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Acids :

• Is a substance that produce hydrogen ions when dissolved in water.

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• All acids contains hydrogen. But all substances with hydrogen contains acida (water).

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• The hydrogen ions produced are responsible for the properties of an acid.

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Acids

Strong acids

• Man made

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• Mineral acids

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• Corrosive

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• e.g. H₂SO₄
• HCL
• Nitric acid

Weak acids

• Found in plants and animals,used in food

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• Organic acid

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• Not very corrosive

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• E.g. Ethanoic acid
• Citric acid

Carboxylic acid :

In IUPAC nomenclature carboxylic acids are named by adding a suffix to the parent name of the longest chain.If th parent chain is non cyclic you need to first find the longest carbon chain containing the –COOH group and change the suffix from ‘ane’ to ‘oic acid’ dropping the ‘e’ and the locant.

Aromatic Acids :

• Aromatic acids are named as derivatives of benzoic acids.
• Ortho ,meta and para prefixes are used to specify the location of a second substituent.
• Number are used to specify locations when more than 2 substituents are present .

INTRODUCTION

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• The functional group of carboxylic acid consist of C=O with –OH bonded to the same carbon.
• Carboxyl group is usually written –COOH.
• Aliphatic acids have an alkyl group bounded to –COOH .
• Aromatic acids have an aryl group.
• Fatty acids are long chain aliphatic acids.

PREPARATION METHODS

1)From alcohol and aldehyde:

Primary alcohol and aldehyde are readily oxidized to the corresponding carboxylic acids by oxidizing agent such as K₂Cr₂O₇ in an acidic medium .

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2) By oxidation of alkylbenzene:

Aromatic acids can be prepared by the oxidation of alkyl side chain on the benzene ring with alkaline KMnO₄ acidic K₂Cr₂O_{7 ,} any sidechain regardless of its length is converted to carboxyl group .

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3)Oxidation of unsaturated hydrocarbon:

Compounds having substituted C=C or triple bond undergo cleavage at the point of un saturation when subjected to oxidation with alkaline KMnO4 or acidic dichromate to yield carboxylic acid.

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4)By oxidation of methyl ketones:

A base catalyzed halogenation of methyl ketones gives a trihalomethyl ketone which on hydrolysis under the reaction conditions yields carboxylic acid .

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5)By carbonation of Grignard reagents:

When an ethereal sol. Of a Grignard reagent is poured into solid carbon dioxide a halomagnesium salt of carboxylic acis is produced which on acidification yield carboxylic acid.

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6) By hydrolysis of esters:

The appropriate ester on boiling with conc. NaOH yield sodium salt of acid. Thus resulting salt when treated with dil. HCL gives the free carboxylic acids.

General reaction:

R-COOR’ + NaOH →R-CO-OH + NaCl

Physical properties

• Smell: The first aliphatic acid i.e. formic acid and propanoic acid are colourless liquids and have pungent smell. The next three acids C4 to C6 are colourless liquids with some what unpleasant smell.
• Solubility:Among the aliphatic acids first four members are very sollublr in water due to hydrogen bonding.the solubility in water gradually decreases with increases in molecular mass.
• Boiling point: BP are relatively high due to intermolecular hydrogen bonding. The molecular mass determination in non polar solvents like benzene show that carboxylic acid exist as cyclic dimers
• Melting point:MP increases regularly with increase in molecular mass.

PHARMACEUTICAL APPLICATIONS

a) Acetic acid: (CH3COOH)

Acetic acid is the main constituent of vinegar. It is used in cooking,cleaning,laundry.

It Is used as ear drop to treat infections of wear canal.

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b)Lactic acid: (C3H6O3)

It is used into pical preparation and cosmetics to adjust acidity and has disinfectant and keratolytic properties.

It is present in sour milk product like butter etc.

It is used in treatment of facial dermatosis and in the prevention of dermatitis.

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3)Tartaric acid: (COOH-CH(OH)-CH(OH)-COOH

• Tartaric acid has a natural sour taste and when added to food it gives flavor. Itt is used to preserve food.
• It is used in gold and silver plating process.
• It is used to make soln. for the determination of glucose.

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4)Citric acid: (C6H8O7)

• It is an excellent chelating agent bind with metals and make them soluble.
• it has useful cleaning properties.

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5)Succinic acid: (C4H6O4)

• It is safe as food additive and dietry supplement.
• It is used to increase germination ,growth and yield during seed treatment.
• It is used as an intermediate in manufacture of dye , perfumes photographic chemical.