Carbonyl Chemistry VI + C O C. 1pm In Geology Room 112. Exam is Monday 11am-1pm. Chemistry /06/02

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1 arbonyl hemistry VI Ō - + hemistry /06/02 Exam is Monday 11am-1pm 1pm In Geology Room 112

2 The Dibasic Acids h - My - Such - hemistry /06/02 Good- Apple- Pie-

3 Fischer Esterification Esters can be prepared by treatment of a carboxylic acid with an alcohol in the presence of an acid catalyst, commonly 2 S 4 or gaseous l 3 Ethanoic acid (Acetic acid) Ethanol (Ethyl alcohol) 2 S Ethyl ethanoate (Ethyl acetate) + 2 hemistry /06/02

4 Decarboxylation Decarboxylation: loss of 2 from a carboxyl group Most carboxylic acids, if heated to a very high temperature (fried), undergo thermal decarboxylation Most carboxylic acids, however, are quite resistant to reasonable heat and melt or even boil without decarboxylation hemistry /06/02

5 Decarboxylation Exceptions are carboxylic acids that have a carbonyl group beta to the carboxyl group this type of carboxylic acid undergoes decarboxylation on mild heating β α warm xobutanoic acid Acetone (Acetoacetic acid) hemistry /06/02

6 Decarboxylation Decarboxylation occurs readily if there is any carbonyl group beta to the carboxyl Malonic acid and substituted malonic acids, for example, also undergo thermal decarboxylation Propanedioic acid (Malonic acid) hemistry /06/02

7 Decarboxylation Thermal decarboxylation of a β-ketoacid involves rearrangement of six electrons in a cyclic six-membered transition state 3 (A cyclic six-membered transition state) 3 enol of a ketone hemistry /06/02

8 Decarboxylation Thermal decarboxylation of malonic acids also involves rearrangement of six electrons in a cyclic six-membered transition state enol of a carboxylic acid hemistry /06/02

9 Saponification of Fat R 2 2 R R 2 Na 2 R - Na + Fat glycerol Fatty Acid Salt "Soap" R = 3 ( 2 ) 16 Stearic Acid 3 ( 2 ) 7 ( 2 ) 7 leic acid etc.

10 Soaps and Detergents Surface Active Agents = surfactants 3 ( 2 ) 16 - Na + Soap 3 ( 2 ) 11 S 'Na + Anionic detergent 3 l 2 N ( 2 ) ationic Detergent

11 hemistry /06/02

12 hemistry /06/02 Diazomethane Diazomethane, 2 N 2, a potentially explosive, toxic yellow gas, is best drawn as a hybrid of two contributing structures Treatment of a carboxylic acid with diazomethane gives a methyl ester + + N N ether R + 2 N 2 R 3 + N 2 Diazomethane N N A methyl ester

13 Diazomethane Esterification occurs in two steps Step 1: proton transfer from the carboxyl group to diazomethane R N N R A carboxylate anion N N hemistry /06/02

14 Diazomethane Step 2: nucleophilic displacement (S N 2) of N 2, an extraordinarily good leaving group, by the carboxylate anion R + + S N 2 3 N N R 3 + N N hemistry /06/02

15 Write the step by step Mechanism for the reaction of this compound with hot aqueous acid 3 + hemistry /06/02

16 arboxyl Derivatives Next, we will study five classes of organic compounds derived from acids by dehydration. Under the structural formula of each is a drawing to help you see its formal relationship to the carboxyl group. Rl An acid chloride RR' An acid anhydride RR' An ester RN 2 An amide R N A nitrile R- -l R- -R' hemistry /06/02 R- -R' R- -N 2 R=N The enol of an amide

17 Nucleophilic acyl substitution An addition-elimination sequence resulting in substitution of one nucleophile for another - + R Nu Y R Nu Y Tetrahedral carbonyl addition intermediate - R Nu Substitution product + Y - hemistry /06/02

18 haracteristic Reactions ere the leaving group is shown as an anion to illustrate an important point... the weaker the base, the better the leaving group NR 2 R R X Increasing leaving ability Increasing basicity hemistry /06/02

19 haracteristic Reactions alide ion is the weakest base and the best leaving group; acid halides are the most reactive toward nucleophilic acyl substitution Amide ion is the strongest base and the poorest leaving group; amides are the least reactive toward nucleophilic acyl substitution RN 2 RR' RR RX Amide Ester Anhydride Acid halide Reactivity toward nucleophilic acyl substitution hemistry /06/02

20 hemistry /06/02