ORGANIC CHEMISTRY II NOTES FREE DOWNLOAD

ORGANIC CHEMISTRY II NOTES FREE DOWNLOAD

ORGANIC CHEMISTRY II

 

ALKANOLS

Alkanols belong to a homologous series of organic compounds with a general formula R-OH and thus  -OH  is the functional group .The first ten alkanols are listed below;

Alkanols like hydrocarbons (alkanes/alkenes/alkynes) form a homologous series where:

1. All members conform to the general molecular formula C_nH_2n+1OH (Generally represented as R-OH, where R is an alkyl group)
2. All members have –OH as the functional group

• Each member differ by –CH₂ group from the next/previous

1. They show a similar and gradual change in their physical properties e.g. boiling and melting points.
2. They have similar chemical properties.

 

Nomenclature of alkanols

Alkanols are named by using the following basic guidelines:

1. The prefix of alkanols are similar to those of alkanes but the suffix is “ol”
2. When naming branched alkanols, identify the longest carbon chain to get the “parent name”

• Number the chain such that the carbon to which the -OH group is attached takes the lowest number possible

1. Identify the type and position of the side branches

 

Isomerism is the existence of compounds with the same molecular formula but different structural formula.

Positional isomerism results from the change in the position of the functional group(-OH group in alkanols) while structural isomerism results from the addition of a branch(substituent) to a straight chain alkanol.

Alkanols exhibit both structural and positional isomerism. Because of this, they can be categorized as primary, secondary or tertiary alkanols

Primary alkanol(1^o) – Alkanol where the hydroxyl group(-OH) is attached to a carbon atom that is attached to one other carbon atom e.g. butan-1-ol

Secondary alkanol(2^o) – Alkanol where the hydroxyl group is attached to a carbon atom that is attached to two other carbon atoms e.g. butan-2-ol.

Tertiary alkanol(3^o) – Alkanol where the hydroxyl group is attached to a carbon atom that is attached to three other carbon atoms e.g. 2-methylpropan-2-ol

 

 

Practice examples

1. Isomers of propanol(C₃H₇OH)

 

            H  OH  H  

       |     |    |   

H – C – C – C – H        propan-2-ol

       |     |    |       

      H   H   H

H   H    H  

       |     |    |   

H – C – C – C – OH     propan-1-ol

       |    |     |    

      H   H   

 

 

1. Isomers of butanol(C₄H₉OH)

 

H   H   H   H

       |     |    |    |

H – C – C – C – C – OH

       |     |    |    |  

      H   H   H   H

Butan-1-ol

      H  OH H   H

       |     |    |    |

H – C – C – C – C – H

       |     |    |    |  

      H   H   H   H

Butan-2-ol

 

                                       H  CH₃ H  

                                  |     |    |   

                           H – C – C – C – H     2-methylpropan-2-ol

                                  |     |    |       

                                 H  OH  H

 

 

1. Isomers of pentanol(C₅H₁₁OH)

 

 

            H   H   H   H   H

       |     |    |     |    |

H – C – C – C – C – C – OH   pentan-1-ol

       |     |    |     |    |

      H   H   H   H   H

 

            H  OH H   H   H

       |     |    |     |    |

H – C – C – C – C – C – H    pentan-2-ol

       |     |    |     |    |

      H   H   H   H   H

 

        

          

 

          H CH₃ H   H

           |    |     |    |

    H – C – C – C – C – H   2-methylbutan-2-ol

           |    |     |    |

          H OH  H   H

           H  CH₃H 

            |    |     |  

  HO – C – C – C – H  2,2-dimethylbutan-1-ol

            |    |     |    

           H  CH₃  H 

 

 

 

1. 2,3-dimethylbutan-1-ol

          H CH₃ H   H

           |    |     |    |

    H – C – C – C – C – OH

           |    |     |    |

          H   H CH₃ H

 

1. 1,2-dichloropropan-2-ol

           H  Cl   H 

            |    |     |  

  HO – C – C – C – H

            |    |     |    

          Cl   H     H

 

1. Ethan-1,2-diol

      OH  OH 

         |     |        

  H – C – C – H

         |     |    

        H     H

 

1. Propan-1,2,3-triol

      OH OH OH 

         |    |     |  

  H – C – C – C – H

         |    |     |    

        H   H     H

 

 

Laboratory preparation of alkanols

Fermentation is the reaction where sugar is converted to alcohol/alkanol using enzymes (biological catalysts) in yeast. Fermentation involves three processes:

1. Conversion of starch to maltose by the enzyme diastase
2. Hydrolysis of maltose to glucose by the enzyme maltase

• Conversion of glucose to ethanol and carbon (IV) oxide gas using the enzyme zymase

 

C₆H₁₂O₆(aq)  2 C₂H₅OH(aq)  + 2CO₂(g)

(glucose)                                    (ethanol)

 

At concentrations greater than 15% by volume, the ethanol produced kills the yeast enzyme thus stopping the reaction. To increase the concentration therefore, fractional distillation is done to produce up to 100% pure ethanol.

 

Laboratory preparation of ethanol by fermentation of glucose

Set up the apparatus as shown in the figure below.

 

 

 

Observations

Calcium hydroxide (lime water) reacts with carbon (IV) oxide produced during the fermentation to form insoluble calcium carbonate and water. Thus a white precipitate formed dissolves to a colourless solution later.

Excess carbon (IV) oxide produced reacts with the insoluble calcium carbonate and water to form soluble calcium hydrogen carbonate (colourless solution).

 

Ca(OH)₂(aq) + CO₂(g) ® CaCO₃(s) + H₂O(l)

H₂O(l) + CaCO₃(s) +  CO₂(g) ® Ca(HCO₃) ₂(aq)

 

The product of fermentation is then distilled at about 78^oC in a set-up as shown in the figure below. A colourless liquid with a characteristic smell is obtained.

 

 

 

 

Physical Properties of Alkanols

• Alkanols have a characteristic pleasant smell and taste
• Alkanols are neutral compounds that have no effect on both blue and red litmus papers
• The table below summarizes some physical properties of alkanols;

Alkanol	Melting point (oC)	Boiling point (oC)	Density gcm-3	Solubility in water
Methanol	-98	65	0.791	soluble
Ethanol	-114	78	0.789	soluble
Propan-1-ol	-126	97	0.803	soluble
Butanol	-90	117	0.810	Slightly soluble
Pentanol	-79	138	0.814	Slightly soluble
Hexanol	-52	157	0.815	Slightly  soluble
Heptanol	-34	176	0.822	Slightly soluble
Octanol	-15	195	0.824	Slightly soluble
Nonanol	-7	212	0.827	Slightly soluble
Decanol	6	228	0.827	Slightly soluble

 

 

Solubility in water

Ethanol is miscible in water. The alkyl group is insoluble in water while –OH functional group is soluble in water because ethanol and water are polar compounds.

Solubility of alkanols decreases with increase in molecular mass. As the molecular chain becomes longer, the molecule becomes less polar.

 

Melting/boiling point

The melting and boiling point of alkanols increase with increase in molecular mass.

This is because the intermolecular forces of attraction between the molecules become stronger.

 

Density

The densities of alkanols increase as their molecular masses increase because the intermolecular forces of attraction between molecules also increase. This reduces the volume occupied by the molecule as it increases their mass per unit volume (density).

      

Chemical Properties of Alkanols

Reaction of alkanols with air(Combustion)

Pure ethanol burns with an almost colourless non-smoky blue flame to form carbon (IV) oxide (in excess air/oxygen) or carbon (II) oxide (in limited air) and water. Ethanol is thus a saturated compound like alkanes.

C₂H₅OH(l) +3O₂(g) ® 3H₂O(l) + 2CO₂(g)  (excess air)

C₂H₅OH(l) + 2O₂(g) ® 3H₂O(l) + 2CO(g)  (limited air)

2CH₃OH(l) + 3O₂(g) ® 4H₂O(l) + 2CO₂(g)  (excess air)

2CH₃OH(l) + 2O₂(g) ® 4H₂O(l) + 2CO(g)  (limited air)

 

Reaction of alkanols with metals

When a piece of reactive metals (potassium, sodium and calcium) is placed in a test tube containing ethanol the following observations are made;

1. Slow effervescence/fizzing/bubbles
2. Colourless gas slowly produced that extinguish a burning splint with explosion/”pop” sound
3. Colourless solution formed turns red litmus paper blue but does not affect a blue litmus paper

 

Sodium/potassium/calcium reacts slowly with alkanols to form basic solution called alkoxides and hydrogen gas.

Metal + Alkanol ® Metal alkoxide   + Hydrogen gas

2M + 2R-OH ® R-OM + H₂

 

Examples

1. Sodium metal reacts with ethanol to form sodium ethoxide

2CH₃CH₂OH(l) + 2Na(s) ® 2CH₃CH₂ONa(aq) + H₂(g)

1. Potassium metal reacts with ethanol to form potassium ethoxide

2CH₃CH₂OH(l) + 2K(s) ® 2CH₃CH₂OK(aq) + H₂(g)

1. Potassium metal reacts with propanol to form potassium propoxide

2CH₃CH₂CH₂OH(l) + 2K(s) ® 2CH₃CH₂CH₂OK(aq) + H₂(g)

1. Sodium metal reacts with butanol to form sodium butoxide

2CH₃CH₂CH₂CH₂OH(l)  + 2Na(s) ® 2CH₃CH₂CH₂CH₂ONa(aq) + H₂(g)

 

 

 

Reaction of alkanols with alkanoic acids (Esterification)

The set-up below is used to carry out the reaction between alkanols and alkanoic acids in the presence of concentrated sulphuric (VI) acid.

 

Alkanols react with alkanoic acids to form a group of pleasant-smelling compounds called esters and water. This reaction is catalyzed by concentrated sulphuric (VI) acid in the laboratory.

 

alkanol   +    alkanoic acid ester   + water

 

Esters derive their names from the alkanol first then alkanoic acids. The alkanol “becomes” an alkyl group and the alkanoic acid “becomes” alkanoate hence alkylalkanoate e.g.

 

ethanol + ethanoic acid  ethylethanoate + water

ethanol + propanoic acid  ethylpropanoate + water

ethanol + methanoic acid  ethylmethanoate + water

ethanol + butanoic acid  ethylbutanoate + water

propanol + ethanoic acid  propylethanoate + water

methanol + ethanoic acid  methylethanoate +water

 

During the formation of the ester, the “O” joining the alkanol and alkanoic acid comes from the alkanol.

 

Examples

1. C₂H₅OH (l) + CH₃COOH(l) CH₃COOC₂H₅(aq)   +    H₂O(l)

Ethanol            Ethanoic acid                            ethylethanoate        water

 

2. C₂H₅OH (l)+ CH₃CH₂COOH(l) CH₃CH₂COOC₂H₅(aq)   +   H₂O(l)

Ethanol         Propanoic acid                            ethylethanoate                water

 

3. CH₃OH (l) +    CH₃COOH(l)  CH₃COOCH₃(aq)   +   H₂O(l)

Methanol           Ethanoic acid                       methylethanoate           water

4. CH₃OH (l) + CH₃CH₂COOH(l)  CH₃CH₂COOCH₃(aq)   + H₂O(l)

Methanol           propanoic acid                       methylpropanoate            water

 

5. C₃H₇OH (l) + CH₃CH₂COOH(l)    CH₃CH₂COOC₃H₇(aq)   +H₂O(l)

Propanol       Propanoic acid                            propylpropanoate       water

 

 

Reaction of alkanols with oxidising agents (Oxidation)

Both acidified KMnO₄ and K₂Cr₂O₇ are oxidising agents (add oxygen to other compounds). They oxidise alkanols to a group of homologous series called alkanals then further oxidise them to alkanoic acids. The oxidising agents are themselves reduced hence changing their colour:

1. Purple KMnO₄ is reduced to colourless Mn²⁺
2. Orange K₂Cr₂O₇ is reduced to green Cr³⁺

 

 

 

Alkanol + [O] ® alkanoic acid

R₁-OH + [O] ® R₂-COOH

 

NB;

The [O] comes from the oxidising agents acidified KMnO₄ or K₂Cr₂O₇

The pH of alkanoic acids show they have few H⁺ because they are weak acids

 

Examples

1. Ethanol + [O] ® Ethanoic acid

CH₃CH₂OH + [O] ® CH₃COOH

 

1. methanol + [O] ® methanoic acid

CH₃OH +[O] ® HCOOH

 

1. Propanol + [O] ® Propanoic acid

CH₃CH₂CH₂OH + [O] ® CH₃ CH₂COOH

 

 

Dehydration of alkanols

Dehydration is a process where a dehydrating agent removes water from compound/substances. Concentrated sulphuric (VI) acid dehydrates alkanols to the corresponding alkenes at about 180^oC i.e.

 

alkanol alkene + water

 

Examples

1. CH₃CH₂OH(l) CH₂=CH₂ (g)  +  H₂O(l)

ethanol                                             ethene         +      water

 

1. CH₃CH₂CH₂OH(l)    CH₃CH=CH₂ (g)  +  H₂O(l)

 propanol                                             propene            +      water

 

1. CH₃CH₂CH₂CH₂OH(l) CH₃CH₂C=CH₂ (g)  +  H₂O(l)

butanol                                                     butene        +             water

 

Uses of some alkanols

1. Methanol is used as industrial alcohol and making methylated spirit
2. Ethanol is used:

• As alcohol in alcoholic drinks e.g. beer, wines and spirits.
• As antiseptic to wash wounds.
• In manufacture of vanishes, ink, glue and paint because it is volatile and thus easily evaporates.
• As a fuel when blended with petrol to make gasohol.

3. Most alkanols are used as solvents and starting materials in numerous industrial processes

 

NB;

• Methanol is poisonous; when ingested, it causes instant blindness and liver damage. It kills the consumer within hours, if taken in large quantities.
• Prolonged intake of ethanol causes loss of co-ordination. It damages vital organs like the liver and kidneys thus causing physical and mental illnesses

 

 

ALKANOIC ACIDS (CARBOXYLIC ACIDS)

Alkanoic acids belong to a homologous series of organic compounds with a general formula C_nH_{2n +1} COOH and thus -COOH as the functional group .The first ten alkanoic acids include:

Alkanoic acids, (like alkanols /alkanes/alkenes/alkynes) form a homologous series where:

1. All members conform to the general molecular formula C_nH_2n+1COOH (Generally represented as R-COOH, where R is an alkyl group)
2. All members have –COOH as the functional group

• Each member differ by –CH₂ group from the next/previous

1. They show a similar and gradual change in their physical properties e.g. boiling and melting points
2. They have similar chemical properties(since they are acids they show similar properties with mineral acids)

 

Nomenclature of alkanoic acids

Alkanoic acids exhibit both structural and position isomerism. The isomers are named by using the following basic guidelines

1. The names of have prefixes similar to those of alkanes but have suffixes ending in -noic acid
2. Identify the longest carbon-carbon chain to obtain the parent name.

• Number the chain such that the carbon to which the -COOH group is attached to has the least value possible

1. Identify the type and position of the side group branches.

 

 

Questions

Name the following compounds:

 

 

1. H CH₃       O

         |    |        

  H – C – C – C

         |    |        

        H   H         OH

 

2. H   H   H         O

         |    |     |  

  H – C – C – C – C

         |    |     |      

        H   H   H           OH

 

 

 

3. H   H   H   H       O

         |    |     |     |

  H – C – C – C – C – C

         |    |     |     |

        H   H   H    H         OH

 

4. H  H  CH₃        O

         |    |     |  

  H – C – C – C – C

         |    |     |      

        H   H   H           OH

 

 

5. H CH₃         O

         |    |        

  H – C – C – C

         |    |        

        H CH₃         OH

 

6. HO O

                 

              C – C

                 

        O               OH

 

 

 

Laboratory preparation of alkanoic acids

Alkanoic acids can be prepared by adding an oxidising agent (H⁺/KMnO₄ or H⁺/K₂Cr₂O₇) to the corresponding alkanol then warming. The set-up below may be used;

 

 

The mixture obtained in the set-up above contains the oxidising agent, water and ethanoic acid. It is distilled at 118^oC to obtain pure ethanoic acid. The oxidation of alkanols to alkanoic acids can be represented by the general equation below;

RCH₂OH   + [O] RCOOH

(alkanol)                                 (alkanoic acid)

Examples

1. Ethanol on warming in acidified KMnO₄ is oxidized to ethanoic acid.

CH₃CH₂OH   +  [O]  CH₃COOH

(ethanol)                                   (ethanoic acid)

 

1. CH₃CH₂ CH₂OH + [O]CH₃COOH

(propanol)                                      (propanoic acid)

 

Physical properties of alkanoic acids

Alkanol	Melting point (oC)	Boiling point (oC)	Density(g/cm3)	Solubility in water
Methanoic acid	8.4	101	1.22	soluble
Ethanoic acid	16.6	118	1.05	soluble
Propanoic acid	-20.8	141	0.992	soluble
Butanoic acid	-6.5	164	0.964	soluble
Pentanoic acid	-34.5	186	0.939	Slightly soluble
Hexanoic acid	-1.5	205	0.927	Slightly soluble
Heptanoic acid	3	223	0.920	Slightly soluble
Octanoic acid	11	239	0.910	Slightly soluble
Nonanoic acid	16	253	0.907	Slightly soluble
Decanoic acid	31	269	0.905	Slightly soluble

 

It can be noted that:

• Melting and boiling point decrease as the carbon chain increases due to increase in intermolecular forces of attraction between the molecules requiring more energy to separate the molecules.
• The density decreases as the carbon chain increases as the intermolecular forces of attraction increases between the molecules making the molecule very close reducing their volume in unit mass.
• Solubility decreases as the carbon chain increases as the soluble –COOH end is shielded by increasing insoluble alkyl/hydrocarbon chain.
• Like alkanols, alkanoic acids exist as dimmers due to the hydrogen bonds within the molecule

 

Chemical properties of alkanoic acids

• All alkanoic acids dissociate to releases the H⁺ ions at the functional group in -COOH to form the alkanoate ion(R–COO^–)

 

R-COOH(aq)  ⇌  R-COO^–(aq) + H⁺(aq)

 

• Alkanoic acids are weak acids that partially/partly dissociate to release few H⁺ ions in solution. Thus the pH of their solutions lies between 4 and 6.

 

Examples

CH₃COOH(aq)           ⇌  CH₃COO^–(aq)  +  H⁺(aq)

(ethanoic acid)       (ethanoate ion)

 

CH₃ CH₂COOH(aq)  ⇌ CH₃ CH₂COO^–(aq)  +          H⁺(aq)

(propanoic acid)          (propanoate ion)

 

Reaction with metals

• Metals higher in the reactivity series displace the hydrogen in all acids to evolve/produce hydrogen gas and form a salt
• Alkanoic acids react with metals to form salt (alkanoates) and hydrogen. Hydrogen extinguishes a burning splint with a pop sound/explosion. Only the “H” in the functional group -COOH is /are displaced and not in the alkyl hydrocarbon chain.

 

alkanoic acid + metal ® alkanoate   +   hydrogen gas

 

Generally;

1. For a monovalent metal with monobasic acid

2R-COOH + 2M ® 2R-COOM + 2H₂(g)

 

1. For a divalent metal with monobasic acid

2R-COOH + M ® (R-COO) ₂M + H₂(g)

 

Examples

1. Calcium reacts with ethanoic acid to form calcium ethanoate and produce hydrogen gas.

2CH₃COOH(aq) + Ca(s) ® (CH₃COO) ₂Ca(aq) + H₂(g)

(ethanoic acid)                  (calcium ethanoate)

 

1. Magnesium reacts with ethan-1,2-dioic acid to form magnesium ethan-1,2-dioate and produce hydrogen gas.

HOOC-COOH    +   Mg ® (OOC-COO)Mg  +   H₂(g)

(ethan-1,2-dioic acid)          (magnesium ethan-1,2-dioate)

 

 

Reaction with hydrogen carbonates and carbonates

• All acids react with hydrogen carbonates/carbonates to form salt, carbon (IV) oxide and water.
• Carbon (IV) oxide forms a white precipitate when bubbled through lime water and extinguishes a burning splint.
• Alkanoic acids react with hydrogen carbonate/carbonate to form salt (alkanoates), water and carbon (IV) oxide.

alkanoic acid + hydrogen carbonate ® alkanoate + water + carbon (IV) oxide

alkanoic acid + carbonate ® alkanoate + water + carbon (IV) oxide

 

Examples

1. CH₃COOH (aq) + NaHCO₃(s) ® CH₃COONa(aq) + H₂O(l) + CO₂(g)

(ethanoic acid)                           (sodium ethanoate)

 

1. 2CH₃COOH (aq) + Na₂CO₃(s) ® 2CH₃COONa(aq) + H₂O(l) + CO₂(g)

(ethanoic acid)                            (sodium ethanoate)

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Esterification (Reaction with alkanols)

Alkanols react with alkanoic acid to form pleasant-smelling compounds called esters, and water. The reaction takes place in the presence of concentrated sulphuric (VI) acid catalyst. Each ester has a characteristic smell derived from the many possible combinations of alkanols and alkanoic acids.

alkanoic acid + alkanol  ester + water

R₁-COOH + R₂-OH  R₁-COO-R₂  + H₂O

 

Esters are alkylalkanoates derived from alkanol(alkyl group) and the alkanoic acid (alkanoate)

During the formation of the ester, the “O” joining the alkanol and alkanoic acid comes from the alkanoic acid.

 

Examples

1. Ethanol reacts with ethanoic acid to form the ester ethylethanoate and water.

C₂H₅OH(l) + CH₃COOH(l)  CH₃COO C₂H₅(aq)    +  H₂O(l)

1. Ethanol reacts with propanoic acid to form the ester ethylpropanoate and water.

C₂H₅OH(l) + CH₃CH₂COOH(l) CH₃CH₂CO C₂H₅(aq)   +H₂O(l)

 

1. Methanol reacts with ethanoic acid to form the ester methylethanoate and water.

CH₃OH(l) + CH₃COOH(l)  CH₃COOCH₃(aq)   +H₂O(l)

 

1. Methanol reacts with propanoic acid to form the ester methylpropanoate and water.

CH₃OH(l) + CH₃CH₂COOH(l)  CH₃CH₂COOCH₃(aq)   +H₂O(l)

 

DETERGENTS

Detergents are substances that improve the cleaning power of water. Detergents are able to dissolve substances which water cannot e.g. grease, oil or fat, and be washed away after cleaning. There are two types of detergents; soapy detergents and soapless detergents

 

Soapy detergents

Soapy detergents, usually called soap, are salts of long chain alkanoic acids. The common soap is sodium octadecanoate. It is derived from reacting concentrated sodium hydroxide solution with octadecanoic acid i.e.

Sodium hydroxide + octadecanoic acid ® Sodium octadecanoate   +   water

NaOH(aq) + CH₃ (CH₂) ₁₆ COOH(aq) ® CH₃ (CH₂) ₁₆ COO ^–  Na⁺(aq) +H₂ O(l)

 

Soapy detergents can thus be represented as;

R-COO^–Na⁺      where R is a long chain alkyl group

 

Soapy detergents are more often made by reacting concentrated alkali with esters from (animal/plant) fat and oil. The process is called saponification. During saponification, the ester is hydrolyzed by the alkali to form sodium salt (soapy detergent) and glycerol(propan-1,2,3-triol)

 

Fat/oil + sodium hydroxide ® sodium salt   + glycerol

(ester)                                          (soap)

 

Fats/oils are esters with fatty acids in their structure as shown in the example below;

 

 

When boiled with concentrated sodium hydroxide solution the following reaction takes place;

 

Ester                           Alkali             Glycerol      Sodium octadecanoate (soap)

 

During this process a little sodium chloride is added to precipitate the soap by reducing its solubility. This is called salting out.

 

The mode of action of soapy detergent

• Soapy detergents are made of a non-polar alkyl/hydrocarbon tail and a polar -COO^–Na⁺

 

 

 

non-polar tail                       polar head

CH₃(CH₂)₁₆                          -COO^–Na⁺

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• The non-polar tail(R) is hydrophobic(water-hating); it does not dissolve in water while the polar head(-COO^–Na⁺) is hydrophilic(water-loving)
• Thus the non-polar tail dissolves in organic matter like grease and dirt. The polar tail on the other hand, dissolves in water.
• Through mechanical agitation/squeezing/kneading, some grease is dislodged of the surface of the garment with the tail end. It is immediately surrounded by more soap molecules. It floats and spreads in the water as tiny droplets that scatter in form of emulsion making the water cloudy and shinny.
• It is removed from the garment by rinsing with fresh water. The repulsion of the soap head ensure the droplets do not mix.
• Once removed, the dirt molecules cannot be re-deposited back because it is surrounded by soap molecules.

 

Advantage soapy detergents

1. Soapy detergents are biodegradable. They are acted upon by bacteria and rot. Thus they do not cause environmental pollution
2. Cheaper than soapless detergents

 

Disadvantages of soapy detergents

1. They are made from fat and oils which are better eaten as food than make soap
2. Form insoluble precipitates with hard water called scum. Scum is insoluble calcium/magnesium octadecanoate salt. This causes wastage of soap

2C₁₇H₃₅COO^– Na⁺(aq) + Mg²⁺/Ca²⁺(aq) ® (C₁₇H₃₅COO^– )₂Mg²⁺/Ca²⁺(s)  +  2Na⁺(aq)

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Soapless Detergents

The carboxylate group in the soapy detergent is replaced by an alkyl sulphonate group in the soapless detergent.

1. Soapless detergents are prepared by the following steps;
2. The reaction of a long, straight-chain alkene, such as dodecene, with benzene to get an alkylbenzene(dodecylbenzene).

Benzene + dodecene ® dodecylbenzene

C₆H₆ + CH₃(CH₂)₉CH = CH₂ ® C₆H₅(CH₂)₁₁CH₃

1. The alkylbenzene is then reacted with concentrated sulphuric (VI) acid to give an alkylbenzene sulphonate group

Dodecylbenzene + sulphuric (VI) acid ® dodecylbenzene sulphonate + water

C₁₈H₃₀ + H₂SO₄ ® C₁₈H₂₉SO₃H + H₂O

• The sulphonate is neutralized with sodium hydroxide to get sodium alkylbenzene sulphonate, the detergent itself.

Dodecylbenzene sulphonate + sodium hydroxide ® sodium dodecylbenzene sulphonate

C₁₈H₂₉SO₃H(aq) + NaOH(aq) ® C₁₈H₂₉OSO₃Na(aq) + H₂O(l)

(soapless detergent)

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1. Soapless detergents can also be prepared starting with long chain alkanols as shown below;
2. Concentrated sulphuric (VI) acid with a long chain alkanol e.g octadecanol, to form alkyl hydrogen sulphate

R–OH + H₂SO₄ ® R-O-SO₃H + H₂O

 

1. The alkyl hydrogen sulphate is then neutralized with sodium/potassium hydroxide to form sodium/potassium alkyl hydrogen sulphate, the detergent.

R-O-SO₃H + NaOH ® R-O-SO₃^–Na⁺ + H₂O

 

The mode of  action of soapless detergents

The action of soapless detergents is similar to that of soapy detergents. The soapless detergents contain the hydrophilic head and a long hydrophobic tail. Soapless detergents are of the general structure shown below;

 

 

 

Non-polar tail                                      polar head

R-C₆H₆ or  CH₃(CH₂)₁₆-C₆H₆               – OSO₃^– Na⁺

 

• The tail dissolves in fat/grease while the polar/ionic head dissolves in water. The tail sticks to the dirt which is removed by the attraction of water molecules and the polar/hydrophilic head by agitation/rubbing
• The suspended dirt is then surrounded by detergent molecules and repulsion of the anion head preventing the dirt from sticking on the material garment.
• The tiny droplets of dirt emulsion make the water cloudy. On rinsing the cloudy emulsion is washed away.

 

Advantages of soapless detergents

1. Do not form scum with hard water
2. Are made from petroleum products but soap is made from fats/oil for human consumption

 

Disadvantages of soapless detergents

1. Soapless detergents are non-biodegradable unlike soapy detergents.
2. They persist in water during sewage treatment by causing foaming in rivers, lakes and streams leading to marine/aquatic death
3. Are expensive to buy

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POLYMERS

Polymers are giant molecules formed when small molecules, called monomers, join together at high temperatures and pressures. This process is called polymerization.

• Natural polymers are found in living things (plants and animals) and they include: proteins/polypeptides making amino acids in animals, cellulose that make cotton, wool, paper and silk, starch that come from glucose, fats and oils and latex in rubber trees.
• Synthetic polymers and fibres are man-made. They include: polyethene, polychloroethene, polyphenylethene(polystyrene), terylene(dacron), nylon-6,6 and perspex(artificial glass)

There are two types of polymerization i.e. addition polymerization and condensation polymerization

 

Addition polymerization

• Addition polymerization is the process where a small unsaturated molecules (monomer) join together to form a large molecule without formation of any other products.
• Addition polymers are named from the monomer making the polymer and adding the prefix “poly” before the name of monomer to form a polymer
• During addition polymerization the double bonds in monomers break and bond to the next via a single carbon-carbon bond.

 

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Examples of addition polymerization

 

1. Polyethene

 

 H    H            H    H                            H     H     H     H                

  |     |              |     |                              |       |      |       |  

 C = C     +    C = C                      —–C —-C—C—C——   or

  |     |              |     |                              |       |      |       |

H     H            H   H                            H      H    H     H

Ethene          Ethene                             (Polyethene)

(monomer)     (monomer)                      (polymer)

 

 

1. Polychlorethene

 

 H    H            H    H                            H     H     H     H

  |     |              |     |                              |       |      |       |  

 C = C     +    C = C                      —–C —-C—C—C——

  |     |              |     |                              |       |      |       |

H     Cl            H   Cl                            H     Cl    H    Cl

Chloroethene     Chloroethene                Polychloroethene(polyvinyl chloride)

(monomer)     (monomer)                              (polymer)

 

• Polyphenylethene

 

 H    H            H    H                             H     H     H     H

  |     |              |     |                               |       |      |      |  

 C = C     +    C = C                      —–C —-C—C—C——

  |     |              |     |                              |       |      |       |

H   C₆H₅         H  C₆H₅                         H  C₆H₅   H    C₆H₅

phenylethene     phenylethene                Polyphenylethene(polystyrene)

(monomer)     (monomer)                              (polymer)

 

 

1. Polypropene

 

 H   H           H    H                             H     H     H     H                          

  |    |             |     |                               |       |      |      |  

C = C     +    C = C                      —–C —C—C—C——         

 |     |             |     |                               |       |      |      |

H   CH₃        H   CH₃                          H     CH₃  H    CH₃

Propene           Propene                              Polypropene

(monomer)     (monomer)                              (polymer)

 

1. Polytetrafluorothene

 

  F    F             F     F                             F      F      F      F               

  |     |             |      |                              |       |      |       |  

 C = C     +    C = C                      —–C —-C—C—C——  

  |     |             |      |                              |       |      |       |

  F    F            F      F                             F      F     F       F

Tetrafluorothene                                 Polytetrafluoroethene(Teflon)

(monomers)                                               (polymer)

 

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1. Perspex

 

        H    H                                        H      H

         |     |                                          |       |   

n      C = C                               ——C—-C——–

         |     |                                          |       |

        H COOCH₃                                                 H  COOCH₃  n

          2-methylpropenate/                    polymethylmethacrylate (perspex)

methylmethacrylate (monomers)                                 (polymer)

 

NB:

1. Since addition polymers are formed by many identical monomers, its relative molecular mass is a multiple of the relative molecular mass of each monomer.
2. Where n is the number of monomers in the polymer. The number of monomers in the polymer can be determined from the molar mass of the polymer and monomer from the following relationship:

 

Number of monomers (repeating units) n =   Relative molecular mass of polymer

Relative molecular mass of monomer

 

Worked Examples

1. The polymer has a general structure as shown below;

H    H

                          |     |

                         C – C

                          |     |    n

                       CH₃  H

If its relative molecular mass is 18900, calculate the value of n (H = 1, C = 12)

 

Working

1. M. M. of monomer = (12×3) + (1×6) = 42

 

n=  = 450

 

2. Polyvinyl chloride is formed by polymerization of the monomer shown below;

                                       H    H

                                        |     |     

                                       C = C    

                                        |     |             

                                       H    Cl

The polymer formed has a relative molecular mass of 50000. Calculate the monomer units, n used to make it.                                                                                  (H = 1, C = 12, Cl = 35.5)

  

Working

35. M. M. of monomer = (12×2) + (1×3) + 35.5 = 62.5

 

No. of monomers, n =   = 800

 

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Condensation polymerization

• Condensation polymerization is the process where two identical or different monomers join together to form a larger molecule with the loss of a small molecule like water or ammonia.
• The monomer(s) have functional groups at both ends to allow the molecules to join up in both ends.

 

Examples of condensation polymers

 

1. Starch (glucose +   glucose = starch  +  water)

 

HO – C₆H₁₀O₄ – OH    +    HO – C₆H₁₀O₄ – OH            HO – C₆H₁₀O₄ – C₆H₁₀O₄   +   H₂O

 

 

1. Protein (Amino acid +  Amino acid =  Protein +  water)

 

 

         O    H   H                        O    H   H                           O   H   H   O   H   H

         ||     |    |                          ||     |    |                            ||    |     |    ||    |     |

HO – C – C – N – H    +    HO – C – C – C – H           HO — C – C – N – C – C – N –H

                |                                       |                                       |                 |

               H                                      H                                     H               H    

 

 

• Nylon-6,6 (hexane-1,6-dioic acid +  hexane-1,6-diamine  =  nylon-6,6  +  water)

              

 

 

 

 

 

1. Polyester (terephthalic acid +  ethan-1,2-diol  =  polyester  + water)

 

 

 

Rubber

• Natural rubber is obtained from the sap of Heavea brasiliensis tree found in areas of South America, West Africa and South East Asia. The sap of the rubber tree is called
• Latex is coagulated using an acid to form a polymer made up of 2-methylbut-1,3-diene /isoprene (CH=CCH₃CH=CH₂)
• Isoprene polymerises as shown below;

 

             H   CH₃ H    H          H   CH₃ H   H                         H          H   H  CH₃  H

              |      |     |     |             |     |     |    |                           |            |    |      |     |

             C = C – C = C    +     C = C – C= C                          C – C = C – C = C – C

        |                  |             |                |                            |    |           |            |

       H                H            H              H                          H   CH₃       H           H

                    (isoprene/monomer)                                 (poly-isoprene/rubber)

 

• Natural rubber is usually soft hence must be hardened to make it more useful. This is done by heating rubber with sulphur in a process called vulcanization.
• Cross-links of sulphur atoms form between polymer chains reducing the double bonds in the rubber.
• Synthetic rubber can also be obtained by polymerization of various monomers e.g. styrene-buta-1,3-diene, 2-chlorobuta-1,3-diene etc.

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Advantages of synthetic polymers and fibres

1. They can be made to desired shapes easily
2. They are stronger
3. They are lighter
4. They are less affected by chemicals e.g. acids, alkalis, water and air
5. They are less expensive

 

Disadvantages of synthetic polymers and fibres

1. Some of them burn to give off poisonous fumes such as hydrogen cyanide and carbon (II) oxide
2. They are not biodegradable, thus cause massive environmental pollution
3. Some of them burn more readily than natural, thus are fire hazards

 

 

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