Enthalpies of formation of 2-methyl-2-ethoxypropane and 2-ethyl-2-ethoxypropane from equilibrium measurements

Article abstract of DOI:10.1006/jcht.1995.0077

The equilibria for the synthesis of C2H5OC(CH3)3 (A) and C2H5OC(CH3)2(C2H5) (B) from C2H5OH (C) and CH2:C(CH3)2 (D) or CH3CH:C(CH3)2 (E) in the liquid phase were investigated at temperatures from 313 K to 412 K.On the basis of experimental equilibrium constants found for n(C)/n(D) or n(C)/n(E) >/= 4, the following values were obtained for Δ_rH⁰_m/(kJ * mol^-1) and Δ_rS⁰_m/(J * K^-1 * mol^-1): (C + D = A), -(35.45 +/- 1.94) and -(82.37 +/- 5.99); (C + A = B), -(34.13 +/- 0.81) and -(87.82 +/- 2.18).The following values of Δ_fH⁰_m(298.15 K)/(kJ * mol^-1) have been derived: C2H5OC(CH3)3(l), -(350.8 +/- 2.6); C2H5OC(CH3)2(C2H5)(l), -(379.8 +/- 1.4).

Full text of DOI:10.1006/jcht.1995.0077

O-565
J. Chem. Thermodynamics 1995, 27, 751–753
Enthalpies of formation of
2-methyl-2-ethoxypropane and
2-ethyl-2-ethoxypropane from equilibrium
measurements
K. G. Sharonov, A. M. Rozhnov,a A. V. Korol’kov,
S. Y. Karaseva,
Samara State Technical University, Department of Chemical Technology,
Samara 443010, Russia
E. A. Miroshnichenko, and L. I. Korchatova
Institute of Chemical Physics of the Russian Academy of Sciences,
Thermochemical Laboratory, Moscow 117977, Russia
(Received 29 August 1994; in final form 2 December 1994)
The equilibria for the synthesis of C2H5OC(CH3)3 (A) and C2H5OC(CH3)2(C2H5) (B)
from C2H5OH (C) and CH2:C(CH3)2 (D) or CH3CH:C(CH3)2 (E) in the liquid phase
were investigated at temperatures from 313 K to 412 K. On the basis of experimental
equilibrium constants found for n(C)/n(D) or n(C)/n(E)e4, the following values were
obtained for DrHm°/(kJ·mol−1
)
and DrSm°/(J·K−1·mol−1): (C+D=A), −(35.4521.94)
and −(82.3725.99); (C+A=B), −(34.1320.81) and −(87.8222.18). The following values of
have been derived: C2H5OC(CH3)3(l), −(350.822.6);
DfHm°(298.15 K)/(kJ·mol−1
)
C2H5OC(CH3)2(C2H5)(l), −(379.821.4). 7 1995 Academic Press Limited
1. Introduction
Alkyl ethers based on methanol or ethanol and an isoolefin are used in industry as
high-octane additives to motor fuels which do not contain tetraethyl lead.
The basic method of producing alkyl tert-alkyl ethers is the interaction of the
appropriate alkanol with an isoolefin in the liquid phase in the presence of a catalyst.
These are equilibrium reactions and investigations of the thermodynamics of synthesis
processes are needed.
Our laboratory is conducting systematic investigations of the synthesis processes of
ethers based on the alcohols C1 to C5 in the liquid and gas phases. Results have been
given previously.(1–8) To continue these investigations, we studied the equilibria of
liquid-phase reactions of ethanol with 2-methylpropene and 2-methylbut-2-ene.
a To whom all correspondence should be addressed.
0021–9614/95/070751+03 $12.00/0
7 1995 Academic Press Limited

752
K. G. Sharonov et al.
2. Experimental and results
Equilibria of the reactions:
C2H5OH+CH2:C(CH3)2=C2H5OC(CH3)3,
(1)
(2)
C2H5OH+CH3CH:C(CH3)2=C2H5OC(CH3)2 (C2H5),
were investigated in the liquid phase in sealed glass ampoules in the presence of
‘‘sulfocationite’’ KU-23 as a catalyst at temperatures from 313 K to 412 K.
As was shown elsewhere,(5) the mole-fraction equilibrium constants Kx
found when C2H5OH is in excess can be used for the calculation of the enthalpy
of reaction in the liquid non-ideal mixture: (alcohol+isoolefin+ether). On the
basis of this conclusion as well as the results from reference 8, the investigation
of equilibrium was made with the mole ratio n(C2H5OH)/n{CH2:C(CH3)2}
or n(C2H5OH)/n{CH3 CH:C(CH3)2}e4. The criteria for equilibrium were the stability
of the equilibrium constants on changing the starting product (direct or reverse
reaction), quantity of the catalyst, and time of the reaction. The analysis of the reaction
products was made by g.l.c. with the help of a ‘‘Crom-4’’ apparatus with a
flame-ionization detector on a packed column 2.5 m long filled with 5 mass per cent
of SE-30 on AW-HMDS Inertone. The column temperature was 363 K, and the
evaporator temperature was 453 K. Helium was used as a carrier gas.
2-Methylpropene (mass fraction, 0.998) and mixtures of methylbutenes (mass
fraction, 0.99), dehydrated ethanol (mass fraction, 0.995), and ethers (mass fraction,
0.995) were used for the investigation of equilibria. Ethers were produced in the
laboratory through the interaction of ethanol and the corresponding isoolefin.
TABLE 1. Results of reations (1) and (2) in the liquid phase in the presence of sulfocationite KU-23; w, mass fraction
of catalyst; t, time of experiment; N, number of experiments; x, mole fraction in equilibrium mixture; ꢀKx ꢁ, mean value
of mole-fraction constant Kx
T/K
102·w
t/h
N a
x
ꢀKx ꢁ
C2H5OH
(CH3)2C:R'
C2H5OC(CH3)2R
Reaction (1): R'=CH2; R=CH3
323
343
363
383
403
10 to 15
10 to 15
10 to 12
8 to 10
20 to 110
2 to 18
7 to 17
1 to 15
8 (6)
12 (4)
6 (6)
9 (6)
4 (6)
0.8400
0.8020
0.7730
0.7675
0.7734
0.0070
0.0178
0.0385
0.0624
0.0938
0.1530
0.1802
0.1885
0.1701
0.1328
26.0220.95
12.6220.36
6.3320.34
3.5520.14
1.8320.13
5 to
8
0.25 to
6
Reaction (2): R'=CHCH3; R=C2H5
313
323
343
363
383
403
412
12 to 15
10 to 15
10 to 15
10 to 12
8 to 10
20 to 100
20 to 80
3 to 20
2 to 10
10 (8)
6 (6)
6 (6)
10 (6)
8 (8)
8 (6)
0.8114
0.8119
0.8125
0.8361
0.8395
0.8462
0.8576
0.0168
0.0232
0.0452
0.0577
0.0827
0.0940
0.0992
0.1718
0.1649
0.1432
0.1062
0.0778
0.0598
0.0432
12.6020.32
8.7520.15
3.8720.10
2.2020.06
1.1220.01
0.7520.01
0.5120.01
0.50 to
8
5
3
5 to
3 to
8
5
0.25 to
0.15 to
6 (10)
a For reaction or, in parentheses, the reverse of the reaction.

DfHm°{C2H5OC(CH3)3 or C2H5OC(CH3)2(C2H5)}
753
The results of the experiments are shown in table 1. The values of the equilibrium
constants of reactions (1) and (2) are described by equations: for reaction (1),
lg Kx=1852(K/T)−4.303, and for reaction (2), lg Kx=1783(K/T)−4.588. The
following values of the thermodynamic quantities in the liquid phase were obtained:
DrHm°(1)=−(35.4521.94) kJ·mol−1
,
DrSm°(1)=−(82.3725.99) J·K−1 ·mol−1,
DrHm°(2)=−(34.1320.81) kJ·mol−1, DrSm°(2)=−(87.8222.18) J·K−1·mol−1.
The values of DrHm° found in the investigation are consistent with the results
for the enthalpies of the liquid-phase reactions of synthesis of ethers. The
values of DrHm° for reactions of CH2:C(CH3)2 with an alcohol were obtained:
CH3OH, −(39.820.4) kJ·mol−1;(9) CH3(CH2)2CH2OH, −(34.822.7) kJ·mol−1;(7)
CH3(CH2)3CH2OH, −(35.6621.96) kJ·mol−1.(5) For the reaction of
CH3OC(CH3)2(C2H5) synthesis, DrHm°=−(35.9523.59) kJ·mol−1 was found.(4)
The values of DfHm° of ethers from chemical equilibria were obtained by combination
of DrHm° from this work and DfHm°(298.15 K) values for CH2:C(CH3)2,(10)
CH3CH:C(CH3)2,(10) and C2H5OH.(11) The values of DfHm°(298.15 K) found for
the ethers are for C2H5OC(CH3)2, −(350.822.6) kJ·mol−1 and for
C2H5OC(CH3)2(C2H5), −(379.821.4) kJ·mol−1.
It can be assumed that the difference in molar enthalpies of formation
of C2H5OC(CH3)3 and CH3OC(CH3)3 (MMOP) will be the same as the difference
between DfHm° of C2H5OC(CH3)2(C2H5) (EEOP) and CH3OC(CH3)2(C2H5).
The molar enthalpy of formation of CH3OC(CH3)3 from reference 12
is −313.56 kJ·mol−1. If we accept for C2H5OC(CH3)3 (MEOP) the value of
DfHm° = −350.8 kJ·mol−1, then D = {DfHm°(MEOP) − DfHm°(MMOP)} = (−350.8 +
313.56) kJ·mol−1 = −37.24 kJ·mol−1. The value of DfHm° of CH3OC(CH3)2(C2H5) is
−340.7 kJ·mol−1.(6) That gives with the increment −37.34 kJ·mol−1 a value of the
molar enthalpy of formation of C2H5OC(C2H5)CH3 equal to −377.94 kJ·mol−1. This
value is close to DfHm°(EEOP) found from chemical equilibria.
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