WINDSOR UNIVERSITY SCHOOL OF MEDICINE

ALCOHOLS, ACIDS & ESTERSTO KNOW WHAT IS RIGHT AND NOT TO DO IT IS THE WORST COWARDICE. CONFUCIUS

Ch.15 J.C. Rowe

Physical properties1. Melting & boiling points2. Solubility & volatilityReactions of alcohols3. Combustion4. Reaction with sodium5. Dehydration & oxidation /reductionPreparation of ethanol

ALCOHOLS

Physical properties of alcohol The properties of an alcohol depend on 2 factors : The functional group (-OH) The length of the hydrocarbon chain Melting & boiling points.Increase with an increase in the hydrocarbon chain length of the alcohol.The boiling point of a substance is the temperature

at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.

The melting point of a substance is the temperature at which the solid melts to become a liquid.

Physical properties of alcohol Cont’d.

SolubilityMore soluble in water than alkanes of a similar molecular mass because of the hydrogen bonds

between water molecules & alcohol molecules. VolatilityIs the ease with which alcohols are converted to

vapour.Alcohols are not as volatile as hydrocarbons with the similar molecular mass because of the hydrogen

bonds between the alcohol molecules

Ethanol

The most Popular formula of Ethanol is its molecular formula C2H5OH. It is simply an Ethyl group (CH3CH2-) attached to Hydroxyl functional group (-OH) to form the structural formula CH3-CH2-OH

Reactions of alcohols

Combustion.The products of combustion of ethanol are carbon dioxide & water.C2H5OH(l) + 3 O2(g) =Heat=> 2 CO2(g) + 3 H2O(g)

Reaction with SodiumSodium reacts with ethanol at room temp to

liberate hydrogen. The hydrogen atom of the hydroxyl

group is replaced by a sodium atom, forming sodium

ethoxide. 2 C2H5OH(l) + Na (s) ==> 2 C2H5ONa (aq) + H2 (g)

Reactions of alcohols Cont’d. Dehydration of EthanolWhen ethanol is mixed with concentrated

sulphuric acid with the acid in excess and heated to

170 deg C, ethylene is formed. (One mole of ethanol

loses one mole of water)

C2H5OH (g)+ H2SO4 (l) = => C2H4 (g) + H2O (g)

Reactions of alcohols Cont’d. Ethanol is oxidised with acidified Potassium Dichromate, K2Cr2O7, or

with acidified Sodium Dichromate, Na2Cr2O7, or

with acidified potassium permanganate, KMnO4,

The oxidising agent [O] usually used for this reaction is

a mixture of sodium dichromate or potassium dichromate

and sulphuric acid which react together to provide oxygen atoms .the alcohol acts as a reducing agent. C2H5OH + 2[O] ==> CH3COOH + H2O

Preparation of ethanol

Preparation Ethanol is prepared as 95% alcohol (i.e. a 95%

solution of ethanol in water) by distillation of the solution which results from the fermentation of sugars.

Manufacture There are two major industrial pathways to

ethanol. Ethanol which is intended for industrial use is made by the first method, while ethanol intended for food use tends to be made by the second method

A. Preparation of ethanol Cont’d. Reaction of Ethene with Steam

Most of the ethanol used in industry is made, not by alcoholic fermentation, but by an addition reaction between ethene and steam.

C2H4 + H2O ==> C2H5OH

B. Preparation of ethanol Cont’d. alcoholic Fermentation A solution of sucrose, to which yeast is

added, is heated. An enzyme, invertase, which is present in

yeast is added and this acts as a catalyst to convert the sucrose into glucose and fructose.

C12H22O11 + H2O + invertase ==> C6H12O6 +

C6H12O6

C. Preparation of ethanol Cont’d. The glucose, C6H12O6, and fructose,

C6H12O6, formed are then converted into ethanol and carbon dioxide by another enzyme, zymase, which is also present in yeast.

C6H12O6 + Zymase ==> 2C2H5OH + 2CO2

The fermentation process takes three days and is carried out at a temperature between 250C and 300C. The ethanol is then obtained by fractional distillation.

D. Preparation of ethanol Cont’d. Absolute Ethanol Whatever method of preparation is used, the

ethanol is initially obtained in admixture with water. The ethanol is then extracted from this solution by fractional distillation.

Although the boiling point of ethanol, 78.3 deg C, is significantly lower than the boiling point of water, 100 deg C, these material cannot be separated completely by distillation.

Instead, an azeotropic mixture (i.e. a mixture of 95% ethanol and 5% water) is obtained, and the boiling point of the azeotrope is 78.15 deg C.

E. Preparation of ethanol Cont’d. In a distillation, the most volatile material (i.e.

the material that has the lowest boiling point) is the first material to distill from the distillation flask, and this material is the azeotrope of 95% ethanol which has the lowest boiling point.

If an efficient fractionating column is used, there is obtained first 95% alcohol, then a small intermediate fraction of lower concentration, and then water. But no matter how efficient the fractionating column used, 95% alcohol cannot be further concentrated by distillation

F. Preparation of ethanol Cont’d. The separation of a mixture by fractional

distillation occurs because the vapour has a different composition from the liquid from which it distils (i.e. the vapour is richer in the more volatile component).

We cannot separate 95% alcohol into its components by distillation, because here the vapour has exactly the same composition as the liquid; towards distillation, then, 95% alcohol behaves exactly like a pure compound.

G. Preparation of ethanol Cont’d A liquid mixture that has the peculiar property of

giving a vapour of the same composition is called an azeotrope (i.e. a constant-boiling mixture).

Since it contains two components 95% alcohol is a binary azeotrope.

Most azeotropes, like 95% alcohol, have boiling points lower than those of their components, and are known as minimum-boiling mixtures.

Azeotropes having boiling points higher than those of their components are known as maximum-boiling mixtures.

Acidic reactions of ethanoic acid1. Reaction with metals2. Reactions with bases3. Reactions with carbonates &

hydrogen carbonatesNon-acidic reactions of ethanoic acid4. Combustion5. Esterification

CARBOXYLIC ACIDS

Naming Carboxylic Acids

1. COMMON NAME (PREFIX + IC + ACID) {PROPIONIC ACID}

2. SYSTEMATIC NAME (DROP (E) & ADD (OIC) & ADD ACID) {HEXANOIC ACID}(C=O CARBON IS #1)

3. COMPLEX COMPOUNDS (ALKANE + CARBOXYLIC ACID) {CYCLOHEXANECARBOXYLIC ACID}

Derivatives of Carboxylic Acid

Acidic reaction of ethanoic acid

Ethanoic acid is a weak monobasic acid that undergoes a neutralization reaction with bases or alkali to form ethanoate salt and water.

This is as expressed by the reaction of ethanoic acid with sodium hydroxide to form sodium ethanoate and water.

2CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(l)

It also attack strongly electropositive metals like magnesium and calcium to liberate hydrogen.

2CH3COOH(aq) + Mg(s) → (CH3COO)2Mg(aq) + H2(g)

Ethanoic Acid and Sodium Carbonate to produce the ethanoate salt (sodium ethanoate), carbon dioxide & water.

2 CH3COOH + Na2CO3 ---> 2 CH3COONa +

H2O + CO2. Ethanoic Acid reacts with metals to

produce hydrogen gas & salt.2 CH3COOH +2 Na ------> 2 CH3COONa

+ H2

Non-acidic reactions of ethanoic acid

Combustion: Ethanoic acid will burn in oxygen to form water and carbon dioxide

CH3COOH (aq)+ 2O2(g) ----> 2CO2 (g) +2H2O (g)

Esterification : Ethanoic acid will react with alcohols in

the presence of concentrated sulfuric acid, to form esters.

ethanol  + ethanoic acid ---> ethyl ethanoate   +   water.

C2H5OH(aq) + CH3CO2H(aq) ---> CH3CO2C2H5(aq)+ H2O(l)

Reactions of esters1. Hydrolysis2. Alkaline hydrolysis of an esterSaponification

ESTERS

Making esters from carboxylic acids and alcohols

The esterification reaction is both slow and reversible. The equation for the reaction between an acid RCOOH and an alcohol R'OH (where R and R' can be the same or different) is:

So, for example, if you were making ethyl ethanoate from ethanoic acid and ethanol, the equation would be:

Reactions of esters

Carboxylic esters hydrolyse to the parent carboxylic acid and an alcohol.

Reagents : aqueous acid (e.g. H2SO4) / heat, or aqueous NaOH / heat (known as "saponification").

it is the C-O bond between the acyl group and the oxygen that is cleaved

Hydrolysis using dilute alkali Here are examples of 2 reactions:

Saponification

Saponification is the process of making soap from excess alkaline hydrolysis of natural esters.

Soap molecules consist of a hydrophobic end & a hydrophilic head

Soapy detergents (made from the hydrolysis of natural esters)do not clean very efficiently in hard water (water containing calcium & magnesium ions). The precipitate formed is called SCUM.

Soapless detergents are made from hydrocarbon products

Reactions of saponification

General reaction of saponification

Lactic Acid – milk Tartaric acid (2,3-dihydroxybutanedioic acid)

– grapes Butanoic acid – rancid smell of butter Fats & Oils Citrus acid – Citrus Fruits Ascorbic Acid – Vitamin C

Natural Sources of Organic Acids

Soap and Saponification

Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard or other animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats and oils occurs, yielding glycerol and crude soap.

In the industrial manufacture of soap, tallow (fat from animals such as cattle and sheep) or vegetable fat is heated with sodium hydroxide.

Once the saponification reaction is complete, sodium chloride is added to precipitate the soap. The water layer is drawn off the top of the mixture and the glycerol is recovered using vacuum distillation.

The crude soap obtained from the saponification reaction contains sodium chloride, sodium hydroxide, and glycerol. These impurities are removed by boiling the crude soap curds in water and re-precipitating the soap with salt. After the purification process is repeated several times, the soap may be used as an inexpensive industrial cleanser. Sand or pumice may be added to produce a scouring soap. Other treatments may result in laundry, cosmetic, liquid, and other soaps.

Cross-section through a micelle

When cleaning with soaps the fat-soluble end of the soap (hydrocarbon tail) will first attack the oil film surrounding the dirt particle.

the dirt particle becomes totally surrounded & a micelle is formed.

How much one actually achieves depends largely on: (1) desire, (2) faith, (3) persistent effort and (4) ability. But if you are lacking in the first three factors, your ability will not balance out the lack. So concentrate on the first three and the results will amaze you.

Norman Vincent Peale