Ethers, Epoxides And Sulfides Flashcards
Describe ethers
Have functional groups R—O—R’
They may be symmetrical or asymmetrical
What is the hybridization of the oxygen atoms in ethers?
Sp3
Describe the structure and angle of ethers
Ethers have a bent structure like water and C—O—C bond angle is about 110 degrees
Describe the polarity of ethers
Ethers contain a highly polar C—O despite not having the hydroxyl group of alcohols
Why are ethers useful as a solvent?
An ether e.g. tetrahydrofuran(THS) provides a strongly polar solvent without the reactivity of a hydroxyl group
Describe the bonding in pure ethers
Pure ether cannot engage in hydrogen bonding as they lack OH groups but they have large dipole moments which have little affect on boiling point
How can ethers engage in hydrogen bonding?
Can engage in hydrogen bonding with other compounds with O-H or N-H groups
Describe all of the reasons ethers are solvents in general
- They dissolve in a wide range of polar and no polar substances
- They easily evaporate from their reaction products because of their low boiling point
Why are no polar substances tend to more soluble in ethers than alcohols?
Because ethers have no hydrogen bonding network to be broken up by the no polar solute
Compare the solubility of polar substances in ether and alcohol and the reason for this
Polar substances are nearly soluble in ether as they are in alcohols
Due to ethers having a large dipole moments as well as the ability to serve as hydrogen bond receptors
The non bonding pairs effectively ________ cations
Solvate
Why are small anions not as soluble in ethers even nearly as much as they are in alcohols?
Ethers are not hydrogen-bond donors so do not solvate small anions well like alcohols
How do cations solvate in ethers?
Cations is strongly solvate strongly in ethers due to being solvated by the ethers lone pair of electrons
Evaluate how soluble are ions are in ethers
Ions are moderately soluble in ethers as cations are strongly soluble but anions do not solvate well
For what reagents can alcohols not be used to solvate?
Alcohols cannot be used as solvents for reagents that are more strongly basic than the alkoxide ion
Why can alcohols not be used as solvents for reagents that are more basic than the alkoxide ion?
This is because the hydroxyl group quickly protonates the base, destroying the basic reagent
What ethers are commonly used for solvents for organic reactions?
THF, Dioxane and DME
Why can ethers be used as solvents for very strong polar bases?
Ethers are nonhydroxylic and are normally unreactive towards strong bases like Grignard reagents that require polar solvents
What are Criwn Ether complexes?
These are cyclic polyethers that specifically solvate metal cations by complexing the metal in the center of the ring
Different crown ethers solvate different cations depending on…
Depending on the relative sizes of the crown ether, the cation and the number of bijding sites of the cation
Complication by crown ethers often allow polar inorganic salts to…
Dissolve in no polar organic solvents
Generally cyclic ethers behave like ______ ______. This is because…
Cyclic ethers
The chemistry of the ether functional group is the same whether it is an open chain or a ring
Cyclic ethers are examples of….
Heterocyclic compounds containing a ring, in which a ring atom is not carbon
What are epoxies?
Epoxides are 3 membered ring ethers, they make up one of the cyclic ethers that behave differently than open chain ethers
Compare the reactivity of epoxides with ethers and give a reason
Epoxides are more reactive than ethers due to the strain of having a 3 membered ring
How are epoxides named?
Formed by adding oxide to the name of the equivalent alkene.
E.g. 2 carbon epoxides ring- ethylene oxide
What peroxy acid is commonly used to synthesize ethers?
Meta-chloroperoxybenzoic acid(MCPBA)
Explain the synthesis of epoxides
An alkene is reacted with peroxy acid to form an epoxides and a carboxylic acid. (An oxygen is donated from a peroxyacid to an alkene)
This reaction is done in the presence of an aprotic acid
Why is an aprotic acid used in the synthesis of epoxides?
An aprotic acid is used to prevent the opening the epoxides
State 2 ways epoxides can be converted to alcohols
- Reaction of epoxides with LiAlH4 and H2O to form the alcohol
- Reaction if epoxides with Grignard and organolithium reagents
Explain the reaction of epoxides with Grignard and orhanilithium reactions
Grignard and organolithium reagents attack epoxides to give ring-opened alcohols after protonation
Attack occurs on less substituted carbon of the ring
Explain the reaction of epoxides with lithium aluminum hydride and water
Epoxides are reduced to alcohols when treated with lithium aluminum hydride
The hydride is transferred to the less substituted cargo
What are oxetanes?
4 membered cyclic ethers
Compare the reactivity of epoxides, ethers and oxetanes
Because the 4 membered ring causing strain which makes them more reactive than ethers but still less reactive than epoxides
What is a furan?
A five membered cyclic ether, which are commonly named after an aromatic member of this group, furan
Tetrahydrofuran (THF) …
Is a saturated five membered ring, is one of the most polar ethers
What is a use for tetrahydrofuran(THF)?
An excellent nonhyydroxilic organic solvent for polar reagents
Shaft are pyrans?
Pyrans/oxanes are six membered cyclic ethers
They are commonly name as derivatives of pyran- an unsaturated pyran e.g.
4-methylpyran
How do dioxanes effect DNA?
They associate with DNA and cause a misreading of the genetic cause
Why are most dioxanes dangerous?
Most dioxanes are toxic and carcinogenic
What are dioxanes?
Heterocyclic ethers with two oxygen atoms in a sex membered ring
What is the mist common dioxane?
Dioxane with two oxygens with 1,4-relationship
List the ways in which ethers can be synthesized
- Williamson method
- Alkoxymercuration-demercuration reaction/ addition of alcohol across a double bond
- Bimolecular condensation of alcohols: industrial synthesis
What mechanism does Williamson ether use?
Sn2 attack
Explain the reasoning of how a Williamson ether synthesis works
- First a strong base is added to deprotonate the alcohol, the alkoxide ion produced then attacks an alkyl halide
- Secondary alkyl halides and tosylate are occasionally used, but elimination competes and the yield is often poor
How to perform a Williamson ether synthesis?
Strong base is added to alcohol and the resulting alkoxide ion reacts with an unhindered primary alkyl halide or tosylate
Why is an ether more volatile than an alcohol with comparable molecular formula?
Inter molecular hydrogen bonding in alcohols
Ethers May be used as solvents because they react only with one of the following reactants?
Acids
Bases
Oxidising agents
Reducing agents
Acids
The boiling point of ethyl alcohol is much higher than that of dimethyl ether though both have the same molecular weight. Why?
Ethyl alcohol shows hydrogen bonding
The Williamson ether synthesis produces ethers by reacting which of the following?
Alkoxide and aldehyde
The reaction given below is known as by which of the following reaction?
C2H5ONa + IC2H5 -> C2H5OC2H5+ NaI
Williamson synthesis
What will be the reactant and the reaction condition for the given reaction?
CH3CH2OH +? -> C2H5OC2H5
H2SO4, 413K
Name 3 ways ethers can be synthesized
- Williamson method
- Addition of alcohol across a double bond: Alkoxymercuration-demercuration reaction
- Bimolecular condensation of alcohols: Industrial synthesis
What is industrial ether synthesis used to make?
Used to make symmetrical ethers from primary alcohols
Review bimolecular condensation as a method for making unsymmetrical ethers
A poor method for making unsymmetrical ethers(like ethyl methyl ether) due to being a random process producing different combinations of both alcohols that will be difficult to separate
What happens when temperature is too high in industrial synthesis in ether?
Alkene forms
What conditions are needed in industrial synthesis of ether?
Sulfric acid( H2SO4)
140 degrees Celsius
Evaluate the bimolecular condensation of ether as a lab and an industrial method
Industrial method- a good method
Lab synthesis- not good
How can ethers be cleaved and what are they cleaved?
Can be cleaved with HBr or HI to give alkyl bromides or alkyl iodine’s
How can ethers be converted to to alkyl bromides or alkyl iodide?
Cleaved with heating with HBr or HI and forms water
Hydrogen halides are most and least reactive
Hydrogen iodide- most reactive
Hydrogen fluoride - is not reactive
What happens in phenyl ether cleavage with hydrogen halides?
Phenyl ether converted to phenol by hydrogen bromide / iodide and alkyl bromide/iodide
Why can phenol not react further with HI or HBr to ecome a hydrogen halide?
SN2 reaction cannot occur on a sp2 carbon
What happens when ethers are stored in the presence of atmospheric oxygen ?
They slowly oxidize to produce hydroperoxides and dialkyl peroxides
Why are hydroperoxides and dialkyl peroxides dangerous?
These are explosive
What is autoxidation?
The spontaneous oxidation by atmospheric oxygen
What are sulfides(thioethers)?
R—S—R’
How are sulfides prepared?
Sulfides are prepared by treating a primary or secondary alkyl halide with a thiolate ion (RS) which is the sulfur analog of an alkoxide ion
Describe the reaction mechanism to synthesize a sulfide(thioether)
Reaction occurs by Williamson ether synthesis which is an SN2 reaction
How are Sulfides/thioethers named?
Replacing the “ether” with “sulfide” in common name or “alkylthio” for “alkoxy” in IUPAC name
E.g.
methyl phenyl sulfide
Methylthiobenzene
What are thiols?
They are sulfur analogues of alcohols
How are thiols named?
In the same way as alcohols but with the suffix -thiol used in place of -ol
What is the functional group of thiols?
The SH group, A.K.A. a Mercapto group
How are thiolates synthesized?
Are synthesized by the Williamson ether synthesis reaction using dithiolate as a nucleophile and reacting with a primary alkyl halide
What ethers and ether compounds can be synthesized by Williamson ether synthesis?
- ethers
- phenyl ethers can be produced by phenoxide ions reacting with a strong base and unhindered primarybalkyl halide
- Thiolates when using dithiolate as the nucleophile and then reacting with a primary alkyl halide
Describe the reaction to produce phenyl ethers using a phenol halides or tosylates
Phenyl halides nor tosylates can be used to synthesize phenyl ethers
Briefly describe the alkoxymercuration-demercuration reaction
Adds a molecule of an alcohol across a double bond of an alkene to produce an ether
Alcohol= ROH
RO bonds to one carbon and H binds to the adjacent carbon
What is the type of molecule formed from the first step of mercurial ether?
A mercurial ether
What are the reagents of alkoxymercuration-demercuration?
- Alkene
- Hg(OAc)2 and R-OH(alcohol)
- NaBH4
What are the reagents in the first step of alkocymercuration-demercuration?
- Alkene
2. Hg(OAc)2 and ROH
What is another name for pyrans?
Oxans- six membered cyclic ethers
How common are oxetanes?
Not very common
