Lecture 12 - 1 CH 310 N T Th 2-3:30 LECTURE 12 Textbook...

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Unformatted text preview: 1 CH 310 N T Th 2-3:30 LECTURE 12 Textbook Assignment: Chapter 17 (begin) Homework (for credit): POW 6 posted Today’s Topics: Reductions of carbonyls; Carboxylic Acids Notice & Announcements: Office Hrs (Dr C): are T & Th 9:30-11 and 1-2 PM for rest of the semester Organic Lecture Series Organic Lecture Series Organic Lecture Series Organic Lecture Series 2 Aldehydes Aldehydes And And Ketones Ketones Organic Lecture Series Organic Lecture Series Organic Lecture Series Organic Lecture Series 3 Reduction Reduction – aldehydes can be reduced to 1°alcohols – ketones can be reduced to 2°alcohols – the C=O group of an aldehyde or ketone can be reduced to a -CH 2- group Aldehydes Can Be Reduced to Ketones Can Be Reduced to O O OH RCH RCH 2 OH RCH 3 RCR' RCHR' RCH 2 R' 2 Organic Lecture Series Organic Lecture Series Organic Lecture Series Organic Lecture Series 4 Metal Hydride Reduction Metal Hydride Reduction The most common laboratory reagents for the reduction of aldehydes and ketones are NaBH 4 and LiAlH 4 – both reagents are sources of hydride ion, H: - a very powerful nucleophile Al H H H H Li + B H H H H Na + H Lithium Aluminum Hydride LAH Sodium Borohydride NaBH 4 Hydride Organic Lecture Series Organic Lecture Series Organic Lecture Series Organic Lecture Series 5 – reductions with NaBH 4 are most commonly carried out in aqueous methanol, in pure methanol, or in ethanol – one mole of NaBH 4 reduces four moles of aldehyde or ketone 4RCH O NaBH 4 ( RCH 2 O) 4 B- Na + H 2 O 4RCH 2 OH A tetraalkyl borate borate salts + + methanol Sodium Sodium Borohydride Borohydride Reduction Reduction Organic Lecture Series Organic Lecture Series Organic Lecture Series Organic Lecture Series 6 • The key step in metal hydride reduction is transfer of a hydride ion to the C=O group to form a tetrahedral carbonyl addition compound Na + H H H-B-H O R-C-R' O BH 3 H R-C-R' Na + H 2 O O- H H R-C-R' This H comes from water during hydrolysis This H comes from the hydride reducing agent + Sodium Sodium Borohydride Borohydride Reduction Reduction 3 Organic Lecture Series Organic Lecture Series Organic Lecture Series Organic Lecture Series 7 – unlike NaBH 4 , LiAlH 4 reacts violently with water, methanol, and other protic solvents – reductions using it are carried out in dry (anhydrous) diethyl ether or tetrahydrofuran (THF) 4RCR LiAl H 4 ( R 2 C H O) 4 Al- Li + H 2 O H + or OH- O H 4RC H R + + aluminum salts A tetraalkyl aluminate ether O LAH Reduction LAH Reduction Organic Lecture Series Organic Lecture Series Organic Lecture Series Organic Lecture Series 8 Lithium tetra-alkyl aluminate Al OC(R) 2 OC(R) 2 OC(R) 2 (R) 2 CO H H H H Li + Organic Lecture Series Organic Lecture Series Organic Lecture Series Organic Lecture Series 9 • Catalytic reductions are generally carried out at from 25°to 100°C and 1 to 5 atm H 2 + 25 o C, 2 atm Pt Cyclohexanone Cyclohexanol O OH H 2 1-Butanol trans- 2-Butenal (Crotonaldehyde) 2 H 2 Ni H O OH Note: Both the olefin and the carbonyl are reduced Catalytic Reduction Catalytic Reduction 4...
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This note was uploaded on 12/08/2008 for the course BIO 365R taught by Professor Draper during the Fall '08 term at University of Texas at Austin.

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Lecture 12 - 1 CH 310 N T Th 2-3:30 LECTURE 12 Textbook...

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