Chapter 10.2 & Chapter 20.1 Organic Reactions ALCOHOLS

Alcohols Ex: Ethanol (alcohol in alcoholic beverages) 3 types of general RXNs Combustion (much like alkanes/alkenes) Form CO2 and H2O (if complete) C and CO (if incomplete) More carbons = higher energy output Oxidation reactions e- are removed and e- density of a molecule is reduced Often involves removal of H atoms from organic molecule Esterification reactions A type of Condensation RXN where water is produced

Alcohols- Oxidation Combustion is considered complete oxidation of alcohols These reactions are actually partial oxidation of alcohols Primary alcohols  aldehyde  carboxylic acid Secondary alcohols  ketone Tertiary alcohols  No reaction 3 types of alcohols

1º alcohols (ex. Ethanol) can be oxidized twice. First oxidation yields aldehyde R—CH=O Second oxidation yields carboxylic acid R—COOH Requires: Oxidizing agent Acidified sol’n of potassium dichromate (K2Cr2O7) or +[O] K2Cr2O7 is orange in color After oxidizes something (been reduced itself) turns green

1º Alcohols- Oxidation In the 1st oxidation: distillation In the 2nd oxidation: reflux Oxidation is the reason why wine (alcohol) turns to vinegar (carboxylic acid) over time exposed to air

1º Alcohols- Oxidation nifty fact Basis for a type of simple breathalyzer test (detect ethanol in the breath) The subject breathes into a device containing orange colored crystals of acidified potassium dichromate If ethanol is present in the breath, it will be oxidized by the acidified potassium dichromate, turning the crystals to a green color This color change is detected by a photocell, and the level of change is proportional to the amount of alcohol in the breath

1º Alcohols- Oxidation Distillation Oxidation of 1º alcohols can occur in two steps So, possible to isolate 2 cmpds in right conditions If want aldehyde: Distillation Used to allow the aldehyde to be removed before the reaction goes further

1º Alcohols- Oxidation Distillation Mixture of the 1º alcohol (ex. ethanol) and the oxidizing agent (acidified potassium dichromate) is heated in a flask As the aldehyde (ethanal) is formed, the heat causes it to boil Aldehyde vapors travel to condenser The cooler temp converts back to a liquid and they are removed

1º Alcohols- Oxidation Reflux If want carboxylic acid: Aldehyde must be oxidized further before it is removed from the reaction chamber This is accomplished by using reflux Aldehyde vapor is not allowed to escape from the condenser Instead, it drips back into the flask where it contacts the heated oxidizing agent and is converted into the carboxylic acid

2º Alcohols- Oxidation Secondary alcohols (ex. propan-2-ol) Only undergo one oxidation Acidified potassium dichromate is a suitable oxidizing agent in this reaction as well

3º Alcohols- Oxidation Tertiary alcohols are not easily oxidized because this would require breaking the carbon skeleton of the molecule (too much E required)

Alcohols- Oxidation For primary alcohols  aldehyde (distillation)  carboxylic acid (reflux) For secondary alcohols  ketone For tertiary alcohols  no reaction All RXNs require at least Acidified potassium dichromate and heat

Alcohols- Esterification Condensation RXN RXN where 2 molecules combine to form a larger one This results in a loss of a small molecule Esterification: a type of condensation RXN Carboxylic acid + alcohol ester + water

Alcohols- Esterification Requires: concentrated H2SO4 The alcohol will lose an -H and the carboxylic acid will lose an -OH to form water R-C=O from carboxylic acid and O-R from alcohol will bond to form the R-COO-R’

Alcohols- Esterification Boiling point of ester < alcohol or carboxylic acid Alcohols and carboxylic acids H-bond Therefore, ester can be separated from RXN via distillation Also, tend to be insoluble so come out of solution (layer on top of reaction mixture)