Carboxylic acids

The combination of a carbonyl group and a hydroxyl on the same carbon atom is called a carboxyl group. Compounds containing the carboxyl group are called carboxylic acids. The carboxyl group is one of the most widely occurring functional groups in organic chemistry.
Aromatic Carboxylic acids: Carboxylic acids have an aryl group bound to the carboxyl group is known as aromatic carboxylic acids. The general formula of an aliphatic aromatic carboxylic acid is Ar-COOH.
Acidity of carboxylic acid:
A carboxylic acid may dissociate in water to give a proton and a carboxylate ion. Dissociation of a carboxylic acid involves breaking an O-H bond gives a carboxylate ion with the negative charge spread out equally over two oxygen atoms, compared with just one oxygen atom in an alkoxide ion. The delocalized charge makes the carboxylate ion more stable therefore; dissociation of a carboxylic acid to a carboxylate ion is less endothermic.
Preparation Methods:
1. Oxidation:
The oxidation of aldehyde with oxidizing agents such as CrO3 to forms carboxylic acids containing the same numbers of carbon atoms with a oxidizing agents like chromic acid, chromium trioxide. The silver oxide (Ag2O) in aqueous ammonia solution (Tollen’s reagent) is mild reagent give good yield at room temperature. E.g. Acetaldehyde reacts with CrO3 in aqueous acid to give acetic acid.
2. Grignard reagents (from CO2):
Carboxylic acid can be prepared by the reaction of Grignard reagent (alkyl magnesium halide) with carbon dioxide (CO2) in presence of dry ether. Grignard reagents react with carbon dioxide to forms a magnesium carboxylates which on hydrolysis by dilute HCl produces carboxylic acids.
3. Hydrolysis of nitrile:
The hydrolysis of nitrile or cyanide in presence of dilute acid to forms a carboxylic acid. In this reaction –CN group is converted to a –COOH group.
4. Hydrolysis Reactions:
All the carboxylic acid derivatives can be hydrolyzed into the carboxylic acid in the acidic or basic media; the hydrolysis reaction is fast and occurs in presence of water with no acid or base catalyst.
1. From Ester (Hydrolysis of ester): Ester can be hydrolyzed in either acidic or basic medium to yield carboxylic acid. The ester is heated with an excess of water contains strong acid or base catalyst.
Properties of Carboxylic Acids:
1. Low molecular weights carboxylic acids are colourless liquid at room temperature i.e. lower member ate liquid up to C9 and have characteristic odors whereas higher members are solid.
2. Carboxylic acids are polar organic compound. Low molecular weight carboxylic acids (first four members) are soluble in water whereas solubility in water decrease as molecular weight and chain lengthing increases.
3. Aromatic acids are insoluble in water.
4. Carboxylic acids have higher melting and boiling point due to their capacity to readily form stable hydrogen-bonded dimers.

1. P.M. Jadhav Assistant Professor Dept. of Chemistry M.S.P. Mandals, Shri Muktanand college, Gangapur, Dist : Aurangabad. Carboxylic acid

2. The combination of a carbonyl group and a hydroxyl on the same carbon atom is called a carboxyl group. Compounds containing the carboxyl group are called carboxylic acids. The carboxyl group is one of the most widely occurring functional groups in organic chemistry. Introduction

3. Carboxylic acids are classified according to the substituent that is attached to the carboxyl carbon. Aliphatic Carboxylic acids: Carboxylic acids have an alkyl group bound to the carboxyl group is known as aliphatic carboxylic acids. The general formula of an aliphatic carboxylic acid is R-COOH . Aromatic Carboxylic acids: Carboxylic acids have an aryl group bound to the carboxyl group is known as aromatic carboxylic acids. The general formula of an aliphatic aromatic carboxylic acid is Ar -COOH. Classification of carboxylic acid

4. Nomenclature 1 . Common Names: Several aliphatic carboxylic acids have been known by their common names according to source of origin . 2 . IUPAC Names: IUPAC names of straight chain aliphatic carboxylic acids are derived by replacing e of the corresponding alkane by the suffix – oic acid . They are named as alkanoic acids. Molecule Origin Formula Formic acid Extracted from Formica HCOOH Acetic acid Isolated from vinegar (acetum) CH 3 COOH Butyric acid Found in butter. C 3 H 7 COOH Formula Structure Common name IUPAC name CH 2 O 2 HCOOH Formic acid Methanoic acid C 2 H 4 O 2 CH 3 COOH Acetic acid Ethanoic acid C 3 H 6 O 2 CH 3 CH 2 COOH Propanoic acid Propanoic acid C 4 H 8 O 2 CH 3 CH 2 CH 2 COOH Butyric acid Butanoic acid

5. A carboxylic acid may dissociate in water to give a proton and a carboxylate ion. Dissociation of a carboxylic acid involves breaking an O-H bond gives a carboxylate ion with the negative charge spread out equally over two oxygen atoms, compared with just one oxygen atom in an alkoxide ion. The delocalized charge makes the carboxylate ion more stable therefore; dissociation of a carboxylic acid to a carboxylate ion is less endothermic . The substituent attached to the carboxyl group of carboxylic acid influence the acidity of carboxylic acids. The electronic factors such as inductive effect, resonance effect and hydrogen bonding exerted by the substituents affect on the acid strength of carboxylic acid. Acidity of carboxylic acid

6. 1. Oxidation: The oxidation of aldehyde with oxidizing agents such as CrO 3 to forms carboxylic acids containing the same numbers of carbon atoms with a oxidizing agents like chromic acid, chromium trioxide. The silver oxide (Ag 2 O) in aqueous ammonia solution ( Tollen’s reagent) is mild reagent give good yield at room temperature. E.g. Acetaldehyde reacts with CrO 3 in aqueous acid to give acetic acid . 2. Grignard reagents (from CO 2 ): Carboxylic acid can be prepared by the reaction of Grignard reagent (alkyl magnesium halide) with carbon dioxide (CO 2 ) in presence of dry ether. Grignard reagents react with carbon dioxide to forms a magnesium carboxylates which on hydrolysis by dilute HCl produces carboxylic acids. Preparation Methods

7. 3. Hydrolysis of nitrile: The hydrolysis of nitrile or cyanide in presence of dilute acid to forms a carboxylic acid. In this reaction –CN group is converted to a –COOH group. 4. Hydrolysis Reactions: All the carboxylic acid derivatives (ester, acid anhydride, acid chloride, amide) can be hydrolyzed into the carboxylic acid in the acidic or basic media; the hydrolysis reaction is fast and occurs in presence of water with no acid or base catalyst .

8. Low molecular weights carboxylic acids are colourless liquid at room temperature i.e. lower member ate liquid up to C 9 and have characteristic odors whereas higher members are solid. Carboxylic acids are polar organic compound. Low molecular weight carboxylic acids (first four members) are soluble in water whereas solubility in water decrease as molecular weight and chain lengthing increases. Aromatic acids are insoluble in water. Carboxylic acids have higher melting and boiling point due to their capacity to readily form stable hydrogen-bonded dimers. Properties of Carboxylic Acids

9. 1 ) Decarboxylation: The reaction in which salt of carboxylic acid on heating with soda lime ( NaOH + CaO ), loses CO 2 to give a product alkanes is called a decarboxylation. Decarboxylation of the most carboxylic acid is exothermic and is slow reaction . 2) Ester formation: Reaction of a carboxylic acid with an alcohol under acidic conditions produces an ester. Esterification is carried out by warming a mixture of a carboxylic acid and an alcohol in the presence of a strong acid catalyst. The excess of alcohol used in the esterification reaction. The acid-catalyst can be provided by strong mineral acids such as H 2 SO 4 , HCl and H 3 PO 4 and dehydrating agent zinc chloride (ZnCl 2 ). Chemical reactions

10. 3) Reduction: The reduction of carboxylic acid leads to the formation of primary alcohols. This reduction carried out using strong reducing agents like Lithium aluminum hydride (LiAlH 4 ). The aldehyde is an intermediate in this reduction, but it cannot be isolated because it is reduced more easily than the acid . 4) Synthesis of Acid Chlorides : The acid chlorides forms by the reaction of a carboxylic acid with thionyl chloride (SOCl 2 ), phosphorous pentachloride (PCl 5 ) or oxalyl chloride ( COCl ) 2 . The reaction of thionyl chloride with carboxylic acid to gives acetyl chloride and produces SO 2 while in phosphorous pentachloride reaction produce HCl and the oxalyl chloride reaction produces HCl , CO, and CO 2 gaseous.

11. 5) Amide Formation: The acid chlorides form by the reaction of a carboxylic acid with thionyl chloride or phosphorous pentachloride which when react with ammonia to give amide . 6 ) Hell- Volhard Zelinsky Reaction: When the carboxylic acid on treatment with bromine and catalytic amount of phosphorus to give selective product α- bromo carboxylic acid (2-bromo acid), the α-hydrogen atom is replaced by the halogen is known as Hell- Volhard Zelinsky Reaction. The reaction in which the hydrogen atom of an carboxylic acid replaces with a halogen atom on the α-carbon of a carboxylic acid.

12. Acrylic acid is the simplest unsaturated carboxylic acid with both double bond and carbonyl group attached to same carbon atom. It is valuable and commonly used chemical intermediate. It is also known as 2-Propenoic acid. It was first prepared by the air oxidation of acrolein . Acrylic acid

13. 1 . Oxidation of acrolein : The air oxidation of acrolein in presence of metal oxide catalyst like V 2 O 5 /MoO 3 , Ag 2 O, to give acrylic acid. 2. From Epoxide : Ethylene oxide on heating with hydrogen cyanide to give ethylene cyanohydrin which on hydrolysis give β- hydroxy propionic acid followed by heating gives acrylic acid. Preparation of Acrylic acid

14. 3. β- hydroxy carboxylic acid (β- hydroxy propionic acid) on heating to give acrylic acid . 4. The reaction of α or β-halo carboxylic acid with alc. KOH or NaOH to give acrylic acid. E.g. 2-chloropropionic acid and 3-bromopropionic acid react with alc.KOH to give acrylic acid.

15. 1. Diels-Alder Reaction: Acrylic acid is acts as dienophile in the Diels-Alder reaction. The varietes of dienes undergo cycloaddition reaction with acrylic acid to give Diel -Alder adduct . 2. Oxidation: The oxidation of acrylic acid to give glyceric acid as intermediate product which further oxidized to give oxalic acid. Chemical Reactions

16. 3. Addition Reactions: The double bond in acrylic acid acts as Michael acceptor and which undergo addition reaction to give different product. The reaction in which addition reaction of acrylic acid with a compound with active methylene group such as malonic ester, acetoacetic ester and cyanoacetic ester in presence of a base.

17. Carboxylic acids containing two carboxyl groups are called dicarboxylic acids. They are named by adding dioic acid as a suffix to the name of the corresponding hydrocarbon. Both the carboxyl carbon atoms are numbered as a part of the main chain. Dicarboxylic acid

18. Preparation: 1 . The reaction of bromosuccinic acid with moist silver oxide to give malic acid . 2. The tartaric acid on partial reduction in presence of hydroiodic acid to give malic acid. Malic acid

19. Malic acid is soluble in water, alcohol and sparingly soluble in ether . It is colourless crystalline solid. Malic acid exhibits optical isomerism as it contains chiral carbon hence exists in two optically active and one inactive form. Physical Properties

20. 1. Malic acid when heated at 150-180°C it gives a mixture of fumaric acid and maleic anhydride . 2. Malic acid on oxidation with mild oxidizing reagent it is converted to oxaloacetic acid. Chemical reaction

21. Preparation 1. The reaction of glyoxal with HCN to give glyoxal cyanohydrin which on hydrolysis to give tartaric acid . Tartaric acid

22. 2. Hydroxylation of maleic and fumaric acids: Maleic acid on oxidation with alkaline KMnO 4 gives meso -tartaric acid whereas oxidation of fumaric acid with alkaline KMnO 4 to gives (±)-tartaric acid. 3. Naturally occurring tartaric acid is dextro rotatory and is potassium salt present in the various fruits such as grapes, plums and argol . In the fermentation of grape juice, the potassium hydrogen tartarate deposits as a reddish brown crust ( argol ) which on crystallization, argol deposits crystals of the salt known as cream of tartar.

23. Malic acid is water soluble in water, alcohol but insoluble in ether. It is colourless crystalline solid. Tartaric acid exhibits optical isomerism as it contains two similar chiral carbons hence exists in two optically active enantiomeric form and meso form. Chemically all the three forms behave in the same way. Tartaric acid behaves as a dicarboxylic acid as well as secondary alcohol. Physical properties

24. 1. Action of Heat: The tartaric acid when heated at 150 C to give tartaric anhydride . The tartaric acid on strong heating above its melting point to gives pyruvic acid . The tartaric acid when heated with cone. H 2 SO 4 , it decomposes to CO 2 , CO and H 2 O. Chemical reactions

25. 2. Reduction : The reduction of tartaric acid with hydroiodic to give malic acid which further reduced to give succinic acid . 3 . Oxidation : The oxidation of tartaric acid with HNO 3 to form tartonic acid which further oxidized to give oxalic acid . When the tartaric acid is oxidized with Fenton’s reagent to gives dihydroxy fumaric acid . 4. Complex formation: Sodium potassium tartarate forms complex with Cu 2+ .

26. Preparation: Citric acid is prepared by the fermentation of sugars (Cane-Sugar, glucose) or by the fermentation of dilute solution of molasses in the presence of certain micro-organisms. Citric acid is also manufactured from the citrus fruit wastes. Citric acid

27. Citric acid is colourless crystalline solid. It is soluble in water and alcohol and sparingly soluble in ether. A molecule of citric acid contains one tertiary hydroxyl group and three carboxyl groups. Citric acid exhibits the properties of both alcohol and carboxylic acid. Physical properties

28. 1. The citric acid on treatment with acetyl chloride forms monoacetyl derivative acetylcitric acid. The reaction takes place on hydroxyl group of citric acid . 2. Reduction : The reduction of citric acid with HI to forms tricarballylic acid. The reaction takes place on hydroxyl group of citric acid. Chemical reactions

29. 3. Salt formation : The citric acid forms a trisodium citrate when treated with the alkali such as NaOH . 4. Effect of heat : When citric acid is heated to 150°C it gives β- hydroxy unsaturaed acid ( aconitic acid) with removal of water molecule.

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