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Chapter 2 Aldehydes and Ketones Table of Contents Introduction 1. Aldehydes 2. Nomenclature of Aldehydes 3. Physical Properties of Aldehydes 4. Chemical Properties of Aldehydes 5. Preparation of Aldehydes 6. Some Important Aldehydes 7. Ketones Chapter 2 Aldehydes and Ketones Table of Contents 8. Nomenclature of Ketones 9. Physical Properties of Ketones 10. Chemical Properties of Ketones 11. Preparation of Ketones 12. Acetone Chapter 2 Aldehydes and Ketones Warm Up • What are the simple C-H-O compounds besides alcohols? • What do you think about why aldehydes and ketones are studied together? • Can you list down some name of solvents that you learn so far? Chapter 2 Introduction • The group C=O is known as carbonyl group. • This group is found in aldehydes, ketones, carboxylic acids, esters and acid derivatives. • In this group carbon atom makes sp2 hybridization. Therefore there are one pi and three sigma bonds in carbonyl group. • Oxygen is more electronegative than carbon in the carbonyl group. Chapter 2 1. Aldehydes • Compounds in which one hydrogen atom and one carbon atom are bonded to the carbon atom in the carbonyl group are called aldehydes. • R may be alkyl or aryl group. • CnH2nO is general formula of aliphatic aldehydes. • The simplest member is formaldehyde, HCOH. O R C H or RCHO is representation of aldehydes. Chapter 2 2. Nomenclature of Aldehydes • Longest chain of carbon atoms containing the aldehyde group is selected. • Number 1 is the carbonyl carbon. • Change –e ending in alkane names with –al. O O H C H Methanal Formaldehyde H3C C CH3 O H Ethanal Acetaldehyde H3C CH CH 2-methyl propanal Chapter 2 2. Nomenclature of Aldehydes Example 2 Name the following compounds CH3 A. H3C O CH C H2 C H H3C C H2 3-hydroxyl butanal H CH 3-bromo-2-nitro butanal O D. O C C NO2 2-ethyl-3-methyl pentanal CH CH H3C C2H5 C. O B. CH OH Br H2 C H C C H2 3-phenyl propanal H Chapter 2 2. Nomenclature of Aldehydes Example 3 Draw the structures of following aldehydes. A. 2-chloropentanal B. 2,3-dihydroxylpropanal C. 2, 2-dibromohexanal D. 3-cyclopropyl-2-methyl-pentanal Chapter 2 3. Physical Properties of Aldehydes • They are polar molecules. • They do not have hydrogen bonds between their molecules; therefore they have lower boiling points than corresponding alcohols but higher boiling points than ethers. • Formaldehyde is a gas at room temperature. • The C2 to C11 are liquids. Higher than C11 are solids at room temperature. • Lower members are soluble in water. • As the molar mass increases solubility decreases. Chapter 2 4. Chemical Properties of Aldehydes 1. Oxidation Reactions • K2Cr2O7, KMnO4 or K2CrO4 can be used in the presence of acids. O R C H aldehyde [O] O H3C C H acetaldehyde O R C OH carboxylic acid O [O] H3C C OH acetic acid Chapter 2 4. Chemical Properties of Aldehydes Reaction with KMnO4 • Aldehydes are oxidized with KMnO4 to carboxylic acids. O 5 R C H + 2MnO4- + 6H+ aldehyde O cold 5 H3C C H + 2MnO4- + 6H+ cold Acetaldehyde O 5R C OH + 2Mn+ + 3H2O carboxylic acid O 5 H3C C OH + 2Mn+ + 3H2O Acetic Acid Chapter 2 4. Chemical Properties of Aldehydes 2. Addition Reactions • In the addition reactions pi bond in the carbonyl group, C=O, is broken. Addition of Hydrogen • Aldehydes are reduced to alcohols in the presence of Ni and Pt catalyst under certain conditions. O R C H aldehyde O H3C C H ethanal + H2 + H2 Ni, Pt Heat, Pressure Ni, Pt Heat, Pressure H2 R C OH primary alcohol H2 H3C C OH ethyl alcohol Chapter 2 5. Preparation of Aldehydes 1. Oxidation of Primary Alcohols OH R CH2 1o Alcohol OH H3C CH2 ethanol [O] O R C H + H2O aldehyde [O] O H3C C H + H2O acetaldehyde ethanal Chapter 2 5. Preparation of Aldehydes 2. Dehydrogenation of Primary Alcohols OH CuO.Cr2O3 O R CH2 R C H + H2 o 250-300 C o 1 Alcohol aldehyde OH CuO.Cr2O3 O H3C CH2 H3C C H + H2 o 250-300 C ethyl alcohol acetaldehyde Chapter 2 6. Some Important Aldehydes 1. Formaldehyde • Colorless gas with pungent odor, soluble in water. • Simplest aldehyde, discovered by the Russian Chemist A. Butlerov in 1859. •Widely used in the manufacture of building materials and household products. • It hardens proteins and prevents them decaying. • % 40 solution of formaldehyde is called formalin, used to store biological products. Chapter 2 6. Some Important Aldehydes 1. Formaldehyde • It is produced from methanol by dehydrogenation with a catalyst of Cu and silver, and it is called Hoffman Method. O H3C OH + 1/2O2 methanol Cu o 250 C H C H + H2O formaldehyde Chapter 2 6. Some Important Aldehydes 2. Acetaldehyde • Colorless, volatile and poisonous liquid, soluble in water. • Used to obtain many organic compounds, such as acetic acid, ethyl alcohol, synthetic rubber. • It has carcinogen effect. Chapter 2 7. Ketones • The compounds in which the two alkyl or aryl groups attached to the carbonyl carbon are called ketones. O • R C R' or RCOR' is representation of ketones. • R may be alkyl or aryl group. • CnH2nO is general formula of ketones. • Ketones might be either symmetrical or unsymmetrical with respect to alkyl groups. Chapter 2 8. Nomenclature of Ketones • For the simple ketones names of alkyl or aryl groups followed by the word “ketone” are used. O H3C O C CH3 H3C Dimethyl ketone acetone O C H2 C C C H2 H2 C CH3 Methyl propyl ketone CH3 CH3 Ethyl phenyl ketone H3C CH O C CH3 isopropyl methyl ketone Chapter 2 8. Nomenclature of Ketones • For the complex ketones IUPAC names are used. • Longest chain of carbon atoms containing the ketone group is selected. • Number 1 to the carbon atom starting nearer to the carbonyl carbon. • Change –e ending in alkane names with –one. CH3 H3C CH Br O O C CH3 3-methyl-2-butanone C 2 H5 C H C CH3 3-bromo-2-pentanone Chapter 2 8. Nomenclature of Ketones Example 7 O Name the following aldehydes O A. H3C H C H2 C C C2H5 B. CH3 Cl 2-ethyl cyclohexanone 4-chloro-2-pentanone C. O H2 C H2 C C D. H2 C 1-phenyl-3-pentanone CH3 H2C O C H H2 C C 4-pentene-2-one CH3 Chapter 2 8. Nomenclature of Ketones Example 8 Write the structural formulae of the following compounds. A. 2-pentanone B. 5-bromo-3-methyl-2-hexanone C. Methyl phenyl ketone D. Isopropyl methyl ketone E. 3-methyl cyclopentanone Chapter 2 9. Physical Properties of Ketones • Lower molecular weight ketones are liquids. More than C11 atoms are solids. • Soluble in water by forming hydrogen bonds. • Liquid ketones are used as solvents in the preparation of paint chemicals. • Solubility decreases with increasing size of the molecule. • They are polar molecules but there is no hydrogen bonding between the molecules. Chapter 2 10. Chemical Properties of Ketones 1. Addition Reactions Addition of Hydrogen O OH R C R' + H2 Ketone Ni heat, pressure R CH R' secondary alcohol OH O H3C C C2H5 + H2 ethyl methyl ketone Ni heat, pressure H3C C C2H5 H isobuthyl alcohol Chapter 2 11. Preparation of Ketones 1. Oxidation of Secondary Alcohols O OH R CH R' secondary alcohol [O] OH CH3CHCH3 + KMnO4 Isopropyl alcohol R C R' Ketone O NaOH CH3CCH3 Acetone Chapter 2 11. Preparation of Ketones 2. Dehydrogenation of Secondary Alcohols H H R C O CuO.Cr2O3 250oC R C R' O + H2 R' Secondary Alcohol ketone H H H3C C O CH3 2-propanol CuO.Cr2O3 250oC H3C C O + H2 CH3 Acetone Chapter 2 12. Acetone • Smallest ketone • Colorless, volatile liquid with pleasant odor. • It is soluble in water, alcohol and ether. • It is a perfect organic solvent used for varnishes, lacquers, resins, plastics, paints, oils and their derivatives. • It burns with a blue dull flame. • It is very difficult to oxidize. End of the chapter 2