carboxylic acids and derivatives

Question 1

carboxylic acids and esters

what are carboxylic acids?

Answer 1

carboxylic acids and esters are two types of carbonyl compounds
carboxylic acids contain the carboxyl functional group
-COOH

Question 2

how do you name carboxylic acids?

Answer 2

to name them you
1. find the longest alkane chain
2. take off the e and add oic acid
3. the carboxyl group is always at the end of the molecule.
when naming its more important than other functional groups.
so all the other functional groups in the molecule are numbered starting from this carbon.

Question 3

HO-C-C-C-C-OH
This is an example
the double bond oxygen goes on the end carbon
there is also a methyl(CH3) group on the second carbon counting from the carbon with the double bond oxygen as the first one.

Answer 3

The longest continuous carbon chain containing the carboxylic acid functional group is 4 carbon atoms.
so the stem is butane.
numbering of the carbon atoms starts at the COOH group so theres a COOH group on carbon-1, a methyl group on carbon-2 and a hydroxy(OH) group on carbon-4.
the name of this molecule is:
4-hydroxy-2-methylbutanoic acid.

Question 4

DISSOCIATION of carboxylic acids

Answer 4

carboxylic acids are weak acids in water, they partially dissociate into a carboxylate ion and an H+ ion.
R-C-OH
the carbon also has a double bond Oxygen.
R-C-O- + H+
There is a missing double bond oxygen
the oxygen on here becomes a negative ion and dissociates from the hydrogen it was bonded to which now becomes a H+
This reaction is reversible but the equilibrium lies to the left because most of the molecules don’t dissociate.

Question 5

what does a carboxyl group contain?

Answer 5

a carbonyl group and a hydroxyl group on the same carbon atom.

Question 6

REACTION with carbonates

Answer 6

carboxylic acids react with carbonates(co32-)
or hydrogen carbonates (HCO3-)
to form a salt,carbon dioxide and water

Question 7

equations and examples of the reactions

Answer 7

2CH3COOH(AQ)+NA2CO3(S)=
ethanoic acid+sodium carbonate
2CH3COONa(Aq)+H2O(L)+CO2(G)
sodium ethanoate
second equation
HCOOH(Aq)+NAHCO3(S)=HCOONa(Aq)+H20(l)+CO2(g)
methanoic acid+sodium hydrogen carbonate=sodium methanoate

Question 8

ESTERIFICATION reactions

Answer 8

if you heat a carboxylic acids with an alcohol in the presence of a strong acid catalyst, you get an ester.
its called an esterification reaction.
carboxylic acid +alcohol(heat under reflux)=ester +water
there is a H+ ion catalyst which comes from the strong acid.

Question 9

what is the strong acid that is used in esterification?

Answer 9

concentrated sulfuric acid is usually used as the acid

catalyst but other strong acids like HCL and phosphoric acid can also be used.

Question 10

what happens when you make esters in the lab?

Answer 10

making esters in the lab by reacting an alcohol and a carboxylic acid under reflux , wont result in a pure product.
you will need to purify your ester using a separating funnel and distillation.

Question 11

what other reactions can esterification reactions be?

Answer 11

they are also condensation reactions because they release a small molecule ( water) when the carboxylic acid and alcohol join.

Question 12

Naming esters

Answer 12

you know that an ester is formed by reacting a carboxylic acid and an alcohol
The name of the ester is made up of two parts
the first bit comes from the alcohol, and the second bit from the carboxylic acid.

Question 13

what steps do you follow to name an ester?

Answer 13

1. look at the alkyl group that came from the alcohol
   this is the first bit of the esters name.
2. now look at the part that came from the carboxylic acid
   swap its oic acid ending for oate to get the second bit of the name.
3. put the two parts together.

Question 14

what if the carbon chains are branched?

Answer 14

the same rules apply if they are branched or if the molecule has a benzene ring attached.
always number the carbons starting from the carbon atoms in the c-o-c bond.
the example is drawn out in book.

Question 15

rules of naming esters

Answer 15

the rules about naming esters only apply if the alcohol is a primary alcohol.
If its a secondary alcohol the first part of the name will be different.
E.g: the alcohol that reacts with methanoic acid to form
1-methylpropyl methanoate is called butan-2-ol not
1-methylpropan-1-ol

Question 16

REACTIONS AND USES OF ESTERS

USEFUL properties of esters

Answer 16

1. esters have a sweet smell-it varies from gluey sweet for smaller esters to a fruity ‘pear drop’ smell for the larger ones.
   this makes them useful in perfumes. The food industry also uses esters to flavour things like drinks and sweets
2. esters are polar liquids so lots of polar organic compounds will dissolve in them.
   They also have quite low boiling points ,so they
   evaporate easily from mixtures. This makes them good solvents in glues and printing inks
3. Esters are used as plasticisers- they are added to plastics during polymerisation to make the plastic more flexible.
   but what happens overtime is that the plasticiser molecules escape and the plastic becomes brittle and stiff.

Question 17

HYDROLYSIS of esters

what is hydrolysis?

Answer 17

Hydrolysis is when a molecule is split up by water- but if you use just water it will be really slow so an acid or alkali is used to speed it up.

Question 18

what are the types of hydrolysis of esters?

Answer 18

There are two types of hydrolysis of esters
they are
1. acid hydrolysis
2. base hydrolysis
with both types you will get an alcohol, but the second product in each case is different.

Question 19

acid hydrolysis

Answer 19

acid hydrolysis splits the ester into an acid and an alcohol
it is the reverse of the esterification reaction that was
carboxylic acid + alcohol= ester + water
But Now….
it is
ester + water = carboxylic acid + alcohol
you have to reflux the acid with a dilute acid, such as hydrochloric or sulfuric acid.
The ester will then split back into the carboxylic acid and alcohol it was originally made from.
EXAMPLE:
methyl ethanoate+water=ethanoic acid+ methanol

Question 20

These acid hydrolysis reactions are reversible so what do you need to do?

Answer 20

you need to use lots of water to push the equilibrium over to the right so you get lots of product.

Question 21

Base hydrolysis

Answer 21

for a base hydrolysis reaction
you have to reflux the ester with a dilute alkali, such as
sodium hydroxide.
OH- ions from the base react with the ester and you get a carboxylate ion and alcohol.
ester+ OH- = carboxylate ion + alcohol
EXAMPLE:
base hydrolysis of methyl ethanoate produces ethanoate ions and methanol.
methyl ethanoate + OH- = ethanoate ion + methanol

Question 22

FATS and oils

Answer 22

animal fats and vegetable oils are esters of glycerol and fatty acids
fatty acids are long chain carboxylic acids
they combine with glycerol
( propane-1,2,3-triol) to make fats and oils.
the fatty acids can either be saturated( no double bonds) or unsaturated ( with c=c double bonds)
most of a fat or oil is made from fatty acid chains so its these that give them many of their properties.

EXAMPLE drawn out showing the structure of a fat/oil

Question 23

Fats

Answer 23

fats mainly have saturated hydrocarbon chains and they fit neatly together.
This increases the vander waal forces between them.
This means higher temperatures are needed to melt them and they are solid at room temperature.
vanderwaal forces are strong.

Question 24

oils

Answer 24

oils have unsaturated hydrocarbon chains- the double bonds mean the chains are bent and don’t pack together well, decreasing the effects of the vanderwaals forces
so they are easier to melt and are liquids at room temperature.