Lecture12 given - Lecture 12 Chemistry 310N Organic...

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ecture 12 Lecture 12 Chemistry 310N Organic Chemistry II for Prehealth Professionals Unique number: 53185 Tu,Th 12:30-2:00 pm, Welch 2.224 rofessor: Jonathan Sessler Ph D Professor: Jonathan Sessler, Ph.D. sessler@mail.utexas.edu
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xidation of Aldehydes Oxidation of Aldehydes Aldehydes are oxidized to carboxylic acids by a variety of oxidizing agents, including H 2 CrO 4 . CHO H 2 CrO 4 COOH Hexanal Hexanoic acid They are also oxidized by Ag + . – In one method, a solution of the aldehyde in aqueous thanol or THF is shaken with a slurry of silver oxide ethanol or THF is shaken with a slurry of silver oxide. O O + + CH HO 3 O 3 O COH Ag 2 O THF, H 2 O NaOH HCl H 2 O Vanillic acid Vanillin
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xidation of Aldehydes Oxidation of Aldehydes Aldehydes are oxidized by O 2 in a radical chain reaction. – Many liquid aldehydes are so sensitive to air that they must be stored under N 2 . OO + CH COH 2 O 2 2 Benzoic acid Benzaldehyde
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xidative Chemical Tests for Aldehydes Oxidative Chemical Tests for Aldehydes NaOH, Tartrate H 2 O
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xidative Chemical Tests for Aldehydes Oxidative Chemical Tests for Aldehydes lad will demonstrate Vlad will demonstrate this (I think!)
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xidation of Ketones Oxidation of Ketones – Ketones are not normally oxidized by chromic acid. – They are oxidized by powerful oxidants at high temperature and high concentrations of acid or base. O O OH HNO 3 O HO Hexanedioic acid (Adipic acid) Cyclohexanone (keto form) Cyclohexanone (enol form) (this is a key precursor to nylon)
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eduction 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 eo es educed o OO OH RCH 2 RCHR' RCH 3 RCR' 2 R'
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etal 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. H H H-B-H H- l- H Li + Na + H: Hydride ion Lithium aluminum Sodium H H hydride (LAH) borohydride
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aBH eduction NaBH 4 Reduction – Reductions with NaBH 4 are most commonly carried out in aqueous methanol, in pure methanol, or in thanol ethanol. – One mole of NaBH 4 reduces four moles of aldehyde r ketone or ketone. O 4RCH NaBH 4 - + H O + methanol ( RCH 2 O) 4 B Na 2 4RCH 2 OH A tetraalkyl borate borate salts +
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aBH eduction NaBH 4 Reduction • The key step in metal hydride reduction is transfer of a hydride ion to carbon of the C=O group to form a trahedral carbonyl addition compound tetrahedral carbonyl addition compound. + This H comes from water during hydrolysis Na + H H-B-H O R- C-R' O BH 3 H 2 O O- H + H H H This H comes from the hydride reducing agent
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iAlH eduction LiAlH 4 Reduction – Unlike NaBH 4 , LiAlH 4 reacts violently with water, methanol, and other protic solvents.
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Lecture12 given - Lecture 12 Chemistry 310N Organic...

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