 + KMnO4 CH3CCH2 isobutylene OH OHCH3 “ + Br2, heat CH2C=CH2 + HBrBrCH3“ + O3; then Zn/H2O CH3C=O + O=CH2CH3“ + KMnO4, heat CH3C=O + CO2,