PREPARATION OF ALDEHYDES AND KETONES /CLASS 12

Summary

In this chemistry session, Anita Raj teaches the preparation of aldehydes and ketones through oxidation processes. She explains how primary alcohols like ethyl alcohol can be oxidized to form aldehydes using acidified potassium dichromate, with controlled conditions to prevent further oxidation. Secondary alcohols are converted to ketones in a similar manner. The video also covers the production of aldehydes and ketones from alkenes through reductive ozonolysis, hydration of alkynes, catalytic hydrogenation of acid chlorides, and dry distillation of calcium salts of carboxylic acids. Additionally, aldehydes can be produced from nitrites via the Stetten reduction process.

Takeaways

• 🧪 Aldehydes and ketones can be prepared by controlled oxidation processes.
• 🌡 Primary alcohols are oxidized to aldehydes using acidified potassium dichromate in a controlled manner to prevent further oxidation to carboxylic acids.
• 🔄 Ethyl alcohol specifically yields acetaldehyde when oxidized with acidified potassium dichromate.
• 🔄 Secondary alcohols, like isopropyl alcohol, are oxidized to ketones under similar conditions, resulting in compounds like acetone.
• ⚖️ Unsymmetrical alkenes undergo reductive ozonolysis to produce two different aldehydes, while symmetrical alkenes yield only one type.
• 🌐 Aldehydes can be obtained from alkenes without branching at the carbon atoms involved in the double bond.
• 🔥 Alkynes, like acetylene, can be hydrated to produce aldehydes, with an intermediate unstable vinyl alcohol forming and then transforming into acetaldehyde.
• 🌀 Ketones are produced from alkenes with branching at the carbon atoms involved in the double bond through reductive ozonolysis.
• ⚛️ Acid chlorides can be reduced to aldehydes and ketones using different methods, including catalytic hydrogenation and reactions with dimethylcadmium.
• 🔬 Aldehydes and ketones can also be derived from carboxylic acids through the dry distillation of their calcium salts.
• 🧪 Stiff's reduction involves the partial reduction of nitriles to aldehydes using zinc and hydrochloric acid at specific temperatures.

Q & A

What is the controlled oxidation process for preparing aldehydes?

The controlled oxidation process for preparing aldehydes involves the use of acidified potassium dichromate, which is potassium dichromate in the presence of sulfuric acid. This process oxidizes primary alcohols, such as ethyl alcohol, to aldehydes like acetaldehyde (CH3CHO), with the removal of hydrogen as water.

Why is the oxidation of primary alcohols to aldehydes a controlled process?

The oxidation of primary alcohols to aldehydes must be controlled because if it proceeds without control, the aldehyde can further oxidize to a carboxylic acid. It's important to remove the aldehyde from the reaction mixture as soon as it forms to prevent further oxidation.

How are ketones produced from secondary alcohols?

Ketones are produced from secondary alcohols through oxidation using acidified potassium dichromate. For example, isopropyl alcohol undergoes oxidation, leading to the removal of hydrogen as water and the formation of a ketone such as acetone (CH3COCH3).

What is reductive ozonolysis and how does it produce aldehydes?

Reductive ozonolysis is a process where alkenes react with ozone to form an ozonide intermediate, which then reacts with zinc dust in the presence of water to produce aldehydes. This method is used for alkenes without branching at the carbon atoms involved in the double bond.

How does the symmetry of an alkene affect the type of aldehydes produced in reductive ozonolysis?

The symmetry of an alkene determines the types of aldehydes produced in reductive ozonolysis. Unsymmetrical alkenes yield two different aldehydes, while symmetrical alkenes yield the same type of aldehyde.

What is the role of zinc in the reductive ozonolysis process?

In the reductive ozonolysis process, zinc reacts with the oxygen from the ozonide intermediate, forming zinc oxide and reducing the ozonide to an aldehyde.

How are ketones produced from alkenes with branching?

Ketones are produced from alkenes with branching at the carbon atoms involved in the double bond through reductive ozonolysis. The branching leads to the formation of ketones rather than aldehydes upon ozonolysis and reduction.

What is the hydration of alkynes and how does it lead to the formation of aldehydes?

The hydration of alkynes involves passing alkynes, such as acetylene, through dilute sulfuric acid in the presence of mercuric sulfate, leading to the formation of aldehydes like acetaldehyde (CH3CHO). This process involves the addition of water across the triple bond.

How are aldehydes and ketones produced from acid chlorides?

Aldehydes can be produced from acid chlorides by catalytic hydrogenation in the presence of a palladium catalyst supported by barium sulfate. For ketones, acid chlorides are treated with dimethyl cadmium in dry ether to produce ketones like acetone (CH3COCH3).

What is the significance of using a poisoned catalyst in the hydrogenation of acid chlorides?

Using a poisoned catalyst, such as one partially poisoned with sulfur, prevents the over-reduction of aldehydes to alcohols, ensuring that the desired aldehyde product is obtained and not further reduced.

How are aldehydes and ketones produced from the dry distillation of calcium salts of carboxylic acids?

Aldehydes and ketones can be produced by dry distillation of calcium salts of carboxylic acids. For example, calcium acetate undergoes dry distillation to produce acetaldehyde (CH3CHO), while calcium salts of other carboxylic acids can produce ketones.

What is the Stiff reduction and how is it used to produce aldehydes?

The Stiff reduction is a process where nitriles are partially reduced to aldehydes using zinc and hydrochloric acid at specific temperatures. This method involves the conversion of nitriles to imine hydrochlorides, which upon boiling with water yield aldehydes.

Outlines

00:00

🧪 Preparation of Aldehydes and Ketones

This paragraph discusses the preparation of aldehydes and ketones through oxidation processes. Aldehydes are produced from primary alcohols like ethyl alcohol using acidified potassium dichromate, with careful control to prevent further oxidation to carboxylic acids. The process involves the removal of hydrogen atoms to form a water molecule, resulting in acetaldehyde. Ketones are obtained from secondary alcohols, exemplified by the oxidation of isopropyl alcohol to acetone. The paragraph also covers the preparation of aldehydes and ketones through reductive ozonolysis of alkenes, distinguishing between symmetrical and unsymmetrical alkenes and the resulting products. The process involves the reaction of alkenes with ozone to form intermediate ozonides, which upon reduction with zinc dust, yield aldehydes. The paragraph concludes with a mention of further topics to be covered in upcoming sessions.

05:01

🌡️ Advanced Synthesis of Aldehydes and Ketones

The second paragraph delves into more advanced methods of synthesizing aldehydes and ketones. It begins with the preparation of ketones from alkenes with branching at the double-bonded carbon atoms, using 2,3-dimethyl-2-butene as an example. The process involves ozonolysis followed by reduction with zinc dust to yield two molecules of acetone. The paragraph then explores the hydration of alkynes to produce aldehydes, using acetylene and mercuric sulfate in dilute sulfuric acid to form acetaldehyde. It also discusses the preparation of ketones from other alkynes under similar conditions. The section concludes with the production of aldehydes and ketones from acid chlorides through catalytic hydrogenation, with acetyl chloride used as an example. The use of a palladium catalyst and the importance of poisoning the catalyst with sulfur to prevent over-reduction to alcohols is highlighted.

10:03

🔬 Further Methods for Aldehydes and Ketones Production

The final paragraph covers additional methods for producing aldehydes and ketones. It starts with the production of aldehydes from the dry distillation of calcium salts of carboxylic acids, using calcium acetate and calcium formate as an example. The process results in the formation of acetaldehyde and calcium carbonate. The paragraph then discusses the production of ketones from the dry distillation of calcium salts of carboxylic acids, again using calcium acetate as an example, which yields ketones and calcium carbonate. The section concludes with the preparation of aldehydes from nitrites through the Stoffenstein reduction, a partial reduction process involving zinc and hydrochloric acid. The process converts methyl cyanide to an adduct, which upon boiling with water, yields acetaldehyde and ammonium chloride. The paragraph ends with a sign-off, indicating that further topics will be discussed in future sessions.

Keywords

💡Aldehydes

Aldehydes are a class of organic compounds containing a carbonyl group (C=O) with the carbon atom of the carbonyl group bonded to a hydrogen atom and an alkyl or aryl group. In the video, aldehydes are prepared from primary alcohols through a controlled oxidation process using acidified potassium dichromate. Ethyl alcohol is oxidized to acetaldehyde, which is a key example of an aldehyde formation.

💡Ketones

Ketones are organic compounds that also contain a carbonyl group, but in this case, the carbon atom is bonded to two other carbon atoms, forming a C=O double bond. The script explains that ketones are produced by the oxidation of secondary alcohols, such as isopropyl alcohol, which is converted to acetone, a common ketone.

💡Oxidation

Oxidation is a chemical reaction that involves the loss of electrons or an increase in oxidation state. In the context of the video, oxidation is used to convert alcohols to aldehydes and ketones. The process involves the removal of hydrogen atoms, which is critical in the formation of the carbonyl group.

💡Acidified Potassium Dichromate

Acidified potassium dichromate is a strong oxidizing agent used in the oxidation of alcohols to aldehydes and ketones. The video describes its use in a controlled manner to prevent over-oxidation of the aldehydes to carboxylic acids, which would occur if the reaction were not carefully managed.

💡Reductive Ozonolysis

Reductive ozonolysis is a chemical reaction where an alkene reacts with ozone, followed by a reduction step, typically using zinc dust, to break the carbon-carbon double bond and form aldehydes or ketones. The video uses this process to explain how aldehydes can be obtained from alkenes without branching at the double-bonded carbon atoms.

💡Alkenes

Alkenes are hydrocarbons with at least one carbon-carbon double bond. The video discusses how alkenes can be converted to aldehydes through reductive ozonolysis, emphasizing the difference between symmetrical and unsymmetrical alkenes in the products formed.

💡Acetaldehyde

Acetaldehyde (CH3CHO) is a specific type of aldehyde mentioned in the video as a product of the oxidation of ethyl alcohol. It is a simple and common aldehyde used to illustrate the oxidation process discussed in the script.

💡Acetone

Acetone (CH3COCH3) is highlighted in the video as a ketone produced from the oxidation of isopropyl alcohol. It is a widely used solvent and serves as a model compound for discussing the formation of ketones.

💡Hydration

Hydration in organic chemistry refers to the addition of water to a molecule. In the video, hydration of alkynes like acetylene is described to form aldehydes, such as acetaldehyde, through an intermediate product, vinyl alcohol.

💡Acetyl Chloride

Acetyl chloride is an acid chloride derived from acetic acid and is used in the video to demonstrate the production of aldehydes through catalytic hydrogenation. The reaction involves the controlled addition of hydrogen gas in the presence of a palladium catalyst.

💡Catalytic Hydrogenation

Catalytic hydrogenation is a reduction reaction where hydrogen is added to a molecule in the presence of a catalyst. The video explains how acetyl chloride can be reduced to acetaldehyde using a palladium catalyst, with the reaction carefully controlled to prevent further reduction to an alcohol.

Highlights

Introduction to the session on aldehydes, ketones, and carboxylic acids.

Preparation of aldehydes and ketones through oxidation using acidified potassium dichromate.

Conversion of primary alcohols to aldehydes, exemplified by the oxidation of ethyl alcohol to acetaldehyde.

Importance of controlled oxidation to prevent further oxidation of aldehydes to carboxylic acids.

Removal of aldehydes by distillation immediately after formation to prevent further oxidation.

Preparation of ketones from secondary alcohols, demonstrated by the oxidation of isopropyl alcohol to acetone.

Explanation of reductive ozonolysis of alkenes to produce aldehydes.

Difference between symmetrical and unsymmetrical alkenes in reductive ozonolysis and the resulting aldehydes.

Production of two different aldehydes from unsymmetrical alkenes, such as propylene.

Formation of ketones from alkenes with branching at the carbon atoms involved in the double bond.

Conversion of alkynes to aldehydes and ketones through hydration.

Use of mercuric sulfate and dilute sulfuric acid in the hydration of acetylene to produce acetaldehyde.

Intermediate product formation during hydration of alkynes and its transformation to aldehydes.

Preparation of ketones from other types of alkynes besides acetylene.

Conversion of acid chlorides to aldehydes and ketones through catalytic hydrogenation.

Role of palladium catalyst and its poisoning with sulfur to prevent over-reduction to alcohols.

Production of aldehydes from acid chlorides using dimethyl cadmium in dry ether.

Preparation of aldehydes and ketones from the dry distillation of calcium salts of carboxylic acids.

Formation of acetaldehyde from calcium acetate and calcium formate through dry distillation.

Stoichiometric reduction of nitriles to aldehydes using zinc and hydrochloric acid.

Conversion of methyl cyanide to acetyl chloride through reduction and subsequent hydrolysis.

Summary of the methods for preparing aldehydes and ketones discussed in the session.

Transcripts

[Music]

hi hello this is anita raj your

chemistry mentor welcoming you for one

more session in aldehydes ketones and

carboxylic acids in this session i shall

teach you the preparation of aldehydes

and ketones by oxidation process it is

possible to prepare aldehydes and

ketones that do in a controlled manner

by using acidified potassium dichromate

okay so let us see how aldehydes are

prepared first see these aldehydes are

prepared from the primary alcohol so i

have taken ethyl alcohol now see this

ethyl alcohol undergoes oxidation in the

presence of acidified potassium

dichromate that means potassium

dichromate in the presence of sulfuric

acid understood so what happens is see

uh this alcohol this under goes

oxidation so one hydrogen from this

carbon and the next hydrogen will be uh

removed as a water molecule okay and

finally we'll be getting acetaldehyde

ch3cho so we are getting acetaldehyde

from ethyl alcohol understood why this

reaction has to be taken place in a

controlled manner because if it is not

controlled this acetaldehyde will be

undergoing further oxidation and that

will be getting converted to a carboxyl

acid understood that's why it has to be

removed this has aldehyde as soon as it

is formed it has to be removed from the

reaction mixture by distillation okay so

let us see how ketones are produced now

see these ketones are obtained by the

oxidation of secondary alcohols okay so

this is a secondary alcohol this is a

isopropyl alcohol understood

isopropyl alcohol

isopropyl alcohol so this is a secondary

alcohol so when this secondary alcohol

when it undergoes oxidation in the

presence of acidified potassium

dichromate we get a ketone okay here

also the hydrogen from this carbon and

this hydrogen will be getting removed as

water molecule and finally we will be

getting a ketone ch3

c

double bond o

ch3 okay this is acetone or dimethyl

ketone plus water molecule okay so this

is acetone acetone or next we shall see

how this aldehydes and ketones can be

prepared by reductive ozonolysis of

alkenes okay see here this aldehydes can

be obtained by the reductive ozonolysis

of alkanes which do not possess

branching which do not process branching

at the carbon atoms

which which are involved in this double

bond okay these two carbon atoms are

involved in the double bond okay and

this should not have branching okay

those type of

alkenes can produce aldehydes okay now i

am taking a unsymmetrical alkene what am

i unsymmetrical i can see here this is a

double bond and this carbon this is

another carbon and here this side is not

same as that of this side so this is

unsymmetrical uh

alkene okay when we are making use of

unsymmetrical alkene and this

unsymmetrical alkene will be undergoing

oceanolysis and finally we will be

getting two types of aldehydes but when

we are making use of symmetrical alkenes

we will be getting the same type of

aldehyde so now let us see how this

works out okay i have taken propylene

methane

and propane so it's a double bond so

propylene this propylene the first

reacts with ozone okay

and it forms a intermediate product so

what happens how this ozone it uh

combines c h

o

c h two

here one o

o

o okay so now

this is called as propylene this is

called as

propylene

ozonoid

propylene ozonoid understood now this

propylene ozonite then it reacts with a

zinc dust okay in the presence of water

and there will be a what what what

happens here oceanologist takes place

okay see here

what happens when it is treated with

zinc test this oxygen right see this

oxygen will combine with zinc and that

will be removed as

zinc oxide okay minus zinc oxide and

finally you will be getting acetola ch3

cho acetolian

h2co mean hcho that is formaldehyde so

two types of products you are getting

acetaldehyde ch3 ch o plus formaldehyde

h c h o so since we are making use of

unsymmetrical alkene we are getting two

different aldehydes if you are making

use of same alkene uh same sorry

symmetrical alkane then you will be

getting same type of altitudes

understood now we shall see how ketones

are produced see ketones are obtained by

the reductive oceanologist of those

alkenes which possesses branching okay

at one carbon or both the carbon atoms

which are involved in double bond

understood so if if the carbon atoms

which are involved in double bond are

having branches then it will be giving

those type of alkenes will be giving

ketones understood so i have taken 2 3

dimethyl but 2 in okay so methane ethane

propane butane and it's having a double

bond in the second carbon so two in and

two methyl groups are there in second

and the third position so two three

dimethyl but two in understood so let us

see how this undergoes also analysis

first it will become this uh alkene will

be combining with ozone to form an

intermediate compound okay so let me

write the compound now

ch3

c

ch3

now there will be a link here oxygen

then again carbon right then here ch3

ch3

oh

just like the previous one we are

getting okay then again this will react

with the sink dust in the presence of

water and again there will be ozonolysis

okay here

here there will be a break and this

oxygen will combine with zinc to form

zinc oxide so minus z10 o and you will

be getting two molecules of acetone ch3

then c double bond o ch3 so you'll be

getting two dimethyl ketones two

molecules of dimethyl ketone or acid

next we shall see how these allots and

ketones are prepared from alkynes that

are triple bonded compounds okay so

aldehydes and ketones can also be

prepared by the hydration of alkynes

okay see here i'm taking acetylene first

for the preparation of aldehydes okay

when this acetylene is passed through

dilute sulfuric acid in the presence of

one percentage of mercuric sulfate at

333 kelvin see that the temperature is

333 kelvin if this acetylene it

undergoes hydration to give acetaldehyde

okay so we'll be getting acetaldehyde

ch3ch

oh right but before the formation of

this acetaldehyde will be getting an

intermediate product okay how how this

intermediacy this water molecule it

splits as h plus

and o h minus okay now this h plus will

be getting attached to this carbon and

this oh will be getting attached to this

carbon and we'll be getting a and

getting an unstable intermediate okay so

what could be the unstable intermediate

c h 2 double bond c h o h okay so this

compound is called as

vinyl alcohol vinyl vinyl alcohol and it

is highly unstable okay so since it is

very unstable immediately it transforms

to acetaldehyde

ch3cho understood students this is how

we shall we will be preparing aldehydes

now we shall take into account the

ketone so how these ketones are prepared

actually instead of acetylene if you are

making use of

other type of

alkynes we'll be getting ketones okay so

instead of acetylene alone will not give

ketone other all the other alkynes will

be giving ketones so i have taken

propane okay methane

when this propane uh is passed to dilute

sulfuric acid in the presence of one

percentage mercuric sulphate will be

getting an unstable product just like

the previous one see here this h2o will

be get splitted up into h plus or h

minus so what happens is this h plus

will be getting added up to this carbon

and this o h will be getting added to

this carbon understood so we'll be

getting the unstable product like this

ch3

single bond c h

c o h

then double bond ch2 okay this is an

unstable intermediate now this will be

since it is unstable immediately it will

be getting transformed to a ketone ch3 c

double bond o ch3 so this is acetone or

dimethyl ketone understood this is how

we'll be preparing

okay next we shall see how this

aldehydes and ketones are produced from

acid chlorides okay see this aldehydes

and ketones can be obtained by the

catalytic hydrogenation of acid chloride

so first let us see how this aldehydes

are produced see actually this in this

method hydrogen gas is passed through a

solution of uh acetyl chloride so i am

taking acetyl chloride as an example so

hydrogen gas is passed through this

acetyl chloride in boiling styling okay

in the presence of palladium catalyst

supported over barium sulfate okay so

palladium catalyst taken in in the

presence of in uh which is supported by

barium sulfate and partially poisoned

with sulphur okay or quinoline so this

process is called as rose and means

reduction so now acetyl chloride i have

taken so hydrogen is passed through this

acetyl chloride the presence of

palladium catalyst supported by barium

sulphate in boiling silent and if this

palladium catalyst is partially poisoned

by sulphur okay so what happens is uh

here we get uh acetaldehyde c h3 cho

plus hcl okay we'll get hcl so this is

what happening right now

why we are making use of this uh poison

sulphur see if this catalyst is not

poison the allocate formed in this

reaction will easily get reduced into

alcohol okay alligator will be further

reduced to alcohol and we'll get an

alcohol instead of algae okay so that's

why we are making use of a poison so

that we can hinder the reaction as soon

as we are getting this

should be removed immediately okay next

comes this ketones actually as i told

you earlier this alternate this process

is otherwise called as rose sentiment

reduction but now this ketones cannot be

obtained by this rose and

okay but it can be prepared easily by

treating this acetyl chloride with dye

methyl cadmium c2 methyl groups are here

so dimethyl cadmium in the presence of

dry ether when this acetylene turret is

treated with dimethyl cadmium in the

presence of dry heater we get as a tone

okay so ch3

c

double bond o

sequence 3 understood so this is what we

are getting acetone

plus cadmium chloride cdcl2

okay so now

next we shall see how this alligates and

ketones are produced from carboxylic

acids actually by dry distillation of

calcium salts or carboxylic acids we can

easily produce aldehydes and ketones

okay first we shall see how aldi gates

are produced see this aldehydes are

obtained when a mixture of calcium salt

of a carboxylic acid here i have taken

uh acetic acid okay so calcium salt of

this acetic acid is treated with calcium

formate okay calcium salt of formic acid

right so now when these two are

subjected to dry distillation it's

possible to get acetaldehyde okay so

this is calcium acetate and how how

there will be removal of two okay like

here also c

c

all right so we'll be getting

acetaldehyde two molecules of acetate

ch3cho

okay plus calcium carbonate all right so

this is how we are preparing

acetaldehyde from calcium acetate and

calcium forming next we shall see how to

prepare ketones okay see ketones can be

obtained by the dry distillation of

calcium salt of carboxylic acid again so

i've taken acetic acid so calcium salt

of this uh

acetic acid that is calcium acetate when

it is undergoing dry distillation it

produces ketone okay so how it's formed

c h3

ch3

c double point o just like the previous

one here also there will be a removal of

calcium carbonate

finally we shall see how this

all gates are produced from the nitrous

okay this preparation is otherwise

called a stiffens reduction what happens

in stiffness reduction is the partial

reduction of a cyanide into an amine

chloride by zinc standard chloride and

hcl at chrome temperature is called

stiffness reduction okay so the immune

hydrochloride on boiling with water gets

catalyzed to get aldehyde okay so let me

take an example methyl sine cyanides are

nitrile okay in a cs3c triple bond and

when it is undergoing reduction okay in

the presence of hcl at uh 290 to 295

kelvin in the presence of ether this

methyl cyanide will be getting converted

to acid acetyl domain okay acetone you

mean hydrochloride ch3 so it's an adduct

ch3 ch

double bond nh

hcl okay so this this gets

get added up to the methyl cyanide and

finally we are getting an uh adduct and

this is called as

epa

acetyl dimin acetyl the mean

hydrochloride okay hydrochloride

this again

uh when it is boiled with water when it

is boiled with water we get acetaldehyde

cho

plus ammonium chloride again h4

okay this is how we are preparing

acetaldehy or aldehyde from the nitrous

buds difference reduction understood

you might have understood all the

preparation of allocates and ketones in

this session i shall meet you with

another important topic in a short

period until then it's santera signing

off from me thanks for watching

you