Chapter 11- Reactions of Alcohols Flashcards
What is oxidation/ reduction in ochem?
Oxidation: gain of O, O2, or X2; loss of H2
Reductuon: gain of H2 or H-, loss of O or O2 or loss of X2
Or Neither
Primary/secondary/tertiary alcohols can be oxidized to what?
Primary- aldehyde then carboxylic acid
Secondary- ketones
Tertiary- cannot be oxidized bc no alpha hydrogen on carbon
How do you oxidize primary alcohols to aldehydes/ carboxylic acids?
How do you oxidize secondary alcohols to ketones?
Primary:
- > Aldehydes- PCC, Swern (DMSO), DMP
- > Carboxylic Acids- Chromic Acid
Secondary:
->ketones- PCC, NaOCl, Swern (DMSO), DMP,
Alcohols are weak nucleophiles and electrophiles. How do we make them strong nu and elec?
Convert to alkoxide ion to make it a strong Nu
Protonate hyrdroxyl group (OH) to make it a strong electrophile (H2O)
TsOH does what to alcohols?
Converts them to tosylate esters (ROTs) which are excellent leaving groups
Tosylate Reactions can occur through what mechanims?
Sn2 or E2
What are the two ways to reduce alcohols to alkanes?
- Dehydrate with H2SO4 (forms alkene) then add H2, forming the alkane
- Make a tosylate (using TsCl/ Pyr) the. Reduce with LiAlH4
What happens when an alcohol is treated with an acid (H+) ?
The hydroxyl group is protonated to a good leaving group (H2O), then substitution or elimination can take place
In reaction of alchols with HBri, tertiary and secondary alcohols react via which mechanism? And primary?
Tertiary and secondary- Sn1 (carbocation)
Primary- Sn2 (inversion of stereochem)
Why is chloride a weaker nu than bromide?
What is used to promote reaction b/w alcohols and HCl?
Because it is small and less polarizable
ZnCl2 is added
In the lucas test, what is the reaction rate for primary, secondary, and tertiary alcohols?
1
Primary/ secondary/ tertiary alcohols react with lucas agent via which mechanism?
Primary- Sn2 (inversion of stereochem)
Secondary/ Tertiary- Sn1 (carbocation)
What are the limitations of HX reactions?
Primary and secondary alcohols give poor yields
Elimination competes with substitution
Rearrangements for carbocations
Limited ability to make alkyl halides
Alcohol react with phosphorous halides to form what? What reagents are used? Which give the best yields?
Alkyl halides, PCl3 for alkyl chlorides, PBr3 for alkyl bromides, P and I2 for alkyl iodides (PI3 not stable).
Primary and secondary alcohols give best yields.
The mechanism with PBr3 occurs via which mechanism?
Sn2
SOCl2 (thionyl chloride) reacts with alcohols to form what? What else is produced?
To form alkyl chloride, gaseous HCl and SO2 are produced as byproducts
H2SO4 does what to alcohols? What mechanism doss it react with?
Dehydrates alcohols to alkenes via E1, thus 3>2>1 because primary rearrange
Vicinal diols undergo two reactions:
Pinacol rearrangement- diol converts to ketone using H2SO4 and heat, dehydration reaction
periodic acid cleavage- glycols are oxidatively cleaved by HIO4 to form ketones and aldehydes, useful determining structure of sugars
What are the fours 5 esterifications?
Fischer- alcohol + carb acid
Tosylate ester
Sulfate esters
Nitrate esters
Phosphate esters
What is the catalyst in fischer esterification? Why is this method seldom used to prepare esters?
Sulfuric acid, and because it is an equilibrium bw reactants and products
What is a better way to esterificate alcohols?
Use acid chloride, reaction is exothermic and only has HCl as byproduct
What is the besr known nitrate ester? How it formed?
Nitroglycerine, results from reaction of glycerol with 3 molecules of nitric acid
What are the 7 types of Alcohol Reactions?
Dehydration to Alkenes Oxidation to aldehye or ketone Substitution to form alkyl halide Reduction to alkane Esterification Tosylation Williamson synthesis of ether
