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A study of esterification reactions

A study of esterification reactions

Introduction: (Initial Observation)

Perfumes and fragrances are among the most widely used chemical substances. Fragrances produce a pleasant odor for body, room, and consumer products. Historically fragrances are extracted from flowers and herbs; however, synthetic version of many of such fragrances are now being produced as well. Interestingly enough, many of these fragrances are esters.

Esters are compounds formed by a combining an alcohol and an acid. An esterification is a reaction which achieves this. An example is the production of methyl benzoate (Artificial flavor/ Essence of Niobe) from methanol and benzoic acid.

Varieties of esters form the ingredients of most artificial flavors, fragrances, and perfumes.

Some esters can polymerize and form plastic fibers and sheets. Plexiglas is among such polymers.

Because of the importance of esters and so many applications that they have, in this project I will study esterification. I would like to know how easy it is to make esters and learn about the procedures, conditions, and requirements of making esters.

Dear

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Objectives:

  1. To acquaint you with the many natural foods and plants that contain an ester.
  2. To learn what an ester is in chemistry.
  3. To learn how an ester is synthesized in the laboratory.

Information Gathering:

Find out about esters and their applications. Read books, magazines or ask professionals who might know in order to learn about esterification as a method of producing many synthetic fragrances. Keep track of where you got your information from.

Following are samples of information that you may find:

Esters are compounds formed by combining an alcohol with an acid, with a molecule of water being taken out. An esterification is a reaction which achieves this. An example is the production of methyl benzoate from methanol and benzoic acid. A concentrated acid catalyst speeds up esterification reactions. The converse, splitting an ester by reaction with water to form the alcohol and the acid, is a form of hydrolysis

Esters encompass a large family of organic compounds with broad applications in medicine, biology, chemistry, and industry. The structure is represented by the following arrangements of atoms:

Atom arrangement in an Ester

(R and R’ represent different arrangements of carbon and hydrogen)

Esters are widespread in nature. They occur naturally in plants and animals. Small esters, in combination with other volatile compounds, produce the pleasant aroma of fruits. In general, a symphony of chemicals is responsible for specific fruity fragrances; however, very often one single compound plays a leading role. For example, an artificial pineapple flavor contains more than twenty ingredients but ethyl butyrate is the major component that accounts for the pineapple-like aroma and flavor. It is amazing that so many fragrances and flavors can be prepared by simply changing the number of carbons and hydrogens (the R groups) in the ester.

The following table gives some ester flavors and fragrances (notice the similarities/differences in the R groups):

Name Chemical Structure Flavor or Fragrance
Propyl acetate Pears
Octyl acetate Oranges
Isoamyl acetate Banana
Ethyl Butyrate Pineapple
Butyl acetate Apple
Amyl Acetate C 7 H 14 O 2 Pear
Isoamyl acetate C 7 H 14 O 2 banana
Amyl Butyrate C5 H11OOCC3H7 apricot
Methyl trans-cinnamate Strawberry

Some esters play an important role in insect communication. Isoamyl acetate, the main component of banana aroma, is also the alarm pheromone of the honeybee. (Z)-6-dodecen-4-olide, a circular ester, is the “social scent” of the black-tailed deer. Circular esters (called lactones) are also found in the oily poisonous secretion of termites.

Esters also have remarkable applications in everyday life. Plexiglas is a stiff, transparent plastic made of long chains of esters. Dacron, a fiber used for fabrics, is a polyester (‘many esters’).

Plexiglas
Dacron

Esters derived from p-aminobenzoic acid (PABA) have local anesthetic properties. Benzocaine and procaine are chemicals used in medicinal preparations to alleviate pain caused by skin burns.

Benzocaine
Procaine

Hopefully this brief overview of Esters will help you appreciate the diverse nature of aromas and flavors.

THE MECHANISM FOR THE ESTERIFICATION REACTION

This page looks in detail at the mechanism for the formation of esters from carboxylic acids and alcohols in the presence of concentrated sulphuric acid acting as the catalyst. It uses the formation of ethyl ethanoate from ethanoic acid and ethanol as a typical example.

The mechanism for the formation of ethyl ethanoate

A reminder of the facts

Ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid as a catalyst to produce the ester, ethyl ethanoate. The reaction is slow and reversible. To reduce the chances of the reverse reaction happening, the ester is distilled off as soon as it is formed.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to experiment and learn about esterification for producing artificial flavors and fragrances.

After you successfully make some esters, you may optionally want to study on any specific question related to esterification. Following are some sample questions:

  1. How does sulfuric acid affect the rate of esterification reaction?
  2. How does the temperature affect the rate of esterification reaction?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

For question number 1:

Independent variable is the amount of sulfuric acid

dependent variable is the rate of reaction

Controlled variables is the temperature

Constants are type, quality and concentration of acid and alcohol as well as method, procedures, and instruments.

For question number 2:

Independent variable is the reaction temperature

dependent variable is the rate of reaction determined by the strength of odor

Controlled variables is none

Constants are:

  • Reaction time
  • Amount, type, quality and concentration of acid, alcohol and sulfuric acid
  • Method, procedures, and instruments.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following are two sample hypotheses.

For question number 1:

Without presence of sulfuric acid, the esterification process will not happen or it will be very slow.

For question number 2:

Temperature has no effect on the rate of esterification reaction.

It is best if your hypothesis is more descriptive than above samples. It is also good to write what is the base of your hypothesis.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Prepare yourself:

1. Try to detect smells of known objects as they are displayed in a hidden form, covered with cheesecloth.

2. See how some plants have a natural odor, eg., sweet alyssum, herbs, etc.

3. Explain what an ester is:

organic acid + alcohol (using sulfuric acid as a catalyst) ” ester + water

Experiment 1:

Make an ester by using fresh peas, brown sugar and some apple.

apple

Procedure:

Get equal amounts of brown sugar, fresh peas and slices of apple. Mix them in a blender to form a soft paste. Smell the mixture. How does it smell?

This mixture, when blended together, will smell, but not taste, like strawberries.

Note: I am not sure that this strawberry odor is from Methyl trans-cinnamate as you have seen above. This experiment shows that mixtures of organic substances may produce esters with specific fragrances.

Experiment 2:

Introduction:

Make a synthetic ester in the lab using one of the following formulas:

acid alcohol sulfuric acid essence
1 gram salicylic acid 2 mL methyl alcohol 8 -10 drops wintergreen
3 mL acetic acid 2 mL octyl alcohol 10 -15 drops orange
4 mL formic acid 2 mL ethyl alcohol 20 drops rum
2 mL butyric acid 2 mL ethyl alcohol 15 -20 drops pineapple
2 mL butyric acid 2 mL methanol 15 -20 drops apple

Procedure:

1. Prepare a hot water bath by filling 1/2 of a 400 mL beaker with water and, placing it on a hot plate, heat it to a point where it is slightly boiling.

2. Look at the formula of the acid-alcohol combination you want to make in the above table. Add the amounts of acid and alcohol that you need in a test tube.

3. Into that solution add the catalyst, sulfuric acid.

4. Then you will place the test tube into the hot water bath for about one minute.

5. Waft the odor and notice the essence. Then place this essence in a small amount of hot water. This will help diffuse the odor throughout the room.

Note: This solution is acidic at this time. In a larger scale production, pure seeence is then separated by distillation.

Performance assessment:

1. What essence have you made using the formula that was given?

________________________________________

2. What is the difference between a natural and a synthetic essence?

________________________________________

3. You have been named to the head of the perfume department at Marshall Field’s. Among the numerous essences under your authority, the CEO has asked that you assemble them according to natural and synthetic fragrances. Since many people today are going back to the natural, it is very important that you do this correctly. What factors would you use to assemble them in their proper section? Name some of the products that can be placed under natural, then name some under synthetic (Optional).

What you learn from this project?

By successful completion of this project you will understand the difference between natural and synthetic essences. You will be able to look at the labels of different fragrances and determine if there is an ingredient having an “yl” (for the alcohol ending) and an “ate” ending (for the acid), then they must have a synthetic fragrance.

Experiment 3:

Introduction:

How does sulfuric acid affect the rate of esterification reaction?

Procedure:

Repeat experiment number 2 with no sulfuric acid and then again with different amounts of sulfuric acid (0 drops, 1 drop, 2 drops, 3 drops,…).

Smell the product and compare the results.

Experiment 4:

Introduction:

How does the temperature affect the rate of esterification reaction?

Procedure:

Repeat experiment number 2 with different temperatures of water bath (Ice cold, warm, hot, boiling).

Smell the product and compare the results.

Materials and Equipment:

List of what you need.

  1. Alcohols, organic acids, sulfuric acid
  2. Beaker for hot water bath
  3. Test tube racks
  4. Grease pencil for marking test tubes
  5. Graduated cylinder and/or plastic syringe
  6. Hot plate
  7. Stirring rods
  8. Gloves
  9. Goggles
  10. Pipette

All alcohols, organic acids and sulfuric acid may be purchased from a local scientific supplier. You may locate a scientific supplier near you by looking up your local phonebook or online phone directory superpages.com. Sulfuric acid also known as battery acid may be found at auto-parts stores. You need very little sulfuric acid; if you know a local chemist, you may be able to get it free. For methyl alcohol, ethyl alcohol, and Isopropyl alcohol supermarkets and pharmacies are good sources. Laboratory supplies such as test tubes may be purchased from MiniScience.com. Organic acids can also be purchased from scientific suppliers.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

No calculation is required.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and find organic chemistry books with chapters or sections about esters and esterification. You may also try books in chemistry section related to perfumes, fragrances or essential oils.

Following are some web links.

http://www.ausetute.com.au/esters.html

http://www.leffingwell.com/esters.htm

http://departments.oxy.edu/tops/Esters/esterspre-post.htm

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