Optimisation of Heterogeneous Catalysed Esterification Reaction for n-Hexyl Acetate Synthesis part 3

Optimisation of Heterogeneous Catalysed Esterification Reaction for
n-Hexyl Acetate Synthesis part 3

EXPERIMENT

Materials and Catalysts

Acetic acid, n-hexanol and n-hexyl acetate were supplied by Sigma-Aldrich UK. Methanol,
n-butanol and acetone were purchased from Fisher Scientific, U.K. These chemicals were used without any further purification. Cation exchange resins, Purolite CT-124, CT-151 and CT-175 were kindly provided by Purolite International Limited, U.K. The
catalysts were washed with deionised water and methanol and

judged alongside by Patel and Saha, (2007), Saha and Sharma (1996) and Saha and Streat (1998), this study will seek to confirm their then dried in a vacuum oven for 6 h at 373 K before it was employed in the experiments. The physical
and chemical properties of the catalysts used can be found elsewhere and are summarised in Table 1.

Esterification Reaction

n-Hexyl acetate was synthesised in the presence of Purolite CT-124, Purolite CT-151 and Purolite CT-175 cation exchange resins using acetic acid and
n-hexanol.

Mechanism Reaction

It was assumed that the mechanism of heterogeneous catalysed esterification reaction is similar to homogeneous catalysed esterification reaction. Figure 1 depicts the conceptualised reaction mechanism. Acidic cation exchange resins
initiate the reaction by denoting a proton to the acetic acid because they are stronger Lewis acids than acetic acid (Chakrabarti and Sharma, 1993).

This protonated carbonyl group is then attacked by
n-hexanol resulting in an intermediate. Another intermediate is formed when one oxygen atom loses proton and another oxygen atom gaining proton, which then gives up a molecule of water to form a protonated ester. 

The protonated ester produced then loses another proton to water molecule to form the desired ester,
n-hexyl acetate (Patel and Saha, 2007). Notice how at the initiation step and the final step, the catalyst retains its H+ state, fulfilling the objective of traditional acid catalysis (albeit as H3O+ (oxonium ion) at the end).

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Posted by Ahmed Tariq on Dec 29 2011. Filed under Sci-Tech. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry