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AQA A2 carbonyls

QuestionAnswer
Ethanoic acid with NaOH. Products? Sodium Ethanoate and water; remember to NOT show the charges on the Sodium Ethanoate
Ethanoic acid with NaOH. what are the conditions? room temperature
Carboxylic acid with Sodium carbonate.Products? Sodium Ethanoate, water and carbon dioxide
what are the observations? colourless gas produced can turn limewater cloudy (this is the test for carboxylic acids)
Ethanoic acid with Sodium Carbonate. What are the conditions? room temperature
How do you convert a carboxylate salt back to a carboxylic acid? (reagents) Dilute HCl
How do you convert a carboxylate salt back to a carboxylic acid? what are the conditions? room temperature
Esterification. what are the reagents? alcohol with carb acid with CONC. H2SO4
Esterification. what are the conditions? Heat under reflux
Products of Hydrolysis of Ethylmethanoate with dil HCl? Ethanol and Methanoic Acid
Products of Hydrolysis of Ethylmethanoate with dil NaOH? Ethanol and SodiumMethanoate
what are the conditions for the Hydrolysis of Esters? heat under reflux
What is the reagent to convert Propanal into Propanoic acid? ACIDIFIED (conc H2SO4) K2Cr2O7
What is the reagent to convert Propanal into Propanoic acid? heat under reflux
A carbonyl compound is placed with potassium dichromate and conc. H2SO4. The colour of the mixture turns from orange to green. What is your inference? The compound has been oxidised; the compound must be an aldehyde
How do you distinguish between aldehydes and ketones? (reagents, conditions and observation) Tollens reagent creates a silver mirror from a colourless solution.OR Fehlings solution, heated, turning from blue to brick red precipitate
How do you convert Propanal to Propanol? (reagents, conditions) NaBH4 with heat
What is the product when Propanal reacts with HCN? 2-Hydroxy Propane Nitrile
What type of reaction: Carbonyl with HCN? Nucleophilic Addition
What type of reaction: Aldehyde into Carboxylic Acid? Oxidation
What type of reaction: Aldehyde into Alcohol? Reduction
What is the product of the reaction between an Acyl Chloride and Ammonia? Amide and HCl
What is the product of the reaction between an Acyl Chloride and an Amine? Amide and HCl
What is the product of the reaction between an Acyl Chloride and an Alcohol? Ester and HCl
What observation during acylation? Misty fumes
CHALLENGE: evaluate the use of Acyl Chloride vs Anhydrides and Carboxylic acids to produce esters Acyl Chloride do not require heating to require (saves energy) BUT Acyl chloride produce acidic fumes that will need neutralising; Anhydrides are best (room temp but no acidic fumes)
Write the equation for the oxidation of CH3CH(OH)CH3 using [O] CH3CH(OH)CH3 + [O] --> CH3COCH3 + H2O
Write the equation for the oxidation of CH3CH2CH2OH using [O], under reflux CH3CH2CH2OH + 2 [O] --> CH3CH2COOH + H2O; the propan1ol is oxidised TWICE
Write the equation for the oxidation of CH3CH2CH2OH using [O], when distilling CH3CH2CH2OH + [O] --> CH3CH2CHO + H2O
Write the equation for the reduction of CH3CH2CHO using [H] CH3CH2CHO + 2[H] --> CH3CH2CH2OH
Write the equation for the reduction of CH3COCH3 using [H] CH3COCH3 + 2[H] --> CH3CH(OH)CH3
CHALLENGE: evaluate the use of NaBH4 as a reducing agent compared to H2/Ni NaBH4 reduces selectively ONLY carbonyls; H2/Ni reduces carbonyls; alkenes; aromatic compounds
Write the equation for the nucleophilic addition of CH3COCH3 with HCN CH3COCH3 + HCN --> CH3C(OH)(CN)CH3
Write the equation for the nucleophilic addition of CH3CH2CHO with HCN CH3CH2CHO + HCN --> CH3CH2CH(OH)(CN)
Describe the mechanism of Nucleophilic Addition of NaBH4 onto a carbonyl 1)show lone pair on H- and polarised C=O; 2) attack of lone pair onto the partially positive C (ensure arrows touch at start and end) 3) C=O bond fold onto O; 4) redraw as you see 5lone pair on O- attacks H from H2O 5) polarised H-O from water folds
Describe the mechanism of Nucleophilic Addition of HCN onto a carbonyl 1)show lone pair on C from CN- and polarised C=O; 2) attack of lone pair onto the partially positive C (ensure arrows touch at start and end) 3) C=O bond fold onto O; 4) redraw as you see 5) lone pair on O- attacks H+
Write the equation for the reaction between CH3COOCH2CH3 and HCl CH3COOCH2CH3 + HCl --> CH3COOH + CH3CH2OH
Write the equation for the reaction between CH3COOCH2CH3 and NaOH CH3COOCH2CH3 + NaOH --> CH3COONa + CH3CH2OH
Write the equation for the reaction between ethanoic anhydride CH3COOCOCH3 and CH3CH2OH CH3COOCOCH3 + CH3CH2OH --> CH3COOCH2CH3 + CH3COOH
Write the equation for the reaction between CH3COOH and CH3CH2OH (with Conc H2SO4) CH3COOH + CH3CH2OH --> CH3COOCH2CH3 + H2O
Write the equation for the reaction between CH3COCl and CH3CH2OH CH3COCl + CH3CH2OH --> CH3COOCH2CH3 + HCl
CHALLENGE: How to distinguish between primary, secondary and tertiary alcohols? add potassium dichromate (vi) acidified with dilute h2s04; if no observation: orange ––––> green then tertiary; do fehlings/tollens on the distilled products of oxidation
CHALLENGE: Explain the trend in boiling point of an alkane, carbonyl compound and an alcohol of similar RMM similar RMM so vdw imf dont influence the boiling point; carbonyls: they have polar c=o, hence they have permanent dd im forces which increases bp; Alcohols can H bond between molecules, therefore they have a higher bp than both alkanes and carbonyls.
Why are carbonyls soluble in water? They can form H bonds with water
CHALLENGE: Explain the trend insolubility with increasing chain length of a carbonyl compound As chain length increases, molecule becomes dominated by the hydrocarbon chain/ the VdW forces between the molecules become stronger than the H-bond, hence the c=o group becomes a smaller portion of the molecule, hence it becomes less soluble in water.
Explain why is the high mean bond enthalpy of c=o surprising Because high mean bond enthalpy suggests that it is unreactive, however c=o is polar hence it is reactive.
Explain why NaBH4 is a selective reducing agent NaBH4 will reduce c=o but not c=c, this is because the hydride ions provided by NaBH4 arent attracted to the region of high electron density around the c=c (like charges repel). However, the hydride ions are attracted to the delta +ve carbon on the c=o.
Why can't you use HCN as a reagent for nucleophillic addition with a cyanide ion? HCN is a toxic gas that binds irreversibly with the haemoglobin in place of oxygen and hence prevents aerobic Respiration. It is also a weak acid so only partially dissociates, hence doesn't provide enough H+
What reagent and conditions do you use instead of HCN for nucleophillic addition? reagents: KCN OR NaCN; Conditions: dilute acid (hcl) to provide H+.
1)Why is nucleophillic addition with a cyanide ion useful? 2)What is the problem for the chemist with the products? 1) It can lengthen the carbon chain 2) It can lead to the production of two optical isomers which are difficult to separate
CHALLENGE: During nucleophilic addition, two optical isomers are produced, yet the mixture is optically inactive. Explain why Equal probability of the nucleophille attacking from above or below the planar c=o. So racemic mixture forms: theres is equal amounts of both enantiomers present, each rotate the plane of polarisation of light by equal amounts in opposite directions.
What is the test for a carboxylic acid? Add sodium hydrogen carbonate: if there is a carboxylic acid present you will observe effervescence due to the production of Co2.
What is the equation for esterification and what are the reagents and conditions for this reaction? alcohol + carboxylic acid < = > ester + H2O reagents: CONCENTRATED H2SO4 or CONC HCl conditions: warm, 50–60, conc h2s04/hcl acid catalyst
CHALLENGE Explain why esterification have to have a warm temp of 50–60? (3 reasons) 1) Increased rate: more successful collisions\n2) increased yield: forward reaction is endothermic 3) Practical: Ester more likely to evaporate hence you can smell it easier.
What is the problem of producing esters by esterification and what is the alternative method? The reaction is reversible hence doesnt go to completion thus meaning there is a low yield. You can also produce an ester via acylation
What the the three uses of esters? (and why they are used for these things) 1) solvents (pd-pd imf hence since like dissolves like they dissolve other molecules) 2) plasticisers (added to plastics during polymerisation to make them more flexible/ reduce effects of im forces between chains) 3) food flavourings/perfumes
1)Why is base hydrolysis more favourable? 2)What is the one problem with it and how is it solved? 1) the reaction goes to completion hence the yield is higher than the other which is a reversible reaction 2) it produces a carboxylate ion(+alcohol) instead of a carboxylic acid. Add excess h2s04 to turn carboxylate ion into carboxylic acid product
Describe how to draw the structure of an oil or a fat The E as a coat hanger; add C=O; add three fatty acid chains = TRIGLYCERIDE
What is the (word) equation for hydrolysis of a triglyceride? triglyceride + 3NaOH –––> 3xcarboxylate salts + glycerol
What can the mixture of carboxylate salts produced during hydrolysis of fats be used as? The mix of carboxylate salts can be used as soap
Describe how the mixture of carboxylate salts works as soaps/ cleaning agents They are ionic salts : Na+ and the –salt. The hydrocarbon chain on salt has weak VdW imf which allow it to bind with grease.The COO–/ ionic/polar head binds with H2O. Therefore the whole salt allows water and grease to mix= good cleaning agent
What are the properties of glycerol and what is it used for ? It has an –OH group so can hydrogen bond with water/is very soluble in water. It is used in cosmetics/creams/ointments/makeup because it forms H-bond with water easily and prevents the cream from drying out. Also used in toothpaste.
Describe how biodiesel is manufactured Extracted from natural ester (rape seed oil from plant): triglyceride + 3CH3OH –––> glycerol + biodiesel THIS IS NOT HYDROLYSIS OR ESTERIFICATION
What is the type of mechanism taking place during acylation? Nucleophillic addition–elimination
What is the condition for any acylation reaction. Explain why anhydrous otherwise the acyl chloride reacts with water to form the carboxylic acid and HCl
Why are acid anhydrides better to use than acyl chlorides for acylation? (5 reasons) 1) anhydrides are cheaper to produce 2) anhydrides products are less corrosive 3) anhydrides reacts less readily with water 4) safer bi–product = acyl chlorides produce HCl which is a toxic gas 5) acyl chlorides reacts vigorously with water
CHALLENGE: What is the one reason acyl chloride is better to use than acid anhydride for acylation? Its products are easier to separate because HCl is a gas, where as acid anhydrides always product carboxylic acids which are more difficult to separate
Created by: UrsulineChem