Carboxylic acids & derivates Flashcards
carboxylic acids, esters and acylation
What is an acyl group?
Carbonyl group (C=O) with an alkyl group attached - derived from a carboxylic acid
What is acylation?
- introduction of acyl group to another molecule
Why aren’t carboxylic acids used as acylating agents?
COOH contain acyl group but OH bonded to acyl group is a very poor leaving group so COOHs not used as acylating agents
- instead 2 carboxylic acid derivatives used
Acylation reaction is used where?
- pharamaceutical (aspirin)
- textile industries (cellulose acetate or rayon)
Why are acid anhydries preffered to Acyl chlorides?
- cheaper to manufacture
- less reactive acylating reactions safer and easier to control
- acyl chlorides produce HCl as product of acylation (this is corrosive), but acid anhydrides produce water
- doesn’t react with water as readily
how to name carboxylic acids
- the ending is -oic acid
- no numbering needed as it’s always at end of the chain COOH
If there are carboxylic acid groups on both ends of the
chain, how do you name it?
it is called a - dioic acid
- Ethanedioic acid
(Note the e in this name)
describe the acidity of carboxylic acids
- weak acids in water and only slightly dissociate, but
they are strong enough to displace carbon dioxide from carbonates
describe the solubility in water of carbonates
- the smaller carboxylic acids (up to C4) dissolve in water in all proportions but after this the solubility
rapidly reduces - they dissolve because they can hydrogen bond to
the water molecules
what do carboxylic acids partially dissociate into?
- a carboxylate ion and H+ ion
carboxylic acids react with carbonates (contain CO3 2- )to form what?
- salt, carbon dioxide and water
carbon dioxide fizzes out of solution
what happens in esterification?
- carboxylic acids react with alcohols, in the
presence of a strong acid catalyst, to form
esters and water
equation to show how esters are formed from alcohols
Carboxylic Acid + Alcohol (H+) Ester + water
backwards reaction is a hydrolysis reaction, forwards is condensation or esterficiation
functional group of esters
- COO -
naming esters
- first part of esters name = alcohol (after the C=O)
- second part of esters name = carboxylic acid (before C=O)
e.g. propanol and ethanoic acid
propyl ethanoate
uses of esters
- Esters are sweet smelling compounds that can be used in perfumes and flavourings - Esters can be used as solvents for polar organic substances Ethyl ethanoate is used as a solvent in glues and printing inks - Esters can be used as plasticisers for polymers
importance of plasticisers
- pure polymers have limited flexibility because the polymer chains can’t move over each other
- incorporating some plasticiser into the polymer allows chains to move more easily and polymer can become more flexible
why do carboxlyic acids have higher boiling points than esters ?
Although polar, they do not form H bonds (reason: no hydrogen bonded to a highly electronegative atom)
- so they have much lower b.p. than the hydrogen-bonded carboxylic acids they came from.
- also almost insoluble in water
why do carboxylic acids have higher boiling points than esters?
Although polar, they do not form H bonds (reason: no hydrogen bonded to a highly electronegative atom)
- so they have much lower b.p. than the hydrogen-bonded carboxylic acids they came from.
- also almost insoluble in water
conditions of esters if they’re to be used as perfumes?
- non-toxic, soluble in solvent like ethanol, volatile (turns into gas easily), and not react with water
can carboxylic acids be oxidized?
- cannot be oxidized by oxidizing agents
- but methanoic acid can be (because its structure is effectively an aldehyde group)
describe the oxidation of methanoic acid
- can be oxidized because its structure is effectively an aldehyde group
- forms carbonic acid (H2CO3) which can decompose to give CO2
hydrolysis of esters
- esters can be hydrolyzed and split up by either heating with acid or with sodium hydroxide
- reaction is the reverse reaction of esterification, when an ester is hydrolyzed a carboxylic acid and an alcohol are formed
product and conditions of acid hydrolysis of esters
- (carboxylic) acid and alcohol
- reflux with dilute acid (hydrochloric or sulfuric)
(equilibrium reaction)
product and conditions of base hydrolysis of esters
- carboxylate ion and (COO-) and an alcohol
- reflux with dilute alkali (i.e. NaOH)
why is the base hydrolysis of esters, not a reversible reaction?
- carboxylic acid salt product is anion of the carboxylic acid
- anion is resistant to attack by weak nucleophiles like alcohols, so reaction not reversible.
fatty acids are long chains of what?
carboxylic acids
- they combine with glycerol to make esters
fat and oils relation to esters?
- fats and oils are ESTERS of glycerol and
long-chain carboxylic acids (fatty acids)
vegetable oils and animal fats can be hydrolyzed to give what?
- soap, glycerol and long-chain carboxylic (fatty) acids
fatty acids can be what?
- saturated (no double bonds) OR
- unsaturated (C=C)
IUPAC name of glycerol
propane-1,2,3-triol
properties of animal fats
- mainly saturated hydrocarbons chains
- fit neatly together, increasing van der waals forces between them so need higher temps to melt them
- so solid at room temp
properties of vegetable oils
- unsaturated hydrocarbon chains
- double bonds mean chains are bent and don’t pack together well, decreasing van der Waals forces
- so easier to melt and liquid at room temp
what is soap and how is it made?
- salt of a long-chain carboxylic acid
- hydrolyzes vegetable oils/animal fats by heating them with sodium hydroxide (NaOH)
what is biodiesel?
- mixture of methyl esters of fatty acids
the equation for formation of methyl esters?
triester + methanol —-> (KOH) glycerol + methyl ester
catalyst for methyl ester (biodiesel) formation?
KOH
potassium hydroxide
acyl chloride functional group
- COCl
naming acyl chlorides
- no numbering because carbon numbering starts at end with -COCl
- suffix is: -oyl chloride
acyl chlorides react with water to form?
vigorous reaction with cold water
- carboxylic acid + HCl
acyl chlorides react with alcohols to form?
vigorous reaction at room temp
- ester and HCl
reaction is irreversible
(easier, faster way to produce an ester than esterification)
acyl chlorides react with ammonia to form?
violent reaction at room temp
- amide and ammonium chloride
amide (-CONH2)
why isn’t HCl really formed in the reaction of an acyl chloride and ammonia?
because any hydrogen chloride formed would immediately react with excess ammonia to give ammonium chloride.
NH3 + HCl —> NH4Cl
what is given off in reactions of acyl chloride with:
- water
- alcohols
- ammonia (not in excess)
- primary amines
misty fumes of hydrogen chloride
products of the reaction of acyl chloride and ammonia (not in excess)
amine and HCl
products of reaction of acyl chloride with primary amines
- N-substituted amide and HCl (misty fumes)
how are acid anhydrides formed and named?
2 identical carboxylic acid molecules
- take away ‘acid’ and replace with ‘anhydride’
e. g. 2 ethanoic acids would be ethanoic anhydride
state products of reactions of water, alcohol, ammonia and primary amines with acid anhydrides
(same as acyl chlorides but -COOH instead of HCl)
water: carboxylic acid + carboxylic acid
alcohol: ester + carboxylic acid
ammonia (not in excess) : amide + carboxylic acid
primary amines: N-substituted amide and COOH
describe products formed in the reaction between acid anhydride and excess ammonia
- amide (-CONH2) and carboxylic acid (COOH)
- COOH produced reacts with excess ammonia to give a salt (e.g. ammonium ethanoate formed if acid produced was ethanoic acid)
write and draw out ammonium ethanoate
CH3COO-NH4+
name of mechanism in acyl chloride reactions with water, alcohol, ammonia and primary amines
nucleophilic addition-elimination
describe the nucleophilic addition-elimination mechanism of an acyl chloride (ethanoyl chloride) and methanol (alcohol)
ADDITION:
- methanol is nucleophile
- attacks partially positive carbon (because C=O is polar), and pair of electrons from C=O bond transferred to oxygen (so double bond breaks)
ELIMINATION:
- pair of electrons on oxygen reform double bond and Cl leaves
- Cl bonds with hydrogen in hydroxyl group
- Oxygen in hydroxyl group has positive charge and stabilized by Hydrogen (arrow from bond between oxygen and hydrogen to positive oxygen)
- HCl eliminated
what is aspirin and how is it made?
aspirin is an ester
- reacting salicylic acid with ethanoic anhydride (or ethanoyl acid)
why is separation necessary in purifying an organic compound?
- product is insoluble, separation allows you to remove any impurities that do dissolve in water
describe how to separate product
once product formed:
- pour mixture into separating funnel and add water
- shake funnel and allow to settle, organic layer and aqueous layer(contains water-soluble impurities) are immiscible so separate out into 2 distinct layers
- open tap and run each layer off into separate container
describe how water can be removed from a purified product
(if separation used to purify product, there’ll still be traces of water - needs to be dried)
- add anhydrous salt (CaCl2 or MgSO4). salt is a drying agent - binds to any water present to become hydrated
- keep adding drying agent until it disperses evenly when you swirl the flask
- filter out mixture to remove solid drying agent
(filter paper in funnel that feeds into flask and pour)
how can impurities be further removed if product still contaminated by leftover reagents or unwanted side products?
- washing the product (adding another liquid and shaking)
- e.g. aqueous sodium hydrogencarbonate added to an impure product in solution to remove acid
- acid reacts with sodium hydrogencarbonate to give CO2 gas and product removed using separating funnel
how can volatile liquids be separated?
- distillation
- connect condenser to round bottomed flask containing impure product in solution
- place thermometer in neck of the flask so bulb sits next to entrance of condenser, temp on thermometer will show boiling point of substance evaporating at any given time
- heat impure product (electric heater because organic chemicals are flammable)
- when product boils (thermometer showing ts boiling point), place flask at open end of condenser to collect pure product
purpose of anti-bumping granules
prevent the formation of larger bubble
how can organic solids be purified?
recrystallisation
describe how to purify an organic solid (recrystallisation)?
- dissolve solid in hot solvent to make saturated solution (max possible ammount of solid dissolved in solvent), let it cool
- as solution cools, solubility of product falls
- when it reaches the point where it can’t stay in solution, it forms pure crystals
describe briefely how to purify an organic solid (recrystallisation)?
- dissolve solid in hot solvent to make saturated solution (max possible ammount of solid dissolved in solvent), let it cool
- as solution cools, solubility of product falls and crystals begin to form
- when it reaches the point where it can’t stay in solution, it forms pure crystals
describe how melting and boiling points are good indicators of purity?
- pure subtances have specific M.P and B.P
- if impure, M.P. lowered and B.P raised
- if very impure, melting and boiling will occur across wide range of temps
describe experimentally how melting point apparatus can determine melting point of an organic solid
- pack small sample of solid in glass capillary tube and place inside heating element
- increase temp until sample turns from solid to liquid
- measure melting range, which is range of temps from where solid begins to melt and where its melted completely
(use MP of substance from data book to compare)
-
what will impurities in sample do to melting range?
- lower MP
- broaden Melting range
what is the carbonyl functional group?
C=O
describe how aldehydes and ketones differ, in terms of position of carbonyl group and naming
- aldehydes have carbonyl group at end of c chain
names end in -al - ketones have carbonyl group in middle of C chain, names end in -one
(numbering required to show which carbon the carbonyl group is on)
aldehydes and ketones can be oxidised into what?
- aldehydes to carboxylic acids (e.g. propanal to propanoic acid)
- ketones can’t be oxidised
