Transcript Organic Chemistry - Snow College | It's SNOWing
Organic Chemistry
Chapter 10
Functional Groups
R O H alcohol R R N R amine R O R ether R C C O epoxide R R S thiol H R M X organometalic
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
group converts an alcohol to a good leaving
Mechanisms
• Wow… we get to draw one……..
From yahoo images
Substitution Rx of R-OH • HBr and HI work well for S N 2 reactions.
• HCl does not work well because Cl is a poorer nucleophile.
• Rate can be increased using ZnCl 2 – Zn 2+ 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 – PCl 3 , PBr 3 , PI 3 , or SOCl 2
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 + HBr D RBr – ROH + HI D RI – ROH + HCl RCl – ROH + PBr 3 – ROH + PCl 3 – ROH + SOCl 2
pyridine pyridine pyridine
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 POCl 3 • 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 tetrahydrofuran 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 H 2 O)
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 CH 3 CH 2 SH ethanethiol CH 3 CH 2 CH 2 SH 1-propanethiol HS CH 2 CH 2 OH 2-mercaptoethanol CH 3 CH 2 CH 2 CH 2 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
Thiol methanethiol ethanethiol 1-butanethiol bp (°C) 6 35 98 Alcohol methanol ethanol 1-butanol bp (°C) 65 78 117
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 carbon-carbon bonds by cross-coupling with alkyl or
aryl or vinylic halides
(Note: cannot use S N 2 with aryl or vinylic halides)