Properties Of Ethanol
Check us out at http://www.tutorvista.com//videos Ethanol is classified as a primary alcohol, meaning that the carbon to which its hydroxyl group is attached has at least two hydrogen atoms attached to it as well. Many of the reactions of ethanol occur at its hydroxyl group. In the presence of acid catalysts, ethanol reacts with carboxylic acids to produce ethyl esters and water: RCOOH + HOCH2CH3 → RCOOCH2CH3 + H2O This reaction, which is conducted on large scale industrially, requires the removal of the water from the reaction mixture as it is formed. Esters react in the presence of an acid or base to give back the alcohol and carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap. Ethanol can also form esters with inorganic acids. Diethyl sulfate and triethyl phosphate are prepared by treating ethanol with sulfur trioxide and phosphorus pentoxide respectively. Diethyl sulfate is a useful ethylating agent in organic synthesis. Ethyl nitrite, prepared from the reaction of ethanol with sodium nitrite and sulfuric acid, was formerly a widely used diuretic. Strong acid desiccants cause the dehydration of ethanol dehydration to form diethyl ether, although under certain conditions ethylene is the product. Millions of kilograms of diethyl ether are produced annually using sulfuric acid catalyst: 2 CH3CH2OH → CH3CH2OCH2CH3 + H2O (on 120'C) Complete combustion of ethanol forms carbon dioxide and water: C2H5OH + 3 O2 → 2 CO2 + 3 H2O(l);(ΔHc = ?1371 kJ/mol) specific heat = 2.44 kJ/(kg•K) Ethanol is a neutral molecule and the pH of a solution of ethanol in water is nearly 7.00. Ethanol can be quantitatively converted to its conjugate base, the ethoxide ion (CH3CH2O?), by reaction with an alkali metal such as sodium: 2 CH3CH2OH + 2 Na → 2 CH3CH2ONa + H2 or a very strong base such as sodium hydride: CH3CH2OH + NaH → CH3CH2ONa + H2 The acidity of water and ethanol are nearly the same, as indicated by their pKa of 15.7 and 16 respectively. Thus, sodium ethoxide and sodium hydroxide exist in an equilbrium that is closely balanced: CH3CH2OH + NaOH CH3CH2ONa + H2O Ethanol is not used industrially as a precursor to ethyl halides, but the reactions are illustrative. Ethanol reacts with hydrogen halides to produce ethyl halides such as ethyl chloride and ethyl bromide: CH3CH2OH + HCl → CH3CH2Cl + H2O These reactions require a catalyst such as zinc chloride. HBr requires refluxing with a sulfuric acid catalyst. Ethyl halides can, in principle, also be produced by treating ethanol with more specialized halogenating agents, such as thionyl chloride or phosphorus tribromide. CH3CH2OH + SOCl2 → CH3CH2Cl + SO2 + HCl Upon treament with halogens in the presence of base, ethanol gives the corresponding haloform (CHX3, where X = Cl, Br, I). This conversion is called the haloform reaction." An intermediate in the reaction with chlorine is the aldehyde called chloral: 4 Cl2 + CH3CH2OH → CCl3CHO + 5 HCl Ethanol can be oxidized to acetaldehyde and further oxidized to acetic acid, depending on the reagents and conditions. This oxidation is of no importance industrially, but in the human body, these oxidation reactions are catalyzed by the enzyme liver alcohol dehydrogenase. The oxidation product of ethanol, acetic acid, is a nutrient for humans, being a precursor to acetyl CoA, where the acetyl group can be spent as energy or used for biosynthesis.