the recovery of succinic acid n-as not significantly increased. The recovery of adipic acid \vas better than 99%. When all the nitric acid was eliminated by heating nithout spattering on the steam bath for 1 t o 2 hours after dryness n-as reached, the recovery of adipic acid was 100 the recovery of succinic acid r a s a t least 98 to 99%, and that of glutaric 95 to 96%. This shows the necessity of completely removing the nitric acid before chromatographing the samples. Copper. Copper is t h e metal catalyst used in largrst a m o u n t in the synthesis of adipic acid from cyclohexanone-cyclohexanol mixtures; hence its effect on t h e determination of t h e dibasic acids n a s investigated. A known solution of the three dibasic acids and copper nitrate in dilute nitric n-as prepared. Anal!-sis of this solution b:+. the extrusion method, after removal of the nitric acid by evaporation. shon-ed that tjhe copper reacted preferentially m-ith the succinic acid. The amount of succinic acid missinp corresponded exactly t o the amount nxessnry to foim copper succinate
(CuC+"IO,) with the knon-n amount of copper present. The amount of succinic acid retained by the copper was determined b y eluting with water the top portion of the column containing the copper salt and titrating the eluate t o a p H of 9.0, The amount of base required for the titration was equal to the amount of acid missing from the succinic acid eluate. This technique of eluting the upper or catalystrcontaining section of the column and reporting the acid found as succinic acid n-ould probably not be accurate in the case of actual oxidation samples because of the possible presence of other acids. T h e formation of copper succinate during analysis was prevented by adding a n amount of oxalic acid slightly in excess of that necessary to react with the copper. It was easily calculated because the copper catalyst concentration in oxidized mixtures was known. A stock oxalic acid solution, 12 mg. of acid per ml., was prepared, a n d 0.5-d. portions were used t o dissolve all the dried copper-containing samples. T h e
excess of oxalic acia which did not react with the copper was eluted behind the succinic acid. This oxaiic acid was separated from the succinic acid by carefully cutting the extruded column after streaking i t with indicator. When the gradient elution method was used with acid samples containing oxalic acid, the developing solutions used were 65 ml. of a 10% solution of 1-butanol in chloroform, 45 nd. of a 20yo solution of 1-butanol in chloroform, and 35 ml. of a 60yosolution of I-butanol in chloroform. LITERATURE CITED
(1) Bulen, W. A . , Varner, J. E., BurreU, R. c., ANAL.CHEU. 24, 187 (1952). ( 2 ) Hamblet, C. H., Mc.4levy, A. (to E. I. du Pont de Kernours & Co.), U. S.Patent 2,557,282 ( J u n e 19, 1951). ( 3 ) Marvel, C. S., Rands, R. D., J. Am. C h m . SOC.72, 2642 (1950). (4) Smith, E. D., Mueller, W. A., Rogers, L. N., ANAL.CHEK,.24, 1117 (1952). (5) Vandenheuvel. F . A., Hayes, E. R., I&., 24, 960 (1952).
RECEIYED for review October 30, 1958. Accepted June 1, 1959. Division of Analytical Chemistry, 133rd Meeting, ACS, San Francisco, Calif., April 1958.
Gas Chromatography Analysis of the Reaction Products from the Hydroformylation of isobutene G. W. WARREN, J. F. HASKIN, R. E. KOUREY, and V. A. YARBOROUGH Development Department, Union Carbide Chemicals Co., Division of Union Carbide Corp., South Charleston, W. Va.
b A gas chromatographic method was developed for the analysis of the reaction products from the hydroformylatim of isobutene, because conventional chemical techniques and other instrumental methods were not directly applicable or were too time-consuming. Of the 20 compounds obtained, 15 were present in concentrations greater than 0.1%. With the exception of two bands (2-methyl- and J-methylbutanol; 2-methyl- and 3-methylbutanal), most of the major components were completely resolved. The ratios of these branched alcohols and aldehydes were determined by mass spectrometric analysis of trapped sampies representative of the particular chromatographic band. The water content was obtained by a chemical method.
T
technique of gas chromatography developed b y James, Martin, and Phillips (4, 6, 7 , 9) has been used by many investigators (9) for HE
1624
0
ANALYTICAL CHEMISTRY
the separation and quantitative determination of members of homologous series (9, 6). T h e application of the chromatographic technique to the analysis of a complex mixture which is produced by the coP1-flame combustion of the hydrocarbons has been demonstrated by Menapace, Kyryacos, and Boord ( 6 ) . Gas chromatography has been used in this laboratory for the analysis of complex mixtsres, which normally are difficult t o analyze b y conventional techniques. A unique application of this technique has been the analysis of the crude reaction products from t h e hydroformylation of isobutene and other olefins. This mixture is composed of at least 20 components boiling between 20" and 176" C. Normally, mass spectrometric or chemical methods or both are used for the analysis of fractions after distillation. Bowever, the chromatographic method gives a more complete analysis, requires much less time, and is equally precise a n d accurate.
PROCEDURE
The Perkin-Elmer Model 154 Vapor Fractometer was used for all determinations. A column, consisting of phenvlI-naphthylamine absorbed on Celite No. 545 (100 to 120 mesh, liquid phase 30% by weight), 4 meters by 6.3 mm. in outside diameter, and operated at 100" C. n-ith a helium flow (measured a t the column outlet) of 100 cc. per minute, was used to effect separations. Each sample was scanned at full sensitivity prior to the quantitative determination. If the presence of components having a boiling point above 150" C. was suspected to be in the sample, p higher column temperaturei.e., 125" C.-was used, provided ad+. quate resolution of the other components was also obtained. Liquid samples (0.01 to 0.02 ml.) were introduced with a hypodermic syringe and a 1.6-cm. N o 27 hypodermic needle through a sihcone-rubber diaphragm into the stream of helium. The detector response wm recorded on a Bronm 0 to IO-mv. strip-citsrt recorder. The signal was attenuated bv a known factor to maximize each &flection on
the chart paper. The base line mas not changed when the signal was attenuated. The areas under the curves were measured with an O t t compensating polar planimeter. The area percentage of each chromatographic band was assumed to be approximately equivalent to the weight percentage. When desired, samples representative 3f the chromatographic bands containing the methyl-branched &arbon isomers of the aldehyde and alcohol were anslyzed mass spectrometrically for determination of the isomer ratio in the sample. The mater content of the watermethanol band was determined by use of the Karl Fischer reagent. Mass spectrometric analysis of samples representative of the chromatographic bands was accomplished by passing the chromatographic effluent at the appropriate time through a U-tube fabricated from 7-mm. borosilicate glass tubing enclosed with 2-mm. stopcocks and immersed in a Dewar flask Wed with liquid air. This trap contained a 10/30 female joint for connection to the m a s spectrometer inlet system.
Gas Chromatographic Determination of Recctian Products from Hydroformylation of isobutene Approximate iletention Time AIinimum Major Component Interval." .irea Detectable Present in Band Minutes ?ercentage Concn., P.P.N. .icetaldehyde 1.0-2 0 L7 20 m 4 Unidentified components Water and methanol 2 2-3 5 28 1 200 4.8-5 6 0 15 200 Ethyl formate 2,%Dirnethylpropanal 5.8-6 2 5 40 lo00 2-Butanol 64-67 0 26 2000 8.7-9.5 2.10 400 2,ZDimethylpro an01 %Methylbutanal 10.3-12.5 47.2 500 3-Methylbutanal 13 .&13.9 0.11 lo00 1-Butanol 2-Methylbutanol 18.2-21.0 13.6 roo bMethylbutano1) Table 1.
}
P
1,1,3-Trimethoxy-2-methylpropane
and/or isomers 23.S25.0 2.28 io0 I-Pen tanol 25.8-27.0 0.60 700 Indicates retention time variation from concentration changes in sample.
RESULTS AND DISCUSSION
A gas chromatographic analysis of the crude reaction product from the hydroformylation of isobutene is shown in Table I. A typical chromatogram is presented as Figure 1. The identities of the major bands were established by mass Spectrometric analysis of trapped samples representatiye of those peaks in the chromatogram. The unidentified bands represent less than 0.270 concentration in the original sample, and therefore, their identification was not considered necessary. The compounds having a retention time of 6 minutes (2,Zdimethylpropanal) and 11.2 minutes (%methylbutanal and 3-methylbutanal) were identified b y mass spectrometric structure studies because calibration standards were not available. T h e diflerences of fragmentation of these three isomers easily established their identity. These components are characterized by their unique mass-to-charge ratios. When the pure compounds were available, all identifications were confirmed by comparing the retention time for the pure material with that of the appropriate peak in the chromatogram of the sample. In some samples, the water content possibly could have been determined by extrapolation of the spur on the methanol peak; however, the Karl Fischer method was used because of its greater accuracy. The combined methyl formate and the methanol contents were determined b y subtraction of the water content from the area percentage of the water-methanolmethyl formate concentration. The methyl formate content was determ n e d b y mass spectrometric analysis
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Figure 1. Chromatogram of crude reaction product from hydroformylation of isobutene
of the trapped sample representative of the methanol-methyl formate band. The Zniethylbutanol and 3-methylbutanol contents were determined from a mass spectrometric determination of the isomer ratio and from the area percentage of that peak. Although these isomers differ by 1.9" C. in their boiling points, chromat,ogrzphic resolution was not obtained using phenyl1-naphthylamine as the liquid phnse. Using a &meter colunin a t IUO" C. with a helium flon' of 100 cc. per minute, the two isomers differed by only 0.5 minute in retention time; with other liquid phases such as didecyl phthalate and silicone oil (Dow Corning S o . 703) under similar conditions, the times differed by 0.2 to 0.3 minute. ?reh i n a r y experiments with Triol-230 (2.4-dimethyl-4-hydrox~;ethox3;methyl1,ci-pentanediol) as the liquid phme indicated that the two isomers differed by 1 minute in their retention times. Normally, a difference of 1 minute in retention time is adequate for the sep-
Table II. Precision of Chromatographic Method for Analysis Qf Unrefined Product from Hydroformylation of lsobutene
ihia.\rea
3lajor perComponent centPresentmBand age 0 2 Acetaldehq de Water ana 280 methanol Ethqiformate 0 2 2,ZDirnethylpropanal 5 9 2,ZDimet hylpropanol 2 1 %Methylbutanal> 47 3-Methylbutanal{
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