Question

1.) Structures & preparation for anionic, cationic, nonionic, amphoteric surfactant

2.) What is Co-surfactant and its working principle

Please conclude a general method for preparation of each type, but not one by one, for example, the anionic one, please provide one or two methods, but not one method for soap, alkylbenzene sulfonates, alkyl sulfates, alkyl ether sulfates. Thank you.

Answer 1

Anionic surfactant

They are the most commonly used surfactants. They include alkylbenzene sulfonates (detergents), (fatty acid) soaps, lauryl sulfate (foaming agent), di-alkyl sulfosuccinate (wetting agent), lignosulfonates (dispersants) etc. Anionic surfactants account for about 50 % of the world production.

preparation: Soaps are prepared by saponification of triglycerides from vegetal or animal source. with a triglyceride containing 3 stearic acid (C18:0) units, the reaction with sodium hydroxide produces 3 moles of sodium stearate and 1 mole of glycerol.

3 NaOH + (C17H35COO)3C3H5--> 3 C17H35COONa + CH2OH-CHOH-CH2OH

The current process takes place in two steps.

a) First, the triglyceride is hydrolyzed at high pressure (240 ºC, 40 atm.) with a ZnO catalyst, which is alkaline but not water soluble and thus does not react with the acids. At the end of the hydrolysis, acids (oil phase) and glycerol (aqueous phase) are separated.

b)Acids are then distilled under vacuum to separate too short and too long species, to keep the proper cut (C10-C20) and fractionate it into its components, particularly the C12-C14 acids which are scarce and more valuable than their C16-C18 counterparts. This process allows formulating soaps with the proper mixture of acids, and with the desired hydroxide.

Cationic surfactant

A very large proportion of this class corresponds to nitrogen compounds such as fatty amine salts and quaternary ammoniums, with one or several long chains of the alkyl type, often coming from natural fatty acids. They are not good detergents nor foaming agents.

FATTY AMINE SYNTHESIS

There are several methods. The most used in practice starts from a fatty acid and transforms it into an amide, nitrile, primary amine, secondary amine, tertiary amine and finally quaternary ammonium.

R-COOH + NH3--> RCONH2 + H2O amide (by dehydration)

R-CONH2--> RC≡N + H2O nitrile (by heating/dehydration)

R-C≡N + 2 H2 --> R-CH2NH2 amine and other products (by hydrogenation)

If the primary amine is transformed in secondary amine by catalytic removal of ammonia, the two alkyl groups are the same. 2 R-NH2--> R-NH-R + NH3

In general, only one long alkyl group is required. Hence, the secondary amine is obtained by methylation, either by reaction of methylamine on nitrile or by reductive methylation with formaldehyde.

R1C≡N + CH3NH2 + H2 --> R1CH2NH-CH3 + NH3

Nonionic surfactant

A large proportion of these nonionic surfactants are made hydrophilic by the presence of a polyethylene glycol chain, obtained by the polycondensation of ethylene oxide.Ethoxylated Linear Alcohols, Ethoxylated Alkyl Phenols, Fatty Acid Esters these are a main nonionic surfactant.

ETHOXYLATED LINEAR ALCOHOLS

Alcohols come from various origins, but today the main point is to select those with linear alkyl groups. Primary alcohols have their -OH group at the end of the chain. They are generally prepared by moderate hydrogenation of fatty acids, so-called catalytic hydrogenolysis (150 ºC, 50 atm H2, copper chromite catalyst):

R-CO-OH + H2--> R-CH2-OH + H2O

They can be prepared too by Ziegler hydroformylation of olefins (OXO process) or controlled oxidation of paraffin.

Secondary alcohols, which have their hydroxyl group attached on the second carbon atom of the alkyl chain, are produced by hydration of alpha-olefins in the sulfuric medium :

Amphoteric surfactant

These surfactant molecule exhibit both anionic and cationic dissociations.

IMIDO PROPIONIC ACIDS

Their general formula is HOOC-CH2-CH2-RN+H-CH2-CH2-COO-. Their isoelectric point is around pH = 2-3. They are thus more water soluble than the previous ones. They are used as textile softeners. Dicarboxylic compounds of alkyl imidazole, in which the alkyl group is located on the carbon placed between the nitrogen atoms, are used in cosmetics and deluxe soap bars.