Kritchevsky alkanolamides

These surfactants are produced by reacting fatty acids or fatty methyl esters with ethanolamine or diethanolamine. With fatty acids, conventional amides (sometimes called Kritchevsky alkanolamides) are obtained that consist of approximately 50% amide, 25% unreacted diethanolamine and 25% of various by-products (the amine ester the amide ester, and the amine soap). With methyl esters, higher-active (90% amide) alkanolamides are produced these are known as super amides . 

Type 2 1 (or Kritchevsky alkanolamide) is a mixture of mono- or dialkanolamide and free mono- or dialkanolamine. It results from the reaction of a fatty acid or ester with mono- or dialkanolamine, this last component being combined at a 2 1 molar proportion. Reaction residues in type 2 1 surfactants are free alka-nolamine, unreacted fatty acid, and ester-amide. 

The original work by Kritchevsky [36] involved heating equimolar quantities of dietha nolamine and fatty acid. This yielded, as expected, a water insoluble waxy solid. However, when the diethanolamine content was doubled the reaction was modified to produce a liquid, which was soluble in water and foamed and wetted well even in hard water. Its properties were quite unlike a physical blend of the 1 1 diethanolamide with diethanolamine. It became known as a low activity1, a 2 1, Kritchevsky or Ninol type alkanolamide. 

A second major type is the Kritchevsky type made from alkanolamine and fatty acids in the ratio of 2 1. Such product contains 60-70% alkanolamide plus byproducts. If diethanolamine is used in addition to the mentioned byproducts, some morpholine and piperazine derivatives are also obtained. The excess alkanolamine renders the product water soluble (29). Both are of commercial importance as detergent and detergent additives. 

Alkanolamides based on DEA are tertiary amides and are not as stable as MEA amides such that a significant amount of esters can remain in equilibrium with the amide. The ester amines and esteramides of DEA have undesirable performance properties, but these components can be reduced by utilizing an excess of DEA to drive equilibrium toward the amide form. The most common version is prepared by the reaction of 2 moles of DEA with 1 mole of coconut fatty add or ester to give the Kritchevsky or Ninol-type DEA amide, which is liquid at room temperature. Products made with slightly more than a 1 1 molar ratio of DEA to fatty acid or ester are referred to as superamides and at reaction temperatures of 140-160°C, the mixture contains high level of ester components and free amine. However, with sufficient time at storage temperatures <50°C, the composition will increase in amide and decrease in ester and free-amine components and thus can be aged into specification for free DEA and ester content. 

Using fractionated methyl ester and alkaline catalyst, a transamidation with no excess of one component is possible—the equilibrium is shifted to the alkanolamide by continuously distilling off the by-product methanol, due to its high vapour pressure this is much easier than to separate the water formed in the Kritchevsky process. 

Early experiments in the preparation of alkanolamides were begun by Kritchevsky (20, 21). It involves condensation reactions of fatty acids, triglycerides, esters, amides, anhydrides, and halides with an alkanolamine. The reaction was carried out at 100-300°C at atmospheric pressure. An important improvement was made by Meade (22), who made use of an alkali metal alkoxide as a catalyst at 100°C at atmospheric and slightly above atmospheric pressure. Fmther refinement was made by Tesoro (23), who conducted the reaction at 55-75°C and a vacuum of 4—8 kPa. Schurman (24) patented a continuous process for making alkanolamide, which makes use of a thin film reactor. It is claimed the short contact time in the reactor produces a high-purity alkanolamide (25). 

---