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52 Cards in this Set

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