Test for aldehydes and Ketones

Summary

This video explores various chemical tests for identifying aldehydes and ketones, key organic compounds with a carbonyl group. It covers general tests like the 2,4-dinitrophenylhydrazine test, and specific tests including the iodoform test, Tollens' test, Schiff test, and chromic acid test for aldehydes, and sodium bisulfite, meta-dinitrobenzene, and sodium nitroprusside tests for ketones. The script also offers practical tips for conducting these tests and highlights the importance of preparation and observation in chemical analysis.

Takeaways

• 🧪 Aldehydes and ketones are organic compounds with a carbonyl group (C=O), distinguished by the presence of a hydrogen or R group bonded to the carbonyl carbon.
• 🌿 Aldehydes and ketones occur naturally, such as cinnamaldehyde in cinnamon bark and vanillin in vanilla.
• 💡 The 2,4-dinitrophenylhydrazine (Brady's) test is a general test for both aldehydes and ketones, producing a yellow or orange precipitate.
• 🔍 The iodoform test is specific for aldehydes with an alpha-hydrogen, like acetaldehyde, and some ketones, resulting in a yellow precipitate.
• 📚 Specific tests for aldehydes include the Tollens' test, Schiff test, chromic acid test, and Fehling's test, each producing a distinct reaction.
• 🔬 The Tollens' test uses silver nitrate and sodium hydroxide to produce a silver mirror when an aldehyde is present.
• 🌸 Schiff's test involves a color change to pink upon reaction with aldehydes, indicating the formation of an aldemine group.
• 🍏 The chromic acid test oxidizes aldehydes to carboxylic acids, changing the solution color to green.
• 🍇 Fehling's test produces an orange to red precipitate when an aldehyde reacts with copper(II) ions.
• 🧪 Sodium bisulfite test is used for ketones, forming a crystalline bisulfite adduct.
• 🌈 The meta-dinitrobenzene test is specific for ketones with an alpha-methyl group, resulting in a purple color due to the Janowski reaction.
• 🔴 Sodium nitroprusside test is another specific test for ketones, forming a deep red complex in alkaline conditions.

Q & A

What are the main differences between aldehydes and ketones?

Aldehydes have a hydrogen atom bonded to the carbonyl carbon, while ketones have two R groups (alkyl or aryl groups) bonded to the carbonyl carbon.

What is the 2,4-dinitrophenylhydrazine test and what does it indicate?

The 2,4-dinitrophenylhydrazine test is a general test for aldehydes and ketones. It indicates the presence of a carbonyl group, resulting in a yellow precipitate for aldehydes and an orange precipitate for ketones with a conjugated C=C-O group.

What is the significance of the orange precipitate in the 2,4-dinitrophenylhydrazine test?

An orange precipitate indicates that the carbonyl compound has a C=C-O group that is conjugated with another C=C bond.

What are some natural occurrences of aldehydes and ketones mentioned in the script?

Cinnamaldehyde in the bark of the cinnamon tree, vanillin in vanilla, and acetone used as a nail polish remover are mentioned as natural occurrences of aldehydes and ketones.

What is the iodine test and which compounds give a positive result?

The iodine test, also known as the iodoform test, is a special test for carbonyl compounds containing an alpha hydrogen. Compounds like acetaldehyde, methyl ethyl ketone, acetone, and some alcohols like isopropyl alcohol and ethyl alcohol give a positive result.

What is the Tollens' test and how does it work?

The Tollens' test is a specific test for aldehydes. It involves the oxidation of aldehydes to carboxylic acids by silver oxide, which is reduced to elemental silver, forming a silver mirror on the inner surface of the test tube.

What is the Schiff test and how does it indicate the presence of an aldehyde?

The Schiff test uses Schiff reagent, which is an aqueous solution of peroxaniline hydrochloride. Aldehydes react with this reagent to form a pink color, indicating their presence.

What happens in the Chromic Acid test for aldehydes?

In the Chromic Acid test, the powerful oxidizing agent chromic acid oxidizes aldehydes to carboxylic acids and is reduced to chromium(III), which forms a green chromium(III) sulfate.

What is the Felling's test and what does the formation of an orange to red precipitate indicate?

The Felling's test is specific for aldehydes. The formation of an orange to red precipitate indicates the oxidation of the aldehyde to a carboxylic acid and the reduction of the copper complex to copper(I) oxide.

How does the Sodium Bisulfite test work for ketones?

In the Sodium Bisulfite test, ketones react with sodium bisulfite to form a crystalline product known as a bisulfite adduct.

What is the Meta-dinitrobenzene test and what color change does it produce?

The Meta-dinitrobenzene test is specific for ketones with an alpha-methyl group. It produces a purple color due to the Janowski reaction, forming a Meisenheimer complex.

What is the Sodium Nitroprusside test and what color change does it indicate for ketones?

The Sodium Nitroprusside test is a specific test for ketones. The formation of a deep red color indicates the reaction of ketones with nitroprusside in the presence of an alkali.

Outlines

00:00

🔍 Introduction to Carbonyl Group Testing

This paragraph introduces the topic of the video, which is the testing of carbonyl functional groups found in aldehydes and ketones. It explains that these organic compounds have a carbonyl group (C=O) and differ in the type of atoms bonded to the carbonyl carbon. Aldehydes have a hydrogen atom, while ketones have two R groups. Examples of these compounds in nature are given, such as cinnamaldehyde in cinnamon bark and vanillin in vanilla. The paragraph also lists various tests for these compounds, including the 2,4-dinitrophenylhydrazine test, iodoform test, and specific tests like the Tollens' test, Schiff test, chromic acid test, and Fehling's test for aldehydes, and sodium bisulfite, meta-dinitrobenzene, and sodium nitroprusside tests for ketones. The video then demonstrates the 2,4-dinitrophenylhydrazine test, which produces a yellow precipitate with aldehydes and an orange precipitate with ketones, indicating the presence of a conjugated C=C-C=O group.

05:02

🧪 Demonstration of Aldehyde Tests

This paragraph details the process of conducting specific tests for aldehydes. The Tollen's test is demonstrated first, where a silver mirror forms upon the addition of an aldehyde to a solution of silver oxide, indicating the aldehyde's oxidation to a carboxylic acid. The Schiff test is also described, using a reagent that turns pink upon reaction with aldehydes, forming an aldemine group that further reacts with bisulfite to produce a purple adduct. The chromic acid test is mentioned, where chromic acid oxidizes aldehydes to carboxylic acids, turning the solution green due to the formation of chromium-3 sulfate. Lastly, the Fehling's test is referenced, which produces an orange to red precipitate, indicating the oxidation of aldehydes to carboxylic acids and the reduction of copper complexes to copper(II) oxide.

10:03

🌐 Ketone Specific Tests and Conclusion

This paragraph focuses on tests specific to ketones, starting with the sodium bisulfite test, which forms a crystalline bisulfite adduct upon the addition of a ketone. The meta-dinitrobenzene test is then described, which results in a purple color due to the Janowski reaction, specific to ketones with an alpha-methyl group. The paragraph also covers the sodium nitroprusside test, where ketones react to form a blood-red complex in alkaline conditions. The video concludes by thanking the Patreon supporters for their financial contributions to enable the experiments and encourages viewers to subscribe, watch for notifications, and join the Discord server for more interaction.

Keywords

💡Carbonyl functional group

The carbonyl functional group is a key structural feature in organic chemistry, consisting of a carbon atom double-bonded to an oxygen atom (C=O). It is central to the video's theme as it defines the class of compounds being discussed: aldehydes and ketones. In the script, this group is the basis for the various tests performed to identify aldehydes and ketones.

💡Aldehydes

Aldehydes are a type of organic compound that contains a carbonyl group with at least one hydrogen atom attached to the carbonyl carbon. They are one of the two main classes of compounds discussed in the video. An example given is cinnamaldehyde found in cinnamon bark, illustrating their natural occurrence.

💡Ketones

Ketones are organic compounds with a carbonyl group where both bonds to the carbonyl carbon are to other carbon atoms (R groups). The video explores various tests to identify ketones, emphasizing their importance in organic chemistry and their presence in substances like vanillin and acetone.

💡2,4-Dinitrophenylhydrazine test

This is a general test for aldehydes and ketones mentioned in the script. It involves the reaction of the carbonyl group with 2,4-dinitrophenylhydrazine to form a yellow precipitate, indicating the presence of aldehydes or ketones. This test is significant as it provides a visual confirmation of these functional groups.

💡Iodoform test

The iodoform test is highlighted in the script as a special test for carbonyl compounds with an alpha-hydrogen. It involves the formation of a yellow precipitate of iodoform, indicating the presence of a specific structural feature in the compound. This test is used to differentiate aldehydes from ketones.

💡Tollen's test

Tollen's test, also known as the silver mirror test, is a specific test for aldehydes as described in the script. It involves the oxidation of aldehydes to carboxylic acids, resulting in the formation of a silver mirror on the inner surface of the test tube. This test is crucial for confirming the presence of aldehydes.

💡Skifl's test

Skiff's test is another specific test for aldehydes mentioned in the script. It uses a reagent that changes color in the presence of aldehydes, forming a pink color upon reaction. This test is significant for its simplicity and visual indication of aldehyde presence.

💡Chromic acid test

The chromic acid test is described in the script as a specific test for aldehydes. It involves the oxidation of aldehydes by chromic acid, resulting in a color change to green due to the formation of chromium-3 sulfate. This test is important for its distinct color change as an indicator of aldehydes.

💡Fehling's test

Fehling's test is mentioned as a specific test for aldehydes. It involves the use of Fehling's reagent, which forms a deep blue copper(I) tartrate complex. Upon the addition of an aldehyde, this complex is reduced, resulting in an orange to red precipitate. The test is highlighted for its distinctive color change.

💡Sodium bisulfite test

The sodium bisulfite test is described in the script as a test for ketones. It involves the reaction of ketones with sodium bisulfite to form a crystalline product, indicating the presence of a ketone group. This test is significant as it provides a clear visual result for the identification of ketones.

💡Janowski reaction

The Janowski reaction is mentioned in the context of the metadinitrobenzene test for ketones. It involves the reaction of 1,3-dinitrobenzene with ketones containing an alpha-methyl group to form a purple color, known as the mesenheimer complex. This reaction is key to identifying specific ketones as described in the script.

Highlights

Introduction to carbonyl functional group tests for aldehydes and ketones.

Explanation of the structure of aldehydes and ketones.

Examples of aldehydes and ketones found in nature.

Description of the 2,4-dinitrophenylhydrazine test for aldehydes and ketones.

Observation of yellow and orange precipitates in the 2,4-dinitrophenylhydrazine test.

Brady's test and its significance in identifying carbonyl compounds.

Tips on performing the 2,4-dinitrophenylhydrazine test effectively.

Iodoform test for carbonyl compounds containing an alpha hydrogen.

Demonstration of the iodoform test and the formation of a yellow precipitate.

Tolerance test as a specific test for aldehydes.

Preparation and reaction of the tolerance reagent with aldehydes.

Skiff test for aldehydes and the formation of a pink color.

Chromic acid test for aldehydes and the observation of a green color.

Fellings test for aldehydes and the formation of an orange-red precipitate.

Sodium bisulfite test for ketones and the formation of a crystalline product.

Metadinitrobenzene test for ketones and the Janowski reaction.

Sodium nitroprusside test for ketones and the formation of a deep red color.

Acknowledgment of Patreon supporters for their financial contributions.

Transcripts

[Music]

hello friends

in this video we will perform various

tests for carbonyl functional group

that is aldehydes and ketones

aldehydes and ketones are organic

compounds

with the c double bond o carbonyl

functional group and when one of the

bond with the carbonyl carbon is

hydrogen it is an aldehyde

when both the bonds with the carbonyl

carbon is an r group

that is a ketone r group can be

aliphatic and aromatic

aldehydes and ketones can be found in

various forms in nature like

cinnamaldehyde in the bark of cinnamon

tree

vanillin in vanilla and even acetone

being used as a nail polish remover

the various tests for aldehydes and

ketones are

the 2 4 dinitrophenyl hydrazine test

which is a general test for aldehydes in

ketones

ioda form test is not specific to

aldehydes and ketones

but most ketones with a ch3 group

attached to the carbonyl carbon

like acetone and methyl ethyl ketone

gives positive result

acetaldehyde is the only aldehyde giving

positive iodiform test

secondary alcohols also give positive

result specific tests for aldehydes are

the tolerance test skiff test chromic

acid test

and the failings test the test for

ketones are

the sodium bisulfite test

metadinitrobenzene test

and sodium nitrofrucide test

let us begin with the 2 4

dinitrophenylhydrous intest

this is a general test given by both

aldehydes and ketones

here i have an aldehyde and a ketone

sample in two test tubes

into the sample i add about 1 to 2

milliliters of 2 4 dinitrophenyl

hydrazine reagent solution

immediately on adding the reagent you

see a yellow colored precipitate that

has formed

you have a similar result when you add

the reagent to the ketone solution

in the second reaction we got an orange

colored precipitate

orange precipitate is obtained from

carbonyl compounds in which c double

bond o group

is conjugated with a c double bond c

this test is also called bradys test

and the brady's reagent is the 2 4 dnp

solution made by dissolving the solid

in concentrated sulphuric acid and

adding

ethanol so what happened here is 2 for

dinitrophenyl hydrogen is getting

converted to

dinitrophenyl hydrazone as the

precipitate looked beautiful i decided

to make more of it by adding the reagent

to aldehyde and ketone solutions in the

conical flask

meanwhile i will give you some tips on

the reaction that you should be careful

about

some aliphatic ketones may not give a

precipitate with two for dinitrophenyl

hydrazone

in such case reverse addition that is

addition of the solution of the carbonyl

compound to the two for dnp reagent

gives better result

it is actually advisable to do a blank

test which i did not do in this case

it is purely the two for dnp reagent

alone without the carbonyl compound

some amines like aniline may give a

precipitate of the salt of amine with

acid

used in the preparation of 2 for dnp

reagent however this precipitate is

soluble in water

another thing is sometimes 2 4

dinitrophenyl hydrogen itself can

precipitate out as an orange solid

which is soluble in dilute sulfuric acid

worth two for dnp hydrozone

is not soluble in acid

iodoform test also known as hypo iodide

test

this test is a special test given by

carbonyl compounds containing an alpha

hydrogen

first of all take 1 to 2 ml of the

organic compound in a test tube

we then add an equal amount of 3 molar

sodium hydroxide solution

after adding the sodium hydroxide

solution mix it well

and then we start adding the iodine

solution

with the help of a dropper this solution

was prepared by dissolving around 12.7

grams of elemental

iodine in a saturated solution of

potassium iodide containing 25 grams of

it distilled water was then added to

make the stock solution

continue adding the iodine solution to

the mixture until we attain a point

where the dark color of the iodine

persists in the solution

even after mixing

when we have attained that point we will

then keep the test tube

in boiling water bath for one to two

minutes

a yellow precipitate of iodoform is

formed

this indicates the presence of ch3c

double bond o

group in the compound it's given by

acetaldehyde

methyl ethyl ketone acetone and some

alcohols like isopropyl alcohol and

ethyl alcohol

tolerance test this is a specific test

for aldehyde

first of all let us make the tolerance

reagent for that

we need a solution of silver nitrate

take about 3 milliliters of silver

nitrate solution which has a

concentration of 0.1 normality

in a test tube then we add

3 molar sodium hydroxide solution to the

silver nitrate

on adding the sodium hydroxide a black

to brown colored precipitate

of silver oxide is immediately formed in

the test tube

now we take the ammonia solution and

start adding it

to the precipitate of silver oxide

you see that the precipitate starts to

dissolve

and the solution becomes clear what's

happening here

is silver oxide is forming a complex

with

ammonia this is the tolerance reagent

tolerance reagent have to be prepared

freshly each time for use

as it is not stable for long time

storage

now for the test we take 1 to 2 ml of

the freshly prepared tolerance reagent

in a test tube

then we add the organic compound into

the

test tube the organic compound here

is an aldehyde when we add it

we get a gray to black colored

precipitate

then we keep the test tube in hot

boiling water bath

for three to four minutes appearance of

a silver mirror can be seen

what's happening here is aldehydes are

oxidized to their corresponding

carboxylic acids

while the silver oxide is getting

reduced from plus one to

elemental form i just did it again

by scaling the reaction a little bit and

i was able to get a nice silver mirror

and i took a picture of it skiff test

it is also a specific test for aldehydes

skiff reagent is an aqueous solution of

periosteal in hydrochloride dye

which is decolorized by adding sodium

sulphite

the peroxaneline reacts with bisulfite

to form decolorized addict

when skiff reagent is added to the

organic compound

a pink color is obtained

when aldehyde groups react with the

amine group of the dye

it forms aldemine group the aldemine

group

is an excellent electrophile and it

undergoes

further reaction with the bisulfite ion

forming a purple colored

bisulfide adduct this is the reaction

you can actually see three aldehyde

groups react with the three sulfonated

amine groups to form the adduct

chromic acid test this is another test

specific to aldehydes chromic acid

reagent was prepared by adding about two

milliliters of concentrated sulphuric

acid

to 0.5 grams of potassium dichromate

the resultant solution will be deep red

in color

now let us do the test few amount of

chromic acid reagent was taken with a

glass dropper and was transferred to a

test tube containing the organic

compound

appearance of a green color is observed

what's happening here is chromic acid

being a powerful oxidizing agent

oxidizes the aldehyde to the carboxylic

acid

and in turn reduces to chromium 3 plus

which reacts with the sulfate ion to

form chromium-3 sulfate which is the

green color

now for the phalanx test which is

specific for aldehyde

i have a separate video on preparation

of the felling's reagent

i will put a link to that in the

description felling's reagent have to be

prepared fresh before its use

for that equal volume of felling's hair

solution that is dilute copper to

sulphate solution

and fillings b solution is to be poured

together fillings b two solution

is a alkaline solution of sodium

potassium tartarate

on mixing these two compounds a deep

blue colored solution is formed which is

the

best tartrate complex of copper two plus

and this is our fillings reagent

now for the test the organic compound is

added into the prepared fillings reagent

and after adding we keep it in a hot

water bath for few minutes

after some time we observe this orange

to

red colored precipitate that is formed

what's happening here is the bistart

rate of

copper complex is an oxidizing agent

which

oxidizes the aldehyde to the carboxylic

acid and in turn gets reduced to form

the copper 2

oxide

sodium bisulfite test for this test

we need a saturated solution of sodium

bisulfite

into that we add the organic compound

on adding that it forms a crystalline

product

which is a bisulfite addict and

the reaction is shown above

metadinitrobenzene test this test is

specific for ketones

in this test i use the metadianatro

benzene

that is one three dinitrobenzene i have

a video for this synthesis of this

compound

i will put a link to that in the

description start by adding the solid

metadinitrobenzene to the organic

compound

then we add few milliliters of the three

molar sodium hydroxide solution

into that this makes the solution

alkaline immediately you see a purple

color

forming what is happening here is called

the janowski reaction

where the 1 3 dinitrobenzene reacts with

the ketone

group containing an alpha methyl group

to form the mesenheimer complex

the same test was repeated with methyl

ethyl ketone

and as we know that methyl ethyl ketone

is insoluble with water

this purple color was observed at the

junction between the two layers

the last test is the sodium nitro

crucite test which is also a specific

test for ketone

for this test we take a few milliliters

of the sodium nitro proside solution in

a test tube

then we add the organic compound into it

after that we add few milliliters of the

three molar sodium hydroxide solution

immediately you observe the formation of

a deep red

color what's happening here is in the

presence of alkali

ketones react with nitro procyte to form

blood red colored complex

i would like to take this opportunity to

thank my patreon supporters who have

financially supported me

so that i could get the materials

required for doing all these experiments

thank you so much for watching this

video if you loved the contents of this

video

do hit the subscribe button and the bell

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also if you want to join my discord

server i will put a link to that in the

description