Schenk, do not inter ‘ere. Compounds containing acid groups however, must first be analyzed for titratable acid and appropriate corrections made in the alkoxy content calculations. An alkenedioxysilme that resists acetylation, perhaps because of steric hindrance in step 4 of the proposed mechanism, is 2,2,4,4,5,5-hexamethyl1,3-dioxa-2-silacyclopentane. A model of this silane suggestri that the oxygen atoms are not sterically hindered froin attack by acetylium as shown in step 3. Experimentally this attack appears to be successful as evidenced by a precipitation in the reaction mixture, which is presumably an alkenedioxysilane acetylium perchlorate. The salt dissolves immediately upon addition of polar and nonreactive solvents as acetone and pyridine. The reaction ceased, however, since upon dissolving, the salt does not quantitatively acetylate (even overnight). 2 - Methyl - 2 - vinyl - 1,3, dioxa-2silacyclopentane and 2,2,4,5-tetramethyl - 1,3 - dioxa - 2 - silacyclopentane (Table 111) acetylate completely, and nithout salt formation. Only the tetramethylethylene group posjesses adequate bulk for steric hindrance.
Acetylation of 2,2,4,4,5,5-hexamethyl1,3dioxa-2-silacyclopentane proceeded, but to a small extent. I t is believed that this occurs during hydrolysis. Acetic anhydride hydrolysis is not immediate. Some of the alkenedioxysilane is evidently hydrolyzed to its alcohol and subsequently acetylated before the hydrolysis of the acetic anhydride is complete. Aminoalkyl side chains on alkoxysilanes can be quantitatively determined by acetic anhydride in the absence of acid catalysts because alkoxysilanes are inert to acetic anhydride unless certain acid catalysts are present. The nucleophilic amines, of course, require no acid catalysts for rapid acetylation by acetic anhydride. Results of nonacid-catalyzed acetylation of an aminoalkylethoxysilane series are shown in Table IV. ACKNOWLEDGMENT
R. V. Viventi was very helpful in supplying alkoxysilane samples. A. Berger suggested that the method of Fritz and Schenk might work for alkoxy groups attached to silicon and also worked out a possible mechanism.
Table
IV.
Analysis of Aminoalkylethoxysilanes
(No perchloric acid; 5-Minute reaction time; single Determinations)
Sample
Per cent of
theory
Aminobutyldimethylethoxysilane 98.8 .4minopropylmethyldiethoxysilane 99.6 Aminopropyltriethoxysilane 99.0
12’-n-Propylaminopropyltriethoxysilane
95.1
LITERATURE CITED
(1) “Analytical Chemistry of Polymers,” G. M. Kline, Ed., p. 372, Interscience,
New York, 1959.
(2) Brown, P., Smith, A. L., ANAL.CHEM. 30, 549 (1958). (3) Burton, H., Praill, P. F. G., J . Chem. Soc. 1950, 1203. (4) Ibid., 1951, 522;! (5) Eaborn, C., Organosilicon Compounds," p. 502, Butterworths, London,
1960.
(6) Frits, J. S., Schenk, G. H., ANAL.
CHEM.31, 1808 (1959). (7) Smith, B., Acta Chem. Scund. 11, 558 (1957). RECEIVED for review December 17, 1962. Accepted May 2, 1963.
Infrared Spectrophotometric Analysis of Calcium Sulfate Hydrates Using Internally Standardized Mineral C)iI MuIIs ROBERT J. MORRIS, .Ir. Research Department, United Stafes Gypsum
b A method is presented for the determination of the two crystallographically different hydrlztes of calcium sulfate using unique infrared absorption bands. The dihydrate is analyzed using the 3390 c m - 1 h,ydrogen-bonded water absorption, and the hemihydrate is analyzed using tlie 1005 cm.-’ perturbed sulfate absorption. When a calcium carbonate internally standardized mineral oil niull is used, the analysis has a mean error of +1.3% for the dihydrate and *2.8y0 for the hemihydrate. About 30 minutes is required for the complete analysis. Total water can be determined to +l,O% using the 1620 and 1685 cm.-I absorption bands.
T
HE infrared absorption of most metallic sulfates is in the region of 1100 t o 1300 em.-’ due to S-0 stretch vibrations ( 2 ) . The other absorption
Co., Des Plaines, 111. maxima in the infrared spectra of calcium sulfate hydrates are due to water molecules bonded to the sulfate or perturbations of the S-0 stretch due to the forced fit of the sulfate ion in a crystallographic lattice site. Absorption maxima at 1620, 3390, 3530, and 3600 cm.-’ occur in the di- or hemihydrate of calcium sulfate (see Figure l), and these vibrations have been assigned to vibrations in the water molecule by numerous authors (3, ?, 10,12). Pimentel and McClellan (9) have made a n extensive review of the literature and history of the hydrogen bond and hare presented a broad discussion of the characteristics of the hydrogen bond. The assignments of the above absorption maxima to various types of hydrogen bonds between water and calcium sulfate are consistent with the discussions of Pimentel and NcClellan. I n addition to the above, absorption maxima occur at 1005 and 1685 cm.-’
which have not been given as much attention and therefore have not received as definite assignments as the other absorptions. A theoretical treatment of the vibrational frequencies of water in complexes (IO)has shown that the bonding of the oxygen atom in water to a metal ion shifts the normal infrared absorption at 1620 cm.-1 to a higher frequency by about 40 to 80 cm.-l The shift observed in calcium sulfate dihydrate is 65 cm.-’, indicating that the 1685 cm.-l absorption must result from an oxygen to calcium bond. References to infrared absorption a t 1000 cm.+ due to vibrations in the water molecule are very vague in their discussion (9). However, Stubican and Rustum (11) have assigned an absorption a t 900 cm.-’ in aluminosilicates to a coordination bond between the hydrogen of the water and the aluminum atom of the silicate. A coordination bond between the hydrogen of the VOL 35, NO. 10, SEPTEMBER 1963
1489
Table 1. Infrared Absorption Maxima of Calcium Sulfate Hydrates and Deuterates
CaS04. 2HZO;
cm.3530
I C A L C W SULFATE DIHYDRATE
I
3390
1685 1620
V
(MONOCLINIC)
1150
100
-l
670
Cla8O4. ZDz0, cm.-'
2650
2520 1240
1205
C R S O ~ . CaS04. '/zHz~I, '/zD2Or cm.cm.'2680 3600 2610 3540 1205 1620 1150 1150
11.50
1120
1095 1005 660
670
1120
1095 1005 660
- 80
A
40 C M U W LUFAZE
H20
-4.6
PO
(-1 1
4000
1
1
1
1
,
9800
,
1900
1
1
1600
,
,
,
1
1
1300
,
1
,
iI o
,
700 600
1000
FREQUENCY IN CM.-'
Figure 1.
infrared spectra of calcium sulfate hydrates
Mineral oil-per
fluorocarbon oil split mull recorded in
water and the calcium atom is a n unlikely possibility because of the ionic nature of the calcium ion. This paper describes a quantitative analysis for the determination of the di- and hemihydrates of calcium sulfate using the 3390 and 1005 em.-' absorption bands, respectively.
% transmittance
binations and overtones of other absorption maxima. For example, Stubican and Rustum (11) found that one absorption thought to arise only from water vibrational frequencies was partially due to water and partially due
to combinations and overtones of the silicate vibrational frequencies. Proof of the assignments of a b s o r p tion maxima to water vibrational frequencies was obtained by replacing the water with deuterium oxide and obserling the ahift in the absorption maxima due to the isotopic substitution. This techniyue has been used by many investigators, notably LeComte, Ceccaldi, and Roth ( 6 ) ,but their work Bas limited to the 3400- to 6000-cm.-' region. Table I shows the absorption maxima due to CaS01.2Dz0 and CaS04.1j2D20 (the spectra for these compounds are shown in Figure 2); those maxima which are shifted are due to water vibrations. No absorptions due to combinations or overtones of sulfate T ibrational frequencies coincide with the water absorption maxima and therefore these maxima can be used for analytical determinations of the dim
EXPERIMENTAL
A11 data were obtained using a BeckThe man IR-7 spectrophotometer. Iyavelength scale was 100 cm.-' per inch in the first order of the grating and 400 em.-' per inch in the fourth order. The scanning speed was 20 em.-' in the first and 80 em.-' per minute in the fourth order, reqpectively. The mulling agent in each case was mineral oil. Calibration standards were prepared by f d l y hydrating C.P. grade anhydrous calcium sulfate to obtain the dihydrate and the subsequent dehydration of the dihydrate by heating in an autoclave under 20 p.s.i.g. steam pressure for 4 hours. These samples analyzed as 99.9% di- and hemihydrate, respectively. Dry reagent grade calcium carbonate wa3 used a$ an internal standard for both determinations by using the 870 mi.-' carbonate abqorption.
CALCIUM SULFATE W E R A T E
CrS04.2 020
.60
- 40 - 90
RESULTS A N D DISCUSSION
Before the water absorption maxima can be used for analytical determinations, they must first be proved to arise only from vibrational frequencies of the water molecules and not from com1490
ANALYTICAL CHEMISTRY
0 4000
2800
1900
1600
1300
1000
FREQUENCY IN CM.-'
Figure 2. Mineral oil-per
Infrared spectra of calcium sulfate deuterates fluorocarbon oil split mull recorded in
% transmittance
700 600
hydrate of calcium zulfate. Table I also shows the absorption maxima due to the hemihydrate and hemideuterate of' calcium sulfate. Again, no interferences due to combinations or overtones of sulfate vibralions were found. I n addition, no shift occurred in the 1005-cm.-l absorption , showing that this absorption i i not due to water vibrations of any tj.pe. The 1005ern.-' vibration must be due to the forced fit of the su fate ion in the hexagonal crystal lattice formed when the monoclinic crystal:, of the dihydrate :ire dehydrated to the hemihydrate. The 1005-cni.-l absorption disappears when the hexagonal crystals of hemihydrate are dehydrated to either hexagonal anhydrous calcium sulfate or orthorhombic anhydrous calcium sulfate. Figure 3 shows these spectra. One of the first re3orted internally standardized quantitalive infrared procedures was reported by Barnes e t al. ( I ) , who used the technique for analyzing penicillin samples using dl-alanine as the internal standard. Calcium carbonate was used as an internal standard by Kuentzel (6). Bradley and Potts (4) used lead thiocyanitte as an internal standard for the quantitative analysis of phthalic acid isomers. Bradley and Potts provide an excellent discussion of the internal standard technique in their paper. A study of the Niller and Wilkins (8) collection cf infrared spectra of inorganic compounds revealed only the thiocyanate and carbonate anions as suitable internal standards in a sulfate analysis. The major problem in any internally standardized method of analysis is in obtaining a n intimate mi\ture of the sample and internal standard. Nixing was accomplished by placing weighed amounts of sample and internal standard into a plastic Wig-LBug vial and vibrating for 5 minutes, transferring the mixture to a stainless steel Wig-L-Bug vial containing a stainle5s steel ball pestle anti several drops of mineral oil, and vibrating for 1 minute only. Vibrating for more than one minute in the stainless steel vial with a stainles. steel ball pesile will cause dehydration of the dihydrate in the samgle being analyzed. The thickness of t i e film of mull formed when the mull is squeezed between two rock salt plates cannot be controlled accurately. Table I1 shows that the accuracy of the analysis does not suffer because of different film thicknesses. The uniformity of mixing of a well prepared sample mull is shown in Table 111. Typical analyses of a series of samples are shown in Table IT.-. I n this table the analyses for dihydrate and hemihydrate are compared for prepared samples of known composition. The mean error of the dihydrate d1:termination is =kl.3yoand the mea,? error for the
CALCUM SULFATE A
m
i I
ccsq (ORlHOFIHoMBIC)
LJ
loo - 80
- 60
9
- 40
- PO
i 9800
4000
1900
Figure 3.
Infrared spectra of anhydrous calcium sulfates
Mineral oil--per
fluorocarbon oil split mull recorded in
hemihydrate is k2.87,. Conventional chemical analyses, ASTllI Standard Method No. C471-61, for these compounds are accurate to =!=0.5% for dihydrate and i.1% for hemihydrate and require about three days lapsed time per analysis. The infrared analysis can be performed in about 30 minutes. The determination of total water by infrared analysis can also be made in about 30 minutes with an accuracy of 3~1.0%using the 1620- and 1685cm.-l absorption bands. This is accompli~hed
Table 111.
700 600
1000
1600 1300 FREQUENCY IN C M . -1
% transmittance
Table II. Mean Error of Method with Various Thicknesses of Sample
Ratio A 3390
cm.-l/
A of CaC03 0.424 0 229 0.176 0.127 0.070
Dihydrate,
AS75
%
Dev.
10.5 12.6 13.0 11.6 11.4 Av. 11.8 Av.
0.8 1.2 0.2 0.4 1.3 0.8
cm.-l
0.831 0.904 0.913 0.873 0.858
Mean Error of Method with Various Parts of Mull
Ratio
Sampling point Vial cap F'ial side Vial bottom
A of CaC08 0.020 0.091 0.10s
A 3390 cm.-l/ A 875 an.-' 1.01 1.00
Dihydrate,
%
0.962 AV.
Table IV.
16.8 15.7 14.7 15.7
Dev. 1.1 0.0 1 .o Av. 0 . 7
Analysis of Known Mixtures of Hydrates
Dihydrate prepared
Found
Error
43.0 17.2 85.8 59.5 52.5 25.1 63.8 82.4 36.8 49.7
40.9 17.0 84.3 59.5 52.4 22.8 66.1 81.9 37.1 53.5
-2.1 -0.2 -1.5 0.0 0.1 -2.3 +2.3 -0.5
+0.3 Av.
+3.8 1.3
Hemihydrate prepared 57.0 82.8 14.2 40.5 47.5 74.9 36.2 17.6 63.2 50.3
Error SO.7
Found 57.7 76.5 14.0 37.2
...
78.8 39.4 18.2 62.9 57.7
-6.3 -0.2 -3.3
+3:9 4-3.2 +0.6 -0.3 +6.S Av. 2 . 8
VOL. 35, NO. 10, SEPTEMBER 1963
0
1491
Table V. Determination of Total Water in Gypsum Samples
Prepared 12.8 9.2 18.9 15.2 14.1 10.1 15.8 18.3 11,s
11.1
Found 12.2 10.5 17.8 14.7 11.5 10.8 16.4 18.3 12.5 13.1
Error -0.6 +1.3 -1.1
-0.5 -2.6
+0.7 +0.6 0.0 +l.O $2.0
Av.
1.0
hy determining dihydrate directly from the 1685 em.-’ absorption and hemihydrate using the 1620 cm.-’ absorption from which the dihydrate contribution has been subtracted. Total water is determined by this method only when volatile additives which interfere with the 3390 cm.-l absorption bend are
of Complex Molecules,” Wiley, New York, 195% (3) Benesi, H. A., Jones, A. C., J . Phys. Chem. 43, 179 (1959). (4) Bradley, K. B., Potts, W. J., A p p l . Spectry. 12, 77 (1958). (5) Kuentzel, L. E., ANAL. CHEM. 27, 301 (1955). (6) Lecomte, J., Ceccaldi, hl., Roth, E. J. Chim. Phys. 50, 166 (1953). (7) LeComte, J., Duval, C., Ibid., page cfi4 ---. ACKNOWLEDGMENTS (8) Miller, F. A., Wilkins, C. H., AXAL. CHEM.2 4 , 1253 (1952). The author thanks hl. T. Schmidt for (9) Pimentel, G. C., MZClellan, A. L., preparing the pure dihydrate and B. AI. “The Hydrogen Bond, Freeman, San O’Kelly for preparing the pure hemihyFrancisco, 1960. (10) Yartori, G., Furlani, C., Damiani, drate for use in calibration. The asA., J. Inofg. Nucl. Chem. 8, 119 (1958). sistance of J. K. Bezpalec, R. K. Hart(11) Stubican, V., Rustum, R., Am. man, and J. F. Lukes in obtaining the Mineralooist 46.,~ 32 11961). experimental data is gratefully acknowl(12) Van Theil, M., Becker, E. D., Pimentel, G. C., J . Chem. Phys. 27, edged. 486 (1957). LITERATURE CITED RECEIVED for review February 20, 1963. Accepted May 6, 1963. This paper wm (1) Barnes, R. B., Gore, R. C., Williams, presented to the Fourteenth ilnnual PittaE. F , Linsley, S. G., Peterson, E. >I., burgh Conference on Analytical Chemistry A N A L . CHEZI. 19, 620 (1947). and Applied Spectroscopy, March 1963. (2) Bellamy, L. J., “The Infrared Spectra
present in the sample and neither the ignition method nor the infrared method can conveniently be used. Table V shows data from analyses of several samples of known water content. The conventional loss-on-ignition water analysis requires about 2 hours and is accurate to *0.02%.
Modifications in Mercury Porosimetry L. K. FREVEL and L. J. KRESSLEY Chemical Physics Research laborafory, The Dow Chemical Co., Midland, Mich.
b Theoretical porosimetry curves are derived for various packings of solid spheres. Their validity has been confirmed by mercury intrusion measurements on different agglomerations of uniform microspheres and of like-mesh particles. The characteristic criterion for a mechanically packed assemblage of like-mesh particles is an abrupt threshold Hg penetration determined by the mesh size and contact angle. This sudden penetration throughout the interconnected voids is followed by the gradual filling of the toroidal voids around the contacting particles. For porous solids prepared from nonporous powder particles, the “interconnected void” model is preferred to a model based on a system of circular capillaries. In general, electron micrographs of thin sections of a porous solid yield decisive morphological details which orient the interpretation of porosimetry data.
A
the measurement of poresize distribution by mercury penetration was first proposed by Washburn (21-23) in 1921, it was not until 1945 that Ritter and Drake (4, 16) published the first extensive esperimental work in this field. More recently, commercial equipment (24) has become available which greatly facilitates the determination of pore LTHOUGH
1492 *
ANALYTICAL CHEMISTRY
sizes in the range of 0.1 t o 0.00003 mm. This paper discusses some experimental and interpretational modifications pertaining to porosity measurements. MODIFICATIONS I N EXPERIMENTAL TECHNIQUE
Loading and Filling of Penetrometer. T o operate a n Aminco-Winslow porosimeter (%$), a weighed sample of
-0.18-ml. pore volume is placed in a weighed penetrometer (a glass tube with capillary stem graduated in divisions of 0.002 ml.). The penetrometer, in turn, is inserted into a glass filling device which is evacuated to 4 0 microns or preferably less. Mercury is then introduced through a three-way stopcock until it reaches a level of 0.026 or 0.028 ml. in the penetrometer bore. By carefully opening the stopcock t o the atmosphere, air is admitted until a n absolute pressure of 6.3 p s i . is reached and thus the evacuated penetrometer is filled with mercury. The exceqs mercury in the filling vessel is withdrawn through a bottom stopcock before porosity measurements are made. The commercially supplied filling tube has two disadvantages: the awkward arrangement of the greased fillingdevice cap which requires regreasing after each loading and which contributes to accidental grease contamination of the penetrometer; and the clumsy and touchy operation of introducing mercury to the right level in the evacuated filling vessel. Both
of these annoying features have bem eliminated by the design shown in Figure 1. The penetrometer evacuation vessel consists of a lower glass tube holding clean mercury and a cap connected through flexible Tygon tubing to a McLeod gauge, a charcoal trap, a Hg manometer, and vacuum pump. An adjustable metal clamp (normally used for spherical joints) holds the cap in place. The glass projections in the top section of the tube position the inserted penetrometer. A rotatable clamp placed just below the stopcock permits tilting the evacuated assembly anywhere from 3” to 25” (depending on the Hg level in the reservoir), so that the open end of the penetrometer will dip -2 mm. into the pool of mercury. In this tilted position dried air or nitrogen is admitted through the Teflon-plug stopcock, preceded by a controllable leak, t o force mercury into the penetrometer. After the penetrometer is filled at a n absolute pressure of 245 mm. of Hg, the vessel is restored to its vertical position before the mercury intrusion measurements are made. The absolute pressure of 245 mm. of Hg is set by the over-all length of the penetrometer tube (242 mm.), an 11mm. section of which is taken up by the sample holder. To ensure a positive pressure of 3 mm. of Hg at the top of the filled vertical penetrometer when out of the pool of Hg, the pressure in the vessel is gradually raised to exactly 245 mm. of Hg during the filling opera-
