carboxyllic acids Flashcards
what’s a property of carboxylic acids with very low molecular mass
why?
they are very soluble in water
because the -COOH forms hydrogen bonding with water
do carboxyllic acids slightly or strongly dissociate in water
so are they strong or weak
slightly
weak
what is formed when carboxyllic acids slightly disassociate
carboxylate ion and hydrogen ion
how do carboxylic acids dissociate
the carbonyl group attracts electrons away from the -OH bond, which leads to the -OH bond being weakened therefore it breaks more easily to form a carboxylate ion and hydrogen ion
why are alcohols not acidic even if they have OH bond
bc the bond in alcohols doesn’t break easily
how does the addition of a halogen onto carboxylic acids changes its acidity
it makes it more acidic
why does the addition of a halogen onto carboxylic acids increase its acidity
the halogen atom is more electronegative and so withdraws electron density away from the carbonyl carbon.
this causes the OH bond to become more polar which results in the OH bond weakening .
the H in the OH bond is lost more easily lost so chloroethanoic acid is more acidic than ethanoic acid
how do we test for carboxyllic acids
reacting with sodium carbonate Na2CO3
effervescence is observed from CO2
eg what is formed when sodium ethanoic acid reacts sodium carbonate
co2 + water + sodium ethanoate
what’s formed when carboxylic acids react with alcohol in the presence of concentrated sulphuric acid
what’s the reaction called
ester and water
esterifcation
what are 3 uses of esters
flavourings , perfume , plasticisers
how do we name esters
alcohol bit then carboxylic acids bit
eg
methyl ethanoate
(methanol+ethanoic acid)
how many ways to make esters
3
are carboxyllic acids and esters isomers of one another
yes, functional group isomers
same molecular formula different structural formula
what are 2 ways the hydrolyse esters
acid hydrolysis
basic hydrolysis
how are esters hydrolysed using acid hydrolysis
this is a reversible reaction.
esters can be hydrolysed using water and dilute H2SO4/HCl to form the alcohol and carboxylic acid
how do we make hydrolysis complete as possible in acid hydrolysis of ester because it’s a reversible reaction
excess of water
as acid hydrolysis of ester is a reversible reaction, this gives a low yield of carboxylic acid and alcohols , therefore there an alternative 2 step method
what is the method
basic hydrolysis
what happens in the first step of basic hydrolysis of ester
when an ester is heated with alcohol , it is hydrolysed into an alcohol and carboxylate salt
what happens in the 2nd step of basic hydrolysis of ester
we add an excess of dilute HCl or dilute H2SO4 to the carboxylate salt to reform the carboxylic acid
how do we make soaps from fats
triglycerides can be hydrolysed using HOT NaOH or KOH to form glycerol (a useful solvent) and sodium or potassium carboxylate salts (these are used to manufacture soaps)
whys glycerol a good solvent
it has 3 OH bonds therefore forms hydrogen bonds easily in water
definition of biodiesel
liquid fuel consisting of a mixture of methyl esters of long chain carboxylic acids from vegetable oils
how do we make biodiesel
the oil is reacted with methanol with a strong acid / alkali catalyst to form a mixture of methyl esters which can be used a fuel in diesel vehicles
the products are mixtures of methyl esters and glycerol
carboxylic acids can be turned into other functional groups to be used in organic synthesis.
so what 2 groups can be formed from carboxylic acids
acyl chlorides
acid anhydrides
how are acyl chlorides formed
the -OH group on the carboxylic acid is replaced with a chlorine atom
how are acyl chlorides named
CH3COCl is derived from ethanoic acid
and therefore it is called ethanoyl chloride
the carboxylic acid derivative (acyl chloride) possesses a good leaving group (Cl) which also…
withdraws electrons from the carbonyl carbon making the carbon more reactive
what’s a good leaving group
a stable species which is removed during a chemical reaction
what reaction do acyl chlorides and acid anhydrous react with nucleophiles
nucleophillic addition elimination
and reduction reaction
what do the reactions of acyl chlorides and acid anhydrous involve
it involves the replacement of the leaving group eg Cl- by the nucleophile
what’s formed when acyl chlorides react with water
carboxylic acids
what’s formed when acyl chlorides react with alcohol
esters
what’s formed when acyl chlorides react with ammonia
amides
what’s formed when acyl chlorides react with amines
substituted amides
why are acyl chlorides more preferred in the formation of esters than carboxyllic acids
1) no need for acid catalyst (H2SO4)
2) purer product
3) more yield as reaction isn’t reversible
why’s the other carboxylic acid derivative acid anhydrides preferred over acyl chlorides in the formation of esters
1) no corrosive HCl formed
2) acid anhydrides less vulnerable to hydrolysis
what’s the -OH group replaced with in carboxylic acids to make acid anhydrides
-OCOR
how are acid anhydrides formed
acid anhydrides are formed when 2 molecules of carboxylic acids join together with the elimination of water
how do we name acid anhydrides
The acid anhydride is named after the carboxylic acid that was used in its synthesis.
then we just add anhydride to the end
eg : ethanoic anhydride
or ethanoic propanoic anhydride
do acid anhydrides have a good leaving group and why
what happens when the good leaving group leaves
yes acid anhydrides good leaving group is - âž–OCOR
because a leaving group is a stable species that is removed during a chemical reaction
when the good leaving group leaves it activates the adjacent carbonyl group by electron withdrawal
acid anhydrides react with the same nucleophiles as acyl chlorides to form the same products which are…
water to form carboxylic acids
alcohols to form esters
ammonia to form amides
amines to form substituted amides
acyl chlorides and acid anhydrides react in the same way as their corresponding
carboxylic acid but ….
will produce a different side product
eg acid anhydrides and alcohol = ester and carboxylic acids
eg acyl chloride and alcohol= ester and HCl
eg carboxylic acid and alcohol = ester and H2O
what do acid anhydrides react with to form carboxyllic acids
water
(nucleophillic addition elimination mechanism too)
what are the 3 ways to make carboxylic acids
1) primary alcohols / aldehydes oxidised by acidified potassium dichromate to form carboxylic acids and water
2) acyl chlorides and water to form carboxyllic acids and HCl
3) acid anhydrides and water to form 2 molecules of carboxylic acids
how do acid anhydrides react with to form esters
with alcohol
what are 3 ways to make esters
1) carboxylic acid and alcohol (esterifcation)
2) acyl chloride and alcohol
3) acid anhydrides and alcohol
