increases in Zu values for phenol and propionic acid. However, it has been shown previously (15) that column oxidation of asphalts results in a decrease of free OH absorbance while hydrogen-bonded OH absorbance increases significantly. Much of this hydrogen bonding remains intact even in dilute solutions so that the net result is a loss of free OH absorbance even though the total OH in the sample has increased. Upon silylation a general decrease is noted in the hydrogen-bonded absorbance; however, no quantitative determination could be made of the hydrogen-bonded region (about 3500-2500 cm-l) because it is overlapped by the C-H stretching region. Repeatability of the Si1ylation Technique. Two separate packings were prepared, using asphalt D as the substrate. Two columns of each packing were processed in the manner described in the Experimental section. The data, included in Table I, show a maximum variation in specitic interaction coefficients for a given test compound on duplicate asphalt samples of three I, units. This is within the normal variation on duplicate runs of the same sample. The preliminary indication is that the technique gives reproducible results. SUMMARY AND CONCLUSIONS
Silylation of a n asphalt within an IGLC column offers a convenient means to study asphalt functionality. More specifically, the reagent, BSA, reacts with most of the phenolic and carboxylic acid hydroxyl groups present in either as-
received or column-oxidized asphalts. Comparison of infrared spectra before and after silylation substantiates this conclusion. Silylation reduces the phenol and propionic acid Zu values on both oxidized and unoxidized asphalts to a common value characteristic for each individual test compound. This results from the blocking of the carboxylic acid and phenolic OH groups in the asphalts. These groups are believed to be the ones by which phenol and propionic acid differentiate among asphalts. The functional groups which interact strongly with formamide remain after silylation. These groups appear to be carbonyl functions. The silylation technique should be applicable to investigations of the chemical structure of macromolecules and nonvolatile materials. ACKNOWLEDGMENT Technical discussions with George Bohner of the Denver Research Institute are gratefully acknowledged. RECEIVED for review March 24, 1969. Accepted May 1, 1969. Work presented in this report was done under a cooperative agreement between the Bureau of Mines, U. s. Department of the Interior and the University of Wyoming. Mention of specific brand names or models of equipment is made for identification only and does not imply endorsement by the Bureau of Mines.
Characterization and Gas Chromatography of Alkoxides of Aluminum and of Some Group IV Elements L. M. Brown Uniuersity of Cincinnati, Cincinnati, Ohio 45221 K. S . Mazdiyasni Air Force Materials Laboratory, Wright-Patterson Air Force Base, Ohio 45433
AI-tris-isopropoxide, tetrakis-isopropoxides of Ti, Zr, Hf, Si and Ge, and tetrakis-tertiary amyloxides of Ti, Zr and Hf have been synthesized as precursor materials for the preparation of single and mixed phase refractory oxides. An attempt has been made to characterize these compounds on the basis of chemical analysis, infrared spectra, proton NMR, mass spectrometry, thermogravimetric analysis, and gas chromatography. The I R spectra (4000-270 cm-1) of the tetrakis-tertiary amyloxides of Ti, Zr, and Hf have been obtained for the first time. In the CsBr region a number of very strong absorption bands are found that are characteristic absorption frequencies for the tertiary amyl compounds. These compounds are liquid (with the exception of the AI compound which is solid), of considerable volatility, and thermally stable at relatively high temperatures when highly pure. Results of the gas chromatography of the above metal alkoxides are reported for the first time. Well resolved peaks have been obtained with a mixture of (i) t-amyloxides of Ti and Zr, (ii) t-amyloxides of Ti and Hf, (iii) isopropoxides of Si, Ge, Ti and AI.
METALALKOXIDES have been a subject of extensive research in recent years because of their potential as precursor materials for several applications. Among these are the preparation of high purity fine particle metal oxide powders ( I ) , the vapor deposition of oxide thin films (2),and the preparation of single and mixed-phase ferroelectric materials ( 3 , 4 ) .
The most recent reviews of alkoxides by Bradley (5, 6) reveal that extensive research has been done on synthesis, structural analysis, and physical-chemical properties of a number of the more common alkoxides. The study of other alkoxides has been limited by expensive starting materials and by difficulties in preparation and handling. Successful characterization of most of the alkoxides is complicated by their extreme sensitivity to moisture, heat, light, and atmospheric conditions. In this paper the results of synthesis and characterization of Si, Ge, Ti, Zr, Hf and A1 isopropoxides and Ti, Zr and Hf tertiary amyloxides are reported. Of particular interest is the vapor phase chromatography of these metal alkoxides. (1) K. S. Mazdiyasni, C. T. Lynch, and J. S. Smith 11, J . Amer. Ceram. SOC.,50, 532 (1967).
(2) K. S. Mazdiyasni and C. T. Lynch, “Special Ceramics 1964,” P. Popper, Ed., Academic Press, New York, 1965, pp 115-38. (3) T. H. Harwood, Chem. Process Eng., 48 (6), 100 (1967). (4) K. S. Mazdiyasni, C. T. Lynch, and J. S. Smith, 11, “Development of New Ceramic Materials (Zyttrite) by Thermal and Hydrolytic Decomposition of Metal Alcoholates,” AFML TR 66-418, Air Force Materials Laboratory, Wright-Patterson Air Force Base, Ohio, 1966. ( 5 ) D. C. Bradley, Progr. Znorg. Chem., 2, 303 (1960). (6) D. C. Bradley, “Preparative Inorganic Reactions,” Vol. 2, Jolly, Ed., Wiley, New York, 1962, pp 169-86. VOL. 41,NO. 10,AUGUST 1969
1243
Table I. Elemental Analysis of Isopropoxides and Tertiary-Amyloxides Carbon, 52.92 52.74 54.50 55.64 50.70 50.24 46.65 46.54 44.00 43.60 37.74 37.17 60.59 61.30 54.62 54.68 45.58 45.86
Compound"
Si(OC3Hd4
a
Calcd. Found
Boiling point "C/mm Hg
Metal, % 13.21 13.88 10.62 9.72 16.85 17.33 23.50 23.64 27.85 27.65 43,03 42.66 12.08 12.00 20.74 20.43 33.87 33.86
Hydrogen, % 10.36 10.27 10.67 10.85 9.93 9.57 9.14 9.12 8.62 8.54 6.80 6.52 11.19 11.54 10.08 10.03 8.41 8.64
140/10 72.5112 96.017 82,015 17210.35 170/0.35 98lO.l 9510.1 9210.1
Analysis for chlorine was negative. Table 11. Characteristic Absorption of Tertiary-Amyloxy Groups (cm -1)
R
= -C(CH;)~C~HS
Compound
Characteristics
ROH Ti(0R)a
Zr(OR14 Hf(OR14
1276 1287 1290 1291
1222 1224 1225
1185 1190 1192 1193
1166 1165 1174 1175
EXPERIMENTAL
The tetrakis-isopropoxides of Si, Ge, Ti, Zr, and Hf have been prepared by the method of Bradley and coworkers (7) MC14
+ 4ROH + 4NH3 CsHe
M(OR)4
+ 4NHC1
(1)
where R is the isopropyl radical. Aluminum tris-isopropoxide was synthesized by the method of Adkins and Cox (8).
Titanium, zirconium and hafnium tetrakis-tertiary amyloxides were formed by the alcoholysis reaction method of Bradley et af (9) and Mehrotra (10).
M(OR)4
+ R'OH + C6H6 e R'OH
M(OR')4 f [ R O H x s H e ] (3) where R' is the tertiary amyl radical. The as-received 99.8% SiCl4 from K & K Laboratories, Inc., was used in the preparation of Si-isopropoxide. High purity 99.999 % GeCL and 99.999 % A1 metal were purchased from Alfa Inorganic, Inc., and 99.5% Tic14 was obtained from Matheson, Coleman, and Bell, and used as-received. (7) D. C. Bradley and W. Wardlaw, J. Chem. SOC.,1951,280. ( 8 ) H. Adkins and J. Cox, J . Amer. Chem. Soc., 60, 1151 (1938). (9) D. C. Bradley, R. C. Mehrotra, and W. Wardlaw, J . Chem. SOC.,1952, 2027. (10) R. C. Mehrotra, J . Indian Chem. SOC.,31,85 (1954). 1244
ANALYTICAL CHEMISTRY
1146 1158 1160
1059 1059 1060 1060
880
901 900 900
780 792 788 785
725 759 755 753
Spectrograde 99.9 % ZrC14and HfC14 used in the preparation of these alkoxides were obtained from Wah Chang Corporation and used as received. Analytical grades isopropyl alcohol and tertiary amyl alcohol were dried over calcium chloride and calcium sulfate and redistilled over calcium hydride. Benzene was dried over magnesium perchlorate. The reactions were carried out in glass apparatus with ground glass joints in inert atmosphere or under reduced pressure. Compounds were handled at all times in a dry box and were stored in evacuated desiccators. Quantitative analyses on all the alkoxides studied were performed by Schwarzkopf Microanalytical Laboratory, Woodside, N. Y . The conventional method of vapor pressure osmometry was used to determine the molecular weight of Si-isopropoxide. Infrared spectra in the 4000-200 cm-' region were obtained for all the alkoxides studied and the two respective groups of compounds were compared. The spectra were recorded with a Perkin-Elmer 521 grating infrared spectrophotometer using cesium iodide windows. All compounds were run as liquid films with the exception of the solid aluminum isopropoxide which was run in the two solvent system of CC14-
cs2.
Proton NMR spectra were measured at 60 MHz at the probe temperature of 37 "C on a Varian Associates Model A-56/60 A spectrometer. Liquid alkoxides were analyzed neat while the solid and highly viscous alkoxides were analyzed in saturated benzene solution. The chemical shift measurements were made on both instrument and chart paper calibrated using the audio side band technique. Tetramethylsilane was used as internal reference. Precise values for the molecular weights of titanium, zirconium, and hafnium tertiary-amyloxides were obtained by high resolution mass spectrometry. The mass spectrometric analyses were made with an Associated Electrical
b
Table 111. CsBr Region Absorption Frequencies of Metal Tetrakis-Tertiary-Amyloxides (cm-l)
73.0 Ilz
R = - C(CH&CSHJ
Ti(OR)a 624 587
CH; Ti-0-
b c d
-
-
h -CHs-CH:
A;
Singlet Multiplet Triplet
Zr(ORh
Hf(OR)a
596
592 542
526
545 528
463
470
390
383
464 377
361 348
354
350
520
305 268
270
d
=
8 7 IIz
IrS6iYI
Figure 1. NMR spectrum of titanium tetrakis-tertiary amyloxide Industries MS-9 double-focusing high-resolution mass spectrometer using ionizing energies of 12 and 70 eV at temperatures of 140-250 “C. Perfluorokerosene was used as reference. The mass spectrum of aluminum isopropoxide was obtained using a CEC Model 21-llOB mass spectrometer and the same experimental conditions as stated above. All the alkoxides studied were successfully chromatographed using a Hewlett-Packard ( F & M) Model 5754 B gas chromatograph with dual column, dual thermal conductivity detector. To minimize moisture contamination, a glove bag was attached to the injection port and continuously purged with dry helium during operation of the chromatograph. Teflon was chosen for the column material because of its inertness. Several solid supports were tried with Chromosorb W and Gas Pack F giving equally good results. Many liquid phases were used at varied concentrations of 1-lOZ. Best results were obtained with lightly loaded columns (1 Z liquid phase) using Apiezon L, Silicon Gum Rubber SE-30, and Silicone Oil DC-200. The longest columns used (1 ft) gave the best separations. DISCUSSION AND RESULTS
Chemical Analysis and Molecular Weight Determinations. The results of elemental analysis and boiling points are listed in Table I. Carbon, hydrogen, and metal analyses were in good agreement with calculated values. Analysis for chlorine was negative for all the alkoxides. The molecular weight found for Si-isopropoxide by vapor pressure osmometry was 293.5 compared to a value of 264.5 calculated for the monomer. The molecular weights of the other alkoxides could not be determined by this method because the compounds decomposed on the osmometer thermistor beads. Infrared Spectra. Infrared spectra of most of the isopropoxides and the characteristic absorption frequencies of the isopropyl group have been reported previously, most recently by Lynch et al(11). The IR spectrum of germanium isopropoxide, obtained for the first time during this study, is consistent with the previously published spectra of Al, Si, Ti, Zr, and Hf isopropoxides (11). Spectra were recorded for both the viscous liquid and solid forms of aluminum isopropoxide. No significant differences were observed when (11) C. T. Lynch, K . S. Mazdiyasni, J. S. Smith, 11, and W. J. Crawford, ANAL.CHEW,36 (12), 2332 (1964).
comparing the two spectra except in the case of the solid compound, where approximately 10% concentration in the twosolvent CS2-CClasystem was used, the peaks in the spectrum were more intense and better resolved perhaps due to the solvent effect as opposed to a neat, highly viscous liquid film (12, 13).
The IR spectra of the tetrakis-tert-amyloxides of titanium, zirconium, and hafnium, obtained for the first time, have been compared with the spectrum of the parent alcohol. The tertiary amyloxides exhibit more complicated infrared spectra than the isopropoxides because of the complexity of the tertiary-amyl alkoxy group. In general, many more peaks are observed. The observed characteristic vibrations of the tertiary-amyl group are given in Table 11. Although the spectrum of the alcohol has no sharp absorption bands at about 1224 cm-l and 1155 cm-I, broad shoulders appear in these regions indicating areas of strong absorption. To differentiate the spectra of the three tertiary-amyloxides, attention is directed to the CsBr region illustrated in Table 111. The spectrum of the titanium compound may be distinguished from the spectra of the zirconium and hafnium alkoxides by additional bands at 624 cm-l and 361 cm-l and the absence of absorption bands at 543 cm-l and 269 cm-1. The zirconium compound exhibits only one additional absorption band at 305 crn-I to distinguish it from the very similar hafnium alkoxide. Some similarities may be observed in the IR spectra of the isopropoxides and tertiary-amyloxides. Both groups exhibit a doublet at about 1375 cm-1 and 1365 cm-1 characteristic of the gem dimethyl structure. Also, these groups, and alkoxides in general, have a strong absorption band in the 1000 cm-’ (967-1041 cm-l) region which has been assigned as the C-0 stretch vibration. It is shifted in each spectrum by the influence of the specific metal atom on the C-0 stretch vibration. No definite correlation has been found for the direction or degree of the shift in band position. In addition to the different characteristic vibrations of the two groups, the isopropoxides always exhibit a characteristic weak band at 2610-2625 crn-I attributed to the carbon-crhydrogen stretch vibration of the isopropyl radical (11,14). NMR Spectra. The results of the NMR study of the alkoxides are given in Tables IV and V and Figure 1. In Table IV, NMR chemical shifts for isopropyl alcohol and some ~
(12) L. J. Bellamy, “Infrared Spectra of Complex Molecules,” 2nd ed., Wiley, New York, 1958, pp 380-2. (13) F. F. Bentley, L. D. Smithson, and A. L. Rozek, “Infrared Spectra and Characteristic Frequencies -700-300 cm-l,” Interscience, Wiley, New York, 1968, pp 160-2. (14) F. H. Seubold,J. Org. Chern.,21,157 (1956). VOL. 41, NO. 10,AUGUST 1969
1245
Table IV. Chemical Shifts for Isopropyl Alcohol and Some Metal Isopropoxides
F3
M-0-C
I\
H
Element M H5 Albt Ale??
Si5 Ge” Tia Zr so1v.b Zrc*
CH proton peaks Hz
ma
ACH rel. to isopropanol Hz
CHa proton shifts Hz
0 26.5 23.7 15.5 16.1 30.7 38.2 37.3 44.3 42.9
69.8 76.5 78.6 68.9 68.6 70.6 83.0 81.9 83.8 82.3
237.8 septet 264.3 (295.5-246.5; 9 pks) 261.5 (293 .O-244; 14 pks) 253.3 septet 253.9 septet 268.5 septet 276.0 septet 275.1 septet 282.1 septet 280.7 (300-250; 14 pks)
ACH3rel. to Coupling isopropanol Constants Hz J 6.3 6.0 6.0 6.0 6.1 6.2 6.2 6.1 6.2 6.2
0 6.7 8.8 -0.9 -1.2 0.6 13.2 12.1 13.8 12.4
Hf solv? HfC** Internal Standard: TMS Neat. b Satd. soh. of M(OCaH&.C3H70Hin benzene n = 3 or 4. c Satd. soh. of distilled product (unsolvated) in benzene. t Additional CH, proton peaks at 101.7:95.5:86.0 (Hz) were observed. tt Additional CH, proton peaks at 98.4:92.2:84.3:81.0:77.8:74.5 (Hz) were also observed. * Additional CHa proton peaks at 80.0:73.9 (Hz) were observed. ** Additional CHI proton peaks at 95.7:89.0:82.6:74(Hz) with intensity ratios roughly 1 :4:4:5:1 were observed.
Electronegativity (16) x 1.5 1.5 1.8 1.8 1.5 1.4 1.4 1.3 1.3
Table V. Chemical Shifts of Tertiary Amyl Alcohol and Some Tetrakis-Amyloxides CH3b
b-singlet
I
M4-C-CH20-CHad
c-multiplet
I
Element M Ha Tib Zl.b 11
d-proton shifts Hz
Ad rel. to t-amyl alcohol Hz
54.2 56.7 56.3 55.0
0 2.5 2.1 0.8
HP Neat: Internal Standard; TMS Neat: Internal Standard; benzene (434.4 Hz)
d-triplet
b-proton shifts Hz
Ab rel. to t-amyl alcohol Hz
c-proton shifts Hz
70.7 73.0 70.4 69.2
0 2.3 -0.3 -1.5
86 87 85 83
of the metal isopropoxides are tabulated. Isopropyl alcohol, Si, Ge, Ti-isopropoxides, solvated Zr-isopropoxide and solvated Hf-isopropoxide all give one doublet which is due to a single species of CH8-group. For these compounds only one septet of CH-protons is found as expected. The unsolvated Zr- and Hf-isopropoxides obtained by vacuum distillation of the solvated complexes developed one and three new minor doublets respectively. Bradley (15) made similar observations concerning these same compounds in cyclohexane. For unsolvated Zr-isoproposide only one CH-septet is observed. For the unsolvated Hf-isopropoxide 14 peaks (2 septets) can be detected. Shifts relative to isopropyl alcohol are tabulated in the 3rd and 5th columns. It is apparent that CH-shifts are more sensitive to the change of element, M, than the CH3-shifts. It is also noted that the CH-shifts are in the order of electronegativity on Pauling’s scale (16). The progressive lower field chemical shifts from Si to Hf may be due to a combina(15) D. C. Bradley and C. E. Holloway, J. Chem. SOC. A (6), 1968, 1316. (16) L. Pauling, “The Nature of the Chemical Bond,” 3rd ed., Cornel1University Press, Ithaca, N. Y., 1960, p 88. 1246
ANALYTICAL CHEMISTRY
Ac rel. to t-amyl alcohol Hz 0 1 -1 -3
Electronegativity (16) X 1.5 1.4 1.3
tion of the deshielding of the CH-protons and the increase in the degree of polymerization. The same trend is observed in the case of the Al-isopropoxides, the chemical shifts of which are given in Table IV. The solid Al-isopropoxide is known to be tetrameric (17). A saturated solution of the solid aluminum isopropoxide in benzene shows a major CH3-proton doublet and two minor doublets in agreement with the report of Shiner et a1 (17). In the CH-proton region, only 9 peaks can be detected. Liquid Al-isopropoxide, a supercooled melt obtained by distillation from the solid, is known to be essentially trimeric which slowly reverts to the tetrameric form at lower temperatures (17, 18). A saturated benzene solution of the liquid Al-isopropoxide shows the major CH3-doublet and three minor doublets. In the CH-proton region, 14 peaks can be detected. The important difference between the liquid and solid Al-isopropoxides is a change in the degree of polymerization (from 3 to 4) and this change is reflected somewhat in the lower field chemical shifts. (17) V. J. Shiner, Jr., D. Whittaker, and V. P. Fernandez, J. Amer. Chem SOC., 85 (15), 2318 (1963). (18) R. C. Mehrotra, J. Indian Chem. Soc., 21, 157 (1956).
Table VI. Mass Spectrometric Analysis of Tertiary Amyloxides of Ti, Zr, and Hf Ti04CZoH44 ZrO4Cz0H44 HfOaCtoH44 Measured m/e Identitya Measured m/e Identity* Measured m/e Identityc 396 w T~O~CZOHU 438 w Zr04GoH44 528 w 381 s TiO4C1~H4~ 423 s Zr04C1& 513 s 367 vs Ti04C18H 39 409 vs Zr04ClaH39 499 vs 309 m Ti04C14H34 351 rn Zr04C~H34 441 m 297 m Ti04C13H2~ 339 rn Zr04C13H29 429 m 280 m TiOaC1tH24 321 m ZrOG2H23 411 m 241 rn Ti04CoH2, 283 rn Z~O~CDHU 371 rn 227 m Ti04C8H10 269 rn Zr04CeH19 359 rn 171 m Ti04C4Hll 213 rn Zr04C4Hl1 301 rn 157 rn Ti04C3He 199 rn ZrO4C3HD 289 m 139 m Ti03C3Hi 181 s Zr03C3H7 271 m 122 m Ti02C3H6 167 m Zr03C2H5 257 rn 73 s OC~HQ 73 s 73 s OC4Ha 70 s CjHio 70 s CjHio 70 s 59 s OC3H7 59 s OC3H7 59 s 55 vs C4Hi 55 vs 55 vs C4H7 43 s C3H7 43 s 43 s C3Hi 42 s C3H6 42 s 42 s C3H6 41 s C3H; 41 s C3H5 41 s 39 s C3H3 39 s C3Ha 39 s 29 vs CzH 5 29 vs 29 vs CzHs 27 s CzH3 27 s C2H3 27 s 18 vs Hz0 18 vs 18 vs H2O 17 s OH 17 s 17 s OH 15 s CH3 15 s CH3 15 s Approximate intensities designated as follows: vs = very strong, s = strong, m = medium, w = weak. = Mass numbers based on 48Ti. * Mass numbers based on goZr. c Mass numbers based on lsoHf.
A typical NMR spectrum of Ti tetrakis-tertiary amyloxide is shown in Figure 1. The b- and d-methyl protons and the c-CH2protons are identified. The b, c, and d proton positions for the tertiary-amyloxides are tabulated in Table V. It appears from the similarity of the NMR spectra and the mass spectrometric analysis discussed in the next section that these three alkoxides are monomers. The same observation made previously by an independent method ( 5 ) supports the monomeric structure of the tertiary amyloxides of Ti, Zr, and Hf. Mass Spectrometry. Mass spectra of the tertiary amyloxides of Ti, Zr, and Hf were recorded merely to obtain precise molecular weights for these compounds. The measured molecular ion peaks listed in Table VI indicate that these compounds are monomeric in the vapor state. Because the molecular ion peaks were too weak to measure accurately, high resolution m/e determinations were made on the P-15 peaks. The masses were measured at 381.2489 for the Ti, 423.2047 for the Zr, and 513.2474 for the Hf compound. The calculated values are 381.2484, 423.2037, and 513.2475, respectively. These values were calculated using the atomic weights of the most abundant isotopes. Fragmentation data obtained from low resolution mass spectra are given in Table VI for the tertiary amyloxides of Ti, Zr, and Hf and in Table VI1 for Al-isopropoxide. For the tertiary amyloxides the m/e values at high mass numbers illustrate the general instability of the molecular ion resulting in successive losses of CH3 and C2H5groups. The thermal instability of these compounds is evident from the presence of strong OH and HzO peaks in the spectra. The mechanism of thermal decomposition (discussed with the TGA results) would explain the appearance of these low mass fragments. Table VI1 lists a few of the m/e values observed in the mass spectrum of freshly distilled Al-isopropoxide. Weak molecular ion peaks were found for the pentamer and tetramer.
However, the presence of a very strong peak at 757 m/e, which corresponds to the tetramer minus an isopropoxy group, indicates that the compound is predominantly tetrameric in agreement with the structure recently reported by Fieggen and coworkers (19). Weak peaks were also observed at m/e (19) W. Fieggen, H. Gerding, and N. M. M. Nibbering, Rec. Trau. Chim. Pays-Bas, 81 (4) 377 (1968). VOL. 41,NO. 10,AUGUST 1969
1247
0CON0 ITIONS :
Sample iveigiit, 0. o l o grins tieat rate, 27 299: rise per niil. A t m p h e r s , helium flow 4occ per min.
a-
-
40-
60-
80"-0-0-0-0-0-0-0-0-
100 J
1 0-
M40-
63-
"1
loo
1
I
I
I
I
I
I
I
I
I
7
0
50
IM)
I50
200
250
300
3.50
400
450
500
TEMPERATURE,
( OC )
Figure 2. Thermogravimetric analysis values corresponding to molecular ions for trimeric, dimeric, and monomeric species, but the fragmentation data tend to show that these peaks result from fragmentation of the larger polymers. Thermogravimetnc Analysis. The results of the thermogravimetric analysis are given in Figure 2. The Si- and Geisopropoxides and Ti-tertiary amyloxide begin to lose weight immediately after the sample is introduced into the balance chamber. The break in the curve for the Si-isopropoxide occurs at 110 "C. The weight loss is approximately 85% which is an indication of partial decomposition at very low temperature. However, the break for the Ge analog takes place at 130 "C with a weight loss of about 7 5 x . Again this is a direct evidence of less stability and more decomposition of the Ge compound compared with the Si compound. Because the Ti and A1 isopropoxides are polymeric in structure and therefore less volatile, the breaks in the curves are at 140 "C for Ti and 175 "C for the A1 compound. The shape of the TGA curves for these two isopropoxides are quite complex and often more than one break in a curve is observed. Similarly the thermogravimetric analyses for the Ti, Zr, and Hf tertiary amyloxides shown in Figure 2 exhibit more than one break in the thermograms. It is interesting, however, to note that the TGA results reported here for these alkoxides follow closely with the vapor pressure measurements reported previously by 1248
ANALYTICAL CHEMISTRY
Bradley et a1 (5). The order of stability toward thermal hydrolysis also increases as the molecular weight increases. The thermal decomposition results from the TGA analysis, supported by the mass spectrometric fragmentation data, suggest that perhaps the high temperature hydrolysis of Ti and A1 isopropoxides and Ti, Zr, and Hf tertiary amyloxides may first involve the formation of secondary or tertiary radicals which then undergo rapid disproportionation and water formation, a mechanism that could account for more than one break in the thermograms. The rate controlling step would then be the rate of dehydration of the ROH. In the case of the tert-amyl compounds, this would be explained in accordance with Equations 4 and 5 . (4)
H2O
+ M(OC5Hi1'>,
+
[MO(OC5Hiit),-~I
+ 2CsHnOH
(5)
Gas Chromatography. Because gas chromatography of various classes of metal compounds has been used successfully in recent years for metal separation, metal purification, and metal analysis, the authors felt that the metal allcoxides perhaps would be another potential and logical candidate class of compounds for gas chromatographic work. There
GAS CHROMATOGRAPHY OF MIXED TITANIUM AND H A F N I U M TERTIARY- AMYLOXIDES
-cca,
: 45 rec .Ge:
105sec
n
-cc'p,
Somple:
24
w i t h 0.6
p?
pl?
Hf (OC,H,1)4
GAS CHROMATOGRAPHY OF MIXED ZIRCONIUM AND HAFNIUM TERTIARY-AMYLDXIDES
Mixed
Ti ( O C 5
Sample: 0.33
milh
Teflon Tubinq I 11 x 114 in IOC I % A ~ 8 e m n L on Cnromororb w 160-80 mesh) l n i e c l i o n P o r t : 217 - C Column : 115'C T.C. D e l e c l o r : 268-C
Sample: 2.5 MI mixed Si, Ge, Ti, and A1 Isopropoxides 1:2:4:15, respectively, in CCla Teflon tubing 1 ft X 1/4-in. (o.,d.) 1% Apiezon L on Chromosorb W (60-80 mesh) Injection Port: 203 OC Temperature program: 60-150 "Cat 15 "C per min Upper limit interval 4 min
is no known report in the literature that a metal alkoxide has ever been chromatographed. For purposes of positive identification of the eluates, the material eluted from the chromatograph was trapped in a glass U-tube cooled with liquid nitrogen. An infrared spectrum was recorded of the clear liquid collected in the trap and the IR spectrum compared with the original spectrum. For all practical purposes, the two spectra were identical. The eluates were also hydrolyzed and the products analyzed for elemental composition by emission spectrometry and atomic absorption methods. The glass inserts in the injection port were also examined for signs of thermal degradation or incomplete volatilization. No residue was observed. Figure 3 shows the chromatographic results obtained for the most volatile isopropoxides. Injected into the chromatograph was a 2.5-plaliquot of a CCI, solution of a mixture of Si, Ge, Ti, and AI isopropoxides in the ratio of 1 :2:4:15, respectively. The column used for this separation was 1 ft X '/(-inch 0.d. Teflon tubing packed with 1 % Apiezon L on Chromosorb W (60/80mesh). The injection port temperature was 203 "C and the thermal conductivity detector was 270 "C. The column temperature varied according to the temperature program running from 60-150 "C at a rate of 15 "C/min and holding for 4 min at the upper limit. The helium gas flow was 100 ml/ min. The Group IV isopropoxides eluted in order of their volatility: silicon in 45 sec, germanium in 105 sec, and titanium in
4
pl? Zr
Mired
H f (OC5
(OCsHl,)4
114 in. 10.0.1 30 o n Cor Pocx F 160-80
Tellen Tubing I f l x I %
SE
mesh1
I n , e c l i o n Port: I 7 6 O C Column: 121*c T.C. D e f e c t o r : 223'C
- Zr
Figure 3. Gas chromatography of mixed Si, Ge, Ti, and A1 isopropoxides
1.67
ond H I : 225
rec
Figure 4. Gas chromatography of mixed tertiar y-am yloxides
255 sec. For these Group I V elements the volatility appears to decrease as the atomic radius increases. The aluminum isopropoxide, because of its polymeric nature-as illustrated by the mass spectrometric, NMR,and TGA analyses-is the last to be eluted from the column in 405 sec. While the zirconium and hafnium isopropoxides are not included in this chromatogram, they have been chromatographed individually. The polymeric structure of these alkoxides leads to a marked decrease in volatility. As a result, relatively high temperatures are necessary to volatilize these compounds, which leads to broad peaks and considerable tailing on the chromatograms. The tertiary alkoxides of Ti, Zr, and Hf are monomeric ( 5 ) and quite volatile because the steric effect of the branched alkoxy group tends to hinder intermolecular association. Vapor pressure measurements on these compounds by Bradley ( 5 ) indicated the tertiary butoxides are the most volatile alkoxides. However, because of their general instability toward moisture, they were excluded from our study. Instead, attention was focused on the tertiary amyloxides, which are more stable and have considerable volatility in the order Hf > Zr > Ti. Gas chromatographic results of these compounds are given in Figure 4. On the left is shown the successful separation of Ti and Hf tertiary-amyloxides. A 3-pl sample of a mixture of one part Ti(OC5H1J4to four parts Hf(OC5H& was separated by a 1 ft X 1/4-inch 0.d. Teflon column packed with 1 % Apiezon L on Chromosorb W (60/80mesh) at 115 "C. The injection port was maintained at 217 "C and the thermal conductivity detector at 268 "C. Helium flow rate was 100 ml/ min. The hafnium alkoxide eluted first in 225 sec followed by the titanium compound in 330 sec. The chromatogram on the right is included to illustrate that no separation of the zirconium and hafnium alkoxides could be achieved under these experimental conditions. In this case, a 2-pl sample of mixed and Hf(OC5H11)4in the ratio of 5 : l was introduced into a 1 ft X l/4-inch 0.d. VOL. 41,NO. 10,AUGUST 1969
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Teflon column packed with 1 Silicone Gum Rubber SE-30 on Gas Pack F (60/80 mesh) at a temperature of 121 "C. The injection port temperature was 176 "C and the TC detector was at 223 "C. Helium flow rate was 100 ml/min. The single peak eluted in 225 sec. In the case of mixed Zr and Hf alkoxides, one peak was always obtained no matter what ratio of compounds was used, indicating very similar volatility and sensitivity to the thermal conductivity detector. The two chromatograms show CC14 peaks because it was necessary to rinse the hypodermic syringe with solvent between injections to prevent clogging after repeated use. A small amount of CC14remained in the needle after rinsing, producing a noticeable peak on each injection.
An attempt is being made in our laboratory to synthesize selected Zr- and Hf-alkoxides with sufficient differences in volatility for the purpose of separating Zr and Hf by capillary column gas chromatography. ACKNOWLEDGMENT
The authors thank Mrs. Peggy Wifall for her contribution to the gas chromatography of the alkoxides, Daniel Dyer and Lee D. Smithson of the Analytical Branch of the Physics Division, AFML, for help in obtaining the NMR and-mass spectra, respectively,and Mrs. JeanneGwinn for typing the manuscript.
RECEIVED for review December 12, 1968. Accepted June 3, 1969.
Gas Chromatography of Catecholamine Metabolites Using Electron Capture Detection and Mass Spectrometry Erik Anggird and Goran Sedvall Department of Pharmacology, Karolinska Institutet, Stockholm, Sweden
Conditions were studied for the gas chromatography of normetanephrine, metanephrine, J-methoxytyramine, 3-methoxy-4-hydroxyphenyl ethylene glycol, vanillylmandelic acid, and homovanillic acid with electron capture (EC) detection and mass spectrometry. Pentafluoropropionates (PFP) and heptafluorobutyrates were more stable and had higher EC-responses than the corresponding trifluoroacetates. These derivatives were also used to separate the amines on XE-60 and the deaminated metabolites on OV-17. The linear range with the 63NiEC-detector was 0.02-0.8 ng for the PFP-derivatives. Mass spectra were obtained from the perfluoroacylated, trimethylsilylated, and acetylated metabolites.
IN HUMANS the major metabolic pathways for epinephrine, norepinephrine, and dopamine is 0-methylation to metanephrine (MN), normetanephrine (NMN), and 3-methoxytyramine (3-MT) and deamination to give vanillylmandelic acid (VMA), homovanillic acid (HVA), and 3-methoxy-4hydroxyphenyl ethylene glycol (MOPEG) ( I , 2). The major separation problems in the gas chromatography of these compounds have been solved by use of various phases and derivatives (3-12). These conditions have been suitable (1) J. Axelrod, Pharmacol. Reu., 39, 751 (1959). (2) I. J. Kopin, Aizesthesiolog.,29, 654 (1968). (3) N. P. Sen and P. L. McGeer, Biochem. Biophys. Res. Comm., 13, 390 (1963). (4) S. Lindstedt, Clin. Chim. Acta, 9, 309 (1964). ( 5 ) E. C. Homing, M. G. Homing, W. J. A. Vanden Heuvel, K. L. Knox, B. Holmstedt, and C. J. W. Brooks, ANAL. CHEM., 36, 1546 (1964). (6) P. Capella and E. C. Homing, ibid., 38, 316 (1966). (7) S. Kawai, T. Nagatser, T. Imanari, and Z . Tamura, Chem. Pharm. Acta, 10, 193 (1964). (8) C. M. Williams and M. Greer, Clin. Chim. Acta, 7,880 (1962). (9) M. G. Homing, K. L. Knox, C. E. Dalgliesh, and E. C. Horning, Anal. Biochem., 17,244 (1966). (10) H. G. Homing, A. M. Moss, and E. C. Homing, Biochim. Biophys. Acta, 148, 597 (1967). (11) C. E. Dalgliesh, E. C. Homing, M. G. Homing, K. L. Knox, and K. Yarger, Biochem. J.,101, 792 (1966). (12) M. Greer, T. J. Sprinkle, and C. M. Williams, Clin. Chim. Acta, 21,247 (1968). 1250
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ANALYTICAL CHEMISTRY
for work with ionization detectors. Lately the high sensitivity of the electron capture (EC) detector has been used for the analysis of urinary VMA, dopamine, and MOPEG as their trifluoroacetates (13-15). Also pentafluoropropionates and heptafluorobutyrates of related compounds have been prepared and reported to give high EC-responses [16-18). An important recent advance in this field was the development of a new acylating reagent, heptafluoroimidazole (19). The present investigation is focused on the analysis of MN, NMN, 3-MT, VMA, HVA, and MOPEG using gas chromatography with electron capture detection and mass spectrometry. It attempts a systematic study of the formation and stability of perfluoroacyl derivatives of these compounds and a comparison of their EC-responses. Conditions for their gas chromatographic separation were also studied. Further, we investigated the mass spectrometric properties of several derivatives of these compounds to get the basic information for their identification with the combined gas chromatograph-mass spectrometer. EXPERIMENTAL
Preparation of Derivatives. The catecholamine metabolites were purchased from the following commercial sources; HVA and 3-MT from Sigma; VMA from K & K Laboratories; NMN and MN from Winthrop Laboratories; MOPEG was from Calbiochem.
(13) S. Wilk, S. E. Gitlow, M. Mendlowitz, M. 3. Franklin, H. E. Corr, and D. D. Clarke, Atzal. Biochem., 13, 544 (1965). (14) D. D. Clarke, S. H. Wilk, S. E. Gitlow, and M. J. Franklin, J. Gas Chromatog., 5,307 (1967). (151 S. Wilk. S. E. Gitlow, D. D. Clarke, and D. H. Paley, Chi. Chim. Acta, 16, 403 (1967). (16) S. Wilk, S. E. Gitlow, M. J. Franklin, and H. E. Corr, ibid., 10, 193 (1964). (17) D. D. Clarke, S. Wilk and S . E. Gitlow, J . Gas Chromatog., 4, 310 (1966). (18) S. Kawai and Z. Tamura, Chem. Pharm. Bull. (Tokyo), 16, 699 (1968). (19) M. G. Homing, A. M. Moss, E. A. Boucher, and E. C. Horning, Anal. Letters, 1 (3, 311 (1968). ~
