Properties of Alcohol

Introduction  Alcohol is any compound in which a hydroxyl functional group (-OH) is bound to a carbon atom.  There are three classes (types) of alcohols: primary secondary and tertiary

Introduction, cont. Primary Alcohol:  In a primary (1°) alcohol, the carbon which carries the -OH group is only attached to one alkyl group. General formula: RCH2OH

Introduction, cont. Primary Alcohol: Methanol Ethanol

Introduction, cont. Secondary Alcohol:  In a secondary (2°) alcohol, the carbon with the -OH group attached is joined directly to two alkyl groups. General formula: R2CHOH

Introduction, cont. Tertiary Alcohol:  In a tertiary (3°) alcohol, the carbon atom holding the -OH group is attached directly to three alkyl groups. General formula: R3COH

Physical Properties of Alcohol  Molecular state: straight chain alcohols with up to 12 carbon atoms are liquids.  Solubility: alcohols with a small organic part as methanol or ethanol are much like water, thus miscible with water. Alcohols with a larger molecular weight are more like alkane and less like water. Alcohols with more than two -OH groups are more water soluble than similar alcohols with only one -OH group.

Physical Properties of Alcohol  In general each -OH group can solubilize four to five carbon atoms.  For example: Glycerol  Boiling point: the boiling point of an alcohol is always much higher than that of the alkane with the same number of carbon atoms. alcohols with two or more – OH groups have higher boiling point.

Physical Properties of Alcohol Methanol, Ethanol and Glycerol: Colorcolorless Odorthey have faint odor (alcoholic odor) except glycerol which is odorless. Solubilitycompletely miscible with water. Flammabilityflammable with blue, non smoky flame. Stateliquid except glycerol which is viscous liquid. Acid-base properties neutral

Chemical Properties of Alcohol Oxidation:  The oxidising agent used is a solution of potassium dichromate (K2Cr2O7) acidified with sulphuric acid (H2SO4).  If oxidation occurs, the orange solution containing the dichromate ions is reduced to a green solution containing chromium ions.

Chemical Properties of Alcohol Oxidation of Primary Alcohol:  Primary alcohol is first oxidised to an aldehyde which is then oxidised further to the carboxylic acid.

Chemical Properties of Alcohol Oxidation of Secondary Alcohol:  Secondary alcohol can be oxidised into a ketone. Oxidation of Tertiary Alcohol:  No reaction.

Chemical Properties of Alcohol Oxidation Tests:  Tests for methanol and ethanol:  In test tube mix 1 part of alcohol, 1 drop of k2Cr2O7, what is the color?  Then add 4 drops of conc. H2SO4.

Chemical Properties of Alcohol Esterification:  The reaction between alcohol and carboxylic acid to make ester.  Esters usually have pleasant, fruit like odors H2SO4

Chemical Properties of Alcohol Esterification Tests:  Test for methanol: Mix in a test tube 1 part of methanol, about 0.2 g of salicylic acid, 3 drops of conc. H2SO4 then warm for 5 min. In a beaker prepare Na2Co3 solution. Add the content of the test tube into the beaker. +H2O methyl salicylateSalicylic acidmethanol

Chemical Properties of Alcohol Esterification Tests:  Test for ethanol: Mix in a test tube 1 part of ethanol, about 1 ml of dil. acetic acid, 3 drops of conc. H2SO4 then warm for 5 min. In a beaker prepare Na2Co3 solution. Add the content of the test tube into the beaker. H2SO4

Chemical Properties of Alcohol Iodoform Reaction:  Test for methanol: Mix in a test tube about 1 part of methanol, 4 parts of dil. NaOH solution, and 1 ml of iodine solution then warm.  iodoform test forms a characteristic for alcohols like ethanol, 2-propanol.  alcohols may be oxidized to form α-methyl carbonyl compounds. -ve

 Test for ethanol: Mix in a test tube about 1 part of ethanol, 4 parts of dil. NaOH solution, and 1 ml of iodine solution then warm. Iodoform Reaction: Chemical Properties of Alcohol

Special Test for Glycerol:  Test for glycerol with a solution of borax: Mix in a test tube about 1 part of borax solution, 1 drop of phenolphthalein solution then shaking. What is the color? Add 1 part of glycerol and shaking.

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