Alcohols in Aerosols What they are, where they come from and what they do… A Montfort A. Johnsen, Ph.D. technicAl eDitor lcohol is vital to the formulation of many aerosol products. Ethanol, our most important alcohol, has been produced by carbohydrate fermentation and used in beverages for an estimated 30,000 years. Historic references to the fermentation process date back 6,500 years. The term “alcohol” originated with “kuhl” in the Middle East, followed by “kuhlol” in Mesopotamia. In 1500, the famous Swiss physician and alchemist Paracelsus called it “alcool vini” (distilled from grapes) in his notebooks. Pure alcohol was first described by J.T. Tobias in 1796. Other alcohols (CnHn+1-OH) began to be identified over a century later, starting with methanol. Ethanol was heavily taxed, starting about 1750, when virtually all of it was used in beverages. Other uses developed very slowly but became fairly important by about 1850. In 1855, England pioneered tax-free ethanol for non-beverage applications. The U.S. finally followed, with the Tax-free Alcohol Act of 1897. In 1907, a few standard formulas for “specially denatured alcohol” were developed. Over 50 of these are available today, each with a cadre of federally approved uses. Meanwhile, other countries have developed a variety of approaches for making tax-free alcohol available, both with and without denaturing additives. During the last 150 years, thousands of organic compounds with the formula R-OH have been synthesized (“R” depicts an organic moiety). The term “alcohol” refers to both ethanol (CH3-CH2-OH) and to compounds where “R” is an alkyl (aliphatic) group—or at least the beginnings of one, as in the case of benzyl alcohol (C6H5-CH2-OH). Complex alcohols are known to be, up to at least C40H81-OH, extracted from waxes. Starting with the two propanols, the higher alcohols have many isomers. Even fairly simple ones, like the octanols (C8H17-OH), which theoretically have 89 isomers, can be a challenge, since only about a third of them have been synthesized. The alcohols do not occur naturally, except in trace amounts. They must be produced by fermentation, reactions of CO and H2, the reduction of carboxylic acids (R-COOH) from naturally occurring glyceryl esters and by other means. Many are used in aerosol formulations, as solvents, thinners, fragrance components, foam modifiers, de-icer formulas and so forth. Physical properties of aliphatic alcohols Following is a description of a number of saturated aliphatic alcohols, including a summary of their aerosol applications. Methanol This was the second alcohol to be identified, after ethanol. It was originally made by the destructive distillation of wood—hence its older name of “wood alcohol.” When the lignin in wood is cooked, the distillate typically contains 2.5% methanol, 1.0% acetone, 5.5% acetic acid, minor ingredients and a preponderance of water. This process has now been eclipsed by one involving the reactions between CO and H2, using zinc chromate as a catalyst, with 450°F (232°C) and 3,000psi (210 bars). It produces almost pure methanol with traces of higher alcohols. Methanol (CH3-OH) is probably the least expensive organic compound. Methanol is usually a better solvent than ethanol. It has the rather unique ability to dissolve many inorganic salts—such as up to 22% calcium chloride (CaCl2), forming methanolates (such as CaCl2.CH3-OH). Compare these to hydrates (such as CaCl2.H-OH). Methanol also forms many azeotropes, but not with water. It is flammable, burning with an almost invisible blue flame. Its flash point (Tagliabue Closed Cup or TCC) is 54°F (12°C). It is also quite hygroscopic, readily absorbing moisture. The toxicity of methanol is well recognized. It acts by producing respiratory failure, retinal collapse and other symptoms. Blindness can occur, usually permanent. The ingestion of as little as 30mL was reported to be lethal in an apparently isolated case. However, from 100–200mL is considered to be the usual LD50 (lethal dose) range. The federal Consumer Product Safety Commission (CPSC) requires special precautionary labeling and childresistant packaging for products containing 4% or more of methanol. For eight hours of workplace exposure, methanol should be kept below 200ppm. Like alcohols up to C12H25-OH, it is considered to be a volatile organic compound (VOC). The main use of methanol in aerosol products is in the formulation of automobile de-icers used, not only for car windshields, but for frosted door locks, glass windows and other iced-over surfaces. A typical composition is shown in Table 1 on facing page. Theoretically, this de-icer should be made toxicologically safer by replacing the methanol with iso-propanol and the ethylene glycol with propylene glycol, and, in fact, this has often been done. However, proponents argue that Paracelsus, swiss philosopher, physician, botanist, astrologer and general occultist, referred to alcohol as “alcool vini” (distilled from grapes) in his notebooks. he is credited as the founder of toxicology and considered a revolutionary for utilizing observations of nature rather than referring to ancient texts. 38 Spray March 2017
Spray March 2017
To see the actual publication please follow the link above