aldehyde and ketone Flashcards
what are carbonyl group
organic compounds containing carbon-oxygen double bond (>C=O) called carbonyl group
explain carbonyl group in aldehyde and ketone
In aldehydes, the carbonyl group is bonded to a carbon and hydrogen while in the ketones, it is bonded to two carbon atoms
what is carboxylic acids
The carbonyl compounds in which
carbon of carbonyl group is bonded to carbon or hydrogen and oxygen of hydroxyl moiety (-OH) are known as carboxylic acids
what is amides and acyl halides
In compounds where carbon is attached to carbon or hydrogen and nitrogen of -NH2 moiety or to halogens are called amides and acyl halides
Esters and anhydrides are derivatives of _______
carboxylic acids
what uses Aldehydes, ketones and carboxylic acids have in nature
They play an important role in biochemical
processes of life. They add fragrance and flavour to nature, for example, vanillin (from vanilla beans), salicylaldehyde (from meadow sweet) and cinnamaldehyde (from cinnamon) have very pleasant fragrances. They are used in many food products and pharmaceuticals to add flavors
Nomenclature of Aldehydes and ketones
aldehydes often called by their common names instead of IUPAC names. The common names of most aldehydes are derived from the common names of the corresponding carboxylic acids by replacing the ending –ic of acid with aldehyde. The location of the substituent in the carbon chain is indicated by Greek letters alpha, beta, gamma, delta, etc.
The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group. The locations of
substituents are indicated by Greek letters, a a’, b b’ and so on beginning with the carbon atoms next to the carbonyl group,
indicated as aa’
the simplest dimethyl ketone is called
acetone.
The name of the simplest aromatic aldehyde carrying the aldehyde group on a benzene ring is
benzene carbaldehyde or the common name benzaldehyde
Formaldehyde formula and real name
HCHO Methanal
Acetaldehyde formula and real name
CH3CHO Ethanal
Isobutyraldehyde formula and real name
(CH3)2CHCHO 2-Methylpropanal
Structure of the Carbonyl Group
The carbonyl carbon atom is sp2-hybridised and forms three sigma (s) bonds. The fourth valence electron of carbon remains in its p-orbital and forms a p-bond with oxygen by overlap with p-orbital of an oxygen In addition, the oxygen atom also has two non bonding electron pairs. the carbonyl carbon and the three atoms attached to it lie in the
same plane and the p-electron cloud is above and below this plane. The
bond angles are approximately 120° as expected of a trigonal coplanar
the carbonyl carbon acts an ________ and carbonyl oxygen acts an _________ and why
The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. Hence, the carbonyl carbon is an electrophilic (Lewis acid), and carbonyl oxygen, a nucleophilic (Lewis base) centre. Carbonyl compounds have substantial dipole moments and are polar than ethers
Preparation of Aldehydes and Ketones
By oxidation of alcohols
By dehydrogenation of alcohols
From hydrocarbons
(i) By ozonolysis of alkenes
(ii) By hydration of alkynes
Preparation of Aldehydes and Ketones By oxidation of alcohols
Aldehydes and ketones are generally prepared by oxidation of primary
and secondary alcohols, respectively
Preparation of Aldehydes and Ketones By dehydrogenation of alcohols
This method is suitable for volatile alcohols and is of industrial application. In this method alcohol vapours are passed over heavy metal catalysts (Ag or Cu). Primary and secondary alcohols give aldehydes and ketones, respectively
Preparation of Aldehydes and Ketones From hydrocarbons By ozonolysis of alkenes:
ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes ,ketones or a mixture of both depending on the substitution pattern of the alkene
Preparation of Aldehydes and Ketones From hydrocarbons By hydration of alkynes:
Addition of water to ethyne in the
presence of H2SO4 and HgSO4
gives acetaldehyde. All other
alkynes give ketones in this reaction
Preparation of Aldehydes
From acyl chloride (acid chloride)
From nitriles and esters
From hydrocarbons (i) By oxidation of methylbenzene
(ii) By side chain chlorination followed by hydrolysis
(iii) By Gatterman – Koch reaction
Preparation of Aldehydes From acyl chloride (acid chloride)
Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund reduction.
Preparation of Aldehydes From nitriles and esters
Nitriles are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid, which on hydrolysis give
corresponding aldehyde.
This reaction is called Stephen reaction.
nitriles are selectively reduced by
diisobutylaluminium hydride, (DIBAL-H) to imines followed by hydrolysis to aldehydes:
esters are also reduced to aldehydes with DIBAL-H.
Preparation of Aldehydes From hydrocarbons
By oxidation of methylbenzene
Strong oxidizing agents oxidize toluene and its derivatives to benzoic acids. However, it is possible to stop the oxidation at
the aldehyde stage with suitable reagents that convert the methyl group to an intermediate that is difficult to oxidize further
(a) Use of chromyl chloride (CrO2Cl2): Chromyl chloride oxidizes methyl group to a chromium complex, which on hydrolysis
gives corresponding benzaldehyde This reaction is called Etard reaction
(b) Use of chromic oxide (CrO3): Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in acetic anhydride. The benzylidene diacetate can be
hydrolyzed to corresponding benzaldehyde with aqueous acid.
Preparation of Aldehydes By side chain chlorination followed by hydrolysis
Side chain chlorination of toluene gives benzal chloride, which on hydrolysis gives benzaldehyde. This is a commercial method
of manufacture of benzaldehyde.
Preparation of Aldehydes By Gatterman – Koch reaction
When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminum chloride or cuprous chloride, it gives benzaldehyde or substituted
benzaldehyde.
Preparation of Ketones
From acyl chlorides
From nitriles
From benzene or substituted benzenes
Preparation of Ketones From acyl chlorides
Treatment of acyl chlorides with dialkylcadmium, prepared by the
reaction of cadmium chloride with Grignard reagent, gives ketones
Preparation of Ketones From nitriles
Treating a nitrile with Grignard reagent followed by hydrolysis yields a ketone.
Preparation of Ketones From benzene or substituted benzenes
When benzene or substituted benzene is treated with acid chloride in the presence of anhydrous aluminum chloride, it affords the corresponding ketone. This reaction is known as Friedel-Crafts acylation reaction
Physical Properties of aldehydes and ketones
Methanal is a gas at room temperature. Ethanal is a volatile liquid. Other aldehydes and ketones are liquid or solid at room temperature. The boiling points of aldehydes and ketones are higher than
hydrocarbons and ethers of comparable molecular masses. It is due to weak molecular association in aldehydes and ketones arising out of the dipole-dipole interactions. Also, their boiling points are lower than those of alcohols of similar molecular masses due to absence of intermolecular hydrogen bonding.
The lower members of aldehydes and ketones such as methanal, ethanal and propanone are miscible with water in all proportions, because they form hydrogen bond with water.
the solubility of aldehydes and ketones and smell of aldehydes and ketones
the solubility of aldehydes and ketones decreases rapidly on increasing the length of alkyl chain. All aldehydes and ketones are
fairly soluble in organic solvents like benzene, ether, methanol, chloroform, etc. The lower aldehydes have sharp pungent odors. As the size of the molecule increases, the odour becomes less pungent
and more fragrant. In fact, many naturally occurring aldehydes and ketones are used in the blending of perfumes and flavoring agents.
Chemical Reactions with aldehydes and ketones
- Nucleophilic addition reactions
- Reduction
- Oxidation
- Reactions due to a-hydrogen
5 Cannizzaro reaction
6 Electrophilic substitution reaction
Chemical Reactions of aldehydes and ketones with Nucleophilic addition reaction(Mechanism of nucleophilic addition reactions)
A nucleophile attacks the electrophilic carbon atom of the polar carbonyl group from a direction approximately perpendicular to the plane of sp 2 hybridized orbitals of carbonyl carbon
The hybridization of carbon changes from sp2 to sp3 in this process, and a tetrahedral alkoxide intermediate is produced. This intermediate captures a proton from the
reaction medium to give the electrically neutral product. The net result is addition of Nu– and H+ across the carbon oxygen double bond
Chemical Reactions of aldehydes and ketones with Nucleophilic addition reaction(Reactivity)
Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. Sterically, the presence of two relatively large substituents in ketones hinders the approach of nucleophile to carbonyl carbon than in aldehydes having only one such substituent. Electronically, aldehydes are more reactive than ketones because two alkyl groups reduce the electrophilicity of the carbonyl carbon more effectively than in former
Some important examples of nucleophilic addition and nucleophilic addition-elimination reactions
(a) Addition of hydrogen cyanide (HCN):
(b) Addition of sodium hydrogen sulphite
(c) Addition of alcohols
(d) Addition of ammonia and its derivatives
Addition of hydrogen cyanide (HCN) to aldehydes and ketones
Aldehydes and ketones react with hydrogen cyanide (HCN) to yield cyanohydrins. This reaction occurs very slowly with pure HCN. Therefore, it is catalyzed by a base and the generated cyanide ion (CN-) being a stronger nucleophile readily adds to
carbonyl compounds to yield corresponding
cyanohydrin.
Addition of sodium hydrogen sulphite to aldehydes and ketones
Sodium hydrogensulphite adds to aldehydes and ketones to form the addition products. The position of the equilibrium
lies largely to the right hand side for most
aldehydes and to the left for most ketones due to steric reasons. The hydrogensulphite addition compound is water soluble and can be converted back to the original carbonyl compound by treating it with dilute mineral acid or alkali. Therefore, these are useful for separation and
purification of aldehydes.
Addition of alcohols to aldehydes and ketones
Aldehydes react with one equivalent of
monohydric alcohol in the presence of dry hydrogen chloride to yield alkoxyalcohol intermediate, known as hemiacetals,
which further react with one more molecule of alcohol to give a gem-dialkoxy compound known as acetal as shown in the reaction Ketones react with ethylene glycol under
similar conditions to form cyclic products known as ethylene glycol ketals. Dry hydrogen chloride protonates the oxygen of
the carbonyl compounds and therefore, increases the electrophilicity of the
carbonyl carbon facilitating the nucleophilic attack of ethylene glycol. Acetals and ketals
are hydrolyzed with aqueous mineral acids to yield corresponding aldehydes and ketones respectively.
Addition of ammonia and its derivatives to aldehydes and ketones
Nucleophiles, such as ammonia and its derivatives H2N-Z add to the carbonyl
group of aldehydes and ketones. The reaction is reversible and catalysed by acid.
The equilibrium favours the product
formation due to rapid dehydration of the
intermediate to form >C=N-Z
Aldehydes and ketones Reduction to alcohols:
Aldehydes and ketones are reduced to
primary and secondary alcohols respectively by sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4) as well as by catalytic hydrogenation
Aldehydes and ketones Reduction to hydrocarbons
The carbonyl group of aldehydes and ketones is reduced to CH2 group on treatment with zinc amalgam and concentrated hydrochloric acid [Clemmensen reduction] or with hydrazine followed by heating with sodium or potassium hydroxide in high boiling solvent such as ethylene glycol (Wolff-Kishner reduction).
Oxidation of Aldehydes and ketones
Aldehydes differ from ketones in their oxidation reactions. Aldehydes are easily oxidized to carboxylic acids on treatment with common oxidizing agents like nitric acid, potassium permanganate, potassium
dichromate, etc. Even mild oxidizing agents, mainly Tollens’ reagent and Fehlings’ reagent also oxidize aldehydes.
Ketones are generally oxidized under vigorous conditions, i.e.,strong oxidizing agents and at elevated temperatures. Their oxidation involves carbon-carbon bond cleavage to afford a mixture of carboxylic
acids having lesser number of carbon atoms than the parent ketone.
Fehling’s test: on aldehyde
Fehling reagent comprises of two solutions,
Fehling solution A and Fehling solution B. Fehling solution A is aqueous copper sulphate and Fehling solution B is alkaline
sodium potassium tartarate (Rochelle salt). These two solutions are mixed in equal amounts before test. On heating an aldehyde with Fehling’s reagent, a reddish brown precipitate is obtained. Aldehydes are oxidized to corresponding carboxylate anion. Aromatic aldehydes do not respond to this test.
Tollens’ test on aldehyde
On warming an aldehyde with freshly prepared ammoniacal silver nitrate solution (Tollens’ reagent), a bright silver mirror is produced due to the formation of silver metal. The aldehydes are oxidized to corresponding carboxylate anion.
The reaction occurs in alkaline medium.
Oxidation of methyl ketones by haloform reaction:
Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom (methyl ketones) are oxidized by sodium hypohalite to sodium salts of
corresponding carboxylic acids having one carbon atom less than that of carbonyl compound. The methyl group is converted to haloform. This oxidation does not
affect a carbon-carbon double bond, if present in the molecule
Reactions due to a-hydrogen on Aldehydes and ketones
Acidity of a-hydrogens of aldehydes and ketones: The aldehydes and ketones undergo a number of reactions due to the acidic nature of a-hydrogen. The acidity of a-hydrogen atoms of carbonyl compounds is due to the strong electron withdrawing effect of the carbonyl group and resonance stabilization of the conjugate base
Iodoform reaction with sodium hypoiodite is also used for detection
of CH3CO group or CH3CH(OH) group which produces CH3CO group
on oxidation
ogay facts
what is aldol reaction
Aldehydes and ketones having at least one
a-hydrogen undergo a reaction in the presence of dilute alkali as catalyst to form b-hydroxy aldehydes (aldol) or b-hydroxy
ketones (ketol), respectively. This is known as Aldol reaction
what is adol condensation
The aldol and ketol readily lose water to give alpha,beta -unsaturated carbonyl compounds which are aldol condensation products and the reaction is called Aldol condensation
what is Cannizzaro reaction:
Aldehydes which do not have an
a-hydrogen atom, undergo self oxidation and reduction (disproportionation) reaction on heating with concentrated alkali.
In this reaction, one molecule of the aldehyde is reduced to alcohol while another is oxidized to carboxylic acid salt.
Electrophilic substitution reaction on aldehyde and ketone
Aromatic aldehydes and ketones undergo electrophilic substitution at the ring in which the carbonyl group acts as a deactivating and meta-directing group
what are uses of aldehyde and ketone
aldehydes and ketones are used as solvents, starting materials and reagents for the synthesis of other products
what are uses of Formaldehyde
Formaldehyde is well known as formalin (40%) solution used to preserve biological specimens and to prepare bakelite (a phenol-formaldehyde resin), urea-formaldehyde glues and other polymeric products
what are uses of Acetaldehyde
Acetaldehyde is used primarily as a starting material in the manufacture of acetic acid, ethyl acetate, vinyl acetate, polymers and drugs.
what are uses of Benzaldehyde
Benzaldehyde is used in perfumery and in dye industries. Acetone and ethyl methyl ketone are common industrial solvents. Many aldehydes and ketones, e.g., butyraldehyde, vanillin, acetophenone, camphor, etc. are well known for their odours and flavours.
what are carboxylic acids
Carbon compounds containing a carboxyl functional group, –COOH are called carboxylic acids
where is formic acid formed
red ant
where is acetic acid formed
vinegar
where is butyric acid formed
from rancid butter
Structure of Carboxyl Group
In carboxylic acids, the bonds to the carboxyl carbon lie in one plane
and are separated by about 120°. The carboxylic carbon is less electrophilic than carbonyl carbon because of the possible resonance structure
Methods of Preparation of Carboxylic
Acids
From primary alcohols and aldehydes
From alkylbenzenes
From nitriles and amides
From Grignard reagents
From acyl halides and anhydrides
From esters
Methods of Preparation of Carboxylic
Acids From alkylbenzenes
Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline potassium
permanganate. The entire side chain is oxidised to the carboxyl group
irrespective of length of the side chain. Primary and secondary alkyl
groups are oxidised in this manner while tertiary group is not affected.
Suitably substituted alkenes are also oxidised to carboxylic acids
with these oxidising reagents.
Methods of Preparation of Carboxylic
Acids From nitriles and amides
Nitriles are hydrolyzed to amides and then to acids in the presence of H+ or OH as catalyst. Mild reaction conditions are used to stop the reaction at the amide stage
Methods of Preparation of Carboxylic
Acids From primary alcohols and aldehydes
Primary alcohols are readily oxidized to carboxylic acids with common oxidizing agents such as potassium permanganate (KMnO4) in neutral, acidic or alkaline media or by potassium dichromate (K2Cr2O7)
and chromium trioxide (CrO3) in acidic media (Jones reagent).Carboxylic acids are also prepared from aldehydes by the use of
mild oxidizing agents
Methods of Preparation of Carboxylic
Acids From Grignard reagents
Grignard reagents react with carbon dioxide (dry ice) to form salts of carboxylic acids which in turn give corresponding carboxylic acids after acidification with mineral acid.
(the Grignard reagents and nitriles can be prepared from alkyl halides are useful for converting alkyl halides into corresponding
carboxylic acids having one carbon atom more than that present in
alkyl halides)
Methods of Preparation of Carboxylic
Acids From acyl halides and anhydrides
Acid chlorides when hydrolyzed with water give carboxylic acids or more readily hydrolyzed with aqueous base to give carboxylate ions which on acidification provide corresponding carboxylic acids. Anhydrides on the other hand are hydrolyzed to corresponding acid(s) with water.
Methods of Preparation of Carboxylic
Acids From esters
Acidic hydrolysis of esters gives directly carboxylic acids while basic hydrolysis gives carboxylates, which on acidification give corresponding carboxylic acids.
Carboxylic acids are higher boiling
liquids than aldehydes, ketones and even alcohols of comparable molecular masses why
This is due to more extensive
association of carboxylic acid molecules through intermolecular hydrogen bonding
Aliphatic carboxylic acids upto ______ carbon atoms are colorless
liquids at room temperature with unpleasant odors
nine
Simple aliphatic carboxylic acids having upto four carbon atoms are miscible in water because?
due to the formation
of hydrogen bonds with water
(the strongest carboxylic acid)
trifluoroacetic acid
Reactions Involving Cleavage of C–OH Bond
Formation of anhydride
Esterification
Reactions with PCl5, PCl3 and SOCl2
Reaction with ammonia
The solubility decreases with increasing number of carbon atoms because
The solubility decreases with increasing number of carbon atoms. Higher
carboxylic acids are practically insoluble in water due to the increased hydrophobic interaction of hydrocarbon
part
Reactions Involving Cleavage of C–OH Bond Formation of anhydride
Carboxylic acids on heating with mineral acids such as H2SO4 or with P2O5 give corresponding anhydride.
The effect of the following groups in increasing acidity order is
Ph < I < Br < Cl < F < CN < NO2
< CF3
Reactions Involving Cleavage of C–OH Bond Esterification
Carboxylic acids are esterified with alcohols or phenols in the presence of a mineral acid such as concentrated H2SO4 or HCl gas as a catalyst
Reactions Involving –COOH Group by reduction
Carboxylic acids are reduced to primary alcohols by lithium aluminium hydride or better with diborane. Diborane does not easily reduce functional groups such as ester, nitro, halo, etc. Sodium borohydride does not reduce the carboxyl group.
Reactions Involving Cleavage of C–OH Bond Reaction with ammonia
Carboxylic acids react with ammonia to give ammonium salt which on further heating at high temperature give amides
mechanism of Esterification of carboxylic acids
step1 Protonation of the
carbonyl oxygen activates the carbonyl group towards nucleophilic addition of the
alcohol
step2 Proton transfer in the tetrahedral intermediate converts the hydroxyl group
into –+OH2 group, which, being a better leaving group, is eliminated as neutral water
molecule
step3 The protonated ester so formed finally loses a proton to give the ester.
Reactions Involving Cleavage of C–OH Bond Reactions with PCl5, PCl3 and SOCl2
The hydroxyl group of carboxylic acids, behaves like that of alcohols and is easily replaced by chlorine atom on treating with PCl5, PCl3 orSOCl2 Thionyl chloride (SOCl2) is preferred because the other two products are gaseous and escape the reaction mixture making the purification of the products easier.
what is Kolbe electrolysis
Alkali metal salts of carboxylic acids also undergo decarboxylation on electrolysis of their aqueous solutions and form hydrocarbons having twice the number of carbon atoms present in the alkyl group of the acid. The reaction is known as Kolbe electrolysis
Reactions Involving –COOH Group
Reduction
Decarboxylation
Reactions Involving –COOH Group by Decarboxylation
Carboxylic acids lose carbon dioxide to form hydrocarbons when their sodium salts are heated with sodalime (NaOH and CaO in the ratio of (3 : 1). The reaction is known as decarboxylation.
Substitution Reactions in the Hydrocarbon Part by Halogenation
Carboxylic acids having an a-hydrogen are halogenated at the a-position on treatment with chlorine or bromine in the presence of
small amount of red phosphorus to give a-halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction.
Substitution Reactions in the Hydrocarbon Part
Halogenation
Ring substitution
Substitution Reactions in the Hydrocarbon Part by Ring substitution
Aromatic carboxylic acids undergo electrophilic substitution reactions
in which the carboxyl group acts as a deactivating and meta-directing
group. They however, do not undergo Friedel-Crafts reaction (because the carboxyl group is deactivating and the catalyst aluminum chloride (Lewis acid) gets bonded to the carboxyl group)
uses of Methanoic acid
Methanoic acid is used in rubber, textile, dyeing, leather and electroplating
industries
uses of Ethanoic acid
Ethanoic acid is used as solvent and as vinegar in food industry
uses of Hexanedioic acid
Hexanedioic acid is used in the manufacture of nylon-6, 6
uses of Esters of benzoic acid
Esters of benzoic acid are used in perfumery
uses of Sodium benzoate
Sodium benzoate is used as a food preservative.
uses of Higher fatty acids
Higher fatty acids are used for the manufacture of soaps and detergents
