Transesterification is an alcoholysis in which one alcohol is capable of displacing another alcohol from an ester in a process similar to hydrolysis, except that alcohol is used instead of water. This process has been widely used to reduce the high viscosity of triglycerides. Transesterification is one of the reversible reactions and proceeds essentially by mixing the reactants. However, the presence of a catalyst (a strong acid or base) accelerates the conversion. The transesterification reaction is represented by the general equation,

Fig. 11.10 Freidel craft acylation of oleic acid

RCOOR1 + R2OH <—> RCOOR2 + R1OH Ester Alcohol Ester Alcohol

Transesterification of triglycerides produce fatty acid alkyl esters and glycerol. The glycerol layer settles down at the bottom of the reaction vessel. Diglycerides and monoglycerides are the intermediates in this process. The mechanism of transesterification is described as follows:

Triglyceride + R1OH $ Diglyceride + RCOOR1 Diglyceride + R1OH $ Monoglyceride + RCOOR1 Monoglyceride + R1OH $ Glycerol + RCOOR1

The stepwise reactions are reversible and an excess of alcohol is used to shift the equilibrium towards the formation of esters. In the presence of excess alcohol, the forward reaction is pseudo-first order and the reverse reaction is found to be second order. Transesterification reaction can be catalyzed by base catalyst and also by acid catalyst. It was found that base catalysed transesterification reactions are faster than acid catalysed reactions [82].

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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