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Further Organic Chemistry Revision.

Carboxylic Acids.

Carboxylic acids contain the groupCOOH. This is called the carboxyl group, because in consists ofthe carbonyl group and the hydroxyl group.

There is hydrogen bonding between the first few carboxylic acids, but as the carbon chains grow, the

hydrogen bonding is inhibited by the zigzag chains. All carboxylic acids have strong smells.

Preparation.

Oxidation of a primary alcohol, or an aldehyde, by heating acidified potassium dichromateunder reflux.

Hydrolysis of an ester. (see ester reactions). Hydrolysis of a nitrile. A nitrile is a compound that contains the CN group.When heated

under reflux with a dilute acid, the nitrile is hydrolysed to a carboxylic acid and an

ammonium salt. When heated under reflux with aqueous alkali, the salt of the carboxylic

acid is formed, and addition of a strong acid protonates it and the carboxylic acid is formed.

The iodoform reaction of a methyl ketone or a secondary alcohol, on addition of a solutionsof iodine in aqueous sodium hydroxide to a methyl ketone, the salt of the acid with one less

carbon is formed, and then the acid can be formed by adding excess strong acid.

Reactions.

with water , carboxylic acids react reversibly with water. with bases, carboxylic acids form salts with bases. All carboxylic acids are weak acids with carbonates and hydrogencarbonates, carboxylic acids produce carbon dioxide when

added to a carbonate or a hydrogencarbonate

esterification, carboxylic acids react with alcohols in the prescence of concentrated sulphuricacid, which acts as a catalyst, in a reversible reaction to form esters.

Reduction, carboxylic acids are reduced by lithium tetrahydridoaluminate, dissolve in dryether, to a primary alcohol.

Formation of acid chloride, a carboxylic acid added to solid phosphorus pentachloride formsthe acid chloride.

Formation of a halogenoacid, if chlorine is bubbled into a boiling carboxylic acid in thepresence of sunlight, or U V, chlorine replaces one of the hydrogen atoms on the carbon

chain. This is an example of free radical substitution.

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Esters .

Have the structural formula of RCOOR, where R will be a hydrogen atom or an organic residue, such

as methyl. R must be a residue of an alcohol with a carbon atom attached to the oxy gen of the

ester. They are named by the alcohol residue, followed by the name of the carboxylate group:

Most esters are liquid at room temperature. They are insoluble in water, as they cannot form

hydrogen bonds, as the oxygens are sterically hindered.

Preparation.

Warm an alcohol with a carboxylic acid under reflux, with a few drops of sulphuric acid. The alcohol can be reacted with an acid chloride at room temperature, and this gives a

higher yield, as the reaction is not reversible.

Reactions.

Hydrolysis, esters are hydrolysed when heated under reflux with aqueous acid, forming acarboxylic acid by a reversible reaction, or with aqueous alkali, forming an acid salt in a nonreversible reaction. The acid can be obtained from the acid salt by adding dilute strong acid.

Transesterification with another organic acid, the acid part of the ester is replaced by theacid reactant. This type of reaction is used in the manufacture of low-fat margarine, where

the incoming acid is saturated and the product acid in unsaturated.

Transesterification with another alcohol, where the alcohol bit of the ester is replaced by thealcohol reactant. This type of reaction is used in the manufacture of biodiesel.

Esters are used as:

Perfumes and flavourings, Solvents, such as nail varnish, Anaesthetics, Biofuels.

Polyesters.Polyesters are condensation polymers, formed when monomers join together with the elimination

of a simple molecule, such as water of hydrogen chloride or water. They are used in the manufacture

of synthetic fibres, thermal insulators and bottles for fizzy drinks.

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A homopolymer is a polymer made from a single type of monomer. This monomer must have a

group at one end that can react with the group at the other end of the molecule. Hydroxyacids are

examples.

Acid Chlorides.Most acid chlorides are volatile liquids at room temperature, and are soluble in several organic

solvents, but react with water.

Preparation.

They are prepared from carboxylic acids. TheOH group is replaced by a chlorine atom. Thereagents which can be used are phosphorus pentachloride, phosphorus trichloride or thionyl

chloride.

Reactions.

With water, ethanoyl chloride reacts vigorously with water, forming ethanoic clouds andclouds of hydrogen chloride gas. As a result of this, when using ethanoyl chloride as a

reactant, all reagents and glassware must be dry.

With alchohols, the reaction is rapid and non reversible, to form an ester and misty fumes ofhydrogen chloride vapour.

With ammonia, the nitrogen atom in ammonia has a lone pair of electrons, which is used fornucleophilic attack on the carbon oxygen double bond. The product is an amide. With excess

ammonia, the hydrogen chloride forms a white smoke of ammonium chloride.

Reaction with amines, is similar to that with ammonia, to form a substituted amide Reaction with lithium tetrahydridoaluminate, reduces acid chlorides to a primary alcohol.