Hydrolysis ethyl palmitate

Fig. 12. Ethyl palmitate films when the molecules are nearly independent. The ester groups are fully exposed to the water, and alkaline hydrolysis is rapid, k = 0.037 min. (Alexander and Schulman, 18).

Alexander and Rideal (30) found that the hydrolysis of a monolayer of ethyl palmitate on alkali became unusually slow as the reaction proceeded. They suggested that the reason for this decrease in rate lay in a reduced concentration of hydroxyl ions at the surface due to repulsion by the negative charge upon the interface, for which the palmitate ions formed in the saponification were responsible. 

In nature, palmitic acid does not often occur as a pure component. In fact, it is usually present as a triglyceride but even tripalmitin is seldom encountered. Usually palmitic acid is present in combination with similar high molecular mass acids in the form of triglycerides. Hydrolysis of these triglyeerides results in a mixture of fatty acids or their esters, which in turn need to be fraetionated to obtain palmitic acid or its ester, usually ethyl palmitate or methyl palmitate. 

If fat-soluble vitamins (A, D and E) are added to a product, the first step in the analysis will often be hydrolysis. In fortified products this converts any esters, for example, vitamin A palmitate or vitamin E acetate, to their free alcohols. The product is then extracted with a hydrophobic solvent, such as hexane or diethyl ethyl or a mixture of these solvents, prior to HPLC analysis often using a reverse-phase (Ci8) column. 

The sodium or potassium salt of palmitic acid, or of stearic acid or the mixed salts of several acids obtained from ordinary fats, is the common substance known as soap. This particular reaction of hydrolysis, is, therefore, known, also, as a reaction of saponification (soap formation). Strictly speaking the reaction of saponification applies only to the alkaline hydrolysis of fats, i,e., of glycerol esters, but, as the hydrolysis of other esters is a reaction of exactly the same character, the term is used to apply equally to the hydrolysis of any ester in presence of an alkali. In the case of the lower alcohol and lower acid esters, e.g., ethyl acetate, the salt formed is not a soap but is a crystalline salt, sodium acetate. 

A membrane cell recycle reactor with continuous ethanol extraction by dibutyl phthalate increased the productivity fourfold with increased conversion of glucose from 45 to 91%.249 The ethanol was then removed from the dibutyl phthalate with water. It would be better to do this second step with a membrane. In another process, microencapsulated yeast converted glucose to ethanol, which was removed by an oleic acid phase containing a lipase that formed ethyl oleate.250 This could be used as biodiesel fuel. Continuous ultrafiltration has been used to separate the propionic acid produced from glycerol by a Propionibacterium.251 Whey proteins have been hydrolyzed enzymatically and continuously in an ultrafiltration reactor, with improved yields, productivity, and elimination of peptide coproducts.252 Continuous hydrolysis of a starch slurry has been carried out with a-amylase immobilized in a hollow fiber reactor.253 Oils have been hydrolyzed by a lipase immobilized on an aromatic polyamide ultrafiltration membrane with continuous separation of one product through the membrane to shift the equilibrium toward the desired products.254 Such a process could supplant the current energy-intensive industrial one that takes 3-24 h at 150-260X. Lipases have also been used to prepare esters. A lipase-surfactant complex in hexane was used to prepare a wax ester found in whale oil, by the esterification of 1 hexadecanol with palmitic acid in a membrane reactor.255 After 1 h, the yield was 96%. The current industrial process runs at 250°C for up to 20 h. 

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