6C- acids, esters and polyesters

what is the name of salt of carboxylic acids

carboxylates e.g. methanoate, propanoate -COO^-

when comparing boiling points of carboxylic acids with other molecules what needs to be considered

similar number of electrons so strength of London Forces are similar e.g. propanoic acid compared to pentane

why is the boiling point of propanoic acid much higher than pentane

propanoic acid has hydrogen bonds whereas pentane only has London forces

are carboxylic acids soluble in water

yes- shorter chains only

why are longer carboxylic acids almost insoluble

all carboxylic acids contain -COOH which is the soluble part (can form hydrogen bonds with water) whereas the alkyl group is insoluble, in smaller carboxylic acids the alkyl group is relatively small so the molecule is soluble, in octanoic acid the alkyl group is much larger so more of the molecule is insoluble so overall the molecule is insoluble

what forms when carboxylic acids react with metals

a salt and hydrogen

e.g. methanoic acid + sodium → sodium methanoate + hydrogen

what forms when carboxylic acids react with alkalis

salt and water

e.g. benzoic acid + potassium hydroxide → potassium benzoate + water

what forms when carboxylic acids react with carbonates

salt, water and carbon dioxide

e.g. propanoic acid + calcium carbonate → calcium propanoate + water + carbon dioxide

what is the test for carboxylic acids

add a carbonate, effervescence occurs

define salt

the product of a reaction in which H⁺ ions from an acid are replaced by metal or ammonium ions

what are the reagents and conditions necessary to form an ester the standard way

heat an alcohol and carboxylic acid under reflux with conc. H₂SO₄

why is the percentage yield of an esterification reaction likely to be low

the reaction is reversible so will not go to completion

what is a carboxylic acid derivative and what are the examples

compounds that can be hydrolysed to form carboxylic acids e.g. acyl chlorides, acid anhydrides, ester, amides

what is the structure of an acyl chloride

R-COCl

how to name acyl chlorides

carbonyl chloride e.g. propanoyl chloride, 2-methylbutanoyl chloride

how to form acyl chlorides

carboxylic acid + SOCl₂ → acyl chloride + SO₂ + HCl

what conditions are needed for acyl chlorides to react with aromatic compounds

halogen carrier catalyst e.g. AlCl₃- must be anhydrous

what happens if acyl chlorides come into contact with water

react violently- must be kept dry, would produce a carboxylic acid and HCl

how reactive are acyl chlorides

very reactive, usually react by substituting the Cl for other groups

what happens if an acyl chloride is reacted with an alcohol or phenol

an ester is formed and HCl

why is forming an ester from an acyl chloride very useful

it is a non-reversible reaction so percentage yield should be higher than alternative methods

what is an acid anhydride

two carboxylic acids joined

how can acid anhydrides be made

reacting two carboxylic acids together

what are the ways esters can be made

carboxylic acid and alcohol (reversible)

acyl chloride and alcohol (higher yield as not reversible)

acid anhydride and alcohol (higher yield as not reversible)

how can an ester be made from an acid anhydride

acid anhydride + alcohol → ester + carboxylic acid

why might using an acid anhydride to synthesise an ester be preferred to using a carboxylic acid

• the reaction is not reversible so higher yield of ester

• heating is not necessary so energy costs are reduced

• reaction does not requires a catalyst so may be less hazardous

are acyl chlorides or acid anhydrides more reactive

acyl chlorides

what can an acyl chloride react to form

a carboxylic acid, an ester, a primary or secondary amide

how does an acyl chloride form a primary amide

react with NH₃

how does an acyl chloride form a secondary amide

react with R-NH₂

what needs to be considered when forming primary amides

further reactions occurring

what is an amide

a nitrogen atom adjacent to a carbonyl group

define hydrolysis

a reaction with water that breaks a chemical compound into two compounds, the H and OH in a water molecule become incorporated into the two compounds

how does the conc. H₂SO₄ affect rate of reaction/position of equilibrium in forming an ester from a carboxylic acid and alcohol (reversible reaction)

conc. H₂SO₄ has a low water conc. so the equilibrium shifts to the right to increase water conc. and so increases yield of ester

also acts as a catalyst to increase rate of reaction by providing an alternative pathways with lower activation energy

what are the methods of ester hydrolysis

• acid hydrolysis- dilute HCl/H₂SO_{4 (aq)}, heat under reflux (reversible)

• alkaline hydrolysis- dilute NaOH/KOH _(aq), heat under reflux (not reversible)

what is the equation for acid hydrolysis of an ester

ester + H₂O ←→ carboxylic acid + alcohol

why is the dilute acid not in the equation of acid hydrolysis of an ester given is it necessary for the reaction to occur

the acid is a catalyst not reagent

what happens when an ester reacts with a dilute acid

acid hydrolysis- ester reacts with the water, acid is the catalyst

why is it impossible to achieve a 100% yield from acid hydrolysis of esters

reversible reactions do not go to completion so there will always be some starting material left

what is the equation of alkaline hydrolysis

ester + NaOH → carboxylate salt + alcohol (not reversible)

what is the more efficient way to break down an ester

alkaline hydrolysis (not reversible so higher percentage yield)

how can a carboxylic acid be recovered from the carboxylate salt from alkaline hydrolysis

carboxylic acids are weak acids, add strong acid solution e.g. HCl, this will cause carboxylate ion to be protonated to form the carboxylic acid

R-COO^- + H⁺ ←→ R-COOH

HCl will increase [H⁺] so position of equilibrium will shift to right

what is the type of polymer produced from an alkene monomer

addition polymerisation

what are the types of polymerisation

addition and condensation

what is condensation polymerisation

joining of many monomers by the elimination of a small molecule such as HCl or H₂O

from what can polyesters be made

• from two monomers (more common): dicarboxylic acid + diol, diacyl chloride + diol

• from one monomer: hydroxy carboxylic acid, hydroxy acyl chloride

what type of polymerisation is used for polyesters

condensation as two small molecules react together to form a larger molecule with elimination of a small molecule e.g. H₂O

what are dimers

two hydroxy carboxylic acids react to form a ring

what is it called when two hydroxy carboxylic acids react to form a ring

a dimer

equation for formation of polyesters from dicarboxylic acid and diol

equation for formation of polyesters from hydroxy carboxylic acid

what is formed in polyester acid hydrolysis

diol and dicarboxylic acid or hydroxy carboxylic acid

what is formed in polyester alkaline hydrolysis

dicarboxylate salt and diol or hydroxy carboxylate salt

what are the conditions for acid hydrolysis of polyesters

dilute HCl_(aq), heat under reflux

what are the conditions for alkaline hydrolysis of polyesters

NaOH_(aq), heat under reflux

how do you synthesis an organic solid

heat under reflux

how do you synthesis an organic liquid

heat under reflux

how do you isolate an organic solid

filtration under reduced pressure- buchner apparatus/funnel

how do you isolate an organic liquid

using a separating funnel

how do you purify an organic solid

recrystallisation

how do you purify an organic liquid

use separating funnel, add anhydrous magnesium sulfate

how do you check purity of an organic solid

measure melting point, compare to data book

how do you check purity of an organic liquid

distillation- measure boiling point