Chapter 8 Alcohol and Ether

Nomenclature of Ethers

The functional group of ether is an oxygen atom bonded to two carbon atoms

R—O—R

◦ The simplest ether is dimethyl ether, CH3OCH3

◦ The most common ether is diethyl ether CH3CH2OCH2CH3

Although ethers can be named according to the IUPAC system, chemists almost invariably use common names for low-molecular-weight ethers.

◦ Common names are derived by listing the alkyl groups bonded to oxygen in alphabetical order and adding the word "ether”.

◦ Alternatively, name one of the groups on oxygen as an alkoxy group (RO- ).

CH O 3 CH3CH2O CH3CHO CH3CH2CHO H3C CO methoxy ethoxy CH isopropoxy sec-butoxy 3 ter-butoxy E.g Name the following molecule

O O OH

E.g Use bond-line to draw

Isopropyl methyl ether 4-ethoxy-2-methyl-1-hexene

CHM 201 Dang 1 Substitution of Alcohols (ROH  RX)

- - CH3Cl + OH  CH3OH + Cl

- - CH3OH + Cl  CH3Cl + OH

 -OH is strongly basic, unstable, not a good LG

 Must convert into a weaker base, in the protonated form (R OH2 )

ROH + NaCl  NR (no LG)

ROH + HCl  RCl + H2O

ROH + HBr  RBr + H2O

ROH + HI  RI + H2O

H Br + CH3 OH + H Br CH3 O H3C Br H2O H SN2

poor LG weak good LG base

o o SN1 mechanism (2 and 3 )

H2O H Br + H Br OH OH Br + H2O

3o alcohol + Br

o SN2 mechanism (1 ) Br

H + H2O + H Br Br OH O H H O 1o alcohol 2

Explain why (S)-2-butanol forms a racemic mixture when it is heated in aqueous sulfuric acid?

CHM 201 Dang 2 E.g Predict the product and provide a mechanism

OH + HI

Elimination reactions of Alcohols

 Aka dehydration of alcohol  lost of H2O

 Required strong acid catalyst

 Formation of alkene follows Zaitsev’s rule: More substituted alkene is the major product

 More stable carbocation will be formed faster

Benzylic/allylic/3o ROH > 2oROH >> 1oROH

OSO3H OSO3H E1 mechanism

HB HA A minor H OSO3H heat O OH H H B + major OSO3H

CHM 201 Dang 3 E2 mechanism H H O + H2O OH H OSO3H H heat + H2SO4

Ether is also obtained; it is the product of a competing SN2 reaction

H O H OSO H O O OH 3 H H o 1 H O ether HO 2

E.g Give the major product formed when each of the following alcohols is heated in presence of H2SO4

Oxidation of Alcohols

CHM 201 Dang 4 Oxidation: increases # C-O bonds and decreases the # of C-H bonds

CH4 CH3OH HCH HCOH O C O

Reduction: decreases # C-O bonds and increases the # C-H bonds

Common reagents: chromic acid, chromate salt, dichromate salt, permanganate

 Oxidation of a 1° alcohol to a carboxylic acid is commonly carried out using potassium

dichromate, K2Cr2O7, in aqueous sulfuric acid.

Further oxidation OH O O K2Cr2O7 K2Cr2O7 R C H C C H SO OH H2SO4 R H 2 4 R H 1o alcohol Aldehyde carboxylic

 Or using pyridium chlorochromate (PCC) as the oxidizing agent in an anhydrous solvent OH O PCC R C H C CH2Cl2 R H H 1o alcohol Aldehyde

◦ Oxidation of a 2° alcohol and cyclic alcohol gives a ketone. OH O K Cr O 2 2 7 C R1 C H R1 R2 H2SO4 R2 Ketone 2o alcohol

K Cr O 2 2 7 CHM 201 Dang 5

cyclohexanol cyclohexanone  Tertiary alcohols are resistant to oxidation R H2CrO4 R OH NR

Consider the following reaction

OH O LiAlH4 a reaction

a agent

Predict the product(s)

H2CrO4

O reagents? alcohol ???? OH

CHM 201 Dang 6