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Carboxylic Acids Carboxyl Group The carboxyl group: Is a carbonyl group (C=O) attached to a hydroxyl group (OH). Is found on carbon 1 in carboxylic acids. Is written in different ways. O CH3—C—OH CH3—COOH CH3—CO2H Properties • Weak acids • In a pure carboxylic acid, hydrogen bonding can occur between two molecules of acid to produce a dimer. • Thus carboxylic acids have a much higher boiling point than alkanes of a similar mass. propan-1-ol CH3CH2CH2OH 97.2°C ethanoic acid CH3COOH 118°C • Low mass carboxylic acids are soluble in water IUPAC Names The IUPAC names of carboxylic acids: • Replace the -e in the alkane name with -oic acid. CH4 methane HCOOH methanoic acid CH3—CH3 ethane CH3—COOH ethanoic acid • Number substituents from the carboxyl carbon 1. CH3 | CH3—CH—CH2—COOH 4 3 2 1 3-methylbutanoic acid IUPAC Names The IUPAC names of carboxylic acids: • Replace the -e in the alkane name with -oic acid. Models of Carboxylic Acids • The three-dimensional models show the geometry of atoms in carboxylic acid molecules. Names and Sources of Some Carboxylic Acids Reactions • Neutralise bases • React with metals metal carbonates and metal oxides to form ionic salts • React with PCl5 or SOCl2 to form acid chlorides (substitution) • Reacts with alcohols to form esters • Reacts with ammonia to form amides Neutralisation • Organic acids will react with bases to form a salt and water E.g. CH3COOH + NaOH CH3COONa + H2O When the acids form salts, H+ is lost and replaced by a metal. Sodium ethanoate, for example, has the structure: The bond between the sodium and the ethanoate is ionic. Don't draw a line between the two (implying a covalent bond). Although the name is written with the sodium first, the formula is always written in one of the ways shown (CH3COO- Na+ or CH3COONa) Acid Chlorides • This is a substitution reaction where Cl replaces OH on the carboxylic acid. • Also referred to as alkanoyl chloride • Are very reactive and so can be used to make other products • Suffix for naming is -oyl chloride e.g. Properties of Acid Chlorides • Low melting points (No H bonding) • Pungent fuming liquids Formation of Acid Chlorides • PCl5 (phosphorous pentachloride) or SOCl2 (thionyl chloride) are the reagents • The acyl chloride can be separated by fractional distillation. • Conc HCl can not be use as the water would react with acid chloride to produce the carboxylic acid Equations Reactivity of Acid Chlorides Acid chlorides are highly reactive because the carbon of the acid chloride group, COCl, is attached to two highly electronegative atoms, ie: • Oxygen (of the C=0 carbonyl group). • Chlorine (of the C-Cl bond). • This allows NH3 and H2O to react with them in nucleophilic substitution reactions. Reaction with Water Produces a carboxylic acid Reaction with Ammonia Produces an amide and ammonium chloride Reaction with Primary Aminoalkanes Produces a secondary amide Reaction with Alcohols Produces an ester and hydrogen chloride Learn This