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DAT > SNS - Organic Chemistry - Carboxylic Acid Derivatives > Flashcards

SNS - Organic Chemistry - Carboxylic Acid Derivatives Flashcards

1
Q

Carboxylic Acid Derivatives

A

Compounds in which the -OH of the -COOH has been replaced with -X, -OCOR, -NH2 or -OR to form acyl halides, anhydrides, amides or esters respectively

Readily undergo nucleophilic substitution (including hydrolysis) and other substitution and addition reactions

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2
Q

Acid Halides

Synthesis

A

Most common are the acid chlorides, although acid bromides and iodides are occasionally seen.

Prepared by reaction of the carboxylic acid with SOCl2 to produce SO2 and HCl as side products

PCl3 or PCl5 can also be used

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3
Q

Acid Halides

Reactions

A
  1. Nucleophilic Substitution - (a) Hydrolysis, (b) Conversion to esters, (c) Conversion to amides
  2. Other - (a) Friedel Crafts acylation, (b) Reduction
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4
Q

Acid Halides

Reactions

Nucleophillic Acyl Substitution

A
  1. Hydrolysis
  2. Conversion into esters
  3. Conversion into amides
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5
Q

Acid Halides

Reactions

Nucleophilic Acyl Substitution

Hydrolysis

A

The simplest reaction of acid halides is their conversion back to carboxylic acids

React very rapidly with water to form the corresponding acid along with HCl

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6
Q

Acid Halides

Reactions

Nucleophilic Acyl Substitution

Conversion Into Esters

A

By reaction with alcohols

Same type of nucleophilic attack as found in hydrolysis leads to the formation of a tetrahedral intermediate with the -OH oxygen as the nucleophile.

Chloride is displaced and HCl released as the side product

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7
Q

Acid Halides

Reactions

Nucleophilic Acyl Substitution

Conversion Into Amides

A

Nucleophilic amines such as ammonia attack the carbonyl group displacing chloride

The side product is ammonium chloride, formed from excess ammonia and HCl

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8
Q

Acid Halides

Reactions

Other

A
  1. Friedel Crafts Acylation
  2. Reduction
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9
Q

Acid Halides

Reactions

Other

Friedel Crafts Acylation

A

Aromatic rings can be acylated via Friedel Crafts

Electrophilic aromatic substitution mechanism, with the attacking reagent an acylium ion formed by the reaction of an acid chloride with AlCl3 or another Lewis acid

Product is an alkyl aryl ketone

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10
Q

Acid Halides

Reactions

Other

Reduction

A

Can be reduced to alcohols or selectively reduced to the intermediate aldehydes

Catalytic hydrogenation in the presence of a ‘poison’ like quinoline permits the latter transformation

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11
Q

Anhydrides

A

Condensation dimers of carboylic acids

General formula RCOOCOR

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12
Q

Anhydrides

Synthesis

A

Synthesised by reaction of an acid chloride with a carboxylate salt

Certain cyclic anhydrides can be formed simply by heating carboxylic acids. Reaction is driven by the increased stability of the newly formed ring, hence only the five and six membered ring anhydrides are easily made. In this case, the -OH of one -COOH acts as a nucleophile attacking the carbonyl on the other -COOH

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13
Q

Anhydrides

Reactions

A

React under the same conditions as acid chlorides, but as they are slightly more stable, they are slightly less reactive. Reactions are slower and produce a carboxylic acid as a side product instead of HCl.

Cyclic anhydrides are also subject to these reactions, which cause ring opening at the anhydride group along with the formation of the new functional groups

  1. Hydrolysis
  2. Conversion into amides
  3. Conversion into esters and carboxylic acids
  4. Acylation
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14
Q

Anhydrides

Reactions

Hydrolysis

A

Converted into carboxylic acids when exposed to water

Leaving group is a carboxylic acid

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15
Q

Anhydrides

Reactions

Conversion Into Amides

A

Cleaved by ammonia, producing amides and ammonium carboxylates

Even though the leaving group is actually a carboxylic acid, the final products are an amide and the ammonium salt of a carboxylate anion

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16
Q

Anhydrides

Reactions

Conversion Into Esters and Carboxylic Acids

A

React with alcohols to form esters and carboxylic acids

17
Q

Anhydrides

Reactions

Acylation

A

Occurs readily with AlCl3 or other Lewis acids catalysts

Proceeds via electrophilic aromatic substitution

18
Q

Amides

Nomenclature

A

General formula RCONR2

Named by replacing the -oic acid ending with -amide

Alkyl substituents are listed as prefixes and their location specied with the letter N, for example N-methylpropanamide

19
Q

Amides

Synthesis

A

Generally synthesised by:

  1. Reaction of acid chlorides with amines
  2. Reaction of acid anhydrides with ammonia
20
Q

Amides

Reactions

A
  1. Hydrolysis
  2. Hofman Rearrangement
  3. Reduction
21
Q

Amides

Reactions

Hydrolysis

A

Can be hydrolysed under acidic conditions via nucleophilic substitution to produce carboxylic acids or basic conditions to form carboxylates

Under acidic conditions the carbonyl oxygen becomes protonated, making the carbon atom more susceptible to nucleophiic attack

22
Q

Amides

Reactions

Hofman Rearrangement

A

Converts amides to primary amines with the loss of the carbonyl carbon

Mechanism involves formation of a nitrene (nitrogen anaog of a carbene). The nitrene is attached to the carbonyl group and rearranges to form an isocyanate which under the reaction condition is hydrolysed to the amine

23
Q

Amines

Reactions

Reduction

A

Can be reduced with LAH to the corresponding amine

Differs from the product of the Hofman rearrangement in that no carbon atom is lost

24
Q

Esters

Synthesis

A
  1. Mixtures of carboxylic acids and alcohols will condense into esters, liberating water under acidic conditions
  2. Can also be obtained by reaction of acid chlorides or anhydrides with alcohols. Phenolic (aromatic) esters are produced in the same manner, although the aromatic acid chlorides are less reactive than aliphatic acid chlorides, so base must be added as a catalyst
25
Q

Esters

Reactions

A
  1. Hydrolysis
  2. Conversion into Amides
  3. Transesterification
  4. Grignard Addition
  5. Condensation
  6. Reduction
26
Q

Esters

Reactions

Hydrolysis

A

Can be hydrolysed to yield carboxylic acids and alcohols

Can take place under either acidic or basic conditions - similar except under basic conditions the C=O oxygen isn’t protonated and the nucleophile is OH-

27
Q

Esters

Reactions

Conversion Into Amides

A

Nitrogen bases such as ammonia will attack the electron-deficient carbonyl carbon atoms, displacing alkoxide to yield an amide and an alcohol side product

28
Q

Esters

Reactions

Transesterification

A

Alcohols can act as nucleophiles and displace the alkoxy groups on ester

Process transforms one ester into another

29
Q

Esters

Reactions

Grignard Reactions

A

These reagents (RMgX) add to the carbonyl groups of esters to form ketones.

These ketones are more reactive than the original esters and are readily attacked by more Grignard reagents

Two equivalents of Grignard reagent can thus yield tertiary alcohols via nucleophilic substiution reaction

The intermediate ketone can be isolated only if the alkyl groups are sufficiently bulky to prevent further reaction

30
Q

Esters

Reactions

Condensation

A

Claisen condensation - in the simplest case, two moles ethyl acetate react under basic conditions to form a beta-keto ester, ethyl-3-oxobutanoate (acetoacetic ester)

Proceeds by addition of an enolate anion o the carbonyl group of another ester followed by displacement of ethoxide ion

Analogous mechanism to that of aldol condensation

31
Q

Esters

Reactions

Reduction

A

May be reduced to primary alcohols with LAH but not NaBH4

Allows for selective reduction in molecules with multiple functional groups

DAT (53 decks)

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