SUBTOPIC: CARBOXYLIC ACIDS

Functional group:

R- COO-H

1) Family: carboxylic acid2) Name of functional group: carboxyl

Uses1) Found in fruits, milk and ants

a. Short chain carboxylic acids1. citric acid (citrus fruits), 2. tartaric acid (grape), 3. oxalic acid (soursop) 4. Butyric acid (Butter)5. Lactic acid (Sour milk, muscle)6. Methanoic acid (Red ants)

b. Long chain carboxylic acids(fatty acids)1. Palmitic acid (Palm oil)2. Oleic acid (olive)

NomenclatureCarboxylic acids with 1 carboxyl group

1) Identify parent chain, which is the longest continuous carbon chain containing carboxyl/carboxy group

2) No need to designate the position of Carboxyl group because it would always assume position number one.

3) Eg:

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Carboxylic acids with 2 carboxyl groupsDicarboxylic acids

Physical properties-Use relative strength of secondary interactions to explain the trend in physical properties.

1) Boiling point/melting point- Carbonyl group is an electron-withdrawing group and it would cause the carboxyl group

in carboxylic acid to be more polar than hydroxyl group in alcohol.

- Therefore carboxylic acids can form stronger hydrogen bonds with other carboxylic acid molecules.

- Require a lot of heat/ high temperature to break stronger hydrogen bonds, hence have high bp/mp

- Hence Carboxylic acids have much higher bp than alcohols due to the formation of stronger hydrogen bonds which are formed between carboxylic acid molecules.

Carboxylic acids Alcohols

Compounds MW Bp (oC) Compounds MW Bp (oC)

Methanoic acid 46 100.5 Ethanol 46 78.3

Ethanoic acid 60 118 1-Propanol 60 97.2Propanoic acid 74 141 1-Butanol 74 117.7Butanoic acid 88 164 1-Pentanol 88 138.0

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- The bps of esters are much lower than their isomeric acids due to presence of hydrogen bondings in acids.

- In esters, only DDI is possible btw esters groups. Thus, lower bp of esters

Esters Carboxylic acidsCompounds MW Bp (oC) Compounds MW Bp (oC)

Methyl methanoate 60 31.5 Propanoic acid 60 97.2

Methyl Ethanoate 74 57 Butanoic acid 74 117.7

- Dicarboxylic acids have much higher bp/mp because they can form extensive (many) hydrogen bonds with other dicarboxylic acid molecules. Hence require much higher temp to break many strong hydrogen bonds between carboxylic acids molecules.

2) Solubility in waterCarboxylic acids with 1 carboxyl group

-Lower carboxylic acids (carboxylic acids with small molar mass) are very soluble in water because water molecules can completely surround the carboxylic acid molecules. Carboxylic acid molecules, which contain very polar carboxyl/carboxyl group, can form strong hydrogen bonds with very polar water molecules.

Diagram:

-Higher carboxylic acids (carboxylic acids with big molar mass) have low solubility in water because even though they contain very polar carboxyl groups, long non-polar hydrocarbon chain outweighs the polarity of carboxyl group rendering the whole carboxylic acid molecule as less polar or non- polar. Consequently, carboxylic acid molecules cannot form strong hydrogen bonds with very polar water molecules. Hence, they are less soluble in water. Example: oleic acid, palmitic acid. These are known as fatty acids because they do not dissolve in water due to their long hydrocarbon chains.

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Dicarboxylic acids-very soluble in water despite their molecular size-they have many very polar carboxyl groups in one molecule-can form extensive strong hydrogen bonds with very polar water molecules, hence very soluble in water.

Carboxylate ions-Very soluble in water in all proportions because they can form ion-dipole interaction with very polar water molecules.-carboxylate ions are much more soluble in water compared to carboxylic acids- Diagram:

3) Taste- Sour

4) Odour- Lower carboxylic acids have sharp irritating pungent odour because of low volatility- Higher carboxylic acids have little odour because of higher volatility

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Chemical reactionsPreparation of carboxylic acids

1) From primary alcoholsa. carboxylic acid could be prepared from oxidation of primary alcohol in the presence of

excess oxidant such as acidified potassium dichromate or potassium permanganate solution

b. Primary alcohol and excess acidified potassium dichromate are placed in the round bottom flask and then heated under reflux

Equation:

Eq: R-OH (l) à R-COOH (l)

Cr2O72- (aq)à Cr3+ (aq)

c. The purposes of reflux are to prevent the volatile compounds from escaping the reaction mixture and to speed up the rate of reaction.

d. Anti-bumping granules are added into heating mixture to promote even heat distribution and to prevent the compounds from splashing out .

Diagram:

2) From aldehydesa. Carboxylic acid could also be prepared from aldehyde by heating aldehyde and oxidant

such as acidified potassium dichromate solution under reflux

Equation:

Eq: R-CHO (l) à R-COOH (l)

Cr2O72- (aq)à Cr3+ (aq)

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3) Acidic hydrolysis of esters

Weak acids1) Carboxylic acids are weak acids.2) Proton donors3) Partially ionize in water to produce low concentration of hydrogen ions4) Calculate pH by using the following formula

a. pH= - log 10 con of H+ (in mol/L)

Neutralisation reactions1) Sodium hydroxide aqueous solution(NaOH)

a. Sodium hydroxide aqueous solution reacts with carboxylic acid to form carboxylate salt and water

Balanced chemical equation:

R-COO-H(aq) + NaOH(aq) à RCOONa(aq) + H2O(l)

Eg: CH3CH2COOH + NaOH à CH3CH2COONa + H2O

2) Sodium carbonate aqueous solution (Na2CO3)a. Sodium carbonate aq. solution reacts with carboxylic acid to form carboxylate salt, water

and carbon dioxide

2 RCOOH(aq) + Na2CO3(aq) à 2RCOONa(aq) + CO2(g) +H2O

Eg:

2CH3CH2COOH(aq) + Na2CO3(aq) à 2CH3CH2COONa(aq) + CO2(g) + H2O(l)

-Observe effervescence of CO2 gas

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3) Sodium bicarbonate aqueous solution (NaHCO3)a. Sodium bicarbonate reacts with carboxylic acid producing sodium carboxylate salt, CO2

and water

RCOOH(aq) + NaHCO3(aq) à RCOONa(aq) + CO2(g) + H2O(l)

Eg:

CH3CH2COOH(aq) + NaHCO3(aq) à CH3CH2COONa(aq) + CO2(g) + H2O(l)

-Observe effervescence of CO2 gas

Applications in drugs1) Aspirin and ibuprofen are carboxylic acids that are used as pain relieving drugs

2) Drugs with analgesic properties such as aspirin (acetyl salicylic acid) and ibuprofen don’t dissolve in water because they have large non-polar hydrocarbon portions.

3) Some people have problem to swallow tablets, so to ease this problem, water soluble aspirin or ibuprofen is created.

4) In a tablet form, Aspirin or ibuprofen is mixed with sodium bicarbonate.5) Upon contact with water, acid-base reaction takes place

a. Chemical equation:

2) Once in the stomach, carboxylate ion reacts with hydrogen ion ( HCl in stomach) to convert

carboxylate ion back into carboxylic acida. Chemical equation

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3) Then absorb into blood stream.

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