II. Reactions of Alcohols A. Oxidation B. Formation of alkyl halides C. Formation of tosylates D. Dehydration E. Formation of esters

A. Oxidation Gain of O, loss of H, or both Degree of oxidation depends on reagents

Oxidation with PCC Pyridinium chlorochromate (PCC) Complex of CrO 3 + pyridine + HCl Mild oxidizing agent 1° alcohol → aldehyde 2° alcohol → ketone 3° alcohol → no reaction Solvent = CH 2 Cl 2

Oxidation with H 2 CrO 4 Chromic acid Chromium trioxide Sodium dichromate in aqueous acid Stronger oxidizing agent 1° alcohol → carboxylic acid (aldehyde intermediate) 2° alcohol → ketone 3° alcohol → no reaction

Oxidation with KMnO 4 Not in Klein textbook Same results as chromic acid Less expensive Better for the environment

B. Formation of Alkyl Halides Substitution reactions If alkyl halide is tertiary, reagents are HCl or HBr (aq) Mechanism = S N 1 Product = racemic mixture (if stereocenter is present) Secondary ROH can react, but requires heat and can rearrange Evidence of reaction = formation of second layer

Formation of Alkyl Halides If alkyl halide is primary or secondary, reagents are thionyl chloride (SOCl 2 ) or phosphorous tribromide (PBr 3 ) Milder conditions than HCl or HBr (better option for 2°)

Reaction with SOCl 2 or PBr 3 Reaction mechanisms are S N 2 Inversion of configuration

C. Formation of Tosylates Used to convert alcohols into other functional groups Alcohol reacts with tosyl chloride (TsCl) to make tosylate Tosylate ion (TosO - or TsO - ) is an excellent leaving group

Formation of Tosylates Stereochemical configuration of alcohol does not change when the alcohol forms the tosylate Reaction occurs at O, not at C If tosylate undergoes S N 2 reaction, inversion of configuration will occur

Reduction of Tosylates Tosylates can be reduced to alkanes with LiAlH 4 Can you think of another method we can use to make an alkane from alcohol?

D. Dehydration Formation of alkene Reaction = E1 Tertiary alcohols react fastest Major product = Zaitsev Reagents = acid (H 3 O +, H 2 SO 4 or H 3 PO 4 );  (sometimes) Protonate -OH to create a better leaving group

E. Formation of Esters Reaction of an alcohol with a carboxylic acid or a carboxylic acid derivative We will cover this later in the semester

Synthesis Problem The following conversion requires more than one step. Show reagents and experimental conditions necessary to bring about this conversion.

Synthesis Problem Propose a synthesis for 3-pentanone from ethanol. You may use any other organic molecule(s) as a source of carbon atoms.

Draw the major organic products formed in the following reactions, clearly showing all appropriate regio- and stereochemistry.

Reactions of Primary Alcohols Provide reagents for each reaction

Reactions of Secondary Alcohols Provide reagents for each reaction

Reactions of Tertiary Alcohols Provide reagents for each reaction