chemical properties of aldehydes and properties of aldehydes and ketones oxidation of aldehydes...

Download Chemical Properties of Aldehydes and Properties of Aldehydes and Ketones Oxidation of Aldehydes Aldehydes…

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  • Chemical Properties of Aldehydes and Ketones

  • Chemical Properties of Aldehydes and Ketones

    Oxidation of Aldehydes

    Aldehydes are very easily oxidized to carboxylic acids.

    R C O HH

    HR C O H

    OR C

    OH

    primary alcohol aldehyde carboxylic acid

    [O][O]

    From the standpoint of the organic component, an oxidation can involve the removal of hydrogen atoms OR the addition of oxygen to the structure.

    Oxidation reagents: MnO4-, Cr2O72-, Ag+, Cu2+ Usually, the metal ion is reduced in the process.

  • Chemical Properties of Aldehydes and Ketones

    Oxidation of AldehydesOxidation of Aldehydes forms the basis of two useful identification tests

    Tollens Test:

    Benedicts Test:

    RC

    H

    O+ Ag+ + 3 OH-

    RC

    O-

    O+ Ag0 + 2 H2O

    RC

    H

    O+ 2 Cu2+ + 5 OH-

    RC

    O-

    O+ + 3 H2OCu2O

  • Chemical Properties of Aldehydes and Ketones

    Benedicts Test for Aldehydes

    Cu2+ Cu+

  • Oxidation of Aldehydes

    + ++ +++

    The degree of reduction varies with time and the concentration of the aldehyde.

  • Chemical Properties of Aldehydes and Ketones

    Tollens Test for Aldehydes

    Ag+ Ago

  • Ketones DO NOT undergo the same

    transformations with these oxidizing agents !!

  • Chemical Properties of Aldehydes and Ketones

    Addition Reactions to Carbon-Oxygen Double Bonds

    REVIEW:Reactions of Carbon-Carbon Double Bonds

    A and B can be the same or different atoms or groups of atoms.

    In some cases, the identity of A and B and the groups attached to the double bond influence the orientation of the addition.

    C

    C

    A

    B

    C

    C

    A

    B C

    C

    A

    B

  • Chemical Properties of Aldehydes and Ketones

    Addition Reactions to Carbon-Oxygen Double Bonds

    Reactions of the Carbon-Oxygen double bond can be viewed in a similar manner.

    A and B can be the same or different atoms or groups of atoms.

    The identity of A and B and the polar nature of the carbon-oxygen double bond influence the orientation of the addition.

    O

    C

    +

    A

    B

    +O

    CA

    B

    O

    C

    A

    B

    ++

    +

  • Addition Reactions to Carbon-Oxygen Double Bonds

    Reduction (Hydrogenation) of Aldehydes and Ketones

    O

    C

    H

    H O

    C

    H

    H

    O

    C

    H

    H

    Break Bonds

    Form Bonds

    Aldehyde or Ketone Alcohol

  • Addition Reactions to Carbon-Oxygen Double Bonds

    Reduction (Hydrogenation) of Aldehydes and Ketones

    2,3-dimethylbutanal 2,3-dimethyl-1-butanol

    H2 Ni (catalyst)

    H3CCH

    CHC

    O

    H

    H3C

    CH3H3C

    CHCH

    CH2

    OHH3C

    CH3

    C6H12O C6H14O

    H3CCH

    CH2C

    O

    CH3

    F

    H3CCH

    CH2 HC

    OH

    CH3

    F

    H2 Ni (catalyst)C5H9OF C5H11OF

    4-fluoro-2-pentanone 4-fluoro-2-pentanol

  • Addition Reactions to Carbon-Oxygen Double Bonds

    Hydrates, Hemiacetals, Hemiketals, Acetals, and Ketals

    O

    C

    H

    O X

    O

    C

    +

    + H

    O X

    X = H, R

    If X=H, H-O-X is water;

    If X=R, H-O-R is an alcohol.

  • aldehyde hydrate ketone hydrate

    hemiacetal hemiacetal (hemiketal)

    Addition Reactions to Carbon-Oxygen Double Bonds

    Hydrates, Hemiacetals and Hemiketals

    OC

    H

    O H R H

    OC

    H

    O H R R

    OC

    H

    O R R H

    OC

    H

    O R R R

    O

    C?

    O

    ?

    O

    C? ?

  • O

    CCH3 H

    H

    O H +O

    C

    H

    O H

    HCH3

    O

    CCH3 CH3

    H

    O H +O

    C

    H

    O H

    CH3 CH3

    acetaldehyde acetaldehyde hydrate

    acetone acetone hydrate

    Addition Reactions to Carbon-Oxygen Double Bonds

    Addition of Water - Hydrate Formation

  • Addition Reactions to Carbon-Oxygen Double Bonds

    Addition of an Alcohol - Hemiacetal Formation

    O

    CCH3CH2 H

    H

    O CH3 +O

    C

    H

    O CH3

    H

    O

    CCH3

    H

    O CH3 +O

    C

    H

    O CH3

    CH3

    propionaldehyde propionaldehyde methyl hemiacetal

    butanone butanone methyl hemiacetal

    CH3CH2

    CH3CH2

    CH3CH2

  • Addition of an Alcohol - Hemiacetal Formation

  • Addition of an Alcohol - Hemiacetal Formation

  • Further Reactions of Hemiacetals

    Reaction with an Alcohol - Acetal Formation

    O

    C

    H

    O CH3

    HCH3CH2

    O

    C

    CH3

    O CH3

    HCH3CH2

    H O CH3

    propionaldehyde propionaldehyde methyl hemiacetal methyl acetal

    ++ H2O?

    O

    C

    H

    O CH3

    CH3CH3CH2

    O

    CO CH3

    CH3CH3CH2

    CH3H O CH3

    butanone butanone methyl hemiacetal methyl acetal

    + ? + H2O

  • Note: Acetal formation from a hemiacetal is another example of an

    INTERMOLECULAR DEHYDRATION or CONDENSATION reaction.

    OC

    H

    O R R H

    OC

    H

    O R R R

    OC

    R

    O R R H

    OC

    R

    O R R R

    Further Reactions of Hemiacetals

    Reaction of a Hemiacetal with an Alcohol - Acetal Formation

    O RH O RH

  • CH3 CH2 CO

    H

    CH3 CH2 COH

    OCH3

    H CH3 CH2 COCH3

    OCH3

    H

    CH3OH, H+ CH3OH, H+

    H2O

    CH3OH

    H2O, H+

    H+

    CH3OH

    Aldehyde Hemiacetal Acetal

    Most hemiacetals are unstable and cannot be isolated.

    The equilibrium forming a hemiacetal lies far to the left, or to the reactant side of the reaction.

    Hemiacetals and Acetals

    The equilibrium forming an acetal from a hemiacetal lies far to the right, if excess alcohol is present.

  • Hemiacetals and Acetals

    CH3 CH2 CO

    H

    CH3 CH2 COH

    OCH3

    H CH3 CH2 COCH3

    OCH3

    H

    Aldehyde Hemiacetal Acetal

    Addition Condensation

    Elimination Hydrolysis

    In the presence of excess alcohol and acid, an aldehyde or ketone is converted into its corresponding acetal.

    In the presence of excess water and acid an acetal is converted into its parent aldehyde or ketone.

    Hemiacetal and acetal formations are reversible reactions:

  • Amylose Maltose Glucose

    Acetal linkages

    Hemiacetal linkage

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