4.3 alcohols and phenols Flashcards
what is a primary alcohol?
an alcohol that has one carbon atom directly bonded to the carbon of the -OH group
what is a secondary alcohol?
an alcohol that has two carbon atoms directly bonded to the carbon atom of the -OH group
what is a tertiary alcohol?
an alcohol that has three carbon atoms directly bonded to the carbon atom of the -OH group
what are the two common methods of forming primary and secondary alcohols?
- from halogenoalkanes by nucleophilic substitution
- from carbonyls by reduction
what type of reaction is the one forming an alcohol from a halogenoalkane?
nucleophilic substitution
what are the conditions for forming an alcohol from a halogenoalkane?
- NaOH (aqueous)
- heat
- reflux
what type of reaction is one forming an alcohol from a carbonyl?
reduction
what does reducing an aldehyde produce?
primary alcohol
what does reducing a ketone produce?
secondary alcohol
what is the usual reducing agent for the formation of alcohols from carbonyls?
- sodium tetrahybridoborate (III), NaBH4, dissolved in water
- but is acceptable to represent it as [H] in equations and balance in the usual way
- but is not powerful enough to reduce carboxylic acids so lithium tetrahydriodoaluminate (III), LiAlH4, dissolved in ethoxyethane/dry ether solvent can be used instead
what are the three reactions of alcohols?
- reaction with hydrogen halodes
- reaction with carboxylic acids
- reaction with ethanoyl chloride
what is the reaction of alcohols with hydrogen halides?
- reacting primary or secondary alcohols with hydrogen halides produce halogenoalkanes
- the most appropriate method depends on which halogen is to be substituted
why can NaBH4 dissolved in water be used in the formation of alcohols from carbonyls?
- it is the reducing agent which provides the H- ion for the reaction
what type of reaction is the one between alcohols and hydrogen halides?
nucleophilic substitution
what is a disadvantage of the reaction between alcohols and hydrogen halides?
- its generally slow and reversible
- and often gives poor yields
what happens in chlorination? (the reaction between alcohol and the hydrogen halide of chlorine)
- pass hydrogen chloride gas into the alcohol
- in the presence of anhydrous zinc chloride (acts as a catalyst)
- or chloroalkanes can also be produced from alcohols using phosphorus (V) chloride, PCl5
- alcohol + PCl5 —> chloroalkane + POCl3 + HCl
- (but phosphorus (V) oxide trichloride, POCl3, is a liquid and needs to be removed. if the halogenoalkane has a similar boiling point to it then separation becomes difficult)
what are the conditions for the reaction of alcohols with hydrogen halides: hydrogen chloride?
- hydrogen chloride gas, HCl
- anhydrous (dry) zinc chloride catalyst, ZnCl2
- heat
what happens in bromination? (the reaction between alcohol and the hydrogen halide of bromide)
- an ‘in situ’ reaction
- alcohol, potassium bromide, KBr, and (50%) concentrated sulfuric (VI) acid is heated
- this produces the hydrogen bromide in-situ
- this then reacts with the alcohol to produce a bromoalkane
- CH3CH2OH + KBr + H2SO4 —> CH3CH2Br + KHSO4 + H2O
what happens in iodination? (the reaction between alcohol and the hydrogen halide of iodine)
- warm damp red phosphorus and iodine together
- to form phosphorus (III) iodide, PI3
- which then reacts with the alcohol present
- 2P + 3I2 —> 2PI3
- 3CH3CH2OH + PI3 —> 3CH3CH2I + H3PO3
what does an alcohol react with a carboxylic acid to produce?
- an ester
- and water
what type of reaction is the reaction between an alcohol and carboxylic acid?
esterification / addition-elimination
what are the conditions required for the reaction between an alcohols and carboxylic acid?
- concentrated sulfuric acid, H2SO4
- heat
what happens in the reaction between alcohols and carboxylic acids?
- are refluxed together with concentrated sulfuric acid, which acts as a catalyst
- alcohol + carboxylic acids—> ester + water
- the reaction is reversible
- to increase the yield of the ester, some sulfuric acid is added and the mixture is heated under reflux
- the products can then be distilled and the ester collected
what is happening in the reaction between alcohols and ethanoyl chloride?
- the (primary or secondary) alcohol reacts with ethanoyl chloride, CH3COCl, to form an ester and hydrogen chloride
- this method gives a better yield of an ester than using a carboxylic acid, as the reaction is not reversible
- however, the cost of acid chlorides means that this is not a cost-effective process in industry
what type of reaction is the reaction between alcohol and ethanoyl chloride?
nucleophilic addition-elimination
what is a phenol?
- an aromatic compound with an -OH group directly bonded to a benzene ring
if other groups are bonded to the benzene ring, the compound is names according to the position of the substituted group
- e.g 2-cholophenol
the presence of the benzene ring tends to (weaken/strengthen) the OH bond
weaken
- this means that phenols are weakly acidic in aqueous solutions as protons are lost
what is phenol’s acidity due to?
- the lone pair of electrons on the oxygen overlapping with the π electron system of the ring
- this causes the hydrogen ion to be lost more easily, forming the phenoxide ion
why is the phenoxide ion more stable than expected?
- as the negative charge tends to be spread ‘around’ the ring
does phenol react with sodium hydroxide?
does it react with sodium carbonate?
- phenol is acidic enough to react with sodium hydroxide (NaOH)
- but it doesnt react with sodium carbonate (Na2CO3)
does carboxylic acid react with sodium hydroxide?
does it react with sodium carbonate?
- yes
- yes
what is a test to distinguish between phenols and carboxylic acids?
- using sodium carbonate
- phenols dont react with sodium carbonate but carboxylic acids do
what is the order of acidity between phenols, alcohols and carboxylic acids?
carboxylic acids > phenols > alcohols
what type of reaction do phenols react by? why?
electrophilic substitution
- due to the delocalised electron system
are phenols more reactive than benzene?
why?
yes
- the increased reactivity of phenol is because of the loan pair of electrons on the oxygen atom
- this electron pair is delocalised into the ring structure
- this increases the electron density of the ring, making it more susceptible to attack from electrophiles
do phenols react with bromine?
yes
(generally carried out in aqueous solution)
what do phenols react with bromine to produce?
- 2,4,6-tribromophenol
- as an immediate white ppt
- the orange bromine water is decolourised
- this reaction can be used as a test for phenol
what are the two reaction of phenols we need to know?
- reaction of phenols with bromine water
- reaction of phenols with ethanoyl chloride
what type of reaction is the one between phenols and ethanoyl chloride?
nucleophilic addition-elimination
what do phenols react with ethanoyl chlorides to form?
aromatic esters
- such as phenyl ethanoate
(and hydrogen chloride HCl)
which reaction is slower: the reaction between phenols and ethanoyl chloride or the reaction between alcohols and ethanoyl chloride?
phenols and ethanoyl chloride
why is the reaction between phenols and ethanoyl chloride slower than the reaction between alcohols and ethanoyl chloride?
- the delocalisation of an electron pair from the oxygen atom in a phenol means that it is more difficult for a phenol to react as a nucleophile
what are 2 tests that can be used to identify a phenol group?
- reaction with bromine water
- reaction with iron (III) chloride solution
what is a positive result for a phenol in the reaction with bromine water?
- white ppt produced
- the orange bromine water is decolourised
what is a positive result for a phenol in the reaction with iron (III) chloride?
- a vivid purple colour
(with the addition of yellow iron(III) chloride solution)
what type of reaction can a halogenoalkane undergo to form an alcohol?
nucleophilic substitution
what acts as the nucleophile in the reaction between chloroethane and warm aqueous sodium hydroxide?
- the hydroxide ion from sodium hydroxide
- OH-
name the type of reaction for the formation of alcohols from aldehydes and ketones
reduction
give the reducing agent for the reduction of aldehydes and ketones to alcohols
NaBH4 dissolved in water
what reagent is required to reduce carboxylic acids to alcohols?
LiAlH4
why is NaBH4 used for the reduction of aldehydes and ketones but not for carboxylic acids?
NaBH4 is not reactive enough to reduce carboxylic acids
why are primary and secondary alcohols useful for organic synthesis reactions?
- the OH- functional group is able to react with various different compounds
what type of organic product is produced in the reaction between alcohols and hydrogen halides?
halogenoalkanes
what catalyst is required for the reaction of primary and secondary alcohols with hydrogen chloride?
anhydrous zinc chloride
what are the reagents required for the reaction of ethanol to form bromoethane?
- instead of directly adding hydrogen bromide, ethanol requires a mixture of potassium or sodium bromide and concentrated sulfuric acid
- this will produce the hydrogen bromide which will react with ethanol to form bromoethane
name the mechanism for the reaction between acyl chlorides and alcohols
nucleophilic addition-elimination
what catalyst is required for an esterification reaction?
- the alcohol and c/a must be heated in the presence of a strong acid catalyst
- e.g concentrated sulfuric acid
name the ester formed in the reaction between butanouc acid and propanol
propyl butanoate
what are the identifying properties of esters?
- sweet smelling
- so often used in flavourings and perfumes
- have low boiling points
- and make good solvents for other polar molecules
what is the acidity of phenol?
- very weakly acidic
- pH between 5 and 6
what is the name of the product formed when phenol reacts with ethanoyl chloride?
phenyl ethanoate
