Alcohols and Phenols Flashcards
What is a primary alcohol?
The carbon bonded to the -OH group is directly bonded to one other carbon atom.
What is a secondary alcohol?
The carbon bonded to the -OH group is directly bonded to two other carbon atoms.
What is a tertiary alcohol?
The carbon bonded to the -OH group is directly bonded to three other carbons.
What are the reagents and conditions of forming an alcohol from a halogenoalkane?
Reflux the alcohol and halogenoalkane together with aqueous NaOH.
Describe the mechanism of the formation of an alcohol from a halogenoalkane
Nucleophillic substitution where the -OH acts as a nucleophillic and attacks the relativity positive carbon of the C-X bond.
What is a nucleophile?
An ion or compound with a lone pair of electrons that can seek out a positive site.
What is the rate of hydrolysis of halogenoalkanes?
C-I > C-Br > C-Cl
How are aldehydes and ketones reduced to alcohols?
Using an aqueous solution NaBH4.
How are carboxylic acids reduced to alcohols?
Using LiAlH4 dissolved in ethoxyethane.
Which reducing agent is safer to use?
NaBH4, as excess LiAlH4 is difficult to dispose of and ethoxyethane is very flammable. LiAlH4 is the more powerful reducing agent and is used to reduce carboxylic acids.
Describe the chlorination of alcohols
Pass HCl into the alcohol in the presence of an anhydrous zinc chloride catalyst
Or
React the alcohol with PCl5
Or
React the alcohol with SOCl2
What is the preferred method used for chlorination?
SOCl2 as both the co-products SO2 and HCl are gaseous and are easily lost from the reaction mixture, ensuring easier separation.
Describe bromination of alcohols
React the alcohol with KBr and 50% H2SO4 and heat ‘in-situ’.
Describe iodination of alcohols
Warm damp red phosphorus and iodine together to form PI3 which then reacts with the alcohol present.
Describe the reaction between alcohols and ethanoyl chloride
Produces an ester and misty fumes of HCl.
What is the advantage in using an acid chloride in esterification?
This gives a better yield of an ester than using a carboxylic acid, as the reaction is not reversible.
What is the disadvantage of using an acid chloride in esterification?
The cost of acid chlorides means that this is not a cost efficient process in industry.
What is the equation for esterification?
Alcohol + carboxylic acid —> ester + H2O
How can you increase the yield in esterification?
Add a little concentrated H2SO4 to the mixture and heat it under reflux. The product can then be distilled and the ester collected at its boiling temperature.
How can you collect the ester after esterification has occurred?
Use a separating funnel and shake with sodium hydrogencarbonate solution to remove any remaining carboxylic acid. The ester is then dried with anhydrous calcium chloride, which reacts with any remaining alcohol. The ester is then redistilled to give a pure product.
What are the uses of esters?
They are widely used in the cosmetics industry as components of perfumes. They are also used as solvents, such as in nail varnish.
What are phenols?
Aromatic compounds where -OH groups are directly bonded to a benzene ring.
Describe the reactivity of phenols
The lone pairs on the oxygen atom can overlap with the delocalised π system, so the C-O bond is shorter and stronger than an alcohol, but bond fission is harder. The higher electron density makes the structure more susceptible to attack by electrophiles.
Describe the acidity of phenols
They are much more acidic then alcohols but are weaker than carboxylic acids.
How does phenol react with aqueous NaOH?
It does not readily dissolve in aqueous NaOH, giving a solution of sodium phenoxide.
Describe the solubility of phenol
It is not very soluble in water as the -OH group is a small part of a largely hydrophobic molecule.
What is a test to distinguish an aliphatic acid and phenol?
Adding sodium carbonate solution. An aliphatic acid will react to give bubbles of CO2 but phenol will not.
What affects the acidity of phenols?
The presence of different substituents on the benzene ring.
Which are the more activated positions for substituents on phenol?
2, 4 and 6. As a result an incoming substituent is likely to replace a H atom at one or more of these positions.
How does phenol react with dilute nitric acid?
Both 2- and 4- nitrophenol are formed in the ratio 70% to 30%.
How does phenol react with bromine water?
A white precipitate of 2,4,6-tribromophenol is produced along with HBr. A colour change from orange to colourless is seen.
What is the mechanism for the bromination of phenol?
Electrophillic substitution, where the electrophile is Brδ+.
How can alcohol and phenols react as nucleophiles?
Because of their oxygen lone pairs. However the delocalisation of an electron pair from the oxygen atom in a phenol means it is more difficult to react as a nucleophile.
How are phenols used in esterification?
They can’t react with carboxylic acids and their reaction ethanoyl chloride is too slow at room temperature, so a base such as pyridine is used to speed up this reaction.
What is used instead of ethanoyl chloride in the esterification of phenol?
Ethanoic anhydride, as ethanoyl chloride is too expensive.
How does phenol react with acyl chloride in esterification?
Aqueous conditions can be used as the acyl chloride is only slowly hydrolysed by water. In this reaction phenol is added to aqueous NaOH and the mixture is shaken.
What is the test for phenol?
Phenol will react with iron (III) chloride to produce a purple colour in the aqueous solution.
