1) List at least three experimental characteristics that differentiate traditional Fisher's esterification from Transesterification (use of reagents, catalyst, experimental procedure, advantages and / or disadvantages, etc.).

2. Explain what is the chemical role played by the following compounds in the transesterification of vegetable oil:

a) CH3OH

b) CH3COOH

c) NaOH

 

3. Why does the use of methanol experimentally condition the Transesterification

reaction? Explain. In this sense, what parallel reactions could occur and what would be

the possible products? Write down the abbreviated mechanisms for Transesterification

reaction and possible secondary reactions. Base on a theoretical basis.

answer (1)

Fischer esterification is the reaction between carboxylic acid and alcohol to form ester and water.

Transesterification is the reaction between ester and alcohol to form a different ester and a different alcohol.

Catalyst used for esterification is strong acid like Sulphuric acid , in some cases dry Cl is also used. This reaction mixture needs to be heated. Strong acids are used as catalyst to favor nucleophilic attack by alcohol on carbonyl carbon of carboxylic acid.

Catalyst used for transesterification are sulphonic acid or sulphuric acid are used as acid catalyst and strong bases like NaOH and KOH are used as base catalysts. Transesterification does not require heat.

Fischer esterification advantages :-

-This process is simple as compared to other esterification reactions.

-It is slow and thermodynamically controlled process which results in formation of most stable ester as the major product.

- The byproducts formed are non toxic .

Disadvantages of Fischer esterification :-

- Reaction is slow.

- Heat needs to be supplied for the reaction to occur.

-It is acid catalyzed reaction hence, it cannot be used for acid sensitive functional groups.

- If the ester formed as product has lower boiling point than water, then the product may be distilled rather than water formed in the reaction as byproduct.

Advantages of transesterification:-

- Reaction occurs faster as compared to Fischer esterification.

- No need to supply heat for the reaction to occur.

-There is better separation between product and byproduct, which occurs in two layers.

Disadvantages of transesterification:-

- It is difficult to control the reaction mechanism.

-This reaction is sensitive to free fatty acids i.e. FFAs.

- Reaction cost is high.

- For acid catalyzed transesterification corrosion resistant material is required.

- High methanol-oil ratio.

answer 02

(a)

Vegetable oil reacts with methanol in the presence of CH3COOH to form free fatty acid. For biodiesel production via transesterification reaction, methanol is the most common alcohol used. This is because the presence of water during transesterification reaction causes hydrolysis of triglycerides to free fatty acids which lead to soap formation and poor yield.

(b)

The presence of acetic acid improved the yield or basically to catalyze the reaction(acid-catalyzed). as mentioned above Vegetable oil reacts with methanol in the presence of CH3COOH to form free fatty acid.

(c)

NaOH reacts with CH3OH to form CH3O- , which further reacts with free fatty acids present in vegetable oil. The presence of NaOH improved the yield or basically to catalyze the reaction(base-catalyzed).

NaOH reacts with CH3OH to form CH3O- , which further reacts with free fatty acids present in vegetable oil.

answer 03

 The transesterification reaction is an eco-friendly process carried out under mild condition.

• In an transesterification process an alcohol molecule and am ester molecule react in either the presence of acid or base to form a new ester.

• For example ethyl ethanoate reacts with methanol in the presence of hydrochloric acid or sodium hydroxide to form methyl ethanoate and ethanol. ( explained in image)

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