reações de redução e oxidação de compostos carbonílicos

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  • QFL0342 Reatividade de Compostos Orgnicos (2016)

    Reaes de reduo e oxidao de

    compostos carbonlicos

  • Reductive amination

    OH2, Ni

    or NaBH3CNCH NH2+ NH3

    OH2, Ni

    or NaBH3CNCH NHR+ RNH2

    OH2, Ni

    or NaBH3CNCH NR2+ R2NH

    1o amine

    3o amine

    2o amine

  • Preparation of AminesReductive Amination

    [1] Nucleophilic attack of NH3 on the carbonyl group forms an imine.

    [2] Reduction of the imine forms an amine.

  • The most effective reducing agent for this reaction is sodium cyanoborohydride(NaBH3CN).

    Preparation of AminesReductive Amination

    Compare to NaBH4

  • Preparation of AminesReductive Amination

    Retrosynthetic analysis

  • How to prepare 2o and 3o amines? Which starting material would you use for it?

    Preparation of AminesReductive Amination

  • How would you prepare methamphetamine?

    Preparation of AminesReductive Amination

  • 8

    Reduo de Wolff-Kishner

  • Reaes de aldedos ou cetonas com diversos

    hidretos

  • Reduo com hidretos metlicos

    Os reagentes mais comuns usados em laboratrio para a reduo de aldedos e cetonas so NaBH4; LiAlH4 NaH (fontes de on hidreto H:-, um poderoso nuclefilo)

    on hidretoHidreto de ltioalumnio

    Boro-hidreto de sdio

    H

    H H

    H

    H-B-H H-Al-HLi +Na+

    H

  • Reduction of carboxylic acid with LiAlH4

    Reduction of aldehyde with LiAlH4

    https://www.youtube.com/watch?v=odkFRsbWLF4

  • LiAlH4 + 4 H2O LiOH + Al(OH)3 + 4 H2

    LiAlH4 reage violentamente com gua, metanol e outros solventes prticos. As redues usando LiAlH4 so realizadas em ter dietlico ou tetra-hidrofurano (THF) anidros.

    https://www.youtube.com/watch?v=odkFRsbWLF4

  • Reduo com LiAlH4

    +

    + Sais de alumnio

    ter dietlicoou THF

    O

    OH

    4 RCR LiAlH 4

    4 RCHR

    tetralcoxi aluminato

    (R2CHO)4 Al-

    Li+ H2 O

  • Uso de LiAlH4 em reaes de reduo

  • RC

    OH

    O

    RC

    OR

    O

    RC

    X

    O

    RC

    NH2

    O

    RC

    O

    O

    C

    O

    R

    haletos de acila

    cidoscarboxlicos

    steresanidridos amidas

    RC

    R'

    O

    RC

    H

    O

    aldedos cetonas

    reduzidos por LiAlH4

    reduzidos por NaBH4 no so reduzidos por NaBH4

  • Redues com NaBH4 podem ser realizadas em metanol aquoso, em metanol puro, ou em etanol

    Um mol de NaBH4 reduz quatro mols de aldedo e cetona

    Um tetralcoxi borato

    Boratos+

    +metanol

    O

    4 RCH NaBH 4

    (RCH2O)4B-Na+ 4 RCH 2 OH

    H2O

  • Reduo com NaBH4

    from

    water

    from the hydride

    reducing agent

    +

    H

    H O O BH3

    OH

    H

    H

    H-B-HNa+

    R-C-R' R-C-R'

    Na+

    H2 O

    R-C-R'

    A partir da gua

    A partir do agente redutor

  • Quimiosseletividade nas redues

    O OH

    RCH=CHCR' RCH=CHCHR'1 . NaBH 4

    2 . H 2 O

    +Rh

    O O

    RCH=CHCR' RCH 2 CH2 CR'H2

    4

    H2O

  • Treatment of a nitrile with a milder reducing agent such as DIBAL-H followed by waterforms an aldehyde.

    (i-Bu2AlH)2

    DIBAL-H (hidreto de diisobutilaluminio) (Hidreto mais brando)

  • Reduo de steres com DIBALH

    O hidreto de di-isobutilalumnio (DIBALH) a -78C reduz seletivamente steres a aldedos

    a -78C, o intermedirio somente liberado aps a hidrlise cida.

  • With DIBAL-H, nucleophilic addition of one equivalent of hydride forms an anion which isprotonated with water to generate an imine. The imine is then hydrolyzed in water toform an aldehyde.

  • RC

    OH

    O

    RC

    OR

    O

    RC

    NH2

    O

    cidoscarboxlicos

    steres amidas

    RC

    R'

    O

    RC

    H

    O

    aldedos cetonas

    LiBH4

    NaBH4

    NaCNBH3

    LiAlH4

    BH3

    RC

    H

    NH

    iminas

    RC

    H

    O

    LiAlH4

    OoC

    viaalcool

    ou DIBAL

    via cloretosde acila

    R NHR R OH R R

    OH

    R OH R NR2 R OH

    reduz

    no reduz

    reduz lentamente

  • Equivalentes biolgicos de hidretos metlicos

    NADH

    (hidreto biolgico)

  • NAD+

    nicotinamida adeninadinucleotdeo

    (forma oxidada)

    NADHnicotinamida adenina

    dinucleotdeo reduzida

  • NAD+ NAD+

    NAD+

  • Redues quimiosseletivas por enzimas

  • Oxidation of Aldehydes and Ketones

    Aldehydes are readily oxidized to carboxylic acid but ketones are unreactive (except under the most vigorous conditions).

    Aldehydes are more easily oxidized because they posses a hydrogen atom bonded to the carbonyl carbon. This hydrogen atom can be removed as a proton with the final result being the oxidation (loss of hydrogen) from the original aldehyde. Ketones have no expendable carbonyl-hydrogen bond.

  • Oxidation of Aldehydes and Ketones Many oxidizing agents will convert aldehydes to carboxylic

    acids. Some of these are Jones reagent, hot nitric acid and KMnO4.

    One drawback to the Jones reagent is that it is acidic. Many sensitive aldehydes would undergo acid - catalyzed decomposition before oxidation if Jones reagent was used

    CCH3(CH2)4

    O

    H CCH3(CH2)4

    O

    OHJones

  • Oxidation of Alcohols and aldehydes with cromic acid

    Ester chromate

    aldehyde gem-diol

    alcohol

    Carboxylic acid

  • A Milder Oxidizing Agent

    For acid sensitive molecules a milder oxidizing agent such as the silver ion (Ag+) may be used. A dilute ammonia solution of silver oxide, Ag2O, (Tollens reagent) oxidizes aldehydes in high yield without harming carbon-carbon double bonds or other functional groups.

  • Oxidizing Agents in Organic Chemistry

    PCC Generally a Mild Oxidant (1 Alcohol Aldehyde)

    Jones Reagent Harsher Oxidant (1 Alcohol Carboxylic Acid)

    Alcohol Often Dissolved in Acetone While Jones Reagent Added

    N H CrO3Cl

    Pyridinium chlorochromate

    (PCC)

    H2CrO4

    Chromic Acid

    (Jones Reagent)

    CrO3/H2SO4

  • General Oxidizing Agent Selection

    MeOH 1Alcohol 2Alcohol 3Alcohol

    PCC H2C=O Aldehyde KetoneNo

    Reaction

    Cr6+

    H2SO4HCO2H

    Carboxylic

    AcidKetone

    No

    Reaction

    Just as in Reductions, Oxidation Products Depend on Reagent

    Generally Dont Oxidize 3 Alcohols (No Texas Carbons)

    PCC Good For Aldehydes From Primary Alchols

    Cr6+/H2SO4 Reagents, KMNO4 Primary Carboxylic Acids

    Use What You Like For Most Ketones

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