21 6 the acetoacetic ester synthesis
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21.6 The Acetoacetic Ester Synthesis

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21.6 The Acetoacetic Ester Synthesis - PowerPoint PPT Presentation


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21.6 The Acetoacetic Ester Synthesis. O. O. C. C. H 3 C. C. OCH 2 CH 3. H. H. Acetoacetic Ester. Acetoacetic ester is another name for ethyl acetoacetate . The "acetoacetic ester synthesis" uses acetoacetic ester as a reactant for the preparation of ketones. O. O. C. C. H 3 C.

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acetoacetic ester

O

O

C

C

H3C

C

OCH2CH3

H

H

Acetoacetic Ester
  • Acetoacetic ester is another name for ethylacetoacetate.
  • The "acetoacetic ester synthesis" uses acetoacetic ester as a reactant for the preparation of ketones.
deprotonation of ethyl acetoacetate

O

O

C

C

H3C

C

OCH2CH3

H

H

Deprotonation of Ethyl Acetoacetate

+

CH3CH2O

  • Ethyl acetoacetate can be converted readily to its anion with bases such as sodium ethoxide.

pKa ~ 11

deprotonation of ethyl acetoacetate1

O

O

C

C

H3C

C

OCH2CH3

H

H

O

O

C

C

••

H3C

C

OCH2CH3

H

Deprotonation of Ethyl Acetoacetate

+

CH3CH2O

  • Ethyl acetoacetate can be converted readily to its anion with bases such as sodium ethoxide.

pKa ~ 11

K ~ 105

CH3CH2OH

+

pKa ~ 16

alkylation of ethyl acetoacetate

O

O

C

C

••

H3C

C

OCH2CH3

H

R

X

Alkylation of Ethyl Acetoacetate
  • The anion of ethyl acetoacetate can be alkylated using an alkyl halide (SN2: primary and secondary alkyl halides work best; tertiary alkyl halides undergo elimination).
alkylation of ethyl acetoacetate1

O

O

C

C

••

H3C

C

OCH2CH3

H

R

X

O

O

C

C

H3C

C

OCH2CH3

H

R

Alkylation of Ethyl Acetoacetate
  • The anion of ethyl acetoacetate can be alkylated using an alkyl halide (SN2: primary and secondary alkyl halides work best; tertiary alkyl halides undergo elimination).
conversion to ketone

O

O

C

C

H3C

C

OH

H

R

O

O

C

C

H3C

C

OCH2CH3

H

R

Conversion to Ketone
  • Saponification and acidification convert the alkylated derivative to the corresponding b-keto acid.
  • The b-keto acid then undergoes decarboxylation to form a ketone.

1. HO–, H2O

2. H+

conversion to ketone1

O

O

C

C

H3C

C

OH

H

R

O

Conversion to Ketone
  • Saponification and acidification convert the alkylated derivative to the corresponding b-keto acid.
  • The b-keto acid then undergoes decarboxylation to form a ketone.

+

C

CO2

H3C

CH2R

example

O

O

CH3CCH2COCH2CH3

Example

1. NaOCH2CH3

2. CH3CH2CH2CH2Br

example1

O

O

CH3CCH2COCH2CH3

O

O

CH3CCHCOCH2CH3

CH2CH2CH2CH3

Example

1. NaOCH2CH3

2. CH3CH2CH2CH2Br

(70%)

example2

O

CH3CCH2CH2CH2CH2CH3

1. NaOH, H2O

2. H+

3. heat, -CO2

O

O

CH3CCHCOCH2CH3

CH2CH2CH2CH3

Example

(60%)

example dialkylation

O

O

CH3CCHCOCH2CH3

CH2

CH2CH

Example: Dialkylation
example dialkylation1

O

O

CH3CCHCOCH2CH3

CH2

CH2CH

O

O

CH3CCCOCH2CH3

CH2

CH2CH

CH3CH2

Example: Dialkylation

1. NaOCH2CH3

2. CH3CH2I

(75%)

example dialkylation2

O

CH3CCH

CH2

CH2CH

CH3CH2

1. NaOH, H2O

2. H+

3. heat, -CO2

O

O

CH3CCCOCH2CH3

CH2

CH2CH

CH3CH2

Example: Dialkylation
another example

O

O

COCH2CH3

H

Another Example
  • b-Keto esters other than ethyl acetoacetate may be used.
another example1

O

O

COCH2CH3

H

CHCH2Br

2. H2C

O

O

COCH2CH3

CH2

CH2CH

Another Example

1. NaOCH2CH3

(89%)

another example2

O

CH2

CH2CH

Another Example

O

COCH2CH3

another example3

CH2

CH2CH

1. NaOH, H2O

2. H+

3. heat, -CO2

O

CH2

CH2CH

Another Example

O

H

(66%)

O

COCH2CH3

malonic ester

O

O

C

C

C

OCH2CH3

CH3CH2O

H

H

Malonic Ester
  • Malonic ester is another name for diethylmalonate.
  • The "malonic ester synthesis" uses diethyl malonate as a reactant for the preparation of carboxylic acids.
an analogy

O

O

O

O

CH3CCH2COCH2CH3

CH3CH2OCCH2COCH2CH3

O

O

CH3CCH2R

HOCCH2R

An Analogy
  • The same procedure by which ethyl acetoacetate is used to prepare ketones converts diethyl malonate to carboxylic acids.
example3

O

O

CH3CH2OCCH2COCH2CH3

H2C

CHCH2CH2CH2Br

O

O

CH3CH2OCCHCOCH2CH3

CH2

CH2CH2CH2CH

Example

1. NaOCH2CH3

2.

(85%)

example4

O

HOCCH2CH2CH2CH2CH

CH2

1. NaOH, H2O

2. H+

3. heat, -CO2

O

O

CH3CH2OCCHCOCH2CH3

CH2

CH2CH2CH2CH

Example

(75%)

dialkylation

O

O

CH3CH2OCCH2COCH2CH3

O

O

CH3CH2OCCHCOCH2CH3

CH3

Dialkylation

1. NaOCH2CH3

2. CH3Br

(79-83%)

dialkylation1

O

O

O

O

CH3CH2OCCHCOCH2CH3

CH3

Dialkylation

CH3CH2OCCCOCH2CH3

CH3(CH2)8CH2

CH3

1. NaOCH2CH3

2. CH3(CH2)8CH2Br

dialkylation2

O

O

O

Dialkylation

CH3CH2OCCCOCH2CH3

CH3(CH2)8CH2

CH3

1. NaOH, H2O

2. H+

3. heat, -CO2

(61-74%)

CH3(CH2)8CH2CHCOH

CH3

another example4

O

O

CH3CH2OCCH2COCH2CH3

O

O

CH3CH2OCCHCOCH2CH3

CH2CH2CH2Br

Another Example

1. NaOCH2CH3

2. BrCH2CH2CH2Br

another example5

O

O

CH3CH2OCCHCOCH2CH3

CH2CH2CH2Br

Another Example
  • This product is not isolated, but cyclizes in the presence of sodium ethoxide.
another example6

O

O

CH3CH2OCCCOCH2CH3

H2C

CH2

CH2

O

O

CH3CH2OCCHCOCH2CH3

CH2CH2CH2Br

Another Example

(60-65%)

NaOCH2CH3

another example7

O

O

CH3CH2OCCCOCH2CH3

H2C

CH2

CH2

H

CO2H

C

H2C

CH2

CH2

Another Example

1. NaOH, H2O

2. H+

3. heat, -CO2

(80%)

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