Paraffin

Paraffin is a common name for a group of alkane hydrocarbons with the general formula C_nH_2n+2, where n is the number of carbon atoms. The simplest paraffin molecule is that of methane, CH₄, a gas at room temperature. Heavier members of the series, such as that of octane C₈H₁₈, appear as liquids at room temperature. The solid forms of paraffin, called paraffin wax, are from the heaviest molecules from C₂₀ to C₄₀. Paraffin wax was identified by Carl Reichenbach in 1830.

Paraffin, or paraffin hydrocarbon, is also the technical name for an alkane in general, but in most cases it refers specifically to a linear, or normal alkane—whereas branched, or isoalkanes are also called isoparaffins. It is distinct from the fuel known in Britain and South Africa as paraffin oil or just paraffin, which is called kerosene in much of the U.S., Australia and New Zealand.

Etymology

The name paraffin is derived from the Latin words parum, meaning "barely," and affinis, meaning "affinity." Thus the combination of words means "lacking affinity" or "lacking reactivity."

Wax

Paraffin wax is mostly found as a white, odorless, tasteless, waxy solid, with a typical melting point between about 47 °C and 64 °C. It is insoluble in water, but soluble in ether, benzene, and certain esters. Paraffin is unaffected by most common chemical reagents, but burns readily.

Pure paraffin wax is an extremely good electrical insulator, with an electrical resistivity of between $10^{13}$ and $10^{17}$ ohm meter. This is better than nearly all other materials except some plastics (notably teflon). It is an effective neutron moderator and was used in James Chadwick's 1932 experiments to identify the neutron.

Paraffin wax (C₂₅H₅₂) is an excellent material to store heat, having a specific heat capacity of 2.14–2.9 J g^–1 K^–1 and a heat of fusion of 200–220 J/g. The substance expands considerably when it melts and this property is exploited in thermostats for industrial, domestic and, particularly, automobile use. For casting of metal and other materials, "investment casting waxes" are used, in which the paraffin wax is combined with several other materials to obtain the desired properties. Paraffin wax is not much used to make original models for casting, as it is relatively brittle at room temperature and usually cannot be cold-carved without excessive chipping and breaking. Soft, pliable waxes such as beeswax are preferred for these purposes.

In industrial uses, it is often useful to modify the crystal properties of the paraffin wax, typically by adding branching to the existing carbon backbone chain. The modification is usually done with additives, such as EVA copolymers, microcrystalline wax, or forms of polyethylene. The branched properties result in a modified paraffin with a higher viscosity, smaller crystalline structure, and modified functional properties.

Liquid paraffin

Liquid paraffin, a mixture of heavier alkanes, has a number of names, including nujol, adepsine oil, alboline, glymol, medicinal paraffin, saxol, or USP mineral oil. It is often used in infrared spectroscopy, as it has a relatively uncomplicated IR spectrum. When the sample to be tested is made into a mull (a very thick solution), liquid paraffin is added so it can be spread on the disks to be tested. Liquid paraffin (medicinal) is used to aid bowel movement in persons suffering chronic constipation; it passes through the alimentary canal without itself being taken into the body, but it limits the amount of water removed from the stool. In the food industry, where it may be called "wax," it can be used as a lubricant in mechanical mixing, applied to baking tins to ensure that loaves are easily released when cooked and as a coating for fruit or other items requiring a "shiny" appearance for sale.

Uses

Gaseous

• Fuels

Liquids

• Fuels
• Medicine (Laxative)
• Culinary

Paraffin wax

• Candle-making
• Coatings for waxed paper or cloth
• Food-grade paraffin wax:
  • Shiny coating used in candy-making; although edible, it is nondigestible, passing right through the body without being broken down.
  • Magic Shell
  • Coating for many kinds of hard cheese, like Edam cheese.
  • Sealant for jars, cans, and bottles
  • Chewing gum additive
• Investment casting
• Anti-caking agent, moisture repellent, and dustbinding coatings for fertilizers.
• Agent for preparation of specimens for histology.
• Solid propellant for hybrid rocket motors.
• Emollient (moisturiser), in dermatology.
• Component of surfwax, used for grip on surfboards in surfing.
• Component of glide wax, used on skis and snowboards.
• Friction-reducer, for use on handrails and cement ledges, commonly used in skateboarding.
• Microwax food additive, a glazing agent with E number E905
• Forensics aid: the paraffin test is used in forensics to detect nitrates and nitrites on the hand of a shooting suspect.
• Anti-ozonant agent: blends of paraffin and micro waxes are used in rubber compounds to prevent cracking of the rubber; the antiozonant waxes can be produced from synthetic waxes, FT wax, and Fischer Tropsch wax.
• Mechanical thermostats and actuators, as an expansion medium for activating such devices.
• "Potting" guitar pickups, which reduce microphonic feedback caused from the subtle movements of the pole pieces.
• Wax baths for beauty and therapy purposes.
• Thickening agent in many Paintballs, as used by Crayola.

See also

• Alkane
• Hydrocarbon
• Mineral oil
• Wax

References

ISBN links support NWE through referral fees

• Hein, Morris, and Susan Arena. 2004. Foundations of College Chemistry. Hoboken, NJ: John Wiley. ISBN 0471328189
• McMurry, John. 2004. Organic Chemistry. 6th ed. Belmont, CA: Brooks/Cole. ISBN 0534420052
• Morrison, Robert T., and Robert N. Boyd. 1992. Organic Chemistry. 6th ed. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-643669-2
• Olah, George A., and Árpád Molnár. 2003. Hydrocarbon Chemistry. Hoboken, NJ: Wiley-Interscience. ISBN 0471417823
• Solomons, T.W. Graham, and Fryhle, Craig B. 2004. Organic Chemistry. 8th ed. Hoboken, NJ: John Wiley. ISBN 0471417998

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