Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
Esterification Lab
| Question | Answer |
|---|---|
| Esters | can be prepared by the reaction of a carboxylic acid with alcohol in the presence of a catalyst such as concentrated sulfuric acid, hydrogen chloride, p-toluenesulfonic acid, or the acid form of an exchange resin. |
| General Walkthrough of Esterification Steps | the mechanism of the reaction involves protonation, nucleophilic attack, proton transfer, removal of LG (water), deprotonation. |
| Draw Fisher Esterification as Hyujun Illustrated | --- |
| Reversibility Tip: | all of the steps in esterification are reversible. The reverse reaction is called hydrolysis. |
| Portions Tip: | The OH from the carboxylic acid and the H from the alcohol work together to form water. The COR in the ester works as an acid fragment and the OR is the alcohol fragment. |
| Super Tip: | to create an ester from a carboxylic acid and alcohol, just replace the OH group on the carboxylic acid with the alcohol group minus one hydrogen. |
| The Potential Catalysts in the Esterification of n-butyl acetate: | H2SO4, HCl, p-toluenesulfonic acid, ion exchange resin (this is the one we used!) |
| General Reaction in the Experiment: | n-butanol + acetic acid ⇌ n-butyl acetate + water CH3(CH2)3OH+CH3COOH<=>CH3COO(CH2)3CH3+H2O |
| Equilibrium Constant of Esterification: | [(n-butyl acetate)(water)] / (n-butanol)(acetic acid)]. Primary alcohols with unhindered carboxylic acid, K is 3-4. If equal quantities of 1-butanol and acetic acid are allowed to react at equilibrium, the theoretical yield of ester is only 67%. |
| How to Shift Equilibrium Using Le Chatelier's Principle: | increase or decrease concentration of alcohol or acid, remove water from the equation, or remove the water as an azeotrope with azeotrope distillation. |
| How does increases or decreases concentration of alcohol or acid shift equilibrium? | These are reactants. If either one is doubled or in excess, the yield increases dramatically. An excess amount of products would shift it back towards the left. |
| What does removing water do to equilibrium? | This is a product, shifts towards right and forms more ester |
| What does azeotrope distillation do to equilibrium? | If you remove the lower layer from the condensate and still return the upper layer to the reaction mixture, then the equilibrium can be upset, and nearly 100% of the ester can be produced in the reaction flask. |
| Why Can’t You Use Simple Distillation: | because the reactants and products make an azeotropic mixture — they have boiling points close to each other. |
| How Was Azeotropic Distillation Actually Achieved: | vapor condenses and runs down to the sidearm, which is closed with a cork. The layers separate with the denser water layer remaining in the sidearm and the lighter ester plus alcohol running down into the reaction flask. |
| For Our Purposes, Azeotropic Distillation Occurs By: | first use the reflux, heat and condense, let the top layer in the side arm run back into the reaction mixture. Dry the product with calcium chloride pellets and get the IR spectra for reactants and products. |
| Azeotrope: | also known as a constant boiling point mixture, where there are two or more liquids whose proportions cannot be altered or changed by simple distillation. |
| Azeotropic Mixture Contains: | 8% butanol, 63% ester, 29% water |
| After Separation, the Organic Layer Contains: | 11% butanol, 86% ester, 3% water |
| Alternatives to Esterification: | There are some other ways in which you can also form esters, like reacting alcohols with anhydrides or acid chlorides. |
| Expected IR for Alcohol Product: | In the IR spectrum of the product (n-butyl acetate), the broad O–H stretch from the alcohol (~3300 cm⁻¹) will disappear, and a new strong ester C=O peak (~1740 cm⁻¹) will appear. These changes confirm ester formation. |
| Expected IR for Acid Product: | During Fischer esterification, the IR spectrum of the product (an ester) loses ugly broad O–H stretch (~2500–3300 cm⁻¹) that was present in the carboxylic acid. Additionally, the C=O stretch shifts higher from ~1715 cm⁻¹ (acid) to ~1740 cm⁻¹ (ester). |
| Ion-Exchange Resin: | It is essentially an immobilized form of p-toluenesulfonic acid, an organic-substituted sulfuric acid. This catalyst has the advantage that at the end of the reaction, it can be easily removed by filtration. |
| Ester IR Spectrum | C=O (carbonyl stretch): ~1740 cm⁻¹ Sharp, strong. C–O stretch (two peaks): ~1050–1300 cm⁻¹ Strong, often doublet. No O–H stretch. |
| Alcohol IR Spectrum | O–H stretch (hydrogen-bonded): ~3200–3600 cm⁻¹ Broad, strong. C–O stretch: ~1000–1250 cm⁻¹ Strong, varies slightly with structure. No C=O peak. |
| Acid IR Spectrum | O–H stretch: ~2500–3300 cm⁻¹ Very broad, overlaps with C–H stretches. C=O stretch (carbonyl): ~1700 cm⁻¹ Strong, sharp. Slightly lower than ester due to hydrogen bonding. C–O stretch: ~1210–1320 cm⁻¹ Medium to strong. |
| In order to ensure that the vapor condenses, you can... | Wrap a wet towel around the column. |
| What is occurring when reactants are mixed and heated and liquid collects in the sidearm of the apparatus? | Azeotropic distillation, aqueous layer is able to vaporize and condense in the side arm, while organic layer, which has a higher BP, remains in the flask. There should be a split of layers in the side arm and organic layer can be tipped. |
| What happens when you add the drying agent? | The mixture slowly became clear as the water was drained. The calcium chloride pellets, as anhydrous salts, were able to remove traces of water so that the byproduct would not interfere with purity or product collection. |
| What's the role of resin? | Assisting with water purification by binding water molecules or acting as a acid catalyst by speeding up esterification. |
| What indicates the purity of the product on the IR spectrum of the product? | The purity of the product on the IR spectrum is determined by whether your peaks are sharp and visible as well as whether they are in the right places. If the peaks were broader or further towards 3000 cm-1, there might be lingering reagents. |
| What causes impurities? | Lingering alcohols and acids or incomplete drying. |
| General Equation for Esterification | RCOOH + R'OH -> RCOOR' + H2O Carboxylic acid + alcohol -> ester + water |
| Structure of an Ester | COOR' (One O is double bonded and the other is attached to an alkyl group) |
| Draw the reaction for an alternative route of producing n-butyl acetate | -- |
| What should be the starting materials for synthesizing the ester on question 1 of the quiz? | -- |
| During the experiment, what did we do that shifted the equilibrium position towards the formation of ester? What technique did we use? | We removed the water, shifting the equilibrium to the right by taking away a product via condensation and heating. The technique we used was called azeotropic distillation, which involved constant boiling points. |
| Draw the reaction of the hydrolysis of the ester that we synthesized in our experiment (draw the structure of the reactants and products) | -- |
| Which catalyst did we use? | Dox Ion-exchange resin |
| Regulations for the apparatus. What detail was wrong on the quiz diagram? | Make sure that the side arm of the distillation apparatus is facing down and that you cork the side arm of the distillation head. In the quiz, the cork was too high; the cork should not block the top so pressure can be released freely. |
Created by:
smurtab