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Carbonyl Compounds Pharmaceutical Organic Chemistry-I Colored Important Notes 2nd Semester B.Pharmacy Lecture Notes,BP202T Pharmaceutical Organic Chemistry I,BPharmacy,Handwritten Notes,Important Exam Notes,BPharm 2nd Semester,

Carbonyl Compounds Pharmaceutical Organic Chemistry-I Colored Important Notes

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Carbonyl Compounds Pharmaceutical Organic Chemistry-I Colored Important Notes

Pharmaceutical Organic Chemistry-I ( BP202T) Carbonyl Compounds Colored Notes

 

BP202T (Carbonyl Compounds)
1 | P a g e
Carbonyl Compounds (Aldehyde and Ketone)
 The ketones are called Symmetrical ketones or Unsymmetrical Ketones according as
the two alkyl groups attached to the carbonyl group are the same or different.
 We assume that both the carbon and oxygen of the carbonyl group are sp2
hybridized.
 One sp2
orbital of carbon overlaps with a sp2
orbital of oxygen to form a σ (sigma) bond,
while the residual p orbitals of the two atoms overlap in a sidewise fashion to form a π
(Pi) bond.
 Therefore, a carbonyl double bond is, in fact, made of one σ (sigma) bond and one π
(Pi) bond.
 The polarization of the bond in carbonyl double bond differs from the carbon-carbon
double bond of alkenes which is non-polar.
 High dipole moment 2.3 to 2.8 D
 The electron diffraction and spectroscopic studies reveal that the carbon, oxygen and the
other two atoms or groups attached to carbonyl carbon lie in the same plane and have
bond angles roughly 120°.
METHODS OF PREPARATION
1. Direct Oxidation of Alcohols
2. Catalytic Dehydrogenation of Alcohols
3. Oxidation of Alkenes with Ozone
4. Hydration of Alkynes
5. Hydrolysis of gem-Dihalides
6. Pyrolysis of Salts of Carboxylic acids
7. Catalytic Decomposition of Carboxylic acids
8. Stephens reduction of Nitriles
9. Rosenmund reduction of Acid chloride
10. From Grignard Reagents
11. From Acetoacetic esters
BP202T (Carbonyl Compounds)
2 | P a g e
Direct Oxidation of Alcohols
 Aldehydes are obtained by the direct oxidation of primary alcohols.
 The oxidants most commonly used are potassium dichromate (K2Cr2O7) in
sulphuric acid or potassium permanganate in alkaline solution.
 The aldehydes have lower boiling points than the corresponding alcohols.
 Ketones also may be prepared by oxidation of secondary alcohols with potassium
dichromate in sulphuric acid.
 Ketones, unlike aldehydes, are not easily oxidized further (carbon-carbon bonds
must be broken), and can be obtained in high yield by this method.
Synthesis of Phenolic aldehydes by Riemann Tiemann
reaction
2. Catalytic Dehydrogenation of Alcohols
3. Oxidation of Alkenes with Ozone
 Some aldehydes and ketones can be obtained by the oxidation of alkenes
with ozone.
 The ozonides formed are not isolated since they are often explosive in the dry
state.
 Instead the reaction mixture is treated under reducing conditions (Zn + acetic
acid; or Pd, H,) to yield aldehydes and ketones.
BP202T (Carbonyl Compounds)
3 | P a g e
4. Hydration of Alkynes
 Acetaldehyde is made by hydration of acetylene in the presence of a solution
of mercuric sulphate (Hg2+) and sulphuric acid (H2SO4).
5. Hydrolysis of gem-Dihalides
 Aldehydes can be prepared by the alkaline hydrolysis of gem-dihalides in which two
halogen atoms are attached to the terminal carbon atom.
 The halogen atoms are first replaced by OH groups and the unstable glycol splits out a
molecule of water to form an aldehyde.
Ketones are prepared by the hydrolysis of such gem-dihalides in which the two
halogens are attached to any carbon atom other than the terminal carbon atom.
 Ketones are prepared by the hydrolysis of gem-dihalides in which the two
halogens are attached to any carbon atom other than the terminal carbon
atom.
6. Pyrolysis of Salts of Carboxylic acids
 Aldehydes and ketones can be prepared by thermal decomposition
(pyrolysis) of suitable calcium salts of carboxylic acids.
 This method is mainly valuable for synthesizing symmetrical ketones.
BP202T (Carbonyl Compounds)
4 | P a g e
 Unsymmetrical ketones are obtained by heating a mixture of calcium salts of
two carboxylic acids (excluding formic acid).
 If one of the two calcium salts taken is derived from formic acid, an aldehyde
is obtained.
7. Catalytic Decomposition of Carboxylic acids
 Simple ketones can be prepared in very good yield (90%) by passing
the vapor of a suitable carboxylic acid (other than formic acid) over
the heated oxide of manganese or thorium.




(
)
 Unsymmetrical ketones are obtained by passing a mixture of vapor of
acids other than formic acid.
 Aldehydes are prepared by passing a mixture of the vapour of formic acid and any
other acid over the heated catalyst.
8. Stephens reduction of Nitriles
 It is a useful procedure to prepare aldehydes.
 Not applicable to the synthesis of ketones.
 Alkane-nitriles are first reduced in ether solution by hydrogen chloride gas (HCl)
and stannous chloride (SnCl2) at room temperature.
 The aldimine hydrochloride produced is filtered off and subsequently hydrolyzed
with warm water to produce aldehyde.
BP202T (Carbonyl Compounds)
5 | P a g e
9. Rosenmund reduction of Acid chloride
 Aldehydes can be prepared by the reduction of acid chlorides with H2 gas in the
presence of a palladium catalyst supported over barium sulphate at 140°C.
 Barium sulphate poisons the palladium catalyst which is deactivated so as not
permit the further reduction of the aldehyde product.
 This is called Rosenmund reduction.
 Formaldehyde cannot be made by this method because formyl chloride (HCOCl) is
very unstable at ordinary temperatures.
 According to a more recent method, an acid chloride can be reduced to aldehydes
using a modified hydride reagent lithium tri-t-butoxyaluminium hydride.
 This reaction is preferred to Rosenmund reaction as it proceeds at low temperature
and the reducing agent is easy to prepare.
 It may be noted that LiAlH4 alone would have reduced the aldehyde product to
primary alcohol.
10. From Grignard Reagents
 Aldehydes can he synthesized by the action of Grignard reagents with excess of formic ester.
 Ketones are obtained by the addition of Grignard reagents to acid chlorides and
subsequent acid hydrolysis.
 Recently organo-cadmium compounds have been used for the preparation of ketones
from acid halides, in preference to Grignard reagents, since they do not react
further with ketone product to form alcohol. (R
’COCl+RCdCl R
’COR+CdCl5)
BP202T (Carbonyl Compounds)
6 | P a g e
11. From Aceto-acetic esters
 Alkyl derivatives of aceto-acetic ester CH3COCH2COOC2H5 upon hydrolysis with
dilute alkalis give the corresponding ketones.
 ⏟






Physical Properties
 Formaldehyde, the first member of the aldehyde series, is a gas at ordinary
temperature.
 The next nine members (C3-C11) are liquids
 Higher members are solids.
 Ketones up to C11 are colourless mobile liquids, and the higher members are
solids.
 Lower aldehydes possess an unpleasant odour but as we go up the series the smell
becomes more and more fruity.
 Ketones are generally pleasant smelling liquids.
 The higher aldehydes (C3-C13) and ketones are used in perfumery.
 The first few members of the aldehyde and ketone series are soluble in water but the
solubility falls rapidly with the increase in the size of the hydrocarbon groups attached
to carbonyl group.
 Those with five or more carbon atoms are sparingly soluble or insoluble.
 The solubility of aldehydes and ketones is accounted for by the electrostatic
attractions between the polar carbonyl group and the water dipoles.
 The boiling points of carbonyl compounds are higher than the non-polar
alkanes of comparable molecular weight.
 The dipole-dipole attraction between molecules of aldehydes or ketones is
weaker than the analogous hydrogen bonding attraction between alcohol
molecules.
 The boiling points of the carbonyl compounds are lower than those of
corresponding alcohol.
 In general melting points, boiling points of the members of both the aldehyde and
ketone series show regular increase as we ascend the respective series.
 Carbon-oxygen bond in aldehydes and ketones is polar.
BP202T (Carbonyl Compounds)
7 | P a g e
Relative Reactivity of Aldehydes and Ketones
 The carbonyl group in ketones being influenced by two alkyl groups is less reactive
than in aldehydes where the carbonyl group is under the influence of one alkyl group
only.
 Formaldehyde having no alkyl group on carbonyl carbon is more reactive than all
other aldehydes which are again more reactive than the ketones.
 As we go higher in the series of carbonyl compounds, reactivity is progressively
decrease.
Electromeric effect
 This effect is very helpful in explaining polarization produced in a substrate
molecule containing multiple bonds.
 When a double or a triple bond is exposed to attack by an electrophilic reagent, a
pair of bonding electrons is transferred completely from one atom to the other.
 The atom that takes charge of the eletrone-pair becomes negatively charged and
the other positively charged.
 “A temporary effect which causes extreme (or whole unit) polarity on atoms joined by
a multiple bond owing to a complete transfer of the it electron pair to one or the other
atom under the influence of an electrophile."
CHEMICAL PROPERTIES
A.nucleophilic addition reactions
1. Addition of Sodium bisulphite
2. Addition of Hydrogen Cyanide
3. Addition of Grignard Reagents
4. Addition of Ammonia
B.nucleophilic addition reactions followed by loss of water
5. Reaction with Alcohols
6. Reactions with Thiols or Thioalcohols
7. Reaction with Ammonia Derivatives, GNH2
C.reactions involving alkyl group
8. Aldol Condensation
9. Perkin Condensation
10.Benzoin Condensation
11.Halogenation
D.reduction of carbonyl compounds
12.Reduction to Acohol
13.Reduction to Hydrocarbon
14.Reduction to Pinacols
BP202T (Carbonyl Compounds)
8 | P a g e
E.oxidation reactions
15.Oxidation to Carboxylic acids
16.Formation of Dicarbonyl Compounds
17.Haloform Reaction
18.Cannizzaro Reaction
1) Addition of Sodium bisulphite
 Saturated solution of sodium bisulphite (NaHSO3) in water, when mixed with
aldehydes and some ketones forms nicely crystalline bisulphite addition
compound.
R R OH
C=O + NaHSO3 C
R R SO3Na
aldehydes or ketones Bisulphite compound
 Almost all aldehydes form bisulphite addition compounds but only a few ketones
(up to C3) under go this reaction.
 The bisulphite addition compounds get decomposed back to the original carbonyl
compounds in presence of acids or alkalis.
 The formation and decomposition of the bisulphite compounds serves as a
powerful means of purification and separation of carbonyl compounds from
non-carbonyl substances.
2. Addition of Hydrogen Cyanide
 Hydrogen cyanide adds on to all aldehydes and methyl ketones to yield
Cyanohydrins, when the reaction is carried with a basic catalyst.
 The hydrogen of cyanohydrins either in acid or basic solution will convert the
nitrite group to the carboxylic acid.
 Since cyanohydrins are hydroxynitriles, this provides a useful route for the
preparation of α-hydroxy acids.
BP202T (Carbonyl Compounds)
9 | P a g e
3. Addition of Grignard Reagents

 These upon hydrolysis with acid yield alcohols.
4. Addition of Ammonia

 The aldehyde ammonia is unstable and lose water immediately to
form aldimine.
⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗
 Ketones also give ketone ammonias but these cannot be isolated.
 Acetone reacts slowly with ammonia to form first acetone ammonia
and then a complex compound.
i.
⃗⏞⃗⃗⃗ ⃗⃗ ⃗ ⃗⃗⃗ ⃗⃗ ⃗⃗⃗ ⃗⃗⃗ ⃗⃗⃗⃗ ⃗⃗⃗ ⃗⃗⃗ ⃗⃗ ⃗⃗⃗ ⃗⃗⃗ ⃗⃗


ii.
⃗⏞⃗⃗⃗ ⃗⃗ ⃗ ⃗⃗⃗ ⃗⃗ ⃗⃗⃗ ⃗⃗⃗ ⃗⃗⃗⃗ ⃗⃗⃗ ⃗⃗⃗ ⃗⃗ ⃗⃗⃗ ⃗⃗⃗ ⃗⃗


5. Reaction with Alcohols
 ( )
⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗ ( )
 ⏟



BP202T (Carbonyl Compounds)
10 | P a g e
 ( )
⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗
6. Reactions with Thiols or Thioalcohols
 Aldehydes react with thiols (or thioalcohols) even more readily than with
alcohols to form Thioaetals.
 Ketones also react with thiols (thioalcohols) to form Thioaketats.
 Thioacetals and thioketals are resistant to acid hydrolysis but can be
readily converted to the original aldehydes and ketones when subjected to
hydrolysis in the presence of HgCl2—CdCO3 mixtures.
 The formation of thioacetals and thioketals is also employed for masking
the carbonyl group of aldehydes and ketones in organic synthesis.
7. Reaction with Ammonia Derivatives, GNH2
 Certain derivatives of ammonia which contain the primary amine group
NH2 add to the carbonyl group of aldehydes and ketones to form unstable
intermediates. These immediately lose a molecule of water to yield the
respective condensation product.
Aldehyde/Ketone Ammonia derivative
Unstable intermediate
BP202T (Carbonyl Compounds)
11 | P a g e
 G stands for the general group bonded to —NH2 group in the ammonia
derivative.
12. Halogenation
 Acetaldehyde upon chlorination yields α-chloroacetaldehyde (CH2ClCHO)
and acetone upon bromination gives α-bromoacetone (CH2BrCOCH3).
13. Reduction to Alcohol
Ni
 Catalysts: platinum, palladium, nickel or copper chromite.
BP202T (Carbonyl Compounds)
12 | P a g e
14. Reduction to Hydrocarbon
 The carbonyl group of aldehydes and ketones may be reduced to methylene group,
yielding hydrocarbons.
Pinacol-Pinacolone Rearrangement
 Upon treatment with hot dii H2SO4, pinacol undergoes a rearrangement and
deyhdration to form a monoketone called pinacolone. This is known as pinacolpinacolone rearrangement.
15. Oxidation to Carboxylic acids
 Aldehydes are oxidised to the corresponding carboxylic acids.
 Ketones are oxidised with difficulty giving acids with smaller number of
carbon atoms.
Milder oxidants
i.Ammoniacal solution of silver nitrate (Tollen's reagent)
ii.Alkaline solution of cupric ions.
 Cupric hydroxide is insoluble it is made soluble by complex formation either with
tartarate ions (Fehlings solution) or with citrate ions (Benedict's solution).
 Popoff's RuleIf one of the n-carbon atoms has fewer hydrogen atoms
than the other, then this is attacked preferentially.
 The oxidation of hexan-3-one gives propionic acid is (The main product )
and with small amounts of butyric acid and acetic acid.
 In the presence of CrO3.
16. Formation of Dicarbonyl Compounds
 Aldehydes and ketones also undergo a special oxidation reaction which
does not involve the cleavage of carbon-carbon bonds.
 Selenium oxide (SeO2) oxidizes a methyl group which is adjacent to the
carbonyl group to form a dicarbonyl compound.
R R
BP202T (Carbonyl Compounds)
13 | P a g e
Example:
 CatalystSelenium oxide (SeO2)
17. Haloform Reaction
 When a methyl ketone is treated with a halogen in sodium hydroxide solution, it
is oxidized to a carboxylic acid containing one carbon less than the original molecule
with the simultaneous formation of trihalomethane.

 The reaction yields trihalomethanes-chloroform, bromoform, or iodoform
depending on the halogen used. Since the common name for halornethanes is
haloform it is called Haloform Reaction.
 Acetaldehyde is the only aldehyde which gives haloform reaction.
BP202T (Carbonyl Compounds)
14 | P a g e
TESTS OF ALDEHYDES AND KETONES
1)Resin test
 Aldehydes when warmed with concentrated NaOH solution form dark coloured
resins which rise to the surface.
 Formaldehyde and ketones do not give this test.
2)Schlff's test
 When dilute solution of an aldehyde is added to magenta solution decolourised by
sulphur dioxide, the intense red colour of the original dye is restored.
3) Formation of Bisulphite compounds

⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗
4) 2, 4-dinitrophenylhydrazone (DNP) test
 2, 4-dinitrophenylbydraZifle solution is prepared by dissolving it in alcohol and
then warming followed by the addition of two drops of conc. sulphuric acid.

⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗

 Addition of 2-3 ml of this reagent to 10 ml of aldehyde or ketone in about 5-10 ml of
alcohol produces a yellow, red or orange 2, 4 . DNP which is filtered, dried
recrystallised from alcohol.
5) Silver mirror test
 Ammonium hydroxide is added drop-wise to a 10% solution of silver nitrate. When
the precipitate first formed is re-dissolved, the solution is warmed with a little
aldehyde solution.
 A shining silver mirror is deposited on the inner wall of the test tube. Ketones,
however, do not respond to this test.
6) Fehling's Solution test
 A little dilute solution of the aldehyde is added to Fehling's solution taken in a test tube.
 Then it is warmed in a water bath for 1-2 minutes.
 Reddish brown precipitate of cuprous oxide separates out.
 Ketones do not give this test.
BP202T (Carbonyl Compounds)
15 | P a g e
A.Formaldehyde (Methanal)
 Formaldehyde is placed in the market as 40% aqueous solution under the name
formalin and is used as such for most purposes.
 Formalin is used for sterilising surgical instruments.
 Formalin is used for preserving biological and anatomical specimens.
 Formalin is used as reducing agent.
B.Paraldehyde
 In ancient time, it is used as a Sedative and Hypnotics.
 It has also been used as anticonvulsant agent for treating seizure.
C.Acetone
 It is used for manufacturing plastic and other industrial products.
 It is used in textile industries for decreasing wool and degumming silk.
 It is widely used for manufacturing of artificial fibres and explosive.
 Making of paper coating, adhesives and heat-seal coating
D.Chloral Hydrate
 It is a sedative used in the short term treatment for insomnia.
 It relieves anxiety and induces sleep before surgery.
 It is also used for post-surgery as a pain killer.
 It eases the alcohol withdraw symptoms.
BP202T (Carbonyl Compounds)
16 | P a g e
E. Hexamine
 It is used as anti-infective agent for urinary tract infections.
 It has antibiotic activity.
 In the body it get converted in to formaldehyde, which is a non-specific
bacterial agent.
 It is an antimicrobial food preservative with a limited use.
F.Benzaldehyde
 It is used in perfumery and dye (and its intermediates).
 It is used as solvent for oils, resins, cellulosic ester, cellulose acetate and nitrates.
 It is also used as flavouring agent in cinnamic acid, benzoic acid and some
pharmaceuticals and soaps.
 It is used as photographic chemicals, baking chemicals, medicines, etc.
G.Vanillin
 It is used as flavoring agent in foods, beverages and Pharmaceuticals
H.Cinnamaldehyde
 It enhances oral health as it fight against tooth decay and bad breath.
 It possesses antifungal and antibacterial activity.
 Inhibit blood clotting.
 It is used in perfumes.
 Used in animal repellent and mosquito repellent.
BP202T (Carbonyl Compounds)
17 | P a g e
 In ancient time, it is used as antidiabetic.


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