4.3 Alcohols and Phenols Flashcards
What is the difference between primary and secondary and tertiary alcohols?
Primary alcohols have no more than 1 carbon atom directly bonded to the carbon of the C-OH group. Secondary alcohols have 2 carbons and tertiary have 3 bonded to the C-OH group.
What are the two common methods of forming primary and secondary alcohol’s?
- From halogenoalkanes by substitution reaction
- By reducing aldehydes, ketones or carboxylic acids.
How is the reaction of making an alcohol from a halogenoalkane done?
By refluxing together the halogenoalkane and an aqueous solution of either NaOH or potassium hydroxide. The products of the reaction are separated as they are both liquids with diff boiling points this fractional distillation can be used to separate.
Do the mechanism on a whiteboard NOW.
What is the written mechanism for forming an alcohol from a halogenoalkane?
It’s a NUCLEOPHILLIC SUBSTITUTION where the hydroxide ion (OH) from the NaOH acts as a nucleophile and attacks the partially positive carbon bonded to the halogen on the halogenoalkane.
How can aldehydes and ketones be reduced to primary and secondary alcohols?
By using a solution of an aqueous solution of NaBH4.
What are the differences between the reduction of an aldehyde and a ketone?
An aldehyde is reduced to a primary alcohol
A ketone is reduced to a secondary alcohol
How are carboxylic acids reduced to alcohols?
NaBH4 is not powerful enough reducing agent for carboxylic acids thus LiAlH4 is used instead. Also water is a product of this reaction.
What happens when alcohols react with hydrogen halides such as Br or Cl?
Halogenoalkanes are produced, each halogen has a different method of reacting.
How does the chlorination of alcohol work?
Use HCL GAS in the presence of anhydrous zinc chloride (ZnCl2) which acts as a catalyst.
How does the iodination of alcohols occur?
Reflux the alcohol with excess hydriodic acid (HI) leaving an I on the carbon and H20 by product.
what occurs when alcohols react with ethanoyl chloride?
An alcohol reacts rapidly with ethanoyl chloride giving an ESTER. During this reaction fumes of hydrogen chloride are seen (observation).
How are the displayed formula of esters named?
They are generally written backwards, with the ‘acid’ part first.
What is a nucleophile? and give examples.
Nucleophiles are ions or compounds possessing a lone pair of electrons that can seek out a relatively positive site (often a delta positive of a carbon atom) Common nucleophile lnclude -OH, -CN and NH3. Nucleophiles can be negatively charged or neutral molecules.
What happens when primary or secondary alcohols are reacted with carboxylic acids?
Primary or secondary alcohols react to give esters. The reason is reversible and eventually the reaction will reach equilibrium. To increase the equilibrium yield of an ester, a little concentrated SULFURIC ACID (VI) is added to the mixture of alcohol and the carboxylic acid and the mixture is heated under reflux. The products can then be distilled and the ester collected at its boiling point.
What are phenols?
Phenols are aromatic compounds where -OH groups are bonded directly to a benzene ring.
How are phenols different to alcohols and why?
Phenols react differently from that of alcohols. This is partly due to one of the lone pairs of the oxygen atom can overlap with the delocalised pie system to form a more extended delocalised system. As a result the C-O bond in phenols is shorter and stronger than in alcohols. The extended delocalisation creates higher electron density in the ring and makes the ring structure more susceptible to attack by electrophiles. Phenols are much more acidic than alcohols.
What is a test to distinguish between phenol and and a simple acid?
Add sodium carbonate solution, the simple acid is strong enough to react and give bubbles of CO2 but phenol will not.
Discuss the process of phenol reacting with bromine.
The -OH group in phenol directly bonded to the benzene allows phenol to be attacked by electrophiles. Each position on the phenol is able to be attacked but the 2,4 and 6 positions are even more open to attack. As a results a bromine is more likely to replace a hydrogen ion on one or more of these positions. Due to the heightened electron density in phenol, Br delta plus—Br delta minus is already formed and thus no catalyst is needed. The reaction is aqueous bromine and phenol produce a white precipitate of 2,4,6- tribromophenol.
Write two different tests for phenol:
-Adding aqueous bromine to a phenol solution, the phenol solution. At first the bromine goes from orange to decolourised and then further bromine is added creating a white precipitate of 2,4,6-triborophenol (the white precipitate is what separates it from a test for alkenes)
- Phenol will react with iron(III)chloride to produce a purple colour in aqueous solution.
What happens if the 2,4 or 6 positions are taken on a phenol and bromine is added?
The bromine will go to one of the remaining 2,4,6 positions available.
How does phenol react with ethanoyl chloride?
The reaction between phenol and ethanoyl chloride is like with alcohol an esterification reaction (ester is made). Phenol like alcohol can react as a nucleophile by use of the oxygen lone pairs, but the delocalisation of an electron pair on oxygen with phenol means that it is more difficult for phenol to react as a nucleophile. As a result they cannot react with carboxylic acids to make esters only ethanoyl chloride, and even this is slow so needs a base such as pyridine that does not react readily with acid chloride.
