Acetic Acid - 100 Most Important Chemical Compounds

CHEMICAL NAME = ethanoic acid CAS NUMBER = 64–19–7 MOLECULAR FORMULA = C₂H₄O₂ MOLAR MASS = 60.1 g/mol

COMPOSITION = C(60%) H(6.7%) O(53.3%) MELTING POINT = 16.7°C

BOILING POINT = 118.1°C DENSITY = 1.05 g/cm³

Acetic acid is a weak carboxylic acid with a pungent odor that exists as a liquid at room tem-perature. It was probably the ﬁ rst acid to be produced in large quantities. Th e name acetic comes from acetum, which is the Latin word for “sour” and relates to the fact that acetic acid is responsible for the bitter taste of fermented juices. Acetic acid is produced naturally and synthetically in large quantities for industrial purposes. It forms when ubiquitous bacteria of the genera Acetobacter and Clostridium convert alcohols and sugars to acetic acid. Acetobacter, especially Acetobacter aceti, are more eﬃ cient acetic acid bacteria and produce much higher concentrations of acetic acid compared to Clostridium.

Vinegar is a dilute aqueous solution of acetic acid. Th e use of vinegar is well documented in ancient history, dating back at least 10,000 years. Egyptians used vinegar as an antibiotic and made apple vinegar. Babylonians produced vinegar from wine for use in medicines and as a preservative as early as 5000 b.c.e. Hippocrates (ca. 460–377 b.c.e.), known as the

“father of medicine,” used vinegar as an antiseptic and in remedies for numerous conditions including fever, constipation, ulcers, and pleurisy. Oxymel, which was an ancient remedy for coughs, was made by mixing honey and vinegar. A story recorded by the Roman writer Pliny the Elder (ca. 23–79 c.e.) describes how Cleopatra, in an attempt to stage the most expensive meal ever, dissolved pearls from an earring in vinegar wine and drank the solution to win a wager. Other Roman writings describe how Hannibal, when crossing the Alps, heated boul-ders and poured vinegar on them to soften and crack them to clear paths. Vinegar is often referred to in the Bible, both directly and indirectly as bad wine. A famous historical Bible

2 ^| Th e 100 Most Important Chemical Compounds

published in 1717 is referred to as the Vinegar Bible because, among its numerous errors, the heading for Luke 20 reads “the parable of the vinegar” rather than “the parable of the vineyard.” Vinegar was thought to have special powers and it was a common ingredient used by alchemists.

Alchemists used distillation to concentrate acetic acid to high purities. Pure acetic acid is often called glacial acetic acid because it freezes slightly below room temperature at 16.7°C (62°F). When bottles of pure acetic acid froze in cold laboratories, snowlike crystals formed on the bottles; thus the term glacial became associated with pure acetic acid. Acetic acid and vinegar were prepared naturally until the 19th century. In 1845, the German Chemist Hermann Kolbe (1818–1884) successfully synthesized acetic acid from carbon disulﬁ de (CS₂).

Kolbe’s work helped to establish the ﬁ eld of organic synthesis and dispelled the idea of vital-ism. Vitalism was the principle that a vital force associated with life was responsible for all organic substances.

Acetic acid is used in numerous industrial chemical preparations and the large-scale produc-tion of acetic acid takes place through several processes. Th e main method of preparation is methanol carbonylation. In this process, methanol reacts with carbon monoxide to give acetic acid: CH₃OH_(l) + CO_(g) → CH₃COOH_(aq). Because the reaction requires high pressures (200 atmospheres), this method was not used until the 1960s, when the development of special catalysts allowed the reaction to proceed at lower pressures. A methanol carbonylation proce-dure developed by Monsanto bears the company’s name. Th e second most common method to synthesize acetic acid is by the catalytic oxidation of acetaldehyde: 2 CH₃CHO_(l) + O_2(g) → 2 CH₃COOH_(aq). Butane may also be oxidized to acetic acid according to the reaction: 2 C₄H_10(l) + 5O_2(g) → 4 CH₃COOH_(aq) + 2H₂O_(l). Th is reaction was a major source of acetic acid before the Monsanto process. It is carried out at a temperature of approximately 150°C and 50 atmospheres pressure.

Acetic acid is an important industrial chemical. Th e reaction of acetic acid with hydroxyl-containing compounds, especially alcohols, results in the formation of acetate esters. Th e largest use of acetic acid is in the production of vinyl acetate (Figure 1.1). Vinyl acetate can be produced through the reaction of acetylene and acetic acid. It is also produced from ethylene and acetic acid. Vinyl acetate is polymerized into polyvinyl acetate (PVA), which is used in the production of ﬁ bers, ﬁ lms, adhesives, and latex paints.

Figure 1.1 Vinyl acetate.

Cellulose acetate, which is used in textiles and photographic ﬁ lm, is produced by reacting cellulose with acetic acid and acetic anhydride in the presence of sulfuric acid. Other esters of acetic acid, such as ethyl acetate and propyl acetate, are used in a variety of applications.

Th e condensation reaction of two molecules of acetic acid results in the production of acetic anhydride and water:

Acetic acid is used to produce the plastic polyethylene terephthalate (PET) (see Ethene [Ethylene]). Acetic acid is used to produce pharmaceuticals (see Acetylsalicylic Acid).

Vinegar was the ﬁ rst form of acetic acid produced through the fermentation of sugars in wine and other substances. Th e name vinegar comes from the French vin aigre meaning “sour wine.” Vinegar is an acetic acid solution between about 4% and 8%, but it should not be equated as simply diluted acetic acid. Because vinegar is produced through fermentation of sugars contained in fruits and vegetables, it contains additional nutrients associated with the source from which it is produced. Industrial production of acetic acid far exceeds the produc-tion of vinegar acetic acid, but the latter is important for the food and beverage industry.

Th e U.S. Food and Drug Administration requires that vinegar must contain in excess of 4 grams of acetic acid per 100 mL of solution and requires vinegars to contain the labeling:

“diluted with water to __ percent acid strength,” with the blank specifying the acid strength.

Most grocery store vinegars are about 5% acetic acid.

Vinegar is most often associated with the fermentation of alcohol and fruit juices, but there are hundreds of sources of vinegar. Diff erent varieties of vinegar have traditionally refl ected the geography from which they were produced. Typical vinegars available in the United States include distilled white, apple cider, balsamic, malt, and wine. Other vinegars come from potatoes, rice, a multitude of fruits, grains, and sugar cane. Th e modern production of vinegar involves charging large vats or casks with alcohol. Th e vats are supplied with seed bacteria (Acetobacter sp.), nutrients, and oxygen in a mixture sometimes called “mother of vinegar.” Th e casks contain wood shavings to provide a large surface area where the vinegar-producing bacteria form a biofi lm. Th e mixture is circulated through the vats until the desired acetic acid concentration is obtained.

Common distilled white vinegar is usually from the fermentation of distilled alcohol, but it can be diluted industrial acetic acid. Many countries specify that vinegar used in food produc-tion must be produced naturally. Th e alcohol in white vinegar usually comes from corn. Apple cider vinegar is produced from the fermentation of apple cider to hard cider and then to apple cider vinegar. Balsamic vinegar dates back more than 1,000 years. Th e name comes from its Italian equivalent aceto balsamico, which translated means soothing vinegar. It is a dark brown, syrupy, smooth vinegar especially valued by chefs for its ﬂ avor. True balsamic vinegar is produce from white Trebbiano grapes grown in the region of Modena, Italy. Th e grape juice is boiled and then progressively aged in casks of various woods. During diﬀ erent stages of the aging process, the product is transferred to progressively smaller casks to compensate for evaporation. Aging occurs for a minimum of 12 years, although some vintages have been aged for decades. Only several thousand gallons of balsamic vinegar are produced each year, making original balsamic vinegar quite expensive. Balsamic vinegars marketed on a large scale in supermarkets are ordinary vinegars to which coloring and other additives have been used to mimic true balsamic vinegar.

Acetic Acid ^| 3

2. Acetone

CHEMICAL NAME = 2-propanone CAS NUMBER = 67–64–1 MOLECULAR FORMULA = C₃H₆O MOLAR MASS = 58.1 g/mol

COMPOSITION = C(62.0%) H(10.4%) O(27.6%) MELTING POINT = –94.9°C

BOILING POINT = 56.3°C DENSITY = 0.79 g/cm³

Acetone is a ﬂ ammable, colorless liquid with a pleasant odor. It is used widely as an organic solvent and in the chemical industry. It is the simplest ketone, which also goes by the name dimethyl ketone (DMK). Acetone was originally referred to as pyroacetic spirit because it was obtained from the destructive distillation of acetates and acetic acid. Its formula was correctly determined in 1832 by Justus von Liebig (1803–1873) and Jean-Baptiste André Dumas (1800–

1884). In 1839, the name acetone began to be used. Acetone was derived by adding the ending

“one” meaning “daughter of ” to the root of acetum (acetic acid) to mean daughter of acetum because it was obtained from acetic acid.

Th e traditional method of producing acetone in the 19th century and the beginning of the 20th century was to distill acetates, particularly calcium acetate, Ca(C₂H₃O₂)₂. World War I placed an increase demand on England to produce gunpowder, explosives, and propel-lants such as cordite. Cordite is a propellant made using nitroglycerin and nitrocellulose, and nitrocellulose is a principal component of smokeless gunpowder. Cordite is made by dissolv-ing nitrocellulose in acetone, mixdissolv-ing it with nitroglycerin, then bakdissolv-ing oﬀ the acetone. One of England’s suppliers of calcium acetate before the war was Germany, and the loss of this source and lack of other sources because of German blockades meant that it was imperative to ﬁ nd another source of acetone. One of these was from the fermentation of sugars. One of England’s leading scientists working on bacterial fermentation was Chaim Weizmann (1874–1952), a Russian-born Jew who was a professor at Manchester University. Weizmann had been working on methods to make butyl alcohol in order to produce synthetic rubber.

Weizmann discovered a process to produce butyl alcohol and acetone from the bacterium Clostridium acetobutylicum in 1914. With England’s urgent demand for acetone, Winston Churchill (1874–1965) enlisted Weizmann to develop the Weizmann process for acetone production on an industrial scale. Large industrial plants were established in Canada, India, and the United States to provide the allies with acetone for munitions. Weizmann, who is considered the “father of industrial fermentation,” obtained signiﬁ cant status from his war contributions and used this to further his political mission of establishing a Jewish homeland.

Weizmann was a leader of the Zionist movement and campaigned aggressively until the nation of Israel was established in 1948. He was the ﬁ rst president of Israel.

Fermentation and distillation techniques for acetone production were replaced starting in the 1950s with the cumene oxidation process (Figure 2.1). In this process, cumene is oxidized to cumene hydroperoxide, which is then decomposed using acid to acetone and phenol. Th is is the primary method used to produce phenol, and acetone is produced as a co-product in the process, with a yield of about 0.6:1 of acetone to phenol.

Figure 2.1 Acetone production using cumene.

Acetone can also be produced from isopropanol using several methods, but the main method is by catalytic dehydrogenation:

Catalytic dehydrogenation

Acetone is used in the chemical industry in numerous applications. Its annual use in the United States approaches 2 million tons and worldwide its use is close to 5 million tons. Th e primary use of acetone is to produce acetone cyanohydrin, which is then used in the pro-duction of methyl methacrylate (MMA). MMA polymerizes to polymethyl methacrylate.

MMA is used in a variety of applications involving plastics and resins. It is used extensively in the production of skylights, Plexiglas, outdoor advertising signs, building panels, and light ﬁ xtures. It is also incorporated into paints, lacquers, enamels, and coatings.

Another use of acetone in the chemical industry is for bisphenol A (BPA). BPA results form the condensation reaction of acetone and phenol in the presence of an appropriate catalyst. BPA is used in polycarbonate plastics, polyurethanes, and epoxy resins. Poly-carbonate plastics are tough and durable and are often used as a glass substitute. Eyeglasses, safety glasses, and varieties of bullet-proof “glass” are made of polycarbonates. Additional

Acetone ^| 5

6 ^| Th e 100 Most Important Chemical Compounds

uses include beverage and food containers, helmets (bicycle, motorcycle), compact discs, and DVDs.

In addition to its use as a chemical feedstock and intermediate, acetone is used exten-sively as an organic solvent in lacquers, varnishes, pharmaceuticals, and cosmetics. Nail polish remover is one of the most common products containing acetone. Acetone is used to stabilize acetylene for transport (see Acetylene).

Acetone and several other ketones are produced naturally in the liver as a result of fat metabolism. Ketone blood levels are typically around 0.001%. Th e lack of carbohydrates in a person’s diet results in greater fat metabolism, causing ketone levels in the blood to increase.

Th is condition is called ketosis. People on low-carbohydrate diets and diabetics may have problems with ketosis because of a greater amount of fat in the diet. An indicator of ketosis is the smell of acetone on a person’s breath.

3. Acetylene

CHEMICAL NAME = ethyne CAS NUMBER = 74–86–2 MOLECULAR FORMULA = C₂H₂ MOLAR MASS = 26.0 g/mol

COMPOSITION = C(92.3%) H(7.7%) MELTING POINT = –80.8°C

BOILING POINT = –80.8 (sublimes)

DENSITY = 1.17 g/L (vapor density = 0.91, air = 1)

Acetylene, which is the simplest alkyne hydrocarbon, exists as a colorless, ﬂ ammable, unstable gas with a distinctive pleasant odor (acetylene prepared from calcium carbide has a garlic smell resulting from traces of phosphine produced in this process). Th e term acetylenes is used generically in the petroleum industry to denote chemicals based on the carbon-carbon triple bond. Acetylene was discovered in 1836 by Edmund Davy (1785–1857) who produced the gas while trying to make potassium metal from potassium carbide (K₂C₂). In 1859, Marcel Morren in France produced acetylene by running an electric arc between carbon electrodes in the presence of hydrogen. Morren called the gas produced carbonized hydrogen. Th ree years later, Pierre Eugène-Marcelin Berthelot (1827–1907) repeated Morren’s experiment and identiﬁ ed carbonized hydrogen as acetylene.

A method for the commercial production of acetylene was discovered accidentally in 1892 by Th omas Willson (1860–1915). Willson was experimenting on aluminum production at his company in Spray, North Carolina. He was attempting to produce calcium in order to reduce aluminum in aluminum oxide, Al₂O₃. Willson combined coal tar and quicklime in an electric furnace and, instead of producing metallic calcium, he produced a brittle gray substance. Th e substance was calcium carbide, CaC₂, which when reacted with water, produced acetylene.

Willson’s work led to the establishment of a number of acetylene plants in the United States and Europe during the next decade.

Th e triple bond in acetylene results in a high energy content that is released when acety-lene is burned. After Willson’s discovery of a method to produce commercial quantities of

8 ^| Th e 100 Most Important Chemical Compounds

acetylene, Henry-Louis Le Châtelier (1850–1936) found that burning acetylene and oxygen in approximately equal volumes produced a fl ame hotter than any other gas. Flame tempera-tures between 3,000°C and 3,300°C were possible using acetylene and pure oxygen, which was high enough to cut steel. Th e hot fl ame from acetylene is due not so much from its heat of combustion, which is comparable to other hydrocarbons, but from the nature of the fl ame produced by acetylene. Acetylene burns quickly when combined with pure oxygen, producing a fl ame with a tight concentrated inner cone. Th e transfer of energy from the fl ame occurs in a very small volume, resulting in a high temperature. During the last half of the 19th century, torches using hydrogen and oxygen were used for cutting metals, but the highest temperatures were around 2000°C. Torches capable of using acetylene were developed in the early 20th century, and acetylene found widespread use for metal working. Another widespread use of acetylene was for illumination. Portable lamps for miners, automobiles, bicycles, and lanterns used water mixed with calcium carbide to generate acetylene that burned to produce a bright fl ame. Street lamps, lighthouses, and buoys also used acetylene for illumination, but by 1920 acetylene as a light source had been replaced by batteries and electric light.

One problem with the use of acetylene is its stability. Although it is stable at normal pres-sures and temperatures, if it is subjected to prespres-sures as low as 15pounds per square inch gauge (psig) it can explode. To minimize the stability problem, acetylene transport is minimized.

Acetylene contained in pressurized cylinders for welding and cutting is dissolved in acetone.

A typical acetylene cylinder contains a porous fi ller made from a combination of materials such as wood chips, diatomaceous earth, charcoal, asbestos, and Portland cement. Synthetic fi llers are also available. Acetone is placed in the cylinder and fi lls the voids in the porous mate-rial. Acetylene can then be pressurized in the cylinders up to approximately 250 pounds per square inch (psi) In a pressurized cylinder, 1 liter of fi ller can hold a couple of hundred liters of acetylene, which stabilizes it. Acetylene cylinders should not be stored on their sides because this could cause the acetone to distribute unequally and create acetylene pockets.

Th e traditional method of producing acetylene is from reacting lime, calcium oxide (CaO), with coke to produce calcium carbide (CaC₂). Th e calcium carbide is then combined with water to produce acetylene:

2CaO_(s) + 5C_(s)→ 2CaC_2(g) + CO_2(g) CaC_2(s) + 2H₂O_(l) → C₂H_2(g) + Ca(OH)_2(aq)

Several processes for producing acetylene from natural gas and other petroleum products developed in the 1920s. Th ermal cracking of methane involves heating methane to approxi-mately 600°C in an environment deﬁ cient in oxygen to prevent combustion of all the methane.

Combustion of part of the methane mix increases the temperature to approximately 1,500°C, causing the remaining methane to crack according the reaction: 2CH_4(g) → C₂H_2(g) + 3H_2(g). In addition to methane, ethane, propane, ethylene, and other hydrocarbons can be used as feed gases to produce acetylene.

Approximately 80% of acetylene production is used in chemical synthesis. In the United States approximately 100,000 tons are used annually. Acetylene saw much wider use in the past, especially in Germany where it was widely used as in chemical synthesis. During recent decades, greater use of ethylene as a chemical feedstock and the development of more eco-nomical chemical production methods that eliminate acetylene has reduced acetylene’s use in the chemical industry. Since 2000, use in the United States has decreased by approximately

50,000 tons a year. Most acetylene production is used for the production of 1,4-butanediol, which is used to produce plastics, synthetic ﬁ bers, and resins. It is also used as an organic solvent and in coatings. Th e traditional process to produce 1,4-butanediol involves reacting acetylene with formaldehyde using the Reppe process named for Walter Reppe (1892–1969).

Reppe, who has been called the “father of acetylene chemistry,” pioneered methods of using acetylene in the chemical industry.

Th is Reppe process using acetylene for 1,4 butanediol is currently being replaced with pro-cesses that start with propylene oxide (C₃H₆O), butadiene (C₄H₆), or butane (C₄H₁₀).

Th e triple bond in acetylene makes its unsaturated carbons available for addition reactions, especially hydrogen and halogens. Reaction with hydrogen chloride produces vinyl chloride that polymerizes to polyvinyl chloride (see Vinyl Chloride). Th is was the chief reaction used to pro-duce vinyl chloride before 1960. Because acetylene is highly reactive and unstable, it presented more diﬃ culties and was more expensive than processes developed in the 1950s that used eth-ylene rather than aceteth-ylene. Th e addition of carboxylic acids to acetylene gives vinyl esters. For example, the addition of acetic acid produces vinyl acetate. Acrylic acid (CH₂ = CHCOOH)

In document 100 Most Important Chemical Compounds_ a Reference Guide (Page 28-37)