Acetic acid

• Acetoxylsäure
• Acetylsalicylic acid (deprecated)
• Acidum aceticum (Latin )
• AcOH
• Äthansäure
• Glacial acetic acid ( Misc for pure acid )
• Acetic acid
• Ethoxylsäure
• HAc
• Wood acid (obsolete )
• Methane carboxylic acid
• Methylene carboxylic acid
• E 260
• Acid vinegar

• G01AD02
• S02AA10

Pungent-smelling liquid with a characteristic odor

Liquid

1.05 g · cm -3

17 ° C

118 ° C

16 hPa ( 20 ° C)

4.76

Completely miscible with water (20 ° C)

1.70 (3 ) D ( 5.7 × 10-30 C · m)

1.371 (20 ° C)

Risk

10 ml · m -3; 25 mg · m-3

3310 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

Acetic acid ( systematically acetic acid, Latin acidum aceticum ) is a colorless, liquid, corrosive and typical smelling carboxylic acid of the composition C2H4O2 (half structural formula CH 3 COOH ). As a food additive it has the designation E 260 Aqueous solutions of acetic acid are trivial only vinegar and pure acetic acid called glacial acetic acid. The salts and esters of acetic acid are called acetates or ( systematic) ethanoate.

• 4.1 Physical Properties
• 4.2 Chemical Properties

• 5.1 nutrition
• 5.2 Material use
• 5.3 Photography

History

Vinegar has been used historically both in Europe and in Asia as a spice for acidification and preservation of food, in Europe the use goes back to ancient times. This vinegar has been traditionally obtained as in the known balsamic vinegar of Modena in the Italian region especially from wine which has been allowed to stand open and fermented. Developed in the Middle Ages in France Orleans method was also based on this process: wine was poured into large vats and flat and put down open. Probably about fruit flies (also known as fruit or vinegar flies ) acetic acid bacteria were added, forming a pellicle on the wine surface, the so-called mother of vinegar.

A further development took place in the 19th century by the first surface of the fermenter. The wine - or alcohol- containing solution was dropped through large wooden generators when tethered or generator methods that were filled for example with book shavings and served as a natural support for the establishment of the bacteria. The oxygen is ensured by a vent at the bottom of the container, rising, is attracted by the heat of reaction, by the generator to the top. Similar procedures for the preparation of ethyl up to the present time in use.

1856 the French scientist Louis Pasteur discovered the role of bacteria in the production of vinegar. In 1868, he was able to develop and use selective growth conditions for the acetic acid bacteria for the first time. He thus laid the foundation for the controlled production of vinegar in the form of wine vinegar with an acetic acid content of about six percent. This method and the yield was only in 1949 through the introduction of a submerged process in the form of Frings Acetators (named after the company Heinrich Frings GmbH & Co KG in Bonn, which was instrumental in the development ), improved and replaced. Today, the submerged method represents the most common form of production of biogenic acetic acid

The first process for producing synthetic acetic acid derived from 1913 by the German company BASF. 1941 showed BASF chemist Walter Reppe the effectiveness of the carbonyls of the metals referred to today as a cobalt group (formerly Group VIII ) as catalysts for the production of carbonyl compounds. Based on this work, a process has been developed, could be reacted with the high-pressure and at high temperatures, methanol and carbon monoxide by Cobaltdiiodid catalyst to acetic acid. The methanol itself represented a commodity which is not primarily based on oil, but could be obtained via synthesis gas from various sources of raw materials such as natural gas and coal. 1960, the BASF process was first implemented on a large scale at a plant in Ludwigshafen, the capacity was initially of 3,600 t / a continuously increased to 45,000 t / a in 1981. 1966 built the American Borden Chemical Co. another plant on the basis of the BASF process with a capacity of 45,000 t / a in Geismar, Louisiana, which was increased to 1981 to 64,000 t / a.

In the late 1960s, Monsanto has developed a process on the basis of rhodium iodide as a catalyst, the production of acetic acid at a substantially lower pressure and at a lower temperature ( about 3 MPa = 30 bar, 180 ° C) at a high yield up to 99 % when methanol is used and 90% when using carbon monoxide enables (Monsanto process). 1970 Monsanto built the first plant in Texas City with an initial capacity of 135,000 t / a, which was increased to 1975 to 270,000 t / a. Shortly after this launch of the BASF process was uneconomical compared and could no longer compete. 1978 built the Celanese Clear Lake Plant in Seabrook, Texas based on the Monsanto process with an initial capacity of 27,000 t / a, by improving the process, the capacity to 900,000 t / y could be increased.

1986 BP Chemicals bought the rights to the Monsanto process, but without the modifications of Celanese and modified it with iridium iodide as a catalyst. This is known as Cativa way process was further developed in the early 1990s and is designed to replace and improve the rhodium iodide process in the Monsanto plant in Texas City.

Occurrence

Acetic acid is a component of plant juices, and essential oils. Alcoholic beverages that are exposed for long periods of air, forming acetic acid by oxidation of the ethanol.

Acetic acid could also occur in interstellar space, a process for their formation has been demonstrated.

Extraction and production

Biotechnological production

The biotechnological and fermentative production of acetic acid is the respiration of ethanol ( 'alcohol' ) by bacteria of the genus Acetobacter or Gluconobacter. It is considered biochemically an incomplete breathing ( not as it is often erroneously described, a fermented form). The bacteria convert arisen through processes of fermentation ethanol by a so-called " subterminal oxidation " acetaldehyde ( ethanal ) into acetic acid.

The oxidation is carried out by membrane-bound alcohol dehydrogenase ( ADH) and aldehyde dehydrogenases ( ALDH ), the prosthetic group pyrroloquinoline quinone ( PQQ ) and the ADH also contain heme c. The liberated during the oxidation electrons are transferred via ubiquinone to also membrane-bound oxidase.

Starting products for the acetic acid formation can be, for example, wine, beer or malt. The bacteria are highly dependent on an adequate supply of oxygen and are very sensitive to oxygen-poor living conditions. Even with an interruption of the oxygen supply of a few minutes, there is a significant decrease in ethanol oxidation. If ethanol as a substrate is not available there will be a reduction of acetic acid to CO2, also by oxidation. The bacteria break down carbohydrates from both glycolysis as via the Entner- Doudoroff pathway to pyruvate, which then enters the citric acid cycle.

Large-scale chemical production

Worldwide there are production capacity for acetic acid in the amount of about 7 million tons per year. Between 1998 and 2006 there was a worldwide average growth of the production of three to four percent per year, with about 70 % of annual production in the U.S. ( 1996: 36 % 2006: 32%), Western Europe ( 1996: 24%; 2006: 17%) and Japan ( 1996: 16% 2006:. 11%) take place, the East Asian production increased compared to these regions from 1996 with 14% to about 18 % in 2006 only about 190,000 tonnes worldwide by fermentation annually produced, with about 70 % of world demand is produced at vinegar in submerged culture in 700 bioreactors.

The currently most important industrial synthesis of acetic acid is the catalytic reaction of methanol with carbon monoxide under pressure ( Monsanto process).

In addition, acetic acid can also be prepared synthetically by the oxidation of acetaldehyde with air or oxygen using Mn ( OAc) 2 as a catalyst or by the partial oxidation of other hydrocarbons.

Technically nor the air oxidation of n-butane at about 180 ° C and 85 bar, the catalytic oxidation of light petroleum and the rectification of wood vinegar used.

Properties

Physical Properties

Acetic acid has at 118 ° C, a relatively high boiling point to polar substances with comparable molar mass ( for example, 1 -propanol: boiling point 97 ° C). The reason for this is the ability of acetic acid molecules to form two carboxyl groups on their " mutual " hydrogen bonds, so that dimers of two acetic acid molecules arise like a duplicate molecule molar mass behave. Therefore, a higher amount of energy is required for the reconciliation of these dimers in the gas phase, recognizable " elevated " to the boiling point.

The vapor pressure function is given by the Antoine equation corresponding to log10 (P) = A- ( B / ( T C )) ( P in bar, T in K) with A = 4.68206, B = 1642.540 and C = -39.764 in the temperature range from 290.26 to 391.01 K.

The temperature dependence of the enthalpy of vaporization can be determined according to equation ΔVH0 = A exp ( - αTr ) (1- Tr) β ( ΔVH0 in kJ / mol, Tr = (T / Tc) reduced temperature ) with A = 22.84 kJ / mol, α = 0.0184, β = -0.0454 Tc = 592.7 K and describe the temperature range 298-392 K. Pure acetic acid has a potential electrolyte one, based only on the autoionization, very low conductivity for electricity. The conductivity of pure acetic acid at 25 ° C 10.06 -7 s · m -1. Only when water enters dissociation and increasing the conductivity.

Chemical Properties

In aqueous solution of acetic acid reacts as a medium strong acid. The pKa of acetic acid is 4.75. In a proteolytic reaction, an equilibrium between the acid and the acetate ion is one that is strong on the part of the acid. As with all carboxylic acids, the carboxylate group of the acetate ion is stabilized by resonance, which contributes significantly to acid reaction of carboxylic acids:

The degree of dissociation of the acid in dilute solutions only in the range of a few percents. In one molar solution, it is just about 0.5%. The resulting oxonium ion ( H3O ) leads to an acidic solution ( pH < 7).

If the pH of a solution of acetic acid increased by the addition of a strong base or by the addition of acetates, a buffer solution is formed. The pH value of the solution is equal to the pKa of acetic acid, acetic acid and acetate ion are present in the same concentrations. This is the optimum point of the acetic acid buffer, acetate buffer, and to support the change of the pH value from the addition of acids or bases. This buffer system is important for biochemical systems in the acidic range, since it has a low pKa value and the components involved not adversely affect most organisms and biomolecules. It is a stable buffer system, that is, the conjugated acid-base pair remains in solution and can not escape, such as, for example, the bicarbonate from the system.

Acetic acid oxidized completely in the air and generates heat to water and carbon dioxide. This happens only very slowly at room temperature. Base metals such as magnesium, calcium, zinc and iron dissolve in dilute acetic acid to form water-soluble acetates and release of hydrogen. With copper, the acetic acid reacts in the presence of oxygen (air ) to copper acetate, a green, harmful salt, which is better known under the name of " verdigris ". Acetic acid reacts with ethanol to acid-catalyzed ethyl acetate, a solvent used much. When 1-pentanol instead of ethanol used to obtain amyl acetate, a strong-smelling esters. Salicylic acid can also be esterified with acetic acid. This creates acetylsalicylic acid, an ingredient in many painkillers. Acetic acid at 800 ° C reacts with dehydration to acetic anhydride. Acetic acid is used in diluted form also to Kalklösen according to the following reaction equation:

The salts of acetic acid are called acetates. They are mostly colorless crystalline salts in their crystal lattices ( ionic lattices ) contain the acetate anion ( CH3COO - ).

Use

Nutrition

Acetic acid has a great importance as a flavoring agent. Acetic acid ( E 260 ) and its salts potassium acetate (E 261 ), sodium acetate ( E 262 ) and calcium acetate (E 263 ) are used as acidifying agent for fruits and vegetables in cans and glass jars ( 0.5-3% acetic acid ) in fish in all variations, canned food, a variety of marinades, deli salads, mayonnaise, salad dressings along with sorbic acid (E 200) or benzoic acid (E 210) and used for loading and washing of fresh meat. The bactericidal effect of acetic acid is that physiological processes can be prevented by changing the pH and also denature proteins. Household vinegar consists of biogenic and vinegar contains 5 % acetic acid. Vinegar is a 25-percent solution of acetic acid in water, smells strongly pungent and may only be used diluted in food.

Material use

For the material use almost exclusively large engineered acetic acid is utilized. In this case, more than 65 % of the world production of polymers based on vinyl acetate ( 43%) and cellulose (25%) to be applied. Vinyl acetate is the basis of polyvinyl acetate ( PVAc), which is used inter alia, in coatings and adhesives, to a lesser extent in the vinyl acetate copolymers (such as ethylene vinyl acetates ), and polyvinyl alcohol. Cellulose acetate is used in particular for the production of cigarette filters, films, and plastic products.

Other uses include various esters such as ethyl acetate and n-butyl ( together 11%), used as a solvent for perfumes and cosmetics. Another 10% are used for the production of acetic anhydride, acetanilide, acetic acid and ammonium chloride.

Photography

In the photo lab practice of " wet" or analogue photography is diluted acetic acid (3-5 % ) was used to neutralize the developer baths as so-called " stop bath ". In many cases, the solution is mixed with an indicator dye, which indicates when the stop bath is alkaline and thus ineffective.

Hazards

Pure acetic acid is considered flammable liquid. Above the flash point is flammable vapor-air mixtures may be formed. The compound has a flash point of 40 ° C. The explosion range is between 4 % by volume (100 g/m3) as the lower explosive limit ( LEL) and 17 vol% (430 g/m3 ) and upper explosive limit (UEL ). The ignition temperature is 485 ° C. The fabric falls within the temperature class T1.

The classification and labeling according to the Dangerous Goods Regulations depends on the concentration. Glacial acetic acid or solutions containing more than 80 % acid by mass are the dangerous goods class with the packing group II assigned to 8 ( Corrosive Substances ) ( medium hazard ). As a subsidiary risk the dangerous goods class 3 must (Flammable liquids) are marked with ( Label 8 /3). Solutions with at least 50% by mass and not more than 80 % acid by mass are only of Class 8 ( Corrosive Substances ) with the Packing Group II (medium hazard ) associated with ( Label 8 ). For solutions containing more than 10% by mass and less than 50 % acid by mass Class 8 ( Corrosive Substances ) applies to the packing group III (low hazard ) ( Label: 8 ).