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Chapter 11
Reactions of Alcohols

11-00-01T01

Title	Types of Reactions of Alcohols
Caption
Notes	Alcohols can undergo dehydration reactions to form alkenes, oxidations to form ketones and aldehydes, substitutions to form alkyl halides and reduction reactions to produce alkanes. They can be used to make esters and ethers. The OH is not a good leaving group but reaction of the alcohol with tosyl chloride forms a tosylate ester that is a good leaving group.
Keywords	dehydration, oxidation, substitution, reduction, esterification, tosylation

11-01

Title	Oxidation and Reductions
Caption
Notes	In organic chemistry increasing the number of bonds to oxygen is considered an oxidation. Alkanes can be oxidized to alcohols (1 bond to oxygen) which in turn can be oxidized to aldehydes or ketones (2 bonds to oxygen). Aldehydes can be further oxidized to the carboxylic acid (3 bonds to oxygen). Tertiary alcohols cannot be oxidized. Reducing the number of bonds to oxygen or reducing the number of carbon-carbon bonds is a reduction reaction.
Keywords	oxidation, reduction

11-01-11UN

Title	Oxidation of Secondary Alcohols to Ketones
Caption
Notes	Chromic acid reagents such as sodium dichromate (Na2Cr2O7) or chromium trioxide (CrO3) are commonly used to oxidize secondary alcohols to ketones. Both species produce chromic acid (H2CrO4) or acid chromate which are believed to be the active species.
Keywords	oxidation, sodium dichromate, chromium oxide

11-01-13UN

Title	Oxidation Mechanism Using Cr(VI)
Caption
Notes	The first step of the mechanim is the formation of the chromate ester. Deprotonation and elimination of the chromate ester produces the oxidized ketone and the reduced chromium species. The reaction can be monitored by color changes since the reagent is orange but the reduced chromium species is green-blue.
Keywords	chromate ester

11-01-15UN

Title	Oxidation of Primary Alcohols to Carboxylic Acids
Caption
Notes	Primary alcohols can be oxidized to the aldehyde or to the carboxylic acid depending on the oxidizing agent used. Sodium dichromate (Na2Cr2O7) or chromium trioxide (CrO3) will oxidize a primary alcohol to the carboxylic acid.
Keywords	primary alcohol, carboxylic acid, sodium dichromate (Na2Cr2O7), chromium trioxide (CrO3)

11-01-17UN

Title	Oxidation of Primary Alcohols to Aldehydes
Caption
Notes	Oxidation of primary alcohols to aldehydes can be accomplished by using pyridinium chlorochromate (PCC) as the oxidizing agent. PCC is a mixture is chromium trioxide, pyridine, and HCl. PCC is capable of oxidizing secondary alcohols to ketones but is mostly used to oxidize primary alcohols to aldehydes.
Keywords	pyridinium chlorochromate, oxidizing agent

11-01-21UN

Title	Swern Oxidation
Caption
Notes	Another way to oxidize a primary alcohol to an aldehyde is by the Swern Oxidation. This reaction uses dimethyl sulfoxide (DMSO) as the oxidizing agent along with oxalyl chloride and pyridine. The byproducts of this reaction can be easily separated from the products making this a convenient reaction. Secondary alcohols can be oxidized to the corresponding ketone with this reaction as well.
Keywords	Swern oxidation, dimethyl sulfoxide (DMSO), oxalyl chloride

11-01-25UN

Title	Enzymatic Oxidation
Caption	Alcohol dehydrogenase catalyzes an oxidation: the removal of two hydrogen atoms from an alcohol molecule. The oxidizing agent is called nicotinamide adenine dinucleotide (NAD)
Notes	NAD oxidizes alcohol to acetalydehyde and then to acetic acid in the body.
Keywords	NAD, enzyme, acetic acid, acetaldehyde

11-01-34UN

Title	Tosylation of Alcohols
Caption
Notes	An OH is not a good leaving group but it can be converted into a excellent leaving group by tosylation. In this reaction the alcohol is reacted with p-toluenosulfonic acid to form the tosylate ester. The tosylate ester can undergo elimination and substitution reactions easily.
Keywords	p-toluenosulfonic acid, tosylate ester

11-01-35UN

Title	Substitution and Elimination Reactions Using Tosylates
Caption
Notes	The tosylate ester can undergo elimination and substitution reactions easily because the tosylate is an excellent leaving group.
Keywords	tosylate ester

11-01-40UN

Title	Reaction of Alcohols with Acids
Caption
Notes	The hydroxyl group can be protonated by an acid to convert it into a good leaving group (H2O). Once the alcohol is protonated a substitution or elimination reaction can take place.
Keywords	protonation, hydroxyl group

11-01-41UN

Title	SN1 Mechanim for the Reaction of a Tertiary Alcohol with HBr
Caption
Notes	The alcohol first gets protonated by the acid creating a good leaving group. Dissociation into a carbocation happens because the carbocation is stable (3o). A bromide ion present in solution will attack the carbocation forming a C-Br bond.
Keywords	dissociation, carbocation

11-01-42UN

Title	SN2 Mechanim for the Reaction of a Primary Alcohol with HBr
Caption
Notes	A primary alcohol will undergo an SN2 reaction because formation of a primary carbocation is not favored. After protonation the bromide ion will attack from the back displacing the water molecule and creating a C-Br bond.
Keywords	primary carbocation

11-01-50UN

Title	Mechanism of Reaction of Alcohols with PBr3
Caption
Notes	The hydroxyl group of an alcohol can be easily substituted for a halide by using phophorus trihalides. The first step of the mechanism of an alcohol with PBr3 is the attack and displacement of a bromide ion from the phosphorus creating an O-P bond. The bromide ion displaced in the first step will serve as a nucleophile in the seconds step of the reaction where it attacks the carbon displacing the leaving group. This reaction is an SN2 reaction and it works poorly with tertiary alcohols.
Keywords	phophorus trihalides

11-01-51UN

Title	Reaction of Alcohols with Thionyl Chloride
Caption
Notes	Thionyl chloride (SOCl2) can be used to convert alcohols into the corresponding alkyl chloride in a simple reaction that produces gaseous HCl and SO2.
Keywords	Thionyl chloride (SOCl2)

11-01-55UN

Title	Mechanism of Acid-Catalyzed Dehydration of Alcohols
Caption
Notes	In an acidic solution the hydroxyl group of the alcohol will be protonated by the acid. The water molecule is lost to produce a carbocation. Water can acts as a base and abstract a proton from the alcohol to produce an alkene. Concentrated sulfuric acid (H2SO4) is commonly used to carry out this reaction.
Keywords	sulfuric acid (H2SO4), dehydration

11-02

Title	Energy Diagram for the Dehydration of Alcohols
Caption
Notes	Dehydration of alcohols usually takes place in an E1 mechanism. The rate limiting step of the reaction is the formation of the carbocation intermediate so the more stable the carbocation the faster it will form. Carbocation intermediates will rearrange to form more stable carbocations so the dehydration of primary alcohols is not a good method for their conversion into alkenes.
Keywords	E1 mechanism, rearrangements, carbocation

11-02-17UN

Title	Pinacol Rearrangement
Caption
Notes	In the pinacol rearrangement a vicinal diol converts to the ketone (pinacolone) under acidic conditions and heat. The reaction is classified as a dehydration since a water molecule is eliminated from the starting material.
Keywords	pinacol, pinacolone, dehydration

11-02-18UN

Title	Mechanism of the Pinacol Rearrangment
Caption
Notes	The first step of the rearragement is the protonation and loss of a water molecule to produce a carbocation. There is a methyl shift to form a resonance-stabilized carbocation which upon deprotonation by water yields the pinacolone product.
Keywords	pinacol, pinacolone, rearragement, resonance-stabilized carbocation

11-02-24UN

Title	Periodic Acid Cleavage of Alcohols
Caption
Notes	Glycols can be oxidatively cleaved by periodic acid (HIO4) to form the corresponding ketones and aldehydes. This cleavage can be combined with the hydroxylation of alkenes by osmium tetroxide or cold potassium permanganate to form the glycol and the cleavage of the glycol with periodic acid.
Keywords	glycols, hydroxylation, oxidative cleavage

11-02-29UN

Title	Fisher Esterification
Caption
Notes	The Fisher esterification is the acid-catalyzed reaction between alcohols and carboxylic acids to form esters. The reaction is an equilibrium between starting materials and products, and for this reason the Fisher esterification is seldom used to prepare esters.
Keywords	Fisher esterification, acid-catalyzed reaction

11-02-31UN

Title	Reaction of Alcohols with Acyl Chlorides
Caption
Notes	The esterification reaction achieves better results by reacting the alcohol with an acyl chloride. The reaction is exothermic and produces the corresponding ester in high yields with only HCl as a by-product.
Keywords	esterification, acyl chloride

11-03-09UN

Title	Williamson Ether Synthesis
Caption
Notes	Ethers can be synthesized by the reaction of alkoxide ions with primary alkyl halides in what is known as the Williamson ether synthesis. This is an SN2 displacement reaction and as such works better with primary alkyl halides to facilitate back-side attack. If a secondary or tertiary alkyl halide is used the alkoxide will acts as a bse and an elimination will take place.
Keywords	Williamson synthesis

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