Exp. 3b: Nitration of Methyl Benzoate – Flashcards
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Methyl Benzoate is ____-directing
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meta?director
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In Electrophilic Aromatic Substitution reactions, a _______ is needed to react with the aromatic ring; In this experiment _____ was used.
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-strong electrophile -nitronium ion
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The nitronium ion will be generated in situ* by mixing ___&____
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mixing nitric acid and sulfuric acid
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in situ* means?
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it forms in the reaction mixture
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n a mixture of the nitric acid and sulfuric acid, ____ will act as the "base" and will be ____
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nitric acid; protonated
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The protonated intermediate ________ leading to nitronium ion formation
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loses water
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Attacks on the ortho and para positions result in _____
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destabilized cationic intermediates (minor products)
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attack at the meta position yields ______
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a less destabilized intermediate (MAJOR PRODUCT)
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how do you "add the pre?cooled concentrated nitric acid/sulfuric acid mixture to the methyl benzoate/sulfuric acid mixture?"
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drop-wise (pipet)
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How is the product isolated?
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--> Collect the product using a Büchner funnel --> Wash the solids with cold water and methanol (very soluble) --> Recrystallize
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product formed in this reaction?
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methyl m-nitrobenzoate
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are aromatic compounds reactive or unreactive to nucleophiles? Why?
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-VERY unreactive -surrounded by pi-electron clouds (nucleophiles attack carbonyl carbon) -electrophiles better sutied
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why are highly reactive electrophilic reagents needed for reacting with aromatic compounds?
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-results in loss of resonance stabilization
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____ acts as a base in this reaction
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nitric acid
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activating group
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-Any substituent on a benzene ring that causes the rate of electrophilic aromatic substitution to be greater than that for benzene -Usually groups that have a lone pair on the atom connecting to the ring directly are activating and thus makes the ring reactive -able to donate a lone pair into the ring to attack another "substrate" for a reaction - allows subsequent substituents to add onto the ring more readily
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deactivating group
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-An electron-withdrawing group (NO2) attached to the benzene ring that decreases the reactivity of the ring towards electrophilic substitution reaction. =Most deactivating groups are meta directors (but halogens are deactivating ortho-para directors) =Any substituent on a benzene ring that causes the rate of electrophilic aromatic substitution to be lower than that for benzene =if the atom attached to the ring is attached to an electronegative atom also= deactivating --> electrons are getting pulled away from the ring, thus unreactive
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what is the deactivating group on methyl benzoate?
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methyl ester group (COOCH3)
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methyl ester group on methyl benzoate is ___-directing?
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meta directing (electron-withdrawing group)
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what is/are the minor product(s) of this experiment?
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ORTHO/PARA PRODUCTS: --> methyl o-nitrobenzoate --> methyl p-nitrobenzoate
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why is the temperature kept at or below 15 degrees?
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-to avoid excessive formation of byproduct -At higher temperatures there is a greater chance of getting more than one nitro group substituted onto the ring (dinitro) -To minimize some side reactions, which occur at a slower rate, while allowing the desired reaction to proceed
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After the nitration reaction of Methyl Benzoate, why is product poured onto ice instead of water? exothermic/endothermic?
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-The reaction between H2SO4/hno3 is exothermic, so splashing is less likely if the heat from disassociation is used to heat the ice -Using ice will prevent the temperature from getting too high
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NMR: ____ is used as solvent
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CDCl3
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NMR: ____ is used as standard
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TMS (tertramethylsilane)
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how was methyl benzoate "weighed?"
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volume necessary using density (D=M/V)
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HNO3 + H2SO4 (yields?)
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[NO2+ (nitronium ion) ] + [HSO4-] + [H2O]
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The higher the temperature, the _____
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the greater the amounts of dinitration products formed from this reaction
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the reaction takes place at the meta position because the ortho and para positions are _______?
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-destabilized by adjacent positives charges on the resonance structure -NO2 is a deactivating group causing itself to be a meta director
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What would you expect the structure of the dinitro products to be?
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1,3-dinitrobenzene; Nitro groups "direct" new groups into the 3 position (and possibly 5 position) -1,3,5-trinitro possible??? --->nitro groups make the ring much less reactive than the original benzene ring. Two nitro groups on the ring make its reactions so slow that virtually no trinitrobenzene is produced under these conditions
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NO2+ nitronium ion that is generated from ____
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HNO3
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If the bottom of the flask is not cool to the touch while adding HNO3:H2SO4 solution, what should you do?
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slow down the rate of addition of the mixture--> exothermic
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why do we wash with methanol?
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because the ortho and para products are more soluble in methanol and impurities can be removed
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Is HNO3 or H2SO4 the catalyst?
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-H2SO4 is the catalyst (not used up) -HNO3 is NOT a catalyst (nitronium ion, NO2+, is formed from this acid)
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[-CO-OCH3] -> ___activating ___ director
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deactivating m director
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[-Br] -> ___activating ___ director
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deactivating o/p director
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[-CO-CH3] -> ___activating ___ director
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deactivating m director
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[-CH3] -> ___activating ___ director
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activating o/p director
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[-OCH3] -> ___activating ___ director
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activating o/p director
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[-CN]--> ___activating ___ director
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deactivating m director
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ortho product=
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(2,6)
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para product=
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(4)
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meta product=
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(3,5)
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[-X]: ___activating ___ director
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deactivating o/p director
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[-OR]: ___activating ___ director
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activating o/p director
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[-OH]: ___activating ___ director
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activating o/p director
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[-NH2/NHR/NR2]: ___activating ___ director
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activating o/p director
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[-CH3]: ___activating ___ director
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activating o/p director
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[-CN]: ___activating ___ director
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deactivating m director
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[-NO2]: ___activating ___ director
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deactivating m director
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[-COOH]: ___activating ___ director
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deactivating m director
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[-COOR]: ___activating ___ director
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deactivating m director
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[-CHO]: ___activating ___ director
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deactivating m director
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[-COR]: ___activating ___ director
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deactivating m director
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[-SO3H]: ___activating ___ director
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deactivating m director
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Why is H2SO4 added to the reaction mixture?
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-To serve as the solvent -To protonate nitric acid, promoting nitronium ion formation -Because it is a stronger acid than HNO3 (weaker base)
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