310-13 - CH 310 N T Th 2-3:30 LECTURE 13 Textbook...

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1 CH 310 N T Th 2-3:30 LECTURE 13 Textbook Assignment: Chapter 17 (begin) Homework (for credit): POW 6 posted Today’s Topics: Carboxylic Acids-pKa and reactions Notice & Announcements: Organic Lecture Series 2 Carboxylic Acids Carboxylic Acids Organic Lecture Series 3 the form of a carboxylic acid present in aqueous solution depends on the pH of the solution: R- C- OH O OH - H + R- C-OH O R-C- O - O H + OH - R- C-O - O + predominant species when the pH of the solution is 7.0 or greater predominant the pH of the solution is 2.0 or less present in equal concentrations when the pH of the solution is equal to the p K a of the acid pH = pK a + log 10 [A - ] [HA]
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2 Organic Lecture Series 4 Henderson-Hasselbalch equation: HA H + + A - pH = pK a + log 10 [A - ] [HA] For organic acids in equilibrium: Organic Lecture Series 5 Reaction with Bases Reaction with Bases Carboxylic acids, whether soluble or insoluble in water, react with NaOH, KOH, and other strong bases to give water-soluble salts ++ Benzoic acid (slightly soluble in water) Sodium benzoate (60 g/100 mL water) COOH COO - Na + NaOH H 2 O H 2 O Acid Base Salt water + + Organic Lecture Series 6 Reaction with Bases Reaction with Bases • They also form water-soluble salts with ammonia and amines + Ammonium benzoate (20 g/100 mL water) Benzoic acid (slightly soluble in water) COOH COO - NH 4 + NH 3 H 2 O
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3 Organic Lecture Series 7 • Carboxylic acids react with sodium bicarbonate and sodium carbonate to form water-soluble salts and carbonic acid – carbonic acid, in turn, breaks down to carbon dioxide and water CH 3 COOH NaHCO 3 H 2 CO 3 3 3 2 3 COO - Na + 3 - + H 2 O 2 H 2 3 H 2 O + + + ++ + Reaction with Bases Reaction with Bases Organic Lecture Series 8 • Reaction with bases Reaction with bases – the acid-base properties of carboxylic acids allow an easy separation of carboxylic acids from water-insoluble nonacidic compounds Exploiting pKa differences Organic Lecture Series 9 • Carbonation of Grignard reagents – treatment of a Grignard reagent with carbon dioxide followed by acidification gives a carboxylic acid MgBr C O O C-O - [MgBr] + O HCl H 2 O C-O H O Mg 2+ A magnesium carboxylate Cyclopentane- carboxylic acid + Carbon dioxide + Preparation Preparation
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4 Organic Lecture Series 10 Reduction Reduction • The carboxyl group is very resistant to reduction – it is not affected by catalytic hydrogenation under conditions that easily reduce aldehydes and ketones to alcohols, and reduce alkenes and alkynes to alkanes; it is not reduced by NaBH 4 Lithium aluminum hydride reduces a carboxyl group to a 1° alcohol – reduction is carried out in diethyl ether, THF, or other nonreactive, aprotic solvent COH O 1. LiAlH 4 2. H 2 O CH 2 OH LiOH Al( OH) 3 + + 4-Hydroxymethyl- cyclopentene Organic Lecture Series 11 – carboxyl groups are not affected by catalytic
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This note was uploaded on 10/18/2008 for the course CH 310M taught by Professor Iverson during the Fall '05 term at University of Texas.

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310-13 - CH 310 N T Th 2-3:30 LECTURE 13 Textbook...

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