6 carboxilic acid and ester

8/6/2019 6 Carboxilic Acid and Ester

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CARBOXILIC ACID

General formula CnH2n+1COOH

One hydrogen atom is replaced with functionalgroup COOH

H O | HCCOH |

H

Formula: HCOOH

O HCOH

Formula: CH3COOH

CARBOXYL GROUP

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Why families known as carboxylic acid

Carboxyl group plays a vital role to gives

acidic properties to carboxilic acid families.

CH3COOH H

+ + CH3COO-

Ethanoicacid Hydrogenion Ethanoateion

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Molecular and Structural Formula

n Name Molecularformula MrStructural

formula

0 Methanoicacid

C0H2(0)+1COOH

= HCOOH46

O

H C OH

1 Ethanoicacid

C1H2(1)+1COOH

= CH3COOH

[C2H4O2]

60

H O|

H C COH|

H

2 Propanoicacid

C2H2(2)+1COOH

= C2H5COOH

74

H H O| |

H C C C OH

| |H H

3 Butanoicacid

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Naming carboxilic acids

Example 1:

C C C

O

O H

H

H

H

H

Carbon number 123

C C COOHH

H

H

H

C

Longest continuous chains: propanoic acid

HH

H

Attached alkyl group: 2-methyl

Carboxyl carbon: carbon number 1

Name: 2-methylpropanoic acid

C4H8O2 / C3H7COOH

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Example 2:

CH3 C COOH

H

C2H

5

Longest continuous chains: butanoic acid

Carboxyl carbon: carbon number 1

Name: 2-methylbutanoic acid

Attached alkyl group: 2-methyl

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Example 3:

Example 4:

C2H

5 C COOH

H

C3H7

Name: 2-ethyl pentanoic acid

C3H

7 C COOH

H

C2

H5

Name: 2-ethyl pentanoic acid

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Ethanoic AsidCan be prepared through oxidation of an

ethanol.Chemical equation:

This is carried out by refluxingethanol withan oxidising agent such as acidified potassiumdichromate(VI) or potassium manganate(VII)

solution.

H H

H C C OH

H H

H O

H C C OH

H

+ 2[O] + H2O

K2Cr

2O

7solutions

+dilute H

2SO

4

reflux

7

CH3CH2OH + 2[O]CH3COOH + H2O

Etanol ethanoic acid


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Preparation of ethanoic acid through refluxing

Condenser is used to prevent the loss of avolatile liquid by vaporisation.

This method of retaining a volatile liquidduring heating is called refluxing.

How to carry out the activity? (must proc]

Tissel tube

Water out

xxxxxxxxxxxxxx

Label the

diagram please

Waterin

Liebig condenser

Rounded bottom flask

Retortstand

Absolute ethanol, C2H

5OH +

Acidified potassium dichromate(VI),K

2Cr

2O

7solution

Heat

Wiregauge

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Physical Properties- pH less than 7

- sharp or unpleasant or sour smell- turn moist/damp blue litmus paper to red- colourless liquid

Chemical PropertiesAcid Properties- Only hydrogen atom in the carboxyl group,[-COOH] can ionize in water to producehydrogen ions, H+.

Ethanoic acid is a weak acid. Why?- it dissociates in waterpartially, most of

the molecules remain unchanged.

CH3COOH

CH3COO- + H+

CH3COO-

Ethanoicacid

Hydrogenion

Ethanoateion

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Reactions with metals- Dilute ethanoic acid reacts with reactive

metal (Zn, Mg, Al)to produce a salt andhydrogen gas.

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2CH3COOH + Mg Mg(CH3COO)2 + H2Ethanoic acid Magnesium ethanoate

2CH3COOH + Zn Zn(CH3COO)2 + H2Ethanoic acid Zink ethanoate

6CH3COOH + 2Al 2Al(CH3COO)3 + 3H2Ethanoic acid Aluminium ethanoate


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Reactions with bases (5.2)- Dilute ethanoic acid neutralizes alkalis suchas sodium hydroxide solution to give an

organic salt and water.

- Black copper(II) oxide powder dissolves indilute ethanoic acid.

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CH3COOH + NaOH CH3COONa + H2OEthanoic acid Sodium ethanoate

2CH3COOH + CuO Cu(CH3COO)2 + H2OEthanoic acid Copper(II) ethanoate


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Reactions with carbonates- Dilute ethanoic acid reacts with metalcarbonates to produce a salt, carbon dioxide

and water.

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2CH3COOH + CaCO3Ca(CH3COO)2+ CO2 + H2OEthanoic acid Calcium ethanoate

2CH3COOH + Na2CO32CH3COONa+ CO2 + H2OEthanoic acid Sodium ethanoate


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Reactions with alcohols [Esterification]

Esterification:Carboxilic acid reacts with alcohol toproduce an esterand water.

Concentrated H2SO4 : catalyst

[will discuss more in next chapter]

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ConcentratedH2SO4Carboxilic acid + Alcohol Ester + Water


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Uses of carboxilic acid:

i. Ethanoic acid is known as acetic acids use in;- Food flavoring- Food preservatives- To make drugs, dyes, paints insectisides,

plastics- To make esters for use as slovents

ii. Methanoic acid is used to coagulate latex.iii. Benzoic acids is used as food preservatives

iv. Fatty acids used in making soapsv. Carboxilic acids use in the manufactured ofpolyester and polyamids (fibres) in textile

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Conclusion on chemical reaction;

Carboxilic acid + reactive metal

carboxylate salt + hydrogen

Carboxilic acid + base carboxylate salt + water

Carboxylate acid + metal carbonate carboxylate salt + carbon dioxide +

Water

Carboxilic acid + alcohol

ester + water

1. Learning task 2.9 Summarizing pg 75[notes book]

2. Effective Practise pg 751, 2, 3[exercise book]

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ESTER

General formula CnH2n+1COOCmH2m+1

R : alkyl group in carboxilic acidR : alkyl group in alcohol

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O

CnH2n + 1C OH + CmH2m+1OH(carboxilic acid) (alcohol)

O

CnH2n + 1C O CmH2m+1 + H2O(ESTER)


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Esterification- Carboxilic acid reacts with alcohol to produce

ester and water.- The functional group of ester is carboxylgroup.

- Concetrated sulphuric acid is catalyst.- Carboxilic acid losses OH and

- Alcohol losses H- The bond that break up will rejoin again

CnH2n+1 C

O

O CmH2m+1

Break upand rejoin

Carboxilategroup, -COO-

Derived fromcarboxilic acid

Derived fromalcohol

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Naming Ester- Name of ester consists of two parts, the name

of alcohol part is given first and followed bythe acid part.

Example: i. Ethanoic acid + methanol methyl ethanoate + water

Chemical equation:

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CH3COOH + CH3OH CH3COOCH3 + H2O


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Q: Draw structural molecule ofi. Methyl metanoateii. Pentyl propanoateiii. Propyl ethanoate

Solutions; i. Methyl metanoate

O

H C

Methanoic acid

H H | |H C C O | |

H H

Ethanol

+

O H H | |

H C O C C H + H2O | | H H

Ethyl methanoate Water

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ii. Pentyl propanoate

Try now

Methyl methanoate

H |H C OH |

H

O H C OH

MethanolMethanoic acid

Break up and rejoin

From alcoholFrom carboxilic acid

O H |

H C O C H + H2O

|H

methyl methanoate Water

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Preparation of ester through reflux

How to carry out this process?[Success pg 378] [pg 49 prac book]

After boiling, Liebig condenser is rearranged

To carry out the fractional distillation at74oC 78oC to collect ethyl ethanoate.

XXXXXXXXXXXXXXX

Tissel tubeLiebig

condenser

Ethanol +ethanoic acid +concentratedsulphuric acid

Porcelain chip

Waterbath

Waterin

Waterout

To preventjumping/effervescent and ensuresmooth boiling

To cold theethanol andethanoic acid

Uniformheating

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Physical properties of ethyl ethanoate- colourless- fragrant / pleasant smell- insoluble in water- lese dense in water- neutral compound

Natural Sources- Most simple esters are found in fruits andflowers.

ex: benzyl ethanoate in Jasmineethyl butanoate in pineapple

- Palm oil are liquid ester.- The higher and complex ester does notproduce pleasant smells

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Uses of ester

- to make perfume, cosmetics

- to make artificial food flavoring[Text Book: Table 2.8 pg 81]- used as organic solvents

eg. ethyl ethanoate used in sunburnlotion, polish removers, glues.

-

to make synthetic polymers/fabrics- to make aspirin (pain reliever)

Exercise:Effective Practise pg 84 no. 1-3[Ex. Books]

Prepared by;

Kamal Ariffin Bin Saaim

SMKDBL

http://kemhawk.webs.com

6 carboxilic acid and ester

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