Standard molar enthalpies of formation of sodium alkoxides

Article abstract of DOI:10.1016/j.jct.2006.07.024

The molar enthalpies of solution of sodium in methanol, ethanol, and n-propanol and of sodium alkoxides in their corresponding alcohols were measured at T = 298.15 K using an isoperibol solution calorimeter. From these results and other auxiliary data, the standard molar enthalpies of formation Δ_f H_m^{{ring operator}} (RONa,cr) of sodium methoxide, sodium ethoxide, and sodium n-propoxide were calculated and found to be {(-366.21 ± 1.38), (-413.39 ± 1.45), and (-441.57 ± 1.18)} kJ · mol^-1, respectively. A linear correlation has been found between Δ_f H_m^{{ring operator}} (RONa) and Δ_f H_m^{{ring operator}} (ROH) for R = n-alkyl, enabling the prediction of data for other sodium alkoxides.

Full text of DOI:10.1016/j.jct.2006.07.024

J. Chem. Thermodynamics 39 (2007) 449–454
www.elsevier.com/locate/jct
Standard molar enthalpies of formation of sodium alkoxides
a
a
b
a,
*
K. Chandran , T.G. Srinivasan , A. Gopalan , V. Ganesan
a
Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, TN, India
b
Industrial Chemistry Department, Alagappa University, Karaikudi 630 006, TN, India
Received 14 April 2006; received in revised form 9 July 2006; accepted 20 July 2006
Available online 12 August 2006
Abstract
The molar enthalpies of solution of sodium in methanol, ethanol, and n-propanol and of sodium alkoxides in their corresponding
alcohols were measured at T = 298.15 K using an isoperibol solution calorimeter. From these results and other auxiliary data, the stan-
dard molar enthalpies of formation Df HꢀmðRONa; crÞ of sodium methoxide, sodium ethoxide, and sodium n-propoxide were calculated
and found to be {(ꢁ366.21 1.38), (ꢁ413.39 1.45), and (ꢁ441.57 1.18)} kJ Æ molꢁ1, respectively. A linear correlation has been
found between Df HꢀmðRONaÞ and Df HꢀmðROHÞ for R = n-alkyl, enabling the prediction of data for other sodium alkoxides.
Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Sodium methoxide; Sodium ethoxide; Sodium n-propoxide; Solution calorimeter; Enthalpy of formation
1. Introduction
viz. methanol [2], ethanol [3], Jaysol SS [4], propanol [5,6],
butyl cellosolve [7], ethyl carbitol [8,9], etc., have been used
world wide for sodium removal purposes.
Liquid sodium is used as coolant in fast reactors (FRs).
During the operation of these reactors, a thin layer of
sodium adheres to the steel components in the coolant cir-
cuit due to wetting. During reactor maintenance, some of
these components need to be replaced or maintained peri-
odically. Exposure of such sodium wetted components to
air could lead to fire and possible hydrogen explosion as
the reaction between sodium and moisture present in air
is highly exothermic in nature. In addition to posing safety
related problems, this reaction also adversely affects the
mechanical properties of the steel components due to the
formation of sodium hydroxide. These problems could be
tackled by using suitable solvent to dissolve sodium under
controlled conditions and avoiding residual sodium
hydroxide on the components. Lutton et al. [1] have
described several sodium removal techniques. The highly
reactive sodium metal can be converted into its less reactive
compound either by using an aqueous or a non-aqueous
reagent. Among the non-aqueous reagents, several alcohols
There were reports of run-away reactions leading to
accident when ethyl carbitol was used for cleaning sodium
storage tanks in France [8] and Germany [9]. Measure-
ments of thermochemical data such as enthalpy of forma-
tion, enthalpy of solution, heat capacity, thermal
decomposition behaviour, etc., of sodium alkoxides are
useful for better understanding of sodium–alcohol reaction
and to avoid recurring of such eventualities during sodium
cleaning processes. The preparation and characterization
of sodium alkoxides namely, sodium methoxide, sodium
ethoxide, and sodium n-propoxide were reported elsewhere
[10]. Heat capacity measurements, crystal structure elucida-
tion, thermal decomposition, and kinetic analysis of all
these sodium alkoxides were studied and reported else-
where [11–13]. Since data on enthalpy of solution of
sodium alkoxides in alcohol and enthalpy of formation of
sodium n-propoxide are not available, the present work
was taken up. The enthalpy of formation of sodium meth-
oxide, and sodium ethoxide was also measured in the pres-
ent study, compared with the reported data [14–19] as
given in table 1 and discussed.
*
Corresponding author. Tel.: +91 44 27480098; fax: +91 44 27480065.
E-mail address: ganesh@igcar.gov.in (V. Ganesan).
0021-9614/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jct.2006.07.024

450
K. Chandran et al. / J. Chem. Thermodynamics 39 (2007) 449–454
2. Experimental
2.1. Chemicals
calorimetric vessel was made up of a double walled, bright
silvered, vacuum-sealed glass Dewar having a capacity of
400 cm3 and fitted with a perspex flange with an O-ring.
The top flange has appropriate provisions to facilitate the
introduction of stirrer, a sample bulb, a calibration heater
and a thermistor probe. The calibration heater used was a
PTFE-coated KARMA wire with a resistance of 4.35 X,
wound non-inductively over a PTFE disc and enclosed in
a glass bulb. The bulb was filled with n-hexadecane
(>0.99 mass fraction purity) from Kasci Kogyo, Tokyo,
enough to submerge the heating element for better heat
transfer. The sample tube had a thin walled bulb at the
base, provision for introducing a plunger, which could
move up and down through a leak tight fitting. Using this
plunger the thin walled base could be broken in order to
introduce the sample in to the solvent. The calorimetric
vessel was kept in a constant temperature water bath hav-
ing a control accuracy of 0.01 K. The temperature of the
bath was maintained at 298.15 K throughout the experi-
ment. A thermistor probe with a sensitivity of 2 Æ 10ꢁ4 K
was used to measure the temperature in the calorimetric
vessel. A HP 34401A, 612 digit, multimeter was used for pre-
cise current measurement. A control unit consisting of a
stabilised power-supply unit, a constant-current power
supply unit with a quartz crystal based timer and glitch free
solid-state relay was used for switching the supply ON and
OFF for a preset time during the electrical calibration.
Both temperature and time data were acquired through a
personal computer. The calorimeter performance was
tested using KCl from NIST (SRM 1655), which had been
heated at T = 800 K to remove occluded water, cooled and
stored in a dry argon atmosphere glove box. Since KCl is
moisture sensitive, weighing and loading operations were
performed in an argon atmosphere dry box. Each addition
of KCl was carried out with 100 cm3 of distilled water. The
calorimeter performance was also tested with tris (hydroxy
methyl) amino-methane (Tris). The enthalpy of solution
Nuclear grade sodium (mass fraction purity 0.995) from
Alkali Metals, India, was further purified by vacuum distil-
lation. The HPLC grade methanol (mass fraction purity
0.998) from Ranbaxy Fine Chemicals, India, absolute eth-
anol (mass fraction purity 0.999) from Hayman, UK, and
AR grade n-propanol (mass fraction purity 0.995) from
SD Fine Chemicals, India, were further purified by distilla-
tion [20] and were used for the preparation of their respec-
tive sodium alkoxides.
2.2. Preparation of sodium alkoxides
The reaction of sodium metal with alcohol to yield the
respective sodium alkoxide was performed in dry argon
atmosphere using a gas-tight glass vessel. Solid sodium
pieces weighing about 500 mg each were added to 150 cm3
of alcohol taken in the reaction vessel. When the alcohol
was nearly saturated, the addition of sodium was stopped.
The excess alcohol was removed by vacuum distillation
and the reaction product was dried at room temperature
for about 6 h. The temperature of the reaction vessel was
subsequently raised to 353 K to remove the final traces of
alcohol. A free flowing milky white powder of sodium alk-
oxide was obtained and stored in the argon atmosphere
glove box. The formation and phase purity of sodium alkox-
ides were confirmed by IR spectroscopy and X-ray powder
diffraction studies and the chemical assay was determined by
Atomic Emission Spectroscopy and CHNS analyser.
2.3. Calorimeter
The schematic of an iso-peribol solution calorimeter
used in the present work was reported elsewhere [21]. The
TABLE 1
Thermochemical data on (sodium + alcohol) systems
Serial No.
1
Author
Reaction scheme
DsolHꢀmðRONa=ROHÞ
=
Df Hꢀ
=
ðkJ ꢂ molꢁ1
Þ
ðkJ ꢂmmðRoOlꢁN1a; crÞ
Þ
Forcrand and Berthelot [14]
Na þ CH3OHexcess ! ½CH3ONaꢃ
þ 1=2H2
ꢁ200.96
ꢁ187.02
ꢁ177.19
CH3OH
Na þ C2H5OHexcess ! ½C2H5ONaꢃ
þ 1=2H2
C2H5OH
Na þ n-C3H7OHexces ! ½C3H7ONaꢃ
þ 1=2H2
C3H7OH
2
3
4
Blanchard et al. [15]
Voice [16]
2C2H5ONa þ 0:1N H2SO4soln ! ½Na2SO4ꢃ
þ ½C2H5OHꢃ
ꢁ490.8 5.7
H2O
H2O
Na þ C2H5OHexcess ! ½C2H5ONaꢃ
CH3ONa þ H2Oexcess ! ½NaOHꢃ
þ 1=2H2
ꢁ189a
C2H5OH
Leal et al. [17]
þ ½CH3OHꢃ
ꢁ58.3 2.4
ꢁ60.9 1.8
ꢁ54.0 1.5
ꢁ113.6 3.0
ꢁ203.95 1.30
ꢁ190.43 1.34
ꢁ180.87 0.84
ꢁ76.84 0.34
ꢁ54.84 0.39
ꢁ41.90 0.66
ꢁ372.4 2.4
ꢁ411.6 1.9
ꢁ461.6 1.7
ꢁ375.7 3.1
ꢁ366.21 1.38
ꢁ413.39 1.45
ꢁ441.57 1.18
H2O
H2O
C2H5ONa þ H2Oexcess ! ½NaOHꢃ
þ ½C2H5OHꢃ
H2O
H2O
i-C3H7ONa þ H2Oexcess ! ½NaOHꢃ
þ ½C3H7OHꢃ
H2O
H2O
CH3ONa þ 0:1 N HCl soln ! ½NaClꢃ
Na þ CH3OHexcess ! ½CH3ONaꢃ
þ ½CH3OHꢃ
H2O
H2O
5
This work
þ 1=2H2
CH3OH
Na þ C2H5OHexcess ! ½C2H5ONaꢃ
þ 1=2H2
C2H5OH
Na þ n-C3H7OHexcess ! ½n-C3H7ONaꢃ
þ 1=2H2
C3H7OH
CH3ONa þ CH3OHexcess ! ½CH3ONaꢃ
CH3OH
C2H5ONa þ C2H5OHexcess ! ½C2H5ONaꢃ
C2H5OH
n-C3H7ONa þ C3H7OHexcess ! ½n-C3H7ONaꢃ
C3H7OH
a
Value taken from figure since no raw data were available.

K. Chandran et al. / J. Chem. Thermodynamics 39 (2007) 449–454
451
TABLE 2
was measured by dissolving known amount of Tris (0.997
mass fraction purity) from MERK, UK, in 100 cm3 of
The molar enthalpies of solution of sodium in alcohols at T = 298.15 K
0.1 mol Æ dmꢁ3 HCl (aq).
Sample
m/g
DH/J
DsolHꢀmðNa=ROHÞ=ðkJ ꢂ molꢁ1
Þ
Na (cr) {methanol}
0.0137 ꢁ121.27
ꢁ203.50
M = 22.9898 g Æ molꢁ1 0.0106
ꢁ94.9
ꢁ205.82
2.4. Calorimeter measurement
0.0181 ꢁ159.69
0.0509 ꢁ450.89
ꢁ202.83
ꢁ203.65
Metallic sodium samples (10 to 40) mg were taken in a
dry sample holder glass bulb kept in high purity argon
atmosphere glove box suitable for handling liquid alkali
metals [22]. Exactly 200 cm3 of the alcohol (methanol, eth-
anol, and n-propanol) were transferred into the calorimetric
vessel. Then it was fitted with the top flange and immersed
in the constant temperature water bath and allowed to
attain thermal equilibrium. The temperature of the calorim-
eter was recorded against time. When temperature of the
solvent reached a stable value, the calorimeter was cali-
brated by electrical heating by applying a constant current
for a known time. The sodium sample was then introduced
in to alcohol by breaking the glass bulb. From the thermo-
gram obtained, true temperature changes (DT) for known
energy input and sample addition were measured as detailed
by Coops et al. [23] and were used for the evaluation of the
energy change for the reaction.
Mean: ꢁ203.95 1.30a
Na (cr) {ethanol}
0.0095
ꢁ78.27
ꢁ189.41
0.0398 ꢁ331.7
0.0151 ꢁ125.82
0.0310 ꢁ255.04
ꢁ191.60
ꢁ191.56
ꢁ189.14
Mean: ꢁ190.43 1.34a
Na (cr) {n-propanol}
0.0093
ꢁ72.88
ꢁ180.16
0.0141 ꢁ111.27
0.0207 ꢁ163.66
ꢁ181.42
ꢁ181.76
0.0108
ꢁ84.63
ꢁ180.15
Mean: ꢁ180.87 0.84a
Note: m denotes the mass of sodium added, M the molar mass of sodium,
DH the measured enthalpy change, and DsolHꢀm the molar enthalpy of
solution.
a
Uncertainties are twice the standard deviation of the mean.
TABLE 3
The molar enthalpies of solution of sodium alkoxides in alcohols at
T = 298.15 K
Similar experiments were carried out by taking samples
of dry sodium alkoxides in powder form (10 to 100) mg to
measure the enthalpy of solution. The quantity of alcohol
was measured before and after sample addition to check
for any evaporation loss of alcohol, which was found to
be insignificant during all these experiments.
Sample
m/g
DH/J
DsolHꢀmðRONa=ROHÞ
=
ðkJ ꢂ molꢁ1
Þ
CH3ONa (cr) {methanol}
M = 54.0244 g Æ molꢁ1
0.0219 ꢁ31.22
0.0281 ꢁ39.99
0.0315 ꢁ44.52
0.0225 ꢁ32.12
ꢁ77.02
ꢁ76.88
ꢁ76.35
ꢁ77.12
Mean: ꢁ76.84 0.34a
3. Results and discussion
C2H5ONa (cr) {ethanol}
M = 68.0516 g Æ molꢁ1
0.0668 ꢁ54.39
0.0605 ꢁ48.76
0.0596 ꢁ47.64
0.0636 ꢁ51.01
0.0921 ꢁ74.37
ꢁ55.41
ꢁ54.85
The molar enthalpy of solution of KCl in distilled water
DsolHꢀm measured in this work to test the performance of
the calorimeter is (17.23 0.02) kJ Æ molꢁ1 which is in close
agreement with the value of (17.21 0.01) kJ Æ molꢁ1
reported by Venugopal et al. [24] and NBS value of
(17.241 0.018) kJ Æ molꢁ1 [25]. The value of the molar
enthalpy of solution of Tris measured in the present work
is DsolHꢀm ¼ ðꢁ30:13 ꢄ 0:23Þ kJ ꢂ molꢁ1, which is in agree-
ment with the NIST value of (ꢁ29.77 0.03) kJ Æ molꢁ1
[26]. The results obtained in this study are listed in tables
2 and 3.
ꢁ54.40
ꢁ54.58
ꢁ54.95
Mean: ꢁ54.84 0.39a
C3H7ONa (cr) {n-propanol} 0.0369 ꢁ18.67
ꢁ41.53
M = 82.078 g Æ molꢁ1
0.0461 ꢁ24.03
0.0353 ꢁ18.07
0.0390 ꢁ19.61
ꢁ42.78
ꢁ42.02
ꢁ41.27
Mean: ꢁ41.90 0.66a
Note: m denotes the mass of sodium alkoxides added, M the molar mass of
sodium alkoxides, DH the measured enthalpy change, and DsolHꢀm the
molar enthalpy of solution.
a
Uncertainties are twice the standard deviation of the mean.
Table 1 gives the data available in the literature on
enthalpies of solution and enthalpies of formation of
sodium alkoxides reported by various authors. These
values are compared with the present measured values.
The molar enthalpies of solution of sodium in various
alcohols namely methanol, ethanol, and n-propanol mea-
sured in the present study are given in table 2. The mean
experimental values of DsolHꢀmðNa=ROHÞ are {(ꢁ203.95
tion among the present values of enthalpies of solution
of sodium in alcohols and that reported by Forcrand
and Berthelot [14]. In the present measurements, the con-
centration of RONa in alcohol is always very low (1 mol
of Na/RONa to (4 to 20) Æ 103 moles of alcohol), assum-
ing this is effectively close to infinite dilution. The present
value for sodium-ethanol case is in good agreement with
the value reported by Voice [16] who made the measure-
ment with the dilution of 1:1000.
1.30), (ꢁ190.43 1.34), and (ꢁ180.87 0.84)} kJ Æ molꢁ1
,
respectively, for the above cases. The values (ꢁ200.96,
ꢁ187.02, and ꢁ177.19) kJ Æ molꢁ1 are reported by Forc-
rand and Berthelot [14]. Voice [16] has measured the
molar enthalpy of solution in (sodium + ethanol) system
and the value is ꢁ189 kJ Æ molꢁ1. There is a small varia-
Molar enthalpies of solution of sodium alkoxides
namely sodium methoxide, sodium ethoxide, and sodium
n-propoxide in corresponding alcohols measured in the

452
K. Chandran et al. / J. Chem. Thermodynamics 39 (2007) 449–454
present work are given in table 3. The mean of experimen-
tal values of DsolHꢀmðRONa=ROHÞ are {(ꢁ76.84 0.34),
(ꢁ54.84 0.39), and (ꢁ41.90 0.66)} kJ Æ molꢁ1, respec-
tively. The values from NBS Table for sodium methoxide,
formation of sodium ethoxide reported by Blanchard [15]
is (ꢁ490.8 5.9) kJ Æ molꢁ1, which is distinctly high com-
pared with the values obtained in the present work and
those reported in the literature [17–19]. The data on sodium
n-propoxide derived in the present work are reported for
the first time.
The derived enthalpies of reaction of sodium and alco-
hols, namely methanol, ethanol, and n-propanol in the
present work are DrHꢀmðNa=ROHÞ ¼ fðꢁ127:11 ꢄ 1:34Þ;
ðꢁ135:59 ꢄ 1:40Þ; and ðꢁ138:97 ꢄ 1:07Þg kJ ꢂ molꢁ1, respec-
tively. The present values of enthalpies of reaction of
sodium with methanol and ethanol are compared by sub-
tracting the values of enthalpies of formation of sodium
methoxide, sodium ethoxide and the corresponding alco-
hols reported in NBS Table and found to be ꢁ129.1 and
ꢁ136.1 kJ Æ molꢁ1. The present measurements are in good
agreement with NBS data.
Leal et al. [17] have reported a linear expression for cor-
relating the enthalpies of formation of sodium methoxide,
sodium ethoxide, and sodium n-butoxide against enthalpies
of formation of their corresponding alcohols. A similar
procedure is followed in the present work for the com-
pounds of sodium alkoxides. The linear expression
obtained is given below and is also shown in figure 1.
and sodium ethoxide are (ꢁ72.36 and ꢁ51.9) kJ Æ molꢁ1
,
respectively [18]. The molar enthalpy of solution of sodium
n-propoxide in n-propanol is reported for the first time.
The reactions from which the standard molar enthalpies
of formation of sodium alkoxides Df HꢀmðRONa; crÞ have been
derived in the present work are given in tables 4 and 5.
Reaction (1) represents the formation of sodium alkoxide
and its subsequent dissolution in excess alcohol. Reaction
(2) represents the dissolution of crystalline sodium alkoxide
in excess alcohol. The enthalpy changes for reactions (1)
and (2) were measured experimentally in the present work.
The enthalpy change for the reaction involving 1 mol of
sodium with 1 mol of alcohol ðDHð3Þ ¼ DrHꢀmðNa=ROHÞÞ
was deduced from DH(2) and DH(1). The enthalpy of for-
mation of sodium alkoxide DHð5Þ ¼ Df HꢀmðRONa; crÞ for var-
ious alcohols obtained from DH(3) and DH(4) [27] are
given in table 5.
Enthalpies of formation of sodium methoxide, sodium
ethoxide, and sodium n-propoxide derived in this work
are
Df HꢀmðRONaÞ ¼ fðꢁ366:21 ꢄ 1:38Þ; ðꢁ413:39 ꢄ 1:45Þ;
and ðꢁ441:57 ꢄ 1:18Þg kJ ꢂ molꢁ1, respectively. Leal et al.
[17] have reported the enthalpy of formation of sodium
methoxide derived by two different methods as given
DHꢀf ðRONa; crÞ ¼ ð1:19 ꢄ 0:02Þ DHꢀf ðROH; lÞꢁ
ð82:10 ꢄ 6:15Þ:
ð1Þ
Good linear correlation (r = 0.9998) is observed in equa-
tion (1), which is in good agreement with the expression
reported by Leal et al. [17]. Similar practices have also been
reported in the literature for many inorganic and organo-
metallic complexes of transition metals of type MXnLm
(M = Ti, Mo, W; X = halogen; L = H, alkyl, aryl, alkoxy,
azobenzene, etc.) and used to estimate the enthalpies of for-
mation of new complexes [28,29].
in table
1
and the values are (ꢁ372.4 2.4) and
(ꢁ375.7 3.1) kJ Æ molꢁ1. The value for sodium methoxide
reported in NBS Table is ꢁ367.8 kJ Æ molꢁ1. The present
derived data for sodium methoxide are in good agreement
with the NBS value [18,19] although a small variation is
observed with the data reported by Leal et al. [17]. The
enthalpy of formation of sodium ethoxide derived in
this work is in good agreement with the value of
(ꢁ411.6 1.9) kJ Æ molꢁ1 reported by Leal et al. [17] and
NBS [18,19] value of ꢁ413.8 kJ Æ molꢁ1. The enthalpy of
In a similar fashion, enthalpies of solution of sodium
and sodium alkoxides in their respective alcohols obtained
TABLE 4
Reaction scheme (T = 298.15 K) for the standard molar enthalpy of formation of RONa(cr) with typical value for CH3ONa(cr)
Reaction
DH/(kJ Æ molꢁ1
)
1
2
3
4
5
Na(cr) + nROH(l) ! [RONa](nꢁ1)ROH + 1/2H2(g)
RONa(cr) + (n ꢁ 1)ROH(l) ! [RONa](nꢁ1)ROH
Na(cr) + ROH(l) ! RONa(cr) + 1/2H2(g)
DH(1) = ꢁ203.95 1.30
DH(2) = ꢁ76.84 0.34
DH(3) = ꢁ127.11 1.34
DH(4) = ꢁ239.1 0.3
DH(5) = ꢁ366.21 1.38
C(cr) + 2H2(g) + 1/2O2(g) ! ROH(l)
Na(cr) + C(cr) + 2H2(g) + 1/2O2(g) ! RONa(cr) + 1/2H2(g)
Df HꢀmðRONa;crÞ ¼ DHð5Þ ¼ DHð3Þ þ DHð4Þ where DH(3) = DH(1) ꢁ DH(2) R = –CH3 group.
TABLE 5
Standard molar enthalpies of formation of sodium alkoxides
DHð1Þ ¼ DsolHꢀmðNa=ROHÞ
=
DHð2Þ ¼ DsolHꢀmðRONa=ROHÞ
=
DHð4Þ ¼ Df HꢀmðROHÞ
ðkJ ꢂ molꢁ1Þ [27]
=
DH(5)=Df Hꢀ
=
ðkJ ꢂ molꢁ1
Þ
ðkJ ꢂ molꢁ1
Þ
ðkJ ꢂ molꢁ1Þ mðRONa; crÞ
R = –CH3
R = –C2H5
R = n-C3H7
ꢁ203.95 1.30
ꢁ190.43 1.34
ꢁ180.87 0.84
ꢁ76.84 0.34
ꢁ54.84 0.39
ꢁ41.90 0.66
ꢁ239.1 0.3
ꢁ277.8 0.4
ꢁ302.6 0.5
ꢁ366.21 1.38
ꢁ413.39 1.45
ꢁ441.57 1.18
Df HꢀmðRONa; crÞ ¼ DHð5Þ ¼ DHð3Þ þ DHð4Þ where DH(3) = DH(1) ꢁ DH(2).

K. Chandran et al. / J. Chem. Thermodynamics 39 (2007) 449–454
453
The enthalpy of formation of sodium n-propoxide cal-
culated using linear fit data of Leal et al. is
(ꢁ438.14 7.7) kJ Æ molꢁ1, which is in good agreement
with the data of (ꢁ441.57 1.18) kJ Æ molꢁ1 derived from
the present work. Similarly the enthalpy of formation of
sodium n-butoxide calculated using the linear fit data of
the present study is found to be (ꢁ471.59 6.16)
kJ Æ molꢁ1, which is in close agreement with the value
of ꢁ463.9 5.0 kJ Æ molꢁ1 derived by Leal et al.
-360
-380
-400
-420
-440
-460
-480
4. Conclusions
The standard molar enthalpies of solution of sodium
and its alkoxides, namely sodium methoxide, sodium
ethoxide, and sodium n-propoxide are measured at T =
298.15 K. Using these values, the standard molar enthal-
pies of formation and reaction of sodium methoxide,
ethoxide, and n-propoxide are derived. The standard molar
enthalpies of formation, reaction and solution of sodium
n-propoxide are reported for the first time.
-340
-320
-300
-280
-260
.
-240
-220
º
-1
ΔHf (ROH, l) / kJ mol
FIGURE 1. Plot of enthalpies of formation of sodium alkoxides against
enthalpies of formation of the corresponding alcohol: , Leal et al. work;
h, values from NBS table; m, present work; ——, present work fitted
data; and – – –, Leal et al. fitted data.
ꢀ
Acknowledgements
in this work are plotted against enthalpies of formation of
corresponding alcohols and are shown in figure 2. The lin-
ear correlation obtained from figure 2 for the enthalpy val-
ues are given in equations (3) and (5), respectively. These
correlations may be used to estimate the enthalpy of solu-
tions of other n-alkyl derivatives of sodium alkoxides.
The authors are grateful to Dr. G. Periaswami, Head,
Materials Chemistry Division, Chemistry Group, IGCAR
for his constant encouragement throughout the course of
the study and useful suggestions during the preparation
of this paper.
DHꢀsolðNa=ROHÞ ¼ ꢁð0:362 ꢄ 0:01ÞDHꢀf ðROH; lÞ ꢁ
References
ð290:70 ꢄ 2:68Þ;
DHꢀsolðRONa=ROHÞ ¼ ꢁð0:551 ꢄ 0:01ÞDHꢀf ðROHÞ ꢁ
ð208:60 ꢄ 3:47Þ:
ð2Þ
ð3Þ
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JCT 06-93