Notes and Study Materials -Aldehydes , Ketones and Carboxylic Acids

Aldehydes , Ketones and Carboxylic Acids : Notes and Study Materials -pdf
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Concepts of Carboxylic Acid
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Aldehyde, Ketones and Carboxylic Acid Reference Book

About this unit

Principles and methods of extraction- concentration, oxidation, reduction electrolytic method and refining; occurrence and principles of extraction of aluminium, copper, zinc and iron.Carboxylic Acids: Nomenclature, acidic nature, methods of preparation, physical and chemical properties; uses.

ALDEHYDES AND KETONES

Aldehydes and Ketones are characterised by the presence of Carbonyl group >C = O in their molecules. Aldehydes contain group and ketones the . If the groups attached to carbonyl carbon are the same, the ketone is symmetrical and if they are different the ketone is unsymmetrical.

NATURE OF CARBONYL GROUP

The carbon and oxygen of the carbonyl group are sp2 hybridised and the carbonyl double bond is made of one s bond and one p bond.
 or  
The electronegativity of oxygen is much higher than that of carbon, the p electron cloud is displaced towards the oxygen. Therefore the C–O bond is polar in nature and carbonyl compounds possess dipole moment (2.3 to 2.8 D)

NOMENCLATURE OF ALDEHYDES

There are two systems
  • Common system : The suffix “-ic acid” is replaced by the suffix “-aldehyde
  • IUPAC system : The suffix “-e” of alkane is replaced by the suffix “-al”.
Compound Common name IUPAC name
HCHO Formaldehyde Methanal
CH3CHO Acetaldehyde Ethanal

NOMENCLATURE OF KETONES

  • Common system : Symmetrical ketones are named as dialkyl ketone and name of unsymmetrical ketone is obtained by naming the alkyl groups alphabetically and adding the third word ketone.
  • IUPAC system : The suffix “-e” of corresponding alkane is replaced by “-one
Compound Common name IUPAC name
H3C.COCH3 dimethyl ketone (acetone)  Propanone
H3C.COC2H5 ethyl methyl ketone butanone
In higher ketones the numbering of C-atoms is must to show the position of carbonyl group. eg. :
3-hexanone
2-methyl-4-heptanone

ISOMERISM IN ALDEHYDES

Aldehydes exhibit two types of isomerism

 

Chain isomerism

 

Functional isomerism
 

ISOMERISM IN KETONES

They exhibit three types of isomerism
Chain isomerism
Functional isomerism
Position isomerism

GENERAL METHODS OF PREPARATION OF ALDEHYDES

  • Controlled oxidation of primary alcohols
    Oxidising agents K2Cr2O7/H2SO4 or KMnO4/H2SO4
PCC is pyridinium chlorochromate known as Collin’s reagent and is specific for oxidation of 1º alcohol to aldehyde.
  • Dehydrogenation of primary alcohol
  • By Rosenmund reduction from acid chloride
  • Hydration of Alkynes (Kucherov reaction)
  • Reductive ozonolysis of alkenes
  • Distillation of Calcium salt of fatty acid with calcium formate
  • From acid
  • Waker’s process
  • Oxo process
  • Stephen’s reduction of nitriles :
  • Hydrolysis of Geminal halides
     
  • From Glycols
  • From Grignard’s reagent
  • From acid chloride by the use of lithium t-butoxy aluminium hydride

GENERAL METHODS OF PREPARATION OF KETONES ONLY

  • Oxidation of 2º alcohol
    Oxidising agent K2Cr2O7/H2SO4 or KMnO4/H2SO4
  • Dehydrogenation of 2º alcohols
  • Hydration of alkynes
  • Reductive ozonolysis of alkenes
  • From Calcium salt of an acid
  • From acid
  • Hydrolysis of non-terminal gem.halide
  • From Grignard’s reagents
  • From acid chlorides

PHYSICAL PROPERTIES

  • Formaldehyde is a gas and its 40% aqueous solution was known as formalin but now it is 40% HCHO, 8% CH3OH, 52% H2O. They are polar in nature and have higher values of b.p. Lower members are soluble in water.
  • Lower aldehydes and ketones (C1 – C4) are soluble in water due to presence of H–bonding.
        
  • Reactivity
It is due to + I effect of alkyl groups which decreases the +ve charge on carbonyl carbon.

 

Steric hindrance : The bulky alkyl group hinder the approach of nucleophile.
a-hydrogen atom is acidic in nature due to Resonance

CHEMICAL PROPERTIES

ADDITION REACTIONS

Their addition reactions are known as nucleophilic addition reactions

 

The followings reaction in different ways with NH3
  
It is used as urinary antiseptic.

NUCLEOPHILIC ADDITION REACTIONS WITH ELIMINATION OF WATER MOLECULE

The control of pH is must for these reactions. The optimum value is around 3.5.

 

Control of pH during formation of ammonia derivatives :
At low pH : H+ concentration is very high. The carbonyl compound and ammonia derivative, both protonated and latter cannot act as nucleophile .
At high pH :  H+ concentration is too small. The protonation of carbonyl group will not occur and reaction will not occur smoothly.
Hence, optimum pH of the medium is around 3.5.

OXIDATION

Ketones are oxidised by strong oxidising agents such as Conc. HNO3, K2Cr2O7/H2SO4, KMnO4/H2SO4

 

OXIDATION WITH SeO2
The CH3 group adjacent to  is oxidised to – CHO and >CH2 group is oxidised to
>C = O group.

 

POPOFF’S RULE
During oxidation of unsymmetrical ketone the carbonyl group is retained by smaller alkyl group.
(major products)
Jone’s reagent : Acidified K2Cr2O7 i.e. chromic acid and sulphuric acid mixture

 

HALOFORM REACTION
Oxidation of acetaldehyde or methyl ketones with Sodium Hypohalite (NaOX) or (X2 + NaOH) gives haloform CHX3. The reaction is of practical value to identify these compounds by forming CHI3.

 

BAYER-VILLIGER OXIDATION
Oxidation of aliphatic Ketones by organic per acids, e.g. perbenzoic acid, peracetic acid or monoperthalic acid to form esters or their hydrolysed products

REDUCTION 

CONDENSATION REACTIONS

ALDOL CONDENSATION
Aldehydes and Ketones having at least one a-hydrogen atom in presence of dil. alkali give b- hydroxy aldehyde or b-hydroxy ketone, which on heating gives a,b-unsaturated carbonyl compound.

 

CROSSED ALDOL CONDENSATION
   

 

INTRAMOLECULAR ALDOL CONDENSATION

 

CANNIZZARO’S REACTION
Aldehydes containing no a-hydrogen atom on warming with 50% NaOH or KOH undergo disproportionation i.e. self oxidation – reduction known as cannizzaro’s reaction.
* 2-methyl propanal (CH3)2CH.CHO has a-hydrogen atom but gives Cannizzaro’s reaction.
Aldehydes containing a-H atoms on heating with conc. alkali give brown resinous mass by undergoing repeated aldol condensation.

 

CROSSED CANNIZZARO’S REACTION

 

TISHCHENKO REACTION
Aldehydes containing a-hydrogen atom with aluminium ethoxide give esters.

 

REFORMATSKY REACTION
It is the reaction between an a-bromo acid ester and a carbonyl compound (aldehyde or ketone) in the presence of zinc to form a b-hydroxy ester.

 

BECKMANN’S REARRANGEMENT
It is rearrangement of keto oxime to N-substituted acid amide in presence of Conc. H2SO4, PPA, SOCl2, PCl5 etc.

 

CONDENSATION PRODUCTS OF ACETONE
Above reactions are not aldol condensations.

 

POLYMERS OF FORMALDEHYDES

 

POLYMERS OF ACETALDEHYDE

BENZALDEHYDE (AROMATIC ALDEHYDES)

PREPARATION

  • Etard’s oxidation
  • Oxidation of toluene
  • Gattermann Koch Synthesis
(Combination of CO + HCl act as formyl chloride HCOCl)
It is an electrophilic substitution reaction, the electrophile is  formylium ion.
  • Gattermann aldehyde synthesis
  • From benzyl chloride (Lab method)
  • Rosenmund reaction
  • Vilsmeyer reaction
  • From Grignard’s reaction
  • From Benzal chloride (manufacture)
  • Partial oxidation of toluene (manufacture)

PHYSICAL PROPERTIES

Colourless, highly refractive liquid b.p. 443K. It has smell of bitter almonds, slightly soluble in water. Steam volatile and poisonous.

CHEMICAL PROPERTIES

REACTION OF CHO GROUP GIVEN BY AROMATIC ALDEHYDES
            
     

REACTIONS DUE TO BENZENE NUCLEUS
CHO group is meta directing with deactivation of benzene nucleus

Benzaldehyde reduces Tollen’s reagent but not Fehling solution.

USES

  • As flavouring agent
  • In perfumes
  • Manufacture of triphenylmethane dyes

ACETOPHENONE (AROMATIC KETONES)

PREPARATION

  • By Friedel Craft’s acylation
  • From benzaldehyde
  • Manufacture

PHYSICAL PROPERTIES

It is colourless crystalline compound m.p. 20ºC, b.p. 202ºC.
At room temperature it is coloured liquid.

CHEMICAL PROPERTIES

  • Reactions due to . It gives almost all reactions due >C = O group.
  • Reactions due to benzene nucleus : –COCH3 is meta directing in nature. Hence electrophilic substitution reactions give meta derivative.
  • It give iodoform test.
  • Some important reactions are :
Its vapour attack nose, throat and lungs. It is used as tear gas.

USES

It is used as hypnotic in medicine.

TEST FOR ALDEHYDE

  • Tollen’s reagent (ammoniacal silver nitrate). All aldehydes give silver mirror.
  • Fehling Solution (alkaline solution of Cu2+ complexed with Sodium potassium tartrate blue colour). All aldehydes give red colour except benzaldehyde.
  • Benedict’s solution (Copper sulphate, sodium citrate and sodium carbonate solution). Aldehydes give reddish brown ppt.
  • Schiff’s reagent (dilute solution of p-rosaniline hydrochloride decolourised with SO2 or H2SO4). Aldehydes give pink colour.
Acetone respond to this test slowly and o-hydroxy benzaldehyde does not give pink colour with schiff’s reagent

 

Note : Formic acid, tartaric acid, a-hydroxy ketones, glucose, fructose reduce  Tollen reagent and Fehling solution.

CARBOXYLIC ACIDS AND THEIR DERIVATIVES

The compounds containing the carboxyl functional group are called Carboxylic acids. The word carboxyl is a combination of two words carbonyl (>C=O) and hydroxyl (–OH).

CLASSIFICATION

Depending upon the number of –COOH groups they are  classified as
  • Monocarboxylic acids: containing one -COOH group
  • dicarboxylic acids: containing two -COOH groups and so on
  • Fatty acids: Aliphatic monocarboxylic acids are commonly called fatty acids because higher members are obtained by the hydrolysis of oils and fats.

NOMENCLATURE

There are three ways of naming carboxylic acids
Common System
The common names are derived from the source of acids.
Formula Common name Source
HCOOH Formic acid Red ant (formica)
CH3COOH Acetic acid Vinegar (acetium)
C3H7COOH Butyric acid Butter (butyrum)
The position of substituents are indicated by Greek letters , , etc. The carbon atom adjacent to carboxyl group is assigned the letter , the next and so on
 
-methyl propionic acid -methyl butyric acid


Derived System
Acids are regarded as alkyl derivatives of acetic acid eg.
 


IUPAC System
They are named as Alkanoic acids eg.
HCOOH  Methanoic acid
C3H7COOH Butanoic acid
While naming the complex acids, the longest chain is picked up and the carbon atoms are numbered starting from carboxyl group which is given number 1.

ISOMERISM


POSITION AND CHAIN ISOMERISM
eg. C6H12O2 represent
 2, 3 – dimethyl butanoic acid All the seven are chain Isomers
   3, 3 – dimethyl butanoic acid


  2, 2 – dimethyl butanoic acid

FUNCTIONAL ISOMERISM

GENERAL METHODS OF PREPARATION

  • Oxidation of 1º alcohols and aldehydes with acid K2Cr2O7 or KMnO4
  • Oxidation of methyl ketones (Haloform reaction) with X2/NaOH
  • Hydrolysis of cyanides : Hydrolysis may be affected by acid or alkali
  • Hydrolysis of an ester: with alkali or acid
Ease of hydrolysis
Alkaline hydrolysis of an ester is known as saponification
  • Hydrolysis of trihalogen derivative of alkanes
  • Carboxylation  of alkenes (Koch reaction)
  • Reaction of Grignard Reagents with CO2
  • By heating sodium alkoxide with CO
  • From Sodium alkyl and CO2
  • Catalytic oxidation of long chain hydrocarbons
  • From alkynes
  • By heating dicarboxylic acids eg oxalic acid or malonic acid
  • By acidic hydrolysis of Malonic or aceto acetic ester


MANUFACTURE OF METHANOIC ACID


MANUFACTURE OF ACETIC ACID
  • By air oxidation of Acetaldehyde
  • By air oxidation of Butane
  • Quick vinegar process
The production is limited to the production of vinegar only which is 5 to 7% acetic acid


Glacial acetic acid
Pure acetic acid when cooled forms ice like solid (glacier) hence it is called glacial acetic acid.

GENERAL PROPERTIES

Acids upto C10 are liquids with unpleasant odours. The higher members are colourless waxy solids. Boiling points of acids increase regularly with molecular weight and higher than alcohols (of comparable molecular mass) due to formation of dimer through H-bonding

SOLUBILITY

Acids upto C4 are completely soluble in water due to H-bonding. Solubility regularly decreases rapidly due to increase in hydrophobic character of alkyl group.

MELTING POINTS

The melting point of even number acid is always higher than the next lower and higher odd number acid (alternation effect or oscillation effect) due to effective crystal lattice being symmetrical in nature*

ACIDITY OF CARBOXYLIC ACIDS

The carboxylic acids on ionisation produce carboxylate ion  which is stabilised by resonance
Electrons releasing alkyl groups decrease the acidity. Hence lower members are more acidic than higher members eg
As the size of alkyl group increases the ionic character of O-H bond decreases
Electrons withdrawing substituents increase the acidity by increasing the ionic character of – O – H bond by inductive effect and dispersing the negative charge of anion formed 

CHEMICAL PROPERTIES

REDUCING CHARACTER OF FORMIC ACID

ACTION OF HEAT ON FORMATES

Sodium formate 2HCOONa COONa + H2
         |
          COONa
       Sod. oxalate
Calcium formate
Ammonium formate

ACID DERIVATIVES

The compounds obtained by replacing –OH group of in acid by –X, –OCOR, –OR or –NH2 are called acid derivatives. They are
                   
Acid halide (X = Cl, Br, I)


Acid anhydride



Ester


Acid amide          


The order of reactivity for nucleophilic substitution reactions (known as acyl substitution reactions) is as follows
The factors affecting the above order are (i) Inductive effect (ii) Resonance and (iii) Nature of leaving group. The more the basic character of the leaving group, the lesser is the reactivity and basic character follows the order

ACID CHLORIDES

IUPAC name Alkanoyl Chloride
 
METHODS OF PREPARATION
  • From acids
  • From Salts (Industrial method)


PHYSICAL PROPERTIES
Acid Chlorides are polar in nature, still insoluble in water due to absence of hydrogen bonding which is also the reason of their having low b.p. than acids.


CHEMICAL PROPERTIES
  


USES
  • As acylating agent
  • Determination of –NH2 and OH group in a molecule

ACID ANHYDRIDE (RCO)2O

IUPAC name Alkanoic anhydride


Formula Common name IUPAC name
 Acetic anhydride Ethanoic anhydride
 Propionic anhydride Propanoic anhydride


METHODS OF PREPARATION
  • (mixed anhydride)


PHYSICAL PROPERTIES
The anhydrides are colourless liquids with irritating smell.
Insoluble in water but soluble in organic solvents.


CHEMICAL PROPERTIES


USES
Acetic anhydride is used as acetylating agent in the manufacture of plastics, cellulose acetate and polyvinyl acetate.

ESTERS

IUPAC name alkyl alkanoate


Formula Common name IUPAC name
 ethyl acetate ethyl ethanoate
 methyl acetate methyl ethanoate


METHODS OF PREPARATION


PHYSICAL PROPERTIES
Esters are pleasant smelling liquids sparingly soluble in water soluble in alcohol and ether.


CHEMICAL PROPERTIES
Note. Alcoholysis is usually effective in replacing a higher alcohol by lower one eg.
Hydrolysis of carboxylic esters may be formulated in two ways
and  Base or acid catalysed bimolecular involving acyl-oxygen heterolysis are very common
Acid catalysed unimolecular involving alkyl-oxygen heterolysis is very common for t-alcohols
occurs in solvent having high ionizing power and alcohol forms stable carbonium ion.


Claisen condensation: Intermolecular condensation of esters containing a-hydrogen atom in presence of strong base to form b-keto ester


USES OF ESTERS
In making artificial essences and flavours.

AMIDES

IUPAC name Alkanamide


Formula Common name IUPAC name
HCONH2 Formamide Methanamide
CH3CONH2 Acetamide Ethanamide


METHODS OF PREPARATION


PHYSICAL PROPERTIES
Except formamide, amides are colourless, crystalline solids, lower members are soluble in water and alcohol. Their m.p.are higher due to hydrogen bonding


CHEMICAL PROPERTIES


USES
In leather tanning and paper industry, preparation of nitrogen compounds.

UREA, CARBAMIDE (H2N.CO.NH2)

It is diamide of carbonic acid
Urea is the normal end product of protein metabolism and excreted in urine about 30 gm in 24 hours by an adult person.
          
PREPARATION
  • Wohler synthesised in 1828, urea the first organic compound by heating ammonium cyanate
  • By the action of ammonia on phosgene, ethyl carbonate, chloroformate or Urethanes.
  • Manufacture


PHYSICAL PROPERTIES
White crystalline solid mpt 132ºC soluble in water, alcohol, insoluble in ether.
It is mono acidic base.


CHEMICAL PROPERTIES
USES
  • It is used as fertilizer
  • making barbiturates
  • urea formaldehyde resin
  • To improve octane number
  • Stabilizer for explosives

SUBSTITUTED ACIDS

The acids obtained by replacing one or more hydrogen atoms from the alkyl group of the acid by groups such as Cl, OH, CN, NH2 etc are known as substituted acids. The position of the latter is indicated by Greek letters like a, b, g, d etc (common system) or by numbers like 1, 2, 3 etc (IUPAC System) eg.
– hydroxybutyric acid (common)
3 – hydroxy butanoic acid (IUPAC)


Distinction between different substituted acids can be made by the application of heat
-Amino acids   
-Amino acids


-Amino acids


-Hydroxy acids


-hydroxy acids

and -hydroxy acids

-Halogeno acids.
They yield -hydroxy acids


-Halogeno acids              


-Halogeno acids

SATURATED DICARBOXYLIC ACIDS

The compounds containing two carboxyl groups are known as dicarboxylic acids. They have the general formula CnH2n (COOH)2


NOMENCLATURE
Their IUPAC group name is Alkanedioic acid
 
GENERAL PROPERTIES
  • All are colourless crystalline solids, soluble in water. Solubility with increase in molecular weight, the odd acids are more soluble than even due to lower symmetry and poor packing.
  • Their melting points follow the Oscillation or alternation rule which states that the melting point of an “even” acid is higher than that of the “odd” acid immediately below and above it in the series. It is also known as “saw-tooth” rule.
  • Acid Strength: The strength of acids decreases from lower to higher member of the series as shown by the pka values
Acid Oxalic acid Malonic acid Succinic acid Glutaricacid Adipic acid
pka 1.271 2.86 4.21 4.34 4.41
This is due to –I effect of the carboxylic group which decreases with the length of the carbon atom chain.
  • Action of heat


Blanc’s rule: On heating the acid with acetic anhydride and then distilling the product at 300ºC, 1, 4 and 1, 5 – dicarboxylic acid give cyclic anhydrides and 1, 6 and 1, 7-dicarboxylic acid give cyclic ketones provided the acids are unsubstituted. If no change the acid is 1, 8 or more.
The rule helps to determine the size of rings.
Note A -keto acid is easily decarboxylated by heating

TARTARIC ACID

It occurs in free state in tamarind and as potassium salt in various fruits such as grapes, plums, etc.


PREPARATION
  • From Argol or Tartar – A brown coloured crystalline mass formed during the fermentation of grape juice known as argol is crystallised from hot water to get cream of tartar which contains impure (+) potassium hydrogen tartrate. Tartaric acid is obtained as follows :
  • From Glyoxal
  • From Fumaric acid
  • From Maleic acid
  • From dibromosuccinic acid


PROPERTIES
It is colourless crystalline solid m.p. 171ºC soluble in water, alcohol, insoluble in ether. Natural tartaric acid is d-tartaric acid.
USES
  • It is used in silvering mirror  
  • Tartar emetic is used to cause nausea and vomiting in case of poisoning  
  • Pot. acid tartrate is used in Baking powder  
  • Rochelle salt is used in preparing Fehling solution.

CITRIC ACID

It occurs in free state in citrus fruits eg.: lemon, orange lime etc. Lemon juice contains about 7% citric acid.


PREPARATION
  • From lemon juice
  • From Sugar – Fermentation of molasses in presence of aspergillus niger or citromyces pfeferianus and inorganic salts. eg.: (NH4)2CO3, MgSO4 etc.
  • From glycerol


PROPERTIES
It is colourless crystalline substance. Its m. pt. is 100ºC soluble in water and alcohol. Insoluble in ether. Optically inactive.
Complex formation : Benedict Solution
It contain Copper Sulphate, Sodium Carbonate and Sodium Citrate. The structure of complex is 
It is more stable than Fehling solution


USES
  • Mg Citrate is used as laxative in medicine
  • As mordant in dyeing and printing
  • Ferric ammonium citrate as Iron tonic
  • It is used in preparing acidulated soft drinks, jams, jellies, etc.

OXALIC ACID, ETHANEDIOIC ACID (COOH)2.2H2O

PREPARATION  
  • Oxidation of Sucrose (Lab Method)
  • Manufacture
  • Hydrolysis of Cyanogen  


PROPERTIES
Colourless crystalline compound. Soluble in water & alcohol, insoluble in ether m.p. 101.2ºC (hydrated) & 189.5ºC (anhydrous)
USES
  • As a mordant in dyeing
  • Volumetric analysis
  • Removing ink stains
  • In photography

BENZOIC ACID

C6H5COOH

PREPARATION
  • By oxidation of alcohol or aldehyde
  • By Oxidation of homologues of benzene : Oxidising agents dil. HNO3, alk. KMnO4, K2Cr2O7 + H2SO4
  • By use of Grignard’s reagent
  • Hydrolysis of Cyanides
  • Manufacture of benzoic acid


PHYSICAL PROPERTIES
It is colourless crystalline compound. Stronger than aliphatic acids and sparingly soluble in water.


Acid Character : Ortho, para directing groups with activation decrease the acid character, while meta directing groups increase the acid character of benzoic acid.


Ortho effect : Ortho substituted benzoic acids are more stronger than benzoic acid regardless of the nature of the substituent Ka of benzoic acid is 6.3 × 10–5
Acidity constants of substituted benzoic acids and order of acid strength (Ka = X × 10–5)


CHEMICAL PROPERTIES
USES
Sodium benzoate is used as food preservative.

SALICYCLIC ACID

o-hydroxy benzoic acid


PREPARATION
  • Kolbe-Schmidt reaction      
   
  • Reimer-Tiemann Reaction   


PROPERTIES
Colourless crystalline substance m. pt. 429 K. Sublimes on heating.


 

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