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__ is often the best reagent for converting an alcohol to an alkyl chloride. The byproducts (__) leave the reaction mixture and ensure there can be no reverse reaction.
Under the proper conditions, __ reacts by the interesting mechanism:
Step one?
Step two?
- thionyl chloride (SOCl2)
- SO2 and HCl
- 1) the nonbonding electrons of the hydroxyl oxygen atom attack the electrophilic sulfur atom of thionyl chloride; a chloride ion is expelled and a proton is lsot to give a chlorosulfite ester
- 2) the chlorosulfite ester ionizes and the sulfur atom quickly delivers chloride to the carbocation. When R is primary, chloride probably bonds to carbon at the same time that C-O is breaking
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This mechanism resembles the __, except that the nucleophile is delivered to the __ by the __, usualy giving __.
Dehydration requires what? Loss of water, followed by loss of a proton, gives the __. An __ is established between reactants and products.
- Sn1
- carbocation
- LG
- retention of configuration
an acidic catalyst to protonate the hydroxyl group of the alcohol and convert it to a good LG
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To drive equilibrium of acid-catalyzed dehydration to the right, we do what?
Alcohol dehydrations generally take place through the __>
remove one or both products as they form, either by distilling the products out of the reaction mixture or by adding a dehydrating agent to remove water
E1 mechanism
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E1 dehydration of an alcohol
Step one is a __, followed by an __ A __ gives the alkene. Because the Rate limiting step is __, the ease of dehydration follows from the ease of formation of carbocations: __. __ are comon.
- mildly exothermic protonation
- endothermic, rate-limiting ionization
- formation of a carbocation
- 3>2>1
- rearrangements
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With primary alcohols, __ and _ of the products are so common that __ is rarely a good method for converting them to alkenes.
- rearrangements
- isomerization
- acid-catalyzed dehydration
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Review the utility of dehydration adn give guidelines for predicting the products
- 1) dehydration usually goes by the E1 mechanism. Rearrangements may occur to form more stable carbocations
- 2) dehydration works best with tertiary alcohols and almost as well with secondary alcohols. Rearrangements and poor yields are common with primary alcohols
- 3) (Zaitsev's rule) if two or more alkenes might be formed by deprotonation of the carbocation, the more subbed alkene usually predominates
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In some cases, a protonated primary alcohol may be attacked by another molecule of __ and udergo an __. The net reaction is a __ to form an __.
This __ is a type of __, a reaction that joins two (or more) molecules, often with the loss of a small molecule such as water. This method is used for the __ and __. Under the acidic dehydration conditions, two reactions compete __ competes with __.
- alcohol
- Sn2 displacement
- bimolecular dehydration
- ether
- bimolecular dehydration of alcohols
- condensation
- industrial synthesis of diethyl ether and dimethyl ether
- elimination
- substitution
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How can we control these two competing reactions?
The __ shows two molecules of alcohol giving two product molecules: one of __ and one of __. The elimination shows one molecule of alcohol giving two molecules: one of __ and one of __.
- ether synthesis (substitution)
- diethyl ether
- water
- ethylene
- water
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The elimination results in an increase in the number of molecules and therefore an __ of the system. The elimination has a more __ in __ than the substitution, and the __ in the __ becomes more favorable for the elimination as the temperature increases. __ is favored around 140 degrees Celsius and below, and __ is favored around 180 degrees Celsius and above. Diethyl ether is produced industrially by heating __ with an acidic catalyst at around 140 degree Celcius
- increase n the randomness
- positive change
- entropy
- -TdS term
- Gibbs free energy
- Sub
- Elim
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The __ is formally a dehydration. The reaction is acid catalyzed and the first step __. Loss of water gives a __. Migration of a __ places the positive charge on the carbon atom bearing the second __ group, where oxygen's nonbonding electrons help to stabilize the positive charge through __. This extra stability is the driving force for the __, which converts a relatively stable __ into an even better __. Deprotonation of the __ gives the product, __.
- pinacol rearrangement
- is protonation of one of the hydroxyl groups
- tertiary carbocation
- methyl group
- -OH group
- resonance
- rearrangement
- tertiary carbocation
- resonance stabilized carbocation
- resonance-stabilized cation
- pinacolone
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__ are common in acid-catalyzed reactions of diols. One of the hydroxyl groups protonates and leaves as water, forming a __. __ gives a resonance0stabilized cation with the remaining __ helping to stabilize the positive charge.
- pinacol-like rearrangements
- carbocation
- rearrangement
- hydroxyl group
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__ are cleaved by __. The produts are the ame __ and __ that would be formed by __. )) followed by __ serves as a useful alternative to __, and the __ by itself is useful for determining the structures of sugars.
__ probably involves a __ intermediate.
- 1,2-diols (glycols)
- periodic acid
- ketones
- aldehydes
- ozonolysis-reduction of the alkene
- dihydroxylation
- periodic acid cleavage
- ozonolysis
- periodate cleavage
- periodic acid cleavage of a glycol
- cyclic periodate intermidate
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To an organic chemist, the term __ normally means an ester of a carboxylic acid unless some other kind of ester is specified. Replacing the -OH group of a carboxxylic acid with the -OR group of an alcohol gives a __. The __ shows the relationship between the alcohol and the acid on the left and the ester adn water on the right.
- ester
- carboxylic ester
- Fischer esterification
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Because the __ is an __, clver techniques are required for good yields.
Another way to form an ester: An __ reacts with an __ in an exothermic reaction to give an ester.
- Fischer esterification
- equilibrium
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In addition to forming esters with carboxylic acids, alcohols form __ with inorganic acids. In each type of ester, the __ of the alcohol replaces a __ of the acid with loss of water.
- inorganic esters
- alkoxy group
- hydroxyl group
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A __ is like a sulfonate ester, except there is no alkyl group directly bonded to the sulfur atom. In an __, __ are bonded to sulfur through oxygen atoms. __ are excellent leaving groups. Like __, __ are good electrophiles. Nucleophiles react with __ to give alkylated products.
- sulfate ester
- alkyl sulfate ester
- alkoxy groups
- sulfate ions
- sulfonate esters
- sulfate esters x2
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__ are formed from alcohols and nitric acid. In __, the __ are the oxidizer and the CH and CH2 groups are the fuel to be oxidized. This intimate association of fuel and oxidizer allows the explosion to proceed at a much faster rate, forming a shock wave that propagates through the explosive and initiates the reaction.
- nitrate esters
- nitroglycerine
- nitro groups
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Alkly phosphates are composed of 1 mole of phosphoric acid combined with 1,2, or 3 moles of an alcohol. For example, methanol forms three __.
We learned ot remove the __ from an alcohol by reduction with an "active" metal such as Na or K. This reaction generates a Na or K salt of an __ and hydrogen gas.
phosphate esters
hydroxyl proton
alkoxide ion
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The reactivity of alcohols toward Na and K decreases in the order __. Sodium reacts quickly with __ and some __. Potassium is more reactive than sodium and is commonly used with __ and some __. Some alcohols react slugglishly with both sodium and potassium. In these cases, a useful alternative is __, usually in tetrahydrofuran solution. __ reacts quickly to form the alkoxide, even with difficult compounds.
- primary
- secondary alcohols
- tertiary
- secondary alcohols
- sodium hydride x2
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The __ is a strong nucleophile as well as a powerful base. Unlike the alcohol itself, the __ reacts with __ and __ to form __. This general reaction, called the __, is an __. The __ must be primary so that a back-side attack is not hindered. When the alkyl halide is not primary, __ usually reasults.
- alkoxide ion x2
- primary alkyl halides and tossylates
- ethers
- Williamson ether synthesis
- Sn2 displacement
- alkyl halide (or tosylate)
- elimination
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Williamson Ether Synthesis: This is the __.
- most important method for making ethers
- 1: Form the alkoxide of the alcohol having the more hindered group
- 2: the alkoxide displaces the leaving group of a good Sn2 substrante
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Int he __ the __ must be a good __. In proposing a __ we usually choose the less hindered alkyl group to be the halide (or tosylate) and hte more hindered gorup to be the alkoxide ion.
- Williamson ether synthesis
- alkyl halide (or tosylate)
- Sn2 substarte (usually primary)
- Williamson snyhtesis
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