Alkenes, Reactions

NR      some NR        Acids Bases Metals Oxidation Reduction Halogens R-H R-X R-OH R-O-R Alkenes

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.Oxymercuration-demercuration.

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

1.Addition of hydrogen (reduction). | | | | — C = C — + H 2 + Ni, Pt, or Pd  — C — C — | | H H a) Requires catalyst. b)#1 synthesis of alkanes CH 3 CH=CHCH 3 + H 2, Ni  CH 3 CH 2 CH 2 CH 3 2-butene 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: CH 3 CH=CH 2 + H 2, Pt  CH 3 CH 2 CH 3 + ~ 30 Kcal/mole ethylene32.8 propylene30.1 cis-2-butene28.6 trans-2-butene27.6 isobutylene28.4

fats & oils: triglycerides O CH 2 —O—CCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 | O CH—O—CCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 | O CH 2 —O—CCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 “saturated” fat

O CH 2 —O—CCH 2 CH 2 CH 2 CH 2 CH=CH 2 CH 2 CH 2 CH 3 | O CH—O—CCH 2 CH 2 CH 2 CH 2 CH=CH 2 CH 2 CH 2 CH 3 | O CH 2 —O—CCH 2 CH 2 CH=CHCH 2 CH 2 CH 3 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 + H 2, 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 — + X 2  — C — C — | | X X a)X 2 = Br 2 or Cl 2 b)test for unsaturation with Br 2 CH 3 CH 2 CH=CH 2 + Br 2 /CCl 4  CH 3 CH 2 CHCH 2 Br Br 1-butene 1,2-dibromobutane

3.Addition of hydrogen halides. | | | | — C = C — + HX  — C — C — | | H X a)HX = HI, HBr, HCl b)Markovnikov orientation CH 3 CH=CH 2 + HI  CH 3 CHCH 3 I CH 3 CH 3 CH 2 C=CH 2 + HBr  CH 3 CCH 3 Br

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.

CH 3 CH 2 CH=CH 2 + HCl  CH 3 CH 2 CHCH 3 Cl CH 3 CH 3 CH 3 CH=CCH 3 + HBr  CH 3 CH 2 CCH 3 Br CH 3 CH=CHCH 3 + HI  CH 3 CH 2 CHCH 3 I

An exception to Markovikov’s Rule: CH 3 CH=CH 2 + HBr, peroxides  CH 3 CH 2 CH 2 Br CH 3 CH 3 CH 3 C=CH 2 + HBr, peroxides  CH 3 CHCH 2 Br “anti-Markovnikov” orientation note: this is only for HBr.

Markovnikov doesn’t always correctly predict the product! CH 3 CH 3 CH 2 =CHCHCH 3 + HI  CH 3 CH 2 CCH 3  I Rearrangement!

why Markovinkov? CH 3 CH=CH 2 + HBr  CH 3 CHCH 2 1 o carbocation |   H or? CH 3 CHCH 2 2 o carbocation  | more stable H + Br -  CH 3 CHCH 3 | Br

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 — + H 2 SO 4  — C — C — | | H OSO 3 H alkyl hydrogen sulfate Markovnikov orientation. CH 3 CH=CH 2 + H 2 SO 4  CH 3 CHCH 3 O O-S-O OH

5.Addition of water. | | | | — C = C — + H 2 O, H +  — C — C — | | H OH a) requires acid b)Markovnikov orientation c)low yield  CH 3 CH 2 CH=CH 2 + H 2 O, H +  CH 3 CH 2 CHCH 3 OH

| | H + | | — C = C — + H 2 O  — 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.

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

CH 3 CH=CH 2 + Br 2 + H 2 O + NaCl  CH 3 CHCH 2 + CH 3 CHCH 2 + CH 3 CHCH 2 Br 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 X 2 to an alkene is an anti-addition.

6.Addition of halogens + water (halohydrin formation): | | | | — C = C — + X 2, H 2 O  — C — C — + HX | | OH X a)X 2 = Br 2, Cl 2 b)Br 2 = electrophile CH 3 CH=CH 2 + Br 2 (aq.)  CH 3 CHCH 2 + HBr OH Br

7.Oxymercuration-demercuration. | | | | — C = C — + H 2 O, Hg(OAc) 2  — C — C — + acetic | | acid OH HgOAc | | | | — C — C — + NaBH 4  — C — C — | | | | OH HgOAc OH H alcohol

oxymercuration-demercuration: a)#1 synthesis of alcohols. b)Markovnikov orientation. c)100% yields. d)no rearrangements CH 3 CH 2 CH=CH 2 + H 2 O, Hg(OAc) 2 ; then NaBH 4  CH 3 CH 2 CHCH 3 OH

With alcohol instead of water: alkoxymercuration-demercuration: | | | | — C =C — + ROH, Hg(TFA) 2  — C — C — | | OR HgTFA | | | | — C — C — + NaBH 4  — C — C — | | | | OR HgTFA OR H ether

alkoxymercuration-demercuration: a)#2 synthesis of ethers. b)Markovnikov orientation. c)100% yields. d)no rearrangements CH 3 CH=CH 2 + CH 3 CHCH 3, Hg(TFA) 2 ; then NaBH 4  OH CH 3 CH 3 CH 3 CH-O-CHCH 3 diisopropyl ether Avoids the elimination with 2 o /3 o RX in Williamson Synthesis.

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

8.Hydroboration-oxidation. | | — C = C — + (BH 3 ) 2  — C — C — | | diborane H B — | | | | | — C — C — + H 2 O 2, NaOH  — C — C — | | | | H B — H OH | alcohol

hydroboration-oxidation: a)#2 synthesis of alcohols. b)Anti-Markovnikov orientation.  c)100% yields. d)no rearrangements CH 3 CH 2 CH=CH 2 + (BH 3 ) 2 ; then H 2 O 2, NaOH  CH 3 CH 2 CH 2 CH 2 -OH

CH 3 CH 3 C=CH 2 + H 2 O, Hg(OAc) 2 ; then NaBH 4  CH 3 Markovnikov CH 3 CCH 3 OH CH 3 CH 3 C=CH 2 + (BH 3 ) 2 ; then H 2 O 2, NaOH  CH 3 anti-Markovnikov CH 3 CHCH 2 OH

Alcohols: nomenclature syntheses 1. oxymercuration-demercuration 2. hydroboration-oxidation hydrolysis of a 1 o / CH 3 alcohol

9.Addition of free radicals. | | | | — C = C — + HBr, peroxides  — C — C — | | H X a)anti-Markovnikov orientation. b)free radical addition c)HI, HCl + Peroxides CH 3 CH=CH 2 + HBr, peroxides  CH 3 CH 2 CH 2 -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 + CH 3 CH=CH 2  CH 3 CHCH 2 -Br (2 o free radical) 4) CH 3 CHCH 2 -Br + HBr  CH 3 CH 2 CH 2 -Br + Br 3), 4), 3), 4)… Terminating steps: 5)Br + Br  Br 2 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). CH 3 CH=CH 2 + HBr, peroxides  CH 3 CH 2 CH 2 -Br

10.Addition of carbenes. | | | | — C = C — + CH 2 CO or CH 2 N 2, hν  — C — C —  CH 2 CH 2 “carbene” adds across the double bond | | — C = C —  CH 2

| | | | — C = C — + CHCl 3, t-BuOK  — C— C — CCl 2  -HCl CCl 2 dichlorocarbene | | — C = C —  CCl 2

11.Epoxidation. | | C 6 H 5 CO 3 H | | — C = C — + (peroxybenzoic acid)  — C— C — O epoxide Free radical addition of oxygen diradical. | | — C = C —  O

12. Hydroxylation. (mild oxidation) | | | | — C = C — + KMnO 4  — C — C — syn | | OH OH OH | | | | — C = C — + HCO 3 H  — C — C — anti peroxyformic acid | | OH glycol

CH 3 CH=CHCH 3 + KMnO 4  CH 3 CH-CHCH 3 OH OH 2,3-butanediol test for unsaturation purple KMnO 4  brown MnO 2 CH 2 =CH 2 + KMnO 4  CH 2 CH 2 OH OH ethylene glycol “anti-freeze”

13.Allylic halogenation. | | | | | | — C = C — C — + X 2, heat  — C = C — C — + HX | | H  allyl X CH 2 =CHCH 3 + Br 2, 350 o C  CH 2 =CHCH 2 Br + HBr a) X 2 = Cl 2 or Br 2 b) or N-bromosuccinimide (NBS)

CH 2 =CHCH 3 + Br 2  CH 2 CHCH 3 Br Br addition CH 2 =CHCH 3 + Br 2, heat  CH 2 =CHCH 2 -Br + HBr allylic substitution

14.Ozonolysis. | | | | — C = C — + O 3 ; then Zn, H 2 O  — C = O + O = C — used for identification of alkenes CH 3 CH 3 CH 2 CH=CCH 3 + O 3 ; then Zn, H 2 O  CH 3 CH 3 CH 2 CH=O + O=CCH 3

15.Vigorous oxidation. =CH 2 + KMnO 4, heat  CO 2 =CHR + KMnO 4, heat  RCOOH carboxylic acid =CR 2 + KMnO 4, heat  O=CR 2 ketone

CH 3 CH 2 CH 2 CH=CH 2 + KMnO 4, heat  CH 3 CH 2 CH 2 COOH + CO 2 CH 3 CH 3 CH 3 C=CHCH 3 + KMnO 4, heat  CH 3 C=O + HOOCCH 3

CH 3 CH=CHCH 3 + KMnO 4  CH 3 CHCHCH 3 OHOH mild oxidation  glycol CH 3 CH=CHCH 3 + hot KMnO 4  2 CH 3 COOH vigorous oxidation

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.Oxymercuration-demercuration

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

CH 3 CH 3 CH 3 C=CH 2 + H 2, Pt  CH 3 CHCH 3 isobutylene CH 3 “ + Br 2 /CCl 4  CH 3 C-CH 2 Br Br CH 3 “ + HBr  CH 3 CCH 3 Br CH 3 “ + H 2 SO 4  CH 3 CCH 3 O SO 3 H

CH 3 CH 3 CH 3 C=CH 2 + H 2 O, H +  CH 3 CCH 3 isobutylene OH CH 3 “ + Br 2 (aq.)  CH 3 C-CH 2 Br OH CH 3 CH 3 CH 3 C=CH 2 + H 2 O,Hg(OAc) 2 ; then NaBH 4  CH 3 CCH 3 OH CH 3 “ + (BH 3 ) 2 ; then H 2 O 2, OH -  CH 3 CHCH 2 OH

CH 3 CH 3 CH 3 C=CH 2 + HBr, peroxides  CH 3 CHCH 2 isobutylene Br CH 3 “ + CH 2 CO, hv  CH 3 C–CH 2 CH 2 CH 3 “ + PBA  CH 3 C–CH 2 O

CH 3 CH 3 CH 3 C=CH 2 + KMnO 4  CH 3 C–CH 2 isobutylene OH OH CH 3 “ + Br 2, heat  CH 2 C=CH 2 + HBr Br CH 3 “ + O 3 ; then Zn/H 2 O  CH 3 C=O + O=CH 2 CH 3 “ + KMnO 4, heat  CH 3 C=O + CO 2