carboxylic acids and esters Flashcards
what is the name of the carboxylic acid functional group?
carboxyl group (COOH)
in their reactions, carboxylic acids can form…
metal salts (carboxylates)
solubility: short chain carboxylic acids are…
very soluble in water
- this is because the polar C=O and -OH can form H-bonds with water.
solubilty: as chain length increases…
solubility decreases (due to longer non-polar hydrocarbon chain)
why do carboxylic acids have a higher b.p compared to alcohols with the same Mr?
due to the formation of DIMERS via hydrogen bonding between two molecules (doubles the size of the molecule)
reactions: Carboxylic acids react with bases, alkalis and reactive metals to form…
salts
what are the observations during a reaction of carb. acids with carbonates?
effervescence and the solid carbonate will be used up, producing a colourless solution
what is the general reaction between a carb. acid and a carbonate?
acid + carbonate → salt + water + carbon dioxide
e.g., * ethanoic acid with sodium carbonate:
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2
e.g., * ethanoic acid with sodium hydrogen carbonate:
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
what are the observations for a reaction between carb. acids and metals?
effervescence and the solid metal will be used up producing a colourless solution
what is the general reaction between a carb. acid and a metal?
Acid + metal → salt + hydrogen
e.g., ethanoic acid with magnesium:
2CH3COOH + Mg → (CH3COO)2Mg + H2
what are the observations for the reaction between a carb. acid and a base?
release of heat and colourless solution remains
what is the general reaction between a carb. acid and a base?
Acid + base → salt + water
e.g., ethanoic acid with sodium hydroxide:
CH3COOH + NaOH → CH3COONa + H2O
what are the observations between a carb. acid and ammonia?
a release of heat + the colourless solution remains
what is the general reaction between a carb. acid and ammonia?
acid + ammonia → ammonium salt
e.g., ethanoic acid with ammonia:
CH3COOH + NH3 → CH3COONH4
(ammonium ethanoate formed)
what is the functional group for esters?
ester group/ester linkage (COO)
what is the general structure of esters?
R-C(=O)-O-CR’
R is from the acid
R’ is from the alcohol
reacting: carb. acids and alcohols react in the presence of…
heat and a strong acid catalyst (ESTERIFICATION)
what is the general reaction for carb. acids and alcohols?
carb. acid + alcohol –> ester + water
esterification is an example of…
a (reversible) condensation reaction
what are some common uses of esters?
- plasticisers
- solvents for paints, glue, printing inks and nail polish remover
- perfumes
- food flavourings
what is the reverse of esterification
hydrolysis
- there are two types: acidic hydrolysis and alkaline hydrolysis
what are the conditions for acid hydrolysis?
Catalyst: dilute hydrochloric acid
Conditions: heat under reflux
Products: carboxylic acid + alcohol
* This is a reversible reaction, giving lower yields
what are the condition for alkaline hydrolysis?
Catalyst: aqueous sodium hydroxide
Conditions: heat under reflux
Products: carboxylate salt + alcohol
*This is an irreversible reaction, giving higher yields - the alkali
catalyst reacts with the carboxylic acid to form a salt.
vegetable oils and animal fats are esters of…
propan-1,2,3-triol (aka glycerol) and three long chain carboxylic acids called fatty acids
fatty acids can be…
saturated (no double bond) or saturated (double bond present)
what state are fats at room temperature?
Fats are triglycerides that are solid at room temp. - This is because fats are mainly made of saturated fatty acids, which are straight (they can therefore fit neatly together) - This increases the van der Waals’ forces between them, leading to higher m.p
what state are oils at room temperature?
Oils are triglycerides that are liquid at room temp. - This is because they mainly have unsaturated fatty acids, which are bent and have kinks that obstructs packing. - This decreases the van der Waals’ forces between them, leading to lower m.p
what is saponification?
the alkaline hydrolysis of fats/oils into glycerol + the salts of the fatty acids present in the fat (AKA soaps)
what is the general equation for saponification?
fat/oil + 3NaOH –> glyerol (propan-1,2,3-triol) + sodium salt (the soap)
what is biodiesel?
a renewable fuel made from vegetable oils such as rapeseed oil, palm oil, and soybean oil
use of biodiesel:
can be used in normal diesel engines to power cars/buses
what is biodiesel composed of?
a mixture of methyl esters of long-chain carboxylic acids
how is biodiesel made?
reacting vegetable oils with methanol in the presence of HEAT and A STRONG BASE CATALYST (e.g., KOH)
this process is known as trans-esterification
what is trans-esterification?
reacting an ester with an alcohol to produce a different ester and alcohol
what is the general equation for trans-esterification?
fat/oil + 3CH3OH –> glycerol + mixture of methyl esters (3 x methyl ester)
what are the advantages of biodiesel?
- renewable
- carbon neutral
what are the disadvantages of biodiesel?
- need lots of farming space to make vegetable oil, crops could be
grown for biodiesel production rather than for food leading to food
shortages. - Not necessarily carbon neutral - energy is used to make the
fertiliser to grow crops (If this energy comes from fossil fuels,
then the process won’t be carbon neutral overall)
