1378 J ournal of Chemical and Engineering Data, Vol. 47, No. 6, 2002
correlation method18 has been applied to derive enthalpies
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of vaporization ∆gl H° (298.15 K) of 3a -c. With use of this
m
method, impurities do not impact the results. We used our
experimental results for ∆gl H° (298.15 K) of the benzyl
(4) Verevkin, S. P.; Heintz, A. Chemical equilibria study in the
reacting system of the alkyl cumyl ether synthesis from n-alkanols
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stituent. Thermochim. Acta 1999, 332, 27-32.
m
halides obtained from the transpiration method as stan-
dards for the GC-correlation method. The following linear
correlation was obtained,
∆gl H° (298.15 K)/kJ ‚mol-1 ) 0.0468J x +2.74
m
(r )0.9948) (5)
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Geminal interactions between phenyl and electron-withdrawing
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Geminal interaction between phenyl and electron releasing
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Data 1999, 44, 1245-1251.
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for the molar vaporization enthalpies of benzyl halides (see
Table 1) using their Kovat’s indices (see Table 2). With eq
5, the values ∆gl H° (298.15 K) of compounds 3a -c have
m
been calculated and are presented in Table 2. The error in
the enthalpies of vaporization obtained by this method is
assumed to be within ((0.3 to 0.6) kJ ‚mol-1
.
3.3. Cor r ela tion of ∆lgH° of Ben zyl Der iva tives
m
with Th ose ∆gl H° of Alkyl An a logs. Taking into ac-
m
count the high chemical reactivity and thermal lability of
the benzyl derivatives, which could aggravate thermo-
chemical measurements, evidence of the reliability of the
results derived in this work seems to be desirable. Values
of ∆gl H° of benzyl derivatives derived in this work could
m
be checked for internal consistency using enthalpies of
formation of alkyl halides and alkyl ethers available from
the literature.10 Considering structures of the benzyl
derivatives presented in Figure 1, it is obvious that benzyl
derivatives (1) are parent to the structure of the ethyl
derivatives C2H5-X, for example, PhCH2-Cl (1b) and
C2H5-Cl. Benzyl derivatives (2) are parent to the structure
of the isopropyl derivatives iso-C3H7-X. Benzyl derivatives
(3) are parent to the structure of the tert-butyl derivatives
tert-C4H9-X. Thus, the correlation of the enthalpies of
vaporization of 1-3 with those of alkyl derivatives alkyl-
X, where X ) Hal or O-R, should give a linear correlation
if the data used for the correlation are reliable. It can be
seen from Figures 6 and 7 that our data for both families
(halides and ethers) of the compounds studied fit very well
in the linear correlation specific for each type of branching.
This relationship can subsequently be used at least as an
indication of the internal consistency of our experimental
results.
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Note Ad d ed a fter ASAP P ostin g
This article was posted in error on 7/27/2002 before all
author corrections had been made. The corrected version
was posted on 9/30/2002.
(23) Gellner, O. H.; Skinner, H. A. Dissociation energies of carbon-
halogen bonds. The bond strengths allyl-X and benzyl-X. J . Chem.
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Received for review February 18, 2002. Accepted May 27, 2002.
Some of us (E.K. and T.V.) gratefully acknowledge
a research
scholarship from the DAAD (Deutscher Akademischer Austausch-
dienst).
J E020034H