aldehyde and ketones.docx
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Aldehyde and Ketones
Preparation of Aldehydes
a. Oxidation of primary alcohols
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Preparation of Ketones:
a) Oxidation of Secondary alcohols:
d) With Organometallics
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Reactions of Aldehydes and Ketones:
a) Aldol condensation
Aldehydes and ketones having alpha hydrogen atom:
) !anni""aro reaction:
Aldehydes and ketones having no alpha hydrogen atom:
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When t#o caronyl gro$ps are present #ithin a molec$le% think of intramolec$lar
reaction.
O&' #ill attack more positively charged caron. (n this case% it is right c*+ gro$p.
c) ,ormation of Keto -sters
-sters having a'hydrogen on treatment #ith a strong ase e.g. !&/O0a. 1ndergo
self condensation to prod$ce 'keto esters. 2his reaction is !laisen !ondensation.
d) Reformatsky Reaction
2his is the reaction of a'haloester% $s$ally an a'romoester #ith an aldehyde or
ketone in the presence of 3inc metal to prod$ce 'hydroxyester.
e) Pinacol'pinacolone Rearrangement
2he acid catalysed rearrangement of 4% diols 56icinal diols) to aldehydes or
ketones #ith the elimination of #ater is kno#n as pinacol pinacolone
rearrangement.
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a) Wittig'7lide Reaction
Aldehydes and Ketones react #ith phosphor$s 7lides to yield alkenes and triphenyl
phosphine oxide. An 7lide is a ne$tral molec$le having a negative caron ad8acent
to a positive hetero atom. Phosphor$s ylides are also called phosphoranes.
Preparation of 7lides
Reaction of 7lide #ith !*O
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Aove things happens in 96O 59ayer 6illiger oxidation). Reagents are either per
acetic acid or peren"oic acid or pertri$oroacetic acid or permonos$lph$ric acid.
e)
Addition of cyanide
f) Addition of is$l;te:
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h) Addition of Alcohols< Acetal ,ormation
(n &=O>% R!&O is regenerated eca$se acetals $ndergo acid cataly"ed cleavage
m$ch more easily than do ethers. Since acetals are stale in ne$tral or asic media%
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they are $sed to protect the ? !& * O gro$p.
k) 2ischenko reaction:
All aldehydes can e made to $ndergo the !anni""aro reaction y treatment#ith aluminium ethoxide. 1nder these conditions the acids and alcohols are
comined as the ester% and the reaction is then kno#n as the 2ischenko reaction<
eg% acetaldehyde gives ethyl acetate% and propionaldehyde gives propyl
propionate.
Oxidation of Aldehydes and Ketones
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a)
2ollen@s test chiey $sed for the detection of aldehydes.
2ollen@s reagent doesnot attack caron'caron do$le onds.
c) Strong Oxidants: Ketones resist mild oxidation% $t #ith strong oxidants at high
temperat$re they $ndergo cleavage of ! ? ! onds on either sides of the caronyl
gro$p.
d) &aloform Reaction
!&=!OR are readily oxidised y 0aO( 50aO& > () to iodoform% !&(=% and R!O0a
-xample:
• Red$ction:
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a) Red$ction to alcohols
!aroxylic Acids:
!aroxylic Acids !ommon 0ames
&!OO& ,ormic acid
!&=!OO& Acetic acid
!&=?!&?!OO& Propionic acid
!&=5!&)!OO& 9$tyric acid
!&=5!&)=!OO& 6aleric acid
!&=5!&)4!OO& Palmitic acid
!&=5!&)4B!OO& Stearic Acid
Physical Properties of !aroxylic Acids
• 2he ;rst three acids are colo$rless% p$ngent smelling liC$ids.
• ,irst fo$r memers are miscile in #ater d$e the intermolec$lar hydrogen
onding #hereas higher memers are miscile in non ? polar solvents like
ether.
• 9en"ene or ethanol $t immiscile in #ater d$e to the increase in the si"e of
lyophoic alkyl chain.
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• 2he .p. of caroxylic acids are higher than alcohols eca$se caroxylic acids
exist as dimers d$e to the presence of intermolec$lar &'onding
• (ncrease in the n$mer of &alogen atoms on a'position increases the acidity%
eg.
!!l=!OO& !&!l!OO& !l!&!OO& !&=!OO&
• (ncrease in the distance of &alogen from !OO& decreases the acidity e.g
!&= ? !& ? !&5!l) ? !OO& !&= ? !&5!l) ? !& ? !OO& !& ? !& ? !& ?
!OO&
• (ncrease in the electro negativity of halogen increases the acidity.
,!&!OO& 9r!&!OO& (!&!OO&
Dethods of Preparations of !aroxylic Acids
a. Oxidation of Aldehydes E Ketones
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-sters
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a) 2ransesteri;cation :
c) Red$ction:
Acid !hlorides:
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c) !onversion of Acid !hlorides into Acid Gerivatives:
Amides
a. &ydrolysis:
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. Acidic !haracter of Amides:
R!O0& > &gO F 5R!O0&)&g > &O
c. 9asic !haracter of Amides:
Amides are very feely asic and form $nstale salts #ith strong inorganic acids.
e.g. R!O0&&!l. 2he str$ct$re of these salts may e ( or ((