Chapter 14 Structure and Synthesis of Alcohols

Classification Primary: carbon with –OH is bonded to one other carbon. Secondary: carbon with –OH is bonded to two other carbons. Tertiary: carbon with –OH is bonded to three other carbons. Aromatic (phenol): -OH is bonded to a benzene ring.

Classify these: =>

IUPAC Nomenclature Find the longest carbon chain containing the carbon with the -OH group. Drop the -e from the alkane name, add -ol. Number the chain, starting from the end closest to the -OH group. Number and name all substituents

Name these: 2-methyl-1-propanol 2-butanol 2-methyl-2-propanol 3-bromo-3-methylcyclohexanol =>

Physical Properties Unusually high boiling points due to hydrogen bonding between molecules. Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases.

Boiling Points FUNCTIONAL GROUP RANKING BY BOILING POINTS Name B.P  Brief Explanation Amide 222o  1  ethanamide hydrogen bonds on both the oxygen and the nitrogen  Acid 118o  2  ethanoic acid or acetic acid hydrogen bonding from the of 2 oxygen atoms.  Alcohol 117o  3   propanol hydrogen bonding from the presence one oxygen

Solubility in Water Solubility decreases as the size of the alkyl group increases. =>

Reactions of Alcohols 1) Combustion: R-OH  CO2 2) Dehydration: R-OH  C=C 3) Oxidation: a) R-OH (Primary)  R-C-HO  R-COOH b) R-OH (secondary)  R1R2-C=O c) Tertiary alcohols NO GO 4) Addition (Markovnikov) 5) Esterification with Carboxylic Acids

Combustion Complete C3H7OH(g) + 4.5O2  3CO2 + 4H2O _________________________________ Incomplete Combustion C3H7OH(g) + 3O2  3 CO + 4 H2O

ALCOHOL OXIDATION 10 gentle heating, a primary alcohol can be oxidised to produce an aldehyde. BUT With strong heating and excess [O] (acidified) a carboxylic acid is formed. To heat strongly we need a Reflux apparatus is generally used to produce carboxylic acids. Note: Aldehydes must be distilled as they are formed to prevent further oxidation to carboxylic acids..

Not hard, nothing special This reaction goes easily and quickly, Nothing special is needed, other than the oxidizing agent is required, a hot water bath will do. The problem is when the aldehyde is made it boils off immediately. To form the –COOH we need to trap the aldehyde and force it back with reflux, or a condenser. Chapter 14

OXIDIZING REAGENTS OXIDIZING AGENTS OXIDAIZING AGENT OBSERVATIONS REACTION ACIDIFIED DICROMATE ORANGE TO GREEN Cr2O72-(aq)  to Cr3+(aq) ORANGE GREEN OXIDIZING AGENTS Chapter 14

OXIDATION OF PRIMARY ALCOHOLS Controlling the products e.g. CH3CH2OH(l) + [O] ——> CH3CHO(l) + H2O(l) then CH3CHO(l) + [O] ——> CH3COOH(l) OXIDATION TO ALDEHYDES DISTILLATION OXIDATION TO CARBOXYLIC ACIDS REFLUX Aldehyde has a lower boiling point so distils off before being oxidised further Forces Aldehyde to condenses back into the mixture and gets oxidised to the acid

OXIDATION OF PRIMARY ALCOHOLS Primary alcohols are easily oxidised to aldehydes e.g. CH3CH2OH(l) + [O] ——> CH3CHO(l) + H2O(l) ethanol ethanal it is essential to distil off the aldehyde before it gets oxidised to the acid CH3CHO(l) + [O] ——> CH3COOH(l) ethanal ethanoic acid Practical details the alcohol is dripped into a warm solution of acidified K2Cr2O7 aldehydes have low boiling points - no hydrogen bonding - they distil off immediately if it didn’t distil off it would be oxidised to the equivalent carboxylic acid to oxidise an alcohol straight to the acid, reflux the mixture compound formula intermolecular bonding boiling point ETHANOL C2H5OH HYDROGEN BONDING 78°C ETHANAL CH3CHO DIPOLE-DIPOLE 23°C (volatile) ETHANOIC ACID CH3COOH HYDROGEN BONDING 118°C

OH all the way to COOH Alcohol 10 Aldehyde Alcohol 10 C.A. A more simplified ONE step Version 1o Alcohol Carboxylic Acid

Secondary Alcohols Secondary alcohols are oxidised to produce ketones, then stop. Gentle heating as with aldehydes

2o OH to Ketones e.g. CH3CHOHCH3(l) + [O] ——> CH3COCH3(l) + H2O(l) propan-2-ol propanone Chapter 14

ALCOHOL TO KETONE e.g CH3CHOHCH3(l) + [O] ——> CH3COCH3(l) + H2O(l) propan-2-ol propanone Chapter 14

Tertiary Alcohols These are resistant to oxidation, there will be no colour change. This is because the carbon (of the alcohol group) is not bonded to any other hydrogen atoms. Thus, NO COLOUR CHANGE WITH [O]

3o lack a hydrogen Remember , hydrogen removal is the Definition of Oxidation, as is the addition of oxygen Chapter 14

Test Results Chapter 14

Dehydration of Alcohols Alcohol  Alkene + water when heated with an acid catalyst:such as a concentrated acid (a dehydrating agent) or pumice, or Al2O3 or H2SO4 with the loss of H and OH to form water alkene alcohol 23