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Esters – structure and properties

Source: www.pixabay.com, licencja: CC 0.

Link to the lesson

Before you start you should know
  • what structure and properties alcohols and carboxylic acids have.

You will learn
  • what the esters are;

  • to describe the structure of esters;

  • what the esterification reaction consists in;

  • to write the equation for the reaction between carboxylic acids and monohydric alcohols;

  • to name esters;

  • to design an experiment to obtain an ester;

  • what the properties and uses of esters are.

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Nagranie dźwiękowe abstraktu 
Task 1

Watch the video and find out how esters are obtained.

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Film pokazuje eksperyment, jak powstają estry, making esters. Potrzebne substancje oraz naczynia laboratoryjne: kwas metanowy, stężony roztwór kwasu siarkowego sześć, etanol, probówka, łaźnia wodna, zlewka z zimną wodą, palnik, pipeta. Do probówki wkrapiamy kilka kropli kwasu metanowego. Dodajemy etanol i stężony kwas siarkowy sześć. Probówkę zanurzamy w gorącej łaźni wodnej. Po pewnym czasie wlewamy roztwór z probówki do zlewki z zimną wodą. Eksperymentator wącha roztwór.
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Jasmine flower
Source: A. Barra, Wikimedia Commons, licencja: CC BY-SA 3.0.

The structure and naming of esters

EstersestersEsters are compounds composed of carbon, hydrogen and oxygen atoms.

General formula for esters is R1COOR2

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General formula of esters
Source: Dariusz Adryan, Wikimedia Commons, licencja: CC BY 3.0.

R1 – hydrocarbon group derived from carboxylic acid
R2 – hydrocarbon group derived from alcohol

Group – COO – is called the ester group.

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Ester group
Source: Dariusz Adryan, Wikimedia Commons, licencja: CC BY 3.0.
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Exercise 1
Przypomnij sobie tytuł abstraktu, wysłuchaj nagrania i spróbuj zaproponować własny temat dla dzisiejszej lekcji.
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Exercise 2
Wymyśl pytanie na kartkówkę związane z tematem abstraktu.

Examples of esters with a characteristic odour.

Esterification

In previous lessons you learned about the structure and properties of two important groups of organic compounds: alcohols and carboxylic acids. Remember their structure.

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Carboxylic acids and alcohols
Source: Dariusz Adryan, Wikimedia Commons, licencja: CC BY 3.0.

The reaction of carboxylic acid and alcohol produces estersestersesters. This reaction is called an esterification reactionesterificationesterification reaction.

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Równanie reakcji estryfikacji. kwas karboksylowy reaguje z alkoholem strzałki w obie strony, nad górną wzór kwasu siarkowego sześć. W wyniku reakcji powstaje ester i woda. Opis: the substrates of the esterification reaction are carboxylic acids and alcohols - in this case ethanoic acid and methanol. Sulphuric acid acts as a catalyst and is necessary to carry out this reaction; arrows in both directions - the esterification reaction is a reversible process; products - as a result of the reaction, ester and water molecule are formed; water molecule - results from the combination of the o ha group of the acid molecule and hydrogen atom of the alcohol hydroxyl group
Source: GroMar Sp. z o.o., licencja: CC BY-SA 3.0.

General equation for the esterification reaction:

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Estersification scheme
Source: Krzysztof Jaworski, Wikimedia Commons, licencja: CC BY 3.0.

R1 – hydrocarbon group derived from carboxylic acid
R2 – hydrocarbon group derived from alcohol

Important!

Formic acid esters HCOOH do not contain a hydrocarbon group derived from acid. Instead, the molecule contains a hydrogen atom.

Properties and uses of esters

In order to examine the properties of esters, we will perform an experiment which will result in ethyl acetate.

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Properties of lower carboxylic acid esters liquids sparingly soluble in water characteristic aromas (fruity or floral) well soluble in organic solvents, Application of esters good solvents for paints and varnishes nail polish removers production of perfumes and cosmetics production of essential oils production of artificial flavors
Task 2

Before you conduct experiment, formulate research question and hypothesis.

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Wykonaj ćwiczenie zgodnie z poleceniem.
Acetic acid reaction with ethanol in the presence of concentrated sulfuric acid
Experiment 1
Research problem

Will the product of acetic acid reaction with alcohol be a substance that dissolves well in water?

Hypothesis

The reaction product will be dissolving well in water.

You will need
  • test tube,

  • beaker,

  • burner,

  • dropper,

  • ethanol,

  • acetic acid,

  • concentrated sulfuric acid,

  • water.

Instruction
  1. Pour 2 cmIndeks górny 3 of ethyl alcohol and acetic acid each into a tube.

  2. Add a few drops of concentrated sulfuric acid.

  3. Insert the tube with the mixture in the beaker with hot water and leave it for a few minutes.

  4. Pour the liquid from the tube into cold water.

Summary
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Observations (Uzupełnij). Conclusions (Uzupełnij).

The use of lower esters of carboxylic acids results from their properties.

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Exercise 3
Assign corresponding ester names to the statements: methanol + ethanoic acid Możliwe odpowiedzi: 1. ethyl formate, 2. butyl butanoate, 3. propyl acetate, 4. methyl butyrate, 5. methyl ethanoate ethanol + formic acid Możliwe odpowiedzi: 1. ethyl formate, 2. butyl butanoate, 3. propyl acetate, 4. methyl butyrate, 5. methyl ethanoate propanol + acetic acid Możliwe odpowiedzi: 1. ethyl formate, 2. butyl butanoate, 3. propyl acetate, 4. methyl butyrate, 5. methyl ethanoate butanol + butanoic acid Możliwe odpowiedzi: 1. ethyl formate, 2. butyl butanoate, 3. propyl acetate, 4. methyl butyrate, 5. methyl ethanoate methanol + butyric acid Możliwe odpowiedzi: 1. ethyl formate, 2. butyl butanoate, 3. propyl acetate, 4. methyl butyrate, 5. methyl ethanoate

Conclusion

  • Esters are an important group of compounds in living organisms.

  • Esters are obtained as a result of esterification reaction, i. e. reaction of carboxylic acids with alcohols.

  • In the esterification reaction sulfuric acid acts as a catalyst, i. e. accelerates the reaction process.

  • General formula for esters is R1COOR2, and the characteristic group is the ester group COO –.

  • Esters are slightly soluble in water, but dissolve well in organic solvents and are therefore used as solvents for paints and varnishes.

  • Some esters have a pleasant smell and these are used, among others, in the production of perfumes and essential oils.

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Grafika przedstawiająca tablicę szkolną, na której znajdują się zdania do dokończenia. Finish selected sentences. 1 It was easy for me (uzupełnij). 2 It was difficult for me (uzupełnij). 3 Today I learned (uzupełnij). 4 I understood that (uzupełnij). 5 It surprised me (uzupełnij). 6. Today I found out (uzupełnij). 7. I was interested in (uzupełnij). 8. I still have to repeat (uzupełnij).
Source: GroMar Sp. z o.o., licencja: CC BY-SA 3.0.

Keywords

esters, esterification, carboxylic acid, alcohol

Glossary

esters
esters
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Nagranie dźwiękowe słówka 

estry – związki chemiczne zawierające grupę estrową – COO –; powstają w wyniku reakcji estryfikacji

esterification
esterification
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Nagranie dźwiękowe słówka 

estryfikacja – reakcja kwasów karboksylowych z alkoholami zachodząca w obecności kwasu siarkowego(VI); w jej wyniku otrzymujemy estry