Evaluation of the Vaporization Enthalpies and Liquid Vapor Pressures

Article pubs.acs.org/jced

Evaluation of the Vaporization Enthalpies and Liquid Vapor Pressures of (R)‑Deprenyl, (S)‑Benzphetamine, Alverine, and a Series of Aliphatic Tertiary Amines by Correlation Gas Chromatography at T/K = 298.15 Chase Gobble, John Vikman,§ and James S. Chickos* Department of Chemistry and Biochemistry, University of Missouri-St. Louis, St. Louis, Missouri 63121, United States S Supporting Information *

ABSTRACT: The vaporization enthalpies at T/K = 298.15 and vapor pressures from T/K = (283 to 313) of a series of tertiary aliphatic amines ranging in size from 12 to 24 carbons are evaluated using the literature values for triethylamine, tributylamine, N,N-dimethylbenzylamine, N,N-dimethyloctylamine, and N,N-dimethyldodecylamine by correlation gas chromatography. The vaporization enthalpies and vapor pressures evaluated are (ΔlgHm(298.15 K/kJ·mol−1, p/Pa (298.15 K)): triisobutylamine (52.3 ± 2.2, 113), tri-nbutylamine (58.0 ± 1.9, 28), N,N-dimethyltetradecylamine (77.3 ± 1.9, 0.091), N,N-dimethylhexadecylamine (84.8 ± 1.0, 0.011), tribenzylamine (92.4 ± 1.4, 5.1·10−4), tri-n-octylamine (100.1 ± 1.4, 1.4·10−4). These amines were used to evaluate the following vaporization enthalpies and vapor pressures (ΔlgHm(298.15 K kJ·mol−1, p/Pa (298.15 K)): (R)-deprenyl (64.3 ± 2.2, 2.5); (S)-benzphetamine (77.2 ± 0.7, 0.04); and alverine (89.3 ± 0.2, 1.4·10−3). The solid−solid and solid to liquid phase transitions of tribenzylamine were also measured; ΔcrcrHm(342.5 K)/kJ·mol−1 = (1.1 ± 0.1); ΔcrlHm(365.6 K)/kJ·mol−1 = (23.0 ± 0.1). Adjusted to T/K = 298.15 and combined with the vaporization enthalpy at this temperature, the sublimation enthalpy resulted as ΔcrgHm(298.15 K)/kJ·mol−1 = (111.3 ± 2.1).

1. INTRODUCTION (R)-Deprenyl ((αR)-N,α-dimethyl-N-2-propyn-1-yl-benzeneethanamine) in combination of L DOPA (L 3,4-dihydroxyphenylalanine) is used in the early stages of Parkinson’s disease.1 It is an irreversible inhibitor of monoamine oxidase (MAO) and has a greater affinity for type B commonly found in the brain. It is partially metabolized in the body to (R)-methamphetamine, found in over the counter nasal decongestants.2,3 ((S)Benzphetamine (2S)-N-benzyl-N-methyl-1-phenylpropan-2amine, Didrex) an anorectic, is used for short-term control of obesity. It is a member of a class of substances, the amphetamines, that include amphetamine and methamphetamine among others.4,5 It is slowly converted to amphetamine and (S)-methamphetamine upon ingestion. (S)-Benzphetamine is a schedule III controlled substance. The vaporization enthalpies and vapor pressures of both amphetamine and (S)methamphetamine as evaluated by correlation gas chromatography have recently been reported.6,7 Alverine is a smooth muscle relaxant. It is used in management of disorders of the GI tract and other organs associated with involuntary muscle spasms.8 The structures of L deprenyl, (S)-benzphetamine, and alverine are provided in Figure 1. These materials are usually prescribed in the form of their ammonium salts. Improper disposal of unused portions of these drugs into the environment can produce the neutral parents. Concern has been raised over the environmental impact of © 2014 American Chemical Society

discarded medications. The aqueous and gas phases are the major routes of dispersal. Very few experimental thermochemical properties such as their vapor pressures and vaporization enthalpies at ambient temperatures, two important properties governing the rate of their dispersal through the atmosphere are available in the literature. The ACD Laboratories software available through SciFinder Scholar9 predicts vaporization enthalpies of [(51.1 ± 3.0), (57.7 ± 3.0), and (60.4 ± 3.0)] kJ·mol−1 presumably at their respective boiling temperatures while EPIWEB software11 predicts subcooled liquid vapor pressures, p/Pa, of (2.1, 4.6·10−2, and 4.5·10−3) at T/K = 298.15 for (R)-deprenyl, (S)-benzphetamine, and alverine, respectively. Since the normal boiling temperatures are in excess of Tb/K = 500, adjustments of ΔlgHm(Tb) to T/K = 298.15 are problematic. A simple two parameter equation described below predicts vaporization enthalpy values of [(68.6 ± 3.4), (87.3 ± 4.4), and (94.0 ± 4.7)]10 kJ·mol−1. The vaporization enthalpies and liquid vapor pressures of these materials at ambient temperatures have been evaluated by correlation gas chromatography and compared to estimated values. Received: April 17, 2014 Accepted: July 6, 2014 Published: July 21, 2014 2551

dx.doi.org/10.1021/je500358r | J. Chem. Eng. Data 2014, 59, 2551−2562

Journal of Chemical & Engineering Data

Article

Figure 1. From left to right: L-deprenyl ((R)-N-methyl-N-(1-phenylpropan-2-yl)prop-1-yn-3-amine), benzphetamine (Didrex, (2S)-N-benzyl-Nmethyl-1-phenylpropan-2-amine), and alverine (N-ethyl-3-phenyl-N-(3-phenylpropyl)propan-1-amine).

triisobutylamine,20 and tri-n-octylamine17 have been investigated previously. Various concerns arose with regards to the information available for these three materials, and these concerns are discussed below. This work describes the evaluation of the vaporization enthalpies and vapor pressures of these tertiary aliphatic amines which in combination with the standards mentioned above have been used to evaluate similar properties for the three drugs described above.

The evaluation of vaporization enthalpy and vapor pressure by correlation gas chromatography relies on the availability of data on functionally similar materials that can serve as reliable standards. The number of moderately sized aliphatic tertiary amines that could function as vaporization enthalpy and vapor pressure standards for these three drugs is remarkably small. The compounds include triethylamine,12,13 tripropylamine,12 N,N-dimethyloctylamine,15 N,N-dimethyldodecylamine,16 and tri-n-octylamine.17 Another objective of this work was to evaluate the vaporization enthalpies and vapor pressures at and near ambient temperatures of a number of additional aliphatic tertiary amines that could also be used as standards in this and in future studies. The compounds investigated include tri-nbutylamine, triisobutylamine, N,N-dimethyltetradecylamine, N,N-dimethylhexadecylamine, and tri-n-octylamine. The structures of both the aliphatic amines evaluated and the standards used are provided in Figure 2. Tri-n-butylamine,18−20

2. EXPERIMENTAL SECTION 2.1. Materials. The source and purity of the amines used in this study are included in Table 1. Since the measurements are conducted by gas chromatography, the purity of the sample is considerably less important than with other methods. All amines in this study were used as commercially available. (R)Deprenyl and (S)-benzphetamine are marketed as their hydrochloride salts. Alverine is available as the corresponding citrate. These materials were neutralized with 1 M NaOH prior to use and extracted with the solvent used in the experiments, hexanes, methylene chloride, or diethyl ether or a mixture of two. The remaining standards were added to these amines until comparable concentrations of all were achieved. Since the drugs were available to us in small quantities as their salts and needed initial treatment with base, each was evaluated in a separate set of correlations. The purity of the drugs as well as their retention times were measured independently by gas chromatography. 2.2. Methods. Correlation gas chromatography experiments were conducted on two HP 5890 gas chromatographs running Chemstation over a T/K = 30 temperature range at T/

Figure 2. Vaporization enthalpies evaluated: tri-isobutylamine, tri-nbutylamine, N,N-dimethyltetradecylamine, N,N-dimethylhexadecylamine, tri-n-octylamine and tribenzylamine. Standards: triethylamine, tripropylamine, N,N-dimethyloctylamine, N,N-dimethyldodecylamine.

Table 1. Origin of the Standards and Targets and Their Analysis C6H15N C9H13N C9H21N C10H23N C12H27N C12H27N C13H17N C14H31N C16H35N C17H21N C18H39N C20H27N C21H21N C24H51N a

compound

CAS RN

supplier

mass fraction

triethylamine N,N-dimethylbenzylamine tri-n-propylamine N,N-dimethyloctylamine triisobutylamine tri-n-butylamine (R)-deprenyla N,N-dimethyldodecylamine N,N-dimethyltetradecylamine (S)-benzphetaminea N,N-dimethylhexadecylamine alverineb tribenzylamine tri-n-octylamine

121-44-8 103-83-3 102-69-2 7378-99-6 1116-40-1 102-82-9 14611-51-9 112-18-5 112-75-4 156-08-1 112-69-6 150-59-4 620-40-6 1116-76-3

Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich TCI Sigma-Aldrich Mallinckrodtc Sigma-Aldrich Sigma-Aldrich Eastmand Sigma-Aldrich

0.98 > 0.99 0.99 0.95 0.98 0.97 > 0.98 > 0.95 > 0.95

GC anal

0.99 + > 0.95 0.99 + 0.98 + 0.98

Available as the hydrochloride. bAvailable as the citrate salt. cMallinckrodt Pharmaceutical. dEastman Organic Chemicals. 2552



Article

Table 2. Vaporization Enthalpies of Some Tertiary Amines as Potential Standards ΔlgHm(Tm)(Tm/K) −1

compounds triethylamine triethylamine tripropylamine triisobutylamine tri-n-butylamine tri-n-butylamine tri-n-butylamine tri-n-butylamine N,N-dimethylbenzylamine N,N-dimethyloctylamine N,N-dimethyldodecylamine tri-n-octylamine a

kJ·mol

−1

J·mol · ·K

34.4 ± 0.2 (313)

222.4

54.3 49.8 48.1 53.9

394.3 413.8 413.8 413.8

(320) (450) (378) (378)

48.9 ± 0.4 (308) 54.0 ± 0.5 (303) 69.3 ± 0.3 (298)

ΔlgCpΔT

Cp(l) −1

−1

kJ·mol

1.0 ± 0.2 2.5 17.9 9.4 9.4

± ± ± ±

0.4 2.4 1.3 1.3

0.8 ± 0.2 0.53

248 360

ΔlgHm(298 K)/(kJ·mol−1) esta

exp 34.9 35.4 46.2 56.8 67.7 57.6 63.4 62.7 49.7 54.5 69.3 110.0

± 0.1 ± 0.3 ± 0.1 ± ± ± ± ± ± ± ±

2.4 1.3 1.3 1.3 0.4 0.5 0.3 15

37.7 37.7 51.8 59.9 65.9 65.9 65.9 65.9 51.8 56.5 75.3 122.2

± ± ± ± ± ± ± ± ± ± ± ±

ref 2.0 2.0 2.6 3.0 3.3 3.3 3.3 3.3 2.6 2.8 3.8 6.1

12 13 12 20 18 20 20 19 14 15 16 20

Estimated using eq 2.

supplied by PerkinElmer. The standardization was checked with calorimetric grade benzoic acid supplied by Fisher and Gold Label scintillation grade naphthalene, w > 0.99 supplied by Aldrich. The samples were run in 50 μL hermetically sealed aluminum pans under a flow of nitrogen. The commercial sample of tribenzylamine analyzed by gas chromatography, mass fraction 0. 98+, was used as supplied. The compound exhibited a broad transition at T/K = (342.5 ± 0.4) and transition enthalpy, ΔHt(343)/kJ·mol−1 = (1.1 ± 0.1), fusion temperature T/K = (365.6 ± 0.1, onset temperature) and fusion enthalpy, ΔcrlHm(366)/ kJ·mol−1 = (23.0 ± 0.1). Details are available in the Supporting Information (Table S1). 2.4. Vaporization Enthalpy Estimations. A three parameter relationship that can be used to estimate ΔlgHm(298.15 K) of molecules containing a single functional group is given by eq 2. The terms nC, nQ, and b refer to the total number of carbon atoms, the number of quaternary sp3 hybridized carbon atoms, and to the contribution of the functional group, in the case a tertiary amine (6.6 kJ·mol−1), respectively.10 For compounds with carbon branching at acyclic sp3 hybridized centers, a correction, C, of −2 kJ·mol−1/branch is also included in the estimation.10

K = 5 intervals. The columns used were a 15 m SPB-5 for some experiments and a 30 m DB5 column for others using helium as the carrier gas at a split ratio of approximately 100/1 at 10 psi. Both columns gave good separations and the shorter column reduced retention times. The column used for each analysis can be identified by the retention time of the solvent, t/t0, where t0/ s = 60. On the 15 m column, t/t0 < 1, and on the 30 m column t/t0 > 2.0. Retention times for each run are provided in the Supporting Information. The temperature was controlled by the spectrometer and monitored independently using either a Fluke digital thermometer or a Vernier stainless steel temperature probe equipped with a Go!Link USB interface running Logger Lite software, depending on the instrument used. The solvents used were not retained by the column at the temperatures of the experiments and were used as a measure of the He flow rate. The amines are arranged in the tables below in order of their elution off the column. The relative retention times of N,N-tri-n-octylamine and tribenzylamine depended on temperature. On the 30 m column, at approximately T/K > 480, N,N-tri-n-octylamine eluted before tribenzylamine, whereas below this temperature the elution order was reversed. The time each analyte spent on the column, the adjusted retention time, ta, was evaluated as the difference between the analyte’s retention time and the retention time of the solvent. Plots of ln(t0/ta) against 1/T were linear with a slope equal to −ΔHtrn(Tm)/R where ΔHtrn(Tm) represents the enthalpy of transfer of the analyte from the stationary phase of the column to the gas phase and R is the gas constant, 8.314 J·mol−1·K−1. The vaporization enthalpy is related to the enthalpy of transfer by eq 1 in which the term ΔHintr(Tm) represents the enthalpy of interaction of each solute with the column at the mean temperature, Tm.21,22 When the standards are properly selected, plots of ΔlgHm(T) against ΔHtrn(Tm) where T/K often is equal to 298.15 are also linear, and the resulting correlation equations can be used to evaluate the vaporization enthalpies of the target substances from their measured ΔHtrn(Tm) values. The quality of the results is directly linked to the quality of the data of the standards used in the correlation and the appropriateness of the compounds chosen to serve as standards. Δl g Hm(T ) = ΔHtrn(Tm) − ΔHintr(Tm)

Δl g Hm(298K)/kJ ·mol−1 = 4.69(nC − nQ ) + 1.3nQ + b + C + 3.0

(2)

2.5. Temperature Adjustments. The vaporization enthalpies of the compounds used as standards are available over a range of different temperatures. Adjustments to a common temperature, T/K = 298.15 were achieved using eq 3. The term ΔlgHm(Tm) in this equation represents the vaporization enthalpy at the mean temperature of measurement and Cp(l) represents the liquid heat capacity at T/K = 298.15.23 Adjustment of the fusion enthalpy to T/K = 298.15 was achieved using eq 4. The Cp(cr) term in this equation represents the heat capacity of the solid also at T/K = 298.15. Since the solid−solid phase transition in tribenzylamine occurred above T/K = 298.15, the enthalpy associated with the transition is also included in eq 4. Both heat capacity terms were evaluated by group additivity. Equations 3 and 4 have been shown to provide reasonable temperature adjustments up to approximately T/K = 500.23−26

(1)

2.3. Fusion Enthalpy. The fusion enthalpy of tribenzylamine was measured on a PerkinElmer DSC 7 instrument running the Pyris Thermal Analysis software. The instrument was standardized with indium metal, mass fraction 0.99999, 2553



Article

Table 3. Constants of the Antoine Equation triethylamine N,N-dimethylbenzylamine N,N-dimethyloctylamine N,N-dimethyldodecylamine tri-n-octylamine

A

B

C

21.1239 24.94825 25.94036 40.49339 23.05555

3071.65 5892.03 6491.58 17623.5 6300.22

−42.35 0 0 135.268 −101.205

T/K range

ref

273 288 283 283 415

13 14 15 16 17

to to to to to

352 328 323 314 537

Table 4. Evaluation of the Vaporization Enthalpy of Tributylamine and Triisobutylamine −slope

ΔlgHm(298 K)/(kJ·mol−1)

ΔHtrn(388 K)

run 1

T/K

intercept

triethylamine tripropylamine N,N-dimethylbenzylamine triisobutylamine N,N-dimethyloctylamine tri-n-butylamine

3262.0 4263.8 4577.9 4858.8 5104.6 5464.5

10.009 10.833 10.842 11.475 11.885 12.285

−1

kJ·mol

(lit) 35.2 ± 0.2 46.2 ± 0.1 49.7 ± 0.4

27.12 35.45 38.06 40.39 42.44 45.43

54.5 ± 0.5

(calc) 35.4 46.0 49.3 52.3 54.9 58.7

± ± ± ± ± ±

1.8 2.0 2.0 2.1 2.2 2.3

Dl g Hm(298.15K)/kJ·mol−1 = (1.27 ± 0.04)ΔHtrn(388 K) + (0.91 ± 1.4) r 2 = 0.9981

(6)

amines has demonstrated that best results for aliphatic primary amines are obtained using aliphatic primary amine standards as opposed to primary aromatic amines.25 Therefore, the existing vaporization enthalpy of tri-n-butylamine was re-evaluated by correlation gas chromatography in this case using tertiary aliphatic amines as standards. Values for N,N-dimethylbenzylamine (49.7 ± 0.4),14 N,N-dimethyloctylamine (54.5 ± 0.5),15 and N,N-dimethyldodecylamine (69.3 ± 0.3)16 kJ·mol−1 are relatively recent and from reputable sources. Finally it should be noted that a ± 15 kJ·mol−1 uncertainty at T/K = 298.15 is associated with the largest tertiary aliphatic amine examined, trin-octylamine,17 and its use as a standard was of some concern. Consequently, along with triisobutylamine and tri-n-butylamine, the following amines, N,N-dimethyltetradecylamine, N,N-dimethylhexadecylamine, and tri-n-octylamine were treated as unknowns and evaluated by correlation gas chromatography experiments. In view of the large difference in retention times between the smallest and largest tertiary amines, it was necessary to evaluate their vaporization enthalpies and vapor pressures in a series of independent correlations. All correlations were performed in duplicate. Details of the second correlation are available in the Supporting Information. The resulting vaporization enthalpies from all the runs are summarized below. 2.72. Vapor Pressure. Vapor pressures of potential standards are also limited and available only over a narrow temperature range, most near ambient temperatures. The vapor pressures of the standards are reported in the form of the Antoine equation, eq 5 where pref/Pa = 1. The constants for this equation and the temperature range to which they are applicable are provided in Table 3. The vapor pressures used in the correlations described below, however, were conducted in the form p/p0 where p0/Pa = 101325. For tri-n-octylamine, the Antoine equation reported in the form log10(p/kPa) has been transformed to the form of eq 5.17

Δl g Hm(298.15 K)/( kJ ·mol−1) = Δl g Hm(Tm) + [(10.58 + 0.26·Cp(l)/( J·mol−1· K−1)) (Tm/K − 298.15 K)]/1000

(3)

Δcr l Hm(298.15 K)/kJ·mol−1 = ΔHt(Tt) + Δcr l Hm(Tfus) + [(0.15Cp(cr) − 0.26Cp(l))/J ·mol−1·K−1 − 9.93] [Tfus/K − 298.15]/1000

(4) −1

2.6. Uncertainties. A standard deviation of 16 J·mol ·K−1 has generally been associated with the temperature independent portion of the second term in eq 3. The uncertainty associated with eq 4 has been estimated as 30 % of the temperature adjustment. The correlations between experimental properties and those evaluated by gas chromatography were analyzed by linear regression. The uncertainty in the slope represents one standard deviation. Uncertainties in combined properties such as temperature adjustments were generally evaluated as (u12 + u22 + ...)0.5 where ui represents the standard deviation associated with measurement i. 2.7. Standards. 2.71. Vaporization Enthalpy. Vaporization enthalpies of the compounds that could serve as potential standards for the three drugs of interest are summarized in Table 2. For triethylamine, two values both in good agreement with each other are available.12,13 An average value of (35.2 ± 0.2) kJ·mol−1 was used for the vaporization enthalpy. A calorimetric value of (46.2 ± 0.1) kJ·mol−1 is available for tripropylamine.12 A single value is available for triisobutylamine from the compendium by Stephenson and Malanowski.17 Since this source does not include original references, it is difficult to judge the quality of the value or its age. A similar situation exists for tri-n-butylamine for which there is a 10 kJ·mol −1 discrepancy in Table 2.17−19 The most recent measurement for tributylamine requires an extremely large temperature adjustment, making this value also questionable.18 The vaporization enthalpy of tri-n-butylamine has also been evaluated previously using correlation gas chromatography. In this instance the evaluation was based solely on using aromatic heterocyclic amines as standards.19 More recent work with

ln(p/pref ) = A − B /(C + T /K) 2554

(5)



Article

Table 5. Evaluation of the Vaporization Enthalpy of Tributylamine and N,N-Dimethyltetradecylamime −slope


ΔHtrn(439 K)

run 3

T/K

intercept

N,N-dimethylbenzylamine N,N-dimethyloctylamine tri-n-butylamine N,N-dimethyldodecylamine N,N-dimethyltetradecylamine

4436.7 4923.4 5268.0 6621.9 7509.0

10.561 11.498 11.850 13.435 14.530

−1

kJ·mol

(lit) 49.7 ± 0.4 54.5 ± 0.5

36.89 40.93 43.8 55.05 62.43

69.3 ± 0.3

(calc) 49.9 54.2 57.3 69.4 77.3

± ± ± ± ±

1.5 1.5 1.6 1.8 1.9

Δl g Hm(298.15 K)/kJ·mol−1 = (1.07 ± 0.03)ΔHtrn(439 K) + (10.4 ± 1.1) r 2 = 0.9995

(7)

Table 6. Evaluation of the Vaporization Enthalpies of N,N-Dimethylhexadecylamine −slope


ΔHtrn(469 K)

run 5

T/K

intercept

N,N-dimethyloctylamine tri-n-butylamine N,N-dimethyldodecylamine N,N-dimethyltetradecylamine N,N-dimethylhexadecylamine

4588.7 4949.2 6240.3 7084.6 7930.6

11.254 11.633 13.157 14.185 15.228

−1

kJ·mol

(lit)

38.15 41.15 51.88 58.9 65.93

54.5 58.0 69.3 77.3

± ± ± ±

0.5 1.9a 0.3 1.9b

(calc) 54.6 57.8 69.5 77.2 84.8

± ± ± ± ±

0.8 0.9 1.0 1.0 1.1

Δl g Hm(298.15 K)/kJ·mol−1 = (1.09 ± 0.013)DH trn(439 K) − (13.0 ± 0.6) r 2 = 0.9997 a

(8)

b

Average value evaluated from runs 1 to 4. Average value evaluated in runs 3 and 4.

Table 7. Evaluation of the Vaporization Enthalpy of Tribenzylamine and Tri-n-octylamine −slope


ΔHtrn(500 K)

run 7

T/K

intercept

tri-n-butylamine N,N-dimethyldodecylamine N,N-dimethyltetradecylamine N,N-dimethylhexadecylamine tri-n-octylamine tribenzylamine

4655.4 5808.2 6566.2 7350.8 8871.4 8091.0

10.504 11.679 12.508 13.405 15.189 13.559

−1

kJ·mol

38.7 48.29 54.59 61.11 73.75 67.27

(lit)

(calc)

58.0 ± 1.9 69.3 ± 0.3 77.3 ± 1.9 84.8 ± 1.0a

58 ± 0.9 69.5 ± 1.0 77.1 ± 1.0 84.9 ± 1.1 100.1 ± 1.2 92.3 ± 1.2

Δl g Hm(298.15 K)/kJ·mol−1 = (1.20 ± 0.013)ΔHtrn(500 K) + (11.5 ± 0.7) r 2 = 0.9997 a

(9)

Average evaluated in runs 5 and 6.

3. RESULTS

Table 8 summarizes the vaporization enthalpies measured in all 8 correlations. Also included are an average value that was used in subsequent runs along with other literature values to evaluate the vaporization enthalpies of (R)-deprenyl, (S)benzphetamine and alverine, also in duplicate. The correlation of one of each respective run is summarized in Tables 9 to 11. Equations 10 to 12 listed below each respective table summarize the quality of the correlations. Details for each duplicate run are available in the Supporting Information. The vaporization enthalpies evaluated for (R)-deprenyl, (S)benzphetamine, and alverine are summarized in Table 12 as are the values obtained for the standards. 3.2. Vapor Pressures. In addition to the correlation between ΔlgH(T) and ΔHtrn(Tm), ln(t0/ta) values of the standards have also been found to correlate linearly with their respective vapor pressures, p, also in the form of ln(p/p0). Reliable vapor pressures of the targets can be obtained using the linear relationship observed between plots of ln(t0/ta) and ln(p/p0) of the standards and the ln(t0/ta) values of the targets to evaluate the vapor pressures of the latter. This correlation repeated as a function of temperature can provide a vapor pressure−temperature profile of the targets.6,7,19,25,27,28

3.1. Vaporization Enthalpies. The vaporization enthalpy of tri-n-butylamine used in a number of subsequent correlations was evaluated in a series of two different correlations that also included separate evaluations of triisobutylamine and N,Ndimethyltetradecylamine. The results of one of the two sets of correlations are summarized in Tables 4 and 5. Equations 6 and 7 listed below each correlation monitor the linearity of the fit. Details for all duplicate runs are available in the Supporting Information (odd numbered Tables S3−S15). The values resulting from runs 1−4 for tri-n-butylamine and runs 3 and 4 for N,N-dimethyltetradecylamine along with several other tertiary amine standards were then used to evaluate N,Ndimethylhexadecylamine, Table 6. The vaporization enthalpy of N,N-dimethylhexadecylamine evaluated in run 5 and its duplicate, run 6, was then used as one of the standards to evaluate tri-n-octyl and tribenzylamine in runs 7 and 8. Equation 8 listed below Table 6 and eq 9 listed below Table 7 provide a measure of the linearity of each respective correlation. 2555


110 ± 15

± ± ± ± ± ± 58.0 69.5 77.1 84.9 92.3 100.1 0.8 0.8 0.9 0.8 0.9 ± ± ± ± ± 54.6 57.8 69.5 77.2 84.8 0.8 0.9 1.0 1.0 1.0 ± ± ± ± ± 4.6 57.8 69.5 77.2 84.8 1.4 1.5 1.7 1.8 ± ± ± ± ± ± ± ± 54.2 57.3 69.4 77.3

1.5 1.6 1.8 1.9

54.3 57.3 69.4 77.2

49.9 ± 1.4 49.9 ± 1.5

1.6 1.8 2.1 2.2 2.2 2.3 ± ± ± ± ± ± 35.4 46.0 49.3 52.3 54.9 58.7 1.6 1.8 2.0 2.1 2.2 2.3 ± ± ± ± ± ± 35.6 46.0 49.3 52.3 54.9 58.7 triethylamine tripropylamine N,N-dimethyl-benzylamine triisobutylamine N,N-dimethyl-octylamine tri-n-butylamine N,N-dimethyl-dodecylamine N,N-dimethyl-tetradecylamine N,N-dimethyl-hexadecylamine tribenzylamine tri-n-octylamine

Vapor pressures near ambient temperatures are available for four of the five compounds used as standards in this study. Vapor pressures for all the standards with exception of N,Ndimethylbenzylamine are available over the temperature range, T/K = (283.15 to 313.15). The vapor pressure for N,Ndimethylbenzylamine required a T/K = 5 extrapolation of the Antoine eq to T/K = 283.15. All vapor pressures for these compounds were calculated using eq 5 and the constants reported in Table 3. An example of the correlation between ln(p/p0) and ln(t0/ta) is illustrated in Table 13 for runs 1 and 2 and runs 3 and 4 at T/ K = 298.15. Values of (t0/ta) were calculated from the slopes and intercepts of the standards listed in Table 4 for run 1 and from the Supporting Information for run 2 (Table S3B), averaged, and then correlated as ln(t0/ta)avg with corresponding values of ln(p/p0) of the standards. Similarly for runs 3 and 4, appropriate values were obtained from Table 5 and the Supporting Information, averaged and correlated with corresponding ln(p/po) values at T/K = 298.15. This resulted in eqs 13 and 14 provided at the bottom of Table 13. Repeating this process over the temperature range T/K = (283.15 to 313.15) at T/K = 5 intervals for runs 1 and 2 provided vapor pressure− temperature profiles for both tri-n-propylamine, triisobutylamine, and tri-n-butylamine that were fit to eq 15. The resulting slopes and intercepts for these compounds reported in column 2 and 3 of Table 14 were then used to evaluate vapor pressures for these materials as needed within the temperature range specified above. In runs 3 and 4 of Table 13, evaluation of the vapor pressure of N,N-dimethyltetradecylamine at T/K = 298.15 is illustrated, now also using the vapor pressures of tri-nbutylamine, evaluated in runs 1 and 2 as a standard. Equation 14 listed below the table summarizes the results of this correlation. Once the temperature dependence of a target was evaluated, it was available for use as a standard as needed. All correlation coefficients, r2, exceeded 0.99 over the temperature range studied. The vapor pressures calculated at T/K = 298.15 by direct correlation of ln(t0/ta) with ln(p/p0) are provided in the last column of Table 13. Similar correlations at T/K = 298.15 for runs 5 through 8 are provided in the Supporting Information along with their vapor pressures at T/K = 298.15 (Table S16). The remaining amines were evaluated by either interpolation or extrapolation. The vapor pressures of N,Ndimethylhexadecylamine were evaluated in runs 5 and 6, and those of tribenzylamine and tri-n-octylamine were evaluated in runs 7 and 8. The slopes and intercepts describing the vapor pressure−temperature dependence for all these materials are provided in Table 14.

Uncertainties are also average values. bValue based from runs evaluated as an unknown; value used as a known in subsequent correlations. cEvaluated in runs 1 to 4. dEvaluated in runs 3 and 4. eEvaluated in runs 5 and 6. fEvaluated in runs 7 and 8.

1.1 1.2 1.3 1.4 1.5 1.6 0.9 1.0 1.0 1.1 1.2 1.2

58.1 69.3 77.0 85.0 92.4 100.0

± ± ± ± ± ±

run 8 run 7 run 6 run 5 run 4 run 3 run 2 run 1

Table 8. A Summary of Vaporization Enthalpies (kJ·mol−1) at T/K = 298.15 of Runs 1 to 8

Article

ln(p /po ) = A′ + B′/T

(15)

The vapor pressure−temperature profile for (R)-deprenyl, (S)-benzphetamine, and alverine were evaluated using the vapor pressures of the standards from the literature listed in Table 3 and those evaluated in this work with the exception of tri-n-octylamine, for the reason discussed above. All vapor pressures were evaluated from T/K = (283.15 to 313.15) at T/ K = 5 intervals and fit to eq 15. The slopes and intercepts for these materials are also reported in Table 14. All correlation coefficients, r2 exceeded 0.99. Typical results of correlations between ln(p/p0) and ln(t0/ta) for (R)-deprenyl, (S)-benzphetamine, and alverine at T/K = 298.15 are illustrated in Table 15 and characterized by eqs 16 to 18, respectively, provided at the bottom of the table. Vapor pressures calculated from these results are provided in the last column of the table.

a

± ± ± ± ± ± ±

1.6 1.6 1.8 2.2 1.9 1.9b,c 1.3 1.9b,d 1.0b,e 1.4b,f 1.4b,f ± ± ± ± ± ± ± ± ± ± ± 35.6 46.0 49.6 52.3 54.9 58.0 69.4 77.3 84.8 92.4 100.1

avga

35.2 46.2 49.7 59.9 54.5 57.6 69.3

lit

0.2 0.1 0.4 3.0 0.5 1.3 0.3


2556



Article

Table 9. Evaluation of the Vaporization Enthalpy of L-Deprenyl −slope run 9

T/K

intercept

N,N-dimethylbenzylamine N,N-dimethyloctylamine tri-n-butylamine L- deprenyl N,N-dimethyldodecylamine

4429.0 4977.6 5344.6 6141.9 6758.5

10.477 11.572 13.720 11.986 12.594

−1

g

Δl Hm(298.15 K)/kJ·mol


ΔHtrn(419 K) kJ·mol

−1

(lit)

(calc)

49.7 ± 0.4 54.5 ± 0.5 58.0 ± 1.9a

36.82 41.38 56.19 44.43 51.06

49.9 54.5 57.6 64.3 69.5

69.3 ± 0.3

± ± ± ± ±

1.4 1.5 1.5 1.6 1.7

= (1.01 ± 0.02)ΔHtrn(419 K) + (12.8 ± 1.1)

r 2 = 0.9989

(10)

Table 10. Evaluation of the Vaporization Enthalpy of (S)-Benzphetamine −slope


ΔHtrn(491 K)

run 11

T/K

intercept

N,N-dimethylbenzylamine N,N-dimethyldodecylamine N,N-dimethyltetradecylamine (S)-benzphetamine N,N-dimethylhexadecylamine tribenzylamine

4694.1 6689.0 7498.9 7493.5 8302.2 9034.0

11.003 13.508 14.436 13.766 15.364 15.491

−1

kJ·mol

(lit)

(calc)

49.7 ± 0.4 69.3 ± 0.3 77.3 ± 1.9a

39.02 55.61 62.34 62.3 69.02 75.11

49.7 69.3 77.2 77.1 85.1 92.3

84.8 ± 1.0a 92.4 ± 1.4a

± ± ± ± ± ±

0.5 0.6 0.6 0.6 0.6 0.7

Δl g Hm(298.15K)/kJ·mol−1 = (1.18 ± 0.01)ΔHtrn(491 K) + (3.69 ± 0.4) r 2 = 0.9999 a

(11)

This work.

Table 11. Evaluation of the Vaporization Enthalpy of Alverine −slope


ΔHtrn(494 K)

run 13

T/K

intercept

tri-n-butylamine N,N-dimethyldodecylamine N,N-dimethylhexadecylamine alverine tri-n-octylamine

4871.8 6033.6 7627.9 8080.2 9186.8

10.997 12.171 13.993 13.926 15.85

kJ·mol

−1

(lit)

(calc)

58.0 ± 1.9a 69.3 ± 0.3 84.8 ± 1.0a

40.5 50.16 63.41 67.18 76.38

58.0 69.3 84.9 89.3 100.1

100.1 ± 1.4a

± ± ± ± ±

0.1 0.1 0.2 0.2 0.2

Δl g Hm(298.15 K)/kJ·mol−1 = (1.17 ± 0.01)ΔHtrn(494 K) + (10.5 ± 0.1) r 2 = 0.9999 a

(12)

This work.

Table 12. A Summary of Vaporization Enthalpies (kJ·mol−1) at T/K = 298.15 of Runs 9 to 14

a

targets

run 9

run 10

(R)-deprenyl (S)-benzphetamine alverine standards N,N-dimethylbenzylamine N,N-dimethyloctylamine tri-n-butylamine N,N-dimethyldodecylamine N,N-dimethyltetradecylamine N,N-dimethylhexadecylamine tribenzylamine tri-n-octylamine

64.3 ± 1.6

64.3 ± 2.7

run 11

run 12

77.1 ± 0.6

77.2 ± 0.7

run 13

89.3 ± 0.2 49.9 54.5 57.6 69.5

± ± ± ±

1.4 1.5 1.5 1.7

50.1 54.2 57.4 69.5

± ± ± ±

2.3 2.4 2.5 2.8

49.7 ± 0.5

69.3 77.2 85.1 92.3

± ± ± ±

0.6 0.6 0.6 0.7

run 14

avga

89.3 ± 0.1

64.3 ± 2.2 77.2 ± 0.7 89.3 ± 0.2

49.6 ± 0.6

69.4 77.3 85.1 92.1

± ± ± ±

0.7 0.7 0.7 0.8

58.0 ± 0.1 69.3 ± 0.1

58.0 ± 0.1 69.3 ± 0.1

84.9 ± 0.2

84.9 ± 0.1

100.1 ± 0.2

100.1 ± 0.1

49.8 54.2 57.8 69.4 77.3 85.0 92.2 100.1

± ± ± ± ± ± ± ±

lit

1.4 2.0 1.0 1.0 0.7 0.4 0.8 0.2

49.7 54.5 58.0 69.3 77.3 84.8 92.4 100.1

± ± ± ± ± ± ± ±

0.4 0.5 1.9b 0.3 3.0b 1.0b 1.4b 1.4b

Uncertainties are also average values. bThis work.

mol−1 is 4.5 kJ·mol−1 smaller than the literature value of 56.8 kJ·mol−1. The value of (58.0 ± 1.9) kJ·mol−1 for tri-nbutylamine is in the lower range of previous measurements. The difference in the vaporization enthalpy between the two isomeric tributyl amines of (5.7 ± 2.9) kJ·mol−1 measured in

4. DISCUSSION 4.1. Vaporization Enthalpies. Column 2 of Table 16 summarizes the results of this study. The vaporization enthalpy evaluated in this work for triisobutylamine of (52.3 ± 2.2) kJ· 2557



Article

Table 13. Correlations between ln(to/ta)avg and Liquid ln(p/po)exp at T/K = 298.15 for Runs 1/2 and 3/4 −slope/K

intercept

ln(t0/ta)avg

p/Pa calc

ln(p/p0)exp

ln(p/p0)calc

−2.41

−2.39

9300

−5.26

524

−6.45

161

−6.80

113

−7.27

71

−8.18

28

Run 1/Run 2 triethylamine tripropylamine N,N-dimethylbenzylamine triisobutylamine N,N-dimethyloctylamine tri-n-butylamine

N,N-dimethylbenzylamine N,N-dimethyloctylamine tri-n-butylamine N,N-dimethyldodecylamine N,N-dimethyltetradecylamine

3282.7 3262.0 4263.8 4290.7 4577.9 4609 4858.8 4892.4 5104.6 5140.7 5464.5 5500.2

10.052 10.009 10.833 10.895 10.842 10.916 11.475 11.553 11.885 11.971 12.285 12.368

4436.7 4544.8 4923.4 5035.8 5268.0 5379.9 6621.9 6732.9 7509.0 7613.6 Run 1 and 2:

10.561 10.804 11.498 11.750 11.850 12.101 13.435 13.685 14.530 14.766

−0.94 −3.48 −4.53

−6.34

−4.84 −5.25

−7.36

−6.06 Run 3/Run 4 −4.38

−6.34

−6.42

165

−5.08

−7.36

−7.25

72

−5.88

−8.18

−8.2

28

−8.83

−11.69

−11.71

0.84

−13.93

0.090

−10.71

ln(p /po ) = (1.13 ± 0.04) ln(to/ta) − (1.32 ± 0.17)

r 2 = 0.9988

(13)

r 2 = 0.9988

(14)

Run 3 and 4

ln(p /po ) = (1.19 ± 0.03) ln(to/ta) − (1.23 ± 0.18)

Table 14. Slopes and Intercepts from ln(p/po) vs ln(to/ta) Correlations and a Comparison of Vaporization Enthalpies from Vapor Pressure Studies and from Correlations of ΔlgHm(298.15) and ΔHtrn(Tm) ΔlgHm(298 K)/kJ·mol−1 targets

−slope/K B′

intercept A′

tripropylamine triisobutylamine tri-n-butylamine (R)-deprenyl N,N-dimethyltetradecylamine (S)-benzphetamine N,N-dimethylhexadecylamine alverine tribenzylamine tri-n-octylamine Standards triethylamine N,N-dimethylbenzylamine N,N-dimethyloctylamine N,N-dimethyldodecylamine

5455.7 6209.8 6965.9 7697.8 9337.0 9299.1 10270.3 10792.7 11175.4 12148.0

13.034 14.028 15.181 15.211 17.399 16.450 18.368 18.087 18.361 20.362

45.4 51.6 57.9 64.0 77.6 77.3 85.4 89.7 92.9 101.0

± ± ± ± ± ± ± ± ± ±

0.1 0.1 0.1 0.2 0.4 0.5 0.2 0.7 0.7 0.1

46.2 52.3 58.0 64.3 77.3 77.2 84.8 89.3 92.4 100.1

± ± ± ± ± ± ± ± ± ±

1.6 2.2 1.9 2.2 1.9 0.7 1.0 0.3 1.4 1.4

4174.3 5909.7 6508.6 8362.0

11.606 13.386 14.567 16.365

34.7 49.1 54.1 69.5

± ± ± ±

0.1 0.1 0.1 0.3

35.6 49.6 54.5 69.4

± ± ± ±

1.6 1.8 1.9 1.3

a

from vpb

from ΔHtrnc

a

Slopes and intercepts of eq 15, the Clausius Clapyron eq, from a plot of ln(p/p0) versus 1/T over the temperature range T/K = 283.15 to 313.15; p0/Pa = 101325; all fits characterized by correlation coefficients, r2 > 0.99; bThe product of (−1/1000), the value of column 2, and the gas constant, 8.314 J·mol−1·K−1. cVaporization enthalpies from direct correlations of enthalpies of transfer with literature vaporization enthalpies (Table 8).

importance of choosing appropriate standards.25 The value obtained for tri-n-octylamine is 10 kJ·mol−1 smaller than the literature value but still well within the uncertainty cited. However, it should be recognized that vaporization enthalpies for molecules larger than N,N-dimethyldodecylamine are extrapolated values. Unlike vaporization enthalpies obtained

this study is consistent with the attenuation of approximately 2 kJ·mol−1/branch observed in other similar systems.10 The value for tri-n-butylamine is (4.7 ± 2.3) kJ·mol−1 smaller than the previous value obtained by correlation gas chromatography using aromatic heterocycles as standards.9 This result is consistent with similar findings on primary amines of the 2558



Article

Table 15. Correlations between ln(to/ta)avg and Liquid ln(p/po)exp at T/K = 298.15 for Runs 9 to 14 −slope/K

intercept

ln(t0/ta)avg

p/Pa calc

ln(p/p0)exp

ln(p/p0)calc

−4.35

−6.34

−6.42

165

−5.06

−7.36

−7.25

72

−5.87

−8.18a

−8.20

27.8

−10.61

2.5 0.84

Run 9/Run 10 N,N-dimethylbenzylamine N,N-dimethyloctyl amine tri-n-butylamine (R)-deprenyl N,N-dimethyldodecylamine

N,N-dimethylbenzylamine N,N-dimethyldodecylamine N,N-dimethyltetradecylamine (S)-benzphetamine N,N-dimethylhexadecylamine tribenzylamine

tri-n-butylamine N,N-dimethyldodecylamine N,N-dimethylhexadecylamine alverine tri-n-octylamine

4429.0 4382.6 4977.6 4858.8 5344.6 5220.4 6141.9 6005.8 6758.5 6607.9

10.477 10.378 11.572 11.298 13.720 11.702 11.986 12.284 12.594 13.382

4694.1 4712.5 6689.0 6752.2 7498.9 7569.9 7493.5 7563.5 8302.2 8373.4 9034.0 9103.8

11.003 11.046 13.508 13.645 14.436 14.59 13.766 13.918 15.364 15.518 15.491 15.642

4908.9 4871.8 6062.7 6033.6 7653.0 7627.9 8105.5 8080.2 9212.8 9186.8 Runs 9 and 10:

11.083 10.997 12.241 12.171 14.055 13.993 13.988 13.926 15.914 15.85

−7.93 −8.86 Run 11/Run 12

−11.69

−11.70

−4.75

−6.34

−6.34

−8.96

−11.69

−11.67

0.87

−10.76

−13.93a

−13.93

0.090

−14.76

0.04

−11.41

179

−12.52

−16.10a

−16.17

0.0097

−14.85 Run 13/Run 14

−19.15a

−19.12

0.000 51

−5.36

−8.18a

−8.20

27.7

−8.08

−11.69

−11.65

0.88

−11.60

−16.08a

−16.13

0.010

−18.14

0.0013/

−20.41

1.4·10−4

−13.19 −14.97

ln(p /po ) = (1.17 ± 0.028) ln(to/ta) − (1.32 ± 0.17)

−20.41a

r 2 = 0.9989

(16)

r 2 = 0.9999

(17)

r 2 = 0.9999

(18)

Runs 11 and 12:

ln(p /po ) = (1.26 ± 0.006) ln(to/ta) − (0.34 ± 0.07) Runs 13 and 14:

ln(p /po ) = (1.27 ± 0.005) ln(to/ta) − (1.40 ± 0.06) a

Value based only on runs evaluated as an unknown.

As noted above, vaporization enthalpies of very few tertiary amines have been reported. The group value of 6.6 kJ·mol−1 for a tertiary nitrogen used in eq 2 in estimating vaporization enthalpies in Table 2 was based on a few values, some of which have been shown here to be too large. Using the literature vaporization enthalpies of the following materials suggested as standards, triethylamine, tripropylamine, N,N-dimethylbenzylamine, N,N-dimethyloctylamine, and N,N-dimethyldodecylamine, a new value for nitrogen in a tertiary aliphatic amine of 3.3 kJ·mol−1 has been evaluated. The group value for a a tertiary amine was evaluated by minimizing the function: Σ[(ΔlgH(298.15 K) − (4.69n + 3.0 + N))/ΔlgH(298.15 K)]2 for N where n refers to the number of carbon atoms and N is the group value for a tertiary aliphatic nitrogen atom. Using this new group value of 3.3 kJ·mol−1 for a tertiary aliphatic nitrogen, new estimated values are provided in column

by interpolation, the standards do not compensate for heat capacity adjustments from the mean temperature of the gas chromatographic measurements to T/K = 298.15 as well for those values evaluated by extrapolation (eq 1). Hence the uncertainty associated with the larger amines is likely to be larger than the standard deviation associated with their reproducibility as cited in the second column of Table 16. While it is not possible to evaluate the probable uncertainty, the uncertainty is likely to increase as the extrapolation increases. An uncertainty of up to 10 % of the value is certainly plausible for the largest tertiary amine, trioctylamine. Uncertainties of (± 4.0, ± 4.0, ± 6.0, ± 7.0, ± 8.0, and ± 10.0) kJ·mol−1 for N,Ndimethyltetradecylamine, (S)-benzphetamine, N,N-dimethylhexadecyl-amine, alverine, tribenzylamine and tri-n-octylamine, respectively, are probably reasonable estimates. 2559



Article

Table 16. A Summary of the Vaporization Enthalpies (kJ·mol−1) and Vapor Pressures at T/K = 298.15 ΔlgHm(298 K) this work triethylamine tripropylamine N,N-dimethylbenzylamine triisobutylamine N,N-dimethyloctylamine tri-n-butylamine (R)-deprenyl N,N-dimethyldodecylamine N,N-dimethyltetradecylamine (S)-benzphetamine N,N-dimethylhexadecylamine alverine tribenzylamine tri-n-octylamine

estimate (eq 2)a

35.2 ± 0.2 46.2 ± 0.1 49.7 ± 0.4

34.4 ± 1.7 48.5 ± 2.4 48.5 ± 2.4 56.6 ± 2.8 53.2 ± 2.7 62.6 ± 3.1 65.3 ± 3.4 72.0 ± 3.6 81.3 ± 4.1 84.0 ± 4.3 90.7 ± 4.5 90.7 ± 4.5 104.8 ± 2.2 118.8 ± 6.0

52.3 ± 2.2 54.5 ± 0.5 58.0 ± 1.9 64.3 ± 2.2 69.3 ± 0.3 77.3 ± 1.9 77.2 ± 0.7 84.8 ± 1.0 89.3 ± 0.2 92.4 ± 1.4 100.1 ± 1.4

p/Pa(298.15 K)

literature

110 ± 15

this workb 9300 524 163 113 71 28 2.5 0.86 0.091 0.04 0.011 1.4·10−3 5.1·10−4 1.4·10−4

literature c

9100 201,d 355e 179c 73,d 70e 65c 21,d 20e(21, 54)f,g 2.1,d 0.8e 0.85c 0.27,d 0.2e 0.04,d 0.02e 0.038,d 0.035e (4.5,d 3.3)·10−3e (5.8,d 3.9)·10−4e 1.32·10−4c,g

Using a group value of 3.3 kJ·mol−1 for nitrogen; uncertainties are based on 5 % of the predicted value.10 bCalculated using eq 15 and the slopes and intercepts listed in Table 14 at T/K = 298.15. cCalculated using eq 5 and the constants in Table 3 at T/K = 298.15. dEstimated ref 11. e Estimated, ref 27. fReference 20. gExtrapolated value. a

K = 298.15. This value differs substantially from the literature value reported17 and the value evaluated in this work. Despite this fact, the vapor pressures calculated at ambient temperatures from the Antoine constants are remarkably close to those obtained by correlation. Figure 3 illustrates how the vapor

4 of Table 16 that are in much better agreement with the results of this work. The uncertainties reported in this column represent 5 % of the predicted value, the standard uncertainty associated with this equation for compounds containing a single functional group.10 4.2. Vapor Pressures. As a means of evaluating the quality of the vapor pressures obtained by correlating ln(t0/ta)avg with ln(p/p0) as a function of temperature, the last two columns in Table 14 compare vaporization enthalpies calculated by two different methods. The values reported in column 4 of Table 14 were calculated from the temperature dependence of vapor pressure using eq 15 measured over the temperature range T/K = (283.15 to 313.15). The vaporization enthalpies reported in the last column of Table 14 were obtained directly by correlation of the enthalpies of transfer with the vaporization enthalpies of the standards at T/K = 298.15. The results agree within the uncertainty associated with their reproducibility. The last two columns of Table 16 compare vapor pressures evaluated in this work at T/K = 298.15 with either literature or estimated values. The vapor pressures reported in this table were calculated using eq 15 and the slopes and intercepts reported in columns 2 and 3 of Table 14. The reproducibility as judged by comparisons of the values obtained by direct correlation at T/K = 298.15, Tables 13 and 15, and those obtained from the temperature dependence of these correlations, Table 16, clearly indicate that the ln(p/p0) and ln(t0/ta) of the standards correlate quite well with temperature. The absolute uncertainties associated with these results are difficult to judge since they are highly dependent on the accuracy of the vapor pressures of the standards. The uncertainty associated with the tertiary amines obtained by extrapolation is certainly likely to be greater than for those obtained by interpolation. The estimated values listed in Table 16 identified by footnotes d and e compare with those of this study within a factor of 4 or less. The vaporization enthalpy and vapor pressures for tri-noctylamine were not used in these correlations since it is known that the Antoine equation does not extrapolate well with temperature. For example, a vaporization enthalpy of 120.4 kJ· mol−1 is calculated for this compound using extrapolated vapor pressures generated by the constants reported in Table 3 at T/

Figure 3. Vapor pressure temperature dependence of tri-n-octylamine: line, vapor pressure of tri-n-octylamine calculated using eq 5 and the Antoine constants of Table 317 over the temperature range T/K = (283−533); circles, vapor pressures calculated from the slope and intercept of tri-n-octylamine from Table 14 plotted as ln(p/Pa).

pressures extrapolated from the Antoine constants vary with temperature. The line represents the values calculated as ln(p/ Pa) using eq 5 and the Antoine constants of Table 3 extrapolated to ambient temperatures while the solid circles represent the vapor pressures evaluated using eq 15 and the slope and intercept from Table 14 for tri-n-octylamine also plotted as ln(p/Pa). The vapor pressure of tri-n-octylamine calculated by extrapolation of the Antoine constants, p/Pa = 1.32·10−4 at T/K = 298.15, compares to a value of p/Pa = 1.4· 10−4 evaluated in this work. This result suggests that while extrapolations of the Antoine equation may not provide reliable vaporization enthalpies, the resulting vapor pressures may be 2560



Article

Table 17. Fusion, Vaporization, and Sublimation Enthalpy of Tribenzylamine at T/K = 298.15 ΔcrcrHt + ΔcrlH(Tfus)a −1

kJ·mol tribenzylamine a

24.1 ± 0.14

ΔCpΔTb

Tt/Tfus

−1

K 342.5/365.6

kJ·mol

−5.2 ± 1.6

ΔcrlH(298 K)

ΔlgHm(298 K)

−1

kJ·mol

18.9 ± 1.6

kJ·mol

−1

92.4 ± 1.4

ΔcrgHm(298 K) kJ·mol−1 111.3 ± 2.1

ΔcrcrHm(342.5 K)/kJ·mol−1 = (1.1 ± 0.1). bCp(l)), Cp(cr))/J·mol−1·K−1 = 490.6, 400.2, respectively, ref 23. (7) Thornton, M.; Gobble, C.; Chickos, J. The Vaporization Enthalpy and Vapor Pressure of (S)(+)-Methamphetamine at T = 298.15 K by Correlation Gas Chromatography. J. Chem. Thermodyn. 2014, 73, 51− 6. (8) http://www.patient.co.uk/medicine/Alverine-citrate.htm (accessed 2/4/14). (9) Advanced Chemistry Development Software, v11.02; ACD/ Laboratories: Toronto, Ontario, Canada, 1994−2012 (accessed through SciFinder Scholar). (10) Chickos, J. S.; Acree Jr., W. E.; Liebman, J. F. Estimating Phase Change Enthalpies and Entropies. In Computational Thermochemistry; Symposiun Series 677; Irikura, K. K., Frurip, D. J., Eds.; American Chemical Society: Washington DC, 1998; Chapter 4. (11) Calculated using the EPI Suite. The EPI Suite is available as a free download from http://www.epa.gov/oppt/exposure/pubs/ episuitedl.htm (accessed 12/1/12). (12) Wadso, I. Enthalpies of Vaporization of Organic Compounds. III. Amines. Acta Chem. Scand. 1969, 23, 2061−4. (13) Mokbel, I.; Razzouk, A.; Sawaya, T.; Jose, J. Experimental Vapor Pressures of 2- Phenylethylamine, Benzylamine, Triethylamine, and cis-2,6-Dimethylpiperidine in the Range between 0.2 and 75 Pa. J. Chem. Eng. Data 2009, 54, 819−822. (14) Verevkin, S. P. Strain Effects in Phenyl-Substituted Methanes. Geminal Interaction between Phenyl and the Electron-Releasing Substituents in Benzylamines and Benzyl Alcohols. J. Chem. Eng. Data 1999, 44, 1245−1251. (15) Verevkin, S. P. Thermochemistry of Amines: Experimental Standard Molar Enthalpies of Formation of Some Aliphatic and Aromatic Amines. J. Chem. Thermodyn. 1997, 29, 891−99. (16) Fulem, M.; Ruzicka, K.; Ruzicka, V.; Hulicius, E.; Simecek, T.; Pangrac, J.; Rushworth, S. A.; Smith, L. M. Measurement of Vapour Pressure of In-Based Metalorganics for MOVPE. J. Cryst. Growth 2004, 272, 42−46. (17) Steele, W. V.; Chirico, R. D.; Knipmeyer, S. E.; Nguyen, A.; Smith, N. K.; Tasker, I. R. Thermodynamic Properties and Ideal-Gas Enthalpies of Formation for Cyclohexene, Phthalan (2,5-Dihydrobenzo-3,4-furan), Isoxazole, Octylamine, Dioctylamine, Trioctylamine, Phenyl Isocyanate, and 1,4,5,6-Tetrahydropyrimidine. J. Chem. Eng. Data 1996, 41, 1269−1284. (18) Gua, Y.; Yang, F.; Xing, Y.; Li, D.; Fang, W.; Lin, R. BubblePoint Vapor Pressure Measurement for System JP-10 and Tributylamine by an Inclined Ebulliometer. Energy Fuels 2008, 22, 510−3. (19) Lipkind, D.; Hanshaw, W.; Chickos, J. S. Hypothetical Thermodynamic Properties. Subcooled Vaporization Enthalpies and Vapor Pressures of Polyaromatic Heteocycles and Related Compounds. J. Chem. Eng. Data 2009, 54, 2930−43. (20) Calculated from the Antoine constants reported at the temperature indicated. Stephenson, R. M.; Malanowski, S. Handbook of the Thermodynamics of Organic Compounds; Elsevier: New York, 1987. (21) Peacock, L. A.; Fuchs, R. Enthalpy of Vaporization Measurements by Gas Chromatography. J. Am. Chem. Soc. 1977, 99, 5524−5. (22) Lipkind, D.; Chickos, J. S. An Examination of Factors Influencing the Thermodynamics of Correlation-Gas Chromatography as Applied to Large Molecules and Chiral Separations. J. Chem. Eng. Data 2010, 55, 698−707. (23) Acree, W., Jr.; Chickos, J. S. Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2010. J. Phys. Chem. Ref. Data 2010, 39, 1−940.

quite reasonable. Similar results have been observed in other studies.28 4.3. Sublimation Enthalpy. Of all the aliphatic amines studied, tribenzylamine is the only crystalline material at ambient temperatures. Adjusting the fusion enthalpy to T/K = 298.15 using eq 4 results in a value of (18.9 ± 1.6) kJ·mol−1 and combining this with the vaporization enthalpy of the subcooled liquid of (92.4 ± 8.0) kJ·mol−1 also at this temperature provides a value of (111.3 ± 8.2) kJ·mol−1 for the sublimation enthalpy for tribenzylamine. Table 17 summarizes these results. Since the vapor pressures of the standards do not extend to T/K = 365.6, the fusion temperature of tribenzylamine, the vapor pressure of the solid was not evaluated.

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ASSOCIATED CONTENT

S Supporting Information *

Tables of the experimental retention times, results of duplicate vaporization enthalpy and vapor pressure measurements evaluations, and fusion enthalpy measurements described in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address §

Wentzville High School, One Campus Drive, Wentzville, MO 63385. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We would like to thank Dr. Gary Nichols from Mallinckrodt Pharmaceuticals for providing us with a sample of benzphetamine hydrochloride.

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REFERENCES

(1) Physician’s Desk Reference, 48th ed.; Medical Economics Data Prod. Co.: Montvale, NJ, 1994; pp 416, 1843, and 2309. (2) Mendelson, J. E.; McGlothlin, D.; Harris, D. S.; Foster, E.; Everhart, T.; Jacob, P.; Jones, R. T. The Clinical Pharmacology of Intranasal l-Methamphetamine. BMC Clin. Pharmacol. 2008, 8, 4. (3) Armstrong, D. W.; Rundlett, K. L.; Nair, U. B. Enantioresolution of Amphetamine, Methamphetamine, and Deprenyl (Selegiline) by LC, GC, and CE. Curr. Sep. 1996, 15, 57−61. (4) Musshoff, F. Illegal or Legitimate Use? Precursor Compounds to Amphetamine and Methamphetamine. Drug Metab. Rev. 2000, 32, 15−44. (5) http://www.inchem.org/documents/pims/pharm/pimg009.htm (accessed 1/16/2014). (6) ̀ The Vaporization Enthalpy and Vapor Pressure of (D)Amphetamine and of Several Primary Amines Used as Standards at T/K = 298 As Evaluated by Correlation Gas Chromatography and Transpiration Thornton, M.; Chickos, J. J. Chem. Eng. Data 2013, 58, 2018−27. 2561



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(24) Roux, M. V.; Temprado, M.; Chickos, J. S.; Nagano, Y. Critically Evaluated Thermochemical Properties of Polycyclic Aromatic Hydrocarbons. J. Phys. Chem. Ref. Data 2008, 37, 1855−1996. (25) Gobble, C.; Rath, N.; Chickos, J. The Vaporization Enthalpies and Vapor Pressures of Some Primary Amines of Pharmaceutical Importance by Correlation Gas Chromatography. J. Chem. Eng. Data 2013, 58, 2600−09. (26) Wilson, J. A.; Chickos, J. S. Vapor Pressures, Vaporization, Sublimation and Fusion Enthalpies of Some Fatty Acids. J. Chem. Eng. Data 2013, 58, 322−333. (27) ACD labs, SciFinder Scholar, substance identifier, thermal properties, https://scifinder.cas.org/scifinder/view/scifinder/ scifinderExplore.jsf (accessed 2/7/14). (28) Gobble, C.; Chickos, J. S.; Verevkin, S. V. Vapor Pressures and Vaporization Enthalpies of a Series of Dialkyl Phthalates by Correlation Gas Chromatography. J. Chem. Eng. Data 2014, 59, 1353−65.

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