Chapter 9_03e49b317bb034290c0439e7e582fae2.pptx
Transcript
Aldehydes and Ketones: Nucleophilic Addition reactions C H A P T E R 9 1 In This Chapter • Nomenclature of aldehydes and ketones • Synthesis of aldehydes and ketones • Reactions of aldehydes and ketones Oxidation Nucleophilic Addition Reactions 2 Introduction 3 Aldehydes (RCHO) and ketones...
Aldehydes and Ketones: Nucleophilic Addition reactions C H A P T E R 9 1 In This Chapter • Nomenclature of aldehydes and ketones • Synthesis of aldehydes and ketones • Reactions of aldehydes and ketones Oxidation Nucleophilic Addition Reactions 2 Introduction 3 Aldehydes (RCHO) and ketones (RCOR’) are characterized by the carbonyl (C=O) functional group. Carbonyl compounds are the most abundant compounds in nature. Many important biological, pharmaceutical, synthetic polymers compounds contain carbonyl groups. Introduction 4 Industrial Applications Acetone and methyl ethyl ketone are important solvents. Formaldehyde is used in polymers like Bakelite . Flavorings and additives like vanilla, cinnamon, and artificial butter. Introduction 5 9.1 The Nature of Carbonyl Compounds 6 In Carbonyl group, C is bonded with O with double bond (C=O). C ═O bond is planar, shorter, stronger, and more polar than C═C bond in alkenes. Carbon is electropositive (Electrophilic) and oxygen is electronegative (Nucleophilic). Carbon is sp 2 hybridized. R-C=O is called as Acyl group . We can categorized carbonyl compounds into two general groups. 1. Aldehyde and Ketone (Acyl group, R-C=O , is bonded to H or C ) 2. Carboxylic acids and their derivativesC O 9.1 The Nature of Carbonyl Compounds 7 General Group of Carbonyl compounds: 9.2 Naming Aldehydes and Ketones 8 IUPAC Naming of Aldehydes: 1. Select the parent (longest) carbon chain containing aldehyde (-CHO) group. 2. –CHO carbon will always be numbered as C- 1 . 3. Replace terminal –e of corresponding alkane with –al. If there are more then one CHO group then use appropriate suffix (di, tri etc) before – al . 4. If the –CHO group is attached to a ring, use the suffix carbaldehyde. C H 3 C H 2 C HC H 3 C H 2 C HO 3-Methylpentanal Cyclohexanecarbalde hydeH O 9.2 Naming Aldehydes and Ketones 9 IUPAC Naming of Aldehyde:O H C l C H 2 C H 2 C H O O H C O H O H 9.2 Naming Aldehydes and Ketones 10 Common Names of Aldehyde: 9.2 Naming Aldehydes and Ketones 11 IUPAC Naming of Ketones: 1. Select the parent (longest) carbon chain containing ketone (- C=O) group. 2. Begin numbering from the end nearer to carbonyl carbon. 3. Replace terminal –e of corresponding alkane with –one. Mention the position of C=O group also. If there are more then one C=O group then use appropriate suffix (di, tri etc) before – one . 2-Butanone 2- methylcyclohexan oneO O 9.2 Naming Aldehydes and Ketones 12 IUPAC Naming of Ketones:H 2C C C H O H 3C H 3C C H 3 O H 3C C H 3 C H 3 C C H 2 C H 2 C H 2 C C H 2 C H 3 O O O O 9.2 Naming Aldehydes and Ketones 13 Common Names of Ketones: 9.2 Naming Aldehydes and Ketones 14 Aldehydes and Ketones as Substituents: The R–C=O as a substituent is an acyl group, used with the suffix –yl. CH 3 CO: acetyl; CHO: formyl; C 6 H 5 CO: benzoyl The prefix oxo - is used if other functional groups are present and the doubly bonded oxygen is labeled as a substituent on a parent chain 9.2 Naming Aldehydes and Ketones 15 Aldehydes and Ketones as Substituents: On a molecule with a higher priority functional group, a ketone is an oxo and an aldehyde is a formyl group . COOH has higher priority on aldehyde. Aldehydes have a higher priority than ketones. 3-methyl-4-oxopentanal 3-formylbenzoic acidC H 3 C C HC H 3 C H 2 C HOO C O O H C H O 9.3 Synthesis of Aldehydes and Ketones 16 Synthesis of Aldehydes Oxidation of primary alcohols (1 ) using pyridinium chlorochromate (PCC) will produce aldehyde. 9.3 Synthesis of Aldehydes and Ketones 17 Synthesis of Ketones Oxidation of secondary alcohols (2 ) using pyridinium chlorochromate (PCC), CRO 3 , Na 2 Cr 2 O 7 will yield ketones. 9.3 Synthesis of Aldehydes and Ketones 18 Synthesis of Ketones Hydration of terminal alkynes in the presence of Hg +2 as catalyst, will produce ketone. 9.3 Synthesis of Aldehydes and Ketones 19 Synthesis of Ketones Friedel-Crafts Acylation of an aromatic ring produces aromatic ketones. 9.3 Synthesis of Aldehydes and Ketones 20 E.g.: How could you prepare pentanal from 1-Pentanol? E.g.: How could you prepare 2-hexanone from 1- hexene? 9.4 Oxidation of Aldehydes 21 Aldehydes oxidized to carboxylic acids. Ketones are unreactive towards the oxidation. Silver ion, AgNO 3 , in aqueous ammonia (Tollens’ reagent) oxidizes aldehydes to acids. Ag deposited on the walls of the reaction flask as a shinny mirror. This test is the simple test to identify the presence of aldehyde group in the molecule. Ketone will be unreactive towards this reaction. 9.5 Nucleophilic Addition Reactions of Aldehyde and Ketones: Reduction. 22 A strong nucleophile attacks the electropositive carbonyl carbon, forming an alkoxide ion that is then protonated to produce alcohol. The sp 2 hybridized carbonyl carbon re- hybridized to sp 3 during forming of alkoxide anion. 9.5 Nucleophilic Addition Reactions of Aldehyde and Ketones: Reduction. 23 Sodium borohydride, NaBH 4 , can reduce ketones to secondary alcohols and aldehydes to primary alcohols. Lithium aluminum hydride, LiAlH 4 , is a powerful reducing agent, so it can also reduce carboxylic acids and their derivatives. a l d e h y d e o r k e t o n eR R (H ) O N a B H 4 C H 3 O H R R (H ) O H H 9.5 Nucleophilic Addition Reactions of Aldehyde and Ketones: Reduction. 24 Nucleophiles can be negatively charged ( : Nu ) or neutral ( : Nu) at the reaction site 9.6 Nucleophilic Addition water: Hydration 25 Nucleophilic addition of water to the aldehydes or ketones gives 1,1-diols ( geminal diols ). It is a reversible reaction. Related Questions: 9.32 (a-c), 9.33 (a-c) 9.6 Nucleophilic Addition water: Hydration 26 Hydration can be catalyzed by both acid or base. In base-catalyzed hydration, nucleophile is the hydroxide ion (OH - ) , which is a much stronger nucleophile than water. 9.6 Nucleophilic Addition water: Hydration 27 In Acid-catalyzed hydration, acid first protonates the carbonyl oxygen. That’s protonation makes carbonyl carbon more electrophilic. That’s facilitate the attack of H 2 O. 9.7 Nucleophilic Addition Alcohols: Acetal Formation 28 Acid-catalyzed addition of alcohols to Aldehydes and Ketones produces Acetals. Acetals have two -OR groups bonded to same carbon. 9.7 Nucleophilic Addition Alcohols: Acetal Formation 29 The first addition of alcohol yields a hydroxy ether, called a hemiacetal (reversible); which further react with second mole of alcohol to yield Acetal and water. 9.7 Nucleophilic Addition Alcohols: Acetal Formation 30 Acetals can serve as protecting groups for aldehydes and ketones It is convenient to use a diol, to form a cyclic acetal (the reaction goes even more readily). Hydrolyze easily in acid; stable in bases, reducing agents and various nucleophiles. 9.8 Nucleophilic Addition Amines: Imine Formation 31 Ammonia ( NH 3 ) and primary amines ( RNH 2 )add to aldehydes and ketone to produce imines ( R 2 C=NR’ ).O C H3N H 2 9.9 Nucleophilic Addition Grignard Reagents: Alcohol Formation 32 Treatment of aldehydes or ketones with Grignard reagents (R - -Mg + X) yields an alcohol Grignard Reagents have alkyl-Metal bond, producing carbanions (R - ). Carbanions will act as nucleophile and attack on the carbonyl carbon to produce magnesium alkoxide intermediate, which on protonation gives alcohol. It is an irreversible reaction. 9.9 Nucleophilic Addition Grignard Reagents: Alcohol Formation 33M gBr H C O H H3O+ + ether M gBr O H H3O+ + etherO C H 3 C H 2 M g B r , e t h e r H 3 O
