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Enthalpy of combustion of pentane-2,4-dione
M-10430 J. Chem. Thermodynamics 1979, 11, 1015-1017
Note Enthalpy
of combustion
J. M. HACKING
of pentane-2,4-dione
and G. PILCHER
Department of Chemistry, University of Manchester, Manchester MI3 9PL, U.K. (Received 6 April 1979)
The enthalpy of formation of pentane-2,4-dione (HPD) is of key importance in determining the enthalpies of formation of pentane-2&dionato derivatives of various metals by reaction calorimetry. AEI“~(HPD,~) was previously determined in 1957 by Nicholson(‘) from the enthalpy of combustion in oxygen: the amount of reaction was calculated from the massof sample contained in a glassampoule and the observed energy of combustion was corrected for the presence of about 2 per cent of xylene impurity. The present note reports a redetermination of this enthalpy of combustion in which the sample was contained in a plastic bag and the amount of reaction was calculated from the mass of carbon dioxide produced. Pentane-2,Cdione (B.D.H. Analar) was dried with Drierite and fractionally distilled using a 30-plate column at atmospheric pressure. The pure fraction was stored over nitrogen. Additional distillations had no effect on the observed energy of combustion and the COZ recovery from combustion of the dry sample was (100.00~0.02) per cent. The bomb calorimeter, subsidiary apparatus, and technique have been described.(2y3)For each combustion, 1 cm3 of water was placed in the bomb which was then flushed and tilled with oxygen to 3.04 MPa. The energy equivalent of the calorimeter was determined from the combustion of benzoic acid (B.D.H. Thermochemical Standard) having a specific energy of combustion under standardizing conditions of -Au, = (26435.1k2.9) J g-r. From twelve calibration experiments, E(calor) = (15399.7&0.7) J K-r, where the error quoted is the standard deviation of the mean. For the cotton-thread ignition fuse, empirical formula CH 1,68600.843,AiY,olM = - 16240J g-1.(4) The liquid HPD was contained in sealed polyester bags made from Melinex (0.025 mm thickness) using the technique described by Skinner and Snelson(5)who determined the specific energy of combustion of dry Mehnex as - Au,0= (22902+ 5) J g-l. This quantity was remeasured; from six combustions the value obtained, -Au,0 = (229052 8) J g-l, agrees with the previous value. Melinex is hygroscopic and was used in an atmosphere of approximately constant relative humidity of 55 per cent. The water content of the film was determined from the gain in mass of the dry film and from the change in its specific energy of combustion. The mass of Melinex used in each experiment was corrected for the mass fraction of water (0.0032), and the 0021-9614/79/101015+03
$01.00/O
0 1979 Academic
Press Inc. (London)
Ltd.
NOTE
1016
mass of carbon dioxide produced from the Melinex was calculated using the factor previously reported.(5) HPD(~)is also hygroscopic and samplesleft for 24 h in a humid atmosphere picked up about 0.3 per cent by mass of water but this had no effect on the specific energy of combustion when based on the carbon dioxide formed. The results of six combustions are given in table 1. Sampleswere ignited at 298.15 K and AU,“/M was calculated by the procedure given by Hubbard et (~1.c~) A@(HNO,) was based on 59.7 kJ mol- ’ for the energy of formation of 0.1 mol dme3 HNO, from Nz, 02, and HzO(l).(@ For HPD(~),p = 0.972 g cmA3 and (au/a& = -0.32 J g-l MPa-1 at 298.15 K. The atomic weights used were those recommended by the IUPAC commission.“) TABLE 1. Combustionresultsfor pentane-2,4-dione GH&) m’(compound)/g m”(Melinex)/g gvpd/” $K-1 -Au(IBP)/J
Au(HN03)/J &lJ -m’JAU~/M(Melinex)/J -m”‘AtJ~~M(fuse)~J
-AUi/M(compound)/Jg-l
0.92122 1.16091 0.16483 0.16818 0.00452 1.85188 18.3 28552.3 5.3 16.9 3175.4 73.4 26792.0
0.00568 2.27520
1.12106 0.14966 0.0055s 2.17849
1.33482 0.16573 O.OOS78 2.57437
2z 3428:0 90.1 26801.1
4.8 24.4 3796.0 93.9 26802.0
19.1 18.9 19.6 35080.9 33589.3 39695.0 6.8 21.3 3852.2 92.2
26796.6
0.89430 0.15103 0.00477 1.78485 18.2 27518.6
26795.0
1.06730 0.14458 0.00436 2.07591 18.7 32007.2 2.4 19.1 3311.6 70.8 26799.7
From table 1,the mean value and its standard deviation are - AUi/M = (26797.7& 1.6) J g-‘. In accordance with normal thermochemical practice, the errors assigned to the molar enthalpies of combustion and formation are twice the standard deviation of the mean and include the uncertainties in calibration and in the values of the auxiliary quantities used. For the molar quantities at 298.15 K, - AU,O(HPD,~) = = (2685.4kO.S) kJ mol-‘. With AZY:(H,O,I) (2682.9hO.S) kJ mol-‘, -AH,O(HPD,I) = -(285.83+0&l) kJ mol-I, and A&(CO,,g) = -(393.51 kO.13) k.Jmol-I,(*) then A&(HPD,~) = -(425.5& 1.0) kJ mol-I. This is in agreement with the value obtained 1.6) kJ mol-‘. At 298.15 K, HPD(I) is the by Nicholson:(‘) AH~O(HPD,I) = -(423.8+ equilibrium mixture : (0.186 keto + 0.814 enol). (‘) The enthalpies of enolization have been reported; in the liquid phase, -(I 1.3kO.4) kJ mol-l,(Q) and in the gaseous phase, -(lO.O+O.S) kJ mol- ’ .(lo) The enthalpy of vaporization of the enol form was derived by Irving and Wadsbc1‘) from the enthalpy of vaporization of the equilibrium mixture, A&‘(HPD, enol) = (43.2kO.l) kJ mol -l. These data permit calculation of AH~O(HPD) in both the keto and enol forms listed below:
HPD,keto mw, en01
A.H,“lkJ mole1 liquid gas -(374.4f 1.3) -(416.3+ 1.1) -(384.4+ 1.3) -(427.6+ 1.1)
J. M. H. thanks the ScienceResearch Council for financial support.
NOTE
1017
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
10. 11.
Nicholson, G. R. J. Chem. Sot. 1957,2431. Fairbrother, D. M.; Skinner, H. A. Trans. Faraday Sot. 1956, 52, 956. Barnes, D. S.; Pilcher, G. J. Chem. Thermodynamics 1975, 7, 377. Hubbard, W. N.; Scott, D. W.; Waddington, G. Chapter 5, Experimental Thermochemistry, Vol. 1. Rossini, F. D.: editor. Interscience: New York. 1956. Skinner, H. A.; Snelson, A. Trans. Faraday Sot. 1960, 56, 1776. Selected Values of Chemical Thermodynamic Properties, Tech. note 270-3. Nat. Bur. Stand.: Washington, D. C. 1968, Atomic weights of the elements, 1971. Pure Appl. Chem. 1972,30,637. CODATA J. Chem. Thermodynamics 1972,4, 331. Reeves, L. W. Can. J. Chem. 1957,35, 1351. Bernstein, H. J.; Powling, J. 1. Am. Chem. Sot. 1951, 73, 4353. Irving, R. J.; Wads& I. Acta Chem. Stand. 1970, 24, 589.
Note Enthalpy
of combustion
J. M. HACKING
of pentane-2,4-dione
and G. PILCHER
Department of Chemistry, University of Manchester, Manchester MI3 9PL, U.K. (Received 6 April 1979)
The enthalpy of formation of pentane-2,4-dione (HPD) is of key importance in determining the enthalpies of formation of pentane-2&dionato derivatives of various metals by reaction calorimetry. AEI“~(HPD,~) was previously determined in 1957 by Nicholson(‘) from the enthalpy of combustion in oxygen: the amount of reaction was calculated from the massof sample contained in a glassampoule and the observed energy of combustion was corrected for the presence of about 2 per cent of xylene impurity. The present note reports a redetermination of this enthalpy of combustion in which the sample was contained in a plastic bag and the amount of reaction was calculated from the mass of carbon dioxide produced. Pentane-2,Cdione (B.D.H. Analar) was dried with Drierite and fractionally distilled using a 30-plate column at atmospheric pressure. The pure fraction was stored over nitrogen. Additional distillations had no effect on the observed energy of combustion and the COZ recovery from combustion of the dry sample was (100.00~0.02) per cent. The bomb calorimeter, subsidiary apparatus, and technique have been described.(2y3)For each combustion, 1 cm3 of water was placed in the bomb which was then flushed and tilled with oxygen to 3.04 MPa. The energy equivalent of the calorimeter was determined from the combustion of benzoic acid (B.D.H. Thermochemical Standard) having a specific energy of combustion under standardizing conditions of -Au, = (26435.1k2.9) J g-r. From twelve calibration experiments, E(calor) = (15399.7&0.7) J K-r, where the error quoted is the standard deviation of the mean. For the cotton-thread ignition fuse, empirical formula CH 1,68600.843,AiY,olM = - 16240J g-1.(4) The liquid HPD was contained in sealed polyester bags made from Melinex (0.025 mm thickness) using the technique described by Skinner and Snelson(5)who determined the specific energy of combustion of dry Mehnex as - Au,0= (22902+ 5) J g-l. This quantity was remeasured; from six combustions the value obtained, -Au,0 = (229052 8) J g-l, agrees with the previous value. Melinex is hygroscopic and was used in an atmosphere of approximately constant relative humidity of 55 per cent. The water content of the film was determined from the gain in mass of the dry film and from the change in its specific energy of combustion. The mass of Melinex used in each experiment was corrected for the mass fraction of water (0.0032), and the 0021-9614/79/101015+03
$01.00/O
0 1979 Academic
Press Inc. (London)
Ltd.
NOTE
1016
mass of carbon dioxide produced from the Melinex was calculated using the factor previously reported.(5) HPD(~)is also hygroscopic and samplesleft for 24 h in a humid atmosphere picked up about 0.3 per cent by mass of water but this had no effect on the specific energy of combustion when based on the carbon dioxide formed. The results of six combustions are given in table 1. Sampleswere ignited at 298.15 K and AU,“/M was calculated by the procedure given by Hubbard et (~1.c~) A@(HNO,) was based on 59.7 kJ mol- ’ for the energy of formation of 0.1 mol dme3 HNO, from Nz, 02, and HzO(l).(@ For HPD(~),p = 0.972 g cmA3 and (au/a& = -0.32 J g-l MPa-1 at 298.15 K. The atomic weights used were those recommended by the IUPAC commission.“) TABLE 1. Combustionresultsfor pentane-2,4-dione GH&) m’(compound)/g m”(Melinex)/g gvpd/” $K-1 -Au(IBP)/J
Au(HN03)/J &lJ -m’JAU~/M(Melinex)/J -m”‘AtJ~~M(fuse)~J
-AUi/M(compound)/Jg-l
0.92122 1.16091 0.16483 0.16818 0.00452 1.85188 18.3 28552.3 5.3 16.9 3175.4 73.4 26792.0
0.00568 2.27520
1.12106 0.14966 0.0055s 2.17849
1.33482 0.16573 O.OOS78 2.57437
2z 3428:0 90.1 26801.1
4.8 24.4 3796.0 93.9 26802.0
19.1 18.9 19.6 35080.9 33589.3 39695.0 6.8 21.3 3852.2 92.2
26796.6
0.89430 0.15103 0.00477 1.78485 18.2 27518.6
26795.0
1.06730 0.14458 0.00436 2.07591 18.7 32007.2 2.4 19.1 3311.6 70.8 26799.7
From table 1,the mean value and its standard deviation are - AUi/M = (26797.7& 1.6) J g-‘. In accordance with normal thermochemical practice, the errors assigned to the molar enthalpies of combustion and formation are twice the standard deviation of the mean and include the uncertainties in calibration and in the values of the auxiliary quantities used. For the molar quantities at 298.15 K, - AU,O(HPD,~) = = (2685.4kO.S) kJ mol-‘. With AZY:(H,O,I) (2682.9hO.S) kJ mol-‘, -AH,O(HPD,I) = -(285.83+0&l) kJ mol-I, and A&(CO,,g) = -(393.51 kO.13) k.Jmol-I,(*) then A&(HPD,~) = -(425.5& 1.0) kJ mol-I. This is in agreement with the value obtained 1.6) kJ mol-‘. At 298.15 K, HPD(I) is the by Nicholson:(‘) AH~O(HPD,I) = -(423.8+ equilibrium mixture : (0.186 keto + 0.814 enol). (‘) The enthalpies of enolization have been reported; in the liquid phase, -(I 1.3kO.4) kJ mol-l,(Q) and in the gaseous phase, -(lO.O+O.S) kJ mol- ’ .(lo) The enthalpy of vaporization of the enol form was derived by Irving and Wadsbc1‘) from the enthalpy of vaporization of the equilibrium mixture, A&‘(HPD, enol) = (43.2kO.l) kJ mol -l. These data permit calculation of AH~O(HPD) in both the keto and enol forms listed below:
HPD,keto mw, en01
A.H,“lkJ mole1 liquid gas -(374.4f 1.3) -(416.3+ 1.1) -(384.4+ 1.3) -(427.6+ 1.1)
J. M. H. thanks the ScienceResearch Council for financial support.
NOTE
1017
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
10. 11.
Nicholson, G. R. J. Chem. Sot. 1957,2431. Fairbrother, D. M.; Skinner, H. A. Trans. Faraday Sot. 1956, 52, 956. Barnes, D. S.; Pilcher, G. J. Chem. Thermodynamics 1975, 7, 377. Hubbard, W. N.; Scott, D. W.; Waddington, G. Chapter 5, Experimental Thermochemistry, Vol. 1. Rossini, F. D.: editor. Interscience: New York. 1956. Skinner, H. A.; Snelson, A. Trans. Faraday Sot. 1960, 56, 1776. Selected Values of Chemical Thermodynamic Properties, Tech. note 270-3. Nat. Bur. Stand.: Washington, D. C. 1968, Atomic weights of the elements, 1971. Pure Appl. Chem. 1972,30,637. CODATA J. Chem. Thermodynamics 1972,4, 331. Reeves, L. W. Can. J. Chem. 1957,35, 1351. Bernstein, H. J.; Powling, J. 1. Am. Chem. Sot. 1951, 73, 4353. Irving, R. J.; Wads& I. Acta Chem. Stand. 1970, 24, 589.