PHYSICAL AND CHEMICAL PROPERTIES OF ALKANOIC ACID

PERIOD 2 AND 3 : PHYSICAL AND CHEMICAL PROPERTIES OF ALKANOIC ACID

PHYSICAL PROPERTIES

1. Alkanoic acds are very soluble in water each alkanoic acid forms hydrogen bond with water molecule. The solubility of alkanoic acid in water decreases as the carbon atom increases. Threrefore, lower members are more soluble in water.

1. They have high boiling and melting points.their two pairs of hydrogen bond per molecule of alkanoic acid. The boiling and melting points increase as the carbon chain increases.
2. they turn blue litmus paper red.

CHEMICAL PROPERTIES

1. Reaction with active metals

Alkanoic acids react with active metals to liberate hydrogen gas.

2RCOOH + Zn (RCOO)₂Zn + H₂

2CH₃COOH + Zn (CH₃COO)₂Zn + H₂

1. Reaction with base.

Alkanoic acids react with bases to form salt and water.

RCOOH + NaOH RCOONa + H₂O

e.g CH₃CH₂COOH + NaOH CH₃CH₂COONa + H₂O

1. Alkanoic acid liberate carbon(iv) oxide from metallic trioxocarbonate (iv) or hydrogentrioxocarbonate (iv)

2RCOOH + CaCO₃ (RCOO)₂Ca + H₂O + CO₂

1. Alkanoic acid reacts reversibly with alkanol in the presence of tetraoxosulphate (vi) acid to form alkanoate (ester). On heating the mixture, a fruity of fragrance aroma is observed. Tetraoxosulphate (vi) acid serves as catalyst. this reaction is called esterification.

RCOOH + R¹OH RCOOR¹ + H₂O

In this reaction the alkyl group of alkanol replaces the acidic hydrogen of the alkanoic acid

Ethanoic acid reacts with ethanol to give ethyl ethanoate.

CH₃COOH + CH₃CH₂OH CH₃COOCH₂CH₃ + H₂O

1. Alkanoic acid are reduced to alkanol by lithium tetrahydridoaluminate (iii) (LiAlH₄)

RCOOH RCH₂OH

CH₃CH₂CH₂COOH CH₃CH₂CH₂CH₂OH

EVALUATION:

1. State three physical properties of alkanoic acid.
2. Explain why methanoic acid is very soluble in water
3. With the aid of a chemical equation only, show how zinc reacts with methanoic acid

TOPIC: ALKANOATES:

1. SOURCES, NOMENCLATURE.

2. PREPARATION AND STRUCTURE.

3. PHYSICAL AND CHEMICAL PROPERTIES AND USES.

PERIOD 1: SOURCES, NOMENCLATURE

Alkanoates are found widely in nature. Short carbon chain simple alkanoates exist as liquids and have a characteristic pleasant smel. They occur in essential oils, many fruits and floers and sometimes called fruit essence because of the pleasant odours. The general molecular formula is C_nH_2n+1COOC_nH_2n+1. The structural formula is[mediator_tech]

The names end in-ate

EVALUATION:

1.State four sources of alkanoate

1. Give the IUPAC names of the following:

(a) CH₃CH₂CH₂CH₂CH₂COOC₃H₇

(b) HCOOC₂H₅

1. Draw the structures of the following”

Ethyl butanoate, propyl ehanoate, propyl propanoate.

PERIOD 2: PREPARATION OF ALKANOATE

Alkanoates are prepared bybesterification reaction between alkanoic acid and alkanols in the presence of concentrated tetraoxosulphate (vi) acid.

RCOOH + R¹OH RCOOR¹ + H₂O

In this reaction the alkyl group of alkanol replaces the acidic hydrogen of the alkanoic acid

Ethanoic acid reacts with ethanol to give ethyl ethanoate.

CH₃COOH + CH₃CH₂OH CH₃COOCH₂CH₃ + H₂O

Ethyl propanoate is prepared by the reaction between ehanol and propanoic acid.

CH₃CH₂COOH + CH₃CH₂OH CH₃CH₂COOCH₂CH₃ + H₂O

Propyl ethanoate is prepared by the reaction of propan-1-ol and ethanoic acid.

CH₃COOH + CH₃CH₂CH₂OH CH₃COOCH₂CH₂CH₃ + H₂O

EVALUATION

Describe he laboratory preparation of ethyl ethanoate.

PERIOD 3 AND 4: PHYSICAL AND CHEMICAL PROPERTIE OF ALKANOATE

PHYSICAL PROPERTIES

1. Short carbon chain alkanoatee have fruity smell. Those found in waxes do not have fruity smell.
2. Lower members are slightly soluble in water but they readily dissolve in organic solvents such as ethanol, benzene e.t.c.
3. Their boiling points are lower than those of the corresponding alkanoic acid and even alkanols because they do not have hydrogen bonds.

CHEMICAL PROPERTIES

1.(a) They are hydrolyzed by water to give their component acid and alkanol.

RCOOR¹ + H₂O RCOOH + R¹OH

Ethyl propanoate is hydrolyzed propanoic acid and ethanol.

CH₃COOCH₂CH₂CH₃ + H₂O CH₃CH₂COOH + CH₃CH₂OH

(b) Alkaline hydrolysis of alkanoate gives salt of the acid and alkanol.

RCOOR¹ + NaOH ⇌ RCOONa + R¹OH

Hydrolysis of ethyl butanoate with sodium hydroxide gives sodium butanoate and ethanol

CH₃CH₂CH₂COOCH₂CH₃ + NaOH ⇌ CH₃CH₂CH₂COONa + CH₃CH₂OH

1. They react with ammonia to give amide and alkanol.

RCOOR¹ + NH₃ RCONH₂ + R¹OH

CH₃CH₂COOCH₃ + NH₃ CH₃CH₂CONH₂ + CH₃OH

USES OF ALKANOATE

1. Alkanoates are used in perfumes and cosmetics
2. they are used in flavouring of foods.
3. Ethyl ethanoate is used as solvent for cellulose nitrate.

EVALUATION:

1. State two uses of alkanoates.
2. Describe the chemical properties of alkanoates

GENERAL EVALUATION

OBJECTIVE TEST

1. The general molecular formula of alkanoate is (a) C_nH_n (b) C_nH_2n+1COOH (c) C_nH_2n+1OH (d) C_nH_2n+1COOC_nH_2n+1
2. What is the function of concentrated tetraoxosulphate(vi) acid in esterification raction? (a) as dehydrating agent (b) as catalyst (c) as coagulant (d) for acidification
3. Alkaline hydrolysis of alkanoate gives (a0 alkanol and alkanoic acid (b) alkanol and sodium sal of alkanoic acid (c) alkanoic acid only (d) alkanol only.[mediator_tech]
4. Which of the following is the functional group of alkanoate? (a) –OH (b) –COOH )c) –CONH₂ (d) –COOR
5. The IUPAC name of HCOOC₂H₅ is (a) methyl methanoate (b) ethyl ethanoate (c) ethyl methanoate (d) acetate.

ESSAY

1. What is hydrolysis?
2. Differentiate between hydrolysis and dehydration