Learning Guide for Chapter 15 - Alcohols (II) I. Introduction to alcohol reactivity II. Reactions of alcohols with acids III. Reactions of alcohols with electrophiles alogenated phosphorus and sulfur compounds Tosyl chloride IV. Reactions of alkoxides V. Reactions of alcohols and diols with oxidizing agents I. Introduction to alcohol reactivity In which of the following ways can an alcohol react? As a base: yes no if the acid has a pka less than -2.4 2 S 4 2 As a nucleophile: yes no if the electrophile is fairly reactive As an acid: yes no if the conjugate acid pka is greater than 18 Na S N 2, E2 As an electrophile: yes no even though C is partially, is not a good LG Can they be oxidized? yes no ox can gain bonds to - become aldehyde, ketone, C
Can they be reduced? yes no LG Ch 15 p 2 II. Reactions of Alcohols with Acids What is the first intermediate formed when an alcohol reacts with an acid? What happens when a protonated alcohol dissociates? 2 S 4 Which of the following alcohols can form a protonated alcohol that can dissociate? What happens to the ones that can't? What are the three things that can happen to a carbocation? Rearrange whenever a more stable C can be formed hydride shift React w/ a S N 1 - rxn substitution product React w/ a base E1 rxn base alkene
What else do we need to know to determine if the carbocation will react as an electrophile or acid? if the conjugate base of the acid is a nucleophile or not What will happen when 2 S 4 or 3 P 4 is used as the acid? LG Ch 15 p 3 2 S 4 2 E1 S not a base or a Could this reaction give constitutional isomers and/or stereoisomers? yes - if there are different 's, or cis/trans Why is the acid catalytic? because 3 is formed Why is heat usually required in this reaction? a C is formed Could this reaction go backward? yes - acid-catalyzed hydration of an alkene The equilibrium constant is near 1.0 - how can we get a good yield? high conc of alcohol - use as solvent remove water - absorb remove alkene - distill off What will happen if or is used as the acid? 2 but not abase In order to make this reaction work well with, what else needs to be added?, Zn 2 - Lucas reagent
LG Ch 15 p 4 ow could you use the Lucas test to determine whether the following alcohols were 1 o, 2 o, or 3 o? Zn 2 no reaction (at room temp) nothing happens slow reaction cloudy, then 2nd layer Zn 2 insoluble fast reaction 2nd layer almost immediately Zn 2 insoluble Predict the products of the following reactions. 2 S 4 2 2 3 P 4 Zn 2
III. Reactions of Alcohols with Electrophiles LG Ch 15 p 5 What electrophile have we previously encountered that can react with an alcohol? carbocation S N 1 E C 3 C 3 C 3 C 3 C 3 2 alogenated phosphorus and sulfur compounds What are the two most common phosphorus and sulfur reagents used as electrophiles with alcohols? phosphorus tribromide P 3 thionyl chloride S 2 What type of compound results when they react with alcohols? alkyl halide P 3 3 P 3 water soluble - wash w/ 2 S 2 pyr gas - bubbles out S 2 pyr- - solid - filter off What advantages do these reactions have when isolating the product? pyr = pyridine N N good for absorbing What is the mechanism of the P 3 reaction? attack-push off P P attack-push off P reacts 3 more times What type of alcohols work best in these reactions? Why? 1 o best, 2 o K steric hindrance
What products will the following reactions give? LG Ch 15 p 6 P 3 3 P 3 P 5 P 3 pyr P I 2 I 3 P 3 If you want to convert an alcohol to an alkyl halide, which is the best way to do it? R- R- R-I 1 o R S 2 P 3 P, I 2 2 o R or S 2 or P 3 I or P, I 2 3 o R I Convert the following alcohols to the products shown. P 3 P I I 2 S 2 pyr
Tosyl chloride What product results when an alcohol reacts with tosyl chloride in pyridine? Ts S pyr S tosyl chloride a tosylate LG Ch 15 p 7 pyr- - Ts pyr Ts ow does this reaction occur? S S N S N S ow do tosylates react? Ts is a leaving group - like S Give the products of the following reactions: S Ts NaC 3 - Ts Ts NaCN N Ts KC(C 3 ) 3
LG Ch 15 p 8 Ts C 3 C 2 Na Ts LiAl 4 IV. Formation and reactions of alkoxides What reagents would be appropriate to form an alkoxide from the following alcohols? Na or Na Na or K Na or K Na Give the products of the following reactions: S N 2 E2 S N 2 Ts S N 2
From what alkoxide and tosylate could each of the following ethers be formed? LG Ch 15 p 9 1 o 2 o Ts Ts yes no - E2 side products Ts Ts yes no reaction V. xidation of Alcohols and Diols What type of reaction is represented by all of the tranformations below? Give a reagent that would be effective for each. NaB 4 C 3 NaB 4 C 3 reductions LiAl 4 2. 3 LiAl 4 2. 3 3 C What products can the following compounds be oxidized to? 1 o 2 o 3 o aldehyde can't be oxidized ketone carboxylic acid gain bonds to, lose bonds to aryl can't be oxidized
Which reagents are commonly used for the following transformations? LG Ch 15 p 10 1 o alcohol aldehyde Cr 3, pyridine = Collin's reagent Cr 3, pyridine, = PCC 1 o alcohol carboxylic acid Na 2 Cr 4 2, 2 S 4 Na 2 Cr 2 7 2, 2 S 4 Cr 3 2, 2 S 4 = Jones reagent 2 o alcohol ketone all of the above Give the products of the following reactions: Cr 3 2, 2 S 4 Na 2 Cr 2 7 2, 2 S 4 PCC Jones reagent
What would you observe when doing a Jones test on the following alcohols? LG Ch 15 p 11 orange --> blue-green positive test stays orange negative test stays orange negative test orange --> blue-green positive test What reagent is needed to cleave vicinal diols? periodic acid - I 4 or 5 I 6 What products will result from the following reactions? I 4 I 4 What reaction of alkenes gives the same result? ozonolysis
Summary of Alcohol Reactions LG Ch 15 p 12 1 o alcohol 1 o alcohol Collins or PCC Jones, etc aldehyde carboxylic acid 1 o alcohol Ts, pyr tosylate ether, alkyne, nitrile, etc 1 o, 2 o alcohol P 3, S 2 etc alkyl halide 2 o alcohol Jones, Collins etc ketone 2 o, 3 o alcohol 2 S 4 alkene 2 o, 3 o alcohol I,, /Zn 2 alkyl halide alcohol, phenol Na, Na, K Na alkoxide RX or RTs ether