Alkenes, Reactions R-H R-X R-OH R-O-R Alkenes NR NR NR some NR NR Metals NR NR NR Oxidation NR NR NR Reduction NR NR NR Halogens NR NR NR NR Acids Bases Alkenes, reactions. Addition ionic free radical Reduction Oxidation Substitution Reactions, alkenes: 1. Addition of hydrogen (reduction). 2. Addition of halogens. 3. Addition of hydrogen halides. 4. Addition of sulfuric acid. 5. Addition of water (hydration). 6. Addition of aqueous halogens (halohydrin formation). 7. Dimerization. 8. Alkylation. 9. Oxymercuration-demercuration. 10. Hydroboration-oxidation. 11. Addition of free radicals. 12. Polymerization. 13. Addition of carbenes. 14. Epoxidation. 15. Hydroxylation. 16. Allylic halogenation 17. Ozonolysis. 18. Vigorous oxidation. 1. Addition of hydrogen (reduction). | | — C = C — + H2 + Ni, Pt, or Pd | | —C—C— | | H H a) Requires catalyst. b) #1 synthesis of alkanes CH3CH=CHCH3 2-butene + H2, Ni CH3CH2CH2CH3 n-butane 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) 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 fats & oils: triglycerides O CH2—O—CCH2CH2CH2CH2CH2CH2CH2CH2CH3 | O CH—O—CCH2CH2CH2CH2CH2CH2CH2CH2CH3 | O CH2—O—CCH2CH2CH2CH2CH2CH2CH3 “saturated” fat O CH2—O—CCH2CH2CH2CH2CH=CH2CH2CH2CH3 | O CH—O—CCH2CH2CH2CH2CH=CH2CH2CH2CH3 | O CH2—O—CCH2CH2CH=CHCH2CH2CH3 Ω - 3 “unsaturated” oil 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. 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. 2) Addition of halogens. | | —C=C— + X2 | | —C—C— | | X X a) X2 = Br2 or Cl2 b) test for unsaturation with Br2 CH3CH2CH=CH2 1-butene + Br2/CCl4 CH3CH2CHCH2 Br Br 1,2-dibromobutane 3. Addition of hydrogen halides. | | | | — C = C — + HX — C — C — | | H X a) HX = HI, HBr, HCl b) Markovnikov orientation CH3CH=CH2 CH3 CH2C=CH2 + + HI HBr CH3CHCH3 I CH3 CH3CCH3 Br Markovnikov’s Rule: In der Hinzufügung einer Säure zu einem alkene wird der Wasserstoff zum Vinylkohlenstoff gehen, der schon den größeren 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 Markovnikov: En la adición iónica de un ácido al doble enlace de un alqueno, el hidrógeno de aquél se une al átomo de carbono que ya tiene el mayor número de hidrógenos. “Al que tiene, le será dado.” “El que tiene, recibirá.” Dans l'addition d'un acide à un alcène l'hydrogène ira au carbone de vinyle qui a déjà le nombre plus grand de hydrogène. 알켄에 산의 추가안에 수소는 이미 수소의 더 중대한 수가 있는 비닐 탄소에는에 갈 것이다. アルケンへの酸の付加で水素はビニールカーボンにへ行く既に 水素の大きい数がある。 В дополнении кислоты к алкен водород будет идти в углерод винила, который уже имеет больший номер(число) водорода. CH3CH2CH=CH2 CH3 CH3CH=CCH3 CH3CH=CHCH3 + + HBr + HCl HI CH3CH2CHCH3 Cl CH3 CH3CH2CCH3 Br CH3CH2CHCH3 I An exception to Markovikov’s Rule: CH3CH=CH2 CH3 CH3C=CH2 + + HBr, peroxides CH3CH2CH2Br HBr, peroxides “anti-Markovnikov” orientation note: this is only for HBr. CH3 CH3CHCH2Br Markovnikov doesn’t always correctly predict the product! CH3 CH2=CHCHCH3 + HI CH3 CH3CH2CCH3 I Rearrangement! Ionic electrophilic addition mechanism 1) 2) C C C C Y + YZ + Z RDS C C Y C C Z Y + Z mechanism for addition of HX 1) 2) C C C C H + HX + X RDS C C H C C X H + X why Markovinkov? CH3CH=CH2 + HBr CH3CHCH2 | H or? + Br- CH3CHCH2 | H CH3CHCH3 | Br 1o carbocation 2o carbocation more stable 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. 4. 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 5. Addition of water. | | —C=C— + H2O, H+ | | —C—C— | | H OH a) requires acid b) Markovnikov orientation c) low yield CH3CH2CH=CH2 + H2O, H+ CH3CH2CHCH3 OH Mechanism for addition of water RDS 1) H + 2) C C H 3) C C H OH2 C C C C H + H2O C C H OH2 C C H OH + H | | — C = C — + H2O H+ | | —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. Mechanism for dehydration of an alcohol = E1 1) C C H OH + H C C H OH2 RDS 2) C C H OH2 C C H + H2O 3) C C H C C + H mechanism for addition of X2 1) 2) C C C C X + X--X + X RDS C C X C C X X + X How do we know that the mechanism isn’t this way? RDS C C X X One step, concerted, no carbocation C C X X CH3CH=CH2 + Br2 + H2O + NaCl CH3CH=CH2 + Br--Br Br CH3CHCH2 Br Br CHCHCH2 Br H2O + CH3CHCH2 OH Br Cl + CH3CHCH2 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. 6. Addition of halogens + water (halohydrin formation): | | | | — C = C — + X2, H2O — C — C — + HX | | OH X a) X2 = Br2, Cl2 b) Br2 = electrophile CH3CH=CH2 + Br2(aq.) CH3CHCH2 + HBr OH Br mechanism for addition of X2 + H2O 1) C C 2) H2O + 3) + X--X C C X RDS C C X C C H2O X -H C C H2O X C C HO X + X 7. Dimerization: CH3 CH3C=CH2 + H2SO4, 80oC CH3 CH3 CH3C-CH=CCH3 CH3 + CH3 CH3 CH3C-CH2C=CH2 CH3 CH3 CH3C=CH2 + H CH3 CH3C CH3 CH3 CH3CCH3 CH3 CH3 CH3 CH3C CH2CCH3 CH3 + CH2=CCH3 CH3 CH3 CH3C CH2CCH3 CH3 -H CH3 CH3 CH3C CH=CCH3 CH3 carbocation as electrophile CH3 CH3 + CH3C CH2C=CH2 CH3 8. Alkylation: CH3 CH3 CH3C=CH2 + CH3CHCH3 + HF, 0oC CH3 CH3 CH3C-CH2CHCH3 CH3 2,2,4-trimethylpentane ( “isooctane” ) Used to increase gasoline yield from petroleum and to improve fuel performance. CH3 CH3C=CH2 + H CH2 CH3C CH3 CH3 CH3CCH3 CH3 + CH2=CCH3 CH3 CH3 CH3 CH3C CH2CCH3 + CH3CCH3 H CH3 CH3 CH3 CH3C CH2CCH3 CH3 CH3 CH3 CH3 CH3C CH2CCH3 + CH3CCH3 CH3 H intermolecular hydride (H:-) transfer Internal combustion engine (four-stroke). Also called an Otto engine. 1. Intake stroke: air/fuel 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 cylinder. <http://www.k-wz.de/vmotor/v_omotore.html> Compression is the key to building a more powerful fourstroke 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 => 1. More powerful engine. 2. Lighter engine (greater power to weight ratio). 3. Greater fuel economy. But, compression of the air/fuel mixture above a certain point causes “knocking”. PV = nRT TP 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 internal combustion engine when fuel ignites spontaneously and prematurely (preignition) during the compression cycle in an engine’s 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 the engine; at worst, it can damage the engine’s 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 mixture. Gasoline + (xs) O2, spark CO2 + H2O + heat The fuel limits how high the compression ratio can be before the engine knocks. CH3CH2CH2CH2CH2CH2CH3 n-heptane CH3 CH3 CH3CCH2CHCH3 CH3 2,2,4-trimethylpentane ( “isooctane” ) knocks like crazy at low compression. resists knocking Octane rating: a measure 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 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 Number 5:1 72 6:1 81 7:1 87 8:1 92 9:1 96 10:1 100 11:1 104 12:1 108 Use the octane rating recommended by your car maker! Using a higher octane gasoline only puts more of your money into the fuel company’s pockets. 9. Oxymercuration-demercuration. | | | | — C = C — + H2O, Hg(OAc)2 — C — C — + acetic | | acid OH HgOAc | | — C — C — + NaBH4 | | OH HgOAc | | —C—C— | | OH H alcohol oxymercuration-demercuration: a) #1 synthesis of alcohols. b) Markovnikov orientation. c) 100% yields. d) no rearrangements CH3CH2CH=CH2 + H2O, Hg(OAc)2; then NaBH4 CH3CH2CHCH3 OH With alcohol instead of water: alkoxymercuration-demercuration: | | | | — C =C — + ROH, Hg(TFA)2 — C — C — | | OR HgTFA | | — C — C — + NaBH4 | | OR HgTFA | | —C—C— | | OR H ether alkoxymercuration-demercuration: a) #2 synthesis of ethers. b) Markovnikov orientation. c) 100% yields. d) no rearrangements CH3CH=CH2 + CH3CHCH3, Hg(TFA)2; then NaBH4 OH CH3 CH3 CH3CH-O-CHCH3 diisopropyl ether Avoids the elimination with 2o/3o RX in Williamson Synthesis. Ethers nomenclature syntheses 1. Williamson Synthesis 2. alkoxymercuration-demercuration reactions 1. acid cleavage 10. Hydroboration-oxidation. | | | | — C = C — + (BH3)2 — C — C — | | diborane H B— | | | — C — C — + H2O2, NaOH | | H B— | | | —C—C— | | H OH alcohol hydroboration-oxidation: a) #2 synthesis of alcohols. b) Anti-Markovnikov orientation. c) 100% yields. d) no rearrangements CH3CH2CH=CH2 + (BH3)2; then H2O2, NaOH CH3CH2CH2CH2-OH CH3 CH3C=CH2 + H2O, Hg(OAc)2; then NaBH4 Markovnikov CH3 CH3C=CH2 CH3 CH3CCH3 OH + (BH3)2; then H2O2, NaOH anti-Markovnikov CH3 CH3CHCH2 OH Alcohols: nomenclature syntheses 1. oxymercuration-demercuration 2. hydroboration-oxidation 3. 4. hydrolysis of a 1o / CH3 alcohol 5. 6. 8. 11. Addition of free radicals. | | | | — C = C — + HBr, peroxides — C — C — | | H X a) anti-Markovnikov orientation. b) free radical addition CH3CH=CH2 + HBr, peroxides CH3CH2CH2-Br 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: 5) Br• + Br• Br2 Etc. 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 12. Polymerization. CH2=CH2 + heat, pressure -(CH2CH2)-n n = 10,000+ polyethylene CH3CH=CH2 CH2=CHCl polymerization -(CH2CH)-n CH3 polypropylene poly… -(CH2CH)-n Cl polyvinyl 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— | | 13. Addition of carbenes. | | | | — C = C — + CH2CO or CH2N2 , hν — C — C — •CH2• | | —C=C— •CH2• CH2 “carbene” adds across the double bond | | — C = C — + CHCl3, t-BuOK -HCl | | — C— C — CCl2 •CCl2• dichlorocarbene | | —C=C— •CCl2• hv CH3CH=CH2 + CH2N2 CHCl3, t-BuOK H H3C C CH2 C H2 H H3C C CH2 C Cl2 14. Epoxidation. | | C6H5CO3H — C = C — + (peroxybenzoic acid) | | — C— C — O epoxide Free radical addition of oxygen diradical. | | —C=C— •O• H3C C C CH3 H H 2-butene + C6H5CO3H peroxybenzoic acid H H H3C C C CH3 O 15. Hydroxylation. (mild oxidation) | | — C = C — + KMnO4 | | —C—C— | | OH OH syn OH | | | | — C = C — + HCO3H — C — C — anti peroxyformic acid | | OH glycol CH3CH=CHCH3 + KMnO4 CH3CH-CHCH3 OH OH 2,3-butanediol test for unsaturation purple KMnO4 brown MnO2 CH2=CH2 + KMnO4 CH2CH2 OH OH ethylene glycol “anti-freeze” 16. Allylic halogenation. | | | | | | — C = C — C — + X2, heat — C = C — C — + HX | | H allyl X CH2=CHCH3 + Br2, 350oC CH2=CHCH2Br + HBr a) X2 = Cl2 or Br2 b) or N-bromosuccinimide (NBS) CH2=CHCH3 + Br2 CH2CHCH3 Br Br addition CH2=CHCH3 + Br2, heat CH2=CHCH2-Br + HBr allylic substitution 17. Ozonolysis. | | | | — C = C — + O3; then Zn, H2O — C = O + O = C — used for identification of alkenes CH3 CH3CH2CH=CCH3 + O3; then Zn, H2O CH3CH2CH=O + CH3 O=CCH3 18. Vigorous oxidation. =CH2 + KMnO4, heat CO2 =CHR + KMnO4, heat RCOOH =CR2 + KMnO4, heat O=CR2 carboxylic acid ketone CH3CH2CH2CH=CH2 + KMnO4, heat CH3CH2CH2COOH + CO2 CH3 CH3 CH3C=CHCH3 + KMnO4, heat CH3C=O + HOOCCH3 KMnO4 CH3CHCHCH3 OHOH mild oxidation glycol CH3CH=CHCH3 + CH3CH=CHCH3 + vigorous oxidation hot KMnO4 2 CH3COOH Reactions, alkenes: 1. Addition of hydrogen 2. Addition of halogens 3. Addition of hydrogen halides 4. Addition of sulfuric acid 5. Addition of water/acid 6. Addition of halogens & water (halohydrin formation) 7. Dimerization 8. Alkylation 9. Oxymercuration-demercuration 10. Hydroboration-oxidation 11. Addition of free radicals 12. Polymerization 13. Addition of carbenes 14. Epoxidation 15. Hydroxylation 16. Allylic halogenation 17. Ozonolysis 18. Vigorous oxidation CH3 CH3C=CH2 isobutylene “ “ “ + H2, Pt CH3 CH3CHCH3 CH3 + Br2/CCl4 CH3C-CH2 Br Br + HBr + H2SO4 CH3 CH3CCH3 Br CH3 CH3CCH3 O SO3H CH3 CH3C=CH2 isobutylene + H2O, H+ CH3 + Br2(aq.) CH3C-CH2Br OH “ CH3 CH3C=CH2 CH3 CH3CCH3 OH + H2SO4, 80oC (dimeriz.) + CH3 CH3 CH3C-CH=CCH3 CH3 CH3 CH3 CH3C-CH2C=CH2 CH3 CH3 CH3 CH3C=CH2 + CH3CHCH3 + HF, 0oC CH3 CH3 CH3C-CH2CHCH3 CH3 CH3 CH3 CH3C=CH2 + H2O,Hg(OAc)2; then NaBH4 CH3CCH3 OH “ + (BH3)2; then H2O2, OH- CH3 CH3CHCH2 OH CH3 CH3C=CH2 isobutylene “ “ “ CH3 + HBr, peroxides CH3CHCH2 Br CH3 + polym. -(CH2C)-n CH3 + CH2CO, hv CH3 CH3C–CH2 CH2 CH3 CH3C–CH2 O + PBA CH3 CH3C=CH2 isobutylene “ “ “ + KMnO4 CH3 CH3C–CH2 OH OH CH3 + Br2, heat CH2C=CH2 + HBr Br CH3 + O3; then Zn/H2O CH3C=O + O=CH2 + KMnO4, heat CH3 CH3C=O + CO2