Detection of Deuterium Oxide in Dimethylsulfsxide-d6 by Nuclear Magnetic Resonance Milton I. Levenberg and Delbert T. Jeter, Jr., Chemical Physics Laboratory, Abbott Laboratories, North Chicago, 111.
u
OF DEUTERATED dimethylsulfoxide-de (DhiSO-dG) as an NhIR solvent for the structure elucidation of alcohols (1) and amines (2) has become accepted practice in many laboratories. Commercial DLfSO-dG often SE
60064
A I
-GH2-
/
protons is r e a h y observable in DMSO, and (3) the five aromatic protons provide a good internal reference standard for integration. RESULTS AND DISCUSSION
C All spectra were run a t about 36' C. in a Varian A-60 NhIR spectrometer and are reported relative to internal ThlS. The NLIR spectrum of benzyl alcohol (reagent grade, without further purification) in freshly opened DRISO-de is shown in Figure 1A. The hydroxyl peak a t 4.83 p.p.m. also includes the HDO peak resulting in a high relative integral as shown in Table I. A portion of the D;\ISO-ds was then stored over anhydrous sodium sulfate for 96 hours. The solrent was filtered and used to obtain the NMR spectrum of benzyl alcohol shown in Figure 1B. The sodium sulfate changed the acid character of the DMSO-de ( 3 ) , and thus retarded the rate of exchange between the HDO proton and the hydroxyl to the point that they now exist as separate peaks a t 3.46 p.p.m. and 5.19 p.p.m., respectively. I n fact, the rate of proton exchange is now so slow that a 6-He. coupling is observed between the methylene and hydroxyl protons. The multiplet a t center peak of the -CH24.53 p.p.ni. can be attributed to the presence of Ph-CH2-OD. The presence of an HDO peak a t 3.46 p.p.m. indicates that sodium sulfate is not an adequate drying agent for this system. Another aliquot of the DhISO-de was then stored for 96 hours over acti-
I
I
I
I
I
I
I
8.0
1.0
6.0
5.0
4.0
3.0
2.0
PPM (6)
Figure 1.
NMR spectrum of benzyl alcohol (20%) in DMSO-&
A. Stock DMSO-de. treated DMSo.de.
Table I.
6.
NaZS04 treated
DMSO-de.
C. Molecular sieve
Comparison of NMR Integrals of Benzyl Alcohol
Relative integrals Solvent DMSO-ds Stock (Figure 1 A ) NapSOa-treated (Figure 1B) Molecular sieve-treated (Figure 1C)
c6H5-
-CH2--
5.00 5.00
2.1 2.0
1.1 (contains HDO peak) 0 . 8 (partly D-form)
5.00
2.0
1.0
~
-OH
~~~
~~~
VOL. 38, NO. 13, DECEMBER 1966
1971
vated Linde Molecular Sieve 4A. The NMR spectrum of benzyl alcohol in this solvent is shown in Figure 1C and is in agreement with the results reported by Chapman and King (1). The hydroxyl and methylene groups are again split; however, no evidence of the presence of Ph-CH2-OD can be seen. The HDO peak has almost vanished. The relative integrals in each of the three systems are compared in Table I.
After essentially complete removal of labile deuterium from the DMSO-dc, further traces of HzO absorbed in the solvent from the atmosphere or introduced with the solute will not adversely affect the integrals of exchangeable protons in the system. This technique has been used routinely to monitor all DMSO-& received in this laboratory. A S a result we have been able to obtain accurate
NMR integrals of labile protons, and provide valuable information for organic structural determinations. LITERATURE CITED
(1) Chapman, 0. L., King, R. W., J . Am. Chem. SOC.86, 1256 (1964). (2) Giessner-httre, Ann. PhW. 9, 557 (1964); C.A 62, 7269d (1965). (3) TraJrnham, J , &,, Knesel, G. A., J. Am. Chem. SOC.87, 4220 (1965).
c.,
ew Technique for Coating and Packing of Glass Bead Columns for Gas Chromatography 0.E. Wilkinsonl and J. H. Gibson, Department of Chemistry, Colorado State University, Fort Collins, Colo. HE PACKING of glass bead columns T p r e s e n t s a difficult problem, especially when the quantity of the stationary liquid phase exceeds approximately 0.10 to 0.25% by weight (2,3). Beads coated with materials that are “tacky” at room temperature-e.g., Apiezon L, silicone grease, Se 30 gum rubber, etc.-tend to clump and are not capable of being packed into tubular columns by conventional packing techniques which require a free flowing material. In addition to the problem of packing beads coated with liquids or grease-like materials, it has been observed by the author and others (3) that in coating the beads themselves with any stationary phase a significant portion of the coating material is lost to the walls of the vessel in which the beads are contained during solvent evaporation. Using weighed portions of the coating materials is, therefore, not a true measure of the final coating concentration. To the authors’ knowledge, no attempt has been made to overcome the latter problem except to use an amount of coating material in excess of the amount desired and to determine the final coating concentration after the solvent has been evaporated and the beads dried. Several approaches have been proposed to overconie the problem of packing glass beads in tubular columns. “On column” procedures (1,4) have been used in which the solvent containing the desired stationary liquid phase
is passed through the column which contains the beads, which were previously packed in the dry uncoated form. In this method, some of the coating material adheres t o the beads, but control of amount deposited is not possible (3). Other suggestions have involved cooling the beads to a temperature sufficiently low t o solidify the coated phase. With silicone grease, or Apiezon L, this requires dry ice temperatures and necessitates keeping the column, as well as the beads, a t this temperature during the packing procedures. Even though the beads are free flowing under these temperature conditions, this technique has not proved practical because of the difficulty of refrigerating both the beads and the column simulbaneously. 9 less difficult and more practical technique involves using a ramrod and tapping the beads into the column small quantities a t a time ( 2 ) . This is possible in l/4-inch diameter tubing, but becomes difficult with smaller ‘/s-inch diameter tubes. Also, it is difficult to assure that no voids are formed which would result in poor column efficiency. Of particular interest in work in this laboratory was the coating of glass beads with such stationary liquid phases as Apiezone L, silicone grease, and Se 30, all of which cause the beads to adhere to one another when the coating phase is in excess of approximately 0.25%. TO facilitate the packing of beads coated with these materials into l/s-inch col-
umns, a procedure was developed which involved the flowing of the beads into the column as in conventional techniques for other supports. This is accomplished by filling the column with a water solution containing a small amount of nonionic surfacant which prevents the beads from adhering to one another. The coated beads, after being mixed and separated in a similar water surfactant solution, are then poured into the column with accompanying vibration. This procedure is analogous to the method normally used with the exception of the presence of the water-surfactant solution which acts to reduce the surface tension between the individual beads, and, therefore, prevents sticking. During the development of this packing technique several attempts were also made to eliminate the problem of the adherence of a substantial portion of the liquid phase material on the walls of the vessel used to contain the beads during the coating procedure. It was found that loss of the coating phase during this sbep could be essentially prevented by carrying out the solvent evaporation step in equipment made of Teflon (Du Pont). (See Tables I and 11) It will be noted that better than 90% of the calculated liquid phase concentration is actually found on the bead surface when using the Teflon beakers. Comparable results are listed for glass equipment in which the loss is approximately 2570 of the liquid phase. EXPERIMENTAL
Table 1.
Recovery of Liquid Phase (Apiezon L) on Glass Beads Using Teflon and Glass Coating Vessels
yo Liq. phase Coating vessel
Wt. beads used
Wt. liquid phase
Theo.
Found
Teflon beaker Glass R. B. flask
77.01 g. 76.54 g.
0.7701 g. 0.7654 g.
0.99 0.99
0.92 0.78
‘1972
e
ANALYTICAL CHEMISTRY
Preparation of the Coated Beads. I n the development of the technique for coating and packing of the glass beads, three stationary phases were studied: Apiezon L, Dow Corning silicone grease, and Se 30 gum rubber. These materials were deposited on the 1 Present address, hlcoa Research Labs. New Kensington, Pa.
