Download - 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
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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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Example: ii. Ethanoic acid + ethanol ethyl ethanoate + waterChemical equation:
H O | H C C OH |
HCH
3COOH
(Etanoic acid)
H |H C O-H |
H
CH3OH
(Methanol)
+
H O H| |
H C C O C H + H2O
| | H H
CH3COOCH
3
(Methyl ethanoat) Water
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CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O
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Example: iii. Methanoic acid + Ethanol
ethyl methanoate + waterChemical equation:
H O | H C C OH
|
H
Ethanoic acid
H H | |H C CO-H
| |H H
Ethanol
+
H O H H| | |
H C C O C C H + H2O
| | | H H Hethyl etanoat Water
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HCOOH + CH3CH2OH HCOOCH2CH3 + 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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Prophyl ethanoate
H H H | | |H C CCOH | | |
H H H
H O | H C C OH
|H
PropanolEthanoic acid
Break up and rejoin
From alcoholFrom carboxilic acid
H O H H H| | | |
H C C O C CCH + H2O
| | | |
H H H H
propyl ethanoate 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.
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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.
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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