Anionic surfactants

As anionic surfactants are called surfactants , a negatively charged functional group possess. Like all surfactants, anionic surfactants are also made up of a polar and a non-polar part. An alkyl radical serves as the non-polar part . The polar, functional group is −COO ^- ( carboxylate ), −SO ₃ ^- ( sulfonate ) or −SO ₄ ²⁻ ( sulfate ).

Typical representatives

• Alkyl carboxylates (= soap ): R − COO ^- Na ⁺ , with R = saturated or unsaturated, linear alkyl radical, depending on the type of fatty acid
• Alkylbenzenesulfonates (ABS): C _n H _{2n + 1} −C ₆ H ₄ −SO ₃ ^- Na ⁺ , for example: sodium dodecylbenzenesulfonate
• secondary alkyl sulfonates (also alkane sulfonates, SAS): C _n H _{2n + 1} -SO ₃ ^- Na ⁺ , also fluorinated, for example potassium-N-ethyl-N - ((heptadecafluorooctyl) sulfonyl) glycinate
• Fatty alcohol sulfates (FAS): H ₃ C− (CH ₂ ) _n −CH ₂ −O − SO ₃ ^- Na ⁺ [n = 8–16], for example: sodium lauryl sulfate
• Alkyl ether sulfates , e.g. B. Sodium dodecyl poly (oxyethylene) sulfate (SLES)
• Sulfoacetates
• Tauride with the general structure:

use

The sulfonates ABS and SAS show good wetting properties and can also be used in hard water; they are mainly used in powdery laundry detergents. The soaps can only be used to a limited extent, as they form lime soaps that are insoluble in hard water and are therefore ineffective.

Manufacturing

Alkylbenzenesulfonates

The alkylbenzene obtained from Friedel-Crafts alkylation is sulfonated with fuming sulfuric acid and neutralized with lye. Reactions:

1st addition:

${\displaystyle \mathrm {H_{3}C-(CH_{2})_{n}-CH=H_{2}C+C_{6}H_{6}\longrightarrow H_{3}C-(CH_{2})_{n}-CH_{2}-CH_{2}-C_{6}H_{5}} }$

The addition is catalyzed by H ⁺ ions.

2. electrophilic substitution :

${\displaystyle \mathrm {H_{3}C-(CH_{2})_{n}-CH_{2}-CH_{2}-C_{6}H_{5}+SO_{3}\longrightarrow H_{3}C-(CH_{2})_{n}-CH_{2}-CH_{2}-C_{6}H_{4}-SO_{3}H} }$

3. Neutralization:

${\displaystyle \mathrm {H_{3}C-(CH_{2})_{n}-CH_{2}-CH_{2}-C_{6}H_{4}-SO_{3}H+NaOH\longrightarrow H_{3}C-(CH_{2})_{n}-CH_{2}-CH_{2}-C_{6}H_{4}-SO_{3}^{-}Na^{+}+H_{2}O} }$

Soap

The soaps are obtained directly by the basic hydrolysis of fats and fatty oils , i. This means that the fats are converted into soaps with bases such as potassium hydroxide or caustic soda ( saponification ). With sodium hydroxide are curd soaps , caustic potash soft soap produced:

In the past, soaps were made from animal fats with the help of soda (Na ₂ CO ₃ ) or potash (K ₂ CO ₃ ):

The soaps described above can be produced with the different cations .

Fatty alcohol sulfates

Fatty alcohol sulfates are obtained by reacting a fatty alcohol with sulfur trioxide . Reaction:

${\displaystyle \mathrm {H_{3}C-(CH_{2})_{n}-CH_{2}-O-H+SO_{3}\longrightarrow H_{3}C-(CH_{2})_{n}-CH_{2}-O-SO_{3}H} }$

${\displaystyle \mathrm {H_{3}C-(CH_{2})_{n}-CH_{2}-O-SO_{3}H+NaOH\longrightarrow H_{3}C-(CH_{2})_{n}-CH_{2}-O-SO_{3}^{-}+Na^{+}+H_{2}O} }$

ecology

Some surfactants are poorly broken down by microorganisms in the water. Mountains of foam therefore covered large areas of the body of water until the Detergent Act in 1961 only allowed surfactants that are at least 80% biodegradable.

Individual evidence

1. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, pp. 503-504.