(Products of Hydrogenation of Carbon Monoxide)
OIL-SOLUBLE OXYGENATED COMPOUNDS D. G. CAIN Research Department, Stanolind Oil and Gus Co., Tulsa, Oklu.
A. W. WEITKAMP AND NORMAN J. BOWMAN Research Department, Standard Oil Co. (Indiana), Whiting, Znd. Oxygenated compounds in the oil stream produced by hydrogenation of carbon monoxide over an iron catalyst are higher homologs of those in the water stream. The main components are acids, alcohols, and carbonyl compounds of the aliphatic series. Yields of these classes decrease with increasing carbon number above five. At a given carbon number, the ratio of the molar quantities of each of the main components to the total molar quantity of oxygenated compounds and hydrocarbons is approximately constant. The alcohols appear to be more closely related structurally to the aliphatic hydrocarbons than are the acids. Branched isomers are more prevalent in the acids. Olefinic unsaturation and aromatic rings are present in some oxygenated molecules, but molecules containing two oxygenated groups have not been detected.
I
N THE extensive research of Fischer and Tropsch on hydro-
carbon synthesis, reaction conditions were investigated by which products were obtained ranging from predominantly oxygenated compounds t o predominantly olefinic hydrocarbon compounds ('7). I n the synthetic fuel processes, the oil-soluble oxygenated compounds were considered undesirable, and the formation of these compounds was minimized by the choice of reaction conditions. Thus, the process, as operated commercially with cobalt-thoria catalyst in Germany, produced low yields of oxygenated compounds (8). The nature of the oil-soluble compounds has not been extensively described in the literature, although it has been reported t h a t up t o about 1% of the products of one German plant consisted of C6 t o Clo fatty acids (11). The hydrocarbon synthesis process using iron catalyst, as developed in this country, typically yields a product in which about 18%.of the converted carbon monoxide appears as oxygenated organic compounds, distributed about equally between the oil and water streams (14). This paper deals with the identity and distribution of the several classes of oxygenated compounds present in the oil stream, with the distribution of acids and alcohols b y carbon number, and with the chain structures of these two classes. The classes of oxygenated compounds in the oil stream were determined by analysis for functional groups. The acids and alcohols, after separation from the oil stream, were investigated for carbon-number distribution and for chain structure. The distribution of aldehydes plus ketones was estimated from the concentration of t h e carbonyl groups in distillation fractions of the acid-free oil stream.
react with the phthalic anhydride reagent; whereas these compounds interfere in the acetic anhydride method (12). Total carbonyl content was determined by reaction between hydroxylamine hydrochloride and the carbonyl group in aldehydes and ketones. A mixture of equal volumes of carbonylfree isopropyl alcohol and 10% aqueous hydroxylamine hydrochloride solution was adjusted to a p H of 3.5, the sample was added, and the mixture was heated one hour a t 80OC. in a pressure bottle. The liberated hydrochloric acid was titrated potentiometrically with standard sodium hydroxide t o a p H of 3.5. Other compounds known t o be present in the oil stream did not interfere. Esters were determined by the conventional saponification procedure (19). The oil stream was stabilized through the butanes a n d was scrubbed with water a t a n oil-to-water ratio of about 2 before analysis. Water-soluble chemicals removed by the scrubbing were includedin the water stream analysis ( 1 3 ) . The composition of a typical oil stream produced in reactor D ( 1 4 ) is shown in Table I. The oil streams produced by this and other reactors ( 1 4 ) generally contained 25 t o 30 weight yo oxygenated chemicals. Carboxyl, hydroxyl, and carbonyl compounds were present in nearly equal amounts. Esters were minor components.
TABLE I. COMPOSITION OF OIL STREAM Functional Group, Meq./Gram Oil 0.664 0 740 0 886 0 1234
Estd. Weight % of Oil Stream
Acids 8.l a 8.0; Alcohols Aldehydes a n d ketones 9.4 Esters l.5d Hydrocarbons 73.0 Total 1oo.oa Average molecular weight of the acid was determined by measurement of t h e weight of sodium salt made f r o m a known molar quantity of acids. Estimated molecular weight = acid molecular welght - 1 4 . Estimated molecular weight = acid molecular weight 16. d Estimated molecular weight = acid molecular weight.
-
ACIDS. Isolation of the acids as a class was accomplished by treatment of the oil stream with aqueous sodium hydroxide. With solutions of 20 to 25 weight yo sodium hydroxide, over 99 mole yo of the acid was neutralized when the p H of the resulting salt solution was 10 f 0.5. Some nonacid chemicals and hydrocarbons, solubilized in the aqueous layer, were removed b y steam stripping. Organic acids were regenerated from t h e stripped salt solution by acidifying with sylfuric acid, a n d were washed with water t o remove residual sulfuric acid. The water-soluble acids remaining in the sodium sulfate solution and in the wash water were discarded. The distribution of the acids by carbon number was estimated by fractional distillation. Analyses of four samples produced a t various conditions of pressure and temperature ( 1 4 ) are presented in Table 11. The carbon-number distributions were similar. An average distribution in the CB t o CIOrange, calculated as moles of acid of a single carbon number per 100 moles of total
ANALYTICAL METHODS
FUNCTIONAL GROUPS. Acids were determined b y titration with standard sodium hydroxide to the phenolphthalein end point. A, homogeneous reaction mixture was maintained by addition of neutral isopropyl alcohol. Alcohols were determined by the phthalic anhydride method (6),which is particularly suited to oil stream analysis. Phenols, aldehydes, and high molecular weight organic acids do not
359
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TABLE 11. DISTRIBUTION O F OILSOLUBLE Carbon Sumber 2 3 4 5 6 7 8 0 10 11
Weight % of Total Acids Sample D-4 Sample D-5 0.0 0.0 1.6 2.3 11.6 15.8 18.1 17.8 14.8 16 6 13 0 11.3 0.7 0.0 7.2 5.8
Sample C - 3 0 0 1.0
4.6 14.0 18.3 15.2 12.2 8.5 5.7 3.8
...
1A
Residue Total
r7
. . ...
...
,.?
-4CIDS
16.7 __
0 6 2 2 13 4 I9 7 $7 9 13 8 9 7 6.8
.2
43 .. 24
23 6 __
100.0
Sample D-6
. .
9.0 100.0
100.0
~
15.9 100.0
Ca to Cl0 acid, is presented in Figure 1 and shows decreasing yields Ivith increasing carbon number above C S . Unsaturation was generally determined by bromine absorption ( 1) of the individual carbon-number fractions obtained by fractional distillation of the acids. I n sample D-2, the bromine absorption values were in good agreement with unsaturation values determined by quantitative hydrogenation over a platinum catalyst a t 25" C. and 1 atmosphere pressure. Sample C-3, which covered a higher molecular n-eigkt range, was esterified before distillation, and bromine absorption was determined on the ester fractions. The unsaturation values, plotted in Figure 2, increased with increasing niolecular weight. 30 r
I
@ ALCOHOLS CARBONYLS 20 ACIDS
s J W
0
I IO
0 3
4
5
6
7
a
9
10
CARBON NUMBER
Figure 1.
Distribution of Oil-Soluble Oxygenated Compounds
Type of unsaturation was investigated in the C7 to Cl0 and the CIS acid fractions. Terminal unsaturation in the C7 to Clo fraction was determined by a chemical procedure (3) t h a t involves treating the acid with potassium permanganate to form glycols, splitting of the glycols with periodic acid, and measuring colorimetrically the formaldehyde produced when terminal double bonds are present. The C15 fraction was examined by infrared analysis for the nontertiary terminal type double bond (RCH= CH,), which absorbs at 10.0 and 11.0 microns, and for the transinternal type (RCH=CHR'), which absorbs a t 10.35 microns. Terminal unsaturation accounted for about 12y0 of the total unsaturation in each acid fraction from C7 to Clo. I n the C15 fraction, nontertiary terminal double bonds accounted for about 10% and the trans-internal type for about 20% of the total unsaturation; the remainder was unidentified. Chain structures of the acids in the C4to Cs range were determined by examination of the distillation data. The normal isomer content of each carbon-number fraction was estimated on the assumption t h a t all branched isomers boil lower than the corresponding normal isomer b u t higher than the next lower normal homolog. These results, presented in Figure 3, show that the
Vol. 45, No. 2
normal-isomer content decreased with increasing molecular weight. Normal-isomer contents of the Cla and C17 fractions, determined by urea extraction ( 2 5 ) to be 167' and 12yG,rcspectively, were consistent with the results on fractions of lower molecular weight. Branched acids t h a t have been identified include isobutyric and the three monomethyl-branched six-carbon acids. Isobutyric acid was separated from n-butyric acid by distillation. Isobutyric acid comprised about 197' of the C , acids. The ethyl esters of the C Sacids were fractionally distilled, and three narrow boiling cuts were selected for further examination. Boiling points and refractive indices of these cuts are compared in Table I11 with appropriate literature values and values obtained with known compounds. The presence of the ethyl esters of 2- and 3-methylpentanoic acids and isocaproic acid is indicated. The infrared spectrum of cut A coincided in every detail with that of a n authentic sample of ethyl 2-methylpentanoate. The spectrum of cut C indicated the principal component to be ethyl isocaproate. The spectrum of cut B differed markedly from that of either A or C, and the melting points of the amide and anilide derivatives confirmed its identification as ethyl 3-methylpentanoate. The distillation data indicated t h a t 2-methylpentanoic acid was the most abundant of the three monomethyl-branchd isomers. The position of the side chains along the main carbon chain was investigated in five of the higher acids by means of an analytical method that depends on the influence of branching on the hydrolysis rate of amides. Branching in the 2 or 3 position exerts a depressing influence on the hydrolysis rate; branching in other positions has little effect ( 5 ) . The rates of hydrolysis were determined in boiling 1-propanol (0.415 N in potassium hydroxide and 0.068 M in the amide). Selected rate curves are shown in Figure 4. The amides of the branched-chain portions of the Cil and C17 acid fractions were hydrolyzed less rapidly than the amide of a typical straight-chain acid but more rapidly than a typical 2-branched amide, 2-ethylhexanamide. On the basis of these rate curves, i t was estimated that about BOO/;, of the branched CI1 acids and 7Oy0 of the branched c17 acids were branched in the 2 or 3 position. Similar results were obtained with the amides of C7, CI3,and C16acid fractions. Although the size of the branches is not known, i t is apparent t h a t branching occurs predominantly a t the positions near the carboxyl group. ALCOHOLS.The C s to Cs and CIOalcohols were separated from appropriate portions of acid-flee oil. The C8 to C, alcohols were isolated by the boratcestermethod(10)from a series of 50" C. distillation cuts of the oil. Other oxygenated compounds and hydrocarbons were removed by distillation, and the alcohols
0
A B
C - 3 ACIDS D - 2 ACIDS ALCOHOLS
INDUSTRIAL AND ENGINEERIN G CHEMISTR Y
February 1953
were regenerated by hydrolysis of the residual borate esters. The decanols were isolated as the benzoate esters b y a similar procedure, except that the benzoate ester was separated from high boiling condensation products by vacuum distillation. IO0
90
v)
a
0o
w
I
8 '10 za
0 I
rl
- 60
a
a
36 1
decenols. These results are plotted in Figure 2 with the data on acids. The chain structures of the alcohols in the Cq t o Cs range were examined by distillation, and in the Cl0 fraction by urea extraction. The Cq alcohols contained about 8% of 2-methyl-1-propanol (IS). I n the Cb fraction, 2-methyl-1-butanol and 3-methyl1-butanol were present in almost equal amounts ( I S ) . From the distillation curves of several C6 to CSalcohol mixtures, the relative amounts of normal and branched isomers were estimated on the assumption that branched isomers boil lower than the corresponding normal isomer but higher than the next lower normal homolog. The precision of this method is limited by the increasing spread in boiling ranges as the number of possible isomers increases and by the fact t h a t some secondary alcohols boil in the range of the next lower primary alcohol. The Clo fraction was found by urea extraction to contain about 46y0 of straight-chain alcohols. The straight-chain alcohol contents are plotted in Figure 3 as a function of carbon number.
Iv) -
#
B
50
40 40
I
I
4
6
I
e
IO
CARBON NUMBER
8 3
N
Straight-Chain Isomer Content of Alcohols a n d Acids
Figure 3.
30
4 > 0
r
The distribution of the alcohols by carbon number was estimated by a combination of fractional distillation of the isolated alcohols and determination of hydroxyl groups in oil fractions. The results of a typical analysis are presented in Figure 1. Beyond five carbons the yields of alcohols decreased steadily.
20
10
TABLE 111. IDENTIFICATION O F BRANCHED SIX-CARBON ACIDS Properties Ethyl eaters Isolated Boiling point, C. Refractive index, Synthesized Boiling point, C. Refractive index. nZno Derivatives Amide m p C. Detchm'inLd Literature Anilide, m.p.. C. Determined Literature (9)
nso
,
(E)
a
Y
2-Methylpentanoic Acid, Cut A
3-iMethylpentanoic Acid, Cut B
Isooaproic Acid, cut c
0 0
159-159.1 1.4055
160.6-161.8 1.4061
153,5-154 1.4032
157-15W 1.4054
161.4-161.7 1.4060
...
122-123 124.9
iii:o
...
84,645.2 87.0
iii'
79.6
92.5
($1.
Secondary alcohols are a minor proportion of the synthesis alcohols. The Ca alcohols included about 20 weight yo 2-propanol ( I S ) . 2-Butanol was present in both the water and oil streams and, based on infrared analysis, made up about 3 t o 5y0 of the C d alcohols. 2-Pentanol was identified in alcohol concentrates by mass spectrometry. The decyl alcohols were separated by urea extraction (16)into straight-chain and branched-chain portions; a maximum secondary alcohol content of 7y0 in the straight-chain portion was estimated by acetylation and urea extraction of the linear primary n-decyl acetate from the nonlinear secondary n-decyl acetate. Unsaturation in the five- and 10-carbon alcohols was determined by bromine absorption ( I ) . The c6 alcohols contained 1 t o 3% pentenols and the Clo alcohols contained about 20y0
e T I M E , HOURS
Figure 4. 154.9-156.3 1.4038
4
Hydrolysis Rates of Amides
OTHERCLASSES. Carbonyl compounds occurred throughout the boiling range of synthesis product. Their distribution, estimated from the carbonyl content of distillation fractions of the oil stream and presented i n Figure 1, was similar t o the distributions of the acids and alcohols. Attempts were made t o differentiate quantitatively between aldehyde and ketone in the oil stream by means of addition, condensation, or oxidation reactions, but no satisfactory procedure was developed. Chain structures of the higher aldehydes and ketones have not been examined. Cyclic ketones-cyclopentanone, 2-methylcyclodetected in the pentanone and 3-methylcyclopentanone-were water stream ( I S ) ; the oil stream may contain higher homologs. Esters are known to occur in the oil stream. Phenols have been detected by ultraviolet absorption. Neither dibasic acids nor acids containing hydroxyl or carbonyl groups were detected, but oxygenated compounds containing aromatic structures ( 4 ) or unsaturated linkages were present. Olefin types in a mixed alcohol-carbonyl cut obtained by silica gel percolation of a n acid-free C16 to CSO product were investigated by infrared analysis. Total unsaturation could not be determined by bromination because of the presence of aldehydes. The ratio of nontertiary terminal double bonds t o trans-internal double bonds was about 0.5, on the basis of the relative intensities of absorption bands characteristic of these configurations.
INDUSTRIAL AND ENGINEERING CHEMISTRY
362
UISTKIBUTION PATTERN
The characteristic distribution pattern of the oil-soluble oxygenated compounds, shown in Figure 1, is due t o t h e water solubility of the lower homologs and decreased yields of the higher homologs. The decrease approximately parallels the decreasing yields of the corresponding hydrocarbon fractions ( 1 4 ) . Thus, the molar proportions of hydrocarbons, alcohols, acids, and carbonyls are about constant throughout the range studied. IO0
10
ae J w
Q
z
Vol. 45, No. 2
and hydrocarbons. As shown in Figure 3, the content of normal isomer diminishes more rapidly with increasing carbon number in the acids than in the alcohols. The branching is not evenly distributed, as in the branched hydrocarbons ( 1 4 ) ,but is largely concentrated near the carboxyl group. However, the acids resemble the alcohols in the distribution by carbon numbereppecially the high yield of the CZ homolog-and in the degree of unsaturation of the carbon chains of corresponding homologs. These similarities and differences suggest t h a t the homologous acids are related t o the corresponding homologous alcohols, but that a separate reaction introduces additional branching into the acid structure near the carboxyl group. Knowledge of the olefin types in the oxygenated compounds is limited t o terminal type in the Cjr t o C ~ O acids, and to the terminal and trans-internal types in a CIS acid and in a mixed alcohol-carbonyl cut of broad molecular weight range. In t,he latter two cases, the observed 0.5 ratio of terminal to trans-internal unsaturation is of a higher order of magnitude than the equilibrium ratio at synthesis temperature for chains of this length. Perhaps the unsaturation was originally in the terminal position, but, as in the case of the aliphatic olefins, was subsequently isomerized t o internal positions.
1.0
coNcLUsIos
The oxygenated compounds in synthesis product are related, structurally and distributionally, to each ot,her and t o t,he aliphatic hydrocarbons. 0.1
I
I
I
I
I
2
4
6
8
10
I
CARBON NUMBER
Figure 5 .
*
Distribution of Acids and Alcohols
Composite distribution curves for oil stream and water stream alcohols a n d acids are compared in Figure 5 with the distribution curve for total hydrocarbons. The similarity of oxygenated compound and hydrocarbon distributions above C , contrasts with the disparity at Cz. T h e low yield of Cz hydrocarbons is largely compensated by high yields of ethanol, acetic acid, and acetaldehyde. The ketone series, and possibly also the secondary alcohol series, show disproportionately high yields of the Ca homolog ( I S ) . These observations suggest a generic relationship among ethanol, acetaldehyde, acetic acid, acetone, and 2-propanol. The structures of the alcohols resembIe the structures of the corresponding aliphatic hydrocarbons. The content of straightchain isomer in alcohols, shown in Figure 3, is about the same a8 the straight-chain isomer content of the aliphatic hydrocarbons ( 1 4 ) over the range examined. Furthermore, distributions of the methyl-branched isomers of the 1-alcohols ( 1 9 ) and 1-olefins ( 1 4 )in the C, and C j groups are similar. These observations suggest t h a t 1-alcohols and 1-olefins are closely associated in the synthesis reaction mechanism. T h e structures of the acids differ from those of the alcohols
LITERATURE CITED
Soc. Testing Materials, Standards on Petroleum Products, Committee D-2, Y e a r Book, 1949, p. 1359. (2) Bentley, W.H., J.Chem. SOC., 67, 264 (1895). ( 3 ) Bricker, C. E., and Roberts, K. H., A n d . Chem., 21, 1331 (1949). (4) Cady, W.E., Launer, P. J., and Weitkamp, A. W., IXD.ENG. CHEM., 45,350 (1953). (5) Cason, J., and Wolfhagen, H. J., J . Org. Chem., 14, 155 (1949). ( 6 ) Elving, P. J., and Warshowsky, B., ANAL. CHEM.,19, 1006 (1947). (7) Fischer, F., and Kuster, H., B r e n m t o f f - C h e m . , 14, 3 (1933). ( 8 ) Gordon, X., et al., “Report on the Petroleum and Synthetic Oil Industry of Germany,” BIOS Over-All Rept. 1, London, His Majesty’s Stationery Office (1947). (9) Huntress, E. H., and Mulliken, S. P., “Identification of Pure Organic Compounds,” pp. 193-4, Sew York, John Wiley & Sons, 1941. (10) Nametkin, S.S., and Zvorykina, V. K., J . Den. Chem. ( U . S . S . R . ) , 4, 906 (1934) ; iVat2. Petroleum S e w s , 3 6 , R-702 (1944). (11) Reichl, E. H., “Synthesis of Hydrocarbons and Chemicals from CO and Hz,” U.S. Naval Mission in Europe, R e p t . 248-45 (1945). (12) Siggia, S., “Quantitative Organic Analysis via Functional Groups,” pp. 4, 24, New York, John Wiley & Sons, 1949. (13) Steitz, A . , Jr., and Barnes, D. K . , IND.ENQ.CHERI.,45, 353 (1953). (14) Weit,kamp,A. W . , Scelig, H. S., Bowman, N. J . , and Cady, 1%’. E., I b i d . , 45,343 (1953). (15) Zitnmerschied, W. J., Dinerstein, R. A , , Weitkamp, A. W., and Marschner, R. F., Ibid., 42, 1300 (1950). (1) Am.
RECEIVED for review January 2 , 1952.
ACCEPTEDSeptember 8, 1932.
