6.1.3 Carboxylic Acids and Esters
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what is a carboxylic acid
• contains the carboxyl functional group • carbonyl (C=O) and hydroxyl (OH) functional group • COOH
what are carboxylic acids often used for
• useful on their own • or as starting materials for other compounds • e.g. aspirin is made from salicylic acid
how do you name carboxylic acids
• the carboxyl group is indicated via the -oic acid suffix • always placed on carbon 1
how would you name a carboxylic acid with a 4 carbon main chain and a methyl group coming off carbon 3
3-methylbutanoic acid
are carboxylic acids soluble, and why
• YES • because both the C=O and O-H bonds are polar • so can form hydrogen bonds with the water • if drawing, remember dipoles
which carboxylic acids are soluble
• a carboxylic acid with up to 4 C atoms
what happens to the solubility as the number of carbon atoms in a carboxylic acid increases
• as the number of carbon atoms increases • the solubility decreases • as the non-polar carbon chain has a grater effect on the overall polarity of the molecule • when comparing, always refer to the RATIO of carbons against COOH group
what is special about dicarboxylic acids and solubility
• have 2 polar carboxyl groups COOH to form hydrogen bonds • so are usually solid at room temperature • but readily dissolve
what type of acids are carboxylic acids
weak acids - so only partially dissociate and release H+ ion - e.g. HCOOH(aq) ⇌ H+(aq) + HCOO-(aq)
what is the basic way in which carboxylic acids act in acid reactions
• undergo redox reactions with metals • and neutralisation reactions with bases, e.g. alkalis, metal oxides and carbonates • FORM CARBOXYLATE SALTS
show how the carboxyl group forms a carboxylate ion
R-COOH → R-COO- • carboxylate is used to name the ions formed
how do carboxylic acids react with metals
• in an aqueous solution • forming hydrogen gas and a carboxylate salt
what would you be able to observe when a carboxylic acid reacts with a metal
• metal disappears • effervescence as hydrogen gas evolves
what is important to remember when constructing equations to show the redox and neutralisation of carboxylic acids
• need to balance out the transfer of protons • e.g. the monoprotic carboxylic acid and the base, whether monoprotic too or diprotic
how would you show the equation between propanoic acid and magnesium
2CH3CH2COOH(aq) + Mg(s) → (CH3CH2COO-)2Mg2+(aq) + H2 • as propanoic acid is monoprotic • and Mg is diprotic (2+) • so need to balance out the charges
how do carboxylic acids react with metal oxides
carboxylic acid + metal oxide → salt + water
what is the equation for ethanoic acid reacting with calcium oxide
2CH3COOH(aq) + CaO → (CH3COO-)2Ca2+(aq) → H2O
how do carboxylic acids react with alkalis
carboxylic acid + alkali → salt + water • you may not see any reaction taking place at all, as 2 solutions are reacting to form an aqueous salt
how would you show ethanoic acid reacting with sodium hydroxide
CH3COOH(aq) + NaOH(aq) → CH3COO-Na+(aq) + H2O (l) • ionically, is the neutralisation equation: • H+ + OH- → H2O
how do carboxylic acids react with carbonates
carboxylic acid + carbonate → salt + water + carbon dioxide • if the carboxylic acid is in excess, you should see any solid carbonate fully disappear
equation for ethanoic acid and sodium carbonate
2CH3COOH(aq) + Na2CO3(aq) → 2CH3COO-Na+ + H2O + CO2
how can you test for the carboxyl group
• can test via the neutralisation of carboxylic acids by carbonates • as they are the only common organic compound acidic enough to react with carbonates • especially useful when distinguishing between phenols • as they aren’t acidic enough to react
what is a derivative of carboxylic acid
a compound that can be hydrolysed to form the parent carboxylic acid
what is the common series of atoms present in all derivatives of carboxylic acids
• the ACYL GROUP • made of R-C=O (and then another line coming off the carbon