"A very helpful volume identifying unusual and practical applications of chemical compounds." —Choice
Why There's Antifreeze in Your Toothpaste: The Chemistry of Household Ingredientsby Simon Quellen Field
A Selection of the Scientific American Book Club
Explaining why antifreeze is a component of toothpaste and how salt works in shampoo, this fascinating handbook delves into the chemistry of everyday household products. Decoding more than 150 cryptic ingredients, the guide explains each component's structural formula, offers synonymous names, and describes
A Selection of the Scientific American Book Club
Explaining why antifreeze is a component of toothpaste and how salt works in shampoo, this fascinating handbook delves into the chemistry of everyday household products. Decoding more than 150 cryptic ingredients, the guide explains each component's structural formula, offers synonymous names, and describes its common uses. This informative resource can serve curious readers as a basic primer to commercial chemistry or as an indexed reference for specific compounds found on a product label. Grouped according to type, these chemical descriptions will dissolve common misunderstandings and help make consumers more product savvy.
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Why There's Antifreeze in Your Toothpaste
The Chemistry of Household Ingredients
By Simon Quellen Field
Chicago Review Press IncorporatedCopyright © 2008 Simon Quellen Field
All rights reserved.
Preservatives have become the favorite target of people who want you to fear your food. Most preservatives are things you would not want to eat. Most preservatives taste bad and are toxic in large quantities, so it is not surprising that they have a bad reputation.
Preservatives generally fall into four categories. There are ultraviolet/UV light absorbers (to prevent light from creating harmful and bad-tasting toxins), color stabilizers, antioxidants, and antimicrobials.
One excellent UV protector for foods is PABA, a B vitamin. Likewise, many of the same antioxidants we ingest as health supplements — such as vitamin C and a similar chemical, erythorbic acid; vitamin E; and lecithin, a source of the important nutrients choline and inositol — occur naturally in food.
Some simple foods can be preservatives in their own right. Honey, salt, sugar, lactic acid, and vinegar are all examples of foods that inhibit microbial action. Some health professionals recommend consuming phytoestrogens from foods such as soybeans to achieve various health benefits. The phytoestrogens in the paraben family, found in blueberries, kill molds and fungi and are often added to food as preservatives.
But you don't have to choose between having sodium benzoate or E. coli bacteria in your soda. Bacteria can be controlled through pasteurization, a process that is used for milk but for some reason not for soft drinks.
Ultraviolet Light Absorbers
Diphenyl ketone benzoyl benzene phenyl ketone diphenylmethanone alpha-oxodiphenylmethane alpha-oxoditane
White crystals with a rose- or geranium-like odor.
Benzophenone is used to prevent ultraviolet light from damaging scents and colors in products such as perfumes and soaps. It allows the manufacturer to package the product in clear glass or plastic. Without it, opaque or dark packaging would be necessary.
It can also be added to the plastic packaging itself as a UV blocker.
Benzophenone is also sometimes used as a flavoring agent.
Ultraviolet light is often divided into two types, UV-A, which has a longer wavelength (320–360 nm) and UV-B, which has a shorter wavelength (280–320 nm). Shorter wavelengths are higher energy wavelengths. UV-B is more damaging than UV-A. Some UV blockers are optimized to block the shorter wavelengths while letting the longer wavelengths get through.
There are many variants of benzophenone. They often have numbers after the name, a type of shorthand to indicate which variant is in use. The variations change features, such as solubility or the ease and functionality of bonding with plastics used in packaging. For example, benzophenone-2 is used in alcohol-based products, while benzophenone-5 is used in water-based products. Benzophenone-6 is used in nail polish, and benzophenone-9 is used in bath and skin-care products.
Some examples are shown below.
Benzophenone-3 can be added to plastic packaging as a UV blocker.
Benzophenone-4 (2-benzoyl-5-methoxy-1-phenol-4-sulfonic acid)
Benzophenone-4 is a water-soluble form used in cosmetics, hair-sprays, and hair dyes.
Benzophenone-bx-ahbp (4-allyloxy-2-hydroxy benzophenone)
This form of benzophenone is also added to plastic packaging as a UV blocker. It bonds with the plastic and will not migrate out.
Benzophenone-1 (2,4-dihydroxy benzophenone)
Benzophenone-2 (2,2',4,4'-tetrahydroxy benzophenone)
Benzophenone-5 (2-hydroxy-4-methoxy-5-sulfonyl benzophenone sodium salt)
Benzophenone-6 (2,2'-dihydroxy-4,4'-dimethoxy benzophenone)
Benzophenone-9 (2,2'-dihydroxy-4,4'-dimethoxy benzophenone-5,5'disulfonate sodium)
Benzophenone-12 (2-hydroxy-4-N-octoxy benzophenone)
Other UV Blockers
Amyl p-methoxy cinnamate
Octyl p-methoxy cinnamate
Para-amino Benzoic Acid
PABA 4-aminobenzoic acid p-aminobenzoic acid ethoxylated ethyl 4-aminobenzoic acid (PEG-25 PABA)
Para-amino benzoic acid (PABA) is considered to be in the B-complex vitamin family. The human body can make it from folic acid, since PABA forms the middle part of that vitamin:
This means that in the strictest sense, PABA is not a vitamin, because the body can manufacture it. But in this sense, too, vitamin A is not technically a vitamin, as the body makes that from beta-carotene.
Bacteria in the intestines produce folic acid if there is PABA present. Microbes need PABA, but it is not strictly necessary for humans. A class of drugs that simulate PABA, sulfa drugs, can fool the microbes into trying to use them instead of PABA, which causes them to die. This is why people taking sulfa drugs are advised not to take PABA at the same time.
PABA is taken orally in vitamin supplements. However, its widest use is as a sunscreen. Taking it orally will not protect a person from the sun; as a sunscreen PABA acts as a topical dye that absorbs ultraviolet light. To block UV rays from the sun, a person needs to paint it directly onto the skin.
PABA is acidic, which means it can sting if it gets in the eyes. Some people are sensitive to PABA when it is applied to their skin. PABA also darkens and can stain clothing. For these reasons, modified forms of PABA have become popular as sunscreens. PABA can be reacted with long-chain alcohols to form PABA esters, such as polyethylene glycol 25 PABA:
This PABA molecule eliminates the irritation and staining problems. Other PABA esters are glycerol PABA, padimate A, and padimate O.
Molecules absorb light when the light's wavelength is just the right length to cause electrons in the molecule to vibrate in time with the light. The electrons resonate in the molecule.
In some molecules, the electrons are not bound to a single atomic nucleus but instead roam free across several nuclei in what are called resonance bonds. You may notice that sometimes a six-sided ring is shown with alternating double and single bonds, while at other times it is shown with a circle inside. Both forms are showing the same thing. The circle just draws attention to the fact that the bonds don't really alternate between double and single — they are more like one and a half bonds. On average, the electron spends half of the time in one place, and half in the other.
In para-amino benzoic acid, there is another resonance structure right next to the six-sided ring. It is a carboxyl group, shown with a single bond between carbons, and a double bond between the carbon and the oxygen. This is also a place where the electron can bounce around between the three nuclei.
It is even possible for an electron to move back and forth across all of the resonance bonds — from one end of the molecule to another. This lets the electron slosh back and forth like water in a bathtub. In the case of para-amino benzoic acid, the rhythm of the sloshing matches the frequency of UV-B light. The electron can move in time with the light wave and absorb its energy. The energy is later released as photons of longer wavelength light such as heat. Knowing this, chemists can design other molecules that have resonance structures that will catch UV-B rays. One such molecule is benzophenone, and a derivative called benzophenone3, also known as oxybenzone.
Notice that both molecules have the six-sided ring, called a benzine ring, and a carboxyl group (the carbon-oxygen double bond). These molecules also protect against UV-A. You can see that they have longer chains of resonance bonds, which means that they will resonate at longer wavelengths.
Getting more creative with the chemistry, a chemist can add other desirable features to these molecules. Adding long chains of hydrocarbons can help it mix better with suntan oils to spread more easily on the skin. The resonance bonds can be modified a little bit to get a broader absorption range, expanding into the longer wave UV-A region.
Such a designer molecule is octocrylene and a similar one known as avobenzone.
Other molecules with the benzine ring and carboxyl group also have side chains added to make them better sunscreens. Two popular ones are 2-ethylhexyl salicylate:
and homomethyl salicylate, also known as homosalate:
Other salicylates used as sunscreens are 4-isopropylbenzyl salicylate, and triethanolamine salicylate, which goes by the trade name Trolamine Salicylate.
Another class of UV-B absorbers is the cinnamates.
These molecules are not water soluble, are able to stick to the skin well, and are highly effective in water-resistant sunscreens. Others in this family are isopentenyl-4-methoxycinnamate, also known as isoamyl 4-methoxycinnamate, and cinoxate.
As you can see, there are many molecules that will absorb ultraviolet light. There are many more in use than I have described here. But they all have resonance bonds in common.
Zinc oxide is a white powder that makes a very opaque paste when mixed with water or oils. It is used as a sunblock and as a colorant in toothpastes and cosmetics. Zinc oxide is used in many of the same products as titanium dioxide.
Chemical Formula TiO2
Titanium dioxide makes a very opaque paste when mixed with water or oils. It is used as a sunblock and as a colorant in toothpastes and cosmetics. Titanium dioxide is used in many of the same products as zinc oxide.
Acrid gas produced when sulfur is burned in air.
Sulfur dioxide is a reducing bleach and can counter the effects of oxidizing bleaches, thus preserving color in fruits dried in the sun. The combination of fruit acids and ultraviolet light would otherwise react with the colorful compounds, making the fruit pale.
Sulfur dioxide is produced by burning sulfur in air for preserving fruit, or by reacting sodium bisulfite in water as part of the process to make products such as wine.
Sulfur dioxide also kills yeasts, molds, and bacteria.
Monosodium sulfite sodium hydrogen sulfite sodium sulhydrate sulfurous acid sodium salt
Clear or milky white liquid with a sulfurous odor.
Sodium bisulfite is used in almost all commercial wines to prevent oxidation and preserve flavor. It releases sulfur dioxide gas when added to water or products containing water. The sulfur dioxide kills yeasts, fungi, and bacteria in grape juice before fermentation. When the sulfur dioxide levels have subsided, after about twenty-four hours, fresh yeast is added for fermentation.
Sodium bisulfite is often combined with an acid such as citric acid to make it produce gas faster. It is also used to sterilize winemaking equipment. It is later added to bottled wine to prevent oxidation, which would change the wine to vinegar and cause it to turn brown. The sulfur dioxide displaces oxygen in the bottle and dissolves in the wine. Without it oxidized wine can turn orange or brown and taste like raisins or cough syrup.
In fruit canning, sodium bisulfite is used to kill microbes and to prevent the browning caused by oxidation.
Light yellow liquid.
Vitamin E is added to some food products as a nutrient, but it is better known for its antioxidant properties, which protect oils and fats from oxidation.
Tocopherols come in various forms only slightly different from the a-tocopherol shown in the structural formula above. Its ß and ? forms differ in where the methyl groups are attached to the ring structure. An ingredients list may single out the a form, or may just list "mixed tocopherols."
Sour-tasting white powder.
Ascorbic acid — vitamin C — is an essential nutrient that the human body cannot manufacture from other compounds. It is needed for the formation of collagen, the protein that makes up connective tissue, and is essential to muscles, bones, cartilage, and blood vessels. It is a strong antioxidant, preventing damage from oxygen free radicals.
Ascorbic acid is added to many foods for its nutritive value. It is used extensively as an antioxidant to prevent flavors and colors from being damaged by oxidation. It is often used in canned or frozen fruits to prevent the browning that accompanies oxidation. While not as powerful an antioxidant as sodium bisulfite, it has a better nutritional reputation.
An isomer (molecule with the same number and type of atoms but in a different formation) of ascorbic acid called erythorbic acid is often used as a less expensive antioxidant than ascorbic acid. It has little or no effect as a vitamin, but it has the same antioxidant properties.
To make ascorbic acid soluble in fats, it is reacted with fatty acids, such as palmitic acid, to form ascorbyl palmitate. This is used to prevent oxidation in fats and oils.
See Ascorbic Acid entry, page 15.
BHA 2-tert-butyl-4-hydroxyanisole 3-tert-butyl-4hydroxyanisole
White or slightly yellow waxy solid.
BHA is an antioxidant. It reacts with oxygen free radicals. It can thus slow down the rate at which ingredients in a product oxidize in direct contact with air, a process that can cause changes in the taste or color. BHA can be added to the food itself, or to the packaging material, and it is used primarily to prevent fats from becoming rancid.
BHT 2,6-di-tert-butyl-4-methylphenol dibutylated hydroxytoluene
White crystals or crystalline powder.
BHT is an antioxidant. It reacts with oxygen free radicals. It can thus slow down the rate at which ingredients in a product oxidize in direct contact with air, a process that can cause changes in the taste or color. BHT can be added to the food itself, or to the packaging material, and it is used primarily to prevent fats from becoming rancid.
Viscous yellow liquid.
Honey is primarily fructose and glucose (in that order), with a little sucrose (about 1 percent), less than 10 percent other sugars, and about 17 percent water.
Honey's water content is high enough that it remains liquid, but low enough to make it thick and prevent spoilage. Because it contains relatively little water, microorganisms that encounter it die as the water in them is extracted by osmosis. In addition, as honey is diluted with water, a chemical reaction between glucose, water, and oxygen produces small amounts of hydrogen peroxide and gluconic acid. The slow release of hydrogen peroxide makes honey a mild antiseptic. The acidity of honey also reduces the number of organisms that can live in it.
Honey is mostly used as a sweetener, but it can also function as an antiseptic for wounds and as a preservative.
White odorless crystals.
Sodium citrate is used in ice cream to keep the fat globules from sticking together. Citrates and phosphates both have this property. It is also an anticoagulant.
As a buffering agent, sodium citrate helps maintain pH levels in soft drinks.
As a sequestering agent, it attaches to calcium ions in water, which keeps them from interfering with detergents and soaps.
Compounds with similar functions are sodium carbonate, sodium EDTA, phosphoric acid, pentasodium pentetate, tetrasodium etidronate, and tetrasodium pyrophosphate.
Light brown or yellow solid.
Lecithin is a phospholipid, a class of compounds that make up cell membranes throughout the body. It is produced in the liver if the diet contains enough of the raw ingredients.
Lecithin is widely used as an emulsifying agent, allowing oil and water to mix. It is used in ice creams, salad dressings, and cosmetics, and it is the main ingredient in nonstick cooking sprays. Lecithin is the emulsifier in egg yolks that allows the oil and water to mix to make mayonnaise.
Lecithin is also an antioxidant, helping to keep fats from going rancid (but in the process, going rancid itself).
Lecithin is often taken as a dietary supplement, since it contains the B vitamin choline.
Excerpted from Why There's Antifreeze in Your Toothpaste by Simon Quellen Field. Copyright © 2008 Simon Quellen Field. Excerpted by permission of Chicago Review Press Incorporated.
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Meet the Author
Simon Quellen Field is the author of Gonzo Gizmos and Return of Gonzo Gizmos and the creator of the popular website www.scitoys.com.
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