DERIVATIVES OF CARBOXYLIC ACIDS - Knockhardy.org.uk

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DERIVATIVES OF CARBOXYLIC ACIDS. Chemical. Properties. • colourless liquids which fume in moist air. • acyl chlorides are more reactive than anhydrides .

Acylation

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DERIVATIVES OF CARBOXYLIC ACIDS ACYL (ACID) CHLORIDES - RCOCl

ACID ANHYDRIDES - (RCO)2O

named from corresponding acid remove -ic add -yl chloride

named from corresponding acid remove acid add anhydride

CH3COCl C6H5COCl

ethanoyl chloride benzene carbonyl chloride

(CH3CO)2O ethanoic anhydride δ−

δ+

δ−

δ+

CH3 C

CH3 C

O

Cl

δ+

CH3 C

δ−

bonding in acyl chlorides

Chemical Properties

• • • • •

O

O δ− δ−

O

bonding in acid anhydrides

colourless liquids which fume in moist air acyl chlorides are more reactive than anhydrides attacked at the positive carbon centre by nucleophiles nucleophiles include water, alcohols, ammonia and amines undergo addition-elimination reactions

Uses of Acylation Industrially

Manufacture of

Cellulose acetate

- making fibres

Aspirin (acetyl salicylic acid)

- analgaesic

Ethanoic anhydride is more useful

Laboratory

Used to make

cheaper less corrosive less vulnerable to hydrolysis less dangerous reaction

carboxylic acid, esters, amines, N-substituted amines

Ethanoyl chloride is used as it

Q.1

• • • •

• is more reactive • gives a cleaner reaction

Investigate how aspirin is made industrially and in the laboratory. Why are the reagents and chemicals different? What properties of Aspirin make it such a useful drug?

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Acylation

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ADDITION ELIMINATION REACTIONS - OVERVIEW Mechanism

• • • •

species attacked by nucleophiles at the positive carbon end of the C=O bond the nucleophile adds to the molecule either Cl or RCOO¯ is eliminated a proton is removed

General example - with water ACID CHLORIDES

H + H O

Cl

Cl C

O

R C O

R

H O H

H O H

O C

HCl

R C

O

OH

R

+

Cl

RCOCl

+

H2O

——>

RCOOH

+

HCl

ACID ANHYDRIDES O O

R C

R C O R C O H O H

H + H O

O R C H O H

O C

O

O

OH

R

+

RCOOH

R C

RCOO

(RCO)2O

+

H2O

——>

2RCOOH

Use these mechanisms to help construct others in the spaces which follow

SYNTHETIC POSSIBILITIES PRODUCT WITH

By-product

WATER

ALCOHOLS

AMMONIA

AMINES

ACYL CHLORIDE

CARBOXYLIC ACID

ESTER

AMIDE

N-SUBSTITUTED AMIDE

HCl

ACID ANHYDRIDE

CARBOXYLIC ACID

ESTER

AMIDE

N-SUBSTITUTED AMIDE

CARBOXYLIC ACID

Acylation

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ADDITION ELIMINATION - the reactions ACYL (ACID) CHLORIDES - RCOCl Water

Product(s)

carboxylic acid + HCl (fume in moist air / strong acidic solution formed)

Conditions

cold water

Equation

CH3COCl(l)

Mechanism

addition-elimination

+ H2O(l) ——>

H + H O

Cl

Cl C

CH3 C O

O

CH3

H O H

H O H

Alcohols

O C

O

ester + hydrogen chloride

Conditions

reflux in dry (anhydrous) conditions

Equation

CH3COCl(l)

Mechanism

addition-elimination

O

CH3

+ CH3OH(l) ——>

H O CH3

+

H O +

O C

CH3 C

Cl

What organic product is formed when the following pairs react? • C3H7COCl and H2O

Q.3

O

CH3

CH3

Q.2

CH3COOCH3(l) + HCl(g)

CH3

CH3 C O H O

HCl OH

Cl

Product(s)

Cl

CH3 C

CH3

+

Cl C

CH3COOH(aq) + HCl(aq)

• C2H5COCl and C2H5OH

How would you synthesis the following? • methyl butanoate

• butyl methanoate

• C6H5COOCH3

• CH3COOC(CH3)2

HCl O CH3

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Acylation

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Ammonia

Product(s)

Amide + hydrogen chloride

Conditions

Low temperature and excess ammonia. Vigorous reaction.

Equation

CH3COCl(l)

+ NH3(aq)

——>

CH3CONH2(s) + HCl(g)

CH3COCl(l)

+ 2NH3(aq)

——>

CH3CONH2(s) + NH4Cl(s)

or Mechanism

Cl

Cl C

CH3 C O

O

CH3

+

H N H H

H H N H

Amines

addition-elimination H + H N H C CH3

O O

CH3 C

HCl NH2

Cl

Product(s)

N-substituted amide + hydrogen chloride

Conditions

anhydrous

Equation

CH3COCl(l) + C2H5NH2(aq)

——>

CH3CONHC2H5(s) + HCl(g)

CH3COCl(l) + 2C2H5NH2(aq)

——>

CH3CONHC2H5(s) + C2H5NH3Cl(s)

or Mechanism

addition-elimination - similar to that with ammonia

Cl

Cl C

O

CH3

CH3 C O +

H N H R

H R N H

H + R N H C CH3

O O

CH3 C

Cl

HCl NH R

Q.4

Why are two moles of ammonia (or amine) required in each equation?

Q.5

What pairs of chemicals would you use to synthesis the following? • butanamide

• C2H5CONH2

• CH3CON(CH3)2

• N-phenylethanamide

Acylation

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A4

ACID ANHYDRIDES - (RCO)2O Water

Product(s)

carboxylic acid (weak acidic solution formed)

Conditions

cold water - but can be slow

Equation

(CH3CO)2O(l)

+ H2O(l) ——>

2CH3COOH(aq)

Mechanism O CH3 C

O CH3 C CH3 C

CH3 C O + H O H

O O

H O H

Alcohols

O

H + H O

O C

O

CH3

CH3 C

OH

CH3COOH

CH3COO

Product(s)

ester + carboxylic acid

Conditions

reflux in dry (anhydrous) conditions

Equation

(CH3CO)2O(l) + CH3OH(l) ——> CH3COOCH3(l) + CH3COOH(aq)

Mechanism

Q.6

What organic product(s) is/are formed when the following pairs react? • (C3H7CO)2O and H2O • (CH3CO)2O and C2H5OH • (CH3CO)2O and (CH3)2CHOH

6 Ammonia

Acylation

A4

Product(s)

Amide + carboxylic acid

Conditions

Low temperature and excess ammonia.

Equation

(CH3CO)2O(l) + NH3(aq)

or

——>

CH3CONH2(s) +

CH3COOH(aq)

(CH3CO)2O(l) + 2NH3(aq) ——>

CH3CONH2(s) +

CH3COO¯NH4+(s)

Mechanism

Amines

Product(s)

N-substituted amide + carboxylic acid

Equation

(CH3CO)2O(l) + C2H5NH2(aq)

or

——> CH3CONHC2H5(s) + CH3COOH(aq)

(CH3CO)2O(l) + 2C2H5NH2(aq) ——> CH3CONHC2H5(s) + CH3COO¯NH4+(s)

Mechanism

Q.7

What organic product(s) is/are formed when the following pairs react? • (C3H7CO)2O and NH3 • (CH3CO)2O and C2H5NH2 • (CH3CO)2O and (CH3)2NH