Transesterification reaction is the use of a kind of oil and an alcohol as substrates to prepare esters and glycerol. The reversible reaction process is also called alcoholysis. To drive the equilibrium to the product direction excess alcohol is often loaded. Various oil rich feedstocks, including vegetable oils, waste oils and microalgae or microorganism derived oils and methanol or ethanol are frequently used for biodiesel production. A catalyst responsible for improving the reaction rate and biodiesel yield can be alkalies acids or enzymes.
Transesterification is the generic concept used to describe the basic form of organic reactions in which an ester is converted into another by the exchange of alkoxy moiety. The method of transesterification is called alcoholysis, as the initial ester reacts with an alcohol. Transesterification is a process in equilibrium, and the transformation takes place simply by adding the reactants. Transesterification, also called alcoholysis, involves the displacement of alcohol from an ester by another alcohol, in a process comparable to hydrolysis.
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Methylation Reaction
Methyl groups are the most common of the molecules that can act as switches to activate or silence a gene. Addition of methyl groups is called “methylation”; removal is called “demethylation”. Phenols can be conveniently methylated to give the methyl ethers, which are useful intermediates for organic synthesis. The nature of the methylation procedure to be used depends on the nature of the compound to be methylated.
The most versatile and common use for methylation of phenols and acids. Methylation can be affected either in an alkaline medium or in anhydrous conditions. Sometimes the hydroxy compounds are converted into acetate and then methylated with dimethyl sulphate and alkali. Diazomethane is used for the esterification of carboxylic acids or methylation of phenolic hydroxyl groups. It is used for methylation of very small quantities of the compound.
Transesterification of Esters
Esters are synthesized by acid-catalysed reactions of carboxylic acids with alcohols, known as Fischer esterification. The preparation of esters from other esters in presence of an acid or a base catalyst is called transesterification. Transesterification is possibly the simplest and best example of the acid catalyzed and base catalysed nucleophilic acyl substitution mechanism because it is an evenly balanced equilibrium with mechanisms for the forward and reverse reactions.
Transesterification Esters undergo transesterification, in which one alkoxy group substitutes for another, under either acidic or basic conditions . When an ester of one alcohol is treated with a different alcohol in the presence of acid or base, the two alcohol groups can interchange. Am equilibrium results and the equilibrium can be driven toward the desired ester by using a large excess of the desired alcohol or by removing the other alcohol. It is possible to conduct a transesterification reaction of soybean oil with ethanol using a commercial immobilized lipase in a solvent free reaction medium as demonstrated by the work presented herein. Esters are less reactive than acid chlorides and acid anhydrides. They are easily converted to carboxylic acids by acids by acid or base catalysed hydrolysis or to another ester by alcoholysis under acidic or basic conditions known as transesterification
