aldehyde and ketones.docx

8/20/2019 Aldehyde and ketones.docx

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Aldehyde and Ketones

Preparation of Aldehydes

a. Oxidation of primary alcohols



Preparation of Ketones:

a) Oxidation of Secondary alcohols:

d) With Organometallics



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:



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.



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



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:



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%



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



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:



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.



• 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



-sters



a) 2ransesteri;cation :

c) Red$ction:

Acid !hlorides:



c) !onversion of Acid !hlorides into Acid Gerivatives:

Amides

a. &ydrolysis:



. 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 ((

aldehyde and ketones.docx

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