IV. Oxidation Three types A. Epoxidation B. Hydroxylation C. Oxidative cleavage

A. Epoxidation Formation of epoxide Cyclic ether Example: Reagent is peroxy acid (RCO 3 H) Stereochemistry = syn

A. Epoxidation Another method: treat halohydrin with base:

B. Hydroxylation Formation of a 1,2-diol/glycol/vicinal diol Methods: 1. Opening of epoxide using aqueous acid Product is trans diol

Hydroxylation 2. Addition of osmium tetroxide (OsO 4 ) or potassium permanganate (KMnO 4 ) How do you know these are both oxidizing agents? Reaction includes some appropriate work-up H 2 O 2 or NaHSO 3, H 2 O for OsO 4 HO - (aq) for KMnO 4 Stereochemistry = syn

Draw the major product of the following reaction.

C. Oxidative Cleavage Oxidize an alkene and split the C=C Results in formation of 2 carbonyls Type of carbonyls depends on alkene structure and the oxidizing agent used Two types of oxidizing agents 1. Ozone 2. Potassium permanganate (not in Klein text!)

Oxidative Cleavage 1. Ozone Ozonolysis Reagents: 1. O 3 2. (CH 3 ) 2 S or Zn, H 3 O + Products = 2 carbonyls (ketones or aldehydes) Terminal alkenes give CO 2

Example Draw the products of the ozonolysis of 1-butene.

Oxidative Cleavage 2. KMnO 4 (not in Klein text!) Reagents: KMnO 4 (excess or concentrated) and heat or acid Use heat and excess KMnO 4 to split intermediate glycol Products = 2 carbonyls (ketones or carboxylic acids) Aldehydes oxidize to carboxylic acids in KMnO 4 Terminal alkenes still give CO 2

Draw the major product for each of the following reactions.

V. Polymerization Polymer = large molecule synthesized by covalently linking single parts (monomers) Biological polymers: proteins, cellulose, nucleic acids Organic polymers: plastics Addition polymers: made from alkene monomers Chain-growth polymerization reactions Cationic, anionic, or radical, depending on conditions/catalyst Example: Radical polymerization of ethylene

Radical Polymerization Mechanism

Alkene Polymers

Draw the structure of poly(vinyl chloride).

Review of Alkene Reactions

Draw the major organic product formed (showing stereochemistry where applicable) for the reaction of the following alkene under each of the reaction conditions listed below.

Preparation of Alkynes Alkenes from elimination of alkyl halides with strong base Alkynes from elimination reactions of alkyl dihalides with strong base Vicinal or geminal

Preparation of Alkynes A two-step process from alkenes 1. Alkenes undergo addition of X 2 to make a vicinal dihalide 2. The vicinal dihalide undergoes 2 elimination reactions to yield the alkyne

How could you prepare 2-butyne from 2-butene? How could you prepare 2-pentyne from 3-pentanol?

Reactions of Alkynes Similar to alkenes, but can also react a second time Mechanism: Alkene: Alkyne: Which is faster, reaction with alkenes or alkynes? Alkenes have more stable carbocation intermediate

Reactions of Alkynes I. Addition of HX II. Hydration III. Halogenation IV. Reduction V. Oxidation

I. Addition of HX Terminal alkynes: regiochemistry = Markovnikov Anti-Markovnikov if peroxides are present Internal alkynes (unsymmetrical) = mixture of products

Addition of HX

II. Hydration Markovnikov addition of water With alkenes: H 2 O in H 2 SO 4 or Hg(OAc) 2, H 2 O with reduction With alkynes: H 2 O in H 2 SO 4 with HgSO 4 Enol (a vinylic alcohol) rearranges to form a carbonyl Keto-enol tautomerism

Keto-enol Tautomerism Tautomers Constitutional isomers which rapidly interconvert Rearrangement reaction, not resonance structures Keto tautomer typically more stable than enol Catalyzed by acid or base

Keto-enol Tautomerism Acid-catalyzed mechanism Base-catalyzed mechanism

Draw the major product for each of the following reactions.

Hydration Anti-Markovnikov addition of water With alkenes: 1. BH 3 THF, 2. H 2 O 2, NaOH With alkynes: 1. BH 3 THF or Sia 2 BH, 2. H 2 O 2, NaOH Sia 2 BH = disiamylborane Sia = siamyl = sec-isoamyl More hindered than BH 3, so prevents addition of 2 borane molecules Product still undergoes keto-enol tautomerism Internal alkynes yield ketones Terminal alkynes yield aldehydes

Draw the major product for each of the following reactions.

Hydration Summary Internal alkynes, both reagents give the same products Terminal alkynes, different products

III. Halogenation Addition of X 2 X 2 = Br 2 or Cl 2 Still anti addition

IV. Reduction Alkyne reduce to alkene or alkane Depends on the reagent/conditions used Types of reduction: Catalytic reduction Chemical reduction

Catalytic Reduction Alkyne → alkane Cannot stop reaction at alkene with these catalysts Can form alkene with Lindlar catalyst Pd + BaSO 4 /CaCO 3 + Pb salt + quinoline Syn addition gives cis alkene

Chemical Reduction Aka Dissolving metal reduction Alkyne → trans alkene Reagents = Li or Na in NH 3 (l)

Summary of Reduction Reactions

V. Oxidation Oxidize with O 3 or KMnO 4 Both cleave C≡C Both oxidize to carboxylic acids Terminal alkynes give CO 2

Draw the major product for each of the following reactions.

Acidity of Alkynes Terminal alkynes are weak acids More acidic than alkenes or alkanes Conjugate base = acetylide ion or alkynide ion Conjugate base is somewhat stable Electron pair closer to nucleus with more s character

Acetylide Ion Strong base Stronger than HO - or RO - Not as strong as - NH 2 Acetylide ion can act as a base or a nucleophile

Acetylide Ion as a Nucleophile React with methyl or primary alkyl halides Undergo substitution reaction Form a new, larger alkyne Alkylation reaction C-C bond making reaction Example:

Alkylation Reaction Examples

Acetylide Ion as a Base React with secondary or tertiary alkyl halides Undergo elimination reaction Dehydrohalogenation (eliminate H-X)

Review of Alkyne Reactions

Synthesis You will be given a product. Your goal is to determine how to make that product from simpler starting materials using reactions we have studied. Consider: How many carbons are in the starting material and product? Do you need to make any C-C bonds? If so, how will you do that? What functional groups are in the starting material? What can you do with those functional groups? What functional groups are in the product? How do you know how to make those functional groups? Try working backwards (retrosynthesis). Look in Klein section 9.13, 10.11, for strategies and worked examples Remember there may be more than one correct answer!

Propose a synthesis of 3-methyl-1-butane from 2-methyl-2- butene.

Provide structures or reagents (including solvent and/or special conditions, such as heat) in the empty boxes below to complete the following reaction scheme.

Propose a synthesis of 1-bromo-2-methylpropane from 2- methylpropane.

Propose a synthesis of cis-3-hexene from acetylene.

Propose a synthesis of 1,2-dichloropropane from acetylene.

Propose a synthesis of 2-butanone from ethylene.