Hydroxy Compounds Flashcards
What are hydroxy compounds?
Organic compounds that contain the hydroxyl (-OH) functional group
What are the two types of hydroxy compounds?
- Alcohols (R-OH)
- Phenols (Ar-OH)
What are monohydric alcohols?
Alcohols that contain one -OH group
What are polyhydric alcohols?
Alcohols that contain more than one -OH group
What is the general formula of acyclic monohydric alcohol?
CnH2n+1OH
With comparable Mr, are boiling points of alcohols or alkanes higher and why?
Boiling points of alcohols are higher because more energy is required to overcome the stronger hydrogen bonds between the alcohol molecules than the weak id-id interactions between alkane molecules
What happens to the boiling point of alcohol as the number of C atoms increases?
As the number of C atom increases, the number of electrons in the molecule increases, more energy is required to overcome the stronger id-id between alcohol molecules, thus boiling point increases
For alcohols with comparable Mr, do branched or straight chain alcohol have a higher boiling point?
Straight chain has a higher boiling point because the surface area of the molecules is larger compared to more spherical, branched molecule. Thus more energy is required to overcome the more extensive id-id in straight chain than branched isomer
Are alcohols soluble in water and why?
Alcohols are soluble in water due to the presence of -OH group, which enable them to form hydrogen bonds with water molecules
As the number of carbon atom increases, what happens to the solubility of alcohol molecules?
As the number of carbon atom increases, the longer non-polar hydrocarbon chain hinders the formation of hydrogen bonds between the alcohol molecules and water molecules
Are alcohols soluble in organic solvents?
Yes
What are the methods to prepare alcohol?
- Electrophilic addition of steam to alkenes (industrial preparation)
- Electrophilic addition of conc. H2SO4 to alkenes, followed by heating with water (lab preparation)
- Nucleophilic substitution of OH- by alkyl halides
- Reduction of aldehydes, ketones, carboxylic acids and esters
- Fermentation of sugars/carbohydrates
What are the reagents and conditions for electrophilic addition of steam to alkenes to prepare alcohol?
steam, high temperature and pressure, H3PO4 catalyst
What is the reagents and conditions for electrophilic addition of conc. H2SO4 to alkenes to prepare alcohol?
cold conc. H2SO4, followed by heating with water
What is the reagents and conditions for nucleophilic addition of OH- on alkyl halides to prepare alcohols?
NaOH (aq) or KOH (aq), heat under reflux
What are the reagents and conditions for the reduction of esters to prepare alcohols?
LiAlH4 in dry ether
What are the reagents and conditions for the reduction of carboxylic acids to prepare alcohols?
LiAlH4 in dry ether
What are the reagents and conditions for the reduction of aldehydes to prepare alcohols?
- LiAlH4 in dry ether
- NaBH4
- H2, Ni catalyst, heat
What are the reagents and conditions for the reduction of ketones to prepare alcohols?
- LiAlH4 in dry ether
- NaBH4
- H2, Ni catalyst, heat
What is the equation of the reduction of aldehydes to prepare alcohols?
RCOH + 2[H] → RCH2OH (primary alcohol)
What is the equation of the reduction of ketones to prepare alcohols?
RCOR’ + 2[H] → RCR’HOH (secondary alcohol)
What is the equation of the reduction of carboxylic acids to prepare alcohols?
RCOOH + 4[H] → RCH2OH + H2O (primary alcohol)
What is the equation of reduction of esters to prepare alcohols?
RCOOR’ + 4[H] → RCH2OH + R’-OH (primary alcohols)
What is the equation for the fermentation of sugar/carbohydrates?
C6H12O6 -(yeast)→ 2CH3CH2OH + 2CO2
What are the reactions of alcohols?
- Combustion
- Elimination reaction
- Nucleophilic substitution of R-OH by -X
- Acid-metal reaction
- Condensation
- Oxidation
What flame do alcohols combust in?
Clean, hot flame
What types of elimination can alcohols undergo?
- Intermolecular dehydration of alcohols to form alkenes
- Intramolecular dehydration of alcohols to form ether
What are the reagents and conditions for the intramolecular dehydration of alcohols to form alkenes?
- Al2O3, heat
- excess conc. H2SO4, heat
What are the reagents and conditions for the intermolecular dehydration of alcohols to form ether?
conc. H2SO4, excess alcohol, heat
What are the types of nucleophilic substitution of R-OH by -X alcohols can undergo?
- Using HX (dry gas or conc. acid)
- Using dry PCl5
- Using PX3
- Using SOCl2
What are the reagents and conditions for the nucleophilic substitution of R-OH by -X using HX?
- HX (g), heat
- conc. HCl, ZnCl2 catalyst, heat under reflux
What is the equation for the nucleophilic substitution of R-OH by -X using HX?
R-OH + HX → R-X + H2O
How can HCl(g) be prepared as a reagent for nucleophilic sub with alcohol?
HCl(g) can be prepared in situ using KCl (s) + conc. H2SO4
How can HBr(g) be prepared as a reagent for nucleophilic sub with alcohol?
HBr(g) can be prepared in situ using KBr (s) + conc. H2SO4
How can HI (g) be prepared as a reagent for nucleophilic sub with alcohol?
KI (s) + conc. H3PO4
What is the order of reactivity of HX (most reactive to least reactive)?
HI > HBr > HCl
The bond energy increases from HI to HCl because the size of halogen atom decreases from I to Cl, and the valence orbitals become less diffused. This results in more effective overlap of orbitals between the small H atom and the larger halogen atom and thus more energy is required to break the stronger H-X bond
What are the reagents and conditions for the nucleophilic substitution of R-OH by -X using PX3?
PX3, room temp
What is the equation for the nucleophilic substitution of R-OH by -X using PX3?
3R-OH + PX3 → 3R-X + H3PO3
How is PBr3 prepared?
In situ by heating P4 and Br2
How is PI3 prepared?
In situ by heating P4 with I2
What are the reagents and conditions for the nucleophilic substitution of R-OH by -X using PCl5?
solid anhydrous PCl, room temperature
What is the equation for the nucleophilic substitution of R-OH by -X using PCl5?
R-OH + PCl5 → R-Cl + POCl3 + HCl
What are the reagents and conditions for the nucleophilic substitution of R-OH by -X using SOCl2?
SOCl2, room temp.
How to identify -OH group in alcohol?
Use PCl5 and SOCl2
White fumes of HCl: OH group present
*note: carboxylic acid also gives white fumes with PCl5 and SOCl2
How to differentiate alcohols and phenols?
Use PCl5 and SOCl2
White fumes of HCl: alcohol
No fumes: phenol
What are the reagents and conditions for acid-metal reaction of alcohol?
Na (or other reactive metals like K and Mg)
What is the equation for acid-metal reaction of alcohols?
ROH + Na → RO⁻Na⁺ + 1/2H₂
What is the observation for acid-metal reaction of alcohols?
Colourless, odourless gas (H₂) evolved extinguishes lighted splint with a pop sound
What are the types of condensation reaction to form esters that alcohols can undergo?
- With carboxylic acids
- With acyl chloride
What is the reagent and conditions for condensation reaction between alcohols and carboxylic acids?
a few drops of conc. H2SO4, heat under reflux
What is the equation for condensation reaction between alcohols and carboxylic acids?
RCOOH + R’-OH -(reversible arrow)-> RCOOR’ + H2O
What is the equation for condensation reaction between alcohols and acyl chlorides?
RCOOH + R’-OH –> RCOOR’ + HCl
What does H2SO4 act as in the condensation reaction between alcohols and carboxylic acids?
- catalyst (to increase rate at which equilibrium is established as the reaction is slow)
- dehydrating agent (to increase the yield of ester by shifting the equilibrium to the right as the reaction is reversible)
What is the reagents and conditions for condensation reaction between alcohol and acyl chlorides?
room temperature
(usually an organic base like pyridine is added to neutralise HCl formed)
Why does pyridine act as a base?
Because of the availability of lone pair on N atom
What is the product and observation when you add acidified KMnO4 to primary alcohol, heat under reflux?
RCOOH (carboxylic acid)
Purple KMnO4 decolourises
What is the product and observation when you add alkaline KMnO4 to primary alcohol, heat under reflux?
RCOO⁻
Purple KMnO4 decolourises to give a brown ppt. MnO2
What is the product and observation when you add acidified K2Cr2O7 to primary alcohol, heat with immediate distillation?
RCOH (aldehyde)
Orange K2Cr2O7 turns green (Cr3+ formed)
What is the product when secondary alcohols undergo oxidation?
Ketones are formed
What is the product when tertiary alcohols undergo oxidation?
No product, tertiary alcohols are resistant to oxidation
How to distinguish primary and secondary alcohols from tertiary and phenols?
Undergo oxidation: primary, secondary alcohols
Resistant to oxidation: tertiary alcohols, phenols
What types of oxidation can hydroxy compounds undergo?
- with KMnO4/K2Cr2O7
- tri-iodomethane/iodoform test
What type of reaction is tri-iodomethane test?
Oxidation
What can tri-iodomethane test be used to identify?
- Alcohol with RCH(CH3)OH structure
- carbonyl compound with RCOCH3 structure
What is the reagent and conditions of the tri-iodomethane test?
Warm with I2 and NaOH
What is the observation for the positive test of tri-idomethane?
Pale yellow ppt. of CHI3 with a characteristic ‘antiseptic’ smell
What is the overall equation for tri-iodomethane test?
CH3CH(OH)R + 4I₂ + 6OH⁻ → RCOO⁻ + CHI₃ + 5I⁻ + 5H₂O
What happens when a geminal diol is formed?
It is not stable and will be converted to either aldehyde or ketone with the elimination of water
What happens when a geminal triol is formed?
It is not stable and will be converted into a carboxylic acid with the elimination of water
What is a phenol?
Contain one or more -OH groups directly bonded to benzene ring
Is the melting point of phenol higher or lower than hydrocarbons of similar Mr?
Phenol has a higher melting point because more energy is needed to overcome the stronger hydrogen bonds between phenol molecules than the weaker id-id between hydrocarbon molecules
Is phenol soluble in water?
- Phenol is slightly soluble in cold water due to hydrogen bonds formed between phenol and water molecules but solubility is low because of the large, non-polar benzene ring
- bigger molecules containing phenol tend to be insoluble
What can increase the solubility of phenol in water?
Increase temperature
Why does phenol not undergo nucleophilic substitution with HX and PCl5?
A lone pair of electrons in the p orbital of the oxygen atom is delocalised into the pi electron cloud of the benzene ring through the sideways overlap of the p orbital of oxygen and the pi electron cloud of the benzene ring, this strengthens the C-O bond, giving it a partial double bond character, making it harder to break to undergo nucleophilic substitution with HX and PCl5
Which is a weaker nucleophile, alcohols or phenols and why?
Phenol because the lone pair of electrons in the p orbital of oxygen atom is delocalised into the pi electron cloud of the benzene ring through the sideways overlap of p orbital of oxygen and pi electron cloud of the benzene ring, making the lone pair of electrons on O less available to attack a electrophilic centre and thus a weaker nucleophile
Do phenol or benzene undergo electrophilic substitution more readily?
-OH group of phenol is strongly ring activating as the lone pair of electrons in p orbital of O is delocalised into the pi electron cloud of the benzene ring through side ways overlay of p orbital of O and the electron cloud of the benzene ring, which increases the electron density in the benzene ring and hence phenol undergoes electrophilic substitution more readily
What does the strength of acid depend on?
The stability of the anion (conjugate base) formed because the more stable the anion, the position of equilibrium lies more to the right and hence the stronger the acid
What is the order of stability of hydroxide, alkoxide and phenoxide ion?
phenoxide ion > hydroxide ion > alkoxide ion
Phenoxide ion is more stable than hydroxide ion because the p orbital of the oxygen atom overlaps sideways with the pi electron cloud of the benzene ring, the negative charge on O is delocalised into the benzene ring, thereby stabilises the phenoxide ion
alkoxide ion is less stable than hydroxide ion because alkyl group is electron-donating and intensifies the negative charge on O, thereby destabilises the alkoxide ion
What is the acid strength of alcohol, water and phenol and what are the implications on the reactions they undergo?
phenol > water > alcohol
- Alcohols being very weak acids, they do not react with bases and can only react with reactive metal
- phenol is stronger acid than alcohol thus can react readily with strong bases like NaOH but weaker than carboxylic acids thus not enough acids to liberate CO2 from carbonates or hydrogencarbonates
What happens when you test alcohols with moist blue litmus paper?
It does not turn moist blue litmus paper red because they are weaker acids than water
What affects the acidity of substituted phenols?
- Electron-donating substituents: reduces the delocalisation of negative charge on O atom into the benzene ring, thereby destabilising the anion, decreasing acid strength
- Electron-withdrawing substituents increases the delocalisation of negative charge on oxygen atom into the benzene ring, stabilising the anion, acid strength increase
What reactions do phenols undergo?
- Reactive metals
- Base
- Formation of ester
- Reaction with neutral FeCl3 (aq)
- Electrophilic substitution
What is the observation when phenols react with reactive metals?
Colourless, odourless gas (H2) evolved extinguishes a lighted splint with a pop sound
What is the observation when phenols react with bases?
Phenol dissolved in aqueous NaOH to give a colourless solution
(sodium phenoxide is very soluble in water due to formation of ion-dipole interactions with water molecules)
Do phenols form esters with carboxylic acids?
Phenol does not form ester with carboxylic acids as phenol is a weaker nucleophile than alcohol
What is the reagents and conditions for phenol to react with acyl chlorides to form ester?
NaOH (aq), room temperature
Why can phenol react with acyl chlorides and not carboxylic acids?
The C bonded to O is more electron deficient than carboxylic acids due to the presence of electron-withdrawing chlorine directly attached to C
Why is NaOH(aq) needed for phenols to react with acyl chloride?
Phenol is too weak of a nucleophile and needs to be first converted to phenoxide ion which is a stronger nucleophile with a full negative charge
What is the equation for the reaction of FeCl3 (aq) /Ferric chloride?
phenol + neutral FeCl3 → violet colouration
How to test for phenols?
Test: add neutral FeCl3
If violet colouration formed, it is phenol
What is the difference for the electrophilic substitution of phenol and benzene?
- Phenol requires milder conditions
- Poly-substitution occurs
What is the reagents and conditions for the halogenation of phenol?
- Br2(aq), room temperature
- Br2 in CCl4
What are the products of phenol and Br2?
tribromophenol (white ppt.)
What are the products of phenol and Br2 in CCl4?
Br mono-substituted in 2 or 4 position
What are the reagents and conditions for nitration of phenol?
- dilute HNO3, room temp.
- conc. HNO3, room temp.
What are the products of phenol and dilute HNO3?
Mono-substituted NO2 at 2 or 4th position
What are the products of phenol and conc. HNO3?
trinitrophenol (yellow ppt.)
What happens when adding KMnO4 or K2Cr2O7 to phenol?
No reaction, phenols are resistant to oxidation
