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The least expensive method for synthesizing simple symmetrical ethers is the __ (joining of two molecules, often with loss of a small molecule like water). __ competes with __. To form an ether the alcohol must have an __, and the temperature must not be allowed to rise too high. If the alcohol is hindered or the temperature is too high, the delicate balance between __ and __ shifts in favor of __, and very little ether is formed. __ is used in industry to make __ from primary alcohols. Because the __ is so limited in its schope, it finds little use in the laboratory synthesis of ethers.
- acid-catalyzed bimolecular condensation
- unimolecular dehydration (to give an alkene)
- bimolecular condensation
- unhindered primary alkyl group
- bimolecular condensation
- symmetrical ethers
If the conditions are carefully controlled, __ is a cheap synthesis of diethyl ether. In fact, this is the industrial method used to produce millions of gallons of diethyl ether each year.
Unlike alcohols, ethers are not commonly used as synthetic intermediates because they do not __. This __ makes ethers attractive as solvents. Even so, ethers do undergo a limited number of characteristic reactions.
- undergo many reactions
How are ethers cleaved?
Ethers are __ toward most __, but they can react under __ conditions. A __ ether can undergo __ or __ with an alcohol serving as a __. Ethers react with concentrated __ and __ because these reagents are sufficiently __ to protonate the ether, while __ and __ are good __ for the substitution. Under these conditions, the __ usually further with HX to give another __.
by heating with HBr and HI to give alkyl bromides or alkyl iodides
- neutral leaving group
- alcohol leaving group
- alkyl halide
In effect, this reaction converts a __ into __. The conditions are very strong, however, and the molecule must not contain any __.
Iodide and bromide ions are good __ but weak __, so they are more likely to substitute by the __ mechanism than to promote elimination by the __ mechanism.
- dialkyl ether
- two alkyl halides
- acid-sensive functional gorups
Cleavage of an Ether by HBr or HI:
Ethers are cleaved by a __ of Br- or I- on the protonated ether.
What is the mechanism?
The step three can ccur by either of two mechanisms depending on the structure of the alcohol and the reaction conditions. the protonated alcohol undergoes either __ or __ by bromide ion.
- 1: protonation of the ether to form a good LG
- 2: Sn2 cleavage of the protonated ether
- 3: Conversion of an alcohol fragment to the alkyl halide (does not occur with phenols)
__ reacts with ethers the same way HBr does. Aqueous iodide is a stronger nucleophile than aqueous bromide, and iodide reacts at a faster rate. We can rank the __ in order of their reactivity toward the cleavage of ethers:
- hydroiodic acid (HI)
- hydrohalic acids
- HI> HBr >> HCl
__ (one of the groups bonded to oxygen is a __) reacts with HBr or HI to give alkyl halides and __. __ do not react further to give halides because the __ of the __ cannot undego the __ (or __) reaction needed for conversion to the halide.
- phenyl ethers
- benzene ring
- sp2-hybridized carbon atom
When ethers are stored in the presence of atomospheric oxygen, they slowly oxidize to produce __ and __, both of which are explosive. Such a spontaneous oxidation by atmospheric oxygen is called __.
Organic chemists often buy large containers of ethers and use small quantities over several months. Once a container has been opened, it contains __, and the __ begins. After several months, a large amount of __ may be prsent. __ or __ concentrates the __ and an explosion may occur.
- dialkyl peroxides
- atm oxygen
- autoxidation process
__, also called __, are ethers with a sulfur atom replacing the oxygen atom of an ether, just like the sulfur in a __ replaces the oxygen atom of an alcohol. The chemistry of __ is much like the chemistry of ethers, except that __ can undergo __ and __ of the sulfur atom.
__ are ethers with a substiuted silicon atom replacing one of the alkyl groups of an ether. __ shre some of the properties of ethers (resistant to some acids, bases, and oxidizing agents), but they are more easily formed and more easily hydrolyzed. These properties make them useful as protecting groups, and __ are frequently used to protect alcohols.
silyl ethers x3
Like __, __ have strong characteristic odors. The odor of __ is reminiscent of oysters that have been kept in the refrigerator for too long. __ are named like ethers, with "__" replaicng "_" in the common names. In the IUPAC names, "__" replaces __.
- dimethyl sulfide
__ are easily synthesized by the __, using a __ as the nucleophile. __ are more acidic than water. Therefore, __ are easily generated by treating __ with __. Becuase __ is larger and more __ than oxygen, __ are even better __ than __. __ are such effective nucleophiles that secondary alkyl halides often react to give good yields of __ products.
- Williamson ether synthesis
- thiolate ion
- thiolate ions
- aqueous sodium hydroxide
- thiolate ions
- better nucleophiles
- alkoxide ions
__ are much more reactive than ethers. In a __, __ is not necessarily filled: Sulfur can form additional bonds with other atoms. Sulfur forms particularly strong bonds with oxygen, and __ are easily __ to __ and __. __ and __ are drawn using either __ or formally charged single-bonded structures.
- sulfur valence
- hypervalent double-bonded structures
The __ cmbo is a good oxidant for sulfides. One equivalent of peroxide gives the __, and a second equivalent further oxidizes the __ to the __. This reagent combo probably reacts via the __, which is formed in equilibrium with the hydrogen peroxide.
Because they are easily oxidized, sulfides are often used as mild __.
- hydrogen peroxide/acetic acid
- reducing agents
Sulfur compounds are more __ than the corresponding oxygen compounds, because sulfur is larger and more __ and its electrons are less tightly held in orbitals that are farther from the nucleus. Although __ are weak nucleophiles, __ are relatively strong nucleophiles. Sulfides attack unhindered alkyl halides to give __.
__ are strong __ agents because the __ is an __. Sulfur's polarizability enhances partial bonding in teh TS, lowering its energy.
- sulfonium salts x2
- uncharged sulfide
__ are common alkylating agents in biological systems.
If we have a compound with two or more __ and we want to modify just one of those __, we often must protect any other __ to prevent them from reacting as well.
- sulfonium salts
- functional groups x3
Alcohol functinal groups are common and useful, but they react with __, __, and __. Alcohols must be __if they are to survive a reaction at another functional group on the molecule. A good __ must be easy to add to the group it protects, and then it must be __to the reagents used to modify other parts of tehmolecule. Finally, a good __ must be easy to remve to do what?.
- acids, bases and oxidizing agents
- protecting group
- protecting grup
- regenerate the original functional group
An ether protecting group can be difficult to remove (__). It often requires __, which can react with teh free __ or other parts of hte molecule. Ethers based on __ (__) are much easier to remove than carbon-based ethers. In aqueous organic solvents, fluoride ion removes __ under gentle conditions because the silicon-fluorine bond is super strong.
- strong acid
- hydroxyl group
- silyl ethers
- silyl ethers
Synthetic organic chemists have developed many different __ that vary widely in their reactivity and are carefully chosen for a specific use.
__ are stable to most acids and bases and oxidizing and reducing agents. Our __ would react with __ and __ to give a protected alcohol. After the __ is completed, protonation of the magnesium alkoxide salt and __ of the __ gives the desired product.
- silyl protecting groups
- TIPS (tri-iso-propyl-Silyl) ethers
- TIPS chloride
- triethylamine (Et3N)
- Grignard reaction
- silyl ether
__ are easily made from alkenes, and (unlike other ether) they undergo a variety of useful synthetic reactions. For these reasons, __ are valuable synthetic intermediates. __ is the process.
__ are used to convert alkenes to epoxides. If the reaction takes place in aqueous acid, the epoxide opens to a __. Therefore, to make an epoxide, we avoid strong acids. Because of its desirable solubility properties, __ is often used for these __. It is a weakly acidic __ that is soluble in aprotic solvents like CH2Cl2
The __ takes palace in a one-step, __ that maintains the stereochemistry of any subtituents on the double bond.
The __ is quite general, with electron-rich double bonds reacting fastest.
__ is a relatively stable water-stable peroxyacid often used in large-scale epoxidations.
- concerted reaction
- peroxyacid epoxidation
A second synthesis of epoxides and other cyclic ethers involves a variatioin of the __. If the __ and a halogen atom are located in the same molecule, the alkoxide may displace a halide ion and form a ring. Treatment of a __ with base leads to an epoxide through this internal __ attack.
- Williamson ether synthesis
- alkoxide ion
__ are easily generated by treating alkenes with aqueous solutions of halogens. Bromine water and chlorine water add across double bonds with __.
- Mark orientation