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52 Cards in this Set
- Front
- Back
Ziegler-Natta catalyst
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One of most important transition-metal catalysts in commerce, brings about polymerization of ethylene & other alkenes at 25 C & 1 atm
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Reason Ziegler-Natta polymerization is better than free radical polymerization of ethylene
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resulting high-density polyethylene has diff prop from low-density polyethylene prod
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Mech Ziegler-Natta polymerization
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Continuation of insertion-ligand association sequence gives polymer
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It is believed that titanium brings about rxn because
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D1 metal cant undergo B-elim (requires filled metal d orbitals) & tendency for B-elim of other metals would terminate rxn
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Hydroformylation
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Tetracarbonylhydridocobalt(1) catalyst produces products like propionaldehyde: involves 1,2 insertion rxn of ethylene & 1,1 insertion rxn of CO
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Homogeneous catalytic hydrogenation of alkenes
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Uses soluble rhodium (I) catalyst called Wilkinson catalyst ClRh(PPh3)3
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Phenoxide ion/ phenolate
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conj base of phenol
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Phenols are ___ acidic than alcohols
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more: due to stabilization of conjugate-base anion due to resonance & polar effect of benzene ring (stabilized neg charge)
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Substituent groups can affect phenol acidity by
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polar & resonance effects: nitro group stabilizes conjugate base anion
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P-nitrophenol is __ acidic than m-nitrophenol
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more despite farther nitro group from phenol Oxygen: resonance (polar effects dec w distance)
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M-nitrophenol has no resonance structure that delocalizes the neg charge into the nitro group
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Acid strengthening resonance effect of O/P nitro groups so large that 2,4,6-trinitrophenol is
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a strong acid
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Factors that govern acidity
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Element (bound to higher atomic #) in row, electroneg (h2o>methane, phenol> toluene) in column, rel bond E (thiols > ROH) charge (pos enhances) resonance, polar (stabiliz charge in conj b enhances)
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Alcohols are not converted completely into alkoxides by aq. NaOH bc
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pKa values water & alcohols are similar
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Equilibrium for reaction of phenol & NaOH lies completely to the
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right
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Phenol treated with one equiv NaOH or NaOC2H5
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phenol OH proton titrated completely to give solution of sodium phenoxide
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Separate water-insoluble phenol 4-chlorophenol from water-insoluble alcohol 4-chlorocyclohexanol
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Sodium or potassium salt like other alkali metal salts has considerable solubility in water bc ionic cmpd
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When mixture phenol & alcohol in ether solution is shaken w aqueous NaOH,
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phenol selectively extracted into aq solution as sodium salt while alcohol remains in ether
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Acidification of aq solution gives
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Phenol separate from solution bc after acidification, no longer ionized
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Phenols are soluble in NaOH solution means that
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if sodium hydroxide added
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Qualitative test for phenols
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Solubility in 5% NaOH & other cmpds of equal/greater acidity
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Can phenoxides be used as nucleophiles?
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Yes
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Quinones
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Most common oxidation products of phenols
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Names of quinones derived from
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names of corresponding aromatic hydrocarbons (benzoquinone, napthoquinone)
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Less stable quinone isomer
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ortho-quinones: ends of C=O bond dipoles w like charges close together
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Coenzyme Q
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Oxidized form ubiquinone: in respiratory chain localized in mitochondrion, converts O2 into H2O & harnesses E released to synth ATP
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Doxorubicin
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isolated from a microorganism: important antitumor drug
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Oxidation of phenols by air
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causes darkening when some phenols stored for time
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Practical applications of phenol oxidation
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Inhibit free-radical rxns resulting in oxidation of other cmpds (semiquinone resonance stabilized) then hydroquinone terminates free rad chain rxns by intercepting free-rad intermed & reducing to RH + effectiveness of several widely used food preservatives
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How does food discolor and spoil and how does preservative like BHT work?
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Oxidation involving free-radical processes -- BHT donates OH hydrogen atom to freee radicals => phenoxy radical too unstable to & unreactive to propagate radical chain reactions
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Vitamin E
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Phenol, major compd in blood prevents oxidation damage by free radicals: acts by terminating radical chains
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EAS of phenols
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OH sometimes has special effects not common (bc strongly activating substituent, phenol can be halogenated once under mild conditions)
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Extensive bromination occurs bc
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bromide reacts w h2o to give protonated hypobromous acid, more electrophile than bromine, then partially ionizes to conj base phenoxide anion: very reactive (not carbocation but neutral mlc), brominates instantly, pulls phenol-phenolate equil right
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P-bromophenol is in equilibrium with conjugate base p-bromophenoxide anion, which brominates again until all o/p positions substituted
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Second & third sub, powerful o/p directing & activating effects of O- group override weaker of bromine substituents
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Phenol is very reactive in EAS such as
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nitration (once under mild conditions)
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The basic conditions of the reaction result in formation of the conjugate-base anion of the prod
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H3O added for neutral phenol
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The great reactivity of phenol is EAS doesn't extend to FC acylation bc
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phenol reacts rapidly with AlCl3 catalyst: adduct is much less reactive than phenol itself in EAS bc O2 delocalized onto Alum. = less available for resonance stabilization of carbocation
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FC acylation/alkylation of phenol
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occurs slowly but can be carried out successfuly at high temp. not highly activated so ring only acylated once
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Carbon-oxygen reactivity of phenols
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Follows poor carbon-halogen reactivity of aryl halides: do not undergo SN1 or E1 reactions for same reasons & phenols do not react under conditions used for Sn1/E1 of alcohols
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Phenols plus conc HBR
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no rxn
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Phenols plus conc H2So4
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no dehydration, but sulfonation
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where X is a good LG
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no reactivity toward SN1/Sn2 conditions
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In aryl ethers, cleavage occurs only
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at alkyl-o2 bond (1 set products)
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Stille Reaction: Aryl triflates with organotin derivatives in presence of Pd(0) catalyst
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Coupling products
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transferred preferentially
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Vinylic, aryl groups, other unsat groups
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If tetraalkylstannane is used
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alkyl groups can be transffered (not plagued by rearrangement)
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Mechanism Stille reaction
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Oxidative addition of aryl triflate to 14e Pd(PPH3)2 = unstable complex, excess chloride ion rescues from decomposition by ligand substitution, R group on organotin compds have carbanion character, nucleophilic substitute for chloride on Pd => reductive elimination
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Principle method used to prepare phenol
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cumene from petroleum produces phenol and acetone through autoxidation (O2 is oxidation agent) and then acid-catalyzed rearrangement
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