2444-102811

2444-102811 - Avg. Stnd. Dev. 19.9 / 25 QUIZ 6 5.6 Chem...

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QUIZ 6 Avg. 19.9 / 25 Stnd. Dev. 5.6 Chem 244410/31 http: //mediasite .dl. uconn . edu/Mediasite/Viewer/ ? peid=1e93 78b4c7dd4db78bea889eb4b82cc91d Chem 244411/2 http: //mediasite .dl. uconn . edu/Mediasite/Viewer/ ? peid=081ba 0908176409498fdcca29ea6c27b1d Ch2444F11 87254
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Carboxylic Acids 2 • Remember that carboxylic acids are good Brønsted-Lowry acids, with a pK a between 1-5 for the most derivatives. • Therefore, if an acid reacts with a “nucleophile that is also basic (sodium hydroxide, sodium methoxide, or sodium amide), the acid-base reaction dominates and the product is the anionic salt of a carboxylic acid. • Butanoic acid ( 7 ) reacts with sodium hydroxide, for example, to give sodium butanoate ( 8 ) as the conjugate base, and water as the conjugate acid. • This means that if a carboxylic acid is formed as a product in the presence of a base such as sodium hydroxide, the initially formed carboxylic acid is converted to the carboxylate salt. O- H O Na + OH O Na + O H -O-H 8 7
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Hydrolysis: acid chlorides 3 • Compound 11 is the key tetrahedral intermediate and it has two leaving groups, OH (from the water nucleophile) and Cl (from the acid chloride) . • Chlorine is a superior leaving group when compared to OH. C 3 H 7 O Cl C 3 H 7 O Cl H C 3 H 7 O Cl H H C 3 H 7 OH Cl O H OH Cl C 3 H 7 O H O H H C 3 H 7 O C 3 H 7 O O H H C 3 H 7 O O H H 2 O H 2 O + H + + H 2 O - H + - Cl - - H + 8 9 10 11 12 7
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Hydrolysis: acid chlorides 4 • Hydroxide is a strong base (it is the conjugate base of water), but it is also a nucleophile in reactions with carboxylic acid derivatives. • If the basic OH ion reacts with acid chloride 8 , attack at the carbonyl carbon gives tetrahedral intermediate 13 directly. The alkoxide unit can donate electrons back to the carbon and regenerate the C=O unit, but there are two leaving groups. Loss of chloride ion from 13 leads directly to the acid, 7 . • Once the acid is formed it is in a solution of hydroxide , which is a strong base (as mentioned above). The acid and the base react immediately to give the anionic salt of the carboxylic acid, 14 . Carboxylate anion 14 is the Fnal product of this reaction . • In order to isolate 7 , an acid must be added to 14 that is signiFcantly stronger than 7 (a mineral acid such as HCl for example) in a second chemical step . Therefore, treatment of 14 with aqueous HCl (shown as H 3 O + ) gives 7 . C 3 H 7 O Cl C 3 H 7 O Cl OH C 3 H 7 O O O– H C 3 H 7 O H 3 O + C 3 H 7 O O H OH OH - Cl 8 13 7 14 7
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Hydrolysis: anhydrides 5 • The base-induced reaction of the symmetrical dipropanoic anhydride ( 15 ) illustrates the mechanism of base hydrolysis with anhydrides, in a reaction that gives two equivalents of propanoic acid. • Acyl addition of the nucleophilic hydroxide gives tetrahedral intermediate
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This note was uploaded on 02/25/2012 for the course CHEM 244 taught by Professor Jardin,j during the Fall '08 term at UConn.

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2444-102811 - Avg. Stnd. Dev. 19.9 / 25 QUIZ 6 5.6 Chem...

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