1. Classification and physicochemical properties of surface-active substances

1.1 Synthetic detergent production

Synthetic detergents are mixtures of surface-active washing substances with auxiliary components and fillers (soda ash, phosphates, and sodium sulfate), strengthening washing action of basic components. Active washing substances in usual fatty soaps – are sodium and potassium salts of fat acids (stearic, palmitic), in synthetic detergents – sodium salts of sulphoacids and sulphoethers with organic radicals С₁₂-С₁₈, and also products of ethylene oxide condensation with various organic compounds, etc. These components are produced on the basis of petrochemical raw material. Solutions of these substances in water have surface-active properties, i.e. reduce surface tension on an interface boundary.

Detergents on the basis of sulphoethers, produced from natural raw material, were known in the XIX century. Since 1880 as a textile-auxiliary substance a sulphurizated castor oil is applied. For the first time sulphoacids and their salts possessing surface-active properties have been produced in 1912 by Petrov G.N. At sulphurization of petroleum fractions he has isolated alkyl aromatic sulphoacids of the average composition C₂₀H₂₇SO₃H. These products have found technical application under the name “Petrov contact” and were applied as surface-active substances. Surface-active substances and detergents on the basis of synthetic carbon acids for the first time have been produced in Germany in 1916. Since 1930 in Germany and since 1932 in the USA detergents on the basis of alkyl benzene sulphonates AlkC₆H₄SO₂ONa with alkyl radical С₁₀-С₁₅ were manufactured. These compounds can be produced at the condensation of chlorinated kerosene with benzene, the subsequent sulphurization and neutralization of the formed product. During the Second World War in Germany alkyl sulphonates AlkSO₂ONa were manufactured at sulphochlorination of paraffin hydrocarbons, and synthetic fat acids and soaps on their basis were made at the oxidation of paraffins. The world production of synthetic detergents began quickly to develop after the Second World War.

Now it is known more than 200 kinds of surface-active substances and over 3000 kinds of trading names from them.

In the advanced countries fatty soap is more and more replaced by synthetic detergents. Mid-annual rates of the SAS world production grow. The fast development of synthetic detergent manufacture and replacement of fatty soap by them is caused by the following reasons:

1) Efficiency of synthetic detergents surpass in 2-4 times efficiency of fatty soap, that reduces synthetic detergent consumption for achievement of the same cleaning effect;

2) Washing action of synthetic detergents is kept in hard water as they do not form some insoluble calcium and magnesium salts. 30-35 % of fatty soap at use is spent for water mitigation (sedimentation of rigidity salts), and in the water having rigidity 200 and higher fatty soaps in general lose washing ability because an insoluble layer of calcium and magnesium salts of fat acids is formed on the soap surface;

3) Maximum of synthetic detergents’ washing ability is achieved at considerably lower temperature, than for fatty soaps. It allows carrying out washing of woolen, silk and synthetic fabrics at temperature less 40⁰C, owing to this fact these fabrics do not lose color and durability;

4) Synthetic detergents are not hydrolyzed and, consequently, do not create an alkaline medium, therefore durability of fabrics from synthetic fibres raises;

5) Synthetic detergents are prepared on the basis of gas and oil refining products; in this connection consumption of food fats for technical needs is reduced, and they can be used for food purposes;

6) Labour expenses for the manufacture of 1 ton of synthetic detergent are lower than labour expenses for the manufacture of 1 ton of raw material for fatty soap in 14-16 times; it causes considerably smaller cost of synthetic detergents;

7) Synthetic detergents keep washing ability in acid solutions.

Soaps are sodium and potassium salts of supreme carbon acids, for example: С₁₇H₃₅СООNa – sodium stearate, С₁₅H₃₁COOK – potassium palmitate. Sodium salts (sodium soaps) represent solid substances, potassium soaps – liquids ones, well soluble in water. Soaps are produced by hydrolysis of fats (saponification) at the presence of alkalis:

С₁₇H₃₅СООСH₂

С₁₇H₃₅СООCH + 3NaOH → CH₂OH – CHOH – CH₂OH + 3С₁₇H₃₅СООNa C₁₇H₃₅СООCH₂ soap

Besides soap can be produced using supreme oil hydrocarbons – paraffins. Paraffin is oxidized up to carbon acids (mixture), necessary acids are separated from the mixture and turned in sodium salts by addition of soda ash Na₂CO₃.

As soaps are salts of strong alkalis and weak acids, they are hydrolyzed in water solutions:

С₁₇H₃₅СООNa + H₂O = С₁₇H₃₅СООН + NaOH

Therefore soap solutions have alkaline reaction. In hard water washing action of soaps is weak. It is caused by interaction of soap with calcium ions that leads to formation of insoluble salts:

2С₁₇H₃₅СОО^- + Сa²⁺ = Ca(С₁₇H₃₅СОО)₂↓

In acid mediums soaps are decomposed forming supreme carbon acids.

Soaps are applied not only as washing substances. They are also used as components of lubricants, reagents for flotation.