The Boiling Point of Acetic Acid: A Comprehensive Guide

The boiling point of acetic acid, also known as ethanoic acid, is a crucial physical property that has been extensively studied and documented. According to the National Institute of Standards and Technology (NIST) WebBook, the normal boiling point of acetic acid is 392.4 K (119.25°C or 246.65°F) with an uncertainty of 1 K. This value is widely accepted as the reference for the boiling point of this important organic compound.

Understanding the Boiling Point of Acetic Acid

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid, and bubbles of vapor form inside the liquid. The boiling point of a compound is influenced by various factors, including:

1. Intermolecular Forces: Acetic acid molecules exhibit strong hydrogen bonding, which increases the intermolecular forces and raises the boiling point compared to non-polar compounds of similar molar mass.
2. Molecular Structure: The linear structure of the acetic acid molecule, with a carboxyl group (-COOH) at one end, contributes to the strong intermolecular interactions and higher boiling point.
3. Molar Mass: The molar mass of acetic acid (60.05 g/mol) is relatively low compared to other carboxylic acids, which also influences the boiling point.

The boiling point of acetic acid can be calculated using the Clausius-Clapeyron equation, which relates the vapor pressure of a substance to its temperature:

ln(P2/P1) = -(ΔHvap/R) * (1/T2 - 1/T1)

Where:
– P1 and P2 are the vapor pressures at temperatures T1 and T2, respectively
– ΔHvap is the enthalpy of vaporization of the substance
– R is the universal gas constant

Using the Clausius-Clapeyron equation and the known enthalpy of vaporization of acetic acid, the boiling point can be determined for a given pressure.

Experimental Determination of Acetic Acid Boiling Point

Researchers have employed various experimental techniques to measure the boiling point of acetic acid, including:

1. Dew-Bubble Point Temperature Method: Kato (1988) used this method to study the vapor-liquid equilibrium of binary systems of acetic acid with ethyl acetate and vinyl acetate, but did not explicitly report the boiling point of acetic acid.
2. Isothermal Vapor-Liquid Equilibrium: Hui et al. (1994) investigated the isothermal vapor-liquid equilibrium for associating systems of acetic acid and propylene glycol monomethyl ether, but did not provide the boiling point of acetic acid.
3. Liquid-Liquid Equilibria: Sayar et al. (1991) studied the liquid-liquid equilibria of the water + acetic acid + cyclohexyl acetate ternary system, but did not report the boiling point of acetic acid.
4. Vapor-Liquid Equilibrium in Strongly Associated Systems: Malijevska et al. (1986) investigated the vapor-liquid equilibrium of the acetic acid-propionic acid and acetic acid-trifluoroacetic acid systems, but did not explicitly state the boiling point of acetic acid.

While these studies provide valuable insights into the thermodynamic properties of acetic acid and its mixtures, the specific boiling point of acetic acid is not always explicitly reported.

Tabulated Data and Measurements for Acetic Acid Boiling Point

To provide a more comprehensive understanding of the boiling point of acetic acid, here is a table summarizing some key data points and measurements:

Property	Value	Reference
Normal Boiling Point	392.4 K (119.25°C or 246.65°F)	NIST WebBook
Boiling Point Uncertainty	±1 K	NIST WebBook
Enthalpy of Vaporization (ΔHvap)	55.07 kJ/mol	NIST WebBook
Vapor Pressure at 20°C	15.7 mmHg	Lide, D.R. (2005)
Vapor Pressure at 50°C	117 mmHg	Lide, D.R. (2005)
Vapor Pressure at 100°C	737 mmHg	Lide, D.R. (2005)

It’s important to note that the boiling point of acetic acid can be influenced by factors such as purity, pressure, and the presence of impurities or other substances. Therefore, the values reported in the literature may vary slightly depending on the experimental conditions and methods used.

Applications and Importance of Acetic Acid Boiling Point

The boiling point of acetic acid is a crucial property in various applications and industries, including:

1. Chemical Processing: The boiling point of acetic acid is essential in the design and operation of distillation columns, evaporators, and other chemical processing equipment used in the production of acetic acid and its derivatives.
2. Solvent Applications: Acetic acid is used as a solvent in various chemical processes, and its boiling point is an important parameter in determining its suitability and performance in these applications.
3. Pharmaceutical and Food Industries: Acetic acid is used as a preservative, pH regulator, and flavoring agent in the pharmaceutical and food industries, where its boiling point is a relevant property.
4. Environmental and Safety Considerations: The boiling point of acetic acid is a crucial factor in understanding its behavior and potential hazards, particularly in terms of storage, transportation, and handling.

Understanding the precise boiling point of acetic acid is essential for accurate process design, optimization, and safety in a wide range of industries and applications.

Conclusion

The boiling point of acetic acid is a well-established physical property, with a widely accepted value of 392.4 K (119.25°C or 246.65°F) reported by the NIST WebBook. This value is influenced by factors such as intermolecular forces, molecular structure, and molar mass. While specific boiling point data for acetic acid are not always explicitly reported in research studies, the available information provides a comprehensive understanding of this important parameter.

The knowledge of the boiling point of acetic acid is crucial in various applications, including chemical processing, solvent use, and environmental and safety considerations. Continued research and data compilation on the boiling point and other thermodynamic properties of acetic acid will further enhance our understanding and facilitate the development of more efficient and safer processes in the industries that rely on this versatile compound.

References:

1. Acetic acid – the NIST WebBook. https://webbook.nist.gov/cgi/cbook.cgi?ID=C64197&Type=TBOIL
2. Hui, Shuxian, et al. “Studies on Isothermal Vapor-Liquid Equilibrium for Associating Systems of Acetic Acid – Propylene Glycol Monomethyl Ether.” Experimental Results for DIPPR 1990-91 Projects on Phase Equilibria and Pure Component Properties, DIPPR Data Series No. 2, p. 1994.
3. Sayar, A.A., Tatli, B., and Dramur, U. “Liquid-Liquid Equilibria of the Water + Acetic Acid + Cyclohexyl Acetate Ternary.” Journal of Chemical Engineering Data, vol. 36, 1991, pp. 378.
4. Kato, M. “Vapor-Liquid Equilibrium Measurements for Binary Systems of Acetic Acid with Ethyl Acetate and Vinyl Acetate by the Dew-Bubble Point Temperature Method.” Journal of Chemical Engineering Data, vol. 33, 1988, pp. 499.
5. Malijevska, I., Sysova, M., and Vlckova, D. “Vapour-Liquid Equilibrium in Strongly Associated Systems. The Systems Acetic Acid-Propionic Acid and Acetic Acid-Trifluoroacetic Acid.” Collect. Czech. Chem. Commun., vol. 51, 1986, pp. 194.
6. Majer, V., and Svoboda, V. Enthalpies of Vaporization of Organic Compounds: A Critical Review and Data Compilation. Blackwell Scientific Publications, Oxford, 1985.
7. Lebedeva, N.D. “Heat of Combustion of A Series of Monocarboxylic Acids.” Zh. Fiz. Khim., vol. 38, 1964, pp. 2648.
8. Galska-Krajewska, A., and Zieborak, K. “Quaternary positive-negative azeotrope.” Rocz. Chem., vol. 36, 1962, pp. 119.
9. Lide, D.R. (2005). CRC Handbook of Chemistry and Physics, 86th Edition. CRC Press.