Due to highly development of chemical and biochemical industries, acetic acid has largely produced to fulfil the needs of world demand in production of daily used products and for pharmaceutical needs. Therefore, this study is carried out to introduce the production of acetic acid using biological pathways which includes the used of microorganisms. In this chapter will briefly explained on the knowledge about acetic acid and the microorganism. The chemical and biochemical pathways of production and usage of this product also will be further discussed in this chapter.
1.2 ACETIC ACID
Acetic acid is commonly known as ethanoic acid with chemical formula CH3COOH (Martin & Geoffey 1917). Basically acetic acid is carboxylic acid group which is the simplest carboxylic acid. The molecular structure of acetic acid is described as figure below:
Figure 1: Molecular structure of acetic acid (Martin & Geoffey, 1917)
The physical characteristics of acetic acid are concluded in table below: Molar mass
60.05 g mol−1
1.049 g cm-3
16-17 °C, 289-290 K, 61-62 °F
118-119 °C, 391-392 K, 244-246 °F
Solubility in water
1.22 mPa s
Table 1 : Physical characteristic of acetic acid (Stephen 2003) Since the acetic acid is in group of carboxylic acid, thus it undergoes all the chemical reaction of carboxylic acid.
The hydrogen center in the carboxyl group (−COOH) in carboxylic acids such as acetic acid can separate from the molecule by ionization: CH3CO2H → CH3CO2- + H+
Because of this release of the proton (H+), acetic acid has acidic character. Acetic acid is a weak monoprotic acid. In aqueous solution, it has a pKa value of 4.75. Its conjugate base is acetate (CH3COO−). A 1.0 M solution (about the concentration of domestic vinegar) has a pH of 2.4, indicating that merely 0.4% of the acetic acid molecules are dissociated.
Cyclic dimer of acetic acid; dashed lines represent hydrogen bonds (Benton 1974)
In solid acetic acid, the molecules form pairs (dimers), being connected by hydrogen bonds. The dimers can also be detected in the vapour at 120 °C (248 °F). Dimers also occur in the liquid phase in dilute solutions in non-hydrogen-bonding solvents, and a certain extent in pure acetic acid, but are disrupted by hydrogen-bonding solvents. The dissociation enthalpy of the dimer is estimated at 65.0–66.0 kJ/mol, and the dissociation entropy at 154–157 J mol−1 K−1. Other lower carboxylic acids dimerize in a similar fashion. (Benton 1974)
Liquid acetic acid is a hydrophilic (polar) protic solvent, similar to ethanol and water. With a moderate relative static permittivity (dielectric constant) of 6.2, it dissolves not only polar compounds such as inorganic salts and sugars, but also non-polar compounds such as oils and elements such as sulfur and iodine. It readily mixes with other polar and non-polar solvents such as water, chloroform, and hexane. With higher alkanes (starting with octane), acetic acid is not completely miscible anymore, and its miscibility continues to decline with longer n-alkanes. This dissolving property and miscibility of acetic acid makes it a widely used industrial chemical. Its solvent properties are mainly of value in the production of dimethyl terephthalate. (Benton 1974)
Acetic acid undergoes the typical chemical reactions of a carboxylic acid. Upon treatment with a standard base, it converts to metal acetate and water. With strong bases (e.g., organolithium reagents), it can be doubly deprotonated to give LiCH2CO2Li. Reduction of acetic acid gives ethanol. The OH group is the main site of reaction, as illustrated by the conversion of acetic acid to acetyl chloride. Other...
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