V O L U M E 25, NO. 10, O C T O B E R 1953 ~.
Table IV.
__
Analysis of Known Blends" Hindered Phenol, % Added Found
Sample No. 1
0.02 0.04 0 06 0 08 0.10 0 :30 0.30 0 60 0.30 0.30 0.30 0.30
2
3 4 6 6 7
8 9 9 9
9 0
Difference
0.02 0.05 0.06 0.07 0.11 0.28 0.31 0.59 0.31 0.30 0 29 0.32
0 00 +0.01 0.00 -0.01 +0.01 -0.02 +0.01 -0.01
+o.oi
0.00 -0.01
+o
02
Gnused base oils plus 4-1nethyl-2,6-di-tert-butylphenol. __.
1463 The speed of the wave length drive is set at 0.5 r.p.m.. and the response of the amplifier is set a t 2. A zero reading is next obtained with the shutter blocking the radiation path. After the zero line has been obtained the shutter is opened, and the heated sample is scanned three times from 11.33 microns to beyond 11.77 microns. Base-line absorbances are obtained as described below, and the average of these three values used in the calculations. The unheated sample is examined in the same manner. Calculations. A base line is drawn connecting the two minima points and a vertical line is drawn through the maximum point (11.63 microns) to intersect this base line. The incident power is measured from the radiation zero t o this base line, and the transmitted power from the radiation zero to the abRorption curve. The log of the ratio of the incident to the transmitted power is the absorbance of the sample a t 11.63 microns. Both positive and negative absorbances may be obtained by this method; those measured above the base line are positive, those below are negative. Figure 3 illustrates the method for measuring base-line absorbance and shows the absorption band at 11.63 microns having a positive base-line absorbance. To obtain the percentage of 4-methyl-2,6-di-tert-butylphenol, the base-line absorbance increment ( a ) per unit quantity ( b ) of the hindered phenol in oil is established. In this work a / b was 0.060/0.30%. The difference (c) between the baseline absorbance of t,he heated unknown sample and the unheated sample divided h y a / b gives the percentage of the hindered phenol in the hindered phenol,
70=
-$).
Where there is
an extreme difference between the gravity of an unknown oil and the oils used in obtaining the ratio a/b! it may be depirahle
to take this difference into account. 11.77 11.63 WAVE LENGTH
Figure 3.
-
11.40 MICRONS
ZERO LINE
Measurement of Base-Line Absorbance
Po = incident power P = transmitted power Base-line absorbance -log P Q / P
for 1.5 hours on a hot plate. A pressure steam plate having a surface temperature around 360" F. (182" C.) is used. After the sample has cooled to room temperature i t is introduced into the sample cell. For the protection of the salt windows of the cell, samples containing water are centrifuged or filtered through paper befor e analysis. Instrumental Conditions. To minimize instrument error, a fixed slit width of 0.500 mm. is used rather than the automatic slit arrangement. The base-line minima and maximum points are determined on blends of the inhibitor in various base oils. The minima points are a t 11.40 and 11.77 microns, and the maximum point is a t 11.63 microns. The micrometer drive is set a t 11.33 microns, and the gain is adjusted so that with the sample in the path of the infrared radiation the pen position is a t approximately the middle of the recording chart. The gain on the amplifier is varied with the type oil being analyzed, some oils having 61 eater background absorbance than others.
ACCURACY AND PRECISI0.V
Blends of base oils with various percentages of the phenol were analyzed. The results listed in Tables I1 nnd I V are indicative of the accuracy and precision. Over a 3-month period, 21 analyses were made of the same sample of lubricating oil blended with the inhibitor nnd a standard (leviation of 0.0170 phenol was found. ACKNOWLEDGMENT
The authors are indebted to Raymond Dolaii for his assistance in the analysis of samples during t h e development of t,his method. LITERATURE CITED
(1) Gibbs, H.D., Chem. Rei'.s.,3,291 (1S26). (2) Lykken, L., Treseder, K. and Zahn, T.. ISD. Exc,. CHEM., h.41.. ED.,18, 103 (194 (3) Snyder, R . E., and Clark. 11. O., .%S.\I,. C H E > f . , 22, 1428 (1950). (4) Stillson, G. H., Sawyer, D. W., and Hunt, C . K., J . A m . Chem. Soc., 67, 303 (1945). RECEIVED for review May 6, 1953. Accepted August 3, 1953. Presented h l a y 11. 1953. before the -4rnerican Petroleum Institute, New York, N. Y.,
Infrared Spectra of Sugar Anomers ROY L. WHISTLER AND LEL..lND R . HOUSE D e p a r t m e n t of Biochemistry, Purdue Unit-ersity, Lafayetie, 2nd. Examination of the infrared absorptions of a number of monosaccharides and monosaccharide derivatives suggests that certain regions of absorption are characteristic of the configuration of the anomeric carbon and may be used to identify its CY- or &structure. A s the absorptions for different sugars are not of the same magnitude and are not located at the same spectral position it is necessary to have knowledge of the sugar type and to have reference absorptions in order to make definite assignment of anomeric configuration.
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T IS f i r q u e n t l ~difficult to assign a-or &configuration to a sugar or sugar tleiiv;ttive when there is available only one member of the anomeric pair. Kuhn (3) reported that differences exist in the infrared absorption spectra of anomeric sugar pairs. Consequently when a number of infrared spectra of sugars and sugar deriv?tivPs became available in this laboratory and elsewhere it
seemed advisable to determine whether infrared absorption spectra might be of general assistance in assigning configuration to anomeric carbon atoms. From the data in hand it would seem that infrared absorption cannot yet be directly and solely employed for unequivocal determination of anomeric configuration. Nonetheless, absorption data are often of value as an aid in assign-
ANALYTICAL CHEMISTRY
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ing configuration when comparison can be made with the absorption spectra of closely related molecules. Comparison of the 'infrared absorption spectra of various anomeric pairs of sugars does not reveal common differences which are universa1l.v characteristic. Comparison of spectra from related compounds, however, reveals rather uniform differences for the particular group, thus permitting tentative configurational assignment to the anomeric carbon of a sugar of known number of carbon atoms and of known type of derivative, if the sugar contains substituents. The occuirence of a 6-deoxy arrangement does not seem to affect anomeric assignment nor does D- or L-configuration of the sugar.
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Spectra were obtained by use of a double beam recording infrared spectrophotometer (Baird Associates) with sodium rhloride prisms and windows. Nujol mulls were used in demountable cells with 0 . 1 - m m . s p a c e r s . To avoid the need of taking the cells apart after each determination, filling holes were drilled in opposite sides of one face plate and salt window. The holes were closed by screws in the face plate. d sample of approximatelv 50 mg. was ground in an agate mortar and sieved through a 325-mesh screen. Forty milligrams of the sample were mulled with 0.270 gram of nujol in a micro flask; the suspension was taken up in a hypodermic syringe and transferred into the cell. Loading wasaccomplished best under pressure produced when the hypodermic needle was pushed through a small rubber stopper held tightly against the cell plate and force applied to the hypodermic piston. Cells were emptied by blowing out with nitrogen and were cleaned with either chloroform or pyridine. If pyridine was used it was removed with chloroform. The cells were then freed of solvent by passage of a stream of nitrogen.
1465
Intensity measurements were made by the base line method (1). Since the mulls were of equal concentration the values la - I were used for comparison of absorption a t specific xave lengths. IOis the height of the base line a t the absorption maximum and essentially represents the per cent radiation transmitted by nujol, while I is the height of the absorption maximum and represents per cent radiation transmitted by the sample and nujol. Absorption values for interfering bands of similar intensities were measured from a common base line. Absorption of broad bands were measured a t the maxima without regard to the effects of small side bands. All bands reported are for absorption between 20% and 80% of the incident radiation. After measurements were made the absorption values were compared on graph paper as vertical lines whose lengths were proportional t o the value 10- Z and whose position on the abscissa represented the wave length a t the absorption maxima. Those data which represented significant absorption differences between anomeric pairs are recorded in Table I . DISCUSSION OF RESULTS
From an examination of the data in Table I it is observed that in the 9.4 to 9.8 p region the a-isomer of most monosaccharides and monosaccharide derivat,ives absorbs at a higher wave length t.han the corresponding anomeric p-form. With free hexoses t,he a-form seems generally to possess a characteristic absorption b e k e e n 10.15 and 10.37 p . The nearest approaching absorption in t8heregion by the anomeric p-forms is absorption in the 9.9 p region by D-glucose and D-mannose. The a-form often exhibits Characteristic absorptions in the region 10.84 t'o 10.97 and 11.92 to 12.23 M . Acetylated hexoses and pentoses show characteristic absorptions for the a-isomer in the regions 9.84 to 9.92 p and 10.63 to 10.74 p. The a-form of the hexose acetates also has a charact,eristic absorption a t 8.55 t,o 8.65 p . It is noted that the anomeric forms of t.he acetylated heptoses have characteristic differences in the amount of absorption in the regions of 8.75 to 8.85 p and 9.75 to 9.85 p. Each of the anomeric pairs of methyl glycosides show characteristic absorption differences between anomers. The a-isomers absorb radiation in the region 8.34 to 8.43 p while t'he p-isomers either do not absorb in this region or do so to only a small extent. Another characteristic difference between the anomers of this type is that those of the a-configuration have a characteristic absorption in the 9.50 to 9.63 p region whereas the corresponding p-isomers have chtuacteristic absorptions at' 9.41 to 9.48 p . In the case of the acetylat,ed pentosides t.he p-isomers seem to absorb more strongly than the a-form in the 9.26 to 9.34 p region. The a-isomers shorn a chai,acteristic absorption a t ahout 10.6 M . Wit,h t,he acet,ylated hesosides a-isomers uniformly evidenced a characteristic side absorption at 8.30 to 8.35 and another low intensity absorption at 11.68 to 11.76 M. In t'he spectral region 9.4 to 9.6 the a-isomer absorlis at higher wave lengths than the corresponding p-isomer, but this observation is of little analytical use unless both isomers :ire availalile for examination. The most pronounced ahsorption differences I)etween anomeric pairs are those between the phenyl glycosides. a-Isomers have a prominent absorption band a t 11.61 to 11.73 p while the corresponding p-isomers do not absorh in this spectral region. On the other hand the p-isomers absorb a t 12.15 to 12.25 p whereas the anomeric a-isomers do not,. I n the neighborhood of 13.2 p the @-isomersseem to absorb at slightly longer m v e lengths than their anomers. ACKNOWLEDGMENT
The authors wish to thank N. K. Richtmeyer for some of the samples used in this work. LITERATURE CITED
(1) Heigl, J. J., Bell, M. F., a n d W h i t e , J. U., ANAL.CHEM., 19, 293 (1947).
S.,Smith, F. A , Creitz, C., Moyer, J. D., and Frush, H. L., J . Research 3 a t L Bur. Standards, in press. (3) K u h n , L. P., ANAL.CHEY., 2 2 , 2 7 6 (1950).
(2) Isbell, H.
RECEIVED for review April 17, 1953. Accepted July 22, 1953. Journal Paper No. 696 of the Purdue Agricultural Experiment Station.
