Alcohols Flashcards
Low volatility of alcohols
Don’t turn into gases easily, as they have hydrogen bonds. These are between the OH groups, and and require a lot of energy to break, meaning they have high boiling points and low volatility
Solubility of alcohols
As hydrogen bonds can form between the polar OH groups of the alcohols and the water molecules, short chained alcohols are soluble. Solubility decreases as chain length increases, as the hydrocarbon chain is non-polar. The first 3 alcohols are all soluble in water.
Making alcohols by hydration of ethene
H(2)C=CH(2)(g) + H2O(g) CH(3)CH(2)OH(l) . Reversible reaction. High temperature, moderate pressure, H(3)PO(4) catalyst, with steam.
Making alcohols by fermentation
C(6)H(12)O(6) -> 2CH(3)CH(2)OH + 2CO(2) . Uses yeast, at 37degC. Can only make ethanol of 14% concentration or enzyme will denature. In an oxygen free environment, so ethanol isn’t oxidised (becoming ethanal or ethanoic acid).
Uses of ethanol
- in alcoholic drinks (via fermentation). For spirits, has to be distilled by fractional distillation
- as a fuel to increase octane rating
- as a solvent
- main component in methylated spirits (used for a solvent for removing paint, ink stains from clothing and a fuel for camping stoves)
Uses of methanol
- petrol additive to improve combustion
- important as a feedstock in the production of organic chemicals - can easily be converted into methanal/methanoic acid
- ingredient in methylated spirits, making them toxic
Primary, secondary and tertiary alcohols
- Primary: OH group attached to a carbon with 1/no alkyl groups attached, e.g. methanol/butan-1-ol
- Secondary: OH group attached to a carbon with 2 alkyl groups attached, e.g. propan-2-ol
- Tertiary: OH group attached to a carbon with 3 alkyl groups attached, e.g. 2-methylbutan-2-ol
Combustion of alcohols
In oxygen, combust completely to form carbon dioxide and water. Careful when balancing equations, the alcohol already has 1 oxygen!! Because of this, generally burn more cleanly than other hydrocarbons
Oxidising agent in oxidation of alcohols
- oxidising agent is a solution with acidified dichromate ions: H+/Cr(2)O(7)2-
- can be made from potassium dichromate, K(2)Cr(2)O(7) and sulfuric acid, H(2)SO(4)
- If oxidation occurs, mixture changes from orange solution to a green solution
Oxidation of primary alcohols
-On gentle heating (and distilling immediately) with acidified potassium dichromate, oxidised to produce an aldehyde. In an equation, use [O] for oxidising agent.
-General equation:
primary alcohol + [O] -> aldehyde + H2O
-On stronger heating under reflux and excess oxidising agent, alcohol will be completely oxidised, going from alcohol to aldehyde to carboxylic acid.
-General equation:
alcohol + 2[O] -> carboxylic acid + H2O
Reflux
Continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry
Oxidation of secondary alcohols
Produces ketones - can’t be oxidised further. Occurs under heating. General equation:
secondary alcohol + [O] -> ketone + H2O
Oxidation of tertiary alcohols
Resistant to oxidation. Agent remains orange.
Esterification of alcohols
-In presence of acid catalyst and heat under reflux, e.g. concentrated sulfuric acid or phosphoric acid
-Alcohol reacts with a carboxylic acid to form an ester and water
-OH from carboxylic acid and H from OH on alcohol is lost to form water
-Get an ester bond: carboxylic acid-C=O
l
O-C-alcohol
-Written as COO, with C being from carboxylic acid, and rest of carboxylic acid before it, and alcohol after it
-called (alcohol)yl (carboxylic acid)oate
Dehydration of an alcohol
-eliminating water
-OH group is lost, as well as a H from an adjacent carbon
-Can get 2 products, if a secondary alcohol
-concentrated H(3)PO(4) or H(2)SO(4) catalyst
-heat under reflux for 40 mins
-General equation:
alcohol -> alkene + H2O
