Adventures in Thermochemistry
James S. Chickos*
Department of Chemistry and Biochemistry
University of Missouri-St. Louis
Louis MO 63121
E-mail:
jsc@umsl.edu
12
Jewel Box
Forest Park
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Applications of the The Correlation-Gas Chromatographic Method
Objectives: To go where no one else has gone
1. Evaluation of the vaporization enthalpies of large molecules
2. Application of Correlation-Gas Chromatography to a Tautomeric
Mixture - Acetylacetone
3. The Vaporization Enthalpies of Drugs and Related Substances
4. Evaluation of the Vaporization Enthalpies and Vapor Pressures of
Plasticizers
5. Identifying unusual interactions in heterocyclic systems
6. Other retention time gas chromatographic methods
Recently Ruzicka, et al. have questioned the accuracy of results from the GC
retention time measurements.
From the Clausius Clapeyron Eq where L = ∆lgHm
1/L1 dln(p1) = 1/(RT2)dT
1/L2 dln(p2) = 1/(RT2)dT
1/L1dln(p1) = 1/L2 dln(p2)
ln(p1) = L1/L2 ln(p2) + C
eq 1
Also p1/p2= ta2/ta1 therefore ln(p1) = ln(p2) - ln(ta1/ta2);
from eq 1, substituting for ln(p1):
L1/L2 ln(p2) + C = ln(p2) - ln(ta1/ta2)
and rearranging ln(ta1/ta2) = (1 – L1/L2)ln(p2) - C
A plot of ln(ta1/ta2) vs ln(p2) should result in a straight line with slope (1-L1/L2) and
intercept – C.
If the vapor pressure of p2 is known, then p1 can be calculated from eq 1
Ruzicka, K.; Koutek, B.; Fulem, M.; Hoskovec, M. Indirect Determination of Vapor
Pressures by Capillary Gas- Liquid Chromatography: Analysis of the Reference Vapor –
Pressure Data and Their Treatment. J. Chem. Eng. Data 2011, 57, 1349-68.
Using dibutyl phthalate as a standard, the vapor pressures (Pa) a variety of
herbicide esters at T = 298.15 K were evaluated including:
Pa
ethyl 2,4-dichlorophenoxyacetate
3.3·10-2
butoxyethyl 2,4-dichlorophenoxyacetate
6.1·10-4
n-butyl 2,4,5 trichlorophenoxyacetate
2.0·10-3
butoxyethyl 2,4,5 trichlorophenoxyacetate
2.0·10-4
n-butyl fenoprop
3.1·10-3
Measurements were made at T = (345 to 455) K and
extrapolated to T = 298.15 K
fenoprop
Hamilton, D. J. Chromatographic Measurements of Volatility of Herbicide Esters J. Chrom.
1980, 195, 75-83
Commercial empenthrin is marketed as a
mixture of several stereoisomers, two of
which could be clearly resolved by the
chromatography.
A vapor pressure of p/Pa = 230·10−4 at T = 298.15 K, evaluated using a variant of the GC
retention time method as reported by Hamilton has been reported by Tsuzuki,using dibutyl
phthalate and 2-ethylhexyl phthalate as standards using a modified variant of the method
reported by Hamilton.
Tsuzuki, M. Vapor pressures of carboxylic esters including pyrethroids: measurement and
estimation from molecular structure. Chemosphere 2001, 45, 729−36.
Empenthrin
Empentrin
This Work
Vapor pressures of p/Pa = (594 ± 380)·10−4 and (601 ±383)·10−4 at T = 298.15 K
∆lgHm (298.15 K) = (87.2 ± 4.8) and (87.0 ± 4.8) kJ·mol−1
Tnb/K = (567.9 and 569.2)
Tsuzuki
p/Pa = 230·10−4 at T = 298.15 K
,
Vaporization Enthalpies and Vapor Pressures of Two Insecticide Components, Muscalure and
Empenthrin, by Correlation Gas Chromatography. Spencer, J.; Chickos, J. Chem. Eng. Data
2013, 59, 3513-20.