Diaminobenzenes: an experimental and computational study.

Area of Science:

• Physical Chemistry
• Thermodynamics
• Computational Chemistry

Background:

• Diaminobenzenes are important organic compounds with applications in various chemical syntheses.
• Accurate thermodynamic data are crucial for understanding chemical stability and reactivity.
• Previous experimental data on the enthalpies of formation for diaminobenzene isomers may be limited or lack precision.

Purpose of the Study:

• To experimentally determine the standard molar enthalpies of formation for 1,2-, 1,3-, and 1,4-diaminobenzene in the gaseous phase at 298.15 K.
• To compare experimental results with theoretical calculations using ab initio methods.
• To assess the thermodynamic stability of the different diaminobenzene isomers.

Main Methods:

• Standard molar enthalpies of combustion were measured using static bomb combustion calorimetry.
• Standard molar enthalpies of sublimation were determined from temperature-vapor pressure data via the Knudsen mass loss effusion method.
• Ab initio molecular calculations at the G3(MP2)//B3LYP level were employed for theoretical estimations.

Main Results:

• The standard molar enthalpies of formation (gaseous phase, 298.15 K) were reported as: 1,2-diaminobenzene (86.6 ± 1.6 kJ·mol⁻¹), 1,3-diaminobenzene (89.6 ± 1.6 kJ·mol⁻¹), and 1,4-diaminobenzene (99.7 ± 1.7 kJ·mol⁻¹).
• Experimental and calculated values showed excellent agreement.
• 1,2-diaminobenzene was identified as the most thermodynamically stable isomer.

Conclusions:

• The experimental determination of enthalpies of formation provides reliable thermodynamic data for diaminobenzene isomers.
• Computational methods (G3(MP2)//B3LYP) are effective in predicting thermodynamic properties for these compounds.
• The findings confirm the superior thermodynamic stability of 1,2-diaminobenzene compared to its isomers.