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Ethers & Epoxides. Uses Galore. General Anesthesia Starter Fluid Antibiotics Pheromones Marijuana Gasoline additives Antifreeze Polyesters. Ethers & Epoxides. R-O-R’ Epoxides—cyclic 3-membered ring ethers. Ethers & Epoxides. - PowerPoint PPT Presentation
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Ethers & EpoxidesUses Galore
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Ethers & Epoxides
General AnesthesiaStarter FluidAntibioticsPheromonesMarijuanaGasoline additivesAntifreezePolyesters
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Ethers & Epoxides
R-O-R’Epoxides—cyclic 3-membered ring ethers
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Nomenclature of Ethers
Name each alkyl or aryl group in alphabetical order, followed by ether
CH3 OCH3
CH3 O CH3
O
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Nomenclature of Ethers
More complex structures require the naming of the –OR group as an alkoxy group. Smaller alkoxy is named as substituent
CH3
CH3
O CH3
OH
O
CH3
O
O
O
CH3
CH3CH3
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Physical Properties of Ethers
ColorlessRelatively pleasant odorsLower bp than ROH with equal C’sAlmost same bp as equivalent HCCannot form H-bonds with itselfCan form H-bonds with ROHLow MW soluble in H2OLess dense than H2O
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Ethers as Solvents
Relatively inertMakes ethers excellent solventsUsed to extract organic cpds from natural
sourcesMay oxidize over time to peroxides
◦Test papers detect peroxides◦Shaken with FeSO4 reduces peroxides
CH3CH2OCH2CH3 + O2CH3CH2OCHCH3
OOH
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The Grignard Reagent: an organometallic compound
Victor Grignard—1912 Nobel in ChemistryWhen Mg turnings (pieces) are stirred with
an ether soln of either alkyl or aryl halide, exothermic rxn occurs
Mg bonds to halogen as does carbon
R—X + Mg R—MgXdry ether
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The Grignard Reagent: an organometallic compound
Though ethers are not normally shown as part of the Grignard reagent, they do play an important role as Lewis bases and stabilize the Mg with lone pairs
R—Mg—X
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The Grignard Reagent: an organometallic compound
2 most common ethers used in Grignard preparation◦diethyl ether◦tetrahydrofuran (THF)
Ether must be perfectly dry…no H2O or ROH
CH3—I + Mg CH3MgIether
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The Grignard Reagent: an organometallic compound
Alkyl or aryl group is usually negatively charged and Mg is positively charged
R—MgXCarbanion is formed
◦Strong base◦Conjugate base of HC(weak acids)◦Grignard reagents react vigorously with weak
acids like H2O or with any cpd with OH, SH, or NH
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The Grignard Reagent: an organometallic compound
R—MgX + H—OH R—H + Mg2+(OH)-X-
This is why the ether must be perfectly dry
stronger base stronger acid weaker acid weaker base
MgBr
+ CH3 OH
H
+ CH3 O
MgBr
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The Grignard Reagent: an organometallic compound
Rxn of Grignard with H2O can be useful in making a radiolabeled cpd
If heavy water (deuterium oxide), D2O, is used, then D can be substituted for X
CH3 BrM g
e th e rCH3 MgBr
D 2 OCH3 D
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The Grignard Reagent: an organometallic compound
Prepare CH3CHDCH3 from CH2=CHCH3
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The Grignard Reagent: an organometallic compound
Organometallic cpds contain a C-metal bond
Acetylides (R-C=C-) act similarly to Grignard reagents
Organolithium cpds are also useful in synthesis rxns
R—X + 2 Li R—Li + Li+X-
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Preparation of Ethers
Most important ether is diethyl ether◦Made from ethanol and sulfuric acid at 140˚C
If at 180˚C, ethene is made Conditions are important
CH3OH
+ CH3OH
H 2 S O 4
1 4 0 °CCH3
O
CH3
+ OH2
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Preparation of Ethers
The preparation of ethene occurs by E2By what mechanism does the preparation
of diethyl ether occur?
CH3OH
+ CH3OH
H 2 S O 4
1 4 0 °CCH3
O
CH3
+ OH2
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Preparation of Ethers
t-butyl methyl ether (MTBE)Octane # enhancerUse has declined due to health concerns
CH3 OH + CH2CH3
CH3 H +
CH3 O
CH3CH3
CH3
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Preparation of Ethers
Write the mechanism of the preparation of MTBE.
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Preparation of Ethers
Williamson Synthesis◦1st step—ROH is converted to alkoxide by
treatment with reactive metal like Na or K or metal hydride
◦2nd step—SN2 displacement btw alkoxide and alkyl halide
2ROH + 2Na 2RO-Na+ + H2
RO-Na+ + R’—X ROR’ + Na+X-
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Preparation of Ethers
Williamson Synthesis◦Write an equation for the synthesis of
CH3OCH2CH2CH3 using Williamson method
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Cleavage of Ethers
With lone pair on O, ethers are Lewis bases
React with strong acids, Lewis acids, and boron halides
HR—O—R’ + H+ R—O—R’
R—O—R’ + Br—B—Br R—O—R’ Br Br—B—Br
Br
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Cleavage of Ethers
Similar to rxn of ROH and strong acidsIf R and R’ are 1˚or 2˚, bond to O can be
broken by strong nucleophile like I- or Br- via SN2CH3
O
CH3
CH3+ HI
CH3
I+ OH
CH3
CH3
O
CH3
+ BBr31 .
2 . H 2 OOH + CH3 Br
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Cleavage of Ethers
If R or R’ is 3˚, a strong nucleophile is not required since rxn will occur by SN1 (or E1) mechanism
O
CH3CH3
CH3
H +
H 2 OOH + CH3
CH3
OHCH3
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Cleavage of Ethers
Write the steps of the mechanism for the first rxn on slide 29:CH3
O
CH3
CH3+ HI
CH3
I+ OH
CH3
CH3
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Ether & Anesthetics
Prior to 1846, asphyxiation, pressure on nerves, narcotics, ROH
William T.G. Morton in 1846 removed tumor from jaw using diethyl ether as general anesthetic
Ceased being used due to flammability, side effects, slow action
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Epoxides
Also known as oxiranes◦3-membered rings containing 1 oxygen atom
Most important is ethylene oxide◦Used as raw material for production of ethylene
glycol
O O
H
H
CH3
CH3
O
H
H
CH3
CH3
CH2 CH2 + O2A g c a ta lys t
2 5 0 °C , p re ssu re O
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Gypsy Moth’s Epoxide
Defoliate hardwood treesin NE
Pheromone disparlure
Synthesized to lure male moths to trapsAlternative to pesticide
O
(CH2)9CH3
H
(H3C)2HC(H2C)4
H
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Reactions of Epoxides
Much more reactive than ordinary ethers due to the strain on the 3-membered ring
Products will show that ring opens
~8.2 billion lbs of (CH2)2(OH)2 are produced annually in this manner
O+ OH2
H +
OH
OH
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Reactions of Epoxides
Show mechanism of previous rxn:
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Reactions of Epoxides
Other nucelophiles add in a similar way
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Cyclic Ethers
Most common other than epoxides are 5- and 6-membered rings
tetrahydrofuran tetrahydropyran 1,4-dioxane
O O O
O
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Cyclic Ethers
THF◦Useful solvent◦Miscible in H2O◦Often superior to diethyl ether for preparation
of Grignard reagents
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Cyclic Ethers
Macrocyclic polyethersCrownsForm complexes with Na+, K+ etcAntibiotics are often crown cpds
[18]crown-6
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Cyclic Ethers
Nonactin◦Selectively binds to K+ in presence of Na+
◦Allows for transport of K+ but not Na+