culations from a particular branch of the isotherm, providing the pore size distribution calculation method does not include a n adjustment factor to facilitate this agreement. The computer program used here has not been so adjusted, and the sum of the pore areas is significant. The sum of the pore areas from adsorption data shows better agreement with the BET area values and, therefore, may be the preferable calculation. The pore volume distribution figures of Table I1 indicate a Tide radius distribution for catalyst 1, with little practical difference between the results from the two branches of the isotherm. For catalysts 2 and 3, however, there are significant differences in the pore
volume calculation from each isotherm branch. The experiments described here provide a quantitative framework against which the rate of nitrogen adsorption experiments can be judged when pore size distribution data are desired. Such a background is essential for the adjustment of mechanically programmed gas dosers, and helpful in manual manipulations. The use of the desorption branch of the nitrogen isotherm has been emphasized as it is widely used for application of the Barrett, Joyner, and Halenda method (6)of calculating pore size distribution. I n laboratory practice, the use of data from the adsorption curve alone can considerably simplify the experimental
procedure and speed up the comparative characterization of catalyst samples. ACKNOWLEDGMENT
The experimental work cited here was performed by William Frazier and Paul Ross. LITERATURE CITED
(1) Ballou, E. V., Doolen, 0. K., ANAL. CHEW32, 532 (1960).
(2) Barrett, E. P., Joyner, L. G., Hnlenda, P. P., J . Am. Chem. SOC.73, 373 (1951). (3) Innas, W. B., ANAL.CHEY.29, 1069
(1957).
(4) Ramser, J. H., Hill, P. B., Ind. Eng. Chem. 50, 117 (1958).
RECEIVED for review June 9, 1961. Accepted December 11, 1961.
Identification of Mercaptans and Disulfides by X-Ray Diff raction of Their Respective 2,4-Dinitrophenyl T hioet her s ROBERT RITTNER, GEORGE TILLEY, ALBERT MAYER, Jr., and SIDNEY SlGGlA Olin Mathieson Chemical Corp., New Haven 4, Conn.
b Reference x-ray diffraction patterns have been obtained for the 2,4-dinitrophenyl thioethers of 2 1 common aliphatic and aromatic mercaptans. Many strong lines, characteristic of the respective derivative, were obtained in all cases, making qualitative identification quite simple. Disulfides, which can be readily reduced to mercaptans, are also included in this study.
I
is only within the past 15 years that x-ray diffraction has been used t o any great extent for the identification of organic compounds. Aldehydes and ketones ( 5 , 6, S), carboxylic acids (12. 13, l e ) , alcohols (7, 16), amines (I,9, Q), and phenols (10, 11) have been studied by this technique with excellent results. A need was felt, therefore, to extend this technique to the identification of organic compounds containing other functional group'. The melting point of a derivativethe physical constant most often used for identification of an unknon-n organic material-is reliable only when the derivative is pure (and sometimes not even then because of the existence of materials with similar melting points. Also, melting point data are not always accurately obtained). The x-ray technique can tolerate small amounts of T
impurities and still give an excellent fingerprint of the unknown sample. rilso, x-ray results are quite conclusive, and there are many lines to a diffraction pattern. The chance that tn-o materials will have the same diffraction pattern is extremely small. EXPERIMENTAL
Apparatus. The x-ray diffraction patterns rvveie made on film, using Philips 114-nim. diameter powder cameras on a standard Philips Korelco x-ray unit. The source n as a coppertarget x-ray tube operated a t 40 kv. and 18 ma. A nickel filter vas employed to provide essentially monochromatic copper K a radiation. Onehour exposures were run. The samples were ground to about 300 mesh and inserted in 0.5-mm. diameter thin-walled glasq capillaries. The relative intensitics were estimated visually. The spectrometer traces were run, using an argon-filled Geiger tube detector, divergence and scatter slits, a 0.006-inch receiving slit, and scanned at per minute from 4' to 3 6 O , 20. Derivative Preparation. MERCAPTANS (THIOLS).All mercaptans, Eastman White Label reagents, nere distilled, and the center cuts mere used for derivative preparation. The method of preparation was essentially that of Cheronis and Entrikin (S), whereby a solution of the mercaptan in methanol is treated with KaOH and then added
to a methanolic solution of 2,4-dinitrochlorobenzene. The solution is refluxed gently for 5 to 10 minutes (if necessary) and then filtered rapidly while hot. The filtrate is cooled, and the precipitate is filtered. Recrystallization of the aliphatic derivatives was carried out in methanol-HzO, whereas methanol alone served quite satisfactorily as the recrystallization medium for the aromatic derivatives. The derivatives were then vacuum-dricd for several hours, using an Abderhalden drying pistol which contained a liquid of appropriate boiling point. The reaction is illustrated in the following equntion:
I NO2
N6, DISULFIDES.To prepare the derivatives of disulfides, it )vas first necessary to reduce them to their mercaptans. This was readily accomplished by a slight modification of the method of Stahl and Siggia (141, whereby solutions of NaBHl and anhydrous A1C13 in Giethylene glycoldimethyl ether ( ydiglyme") were added together slowly In a round-bottomed flask immersed in an ice bath. After sufficient cooling, the flask is removed from the ice bath, the disulfide is added, a reflux condenser is VOL. 34, NO. 2, FEBRUARY 1962
237
Table 1.
Mercaptan (Thiol) Methanethi01 Ethanethiol 1-Propanethiol 2-propanet hi 1-Butanethiol 2-Methyl-1-propanethiol 1.1-Dimethvl' ethanethiol 1-Pentanethiol 2- hfethyl-l-butanethiol 1-Hexanethiol 1-Heptanethiol 1-Octanethiol 1-Nonanethiol 1-Decanethiol 1-Dodecanethiol Benzenethiol Phenylmethanethiol 2-Phenylethanethiol 2-Methylbenzenethiol 3-Methylbenzenethiol PMethylbenzenethiol
80" 601
Melting Point, O C. Literature Value Found (4) 127 -128 128 114 -115 115 85 - 86.5 81 93.5- 95 94 65.5- 66 66 74.5- 75 109 -111 79 5- 80 5
78 - 79 73 81 76 84 83 84 119
E
loo
130
24
89.5
100 -101.5 103
RESULTS A N D DISCUSSION
Melting Points. Most of the melting points of t h e prepared derivatives agree quite well with the literature values (4) as shown in Table I. I n a few cases, the melting points differed by 4" to 5'. I n these instances, and also when the literature values were not available, elemental analyses for carbon, hydrogen, and nitrogen were run t o verify the purity and identity of the derivative. These are tabulated in Table 11.
16
20
8
12
4
60
I
20
A 32
28
24
20
16
8
12
DEGREES, 2 8
Figure 1 . Spectrometer traces for 2,4-dinitrophenyl thioethers of two isomeric mercaptans
Table II. Elemental Analyses of Derivatives Whose Melting Points Differ b y More Than 2' from Literature Values or Whose Melting Points Are Not Recorded in the Literature Derivative
ANALYTICAL CHEMISTRY
28
1
2,4-DINlTROPHENYL THIOETHER OF 2-METHYLI-BUTANETHIOL
98 - 99 5
102 5-104
32
40
59 74 82 78 86
128.5-129.5 94.5
36
P
1
80
89 121
-
t-,
0
36
5- 75 - 82 -77 5 -85 5- 85 5 - 85 5 5-120 5
93
4 201
76
attached, and the mixture ,is allowed to react a t room temperature for a sufficient time ( l / 2 hour) to assure complete reduction. One normal HC1 is then added slowly to the reduced mixture immersed in a n ice bath to acidify the gelatinous material and separate the inorganic solids from the diglyme solution. The liquid is then decanted or filtered into a separatory funnel, the flask rinsed with ether, the wash added to the funnel, water is added, and the solution is extracted twice with ether. The ether layer is then poured into a beaker, made alkaline with 611- NaOH, and the ether is removed on a hot-water bath. The remaining diglyme solution, containing the sodium salt of the mercaptan, is added to a solution of 2,4-dinitrochlorobenzene in methanol. Water is then added to the solution to precipitate the derivative. The precipitate is then filtered, recrystallized, and dried as in the procedure for mercaptans.
238
2,4- DINITROPHENYL THIOETHER OF I-PENTANETHIOL
Melting Point Data on 2,4Dinitrophenyl Thioethers
1-Propanethiol 1,l-Dimethylethanethiol 2-Methyl-1-butanethiol 1-Decanethiol 1-Dodecanethiol 2-Phenylethanethiol 2-Methylbenzenethiol 3-Methylbenzenethiol
Table 111.
Theory H
N
C
Found H
IG
44.62 46.86 48.87 56.44 58.W 55.25 53.60 53.60
4.16 4.i2 5.22 7.11 7.66 3.98 3.81 3.81
11.57 10.93 10,3i 8.23 7.60 9.21 9.62 9.62
44.67 46.71 48.80 56.18 58.42 55.37 53.61 53.83
4.39 4.51 5.51 7.41 i.70 4.27 3.71 3.68
11.84 10.80 10.09 8.29 7.52 9.37 9.92 9.53
Diffraction Data for 2,4-Dinitrophenyl Thioethers of Mercaptans
RIethanethiol d , h. 1021/Ii 1.5 0 30
3.55 3.38 3.22 3.05 2.65 2.57 2.20 2.10 1.97 1.86 1.75
C
100 80 10 60 10 50 20 5 5 5 5
Ethanethiol d , A. 1021/11 80 10.4 '70 9.5 6.4 30 5.30 80 4.50 70 4.14 80 90 3.82
Ethanethiol d, A. 1021/11 3 6.5
3.10 2.95 2.86 2.72 2.45 2.36 2.10 2.05 1.90 1.81 1.76 1.62 1.58 1.35 1.28
50 10 15 20 20 10 40 10 5 30 5 5 5 5 5
1-Propanethiol d, -4. 1021/Ii 10.5 5 8.0 100 5.9 5
1-Propanethiol d , A. 102I/Il 2
3.75 3 45 3.33 2.81 2.75 2.65 2.25 2.18 2.00 1.91 1 .66
30 7
90 20 5 10 2 5 10 1 2
2-Propanethiol d, A . 1021/Ii 40 8.7 7 7 60 20 _. 6.; 5.35 100 4.50 20 4.25 10
2-Propanethiol d , A. 1021/Ii 3 92 20
3.09 2.90 2.57 2.35 2.24 2.17 1.97 1.90 1.72 1.63
50 2 30 5 10 5 2 3 2 2
- 1-Butanethiol d, A. 1021/Ii 100 16.0 11.0 90 10 7.8 70 6.3 5.6 70 5.1 5
(Continued)
Table 111.
1-Butanethiol d, A . 102Z/Z1 4.6
4.4 4.32 4.06 3.85 3.58 3.42 3.32 3.18 3.08 2.90 2.75 2.50 2.30 2.20 2.13 2.07 1.98 1.88 1.81 1.73
80 5 TO 50 10 80 60 30 20 40 10 20 10 3
5 10 5 5 3 3
5
1.66
3
2-Methyl-lpropancthiol d, A. 10'I/Z1 10.1 7.6 6.4 5.1 4.84 4.62
80 100 20 40 30
4.SB
10 90 '20 100 50 70 5 20 5 20
4.15 3.60 S.S'J
3.22 3.09 2.98 2.b5 2.70
-'>. (j(j 2.45 2.3i
"7 2.17 2.07 2.0s 1.92 1.89 1.83 l.ti9 l.ti5 '>
I . *
3
5 J
10 50 20 2 10 3
5 20 0
1.w 1.N
10
1.45 1.3B 1.3:1 1.30 1.23 1.21 1.165 1.15 0 . 794 0.786
3 3
L5
5
5 3 3 3 3 3 3
1,l-Dimethylethanethiol d, .4. 102z/z1
5.0 4.5 4.3 4.1
40 40 5 5
Diffraction Data for 2,Q-Dinitrophenyl Thioethers of Mercaptans (Continue, 1,l-Dimethyl1-Hexanethiol 1-Sonanethiol Benzenethiol ethanethiol d, -4. lo=z/I1 d, h. 1U'Z/Z1 d, A. 102Z/11 d, A. lO'I/Ii 2.62 10 3.36 30 5.3 20 3.86 10 2.55 10 2.98 5 4.52 40 3.74 100 2.37 1 2.84 5 4.28 10 3.62 20 2.15 1 2.60 10 4.00 5 10 3.44 2.02 2 2.40 5 3.79 100 3.15 10 1.80 2 2.22 5 3.57 100 2.88 5 1.75 1 2.03 5 3.32 80 2.60 20 1.97 10 3.08 60 2.53 10 1.79 5 2.86 20 2.20 10 1.67 2 2.60 3 2.06 5 1-Heptanethiol 1.54 2 2.30 5 1.86 2 d, A. 102Z/Z1 2.22 3 1.71 2 2.13 3 12.5 30 1.92 5 1-Decanethiol 2 9.0 1.79 2 d, A. 1O'I/Z1 6.5 50 1-Pentanethiol 1.73 3 5.95 60 d, 8. 1021/11 7.6 5 5.30 30 6.6 10 4.70 30 20.0 100 Phenyl6.2 50 4.40 40 11.4 60 methane Thiol 5 . 7 40 4.10 40 6.0 io 5.1 30 d, A. 1021/11 3.60 100 4.6 30 4.6 80 3.44 20 4.32 40 11 . 8 80 4.4 2 3.31 10 50 4.08 -. 7.0 60 4.13 .in -3.18 5 3.62 100 6.3 50 3 . 9 2 60 2.95 10 3.56 80 5.82 40 3.59 100 2.73 2 3.29 40 5.10 50 3.39 50 2.60 20 3.16 10 4.65 10 3.10 5 2 . 5 5 20 2.56 20 4.43 10 2.96 10 2.27 10 5 2.17 4.10 40 2.84 5 2.20 10 2.10 .( 3.95 30 .5 2.79 2.12 5 2.05 5 3.66 50 2.70 2 2.03 10 1.82 5 3.52 30 2.64 10 1.80 10 1.75 5 3.42 2 2.60 15 1.74 2 3.21 100 2.55 5 1.54 3 3.10 5 2.41 5 2-hIethyl-l1.32 2 2.90 20 2.36 butanethiol 2.70 3 d, A, 102Z/Z1 2.60 3 2.45 3 20.0 100 2.40 4 10.8 90 2.23 3 7.2 10 2.15 10 13.2 20 6.22 50 2.08 5 6.6 40 5.52 20 2.05 3 5.20 . _ 0_i - 1-Dodecanethiol 6.1 40 1.76 2 4.80 10 5.5 50 d, -4. 1O'I/11 1.66 2 4.9 40 4.46 10 1.61 2 8.6 40 4.3 50 4.22 60 6.5 40 4.0 40 3.87 10 5.85 30 3.58 3.72 100 100 _.. 2-Phenyl5.60 30 3.53 90 3.38 30 ethanethiol 4.85 30 3.32 5 3.10 20 40 4.60 d, A. 1OZI/I1 3.20 30 3.04 20 4.39 60 2.95 10 2.90 5 12.5 40 4.20 2 2.85 5 2.75 5 6.8 30 3.88 70 2.60 40 2.62 10 6.0 70 3.70 2 2.52 10 2.56 10 5.18 20 3.57 100 5 2.26 10 2.50 4.90 20 3.45 10 2.40 3 2.20 5 4.48 70 10 3.35 2.25 3 2.14 10 3.85 30 3.10 10 2.20 4 2.50 5 3.62 100 2.92 5 2.14 5 1.82 3 3.35 20 2.80 5 1.70 2 2.00 10 3.07 80 2.60 10 1.52 2 1.79 5 2.70 5 2.37 2 1.32 2 1.75 5 2.57 10 2.25 5 1.70 5 2.44 5 2.18 10 1.56 3 2.24 1-Hexanethiol 2.00 10 1.79 3 d, A. 102Z/Ii 1.69 2 21.0 100 12.5 80 6.4 30 5.8 50 2-Methyl5.2 10 benzenethiol 5.0 20 6.7 20 10.4 40 cl, il. 10'Z/I1 4.55 30 5.8 60 9.3 60 4.14 20 4.7 10 7.5 2 10.1 40 3.65 100 4.45 40 7.1 5 9.1 2 3.30 20 4.20 20 6.6 30 8.3 100 2.92 2 3.92 50 6.2 20 7.2 70 2.73 3 3.58 100 5.7 5 6.7 10
-
2-Methyl benzenethiol d, A. 102I/Ii 6.3 10 5.5 30 5.3 20 5.05 20 4.83 70 10 4.59 4.41 30 4.23 10 3.93 30 8.66 40 3.52 20 3.28 70 3.18 80 3.09 5 2.96 20 2.80 5 2.70 10 2.62 3 10 2.55 2.49 7 2.37 10 2.32 5 2.27 10 2.10 3 2.05 0 1.92 3 3-Methylbenzenethiol d, A. 10'I/Ii 7.8 6.2 5.6 5.3 5.05 4.66 4.40 4.00 3.88 3.54 3.42 3.01 2.88 2.62 2.37 2.27 2.08 2.01 1.92 1.89 1.83 1.80 1.61
100 30 5 5 30 10 10 20 40 90
10
70 50 5 10 5 5 5 2 3 2 5 5
4- RIethylbenzenethiol d, A.
1O'Z/Z1
11.3 8.4 6.4 5.7 5.1 4.9 4.20 3.65 3.37 3.24 3.15 3.01 2.81 2.62 2.52 2.40 2.27 2.12 2.04 2.00 1.71
100 90 90 50 5 5 80 70 80 60
VOL. 34, NO. 2, FEBRUARY 1962
70 5 20 10 10 1 2 20 2 5 3
0
239
In the case of the derivative of 2methyl-1-butanethiol, a considerable discrepancy exists (20’). Since the melting point value obtained seems t o agree quite well with that of the isomeric 1-pentanethiol, it was thought that perhaps the Eastman sample was mislabeled. However, a mixed melting point determination of the derivative of 1-pentanethiol and the supposed 2methyl-1-butanethiol gave a substantial depression. Furthermore, a n intensive N M R study of the questionable derivative, the mercaptan from which it was prepared, and the sulfone of the derivative. established unequivocally its identity as the 2,4-dinitrophenyl thioether of 2-methyl-1-butanethiol. Diffraction Data. The diffraction data for all the derivatives of the mercaptans included in this study are given in Table 111. Many strong lines characteristic of the respective derivative were obtained in all samples, making qualitative identification quite simple. The unique character of the diffraction patterns of mercaptans which are quite similar in structure is demon-
strated by the spectrometer traces of the isomeric 1-pentanethiol and 2methyl-1-butanethiol derivatives, Figure 1. Disulfides. The 2,4-dinitrophenyl thioethers of representative aliphatic and aromatic disulfides have been prepared. Those chosen were the n-butyl disulfide and phenyl disulfide. They were prepared by the method described in the experimental section and gave derivatives which checked exactly with their respective thiol derivatives in regard to melting point and x-ray diffraction patterns. Therefore, the identification of disulfides may also be accomplished quite readily by this same procedure. ACKNOWLEDGMENT
The authors thank Robert Culmo for the elemental analyses and Harry Agahiginn and George Vickers for their NMR interpretations. LITERATURE CITED
(1) Brock, M. J., Hannum, M. J., ANAL. CHEJI.27, 1374 (1955).
(2) Charles, R. G., Johnston, ‘8. D., Ibid., 29, 1145 (1957). (3) Cheronis, K. D., Entrikin, J. B.,
“Semimicro Qualitative Organic Analysis,” p. 321, Crowell, Kew York,
1947. (4) Ibid., p. 441. ( 5 ) Clark, G. L., Kaye, W.I., Parks, T. D., ANAL.CHEW18,310 (1946). (6) DeLange, J. J., Houtman, J. P. W., X e c . trav. c h i m . 65, 891 (1946). (7) Garska, K. J., Douthit, R. C., Yarbroueh. V. A s AXAL. CHEX 33,. 392,. (196ij.’ (8) Gordon, B. E., Vopat, F., Jr., Burnham, H. D., Jones, L. C., Jr., Ibid., 23, 1754 (1951). (9) Gould, C. IT,,Gross, S. T., I b i d . , 25, 749 (1953). (10) Hofer. L. J. E.. Peebles. TI-. C . , I b i d . , 27, 1852’(1955). ’ (11) McKinley, J. B., Kckels, J. E., ~
Sidhu, S. S., IND.ENG.CHEM.,ANAL. ED. 16,301(1944). (12) .Matthews, F. W., hlichell, J. H., Ibzd., 18, 662 (1946). (13) Rose, H. A4.JVan Camp, A. J., A N A L . CHEM. 28, 1430 (1956). (14) Stahl, C. R., Siggia, S., Ibid., 29, 154-5 (1957). (15) Warren, G. G., hlatthews, F. IT7., I b i d . , 26, 1986 (1954). (16) Wurtz, D. H., Sharpless, K. E., Zbid., 21, 1446 (1949). RECEIVEDfor revie-, October 11, 1961. Accepted December 13, 1961.
Precision in X-Ray Spectrochemical Analysis Fixed-Time vs. Fixed-Count L. S. BIRKS and D. M. BROWN
U. S.
Naval Research laboratory, Washington 25,
A comparison of the statistics for fixed-time and fixed-count rneasurernents o f line minus background in x-ray spectrochemical analysis shows that the relative standard deviation for fixed-time operation i s never greater than 1.1 times that for fixedcount operation. Therefore, the more convenient fixed-time mode of operation is recommended for all measurements.
P
in x-ray spectrochemical analysis depends on both the linepeak intensity, I L , and on the background intensity, I B , where IL and I B are in arbitrary units such as counts per second or counts per minute. Mack and Spielberg (3) showed equations for the optimum division of counting time for the peak and background positions in order to obtain maximum precision in the peak minus background, ILl e , measurement. For routine analysis, it is not convenient to make the necessary calculations for each line in the spectrum and even less convenient to readjust the counting time for each RECISION
240
ANALYTICAL CHEMISTRY
D. C.
measurement. Thus, the only commonly used modes of operation are fixed-time and fixed-count. I n fixedtime operation, the number of counts, iYL, collected a t the line peak is larger than the number of counts, N B , collected at the background position. I n fixed-count operation, the number of background counts, N E ‘ , is arbitrarily made equal to the peak counts, NL‘, by extending the measurement time a t the background position. It is well recognized that precision of the ILIo value is better for fixed-count operation. The question that has not been answered heretofore in a simple fashion is: “Just how much better is the precision for fixed-count operation and how does it depend on the relative intensity of the background?” To answer the question, one must consider the relative standard deviations for the fixed-time and fixed-count modes of operation. CALCULATIONS
be the standard deviaLet U L and tions of measurements a t the line peak
and a t the background position, respectively. The standard deviation of the peak minus background value is obtained by the usual rule for adding variance U,?,
-E
=
(UL2
+
UB’)’
*
The relative standard deviation is U L -E%
100 ( U L *
+
UB’)’
‘/(IL - I B )
(I)
So far this is completely general and holds for any distribution of counting time. The difference in the results for fixed-time and fixed-count operation will depend on changes in U L or U B values. Some relationships may be expressed that will simplify the evaluation. First, in order to normalize the comparison, N L should be made equal to NL‘ by choosing the proper counting interval. If this is not done, then either fixed-time or fixed-count operation can be more precise dependent only on the particular value of N L or NL’ for each individual measurement. Sec-
