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8.3: Functions and Applications of Esters

Difficulty Level: At Grade Created by: CK-12
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The Controversy Surrounding Methyl Paraben

Methyl parabens are widely used in cosmetics.

One of the more controversial esters is methyl paraben. Its chemical formula is CH3(C6H4(OH)COO). This is an ester that is employed more for its preservation properties than for its distinctive smell. It is widely used in cosmetics, toothpastes, hair care products, moisturizers, and deodorants. It is also used as a food preservative and as a product to protect pharmaceuticals against fungal decay. The use of parabens in everyday products is so prevalent that scientists found in a random sampling that 96 out of 100 people had methyl parabens present in their urine.

Although it has been deemed safe for use by the United States Environmental Protection Agency, both Japan and Sweden have banned the use of parabens in any cosmetics due to potential health concerns. Many discoveries have come to light about the potential side effects of methyl paraben usage. One of these discoveries linked methyl parabens with breast cancer. In the study, twenty samples of breast cancer tissues were examined and were all found to contain parabens. Methyl paraben accounted for 62% of the parabens discovered in the samples. However, this does not conclusively prove that methyl paraben causes any harmful effects. Their presence in the tissue samples could simply be because methyl paraben is readily absorbed by skin contact. The study does demonstrate the need for further research on how parabens affect the human body.

One proven side effect of methyl paraben is oxidative stress. Oxidative stress describes the level of damage that has been done to the body by reactive oxygen species. Our bodies are constantly reacting with the oxygen that we breathe in, producing free radicals and peroxides. Under normal circumstances, we produce enough antioxidants to counteract this effect. However, external factors can cause a surge in oxidative stress. When this happens, it can lead to dangerous diseases such as Alzheimer’s and cancer. In one study done on the effects of methyl paraben on oxidative stress, skin cells were treated with methyl paraben containing creams. When exposed to the sun’s UVB rays, the skin cells died due to the oxidative stress that had occurred.

Researches found that this was because the sunlight had reacted with the methyl paraben to produce p-hydroxybenzoic acid (PHBA) and 3-hydroxy methyl paraben (MP-3OH). When the MP-3OH met with a skin esterase, which is an enzyme that splits esters into acids and alcohols, it was split into protocatechuic acid. This acid caused considerable amount of damage to DNA. Researches also noted that if the protocatechuic acid binds with NADH, a hydrogen carrier in the body, the oxidative damage is increased by five times.

What scientists find startling is how little is know about methyl parabens, yet parabens are widely used in products that come in direct contact with skin, such as pore strips and hair conditioners. Scientists know that this direct contact is enough for methyl parabens to transfer into the body and the bloodstream. However, scientists do not actually know what methyl parabens do once they get inside the body.

ACTIVITY: Methyl Paraben in Cosmetics

Methyl parabens are a popular component of many cosmetics and hair products. Take a look at the cosmetics and hair products in your own house to see if methyl paraben is present in the ingredients.

How many of your products contain methyl parabens? How often do you use these products?

Ethyl Acetate and Wine

Ethyl acetate is the best known of the esters, especially in the wine industry. It has the formula of CH3COOCH2CH3. It is a colorless liquid with a “fruity” smell. Ethyl acetate is used as a solvent in many products, such as oil-based lacquers and enamels.

Ethyl acetate causes an unpleasant “nail polish” scent in wines.

However, ethyl acetate is probably best known for its presence in wine. In wine grapes, sometimes aerobic bacteria enter the grape through “wounds” and create acetic acid. During fermentation, this acetic acid comes in contact with ethanol. This starts off the esterification process that creates ethyl acetate. Although barely perceptible amounts of ethyl acetate occasionally add to the “fruitiness” of the wine, it is generally viewed as a wine fault if there is ethyl acetate present. In large amounts, it gives the wine the unpleasant aroma of nail-polish remover.

Ethyl acetate is also used for coffee decaffeination. After the coffee beans are soaked in water, the caffeine is extracted by adding ethyl acetate to the water. Ethyl acetate is used because of its low boiling point of 77°C (171°F) and its ability to bind with both water and caffeine. It is able to decaffeinate the coffee without affecting the taste of the beans. When the coffee beans are drained, a solution of ethyl acetate, caffeine, and water is removed. This process is repeated multiple times until the coffee beans are completely decaffeinated.

Ascorbyl Palmitate Versus Vitamin C

Ascorbyl palmitate is the ester form of Vitamin C. It provides most of the same benefits to the human body as Vitamin C does. However, because ascorbyl palmitate is an ester, it is soluble in both fats and water. This solves one of Vitamin C’s inherent issues: Vitamin C is only soluble in water and thus cannot stay in the body. This makes it so that all surplus Vitamin C is removed form the body and must be continually added. Unlike Vitamin C, ascorbyl palmitate is able to bind with lipid cell membranes, which are made up of fats. This allows the body to store it up and access it when it is needed. Ascorbyl palmitate’s fat solubility also makes it extremely easy for it to penetrate cells and skin. Vitamin C is unable to access many parts of the body, such as adipose tissue and the brain. However, ascorbyl palmitate can be absorbed by cells and skin and can enter the bloodstream to quickly access the parts of the body that Vitamin C is unable to enter. This makes ascorbyl palmitate invaluable as a medicine. It is also a stronger antioxidant than Vitamin C. In the body, ascorbyl palmitate is able to bind with Vitamin E because of their similar fat-soluble properties. Once bounded, ascorbyl palmitate protects the Vitamin E from oxidation.

Another benefit of ascorbyl palmitate over traditional Vitamin C is that it does not irritate the skin. Traditional water-soluble Vitamin C is irritating to the skin and often causes rashes or inflammation. However, ascorbyl palmitate has none of these side effects and also has collagen strengthening and antioxidating properties. It is also readily absorbed through skin contact. For these reasons, ascorbyl palmitate is often a major component of skin care products. The downside of ascorbyl palmitate that hinders it from being widely used is its economic costs. Ascorbyl palmitate is much more expensive than traditional Vitamin C and ascorbic acid. Because many of the benefits of ascorbyl palmitate are already covered by both Vitamin C and ascorbic acid, it is less cost-effective for industries to use the more expensive ascorbyl palmitate.

The Bitterest Chemical on Earth

Denatonium benzoate, with the chemical formula C6H4(CH3)2NHCON(C2H5)2C6H5COOC6H5, is a very special ester. It is the bitterest, nontoxic chemical on earth. Because of these two properties, denatonium benzoate is often added to harmful chemicals in order to prevent people from consuming them. It only takes 10 ppb (parts per billion) for people to be able to detect denatonium benzoate. Most countries recommend 4-40 ppm (parts per million), about 10 times more than the threshold detectable amount, to be added to harmful chemicals as a deterrent. Denatonium benzoate is added to hundreds of different chemicals, from air fresheners and fertilizers, to hair dye and liquid potpourri.

One of the reasons that denatonium benzoate works so well as a deterrent is because, through evolution, humans have developed an extreme aversion to bitter flavors, which often are the mark of poisonous plants. Children are especially sensitive to it.

Denatonium benzoate has been branded under the name Bitrex®. If you would like to see its official website, it is located at:


Methyl Formate and Space

Methyl formate has been discovered in the comet Hale Bopp.

In spring 1997, scientists identified methyl formate by analyzing ten lines in the spectra of the comet Hale Bopp. With a chemical formula of C2H4O2, methyl formate is the simplest ester. Some of its important attributes are its high vapor pressure, solubility in water, and miscibility in most organic compounds. This makes it useful as a solvent in quick drying coating finishes and spray applications. Methyl formate can be added to these solutions because it is soluble in water. When the methyl formate in the solution is exposed to the outside environment, its high vapor pressure will be able to overcome the forces acting on it from environmental pressure and intermolecular forces. This will make it evaporate very quickly, causing the “quick drying” property of many of the coating finishes and spray applications.

Methyl formate has also been located in space. Scientists have found its gas form in large quantities in the clouds that dot our Milky Way galaxy. They estimate that a typical dust cloud would contain a thousand trillion trillion (1027) gallons of the liquid form of methyl formate. This discovery sheds new light on the creation of stars, suggesting that there are more molecules at work than scientists had previously estimated.

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