9_nano_carbonyl_post

9_nano_carbonyl_post - Chapter 20 Carboxylic acids and...

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Carbonyl compounds 1 Carboxylic acids and Derivatives C O R OH C O R O R C O R O C R O C O R Cl C O R NH 2 Carboxylic Acid Ester Carboxylic Acid Anhydride Acid Chloride Amide R O Cl NaCl R O ONa ROH R O O O R RR'NH HCl HCl R O OH ROH RR'NH R O OH R O O R ROH RR'NH R O N R R' R' could be a hydrogen All downward arrows indicates that this conversion is possible in one step Chapter 20
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Carbonyl compounds 2 Nucleophilic Addition-Elimination at the Acyl Carbon The nucleophile reacts at the carbonyl group to form a tetrahedral intermediate The tetrahedral intermediate eliminates a leaving group (L) The carbonyl group is regenerated; the net effect is an acyl substitution
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Carbonyl compounds 3 To undergo nucleophilic addition-elimination the acyl compound must have a good leaving group or a group that can be converted into a good leaving group Acid chlorides react with loss of chloride ion Anhydrides react with loss of a carboxylate ion Esters, carboxylic acids and amides generally react with loss of the leaving groups alcohol, water and amine, respectively (These leaving groups are generated by protonation of the acyl compound) Aldehydes and ketones cannot react by this mechanism because they lack a good leaving group
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Carbonyl compounds 4 Relative Reactivity of Acyl Compounds The relative reactivity of carboxylic acids and their derivatives is as follows: In general, reactivity can be related to the ability of the leaving group to depart Leaving group ability is inversely related to basicity Chloride is the weakest base and the best leaving group Amines are the strongest bases and the worst leaving groups As a general rule, less reactive acyl compounds can be synthesized from more reactive ones Synthesis of more reactive acyl derivatives from less reactive ones is difficult and requires special reagents (if at all possible)
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Carbonyl compounds 5 Acid Chlorides Synthesis of Acid Chlorides Acid chlorides are made from carboxylic acids by reaction with thionyl chloride, phosphorus trichloride or phosphorus pentachloride These reagents work because they turn the hydroxyl group of the carboxylic acid into an excellent leaving group
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Carbonyl compounds 6 Mechanism with Thionyl Chloride (Nucleophilic addition-elimination reaction) O C OH R S O Cl Cl + Mechanism 1 sec. 19-8
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Carbonyl compounds 7 Mechanism with Phosphorous Trichloride (Nucleophilic addition-elimination reaction) O C R OH P Cl Cl Cl + δ + δ - δ - δ - O C R O P Cl Cl H + Cl + O C R O P Cl Cl H Cl + O C R Cl + HO P Cl Cl reacts two more times Reactions of Acyl Chlorides Acyl chlorides are the most reactive acyl compounds and can be used to make any of the other derivatives Since acyl chlorides are easily made from carboxylic acids they provide a way to synthesize any acyl compound from a carboxylic acid Acyl chlorides react readily with water, but this is not a synthetically useful reaction
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Carbonyl compounds 8 δ + δ -
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Carbonyl compounds 9 What are is the major product formed in the following reaction CH 3 OH (solvent) (thus in large excess) A) B)
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9_nano_carbonyl_post - Chapter 20 Carboxylic acids and...

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