ORGANIC COMPOUNDS

Hydrocarbons and their derivatives i.e., carbon compounds with the exception of CO, CO₂, carbonates and bicarbonates are called Organic compounds. The term ‘hydrocarbon‘ means compounds of hydrogen and carbon only. Their natural source is petroleum or crude oil. Hydrocarbons are of different types.

Depending upon the carbon-carbon bond present, they can be classified into three main categories:

SATURATED HYDROCARBONS

They contain carbon-carbon and carbon-hydrogen single bonds. They are of two types:

1- ALKANES OR PARAFFINS

Paraffin is a Latin word meaning less affinity, thus, these are chemically inert (or non-reactive) towards most of the chemicals. In these compounds different carbon atoms are joined together to form open chain of carbon atoms with single bonds. General formula for alkanes is C_nH_2n+2 (where, n=1,2,3….)

Methane(CH₄) is the first member of this family. Other members of this family are as follows:

Ethane(C₂H₆) < Propane(C₃H₈) < Butane(C₄H₁₀) < Pentane(C₅H₁₂) < Hexane(C₆H₁₄) < Heptane(C₇H₁₆) < Octane(C₈H₁₈) < Nonane(C₉H₂₀) < Decane(C₁₀H₂₂).

2- CYCLO-ALKANES

In cycloalkanes, carbon atoms form a closed chain or a ring. General formula for cyclo-alkanes is C_nH_2n.  Cyclo-propane(C₃H₆) is the first member of the family. Distance Between two carbon atoms bonded through a single bond is always larger than that present between two carbon atoms joined together through multiple bonds(double or triple bond). Thus C – C bond length in ethane is greater than that of ethene or ethyne.

UNSATURATED HYDROCARBONS

They contain carbon-carbon multiple bonds i.e., double bonds, triple bonds. These are of two types:

1- ALKENES

They contain atleast one carbon-carbon double bond. These are also called as Olefins(oil forming), since the first member of the family ethylene or ethene(C₂H₄) was found to form an oily liquid on reaction with chlorine. General formula for alkenes is C_nH_2n.

Ethylene(CH₂=CH₂) is prepared by heating ethyl alcohol with conc. H₂SO₄ at 170 ⁰ C. It is used in making mustard gas, In ripening fruits artifically, In oxyethylene flame, in fruit preservation and as an anaesthesia. Trichloroethylene is used for dry cleaning purposes.

Butene(CH₃-CH=CH-CH₃) is a constituent of liquified petroleum gas and is used as a fuel.

2- ALKYNES

They contain atleast one carbon-carbon triple bond. General formula for alkynes is C_nH_2n-2. Ethyne(C₂H₂) Acetylene is the first member of this family. Reaction of acetylene with silver nitrate shows its acidic property.

Acetylene(C₂H₂) was prepared for the first time by the American scientist Wilson. It is prepared by the reaction of calcium carbide with water. It is used in the synthesis of benzene, In oxy-acetylene welding and cutting as a raw material for plastics, In making Camphor, In making Neoprine(artificial rubber).

AROMATIC HYDROCARBONS

Aroma means pleasant smelling. These are also known as arenes. Most of them possess pleasant odour. Most of these compounds contain benzene ring. e.g., benzene, toluene, naphthalene, anthracene, etc. General formula for arenes is C_nH_2n-6.

Benzene(C₆H₆)

It was first isolated by Faraday in 1825, from the cylinders of compressed illuminating gas obtained by the pyrolysis of whale oil. Hofmann obtained benzene by fractional distillation of coaltar. It was first synthesised by Berthelot by passing acetylene through red hot tube. It is used in the production of various organic compounds, manufacturing of explosives, dry cleaning, as a solvent and fuel in motor vehicles.

Toluene(C₆H₅CH₃)

It was first extracted from tolu balsam, a resin. It is used in the manufacturing of TNT explosives, as antifreezer, in artificial sweetener saccharin.

ORGANIC COMPOUNDS CONTAINING C, H & O

These are phenols, ethers, aldehydes, ketones, carboxylic acids, esters and alcohols.

1- PHENOLS

(C₆H₅OH) These are formed when the hydrogen atom in an aromatic hydrocarbon is replaced by -OH group. Phenol is the simplest hydroxy derivative of benzene. Ferric chloride test is used to indicate presence of phenols.

It is commonly known as Carbolic acid and was prepared by Runge in 1834. It is used to prepare many compounds like salol, bakelite, phenolphthalein, aspirin, salicylic acid, phenyl(germicide), and in explosives like picric acid.

2- ETHERS

These are formed when a hydrogen atom in a hydrocarbon is replaced by alkoxy or aryloxy(R-O/Ar-O group). e.g., dimethyl ether, diethyl ether, ethyl methyl ether, etc. General formula for ethers is C_nH_2n+2O.

Diethyl ether(C₂H₅-O-C₂H₅) is commonly called ether.

It is obtained by heating ethanol with Conc. H₂SO₄  at 140 ^oC. Other method for its synthesis is Williamson Synthesis.

3- KETONES

General formula for ketone is C_nH_2nO or (C_nH_2n+1)₂CO .e.g., acetone or dimethyl ketone, ethyl methyl ketone, etc.

Acetone(CH₃COCH₃) is a common industrial solvent.

It is used in cosmetics. It is also used in making artificial silk, synthetic rubber, nail polish remover and medicines.

4- CARBOXYLIC ACIDS

Carbon compounds containing a-COOH functional group(carboxyl group), are called carboxylic acids. General formula for carboxylic acids is C_nH_2nO_2. e.g., formic acid(HCOOH), acetic acid(CH₃COOH), propionic acid(C₂H₅COOH), etc.

Formic acid(HCOOH) was firstly prepared by the distillation of water with red ants so named as formic acid(in latin formicus means red ants). It is used in rubber, leather textile, dyeing and electroplating industry, in the production of medicines of artherites and various compounds. It is also used as insecticide and juice preservative.

Acetic acid(CH₃COOH)

It is obtained from pyroligneous acid. It is a common laboratory reagent and is used to form various organic compounds like alcohol, acid as a solvent and as vinegar in food. Its 4-6% aqueous solution is called vinegar. It is also used in making photographic film, rayon, etc.

Oxalic acid(C₂H₂O₄)

It is a dicarboxylic acid, which in the form of potassium-hydrogen salt, is present in the family of plants as oxalis and rumex. It is used in metallurgy, in colouration and printing of clothes. It is used in cleaning the spot of ink(10% solution) and bleaching of leather. It is also used in photography in the form of ferrous oxalate. It is also used for making ink and coaltar.

Lactic acid(CH₃CH(OH)COOH)

It is a monohydroxy carboxylic acid. It is present in milk and provides it sour taste. It is also present in muscles during hard core exercise. It is soluble in water.   

Salicylic acid(C₆H₅( OH)COOH)

It is a white crystalline aromatic acid used in medicines.

Citric acid is a monohydroxy tricarboxylic acid. It is present in all citrus fruits such as oranges, pineapple, lemon, etc.

5- ALDEHYDES

These organic compounds contain -CHO functional group. General formula for aldehydes is C_nH_2nO. e.g., formaldehyde(HCHO), acetaldehyde(CH₃CHO), etc. These are identified by Tollen’s reaagent, Fehling solution and schiff’s reagent.

Formaldehyde(HCHO) is used as a tissue fixation and embaalming agent. It is used as a disinfectant and its 40% aqueous solution is known as formalin, it is used as preservative for preserving biological specimens.

6- ESTERS

These organic compounds contain -COOR functional group and fruity smell. General formula of this class is C_nH_2nO₂ or C_nH_2n+1COOR.e.g., methyl formate(HCOOCH₃), methyl acetate(CH₃COOCH₃), ethyl acetate(C₂H₅COOCH₃), etc. Ethyl acetate is used for making artificial perfumes, scented colours, dyes, etc.

7- ALCOHOLS

These are formed when a hydrogen atom of aliphatic hydrocarbon is replaced by -OH group. General formula for alcohol is C_nH_2n+1OH. Alcohols are classified as Mono-, di-, tri-, and polyhydric compounds depending on whether they contain one, two, three or more hydroxyl group respectively.

Monohydric alcohol- Methanol, Ethanol.

Dihydric alcohol- Glycol.

Trihydric alcohol- Glycerol.

Presence of this group is identified by esterification test. Formation of pleasant smelling compound with carboxylic acid shows the presence of alcohol.

 ALCOHOLIC BEVERAGES

Alcoholic beverages are produced by the fermentation of grapes, maize, sugarcane, etc. The amount of alcohols is different for different beverages. These beverages contain ethanol as their prime constituent. Yeast contains rymase enzyme which converts glucose into ethyl alcohol.

TYPES OF ALCOHOLIC BEVERAGES

Alcoholic beverages can be of the following types:

1- Distilled beverages– These beverages are prepared by distillation. Amount of alcohol in them may vary from 40-55%.

• Brandy – 40-50% – Grapes(fermented)
• Rum – 45-55 % – Sugarcane
• Vodka – 30-40% – Corn, wheat
• Whisky – 40-50% – Molasses
• Gin – 35-40% – Maize

2- Undistilled beverages– These are prepared by the addition of substances for flavour, perfume and colour. The amount of alcohol varies from 3-15%.

• Beer – 4-6% – Barley
• Cider – 2-6% – Apples
• Champagne – 10-15% – Grapes
• Port and sherry – 15-25% – Grapes

SOME TERMS RELATED TO ALCOHOL

• Denatured Alcohol– Some substances like pyridine, acetone, methyl alcohol are added to ethyl alcohol(ethanol) to make it poisonous and unfit for drinking.
• Spirit– It is an alcoholic beverage containing ethanol. It is produced by the distillation of ethanol which is obtained by the means of fermentation of grains, vegetables and fruits.
• Wine– It is an alcoholic beverage made from fermented grapes, apples, berries, etc. It contains 9-16% ethanol by volume.
• Grain alcohol– Ethyl alcohol is called grain alcohol because it is obtained by the fermentation of starched food grains.
• Absolute alcohol– It is a pure ethyl alcohol which is volatile and colourless liquid. It contains less than 1% of water by weight.
• Power alcohol– Mixture of purified spirit, benzene and petrol is used in propelling engine, thus termed as power alcohol.
• Rectified spirit– It contains 95% of ethanol and 5% of water. It is purified by the means of repeated distillation called rectification, thus termed as rectified spirit.
• Wood spirit– It is produced by the destructive distillation of wood and contains methanol.
• Oenology– It is a branch of chemistry which deals with the study of all aspects of wine and wine making.

POINTS TO REMEMBER

•  To check alcohol level in the blood of the person, a test is performed in which he has to blow into the mouthpiece of a bag containing sodium dichromate solution in acidic medium. On reaction with ethanol, the colour of the solution converts from orange to green.
•  In nail polish remover the main ingredient is ethyl acetate or butyl acetate.
•  The tracking of people by trained dogs is based on the release of carboxylic acid in the sweat from feet.
•  In plant cells, oxalic acid occurs in the form of calcium oxalate.
• Calcium oxalate is also present in human urine. Sometimes, this compound deposits in the kidney and appears as kidney or prostate stone.
• Alkanes are inert under normal conditions as they do not react with acids, bases and other reagents. Hence, they are also known as paraffins.
•  Saturated and unsaturated hydrocarbons are collectively called aliphatic hydrocarbons.