Vapor Pressures of Acetonitrile Determined by Comparative Ebulliometry

• Published in: Journal of chemical and engineering data 2004-05, Vol.49 (3), p.486-491
• Main Authors: Ewing, Michael B, Ochoa, Jesus C. Sanchez
• Format: Article
• Language: English
• Subjects: Chemical thermodynamics; Chemistry; Exact sciences and technology; General and physical chemistry; General. Theory
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/je034144f

The vapor pressures of acetonitrile have been measured over the temperature and pressure range of 278 K and 4.3 kPa to 540 K and 4455 kPa. The upper limit exceeds the temperature at which decomposition of acetonitrile begins (about 536 K) so we were able to assess the effect of pyrolysis on the vapor pressures. Acetonitrile is strongly hygroscopic, and a comparison of results obtained with “wet” and “dry” samples allowed us to investigate in a similar way the effect of water as an impurity. The results have been correlated using generalized Wagner equations, a key feature of which is the use of the reversed reduced temperature τ = 1 − T/T c where T c is the critical temperature. The standard form with terms in τ, τ 1.5, τ 2.5, and τ 5 produced unacceptable systematic deviations; but the equation ln(p/p c) = (T c/T)(c 1τ + c 1.5τ1.5 + c 2τ2 + c 2.5τ2.5 + c 5.5τ5.5), where p c is the critical pressure, fits our results from 291 K to 535 K with a standard deviation of 63 × 10-6 in ln p and significantly extends the range of correlation, toward both the triple and critical points, compared with work already in the literature. By extrapolation to T c = 545.46 K, we obtain 4835 kPa for the critical pressure p c and 167 Pa for the triple-point pressure at T s+l+g = 229.35 K. An Antoine equation that describes the results below a pressure of 125 kPa with a standard deviation of 1.5 mK in the condensation temperature has also been obtained.