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560
Vol. 66
bands, etc., of the stabilizer disappear and some characteristic bands of silver salt are observed at 1393, 1280, 1000 cm.-l, etc. It is seen from the b, e, d and e spectra in Fig. 1 that the spectrum of the silver salt is equal to that of the stabilizer in the adsorption state and that of an aqueous solution of the sodium salt of the stabilizer (negative ion of stabilizer). It is very interesting that the spectrum of adsorbed stabilizer I at 0 = 1/2 is the same as that a t 0 = 7. From the above experimental results, it may be concluded that stabilizer I is adsorbed on silver bromide as a silver salt in both lorn and high adsorption ratios and that the state of the adsorbed stabilizer is the same as that of the negative ion of the stabilizer. These results suggest that the silver salt of stabilizer I is in an ionic crystal state and e Sodr‘m hydroxide that stabilizer I reacts with silver bromide crystals solutioo ofsiabilizer 1 and forms a silver salt ionic crystal on the surface of the silver bromide. The band at 2902 cm.-l is assigned to methanol adsorbed on silver bromide. 0 This band cannot be found in higher adsorption 3003 2000 1600 1230 1WI) 800cw’ ratios (Fig. Id). This fact indicates that the Fig. 1.-Infrared spectra of 2-mercaptobenzothiazole (stastabilizer is adsorbed more firmly than methanol in bilizer I) in various states. silver bromide. i Though the situation of stabilizer I described a r n above also was observed for stabilizers I1 and 111, 4 the infrared spectra of stabilizers IV and V adsorbed on silver bromide were somewhat different from 2 - Mercapto - benzo t h iaz ole those of the silver salts or aqueous solutions of the sodium salts. As the difference is minor, it may be stated that these photographic stabilizers exist on silver bromide as silver salts of the stabilizers, although these stabilizers were not adsorbed more than6 = 1. On the mechanism of the stabilizing action of stabilizers on photographic emulsion, we consider for the present that the negative ion of the stabilizer Q adsorbed in incomplete regions on the silver broE q u i l i b r i u m concentration p M / 1 . mide surface by exchange reaction with bromide ion Fig. 2.-Adsorption isotherm of 2-mercaptobenzothiazole on exerts a stabilizing, or antifoggant action by resilver bromide. tarding the growth of fog nuclei or reducing the rate of development. buffer solution for adjustment of the pH. The noticeable change in the ultraviolet absorption of the stabilizers before and after adsorption was not PROTON K.M.R. SPECTROSCOPY, XIV. observed. The specific surface of the silver bromide ACCURATE MEASUREMENT OF THE adsorbent was determined by using 3,3’-diethyl-9SPECTRAL POSITION OF THE FORMYL methyl-thiacarbocyanine dye. The adsorption OF p-ANISALDEHYDE, USEFUL FOR PEAK ratio, 6, was calculated from the dimension of the CHECKlNG THE CALIBRATION OF stabilizer molecules and the specific surface of the silver bromide adsorbent. There was no difference N .M R SPECTROMETERS between the infrared spectrum of the dye adsorbed BY GEORGEV. D. TIERSAND DONALD R. HOTCHKISS on silver bromide and that of the dye (as a silver No. d l 3 j r o m the Central Research Dept. of the Manneaota bromide disk). This fact shows that the force of Contiabutton Manzng and Manufacturzng Co., St. Paul, 19, Mann. the adsorption between cyanine dye and silver broReceked September 18, 1961 mide is not of the nature of the covalent bond A persistent problem in high-resolution n.m.r. The curves a, b, c, d and e in Fig. 1 show the infrared spectra of stabilizer I in various states. spectroscopy has been the accuracy of shielding Figure 2 shows the adsorption isotherm of stabilizer value (“chemical-shift”) measurements. ComI on silver bromide. The curves of c and d in Fig. mercial spectrometers1 as supplied are inadequately 1 are the infrared spectra of the adsorbed stabilizer calibrated, since the dial readings of the audiooscillator which is used for precision determination at c and d on the adsorption isotherm in Fig. 2. Making a comparison between a and b spectra in of spectral position2V3are well known to be rather Fig. 1, we see marked differences between the in(1) For example the V-4300-B (40 Mc./seo.) and t h e HR-BO (60 frared spectrum of stabilizer I and that of the Mc./sec.) spectrometers available from Vsrian Associates. Inc., Palo silver salt of stabilizer I. The V N H and amide I1 Alto, Calif. I
I
/
. .
March, 11962
NOTES
561
inaccurate. Virtually all owners of these instru- 0.57 f 0.03 c./sec.' However, for numerical ments recognize this problem, and most have solved evaluatim of resolution, line widths a t half-height it by installatiou of a precision frequency ~ o u n t e r . ~are refera able,^ With this addition these n.m.r. instruments truly Experimental become ,spectrometers, reprodixibilit'y of measureThe n.m.r. equipment arid techniques haye been dement between different laboratories being 50.001 scribed in detail.3 The p-anisaldehyde, from the Eastman p.p.m., or one part in lo4 of the peak separation Kodak Co., was distilled before use to removc oxidation products; a 4.OY0 (by volume) solution of it was made in studied? "spectro grade" carbon tetrachloride (hfat,heson Coleman The recent introduction of the remarkablg Varian & Bell) which already contained 1.0% (by volume) of A-60 spectrometer, which combines convenience of tetramethylsilane (Anderson Laboratorirs, Divieion of the Stauffer Chemical Co.). Sixteen n.m.r. tubes were filled operation with very high reso1utionj6has prompted with this solution; each tube then was sealed after having a reconsiderat'ion of the question of spectrometer benn purged with a fine stream of oxygen-free nitrogen to accuracy, since the calibration of this instrument is sweep out dissolved oxygen. Sample tubes so prepared have dependent on the accura.cy of certain potentmiom- remained unchanged for a period of two years. Caution: n.m.r. t,ubes should no2 be exposed to a high level of eters. There is no method for internal calibra- These over a long period of time. One of the tubes, in tion, though p-rouision has been made for intro- illumination bright light for several weeks, mas found by n.m.r. analysis duction of sidebands if one should have an audio- to contain some chloroform and p-anisyl chloride, formed by oscillator (which of course must be monitored by a the free-radical reaction frequency counter). It seems likely that most hv Ar-CHO + CCl, --+Ar-COG1 C".% owners will not provide this a,ccessory equipment. Inasmuch as t'he manufacturer does not claim iniA very large number of n.ni.r. measurements were made, tial accuracy better than AQ.102 p.p.m., there is a 12 separate determinations being made on each of the 16 reasonable chance that, with use, these instruments tubes. It thus was possible to reduce the standard deviation the averaged value to zkO.0005 p.p.m. even though the may develop yet more serious errors in spectral in standard deviation for a single determination, namely position measurement despite excellent resolution 1-0.007 p.p.m., was much higher. The fundamental acand general performance. Accordingly it should curacy of this procedure is indicated by the remarkably be regarded as rather importmtt to check, occasion- good agreement, wit,hin +0.001 p.p.m., of odr averaged value a t 25.0°, 0.1970 T, -I: 0.0005, with final results from ally, the calibration of all A-60 spectrometers. each of several other careful workers6; in most cases their For this purpose we recommend the formyl peak standard deviations for a single measurement were appreciof p-anisaldehyde, which is a t the extreme low-field ably smaller than ours. series of 26 measurements was made a t +77", end of the normal proton spectrum, +0.197!, 7 theA further Varian variable-temperature apparatus and probe (i~0.0005). The large sepa'ration, nearly ten modification being employed, and the formyl peak was p.p.m., between this peak and that of the internal found to have shifted very slightly, to +0.181 T, ztO.003. reference, tetramethylsilane, is desirable from the From this observation the temperature coefficient of the st,andpoi:nt of magnifying percentage errors; how- 7-value for the formyl peak (assumed constant over the temperature range studied)was evaluated as -0.0003 p.p.m. ever t'hiEi is also a shortcoming in that the usual per degree temperature rise. This correction was applied to spectrum produced by the A-6'0 spectrometer does certain results obtained5 a t slightly difierent temperatures. not include peaks below +1.67 T , making it neces(7) First observed by C. A. Reilly at the Shell Development Co. sary to rise the "spectrum-offset" device to bring the form;yl peak on scale. The lorn 7-value is not a serious limitation, however, since this offset feature is required whenever a region of the spectrum is to SOLVEST GLASSES FOR LOW be expaiilded for more detailed investigation; thereTEMPERATURE SPECTROSCOPIC fore this unit also should be checked for accuracy. STUDIES The methoxyl peak, a t 6.139 5 0.002 7,may be used as a test of linearity, and the aromatic peaks BYDONALD R. SCOTT^ AXD JEAN B. ALLISON' provide a convenient visual est'irnateof performance. Spectroscopy Laboratory, Chemastry Department, Universitg of Houston, Houston 4, Texas A better .test of resolution is seen in t'he formyl peak Received September BS. 1D61 itself, which is a closely-spaced triplet having J = We have compiled in the accompanying Table I a (2) 1. T. Arnold and 1LI. T. Packard. J . Chem. Phys.. 19, 1608 (1951). series of solvent systems which are particularly (3) G. V. D. Tiers, .I. Phys. Chem., 62, 1151 (1958). useful for electronic emission spectral studies a t (4) For example, the 522-B counter, manufactured bv the Ilewlettliquid nitrogen temperature, 77°K. All of these Packard Co., Palo .41to, Calif.: any counter giving precision t o f0.1 c./sec. is equivalent. systems form transparent, rigid glasses at that ( 5 ) A cooperative study was carried out for the N M R Subcommittemperature when proper precautions are taken to tee of A.S.T.RI. Committee E-I3 on P,bsoi.ption Spectroscopy b3' the ensure that all components are anhydrous and of authors togeOher with the following (amon,%others). At 40 Rlo./sec.: high purity.2 Many of these glasses have been P. C. Lauterbur, Mellon Institute; C. A. Reilly, Shell Development employed in this Laboratory and in others for C o . ; C. R I . Huggins, General Electrio Research Lab.; R. E. Glick, Pennsylvania State Univ.; D. P. Ames, bfonsanto Chemical Co. several years for low temperature electronic specAt 60 Mc./eec.: A. A. Bothner-By and B. L. Shapiro, Mellon Intral studies. However, several of the systems are stitute: .I. N. Shoolery and L. F. Johnson, Varian Associates; E. D. known to be original with this Laboratory. Several Becker. A'atl Inst. of Health; K. J. Palmer, U.S.D.A. Western Util. of the more unusual systems are useful when one Research Div.; N. F. Chamberlain, Humble Oil Co.: M. T. Rogers, Michigan State Univ. All of the above workers reported final rewishes to study a compound which has a limited siilts for the s-value of the formyl peak o l panisaldehyde f a t 4.0% solubility in the usual hydrocarbon or hydroxylic concn. by volume in CC1a) within f0.001 p.p.m. of the "best averaged
+
value" obtained in our measurements. (6) G. V. I). Tiers, J. Phys. Chem., 66, 1916 (1961).
(1) Robert A. Welch Foundation Pre-doctoral Fellow. ( 2 ) W. J. Potts, Jr., J . Chem. Phys., 21, 191 (1953).
