Test for aldehydes and Ketones
Summary
TLDRThis 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
🔍 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.
🧪 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.
🌐 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.
Mindmap
Keywords
💡Carbonyl functional group
💡Aldehydes
💡Ketones
💡2,4-Dinitrophenylhydrazine test
💡Iodoform test
💡Tollen's test
💡Skifl's test
💡Chromic acid test
💡Fehling's test
💡Sodium bisulfite test
💡Janowski reaction
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
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