Acids, Bases and Salts

Acetic Acid

Acetic acid or ethanoic acid is a colourless liquid organic compound with the molecular formula \(CH_ {3} COOH\). When acetic acid is dissolved in water, it is termed glacial acetic acid. Vinegar is no less than 4 per cent acetic acid by volume, aside from water, allowing acetic acid to be the main ingredient of vinegar. It is produced primarily as a precursor to polyvinyl acetate and cellulose acetate, in addition to household vinegar.

It is a weak acid since the solution dissociates only slightly. But concentrated acetic acid is corrosive and can damage the flesh. The second simplest carboxylic acid is acetic acid (after formic acid). It consists of a methyl group to which a carboxyl group is bound. It is an important chemical reagent and industrial chemical which is mainly useful for the manufacture of photographic film cellulose acetate, wood glue polyvinyl acetate, and synthetic fibres and fabrics.

Acetic Acid

                                                                                                     Acetic Acid

Properties of Acetic Acid

  • Acetic acid is a smooth, colourless liquid with a 1 ppm visible, poisonous and destructive, unpleasant vinegar odour. The melting point is 16.73 ° C and the usual 117.9 ° C boiling point.
  • At 20°C, the density of pure acetic acid is 1.0491. It is highly hygroscopic acetic acid. It is possible to link the purity of the water solutions to their freezing point.
  • In carboxylic acids such as acetic acid, the hydrogen centre in the carboxyl group \(−COOH\) can differentiate from the molecule by ionization:

\(CH_ {3} COOH\leftrightharpoons CH_ {3}CO_ {2} ^ {-1} + H^ {+1}\)

Due to this proton \(H^ {+1}\) release, acetic acid has an acidic character. Acetic acid is a weak monoprotic acid. It has a pK value of 4.76 in an aqueous solution. Acetate \(CH_ {3} COO^ {-1}\) is the conjugate base.

  • For polar and non-polar solvents such as acid, chloroform, and hexane, it is miscible.
  • The molecules form chains in solid acetic acid, with hydrogen bonds interconnecting individual molecules. Dimers can be found in the vapour at 120 °C. In the liquid form, dimers often exist in dilute solutions in non-hydrogen-bonding solvents and, to a certain degree, in pure acetic acid; but are interacted with by solvents that bind to hydrogen.
  • Acetic acid is normally completely ionized to acetate at physiological phis. It is central to the metabolism of carbohydrates and fats when bound to coenzyme A. Acetic acid does not exist in natural triglycerides, unlike longer-chain carboxylic acids (fatty acids).

Acetic Acid Dehydration

Dehydration of acetic acid is one of the most important industrial uses of AD in the manufacture of aromatic acids such as terephthalic acid (TA), which involves a high purity of acetic acid. Two major parts are used in the manufacturing process: oxidation (where p-xylene is catalytically oxidized to produce crude TA) and PTA purification. Acetic acid, present as a solvent in the oxidation reactor but also helpful to the reaction itself, must be isolated from the oxidation-produced water.

For the effective and economical operation of a TA facility, the recovery and storage of the acetic acid solvent are important. At high water temperatures, water, and acetic acid show a pinch point, make recovering the pure acid very difficult. Two absorbers (low and high pressure) and an acid dehydration column consist of a traditional acetic acid recovery unit in a PTA phase. Tall columns of 70–80 trays require the separation of acetic acid and water by traditional distillation. N-butyl acetate, which exhibits minimal miscibility with water and forms a heterogeneous azeotrope (b.p. 90.23°C), which is a typical azeotropic agent. With all the water being fed to the dehydration column, n-Butyl acetate is added in appropriate amounts to form an azeotrope.

On condensation, the heterogeneous azeotrope forms two phases; an organic layer containing almost pure n-butyl acetate and an aqueous layer phase containing almost pure water. The organic phase is recycled back to the column of dehydration, while the aqueous phase is fed to a column of stripping. The amount of acetic acid lost in the aqueous discharge is cut by approximately 40 per cent as AD results in a cleaner separation.

Uses of Acetic Acid

The chemical reagent for the processing of chemical compounds is acetic acid. In the production of vinyl acetate monomer, acetic anhydride, and ester production, the use of acetic acid is important.

  • Vinyl Acetate Monomer: Vinyl acetate monomer (VAM) processing is the main application of acetic acid. Vinyl acetate undergoes polymerization to produce polyvinyl acetate or other polymers, which are components of paints and adhesives. The reaction consists of ethylene and acetic acid with oxygen over a palladium catalyst.

\(2CH_ {3} COOH + 2C_ {2}H_ {4} + O_ {2} \rightarrow 2CH_ {3}CO_ {2}CH= CH_ {2} + 2H_ {2}O\)

Wood glue also utilizes vinyl acetate polymers.

  • Acetic Anhydride: Acetic anhydride is the result of the condensation of two acetic acid molecules. Significant use is the worldwide processing of acetic anhydride, utilizing about 25 per cent to 30 per cent of global acetic acid production. The key method includes acetic acid dehydration to give ketene at 700-750 °C.

\(CH_ {3}CO_ {2}H\rightarrow CH_ {2} = C= O + H_ {2}O\)

\(CH_ {3}CO_ {2}H + CH_ {2} = C= O \rightarrow {CH_{3}CO} _ {2}O\)

  • It is great for general disinfection and fighting mould and mildew since acetic acid kills fungi and bacteria. It is useful in a range of traditional and green cleaning materials, such as mould and mildew cleaners, floor cleaners, sprays for cleaning and dusting, and roof cleaners, either as vinegar or as an element.
  • The acetyl group is in use widely in the biochemistry field. Products made from acetic acid are an effective metabolizer of carbohydrates and fats when bound to coenzyme A.
  • As a treatment for otitis externa, it is the best and most effective drug in a health system on the World Health Organization’s List of Essential Medicines.

FAQs about Acetic Acid

Q.1 Explain the nomenclature of acetic acid?

Ans. the most chosen IUPAC and the trivial name is acetic acid. According to the substitutive nomenclature, the systematic term ethanoic acid, a true IUPAC name, comes from acetum, the Latin word for vinegar. It is synonymous with the word acid itself. Glacial acetic acid is a term for an acetic acid that is water-free (anhydrous). The name comes from the ice-like crystals which form slightly below room temperature at 16.6 °C, similar to the German name Eisessig (ice vinegar).

Q.2 Explain the structure of acetic acid?

Ans. It is observed that there is a chain of molecules in the solid-state of acetic acid where individual molecules are bound by hydrogen bonds to each other. In its vapour phase, dimers of ethanoic acid can be found at temperatures approximating 120. Also, in the liquid form of ethanoic acid, as it is found in a dilute solution, the dimers can be seen.

Q.3 What are the effects of acetic acid?

Ans. Concentrated acetic acid makes the skin corrosive. These burns or blisters don’t need to occur hours after exposure. Any irritation of the eyes, nose, and throat can result from excessive inhalation exposure (eight hours) to acetic acid vapours at 10 ppm; 100 ppm may result in marked lung irritation and potential damage to the lungs, eyes, and face.

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