Separation and Identification of
Ca Aldehydes
Use of Gas-Liquid Chromatography, Nuclear Magnetic Resonance, and Infrared Spectroscopy JOSEPH S. MATTHEWS,' FRANK H. BUROW, and ROBERT E. SNYDER
Gulf Research & Development Co., Pittsburgh, Pa. A , method for the separation and identification of aldehyde isomers depends upon the separation of an isomer approximately 90% pure b y large volume gas-liquid partition chromatography. The separated aldehyde i s examined by nuclear magnetic resonance to determine the number of a-hydrogens, CHa-, CHx-, and CHgroups and by infrared spectroscopy to establish the presence or absence of -(CH2)3-or -(CH2)n- groups, where R i s equal to or greater than 4. Finally, the aldehyde i s reduced to a hydrocarbon by the Wolff-Kishner reaction and the hydrocarbon identified b y comparison with API standards by gasliquid partition chromatography. The combined information from nuclear magnetic resonance, infrared spectroscopy, and the reduction step makes possible the identification of separated aldehyde isomers. This method has been used for the separation and identification of several isomers in an octyl aldehyde mixture derived from the oxo process.
T
separation and identification of chain or position isomers are difficult and the complexity increases rapidly with increasing molecular weight. Thus, most of the isomer separiitions and identifications reported in the literature have been on compounds of relatively low molecular weight, where the number of possible isomers is small or where comparison with known materials is feasible. For example, aliphatic carboxylic acid isomers have been separated (2, 7) by paper chromatography, but in these cases only two isomers of each acid were involved. Many separations have occurred in recent years since the advent of gas chromatography (1, 3, 4,6, 8). Chromatographic identification, however, still depends on known retention times or R, values, and this in turn depends upon the availability of the pure isomers. HE
In the aliphatic octyl aldehyde series there are 39 possible isomers; however, only three of these are commercially available in the purified form. Therefore,' a direct comparison with known aldehydes by gas-liquid chromatography or other conventional techniques is currently not possible. If, however, the aldehydes represented in a mixture could be separated into their respective isomers by large volume gas chromatography in sufficient purity for examination by infrared spectroscopy and nuclear magnetic resonance, it was believed an identification scheme could be developed. The method described here illustrates a scheme whereby C8 isomeric aldehyde mixtures can be separated and identified. The paper does not present a complete breakdown of the octyl aldehydes comprising an oxo process mixture, but rather illustrates how the combined usage of instrumental techniques can be employed to solve difficult analytical problems. In brief, the aldehyde is separated into its individual isomers or groups of isomers by large volume gas-liquid partition chromatography and the respective fraction: are collected in liquid
nitrogen-cooled traps. These fractions are then examined by nuclear magnetic resonance and infrared to characterize the carbon-hydrogen groups present, followed by a Wolff-Kishner reduction to the hydrocarbon. The reduction product in turn is identified by cornparison with API standards using a selective gas-liquid partition chromatographic column suitable for hydrocarbon analysis. This combination of techniques provides a reliable identification scheme which should be applicable to any of the isomeric aldehydes, if they can be separated with a purity of approsimately 90%. EXPERIMENTAL
Apparatus. The large volume gas chromatographic column used for isolating the aldehyde isomers consisted of four U-shaped stainless steel tubes 5 feet X 1 inrh in inside lliameter connected in series by l,'i-inch stainless tubing. The :der 'I wa5 packed with cornrnercisi 'fide detergent which had been dried for 36 hours a t 125' C. and for 48 hours a t 180' C. The flash evaporator consisted of a 6 X 0.5 inch stainless steel tube filled with stainless steel Heli-Pak
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Figure 1. Steam-distillation apparatus
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31MM.O.D 4" 10 MM. O.D.
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5 M M. O.D.
TEFLON STOPCOCK OF I TO2MM.BORE
1 Present address, Syntex, SA., Mexico City, Mexico.
VOL. 32, NO. 6, MAY 1960
0
691
3,I;DIMElHYLHEXANAL
mv.
-IO
I 30 T I M E , M I N U T E S
Figure 2.
u I mv.
10
20
30 TIME, MINUTES
40
Chromatogram of iso-octyl aldehyde
Figure 3.
No. 2917 packing (Podbielniak). During use, the flash chamber was heated to 240' C. To avoid the coolin effect of the nitrogen carrier gas on t e flash chamber, the gas was preheated to approximately 300' C. while the sample was being introduced. The thermal conductivity cell was a modified GowMac cell with a 0.5-inch bore. An analytical gas-liquid partition chromatographic column 0.25 inch X 20 feet, fitted with a standard Gow-Mac thermal conductivity cell, was employed for this study. The packing was 35/60 mesh Tide detergent dried as described above. The distillation apparatus shown in Figure 1 allows small quantities of hydrocarbon to be steam-distilled and collected. Standards. The n-octyl aldehyde, obtained from Chemical Research and Intermediates Laboratories, Akron, Ohio, was purified by fractionation on a Podbielniak spinning band column. A fraction collected a t 78' C. a t 30 mm. of mercury was used as the standard. The 2-ethylhexanal was obtained from Eastman Chemical Products, Inc. This aldehyde was fractionated, and a fraction boiling a t 76' C. a t 44 mm. of mercury was collected.
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The 2-ethyl-Pmethylpentanal was obtained from Eastman Chemical Products, Inc. A fraction boiling a t 87' C. at 10 mm. of mercury was collected. The purity of the above aldehyde fractions was determined by reduction to the hydrocarbon and examination on a 0.25-inch analytical gas-liquid chromatographic column. In each case the purity was better than 99 mole %. The API standard hydrocarbons were purchased from the Petroleum Research Laboratory, Carne ie Institute of Technology, Pittsburgf, Pa. Procedure. Approximately 5 ml. of the Ca aldehyde mixture to be separated was introduced by a syringe into the large volume gas-liquid partition column maintained a t 125' C., using a nitrogen flow rate of 1000 to 1500 cc. per minute. Fractions were collected in spiral glass traps cooled in liquid nitrogen. The purity of each aldehyde fraction was determined a t 125' C. on an analytical gas chromatographic column 0.25 inch X 20 feet. Fractions which were approximately 90% pure, as shown by gas-liquid partition chromatography or by reduction to the hydrocarbon, were analyzed by nuclear magnetic resonance for the number of C&- groups. the number of CHI- and/or CH- hydrogens not alpha to the carbonyl group,
Table I. Analysis of Known Isomeric Cs Aldehydes
Structure CHs(CH2)aCHO CHs(CH2),-CH-CHO
Nuclear Magnetic Resonance Infrared CHs- CHI- CH- CY-H-(CH&- -(CH&- Profile 1 6 0 1 160201A 0 2 2 4 1 0 241110B 1 1
AEH6 CHs-CH-CH2-CH-CHO CHI I
3
2
2
1
0
0
3221000
AH6
Table II. Analysis of Peak A Found by Nuclear Magnetic Resonance Found by Infrared CHsCHzCHa-H -(CHa)s-(CHz)n3 2 2 2 0 0
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ANALYTICAL CHEMISTRY
20
10
Chromatogram of peak A
'and the number of C H r and/or CH- hydrogens alpha to the carbonyl group. From this information and the number of carbons and hydrogens in the molecule, the number of CHS-, CH2-, CH-, a-hydrogens can be deduced. The fractions were also examined by infrared for the presence or absence of groups. -(CH,)aand -(CH2),,-In the latter group n may be equal to or greater than 4. Absorption for these groups occurs a t 13.71 to 13.77 and 13.78 to 13.81 microns, respectively. The aldehyde isomer was reduced to its hydrocarbon by the Wolff-Kishner reaction. A modified procedure (6) was used in which approximately 0.2 to 0.3 gram of the aldehyde isomer reacted with 1 ml. of 85% hydrazine hydrate and the reaction was allowed to proceed for 5 to 10 minutes. To the formed hydrazide (or azine) were added 10 ml. of diethylene glycol and 1.4 grams of potassium hydroxide and the mixture was refluxed for 5 hours. Approximately 80 ml. of water was then added and the formed hydrocarbon separated by steam distillation in the apparatus shown in Figure 1. To minimize losses and contamination, the hydrocarbon was dried directly with anhydrous magnesium sulfate without the use of solvents and decanted after drying. Yields of up to 70% have been obtained by this procedure. Steam distillation of 0.3 gram of n-octane under the same conditions resulted in a 73-7% recovery of the hydrocarbon, indicating that the losses are largely mechanical. RESULTS AND DISCUSSION
An examination of the 39 isomeric formulas of the octyl aldehyde series makes it readily apparent that they differ in carbon-hydrogen group distributions. Furthermore, these aldehydes reduce to 18 Ca paraffin isomers. With this available information it was possible to devise a system which would permit an identifkation of the aldehyde isomers.
I n the development of the scheme a letter was assigned to each of the 18 paraffin isomers which can be obtained on reduction of the Cualdehyde isomers. The carbon-hydrogen groups were represented by the number of each group which was present in an isomer and the following group order was used: C H r , C H r , CH-, a-hydrogen, -(CHJs-, and -(CHZ).--. When described in this manner, each of the Ca aldehyde isomers has a number or “profile.” ks an example, if n-octane is represented by the letter A, the profile for n-octyl aldehyde is 160201A. Doing this for the 39 CS aldehydes reveals that there are 34 different profiles resulting in a duplication in only five isomers. I n no case are there more than two isomers with the same profile. Thus, the identification problem is simplified considerably. To test the reliability of the infrared and nuclear magnetic resonance procedures, the three available isomer CI aldehydes were inspected for the information described above (Table I). This analytical scheme waa applied to fractions cut from a mixture of isomeric Cs aldehydes (Figure 2) aa described above. The first fraction, peak A, was examined on the ‘/r-inch partifion column and found to be almost 100% pure aldehyde isomer as shown in Figure 3. A Wolff-Kishner reduction yielded a hydrocarbon which was 96%
2,4-dimethylhexane (hydrocarbon C). Peak A was also analyzed by infrared and nuclear magnetic resonance (Table 11). Out of the 34 different profiles, the onlv Dossible one is 3222000 or 3.5-dimethilhexanal, CHsCH(CHa)CH;CH(CH8)CHoCHO. Peak B (Figure 2) was also separated by this scheme and, on reduction, nine CI paraffins were obtained, the most abundant of which was only 40%, which showed the fraction was not a single isomer. About 20% of this hydrocarbon mixture was 2,4dimethylhexane, the same as the reduction product from peak A. Because peaks A and B had different chromatographic retention times, the major portion of peak B could not be 3,5-dimethylhexanal. Only three C8 aldehyde isomers can reduce to 2,4dimethylhexane: 3,5-dimethylhexanal, %ethyl-4-methylpentanal, and 2,4-dimethylhexanal. Pure 2-ethyl4 methylpentanal had a retention time different from peak B; therefore, peak B contained 20% 2,4-dimethylhexanal. Although no attempt wm made to identify all the isomers in the aldehyde mixture, this schematic approach should make possible the identification of all the components, provided they can be separated in sufficient purity. The separated components should have a purity of 90% or better for infrared and nuclear magnetic resonance to be
applicable. The method requires a minimum of about 0.2 ml. When working with these small volumes, the cut should be analyzed first by nuclear magnetic resonance and then by infrared. This amount is sufficient for the reduction and identification of the hydrocarbon by gas-liquid partition chromatography after these examinations. ACKNOWLEDGMENT
The authors are indebted to L. R. Cousins and R. J. Martin for the infrared and nuclear magnetic resonance data. LITERATURE CITED
(1) Bens, E. M., McBride, W. R., ANAL. CWEM. 31, 1379 (1959). 2) Brown, F.,J. Biochem. 47, 590 (1950). 3) Desty, D. H.,Goldup, A,, Swanton, W. T.,Nature 183, 107 (1959). (4) Desty, D. H., Wh an, B. H. F., ANAL.CEEM.29,320c57). (5) Huang-Minlon, J . Am. Chem. SOC. 68,2487(1946). (6) Keulemys, A. I. M., “Gas Chromatography, pp. 34-53, Reinhold, New York, 1957. (7) OstJeux, R., Guillaume, J., Laturaze, J., J. Chromatog. 1,70 (1958). (8) Zlatkis, A,, Ling, S., Kaufman, H. R., ANAL.CHEM.31,945 (1959).
R E C ~ I V Efor D review October 21, 1959 Accepted January 13, 1960.
Chromatographic Separation of 2,4-Dinitrop henylhydrazine Derivatives of Highly Oxygenated Carbonyl Compounds M. L.
WOLFROM and G.
P. ARSENAULT
Department of Chemistry, The Ohio State University, Columbus
V The chromatographic separation of 2,4-dinitrophenylhydrazine derivatives of highly oxygenated two- and threecarbon carbonyl compounds .effected on silicic acid-Celite.
1
N CONNECTION with
was
the ignition decomposition of cellulose nitrate (I@, i t was necessary to separate a complex mixture of 2,4-dinitrophenylhydrazine derivatives of short carbon chain (two and three carbon atoms) sugars and oxidation products thereof, without carbon fragmentation. The chromatographic separation of 2,4-dinitrophenylhydrazine derivatives of carbonyl compounds has been studied extensively
IO, Ohio
and detailed reviews have appeared (1, 4). The compounds of interest (Table I) are somewhat rare 2,4-dinitrophenylhydrazine derivatives. A thorough study of their chromatographic separation has not been reported, although the chromatographic properties of methylglyoxal bis(2,4--dinitrophenylhydrazone) (6, 8), glyoxal his(2,4-dinitrophenylhydrazone) @), hydroxypyruvaldehyde bis(2,4-dinitrophenylhydrazone) (8), and glycolaldehyde 2,kiinitrophenylhydrazone (10) have been recorded. Silicic acid has often been used to separate 2,4-dinitrophenylhydrazine derivatives. In the work herein reported, silicic acid was used and was
deactivated by the addition of water. This adsorbent, silicic acid-Celite (5 to 1; 8% water), was highly satisfactory for the separation of 2,4dinitrophenylhydrazine derivatives of highly oxygenated carbonyl compounds. A chromatographic adsorption series of the 2,4-&nitrophenylhydrazine derivatives is shown in Table 11, listed in descending order of adsorptive strength. The adsorptive strength of a compound was determined by the position of its adsorption zone after development with the given developer. Substanceswritten in a vertical sequence within a group are separable under the conditions specified, whereas those written in a horizontal sequence are not, VOL. 32, NO. 6, MAY 1960
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