Determination of Aromatic Aldehydes by Near-Infrared Spectrophotometry R. M. POWERS, J. L. HARPER, and HAN TAI A. E. Staley Manufacturing Co., Decatur, 111.
b Aromatic aldehydes have strong absorption bands in the 2.2-micron region. A study of deuterobenzaldehyde confirms assignment of these bands as the combination of formyl C-H (about 2720 and 2820 cm.-l) and C-0 stretching (about 1710 crn.-l) frequencies. Quantitative applications are demonstrated by the determination of benzaldehyde in the presence of aromatic ketones and by the analysis of mixtures of nitrobenzaldehydes.
I
N THE past few yews there have been many applications of near-infrared spectrophotometry for the tletermination of organic compounds. Such functional groups as --OH ( 1 , 4,-SH (IW), vinyl c'- 1% (S), epoxide ( 5 ) , and --OH (8) Iiaw been studied. In this paper tliv svope of the determination has been t,stenclcd to incalude aromatic aldehydes. Kaye (9) report.. two liands, 1.0 and 2.1-micron, that arc indicative of the aldehyde C-H ' group. Holmnn and Edmondson (77 briefly mention that niyristaldchydt~ h:ts a weak band a t 2.21 niirrons, \\\liich they assign to the --C€I=O structure. To the authors' knowlrdgr there has been no extensive study of aromatic. a l d c ~ h y din ( ~the ~ nearinfrared rcgion. Three hiids arc' c.liarnctc>ristic of aromatic. aldclij dcs. Two relatively strong bands nerc found a t 2.21 and 2.25 microns and a neak band at 1.25 microns. Ailthough the 1.25-micron band is too ~ c a kto be of quantitative significwicc, it is characteristic of aromatic aldrhydr. in the prcxmcc of other cwbonyl rompounds. Although difficult. aldehydes have been determined in the presence of ketones in several n a y s (2, 6). A relatively simple method for determining aromatic aldehydes in the presence of aromatic ketones is presented here. EXPERIMENTAL
A11 measurements were made using a Beckman Model DK-2 spectrophotometer. The following instrument settings were used: %canningtime 20, time constant 0.2, scale c.xpansion 2X, slit width 0.025 mm. a t 2.210 micron..
For qualitative \I ork setting\ \\ crc used as described by Goddu (4). Quartz cells 1, 5, and 10 cm. long were used. These cells wcrv matched to 0.01 absorbancc unit o w r the region covered. Infrared nieaiurenieiit> for Table I were made with a 13eckman infrared -pectrophotometer Model IR-4. Thc instrument settings were: gain. 6%; period, 8 seconds, ~ m i i i i n g infrared region have been reported by Pinchas ( I O , 11). Solutions of benzaldehyde in carbon tetrarhloride were used for Beer’b law study of the 2.21-micron band. By utilizing different cell lcngths1, 5 , and 10 cm.-the concentration range 0.006 to 0.600 mole per liter was studied. The relationship between nbsot Iiance and concentration was linear o w the entire range.
, I
1
I
I
IS
u
Wave Length, Microns
Figure 1.
Spectrum of benzaldehyde
3.3% b y weight in carbon tetrochloride
DETERMINATION OF BENZALDEHYDE
Synthetic mixtures of benzaldehyde with acetophenone and benzophenone in carbon tetrachloride were analyzed to test the applicability of the 2.21micron band for aromatic aldehydes in the presence of other carbonyl compounds. Results are listed in Table 11. A 3.3% error was obtained when the amount of benzophenone was twice that of benzaldehyde by weight. However, a iiiisture of a 1 to 1 ratio hg w i g h t
Table 111.
JJ-ave Length,
Rlirrons 2 176 2.203
1288
Wave Length, Microns
Figure 2.
Spectrum of deuterobenzaldehyde
4.6% b y weight in carbon tetrachloride
Table IV.
Absorptivities of Nitrobenz-
Determination of Nitrobenzaldehydes
a Idehyd es
Mixture
(Unit, liter/mole-em.)
NO.
Ortho
Para
1 2 3 4
8.00
4.00 ti . 00
Ortho
Meta
Para
1.280
0.431 1399
0.365
0.456
ANALYTICAL CHEMISTRY
1.400
5 6
Prp.sent, Grams/Liter
6.00
4.00 8.00 6.00 4.00
8 .00
XIetu ... ... ...
4.00
...
. .
6.00 8.00
__ Foutid, Grums/Litrr Orttio Para L1et;i
7 99 LO1 :i .8T
4.00 6.01
...
8.0:$
8.05 ti.08 3 . 9(j
...
... 3.02 5,85
...
7.88
...
of acetophenone and benzaldchydc introduced an error of 7.7%. The presence of acetophenone causes higher deviations than does benzophenone. Since the methyl carbonyl group has weak absorption closr to the 2.21-micron band, the overlapping could introduce error in locating the base line. The results were not imljroved when the ratio of intensities betn-ern 2.210 and 2.185 mirrons n as used for measuring the absorbances ( 1 4 ) . DETERMINATION
OF NITROBENZALDEHYDES
The near-infrarotl y)ectra of nitro1)c~iizaldeIiydrsare very siniihr. Honv\.cr, the oonibination hand. of o-nitroI)cmzaldeliytlc was a t 2.176 microns, n hile for m- and p-nitrobcIizaldeh\-dc it \vas a t 2.203 microns. Thih tliffcrcwe in position makw possiblc the detwmination of a nii.\tiir.e of (ither the ortho and pnra isomers or the ortho and nwt:i isomers. ‘ l hulimpti\-itics
at each wave length were measured (Table 111), and from the measured absorbances the concentration of each component mas calculated by simultaneous equations. ,2 good agreement betmen the actual and calculated amount was obtained (Table IV) . The spectra of the nieta and the para isomers are almost identical. Only the weak bands a t 2.474 and 2.266 microns seemed to he characteristic of the nieta and t h r para isomer. respectively. The authors tried to utilize these two bands for dcterniining these two isomers, but the deviations \$ere too large to be of practical significance.
ACKNOWLEDGMENT
The authors thank C. E. Irdand for helpful suggestions. and Leon Mandcll for the XhlR nnalj-sis of tlcwterohrnzaldehyde.
LITERATURE CITED
(1) Crisler, It. O., Burrill, A. hl.. .4x.41,. CHEW31,2055 (1959).
(2) Fowler, I,., Mitchell, R. S.,Ihid., 27,1688 (1955). (3) Goddu, R. F., Ibid., 29,1790 ( 1 9 5 i ) . (4) Ibid., 30, 2009 (1958). (5) Goddu, R. F., Delker, I). .4.,Zbid., 30,2013 (1058). ( G ) Gorden, B. E., mopat, F., Jr., 13urham, H. D., Jones, L. C., J r . , Ibitl., 23, 1754 (1951). ( 7 ) Holman. R. T., Edmontlmn. 1’. 1i.. Ibid., 28, 1533 (lobe). ( 8 ) Holman, R. T., Sickell, C‘., I’rivc>tt, 0 . S.,lcdmondson, 1’. It., J . i l t r 1 . Oil Chemists’ SOC.35, 422 (1958). (9) Kaye, W., Spectrochirn. .4cfn 6, 281 (1054). (10) Pinchas, s., ASAL. C m X . 27, 2 (1955). ( I 1 ) Ibid., 29, 334 (195i). (12) Whekel, K., Roberson, T\-. E , Krell, hf. \V.,Ibad , 30, 1954 (1958). (13) Wiberg, K. \T .. J 4m. C ~ P , , ,Yo( I 76,5372 (19a4). (14) Willard, 11. H., Merritt, Jr , 1, I, , Dean. J. A.. “Instrumental hfpthotls of Analysis,” p, 14i, 3rd ed., J7:m SOPtrand, l’rinreton, S. J., 1958. RECEIVED for review Frbrnary 18. 1!)GO. Acceptrd June 3, 1960 ~
Determination of Lanthanum, Cerium, Praseodymium, and Neodymium as Maior Components by X-Ray Emission Spectroscopy DAVID R. MANEVAL and HAROLD L. LOVELL Department of Mineral Preparation, College o f Mineral Industries, Pennsylvania State University, University Park, Pa.
b The advantages of the fused disk technique in x-ray emission spectroscopy suggest its application to analyses of the rare earths. Improvements in accuracy, convenience, speed, and economy result from this process. Standard disks for cerium, lanthanum, praseodymium, and neodymium are prepared by fusion with sodium borate and are employed for daily calibration. The analyses of four samples of widely varying composition show a With mean error of less than 5%. these four elements, interference from other rare earth oxides is generally insignificant.
N
o m i p m TECHNIQUE^ is available for the mrt-chemical dctcrniination of Irznthanuni, prascotlyiiiium, or niwdymium Spectrographic :tnalysis of t h r rare carths is ni:ide diffic lilt by t h r compleuity of tclc hniquc antl t h r lot ation of cyanogen band. i n the region of tlic rarc earth RU Iinc’-. -\]though :ipplictl in our laboratoriei t o minerals or rarc carth coniplc\cs (of n idely
varying nature), the use of a constant matrix permits applications t o most any type of rare earth-containing substance with lanthanum, cerium, praseodymium, or neodymium as a major component). I n very unusual circumstances a preliminary oxalatc separation ma>- be helpful to reniovc interferences or achieve concentration. The procedure set forth hert‘>in can be used for the determination of lant,hanum, ccrium, praseodymium, anti ncodymium with sufficient accuracj. for most separation or caontrol purposes. The three simpk Qrocc.dnl(,s--u-eighing, disk preparation, antl intensity tletcrniination-can be readily accomplishcd by a technician. Also, spectrochemical analysrs have heen chnractcristically npplicd to low concrntration ranges. ‘The errors rrlatcd to self-ahsorption, excitation vwiablcs, hackground effects:. and densit’ometry of intensc lines tend t’o hc morc prwalent at high concentrations arid arc additive to the uncontrollablc variables charac,teristic of photographic emission spectroscopy.
Q u a n t i t h w x-ray fluorescencc prowdures art’ widely used (9, 12, 15) foi, the an:tIysis of minerals because of thi. simplicity of standardizat,ion, specvl of analysis (clapsed time). infrcqwiit interfcwnw between components. and :tccurnry at’tainablc a t high concwitrations. Early in the Manhattan District Project, Clarke (3) investigatcd the possibilities of x-ray analysis of thc: rare earths, while in 1955 Dunn ( 5 ) studied the quantitative aspects ~ n i ploying :tn internal standard but without cmrections rclated to particii1:ir systems. Romans (11) used a comparison-type proccdurc based on synthctic 1nixturt.s. Salmon and Blacklrdgc (12) have rcportcstl a semiqumtitn t i w method utilizing otnpirical caorrections. Rewntly Lytlc, h t s f o r d , a n d Hvllw (7) as w 1 1 as Lytlc and H w l y (8) deseribcd :L potvtler-t>ype x-ray fluor(+ cence analysis of bastnaesite :tnd high purity rarc cnrth oxides. Standartiization rtwiltcd from s y n t h h c ~niiililw packed into a plastic holder. ’Tho authors found several disadv:int:igcs VOL. 32, NO. 10, SEPTEMBER 1960
1289
