Wednesday, 15 July 2015

Alcohols, carboxylic acids, esters and macromolecules

1. Alcohols
Alcohols are compounds with the -O-H functional group, and the general formula of CnH2n+1OH.

Molecular Formula
Full Structural Formula

methyl alcohol, structure of methanol, chemical formula, organic chemistry, o level organic chemistry, Ch3oh
structure of methanol


ethyl alcohol, structure of ethanol. organic chemistry for o level, alcohol
structure of ethanol


propyl alcohol, structure of propanol, o level oragnic chemistry, alcohol
1- propanol


butyl alcohol, 1- butanol, o level organic chemistry, alcohol
1- butanol

Alcohol reactions
  • Combustion: Alcohols undergo complete combustion to form carbon dioxide and water.
word equation:  alcohol + oxygen ----> carbon dioxide + water
  • Oxidation: Alcohols (actually, only primary alcohols) undergo oxidation to form carboxylic acids. The oxidizing agent used can be atmospheric oxygen (making it a slow process), acidified potassium dichromate (VI) or acidified potassium manganate (VII).
          Example in daily life: Wine (which contains ethanol) turns sour when exposed to air, as ethanol is oxidized to ethanoic acid (vinegar).
  • Esterification: Alcohols react with carboxylic acids (in the presence of concentrated sulfuric acid as catalyst, and heating under reflux) to form esters and water. 
2. Formation of ethanol

2.1. By fermentation
Glucose undergoes fermentation to form ethanol and carbon dioxide. Yeast is used as a catalyst. Optimum reaction temperature is about 37oC. The higher the temperature, the faster the rate of reaction. However, at temperatures above 37oC, yeast which is a biological molecule (enzyme) will be denatured. 

glucose ----> ethanol + carbon dioxide
C6H12O6 ----> 2C2H5OH +2 CO2

This ethanol is usually used to make alcoholic drinks. As the concentration of the ethanol formed from fermentation is relatively low, fractional distillation is used to increase the concentration of ethanol.

2.2 By hydrolysis of ethene
Ethene reacts with steam in the presence of phosphoric acid as catalyst, at 300oC and 60 atmospheres, to form ethanol. 
 ethene + steam ----> ethanol
C2H4      + H2----> C2HOH

3. Carboxylic Acids
Carboxylic acids are compounds with the -COOH functional group, and have a general formula of CnH2n+1COOH or CnH2nO2.
Molecular Formula
Full Structural Formula
methanoic acid

HCOOH, carboxylic acid, methanoic acid, o level organic chemistry
structure of methanoic acid
ethanoic acid
structure of ethanoic acid, o level organic chemistry, carboxylic acid, CH3COOH, acetic acid
structure of ethanoic acid
propanoic acid

structure of propanoic acid, o level organic chemistry, carboxylic acid, CH3CH2COOH,
structure of propanoic acid
butanoic acid
structure of butanoic acid, o level organic chemistry, carboxylic acid, CH3CH2CH2COOH,
structure of butanoic acid

Reactions of carboxylic acids
  • Acid reactions
 Carboxylic acids are weak acids. They dissociate partially in water to produce hydrogen ions.
Being an acid, they undergo acid reactions:
acid + base ---> salt + water
acid + carbonates ---> salt + water + carbon dioxide
acid + metal ---> salt + hydrogen

  • Esterification
Alcohols react with carboxylic acids (in the presence of concentrated sulfuric acid as catalyst, and heating under reflux) to form esters and water.

Esters are compounds with the functional group of O-C=O or O=C-O.

There is two parts to the naming of esters, and generally look like this: ___yl ___oate.
You name the part from alcohol first, followed by the carboxylic acid part. The alcohol part will end with ___yl, while the acid part will end with ____oate. For instance, if you see ethyl methanoate, it means that it is formed from ethanol and methanoic acid.

The following is the structure of ethyl methanoate:

ethyl methanoate, ester, ethanol, methanoic acid, ester bonds, organic chemistry, o level chemistry
Structure of ethyl methanoate

4. Uses 
4.1 Uses of esters
Esters have a sweet smell. The commercial uses of esters include perfumes, flavorings, and solvents.
4.2 Uses of ethanol 
Ethanol are often used as solvents, fuel, and constituents of alcoholic beverages.

5. Polymers
Polymers are large molecules formed from smaller molecules called monomers. There are two types of polymers, addition and condensation polymers.

5.1 Addition polymers
Addition polymerization is a process where the monomers are added together to form the polymer, without a loss in any part of the monomer.  

Alkenes undergo addition polymerization.

E.g. ethene ---> poly(ethene)
polyethene, chemical equation, formation of macromolecule, formation of additional polymers, o level organic chemistry
formation of poly(ethene) from ethene

5.2 Condensation polymers
Condensation polymerization is a process where the polymer is formed from smaller molecules, with the loss of some parts of the molecules e.g. as water.

  •  Polyamide

Nylon is an example of a synthetic polyamide. Protein is a naturally occuring polyamide.
Uses of nylon include fishing nets, ropes, parachutes, and sleeping bags.

The amide linkage looks like this:
peptide bond, amide bond, o level organic chemistry
amide linkage

Nylon can be formed from diamines and dicarboxylic acid, as shown below:
nylon, structure, organic chemistry, polymer, condensation polymer,o level organic chemistry amide linkage, amide bonds, polyamide, macromolecules
Structure of Nylon - formed from dicarboxylic acid and diamine

  • Polyester
Terylene is an example of a synthetic polyester. Uses of terylene include clothes, light weight sail, and conveyor belts.
The ester linkage looks like this:
ester linkage, o level organic chemistry
ester linkage

Terylene is formed from diols and dicarboxylic acids, as shown below:
terylene structure, organic chemistry, polymers, condensation polymers, polyol, o level organic chemistry
Structure of Terylene, formed from dicarboxylic acid and diol

Related Post
Alkanes and alkenes

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