Transcript Organic Chemistry - Snow College | It's SNOWing

Organic Chemistry
Chapter 10
Functional Groups
R O H
alcohol
R N R
R
amine
R C C R
O
R S H
R M X
thiol
organometalic
epoxide
R O R
ether
The Key To Substitution Reactions
• The Leaving Group Goes
Substitution Rx of R-OH
• Alcohols have polar groups which make
substitution probable
• Alcohols have a strongly basic leaving group
(OH-) which make it not probable
• Protonation converts an alcohol to a good leaving
group
Mechanisms
• Wow… we get to draw one……..
From yahoo images
Substitution Rx of R-OH
• HBr and HI work well for SN2 reactions.
• HCl does not work well because Cl is a poorer
nucleophile.
• Rate can be increased using ZnCl2
– Zn2+ is a Lewis Acid
– Complexes with the O:
• (this weakens the C-O bond)
Lucas Test
• .
Rearramgement
• OH ya, don’t forget -
“Grain” and “Wood Alcohol”
• .
Conversion of Alcohols
• Use phosphorous trihalides or thionyl
chloride
– Better yields and no rearrangements
– PCl3, PBr3, PI3, or SOCl2
Do the Mechanism……………………..
From yahoo images
Conversion of Alcohols
Pyridine is used as
the solvent because
it prevents formation
of HCl or HBr and is a
poor nucleophile.
Conversion of Alcohols
• Commonly Used Methods for Converting Alcohols into
Alkyl Halides
D
– ROH
– ROH
– ROH
– ROH
– ROH
– ROH
+
+
+
+
+
+
HBr
HI
HCl
PBr3
PCl3
SOCl2
D
D
pyridine
pyridine
pyridine
RBr
RI
RCl
RBr
RCl
RCl
Sulfonate esters leaving groups
• Conversion of alcohols to sulfonyl
chlorides
– p-toluenesulfonyl chloride (tosyl chloride, TsCl)
– methylsulfonyl chloride (mesyl chloride, MsCl)
– trifluoromethanesulfonyl chloride (trif)
• They are up to 100 x better than Cl- as leaving groups
Sulfonic acid has a
pKa of – 6.5 wow!!
That ought to be on stable base now don’t ya think?
Reaction steps
Dehydration of Alcohols
• Zaitsev’s Rule – more substituted formed
Dehydration of Alcohols
• Dehydration is the reverse of Hydration
– vary conditions to control equilibrium
– Remove the alkene by distillation
Dehydration of Alcohols
• Reaction may involve rearrangement
Dehydration of Alcohols
• rearrangements with ring opening
Dehydration of Alcohols
E and Z produced, major product will have
most bulky groups on opposite sides
Dehydration with POCl3
• Uses a better leaving group
• Conditions are not as extreme
• Phosphorous oxychloride and pyridine
• No rearrangements
• Mildly basic conditions favor E2
Oxidation of Alcohols
Look at reaction and conditions
For Primary and Secondary
Alcohols
From yahoo images
Substitution Rx of Ethers
• Ethers can be activated by acid
• High concentration of HI, HBr will form the
alkyl halide
Ethers as Solvents
• Ethers are relatively unreactive so they are
frequently used as solvents
– diethyl ether (ether)
– tetrahydrofuran (THF)
– 1,4-dioxane
– 1,2-dimethoxyethane (DME)
– methyl t-butyl ether (MTBE)
O
O
CH 3 CH 2 O CH 2 CH 3
diethyl ether
tetrahydrof uran
O
1,4-dioxane
Addition of Peroxyacids
• Alkenes can be oxidized to an epoxide by
a peroxyacid.
Reactions of Epoxides
• Because of 3 membered ring, epoxides
are much more reactive than normal
ethers
• Undergo ring opening reactions at room
temp
Reactions of Epoxides
(oxiranes)
Formation of glycols (addition of H2O)
Reactions of Epoxides
(oxiranes))
Unsymmetrical additions yield the product
resulting from Nu: attack on the more
substituted carbon
Reactions of Epoxides
(oxiranes)
Under basic conditions, Nu: attack is at the less
hindered C
The epoxide is reactive enough that you don’t
need to protinate to get the reaction to go
Crown Ethers
Crown Ethers
• Cyclic compounds with ether linkages
• Bind cations as “host” and “guest”
Crown Ethers
• Naming – [x]-crown-Y
• X = total number of atoms in the ring
• Y = total number of oxygens
Thiols and Sulfides
Thiols and Sulfides
• Thiols are sulfur analogs of alcohols
• Also called mercaptans (mercury capturing)
Thiols and Sulfides
• Thiols are named by adding suffix “thiol”
• Remember to keep the e
• Common names are alkyl mercaptans
CH3 CH2 SH
ethanethiol
CH3 CH2 CH2 SH
1-propanethiol
HS CH2 CH2 OH
2-mercaptoethanol
CH3 CH2 CH2 CH2 SH
butyl mercaptan
Physical Properties-Thiols
• The difference in electronegativity between S
(2.5) and H (2.1) is 0.4.
• This creates a bond with low polarity
• show little association by hydrogen bonding
• have lower boiling points and are less soluble in
water than alcohols of comparable MW
Th iol
bp (°C)
me th an e th iol 6
e th an e th i ol
35
1-bu tan e th iol 98
Al coh ol bp (°C)
me th an ol
65
e th an ol
78
1-bu tan ol 117
Thiols act as Nucleophiles
• Thiolate anions are weak bases (weaker than
alkoxides) and in protic solvents are better
nucleophiles (better than alkoxides since they don’t H bond)
Sulfides or thioethers
• Sulfur analogs are called sulfides or
thioethers
• Most sulfides react readily to form
sulfonium salts
Sulfides or thioethers
• The sulfonium salt easily reacts in a
substitution reaction:
Organometallic Compounds
So far, we have seen reaction in which carbon is bonded to
a more electronegative atom. What happens when it is
connected to a less electronegative atom?
Organometallic Compounds
A compound that contains a carbon-metal bond
Organolithium
Organomagnesium (Grignard Reagent)
Organometallic Compounds
Organometallic Compounds
Organometalics act as nucleophiles
Reactions must be carried out in very dry solvents and
nothing acidic Can be in the reaction mixture
Organometallic Compounds
The greater the polarity difference, the greater
the reactivity of an organometalic reagent
Coupling Reactions
•
•
•
•
Gilman Reaction
Heck Reaction
Stille Reaction
Suzuki Reaction
Gilman Reagents
Henry Gilman
1893-1986
Prepared from an organolithium reagent and
copper(I) iodide
Gilman Reagents
• Gilman reagents can be used to form new
carbon-carbon bonds by cross-coupling
with alkyl or aryl or vinylic halides
Henry Gilman
1893-1986
(Note: cannot use SN2 with aryl or vinylic halides)
The Heck Reaction
The Stille Reaction
The Suzuki Coupling