Electrophilic addition to alkenes

This is the Power Point Presentation for "Electrophilic Addition to Alkenes". This is as per syllabus of University of Mumbai for S.Y. B. Pharmacy students.

1. Electrophilic Addition to Alkene
Dr. Firoz Khan
Assistant ProfessorAssistant Professor
AIKTC, School of Pharmacy,
Panvel, NaviMumbai, India.
https://scholar.google.co.in/citations?user=FkGHPWQAAAAJ&hl=en

2. Contents
1.Addition of bromine
2.HBr(in presence and absence of peroxide)
3.Reaction with N-bromosuccinimide.
4.Water
5.Oxidation of alkenes to epoxide
6.Hydroboration-oxidation
5.Oxidation of alkenes to epoxide
6.Hydroboration-oxidation
7.Dimerization
8.Oxymercuration-demercuration
9.Ozonolysis
10.Periodatecleavage

4. Addition of bromine (Halogens)
Reaction
Mechanism

5. Formation of Halohydrin
Mechanism
Example

6. Addition of HBr(Absence of peroxide)

7. Markovnikov’srule
Addition of hydrogen to an unsymmetrical alkeneoccurs at those
carbon atoms with maximum number of hydrogen atoms.
Such an addition leads to a stable carbocation.

8. Addition of HBr(Presence of peroxide)
In the presence of peroxides, HBradds to an alkeneto
form the “anti-Markovnikov” product.
Peroxides produce free radicals.
Free-Radical Initiation
Propagation Steps

9. Addition of HBrto alkene

10. Reaction with N –Bromosuccinimide(NBS)

12. Addition of Water
TheMarkovnikovadditionofwatertothedoublebond
formsanalcohol.
UsesdilutesolutionsofH
2
SO
4
orH
3
PO
4
todriveequilibrium
towardhydration.

13. Mechanism

14. Orientation

15. Epoxidation
Alkenereactswithaperoxyacidtoformanepoxide
(alsocalledoxirane).
Theusualreagentisperoxybenzoicacid.
Theperoxyacidandthealkenereactwitheachother
inaone-stepreactiontoproducetheepoxideanda
moleculeofacid.
Themostcommonperoxyacidusedismeta-
chloroperoxybenzoicacid(m-CPBA).

16. Mechanism
Example
Stereospecific

17. More substituted alkenes
epoxidizefaster
One equivalent of peroxyacid
epoxidizeone alkene
Ring Opening

18. Anti-addition will
be formed.

19. Hydroboration-Oxidation of Alkenes
OneBoranereactswiththreealkenestoformtrialkylboranewhichon
furtheroxidationwithH
2
O
2
formthreemoleculesofalcohol.

20. ThereactionaddsBH
3
acrossthedoublebondwith anti-
Markovnikovorientationandformsthealcohol.

21. OH
H
BH
3
H
2
O
2
CH
CH
3
HC
CH
3
Examples for Hydroboratio-oxidation reaction
CH
3
HH
H
3
C
BH
3
H
2
O
2
CH
3
OHH
H
3
C
BH
3
H
2
O
2
OH
H

22. DimerizationDimerization

23. Oxymercuration-demercuration
Reagentismercury(II)acetate,whichdissociatesto
form
+
Hg(OAc).form
+
Hg(OAc).

+
Hg(OAc)istheelectrophilethataddstothepibond.
Theintermediateisathree-memberedringcalledthe
mercuriniumion.
OveralltheadditionofwaterfollowsMarkovnikov’s
rule.

24. Mechanism of Oxymercuration-demercuration

25. Example

26. Ozonolysis
Ozonewilloxidativelycleave(break)thedoublebondto
producealdehydesandketones.
Asecondstepoftheozonolysisisthereductionofthe
intermediatebyzincordimethylsulfide.

27. Mechanism
Theozoneaddstothedoublebond,formingafive-memberedring
intermediatecalledmolozonide,whichrearrangestoformthe
ozonide.
Theozonideisnotisolated,butisimmediatelyreducedbyamild
reducingagent,suchaszincordimethylsulfide,togivethe
aldehydesandketonesasthemainproducts.

28. Ozonolysiscanbeusedtogeneratenotonlyaldehydes,butalso
otherfunctionalgroups.
CompletingthereactionwithoxidizingagentssuchasH
2
O
2
will
givecarboxylicacids,andmorepowerfulreducingagentssuchas
NaBH
4
willgivealcohols.

29. Periodatecleavage
This can be done in two steps using OsO
4
in conjunction with the
reagent sodium periodate, NaIO
4
/HIO
4
.
The diolproduct forms a periodateester, which decomposes to give
two molecules of aldehydeor ketone.

30. Mechanism

31. WhenKMnO
4
isusedinsteadofOsO
4
,theketone
willremainketone,aldehydewilloxidiseto
carboxylicacidandformaldehydewillformCO
2
.