Transcript Diels-Alder Reactions

Diels-Alder Reactions
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1,2,3,4-Tetraphenylnaphthalene
Hexaphenylbenzene
Dimethyl Tetraphenylphthalate
Triptycene
Experimental Write-up
1,2,3,4-Tetraphenylnaphthalene
Large rxn tube
& boiling chip
1. 500 mg tetraphenylcyclopentadienone (purple solid)
2. 3 mL glyme (1,2-dimethoxyethane)
3. 0.35 mL isoamyl nitrite
Caution: Remove any plastic coatings from reaction tubes.
1. Heat to a gentle reflux and then time for 2-5 min.
2. In a separate small vial dissolve 250 mg anthranilic acid in 2 mL glyme.
3. Add the acid/glyme mixture to the refluxing solution dropwise with a pipette.
• Bubbling should occur.
• Look for a color change from dark brown to yellow.
• If color change does not occur add an additional 0.35 mL isoamyl nitrite.
• Heat for an additional 2 min.
4. Cap and shake tube and let it stand at room temperature. (Move on to next reaction
while compound precipitates out.)
5. Add 10 mL ethanol and 5 mL saturated sodium bicarbonate, shake well and allow
solid to form.
6. Vacuum filter: wash with cold water twice followed by cold ethanol.
7. Recrystallize with nitrobenzene/ethanol.
8. Weigh and record MP.
Tetraphenylnaphthalene
Benzyne – Solvent?
An Intermediate
Glyme (1,2-dimethoxyethane) boils at
In the procedure
it talks
about
Benzyne
willisbe
created
inthe
situ
from
It is This
important
to note
85ᵒC.
higher
than
most
other
bubbling.acid
Thisand
givesisoamyl
us an nitrite. Its
anthranilic
structure
ofuse
your
and
solvents
weclue
inreagents
thethelab
which
important
about
nature
instability
will
cause
it
to
react
immediately
product.
speeds
up
the
formation
of
of this
reaction. What is it? the
with
tetraphenylcyclopentadienone.
intermediate.
These give important clues such as
steric hindrance and stability. Is our
product
planarstructures
or non-planar?
Intermediate
will
Does
have
a partfull
to
needresonance
to be shown
in your
play?
You will
need to answer
extended
write-up.
these questions in your paper.
Hexaphenylbenzene
A neat reaction (without solvent)
Small DRY rxn tube
100 mg tetraphenylcyclopentadienone
500 mg diphenylacetylene
Caution: Remove any plastic coatings from reaction tubes.
1. Turn heat up all the way on sand bath. Reaction requires a temperature of
~300ᵒC.
• Use a spatula to build up sand around the base of the tube to increase
heat.
• Lightly place a cap on reaction tube in case it bumps.
2. Heat mixture until mixture changes color from purple to brown.
3. Pull out of sand and lightly shake to observe if any white solid forms at the
bottom while mixture is cooling.
• Reflux longer if no solid forms upon cooling.
4. Cool and then add 2 mL diphenyl ether and heat in sand bath until solid is
dissolved.
5. Cool tube to RT before placing 2 mL of toluene into the product.
• Let tube cool or ice bath will make tube shatter if it’s hot.
6. Vacuum filter and wash white solid with toluene.
Hexaphenylbenzene
A similar
intermediate.
O
Stability is a key factor
in all of these reactions.
How stable is this
product compared to
the others? Again, think
in terms of sterics and
resonance.
O
O

3
vs.
-CO
A neat reaction is performed without a
CH
solvent. For aO neat vs.
reaction to work the
melting pointO of
the reactants must be
CH
O
met. Tetraphenylcyclopentadienone has a
melting point of 219-220ᵒC. Solvents that
reach this high of a temperature without
boiling off or breaking down are
expensive.
3
Dimethyl Tetraphenylphthalate
Small rxn tube
& boiling stick
100 mg tetraphenylcyclopentadienone
0.1 mL dimethyl acetylenedicarboxylate
1 mL nitrobenzene
Caution: Remove any plastic coatings from reaction tubes.
1. Heat rxn tube & contents until reflux.
Color will change from purple to a tan.
2. Cool to room temp FIRST then add 3
mL ethanol.
3. Cool in an ice bath.
4. Vacuum filter w/ cold ethanol, dry,
and weigh.
Dimethyl Tetraphenylphthalate
Higher BP solvent. Why?
(Hint: Think in terms of
activation energy.)
O
O
Similar intermediate.
C
C
O
CH3
O
CH3
O
Triptycene
Rxn Tube 1 –
w/ boiling chip
Rxn Tube 2
400 mg anthracene
0.4 mL isoamyl nitrite
4 mL glyme (1,2-dimethoxyethane)
520 mg anthranilic acid
2 mL glyme (1,2-dimethoxyethane)
1. Add contents of tube 2 into tube 1 dropwise over 20-minute period through a
septum.
2. After 20 min addition, add 0.4 mL isoamyl nitrite.
3. Reflux for 10 min and then cool to RT.
4. Add 5 mL EtOH followed by 10 mL sodium hydroxide soln (3 M).
5. Vacuum filter and wash with cold ethanol then cold water (brown color should
fade). Weigh and record this crude product.
6. Place your crude product in 25 mL round bottom flask and add 200 mg maleic
anhydride & 4 mL triglyme (NOT glyme). Fit with a reflux condenser and reflux on
sand bath for 5 min. Cool to RT.
7. Add 2 mL EtOH and 6 mL sodium hydroxide soln (3 M). Filter and rinse with cold
EtOH followed by cold water.
8. Recrystallize with methanol and filter, dry and weigh.
Triptycene cont.
Anthranilic acid
NH2
H3C
H3C
(2-aminobenzoic acid)
OH
mp: 144-145oC
O
O
O
N
O
O
Isoamyl nitrite
bp 99°C, d 0.87
O
-
O
N
+
N
N
N

-N2, CO2
Anthracene
mp: 216oC
+
Triptycene
mp: 225oC
The answer lies in resonant
Solvent
is always
important
structures.
Whichan
rings
in
factor.
Normally
done in
anthracene
havethis
the isgreatest
dichloromethane
(BP: 41ᵒC) but
resonance stability?
we are going to use isoamyl
nitrite (BP: 85ᵒC). Why?
Deprotonation
anthranilic acid
Final productofmechanism
hasleads
no to
benzyne precursors through the release of
intermediate but why did the benzyne
nitrogen and carbon dioxide gas just as in the
addreaction.
to the anthracene
at the middle
of
first
Having the anthrinilic
acid and
the ring
and seperated
not on the
side?
isoamyl
nitrite
is key
since side
products are formed if they are added
together. This is why the addition must be done
dropwise over a 20 min period.
Experimental Write-Up
Significant figures must be a
Reaction
title
is bold andsince
there is
part of your
experimental
Compound
names
are not
acapitalized
period
title.
Title is
they
couldafter
playevery
a limiting
role.
Solvent
volumes
be
unless
at should
the
Decimals
always
have zeros
in
part
of the
placed
after
solvent
name,
beginning
ofparagraph.
a sentence.
Italicized
front
them.
notof
before.
words
will
never be capitalized.
Example:
Notice that all reactants have the same
amount ONLY
of sig reactants
figs while require
solventsmmol
only
amounts,
NOT
solvents.
Use
The only
Common
exception
abbreviations
is %have the
requireAlways
one.
Your
product
will
include
spaces
correct
for
mL (not
recovery.
are
acceptable
use.
same number
ofnotation
sig figstoas
your
limiting
between
amounts
and
units.
ml
or
ML).
reagent (including your % yeild).
2,5-Di-tert-butylacenaphthene. A soln of acenaphthene (15.1 g, 97.7 mmol)
and aluminum chloride (2.65 g, 19.9 mmol) in carbon disulfide (100 mL) were
added to tert-butyl-chloride (20. mL, 180 mmol) dropwise via syringe over 25
min. The soln was stirred for an additional 3 h, then refluxed for 1 h. Upon
cooling, water (100 mL) was cautiously added, followed by concentrated HCl
(5 mL) and stirring was continued until all of the dark solid had dissolved. The
mixture was extracted with carbon disulfide, dried over Na2SO4, and filtered.
The solvent was removed under vacuum and the resulting yellowish wax was
recrystallized once in glacial acetic acid and then once in toluene/ethanol to
yield a white precipitate (7.42 g, 27.8 mmol, 30.3%): mp 161-162 ºC.
Any color changes and descriptions
must be given. Always include a
description of your product.
No space on %
recovery
Melting point must be
given as a range ONLY if
you recorded one.
A Write-Up Checklist
What you do NOT need to do:
•
To explain processes such as recrystallization, how to set up an apparatus, or include what you think
happened.
Check these off after you have completed your write-up.
o
o
o
o
o
o
o
Correct tense – Are there any “I”, “you”, “me”, “they”, “he”, “she” or present tense words (-ing, -es
words), etc… in the experimental? Remove them and restructure your sentence(s) to reflect a past
tense, 3rd person point of view.
All reactants are given mmol amounts while solvents were not. Liquid reactants should have mass
included (e.g. “isoamyl nitrite (0.35 mL, 0.30 g, 2.6 mmol)”).
Provide information about the product if it was requested in the procedure (mass, MP as a range,
BP, % yield). A description of the product should always be included (color, texture, phase, smell,
etc…).
Crude weights are included in the same experimental paragraph.
Shorthand may be used but always define it in its first mention (e.g. “hydrochloric acid (HCl)”).
Include conditions such as time under reflux, ice bath, temperatures, crystallization solvents,
filtration method, etc…
Mass, mmol, and % yield of product reported at end along with MP range if recorded.