V O L U M E 28, NO. 2, F E B R U A R Y 1 9 5 6
269
X-Ray Powder Diffraction Data
-
( T h e camera radius was 7.181 cm. X for C u K a 1.5418 A . and a nickel filter was uscd. T h e relative intensities were visually determined with a calibrated intensity scale) d 14.66 10.38 i.31 A 54 5 73 3.21 5 03 4 88 4 67 4 54 4.86 4.25
1,’Il
d
I/Ii
0 09 035 0 06 0.10 0.18
4 14
0.08 0.20 0.07 1.00 0.30 0.10 0.20 0.08 0.02 0.25 0.11 0.11
0.04
0 04 0 23 0 20 0.20 0.20 0 3.5
4.04 3.94 3.87 3.68 X55 3.46 3.33 3.23 3.14 3.08 2.997
d 2.924 2.849 2.779 2.fi87 2.589
2.506 2.447 2.370 2.320 2.261 2.163 2.070
1/11
d
I/Ii
0.05 0.09 0.09 0.08 0.06 0.06 0.02 0.04 0.02 0.08 O.0fi 0.06
2.030 1.988 1.956 1.919 1.862 1.795 1.729 1.695 1.659 1.617 1.572
0.02 0.02 0.02 0.01 0.02 0.02 0.01 0.01 0.01 0.01 0.01
Acute Bisectrix. y . Pleochroism. Slight, y orange yellon-, N greenish yelluw. FVSION.When crystals on a slide are n-armed to ahout. 150’ C. they become opaque and orange in color. Continued heating with a cautery needle held close to t’he cover glass c a w ’ s t’he c r y ~ t ~ a to l s melt with slight bubbling t o an amber liquid. Overheating will cause darkening. If the nielt is kept warm, unmelted crystal fragments will seed regrowth of hairs ant1 needles, Unseeded drops of warm melt will develop “isotropic” spherulites which resemble the “gel” reported by White and Secor ( 2 ) . These spherulites appear predominantly around the margins of the melt. LITERATURE CITED
(1) White, L. AI., and S e m r , G . E., .%SAL. C m x . 27, l O l G (19551, ( 2 ) White, L. 11..and Secor. G . E.. J . .4m.Chen?.SOC.75, 6313 (1953).
1)ispersion. ( v > T ) strong. Optical Character. (+). Optic .ksial Plane. (010). Fragments usually lie on (010) and shorn an optic normal interference figure.
COSTRIBLITIONS of crystallogragliic d a t a for this section should be s p n t tu Walter C. RIcCrone, Analytical Research, Armour Research Foundation of Illinois Institute of Technology, Chicago 16, Ill.
SCIENTIFIC C O M M U N I C A T I O N
Analysis of Phosphorus Compounds Use of Nuclear Magnetic Resonance Spectra in Differential Determination of the Oxyacids of Phosphorus TUDIES
;ire now under way on developing the nuclear magnetic
S resonance technique ( 3 ) as a qualitative and quantitative analyticid tool in phosphorus chemistry. Suclear magnetic resonance is a rapid and elegant method for carrjing out chemical analyses; and, as this work on mixed osyacids of phosphorus demonstrates, the nuclear magnetic resonance method offers a fresh approach t o analytical problems for which wet-chemical prowdures have not been satisfactory. This technique is unique as a n analytical tool, in that there can be no interference from compounds of any element other than the one under study, as long as the substances being studied are not precipitated from solut i on. It has been pointed out (6) t h a t isolated PO, ions, end PO4 g r o u p , and middle PO, groups in the phosphates (,$, 5 , 8) give definite, resolved resonance peaks. This means that all mixtures of orthophosphates, chains, and rings ( 7 ) can be characterized in terms of the relative number of moles of phosphorus pentoside present as orthophosphates, end groups, and middle groiips (4). Suclear magnetic resonance can be used equally well t o identify anions of the phosphorus oxyacids of lower oxidation etates. Three resonance peaks are found for hypophosphite, trvo for ortho- or pyrophosphite (which cannot be differentiated by this method), and one for hypophosphate, in accordance with their structures ( 1 , 4). In Table I, the anions of the various oxyacids of phosphorus are listed in the order of t,heir chemical shift. The intensity factor shown indicates the relative area (and t o a rough approsimation, the height) of the resonance peak for equal numbers of phosphorus atoms. Thus, a t equal molar concentrations the hypophosphite peak a t 133 p.p.m. shift is only one quarter of the area of the orthophosphate peak with a shift of 100 p.p.m. under the same experimental conditions. (Practical measurements are conveniently made with respect to orthophosphoric acid, and this compound is therefore used as a reference for a il40-gauss field. -4value of +lo0 p.p.m. is arbitrarily added t o tlie shifts
measured with respect to orthophosphoric acid in order to convert all shifts to positive values. The chemical shifts between the various oxyacids of phosphorus are precise t o ea. =k2 p,p.m. and can be made still more precise if the need arises.) Even thoiiph
Table I. Nuclear 3Iagnetic Resonance Peaks for Oxyacids of Phosphorus
-4nion
Chemical Shifta, P.P.M. e P.P.31.
*
Relative Intensity 1
Bcillea, P.P.M.
0.5
0
7 140
Hypophosphite
133
Phosphate middle groups and ortho- and pyrophosphites Phosphate end groups Orthophosphate
120
120h
109 100
100
Hypophosphate Hypophosphite
$11
Ortho- and pyrophosphites
64
Hypophosphite
42
87
40
a Measured in p.p.m. of a 7140-pai1.;~ field witti a limb? rrsonating a t 12.3 mc. Reference substance from which the shifts are ineasiired is 85% orthophosphoric acid. T h e position of the orthophosphoric acid reference standard was arbitrarily defined as A100 on the p.p.m. scale of chemical shifts. Other chemical shifts are then defined by the relation 6 = 100 10‘ X ( I I H H S P O I,”HPPO~. ) b Phosphate middles shown as black b a r and phosphite? as cross-hatched bar.
+
270 the peak for phosphate middle groups and one of the peaks for phosphite (ortho- or pyro-) exhibit the same chemical shift of 120 p.p.m., it is possible t o determine both of these species in a mixture by using the second phosphite peak a t 64 p.p.m. t o determine the relative amount of phosphite and subtracting this value from the relative amount of the middle group plus phosphite as determined from the 120 peak. The other case where interference is possible is between the hypophosphate and hypophosphite, but here again another peak for the hypophosphite at either 42 or 133 p.p.m. can be used. The relative concentrations of the different phosphorus-containing anions listed in Table I are determined by measuring the area under the respective peaks. So far we have measured relative amounts in various mixtures with an accuracy within 2 to 10%. These relative values can be converted t o absolute quantitier! by adding a known amount of one of the phosphoruscontaining anions t o the solution being analyzed. However, the easiest procedure is t o determine total phosphorus by one of the standard procedures (such as a molybdate titration following conversion of all of the phosphorus to the orthophosphate form). At the present stage of the art, analyses by nuclear magnetic resonance are applicable only t o relatively concentrated solutions containing a t least a few moles of phosphorus per liter. Thic: restricts this method of analysis to the acids, alkali metal, and ammonium salts in most cases. However, cations causing precipitates can be removed prior t o analysis by ion exchange resins ( 2 ) ; and concentration by evaporation has proved feasible. In some cases, it is convenient t o make the spectral measurementi on supersaturated solutions. The spectrometer used in these studies was a high-resolution instrument manufactured by Varian Associates (9), equipped with a 12.3-mc. probe. By using a 17.2-mc. probe and a 10,000Gauss field, the resolution and signal-to-noise ratio should improve substantially, and give much higher accuracy and less difficulty with interferences. Comecutive analyses can be car-
ANALYTICAL CHEMISTRY ried out at the rate of approximately 12 samples per hour. The resonance measurement itself takes less than a minute. .4 detailed paper on this subject will be published as soon as certain effects now under study are precisely evaluated. These effects include a slight, theoretically predicted, shift‘ of the resonance peak with pH, and the interference between phosphate middles and pyrophosphite, as well as the interference betveen hypophosphate and hypophosphite. Substitution of nitrogen for oxygen in the inorganic acids seems to cause very little shift in the resonance peak. Thus, mono- and diamido-orthophosphates resonate very close t o the regular orthophosphate ion. LITERATURE CITED
(1) Gutowsky, H. S.,JIcCall, D . W., and Slichter, C. P., J . Chem. Phus. 21, 279 (1953). (2) Helrich, K., and Rieman, W., ASAL. CHEM.19, 651 (1947). (3) Shoolery, J. S . ,Ibid.,26, 1400 (1954). (4) Van Waser, J. R., “Encyclopedia of Chemical Technology,” Kirk and Othmer, editors, vol. X, pp. 403-29, 469-72, 482, 488-92, Interscience, New York, 1953. (5) Van Waser, J. R., J . A m . Chem. Soc. 72, 644, 647 (1950). (6) Van Waser, J. R., Callis, C. F., and Shoolery, J. N., Ibid., 77, 4945-5 (1955). (7) T-an Waser, J. R., Griffith, E. J., and McCullough, J. F.. ANAL. CHEM.26, 1755 (1954). (8) Van Wazer, J. R., and Holst, K. A,, J . Am. Chem. SOC.72, 639 (1950). (9) Tarian .4ssociates, Palo Alto, Calif., Radiofreguency Spectroscopy 1, KO.1 (1953), No. 2 (1954), S o . 3 (1955). RECEIVED for reriew August 19, 1955. Accepted November 7, 1955
Inorganic Division Research Laboratory Monsanto Chemical Co. Dayton, Ohio Varian Associates Palo Alto, Calif.
C . F. CALLIS J. R. V.4N WAZER
J. K, SHOOLERY
MEETING R E P O R T
Society for Analytical Chemistry meeting of the Scottish Section with the StirlingATshirejoint Sections of the Royal Institute of Chemistry and the Society of Chemical Industry, held at Grangemouth on November 2, the following lecture was given. Some Industrial Applications of Ion Exchange Materials. T. R. E. KRESSMAN, Permutit Co., Ltd., London. Ion exchange resins are now widely used in industry. The major use is still in the field of water treatment, but the high capacity and stability of the modern resins based on polystyrene have enabled them to be used in many fields other than water treatment-in metal finishing, in glycerol and gelatin manufacture, and in the manufacture of antibiotics. The conventional method of demineralizing water and solutions of nonelectrolytes is with a column of cation and a column of anion exchanged material in series. More recently, the mixed-bed technique has been applied, in which the liquid is flowed through a single column of an intimate mixture of the two exchangers. Brackish waters, and solutions of high electrolyte content, cannot be economically treated by the column method. A very recent process whereby they can be desalted economically makes use of an electric current in a multiconipartment electrodialysis cell in which cation and anion exchange membranes are arranged alternately between a pair of electrodes. Much development work still needs t o be done on this, however, before it becomes a commercial possibility.
.It a meeting of the Midlands Section held in Kottingham October 25 a lecture demonstration on ring-oven technique was given by H. Weisz, Technical University, Vienna, winner of the Feigel Prize, 1955. The ring-oven technique is a simple method for separating ions, or groups of ions, in one single drop. An apparatus called the ring oven is designed to mash soluble materials out from a spot on a filter paper and to concentrate them in a sharply bounded circular ring zone, where they can be detected. Some other pieces of equipment have been developed for this purpose. With the aid of this method an analytical scheme for 14 commoner ions has been worked out; one drop of about 1.5 pl. is sufficient for the analysis. The method has also been employed for ring colorimetric analysis. The Physical Methods Group met jointly with the Western Section at Bristol University on October 28. The following papers Fere presented and discussed. X-Ray Analysis of the Structure of Vitamin BIZ. DOROTHY CROWFOOT
HODGKIN.
Since the isolation of crystalline vitamin BIZ7 years ago, we have used x-ray diffraction methods to assist in finding the chemical structure of the vitamin. Our examination has been closely interlocked with chemical investigation8 carried out in a number of laboratories. These showed that the vitamin had approximately the formula CSI-UHBI--O?NMOIBIJPCO,and contained a CN group, a nucleotidelike group built of bensiminasole, ribose, and phosphate units, a
