carboxylic acids and esters
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what is the general formula for carboxylic acids/
CnH2n+1COOH
what is the carboxyl group made from?
carbonyl group and hydroxyl group
what is the solubility in water like for carboxylic acids?
smaller ones (up to C4) dissolve in water in all proportions but after this solubility rapidly decreases they dissolve because they can hydrogen bond to water molecules
what is an acid?
a proton donor, which means it is a molecule that gives up protons or hydrogen ions (H+) the number of hydrogens given away depends entirely on the molecule (a base is a proton acceptor)
what type of acid are carboxylic acids and why?
weak acids that don’t dissociate fully in water, some of their H+ ions stay attached to the acid molecule the dissociation of a weak acid in water is a reversible reaction HA (reversible arrows) H+ + A-
where does equilibrium lie for carboxylic acids dissociation in water?
more to left as most molecules don’t dissociate BUT ethanoic acid is a typical weak acid with its ions in dynamic equilibrium with the un-dissociated acid (the reaction is moving in both directions at same rate)
what are the three ways carboxylic acids can form salts?
reaction with metals, alkalis and carbonates
write a word equation for the reaction of a carboxylic acid with a metal?
carboxylic acid + metal —–> salt + hydrogen
write a word equation for the reaction of a carboxylic acid with an alkali?
carboxylic acid + alkali —–> salt + water
write a word equation for the reaction of carboxylic acids with carbonates?
acid + carbonate ——-> salt + water + carbon dioxide
what is the test for carboxylic acid functional group?
react with sodium carbonate or sodium hydrogen carbonate, effervescence observed dur to CO2 and this can be bubbled through lime water and milky white emulsion seen if positive
can carboxylic acids be oxidised?
NO but methanoic acid is the exception because its structure is technically an aldehyde group it forms carbonic acid that can decompose to give CO2
what is meant by esterification?
carboxylic acids react with alcohols in the presence of a strong acid catalyst to form an ester and water it is a REVERSIBLE reaction and a CONDENSATION reaction
write an equation for esterification?
Carboxylic acid + alcohol (reversible arrows with H+ on top) ester + water
what are the conditions for esterification?
Heat (under reflux) the acid and alcohol under presence of a strong acid catalyst (usually sulfuric but can be phosphoric or hydrochloric)
what is the ester functional group?
COO
how do we name esters?
the first part ends in -yl and this comes from the alcohol the last part ending in -oate comes from the carboxylic acid used and includes the C in the C=O
what is bad about esterification?
yield is usually low (approx 50% yield)
what are uses of esters?
• they are sweet smelling compounds that can be used in perfumes and flavourings • can be used as solvents for polar and organic substances eg ethyl ethanoate is used as solvent in glues and printing inks • esters can be used as plasticisers for polymers
what are the conditions for if esters are used as perfumes?
need to be non-toxic, soluble in solvent such as ethanol, volatile, and not react with water
although polar, what do esters not form and why?
hydrogen bonds because there is no hydrogen bonded to a highly electronegative atom they have a lower b.p. than the hydrogen-bonded carboxylic acids they came from and are almost insoluble in water due to this
what is the benefit of esters being used as plasticisers?
often pure polymers have limited flexibility because the polymer chains cannot move over each other incorporating some plasticiser into the polymer allows the chains to move more easily and the polymer can become more flexible
how can esters be hydrolysed?
with water, acid or alkali
what are the reagents and conditions for hydrolysis of esters with acid catalyst?
reagents; dilute acid (eg HCl) conditions: heat under reflux