Formulation Chemistry

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Formulation chemistry is the branch of manufacturing that addresses substances that do not react with each other, but have desirable properties as a mixture. These products include paints, varnishes, cosmetics, petroleum products, inks, adhesives, detergents, pesticides, and a broad range of household products.

Successful formulation requires a blend of art and science. Components are chosen for compatibility rather than reactivity. Formulation chemists think in terms of kilograms or tons rather than moles and place more emphasis on solubility than molecular weight.

Paints

Paints are suspensions of pigments, binders, drying agents, and vehicles. Vehicles are solvents in which the pigment is mixed. Pigments are powders made from insoluble chemicals, such as titanium dioxide, that give color to the preparation. Titanium and zinc oxides have largely replaced lead pigments in paint.

Binders bind pigments to surfaces. They solidify by drying, cooling, or reacting to produce polymers. Acrylic paints use polymer resins as vehicles. They can be thinned with water, but dry readily. Drying agents aid in the evaporation of a vehicle or help paint mixtures to polymerize.

Cosmetics

The cosmetic industry provides a wide assortment of formulated products. A typical bathroom contains a full range of perfumes, moisturizers, rouge, lipstick, antiaging skin products, face powder, emollients, nail polish, sunscreen, hair conditioning and coloring products, aftershave, drugs, and deodorants as well as medications.

Nail polish consists of flexible lacquers, pigments such as organic dyes, iron or chromium oxides, and ultramarine blue along with drying agents and binders or vehicles such as ethyl acetate that evaporate on drying. Nail polish remover is usually an organic solvent such as acetone or ethyl acetate.

Perfumes have been used since the days of ancient Egypt. Perfume bottles are among the most ancient glass items recovered in Asia, where perfumes were probably first extracted from plant materials such as roses, geraniums, or lemon oils. Later processes blended animal products such as ambergris and musk. The first perfumes were probably developed to mask the odors of disease or poor hygiene. Modern perfumes include components blended to produce a combination of scent that will last for several hours and provide a combination of notes (or fragrance impressions). The first note is the odor perceived when one sprays or applies perfume from a bottle. The second note or odor develops after the perfume has made contact with the skin, and the third note is the ability of fragrance to linger.

Most perfume preparations are not patented, but considered trade secrets, so manufacturers are not required to list their ingredients. High-quality perfumes are mixtures of substances that appeal to certain individuals. Typical ingredients include extracts of flowers and fragrances such as valerian, lavender, chamomile, passionflower, ylang-ylang or vanilla, geranium, mint, lemon, fixatives such as ambergris or musk, and water or alcohols. The formulation of perfumes is an art practiced by technicians who have developed abilities to perceive individual and blended fragrances. In addition to products for personal application, perfumes are used in numerous cleaning products.

Detergents

Detergents are among the most common household products and act as wetting agents . Water is a polar compound that readily dissolves most salts and polar compounds such as sugar. Nonpolar solvents such as gasoline or carbon tetrachloride (CCl ₄ ) do not mix well with water, but dissolve nonpolar substances such as grease or oil.

Shampoo contains a mixture of ingredients, including detergents, that allow water to wet the nonpolar oils found in bodily secretions such as sebum, the oily substance which holds dirt and dead skin in hair. Common anionic detergents include sodium or ammonium lauryl sulfates. Cationic detergents, which act to condition hair as well remove dirt and oil from it, include alkyl ammonium compounds such as stearylammonium chloride or sulfate. Other components of shampoo include surfactants such as polyethylene glycol, antifoaming agents, thickeners, antistatic agents, and pH balancers. Formulation chemists add coloring or pearlizing agents and perfumes to shampoos to make them more attractive.

Much of the scum that forms on the walls of showers is a soap film, actually calcium or magnesium salts of fatty acids. Most soaps are sodium or potassium salts of fatty acids that function well as surface active or wetting agents, but calcium and magnesium ions in hard water form insoluble compounds with these fatty acids that dull shower walls. Shower cleaners typically contain chelating agents such as ethylenediamine tetraacetate (EDTA) that form soluble complexes with the ions. In addition, a surfactant such as an ethylene glycol ether wets the wall so water droplets run off. Isopropyl alcohol is a solvent both for the ingredients and for substances such as oils that are not water-soluble.

Sunscreen

A well-designed sunscreen does two things: It blocks harmful ultraviolet (UV) rays and allows the skin to tan. UV rays carry high energy and are suspected to cause cancer by damaging DNA . In addition, excess UV exposure causes increased wrinkling of the skin. Zinc oxide (ZnO) and titanium dioxide (TiO ₂ ) are the long-term ingredients of most sunblockers, considered broad-spectrum agents because they block all UV light. Many sun worshipers or outdoors enthusiasts apply a coat of reflective zinc oxide and cream to their noses and ears for extra protection.

High energy in sunlight comes in two portions: UV-A (320–400 nanometers, or 1.2 × 10 ⁻⁵ –1.6 × 10 ⁻⁵ inches) and UV-B (290–320 nanometers, or 1.1 × 10 ⁻⁵ –1.2 × 10 ⁻⁵ inches). Since the light of shorter wavelength radiation is more energetic, UV-B causes burning, while UV-A promotes tanning. Although not as likely to result in sunburn as UV-B, exposure to UV-A does cause eventual wrinkling and aging of the skin. p-Aminobenzoic acid (PABA) in sunscreen absorbs the energy of UV-B while allowing UV-A to pass through. Other aromatic organic compounds such as benzophenone or oxybenzone are used with or in place of PABA. In the formulation process chemists must choose emollients and sunscreens that remain dispersed without precipitating from solution and feeling gritty.

Although probably harmless at the low concentrations used, most aromatic organic compounds pose some risk of cancer or of interference with bodily hormones, but this risk is probably lower than that of skin cancer or wrinkles. New technology allows encapsulation of the active ingredients of sunblockers in tiny polymer bags that keep the chemical agents away from the skin.

Dihydroxyacetone (DHA) acts as a self-tanning agent to give sunless tans. The browning action probably involves the reaction of DHA with free amino acids to form melanoidins. Melanoidins probably offer only slight UV protection.

Ancient Romans were aware of the bleaching effects of sunlight and used this and other processes to lighten hair. Modern bleaching is done with oxidizing agents such as hydrogen peroxide that destroy melanin, the natural pigment of hair. Hair containing no pigment is light-colored or white.

Hair Coloring Products

Hair coloring products are either temporary or permanent. Temporary hair colors attach to the surface of hair and wash out after repeated shampoos. A dye is considered permanent if it penetrates into the hollow hair shaft. Coloring of hair starts with a treatment of substances such as hydrogen peroxide and ammonia. The ammonia causes hair shafts to swell and open, allowing dye intermediates and couplers to penetrate. Dyes applied during the second step of coloring react with the precursors to form pigments that remain in the hair.

Melanin compounds may appear brown, black, or red. The type of melanin determines hair color, and the density of melanin granules determines the shade. Dark shades of dyed hair contain higher concentrations of dyes. Most hair colors are combinations of organic compounds chosen to produce particular shades. Resorcinol produces a yellow color; aminohydroxytoluene produces a redder hair, and nitrophenylenediamine dye results in very red hair. Graded dyes favored by men often contain lead acetate. The lead ions penetrate into hair and form lead sulfide (PbS), a dark-colored compound.

Deodorants

Deodorants and antiperspirants are frequently compounded together. Deodorants seldom actually remove odor; they simply mask odors or inhibit the microorganisms that cause body odor. Deodorants include several strong perfumes, often with minty or musky odors. Odors can be lessened somewhat by decreasing perspiration. Most underarm perspiration comes from the apocrine or eccrine glands. Perspiration probably functions primarily to cool the skin and get rid of excess heat, but may also carry pheromones and fatty acids and excrete excess salt. The active ingredients of antiperspirants are usually aluminum salts such as aluminum chloride (AlCl ₃ ). Aluminum ions are absorbed by cells in the epidermis that squeeze the sweat gland ducts closed. Talcum powders may be used to absorb excess perspiration.

Gasoline

Civilization runs on gasoline. Gasoline is a solution of hydrocarbons chosen by composition and boiling point as a fuel for internal combustion engines. Petroleum from oil wells is a mixture of thousands of different hydrocarbons that must be refined and separated into useful components. In general, the longer and larger molecules vaporize at higher temperatures. Gasoline is a mixture of hydrocarbon chains typically seven to eleven carbons long.

Gasolines are blended to produce mixtures that vaporize rapidly in carburetors or by passing though fuel injectors. In addition, blends are chosen to give certain octane ratings. The traditional octane rating system compares the knocking characteristics of fuels to n -heptane (C ₇ H ₁₆ ), a fuel that knocks badly and is assigned an octane rating of zero, and isooctane (2,2,4-trimethylpentane, an isomer of octane, C ₈ H ₁₈ ). Isooctane can be used without knocking in high-compression engines, yielding more power than low-octane fuels. The octane ratings of low-octane fuels can be raised by adding branched-chain or cyclic hydrocarbons, or by adding octane enhancers.

The first octane enhancers were lead compounds such as tetraethyl lead (TEL) or tetramethyl lead (TML). A few milligrams of either converted inexpensive, low-octane gasoline into high-test fuels. As the danger of lead to

the environment and to catalytic converters became apparent, lead compounds were phased out and lead-free gasolines introduced. Typically, lead-free gasoline contains cyclic compounds such as benzene and oxygenated additives such as ethanol, methanol, or methylcyclopentadienyl manganese tricarbonyl (MMT). Oxygenated fuels burn cleaner in cold engines.

Pesticides

Pesticides are chemical agents used to kill pests such as insects, snails, spiders, birds, or fish. Any living thing can be a pest at times; many weeds are simply plants growing in unwanted places, and prairie dogs look cute in the zoo, but their eating habits can cause widespread damage to cropland or livestock. Pesticides are, however, seriously poisonous substances.

Dichlorodiphenyltrichloroethane (DDT) is a halogenated hydrocarbon used during the 1940s to control mosquitoes and other disease vectors. Unfortunately, DDT accumulated in the environment until its high levels in the fatty tissues of birds began to cause thin eggshells and loss of life. Although its use is banned in many countries, including the United States, DDT remains a potent weapon against malarial mosquitoes in other parts of the world.

Organophosphate pesticides act by blocking cholinesterase, an enzyme that breaks down the neurotransmitter acetylcholine after a nerve impulse crosses the synapse. Most poisons require a lethal dose that depends on the weight of the animal. Because insects weigh much less than humans, the amount needed to kill an insect may be harmless to us. One early pesticide still in use is nicotine, an active ingredient of tobacco. Potent insecticide solutions can be made by soaking tobacco in water, but the formulation chemist produces safer preparations of standard toxicity.

SEE ALSO Cosmetic Chemistry ; Detergents ; Gasoline ; Pesticides ; Solution Chemistry .

Dan M. Sullivan

Bibliography

Conaway, Charles F. (1999). The Petroleum Industry: A Nontechnical Guide. Tulsa, OK: PennWell.

Flick, Ernest W. (1999). Advanced Cleaning Product Formulations, Vol. 5. Westwood, NJ: Noyes.

Laden, Karl (1999). Antiperspirants and Deodorants. New York: Marcel Dekker.

Lowe, Nicholas J.; Shaath, Nadim A.; and Pathak, Madhu A., eds. (1997). Sunscreens: Development, Evaluation, and Regulatory Aspects, 2nd edition, revised and expanded. New York: Marcel Dekker.

Internet Resources

Chemical and Engineering News web site. Available from http://pubs.acs.org/cen .

The Cosmetic Industry Resource Center web site. Available from http://www.gmp1st.com/csind.htm .

"The Extraordinary Chemistry of Ordinary Things." Available from http://www.howstuffworks.com .