Ciencias de la tierra II Alcohols (Session 35) Ciencias de la tierra II

Ciencias de la tierra II Alcohols Alcohols are organic compounds that have an hydroxyl group, -OH united to a carbon atom of a aliphatic chain. Alcohols are classified as primary, secondary and tertiary depending on if the OH group is bonded a primary, secondary or tertiary carbon. CH3 CH3 - CH2 – OH CH3 - CH – CH3 CH3 - C - CH3 OH OH Alcohol Alcohol Alcohol Primary secondary tertiary Ciencias de la tierra II

Ciencias de la tierra II Nomenclature IUPAC system. Alcohols are named changing the ending ene of alkene to ol. The hydrocarbon base is the one having the hydroxyl group, also has the longest carbon chain. The presence of other hydroxyl groups is indicated changing the ending of ol fo for diol, triol, etc., in the base name of the hydrocarbon. The position of each hydroxyl is indicated by the number put in front of the modified name of the hydrocarbon base. If the alcohols has other substitutes these are indicated putting in front their name and position of the substitute to the name of the alcohol base. Cl - CH2 - CH2 - CH - CH2 - CH2 - CH3 OH 1-cloro-3- hexol Ciencias de la tierra II

Common nomenclature of alcohols The small alcohols are normally called trivial names. These names are formed putting the work alcohol in front of the radical name with the lic ending. For example: CH3 - OH CH3 - CH2 - OH Methyllic Alcohol Ethyllic Alcohol Ciencias de la tierra II

Ciencias de la tierra II Physical properties Since alcohols have a hydrogen atom bonded to an oxygen atom, it is a very electronegative atom, They present a polar bond and furthermore the formation of hydrogen bridges within the alcohol molecules. R R δ- δ- O O δ+ δ+ δ+ δ+ H H H H δ- δ- O O R R Hydrogen bridges within Alcohols Ciencias de la tierra II

Ciencias de la tierra II Alcohols have boiling points relatively high comparing them with other compounds with similar molecular weight with exception to the carboxylic acids. (due to the ability of the molecules to form hydrogen bridges) Alcohols of low molecular weight are very soluble in water. The solubility decreases when the carbon chain increases. Alcohols are liquids at room temperature. Methanol is very poisonous two teaspoons of methanol can cause blindness and to spoonfuls can cause death. Ciencias de la tierra II

Ciencias de la tierra II Chemical properties Oxidation of Alcohols Primary alcohols can be oxidized to aldehydes and afterwards become carboxyl acids: ∆ R - CH2 - OH + K2 Cr2 O7 R - CH = O aldehydes ∆ R - CH = O + K2 Cr2 O7 R - COOH Carboxylic acid ∆ R - CH2 - OH + K Mn O4 R - COOH Carboxylic acid Ciencias de la tierra II

Ciencias de la tierra II Secondary alcohols can be oxidized to ketones: R- CH - R + K2 Cr2 O7 σ Cr O2 R - C - R OH O ketone R R - C - OH + K Mn O4 There is no reaction R Tertiary alcohols are resistant to oxidation. Ciencias de la tierra II

Ciencias de la tierra II Formation of Esters O O R – CH2 – OH + C – R’ H+ R – CH2 – O – C – R’ + H2 OH Alcohol carboxylic acid ester Formation of alkyl halides R – CH2 – OH + HX R – CH2 – X + H2O Alkyl halides HX = HI , H Br y H Cl Ciencias de la tierra II

Importance and applications of alcohols Antifreeze (methanol y ethylene) Elaboration of alcoholic beverages Medicine (disinfectants, syrups, etc.) Industry solvents. Raw material for the production of acetic acid. Fabrication of essences and perfumes Ciencias de la tierra II

Importance and applications of alcohols Glycerol (1,2,3 propanotriol) is used in the industries of bread, tobacco, as humectants for lotions, shaving soaps, toothpaste, Wrapping material, for example cellophane, it acts as a plasticizer, nitroglycerin is fabricated a basic component for dynamite and many other products. Ciencias de la tierra II

Ciencias de la tierra II Bibliography Bloomfield, M. (1997) Chemistry in Living Organisms. 1st ed. Mexico: LIMUSA Rakoff, H. et al. (1992) Fundamental Organic Chemistry. 1st ed. Mexico: LIMUSA Solomons, G. (1996) Fundaments of Organic Chemistry. 2nd. ed. Mexico: LIMUSA Ciencias de la tierra II