Exercise 10: ALDEHYDES AND KETONES Flashcards by Blueberry Cheesecake

organic compounds both containing a carbonyl functional group
(C=O)

 has two more bonds that may be occupied by hydrogen or alkyl or
aryl substituents

ALDEHYDES AND KETONES

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if one R is hydrogen =
If both R are neither H =

aldehyde

ketone

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naturally occurring
organic
compounds, often
combined with
other functional
groups

 can be found in
plants, animals,
and even
microorganisms

ALDEHYDES AND KETONES

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(cinnamon bark)

cinnamaldehyde

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(musk deer)

muscone

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(vanilla bean)

vanillin

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(male sex hormone)

testosterone

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(lemongrass)

citral

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(female sex hormone)

progesterone

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(a fungal toxin)

helminthosporal

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(spearmint & caraway

carvone

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(adrenal hormone)

cortisone

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camphor tree)

camphor

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largely responsible some of the shared physicochemical
properties of aldehydes and ketones

a - group because of the greater
electronegativity of the oxygen

as a result of this polarization, the carbonyl group is
susceptible to

CARBONYL GROUP

highly polarized

nucleophilic attack

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commonly
synthesized in the
laboratory through

of alcohols

oxidation reaction

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are oxidized to
aldehydes while

are oxidized to ketones

primary alcohols

secondary alcohols

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TEST FOR CARBONYL GROUP

• 2,4-DNPH TEST
• SODIUM BISULFITE TEST

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2,4-DNPH (BRADY’S) TEST results

acetone

clear orange solution

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2,4-DNPH (BRADY’S) TEST results

acetophenone

yellow-orange precipitate

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2,4-DNPH (BRADY’S) TEST results

acetone

Clear orange soln

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2,4-DNPH (BRADY’S) TEST results

formaldehyde

reddish orange precipitate

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detect the presence of carbonyl
group

2,4-DNPH (BRADY’S) TEST

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 reagent: Brady’s reagent

named after Oscar Brady

(2,4-
dinitrophenylhydrazine in methanol);

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positive result: 2,4-DNPH (BRADY’S) TEST

yellow to orange precipitate for
aldehydes

red to orange precipitate for
ketones

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condensation reaction; aldehyde reacts with 2,4-DNPH to forms an while ketone reacts with to form a

aldehyde 2,4- dinitrophenylhydrazone ketone 2,4-dinitrophenylhydrazone

SODIUM BISULFITE TEST results acetaldehyde

white precipitate

SODIUM BISULFITE TEST results acetone

white precipitate

used to determine if a compound is an aldehyde or an aliphatic methyl ketone

SODIUM BISULFITE TEST

 reagent: sodium bisulfite

SODIUM BISULFITE TEST

SODIUM BISULFITE TEST  positive result:

white precipitate

the reacts with sodium bisulfite by breaking the pi bond of the carbonyl group through - attack; the - then attaches to the original carbonyl group to form the bisulfite addition compound

aldehyde or the methyl ketone nucleophilic bisulfite ion

with ketones, only will yield positive result (ketones with - groups sterically hinders the bisulfite ion in attaching to the carbonyl group)

methyl ketones, bulky

SCHIFF’S TEST resuts acetophenone

Clear colorless soln

SCHIFF’S TEST resuts acetone

clear colorless solution

SCHIFF’S TEST resuts acetophenone

clear colorless solution

SCHIFF’S TEST resuts benzaldehyde

magenta red solution

SCHIFF’S TEST resuts formaldehyde

magenta red solution

used to differentiate aldehydes from ketones

SCHIFF’S TEST

 reagent: Schiff’s reagent (); named after Hugo Schiff

sodium bisulfite with the organic dye pararosaniline hydrochloride

SCHIFF’S TEST  positive result:

magenta red solution

oxidation of aldehyde to carboxylic acid; reaction involved is the same as explained in the sodium bisulfite test  some ketones may also produce a color change but not a magenta red color

SCHIFF’S TEST

TOLLENS’ TEST results acetone

clear colorless solution

TOLLENS’ TEST results 5% glucose

silver mirror precipitate

TOLLENS’ TEST results benzaldehyde

turbid gray solution

TOLLENS’ TEST results formaldehyde

silver mirror precipitate

used to differentiate aldehydes from ketones

TOLLENS’ TEST

 reagent: Tollens’ reagent (to render solution colorless); named after Bernhard Tollens

silver nitrate with sodium hydroxide and excess ammonium hydroxide

TOLLENS’ TEST  positive result:

silver mirror precipitate

oxidation of aldehyde to carboxylic acid; the - is reduced to silver while producing the carboxylic acid-ammonium salt product  can detect both aliphatic and aromatic aldehydes

ammoniacal silver nitrate Tollens’ test

FEHLING’S TEST acetone

clear blue solution

FEHLING’S TEST 5% glucose

brick red precipitate

FEHLING’S TEST benzaldehyde

clear blue solution

FEHLING’S TEST formaldehyde

brick red precipitate

used to differentiate aldehydes from ketones

Schiff’s Test Fehling’s Test

 reagent: Fehling’s reagent (a solution of Fehling’s A prepared by mixing and Fehling’s B prepared by mixing named after Hermann von Fehling

concentrated sulfuric acid with aqueous solution of copper sulfate pentahydrate sodium hydroxide with potassium tartrate);

FEHLING’S TEST  positive result:

brick red precipitate

oxidation of aldehyde to carboxylic acid; aldehyde reduces the cupric ions in complex with- to cuprous ions; forming cuprous oxide Fehling’s test is very specific to produce the positive result with an- ; - and - give a negative result with this test

tartrate ions aliphatic aldehyde aromatic aldehydes, ketones

TEST FOR METHYL KETONES

• SODIUM NITROPRUSSIDE TEST • IODOFORM TEST

SODIUM NITROPRUSSIDE TEST results acetone

wine red solution

SODIUM NITROPRUSSIDE TEST results ethyl methyl ketone

wine red solution

function of test: identify the presence of an acetyl group (CH3C=O)

SODIUM NITROPRUSSIDE TEST

 reagent: sodium nitroprusside

SODIUM NITROPRUSSIDE TEST

SODIUM NITROPRUSSIDE TEST  positive result:

wine red solution

in presence of alkali, a methyl ketone such as acetone is converted to - ion which reacts with nitroprusside ion [Fe(CN)5NO]2- to give

CH3C=OCH2- , highly colored ion [Fe(CN)5NOCH2C=OCH3]2-

is also used in clinical tests to detect the presence of acetone in urine

sodium nitroprusside test

IODOFORM TEST results acetone

canary yellow precipitate

IODOFORM TEST results ethyl methyl ketone

canary yellow precipitate

IODOFORM TEST results ethyl acetate

clear colorless solution

used to identify methyl ketones or secondary alcohols adjacent to a methyl group

Iodoform test

 reagent: Wagner’s reagent ()

iodine in potassium iodide in sodium hydroxide

IODOFORM TEST  positive result:

canary yellow precipitate

solution of I2 in KI in sodium hydroxide reacts only for compounds with the structure - to form iodoform

RCH(OH)CH3 or RC=OCH3

this test is very specific test and it does not work for all ketones and does not work also for water-insoluble compounds

IODOFORM TEST

TEST FOR SACCHARIDES

• MOLISCH’S TEST • BIAL’S TEST

MOLISCH’S TEST 5% glucose

purple ring at junction of two layers

MOLISCH’S TEST 5% starch

purple ring at junction of two layers

MOLISCH’S TEST benzaldehyde

dark red solution

general test for saccharides

MOLISCH’S TEST

 reagent: Molisch’s reagent ( named after Hans Molisch

10% α-naphthol in 95% ethanol);

MOLISCH’S TEST  positive result:

purple ring at junction of two layers

Molisch reagent dehydrates pentoses to - and hexoses to -; furfural compounds further react with- producing a purple- colored product

furfural derivatives 5-hydroxymethyl furfural derivatives α-naphthol

 yield rapid results while react slower

monosaccharides disaccharides

BIAL’S TEST results 5% ribose

dark blue solution

BIAL’S TEST results 5% glucose

clear golden brown solution

specific test for pentoses (or carbohydrates with five carbon chain)

BIAL’S TEST

 reagent: Bial’s reagent (; named after Manfred Bial

orcinol, hydrochloric acid and ferric chloride)

BIAL’S TEST  positive result:

blue solution

Bial’s reagent dehydrates pentoses to form -; the furfural further reacts with - and the - present in Bial’s reagent producing a blue product

furfural orcinol, ferric ion

Exercise 10: ALDEHYDES AND KETONES Flashcards

(88 cards)