aldehyde & ketone reactions. formation of an aldehyde oxidation of primary alcohols general...
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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
CO
RH
R
H[O ]
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 acid1-butanol
2-methyl-1-propanol
[O ] [O ]
[O ] [O ]
Reduction Reactions
• Both aldehydes and ketones are easily reduced back to the corresponding alcohol. This process is called hydrogenation.
O
R1 R2
+H
HH
R2R1
OH
Catalyst
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 OR-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. 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 – 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 OH red precipitate
Addition ReactionsI. Addition of an Alcohol to an Aldehyde – Acetal
formation O H H+ OH HR1-C-H + O-R2 R1-C-OR2 + O-R2
HAldehyde alcohol Hemiacetal (quite reactive)
OR2
H+ R1-C-OR2
HAcetal
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 formationO H OH H
R1-C-R2 + O-R3 H+ R1-C-OR3 + OR3
R2
Ketone alcohol Hemiketal
OR3
H+ R1-C-OR3
R2
Ketal
Keto-Enol Tautomers
• Many aldehydes & ketones exist in a mixture of two constitutional isomers, informally referred to as tautomers.R
1
R2
R3
O R1
R2
R3
OH
Keto form Enol form
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.
R1
O
R2
O
+O H - o r
e n z ym eR
1
OH O
R2
Aldehyde Aldehyde Aldol
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