Aldehyde & Ketone Reactions
Formation of an AldehydeOxidation of Primary Alcohols • General equation: • Primary alcohol aldehyde RCH2CH=O EXAMPLE: 1-propanol
Formation of a KetoneOxidation of Secondary Alcohols • General equation: • Secondary alcohol ketone O R-C-R EXAMPLE: 2-propanol
Review from Chapter 13!!Oxidation of Tertiary Alcohols • General equation: • Tertiary alcohol NO REACTION!!!
YOU TRY THESE! • Write an equation showing the oxidation of the following alcohols. Be sure to name the product formed. (a) 1-pentanol (b) 2-butanol
Oxidation of Aldehydes • Aldehydes are easily oxidized further to form carboxylic acids. • Oxidation process: Primary alcohol Aldehyde Carboxylic acid 1-butanol 2-methyl-1-propanol
Reduction Reactions • Both aldehydes and ketones are easily reduced back to the corresponding alcohol. This process is called hydrogenation.
Reduction ReactionsPractice Problems • Reduce 3-pentanone (ketone 2o alcohol) • Reduce hexanal (aldehyde 1o alcohol)
HOMEWORK Oxidation and Reduction Reactions p 419 #41, 42, 45, 57, 60 & 68 (a, c, & d) p 410 # 13 – 16 (a, c, & d)
Lab Tests for Aldehydes and Ketones Tollen’s Test Tests for ALDEHYDES (not ketones) Silver ion is reduced to silver metal The aldehyde is oxidized to a carboxylic acid anion AKA the Silver Mirror Test
Tollen’s Test O O R-CH + Ag(NH3)2 + R-C-O- + Ag0 Aldehyde silver ammonia carboxylic silver complex acid anion metal “Tollen’s Reagent” mirror
Write equations for the following reactions 1. ethanal + Tollen’s reagent • 2- pentanone + Tollen’s reagent • propanal + Tollen’s reagent
Benedict’s Test • Indicates the presence of an aldehyde • A buffered aqueous solution of copper (II) hydroxide and sodium citrate • Reacts to oxidize aldehydes • Forms a red solid – Cu2O
Benedict’s Test • All sugars are aldehydes or ketones • Benedict’s solution can be used to test urine for glucose (an aldehyde), which is common in uncontrolled diabetes • The amount of red precipitate formed is directly proportional to the amount of glucose in the urine.
Benedict’s Test • O OH OH H H HC – C - C - C - C - CH2OH + 2Cu+2 H H OH OH (from Benedict’s Solution) O OH OH H H -O - C - C - C - C - C -CH2OH + Cu2O H H OH OHred precipitate
HOMEWORK p 419 #14.46, 47, & 48
Addition Reactions Addition of an Alcohol to an Aldehyde – Acetalformation O H H+ OH H R1-C-H + O-R2 R1-C-OR2 + O-R2 H Aldehyde alcohol Hemiacetal (quite reactive) OR2 H+R1-C-OR2 + H2O H Acetal
Addition Reactions • -OR group is an alkoxyl group • Hemiacetals are very reactive, so in the presence of acid and excess alcohol, will continue to react to form an acetal
Addition Reactions • Addition of an alcohol to a ketone – KETAL formation O H OH H R1-C-R2 + O-R3 H+ R1-C-OR3 + OR3 R2 Ketone alcohol Hemiketal OR3 H+ R1-C-OR3 + H2O R2 Ketal
Practice Problems • Propanal + Methanol • 3-hexanone + ethanol
HOMEWORK p 419 #49-56
Keto-EnolTautomers • Many aldehydes & ketones exist in a mixture of two constitutional isomers, informally referred to as tautomers.
Keto-EnolTautomers • constitutional = structural • They differ in the placement of a hydrogen atom & a double bond • The “keto” form is more stable
Practice • Draw the enol form of the aldehydes and ketones listed below. • Ethanal • 2-pentanone • Butanal
Aldol Condensation • Reaction in which aldehydes & ketones react to form larger molecules. A new carbon-carbon bond is formed in the process. • Actually occurs between an aldehyde in the keto form and one in the enol form. • Used in our cells to make glucose “gluconeogenesis”
Aldol Condensation • The new carbon-carbon bond forms between the carbonyl carbon of one molecule and the α-carbon (the carbon next to the carbonyl carbon) of the other O O • CH3CH + CH3CH
Example • Write an equation for the aldol condensation of two molecules of butanal.
More PracticeTry these: • The aldol condensation of 2 molecules of : propanone butanone
HOMEWORK p 419-420 #62, 63, & 64