Aldehyde & Ketone Reactions

Formation of an Aldehyde Oxidation of Primary Alcohols General equation: – Primary alcohol aldehyde RCH 2 CH=O EXAMPLE: 1-propanol

Formation of a Ketone Oxidation 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 Reactions Practice Problems Reduce 3-pentanone (ketone 2 o alcohol) Reduce hexanal (aldehyde 1 o 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(NH 3 ) 2 + R-C-O - + Ag 0 Aldehyde silver ammonia carboxylic silver complex acid anion metal “Tollen’s Reagent” mirror

Write equations for the following reactions 1. ethanal + Tollen’s reagent 2.2- pentanone + Tollen’s reagent 3.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 – Cu 2 O

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 - CH 2 OH + 2Cu +2 H H OH OH ( from Benedict’s Solution) O OH OH H H - O - C - C - C - C - C -CH 2 OH + Cu 2 O H H OH OH red precipitate

HOMEWORK p 419 #14.46, 47, & 48

Addition Reactions I.Addition of an Alcohol to an Aldehyde – Acetal formation O H H+ OH H R 1 -C-H + O-R 2 R 1 -C-OR 2 + O-R 2 H Aldehyde alcoholHemiacetal (quite reactive) OR 2 H+ R 1 -C-OR 2 + H 2 O 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 2.Addition of an alcohol to a ketone – KETAL formation O H OH H R 1 -C-R 2 + O-R 3 H+ R 1 -C-OR 3 + OR 3 R 2 Ketonealcohol Hemiketal OR 3 H+ R 1 -C-OR 3 + H 2 O R 2 Ketal

Practice Problems Propanal + Methanol 3-hexanone + ethanol

HOMEWORK p 419 #49-56

Keto-Enol Tautomers Many aldehydes & ketones exist in a mixture of two constitutional isomers, informally referred to as tautomers.

Keto-Enol Tautomers 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 CH 3 CH + CH 3 CH

Example Write an equation for the aldol condensation of two molecules of butanal.

More Practice Try these: The aldol condensation of 2 molecules of : propanone butanone

HOMEWORK p #62, 63, & 64