CARBON COMPOUNDS

ORGANIC COMPOUNDS  The compounds of carbon( except the oxides of carbon, carbonates, hydrogen carbonates and carbides) are called organic compounds.  The study of organic compounds is called organic chemistry.

FUNCTIONAL GROUPS   A functional group in an organic compound is an atom or a group of atoms bonded together in a unique fashion, which is usually the site of chemical reactivity in an organic molecule.   For Example - The hydroxyl group in ethanol (C 2 H 5 –OH) is known as a functional group. The functional group in ethene is, and in ethyne, it is – C ≡ C –.   Thus, we see that the properties of a compound depend on the functional group.

ALCOHOLS   Alcohols are carbon compounds containing – OH group attached to a carbon atom.   The general formula of alcohols is R-OH, where R is an alkyl group and –OH is a functional group.   An alcohol may also be considered as derived by replacing a hydrogen atom of an alkane by a hydroxyl group.   The name of the alcohol is derived by replacing –e in the name of alkane (from which it is derived) by the ending –ol.   For example, methanol (CH3OH), an alcohol, is derived by substituting one H in methane (CH 4 ) by a hydroxyl (-OH) group.

ETHANOL   Ethanol, commonly known as alcohol, is a constituent of all alcoholic beverages, namely beer, wine, whisky, some cough syrups, digestive syrups, etc. In industries, alcohol is produced by the fermentation of sugar.

FERMENTATION   The slow decomposition of organic matter into simpler substances in presence of enzymes is known as fermentation.   Fermentation was used for the preparation of alcoholic beverages from grape juice and other fruit juices in presence of yeast, which contains proper enzymes. This process is called fermentation, as the liquid appears as boiling (fervour – to boil) due to the liberation of carbon dioxide gas.

  In this process, the sugar from molasses or sugarcane, or fruits, or starch from various grains, is first converted to glucose and fructose, (isomers) both of them have the formula C 6 H 12 O 6, in presence of an enzyme, invertase. Invertase C 12 H 22 O 11 + H 2 O  C 6 H 12 O 6 + C 6 H 12 O 6 Sugar Glucose Fructose

  Glucose and fructose are both converted to ethanol and carbon dioxide in presence of another enzyme, zymase. Both the enzymes, invertase and zymase, are present in yeast. Zymase C 6 H 12 O  2C 2 H 5 OH + 2CO 2 Glucose and Fructose Ethanol Nowadays, a large amount of ethanol used for commercial purposes is produced by hydration of ethene, that is, by reacting ethene with water in presence of sulphuric acid. H 2 SO 4   H 2 C = CH 2 + H 2 O  H 3 C - CH 2 -OH Ethene Ethanol

PROPERTIES OF ETHANOL   Pure ethanol is a colourless liquid with a boiling point of 351 K. It is miscible with water in all proportions. (i) Combustion: Ethanol is a highly inflammable liquid, i.e., it catches fire easily. It burns with a blue flame to form carbon dioxide and water. C 2 H 5 OH + 3O  2 CO 2 + 3H 2 O   The reactions of ethanol with other reagents are due to the presence of hydroxyl (–OH) group.

(ii) Reaction with Sodium: Ethanol reacts with sodium to produce sodium ethoxide and hydrogen. 2 C 2 H 5 OH + 2Na ----  2 C 2 H 5 ONa + H 2 Ethanol Sodium Sodium ethoxide

(iii) Oxidation : a) With chromic anhydride (CrO 3 ): Chromic anhydride oxidises ethanol to ethanal. CrO 3 in CH 3 CH 2 OH  CH 3 CHO Ethanol CH 3 COOH Ethanal (b) With potassium permanganate : Alkaline KMnO 4 oxidises ethanol to ethanoic acid. Alk. KMnO 4 CH 3 CH 2 OH  CH 3 COOH Ethanoic acid

ESTERIFICATION (iv) Reaction with ethanoic acid : Ethanol reacts with ethanoic acid in presence of concentrated sulphuric acid to form ethyl ethanoate and water.  The compound formed by the reaction of an alcohol with a carboxylic acid is known as ester, and the reaction as esterification.  Esters are sweet smelling compounds used for making perfumes.

H 2 SO 4 C 2 H 5 OH+ CH 3 COOH-----  CH 3 COOC 2 H 5 +H 2 O   On treating with an alkali solution, sodium hydroxide, the ester is converted back to the constituent alcohol and sodium salt of the acid. CH 3 COOC 2 H 5 +NaOH-----  H 3 COONa+C 2 H 5 OH   This reaction is hydrolysis of an ester. It takes place in presence of alkali, and is known as saponification.

USES OF ALCOHOL   Ethanol is one of the most important organic chemical.   In industries, ethanol is used as a solvent for lacquers, varnishes, perfumes, medicines, etc.   It is used for sterilising wounds, as it is a good antiseptic.   Ethanol is an important industrial chemical. Therefore, it is subjected to very small excise duty.

DENATURED ALCOHOL   To prevent its misuse for drinking purposes, the alcohol supplied for industrial purpose is rendered unfit by mixing it with some poisonous substances, such as methanol, pyridine, copper sulphate, etc.   It is known as denatured alcohol.   Ethanol containing 5 per cent water is known as rectified spirit.

HARMFUL EFFECTS OF ALCOHOL  Alcohol is an intoxicant, so under the influence of alcohol, a person loses his sense of discrimination. He can’t distinguish between good and bad, right or wrong.  The consumption of alcohol in large quantities may even cause death by damaging the liver.  If methanol is consumed in small quantities, it causes serious poisoning resulting in the loss of eyesight.

ALDEHYDES AND KETONES   Aldehydes and ketones are carbon compounds containing carbonyl ( C=O) group.   In aldehydes, carbon of carbonyl group is attached to a carbon atom and a hydrogen atom in addition to oxygen.   In ketones, carbon of carbonyl group is attached to two carbon atoms.   However, formaldehyde is an exception. It is an aldehyde in which the carbon atom of –CHO group is attached to a hydrogen atom instead of another carbon atom.