[PDF] Experiment C: Hydrolysis of a Carboxylic Acid Ester: PDF Hydrolysis%20Lab%202006.pdf

Hydrolysis reactions are normally sensitive to a variety a catalytic influences that include specific acid and base catalysis, general acid and base catalysis,

3 jui 2013 · ABSTRACT: The acid-catalyzed hydrolysis of linear esters and lactones was studied using a hybrid supermolecule−polarizable continuum

[PDF] Page 1 of 12 CHEM 100L Lab 7: Ester Hydrolysis Purpose: In the

Figure 7 2 Mechanism for acid-catalyzed ester hydrolysis (From Organic Chemistry by Bruice, 8th Ed ) Once the reaction is complete, you will collect the mass

[PDF] Lecture 6: Hydrolysis Reactions of Esters and Amides

draw the mechanism of ester hydrolysis under acidic and basic reaction conditions form new esters by base- or acid-catalysed transesterification mechanisms;

[PDF] HYDROLYSIS

carbon centre, such as with carboxylic acid derivatives including esters, Epoxides undergo hydrolysis by neutral and acid catalyzed mechanisms under

[PDF] Experiment C: Hydrolysis of a Carboxylic Acid Ester:

Hydrolysis reactions are normally sensitive to a variety a catalytic influences that include specific acid and base catalysis, general acid and base catalysis,

Reaction of p-Nitrophenyl Acetate

Background:

The investigation of anthropogenic organic chemicals in the environment, includes both biotic and abiotic chemical transformations that take place under environmental conditions. The major abiotic environmental processes by which pollutants are transformed are hydrolysis, photolysis, oxida tion and reduction. A primary pathway for the transformation of organic esters in aquatic environments is hydrolysis. Hydrolysis reactions are normally sensitive to a variety a catalytic influences that include specific acid and base catalysis, general acid and base catalysis, nucleophilic catalysis, metal oxide surface catalysis and metal ion catalysis (1,2). Hydrolysis (reaction with water) is usually the most important reaction for mol ecules susceptible to nucleophilic attack. In freshwater, hydroxide ion and water are the dominant nucleophiles with OH- being about

10,000 times more reactive than H

2 O in substitution at carbon (1,2). The hydrolysis of a carboxylic acid ester may proceed by a number of different mechanisms, depending on the substrate structure, the pH and the presence of catalyzing species (3-6). Under neutral conditions, the reaction generally proceeds via addition to the carbonyl carbon to produce a tetrahedral intermediate. The slow step is attack by water. R 1 OO R 2H 2 OR1 O OH 2 OR 2 k H 2 O slow Once formed, this intermediate may proceed through a number of proton transfer steps and elimination of an alkoxide ion or alcohol leaving group. R 1 OH OH OR 2 R 1 O OHOR 2 HR 1 O OH 2 OR 2 R 1 OH OH OR 2+ R 1 O OH HOR 2 The kinetics of hydrolysis at constant pH (natural systems are usually well buffered) can be described by pseudo first order kinetics;

Rate (overall) = -

dtdester][ = k h [ester]

Where k

h is the overall pseudo first order hydrolysis rate constant (s -1 ). The hydrolysis of a carboxylic acid ester can proceed via three distinct bimolecular mechanisms; acid catalyzed, neutral and base enhanced.

Acid catalyzed rate = k

A [H ] [ester]

Neutral rate = k

H2O [H 2

O] [ester] Base enhanced rate = k

B [OH ] [ester] where k A , k H20 and k B are second order rate constants (M -1 s -1 Chemistry 331: Laboratory Manual Environmental Organic Chemistry The overall hydrolysis rate will be the sum of these individual rates. Thus;

Rate (overall) = {k

A [H ] + k H2O [H 2

O] + k

B [OH ] } [ester] And the pseudo first order rate constant is given by; k h = k A [H ] + k H2O [H 2

O] + k

B [OH

Since in aqueous solution, the concentration of H

O remains virtually constant at ~55.5

M, the neutral contribution is generally expressed as a pseudo first order constant, k N k H2O [H 2 O]. k h = k A [H ] + k N + k B [OH Ester hydrolysis has been shown to be accelerated by both acid and base so the rate is pH dependent as shown below. At high pH, the dependence of log k vs pH increases with a slope of +1 (specific base 'catalysis'). In general, reaction with OH is important even at pH values below pH 7. Specific acid catalysis is relevant only at relatively low pH's and only for compounds showing rather slow hydrolysis kinetics under neutral conditions (2). log k h versus pH -5.0-3.0-1.01.03.05.0quotesdbs_dbs4.pdfusesText_7

[PDF] [PDF] Experiment C: Hydrolysis of a Carboxylic Acid Ester:

[PDF] Mechanisms of Lactone Hydrolysis in Acidic Conditions

[PDF] Page 1 of 12 CHEM 100L Lab 7: Ester Hydrolysis Purpose: In the

[PDF] Lecture 6: Hydrolysis Reactions of Esters and Amides

[PDF] HYDROLYSIS

[PDF] Experiment C: Hydrolysis of a Carboxylic Acid Ester:

Reaction of p-Nitrophenyl Acetate

Background:

10,000 times more reactive than H

Rate (overall) = -

Where k

Acid catalyzed rate = k

Neutral rate = k

O] [ester] Base enhanced rate = k

Rate (overall) = {k

O] + k

O] + k

Since in aqueous solution, the concentration of H

O remains virtually constant at ~55.5