Thermal Polymerization of Ethvl Eleostearate and 9,ll- and 9,lZ-Ethy1 Linoleate J
J
T
HE reaction of primary imJOHN S. BROD, WESLEY G. FRANCE, double bonds. The compounds p o r t a n c e i n t h e thermal chosen were the ethyl esters of aAND WM. LLOYD EVANS polymerization of drying oils eleostearic acid from tung oil and The Ohio State University, Columbus, Ohio is probably one of intermolecular the 9.11- and 9.12-linoleic acids attachment between two or more obtained from the dehydration of glyceride molecules a t the double-bond systems of their unricinoleic acid derived from castor oil. Their chemical saturated acid chains. In order to study the manner in which formulas are as follows: this intermolecular attachment of unsaturated acid chains Ethyl eleostearate or 9 11,la-ethyl octadecatrienate: occurs, it is advantageous to work with the monohydric alcohol C H ~ ( C HCH=CH-~H=CH-CH=CH ~)~ (CHJ~COOC~H~ esters of these acids, since di- and trihydric alcohol esters 9,ll- and 9,12-ethyl linoleates or 9,ll- and 9,12-ethyl octapermit the formation of complex linear and three-dimendecadienates: sional polymers by interesterification. I n the past decade CH,(CHz),CHzCH=CH-CH=CH (CH2);COOCzHs CHI(CHZ)~CH=CH-CH~-CH=CH (CHz);COOC2Hs considerable progress has been made towards the elucidation of the mechanism of this primary polymerization reacThe mixed linoleic acids are found in several cofimercial syntion (8, 9, 10, 12, 13, 16, 16, 17). Nevertheless, much more thetic drying oils. systematic experimentation is necessary before the final goal can be achieved. Preparation of Compounds The purpose of this research was to investigate the highPurified ricinoleic acid obtained from castor oil was detemperature polymerization of the monohydric alcohol esters hydrated according to the method of Boeseken (1) by heating of the principal acids of drying oils which contain conjugated it with activated alumina and distilling in vacuo. The linoleic acids thus obtained distilled a t 202-208 " C. under 0.5 mm. pressure, and at 228-234" C. under 16 mm. pressure. A.Refracti$e Index 1 They were esterified by refluxing for 4 hours with absolute Time of Polymerization ethyl alcohol containing 1 per cent concentrated sulfuric acid. , After the reaction mixture was washed with salt water and l sodium carbonate solution in the usual manner to remove free acid, the ethyl linoleates were distilled a t 100-110" C. in a Hickman high-vacuum still ( 5 ) . Only the clear colorless middle portion was used in the later polymerization experiments. Iodine values were determined by the standard Wijs procedure with a reaction time of 4 hours. In view of the known failure of iodine values t o give a correct indication of the number of double bonds present in either compounds containing conjugated double bpnds or their polymers (14), the iodine values recorded should be interpreted as indicating whether the relative degree of unsaturation has increased or decreased upon polymerization. Diene values were determined by a modification of the method of Ellis and Jones (4): Samples of 0.2-0.3 gram were refluxed with 25 cc. of 1 per cent maleic anhydride in toluene solution, and the excess maleic anhydride was titrated with 0.2 N potassium hydroxide. Recently boiled water was used. The diene values were checked within 1 per cent.
100
The following constants were determined: nz: 1.4663, d$O 0.8796, acid value < 1, saponification value 182.0 (theoretical, 181.9), iodine value 105, diene value 28. These data indicate that the mixed ethyl linoleates used in these polymerization experiments contained from 30 to 50 per cent of the 9,11linoleic acid. a-Eleostearic acid which had been prepared by saponification of tung oil was twice recrystallized from 90 per cent alcohol and esterified in the above manner. The ethyl eleostearate distilled between 105" and 115" C. in the Hickman still, the portion retained for the polymerization experiments being the clear colorless middle fraction. Its constants were:
mi
B.Averaye Molecular Weight Time o f Polymerization I
0;
4
I
1
1
8 R /6 H o u r s o f H e a t i n g a t 30OoC.
I
20
FIGURE 1. EFFECT OF POLYMERIZATION PERIOD ON (A) REINDEX AND ON ( B ) AVERAGE MOLECULAR WEIGHT
FRACTIVE
114
JANUARY, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
--
DETERMINED AFTER VARIOUSTIMES TABLEI. CONSTANTS Heating Time a t
300'
Ethyl Oleate n"n"
---so
Ethyl Linoleate
__h-
Mol.
wt.
n
Mol. Wt. 315
0 min. 1.4603 295 1.4663 5 min. .... ... ..... . .. 10 min. 1,4501 .. . 1.4667 . .. 1 hr. 1.4500 ... 1.4672 380 5 hr. 1.4503 . . 1,4703 500 10 hr. 1.4512 330 1.4722 570 12 hr. .... . 1.4730 560 20 hr. . , 1.4740" 520 a These data were checked by making duplicate taining 0.02 per cent hydroquinone as an antioxidant.
....
. .. .
Ethyl Eleostearate
Mol. nso Wt. 1.5052 310 1.4916 440 1.4881" 490 1.4868 510 1.4868 505 1.4877 480 1.4880 500 1.4892a 465 runs with esters con-
nz: 1.5052, d:' 0.8936, acid value:l, sapon5cation value 183.3 (theoretical, 183.1), iodine value 152, diene value 66. At all times during their preparation the esters were kept under a blanket of carbon dioxide. Also, both they and their polymers were stored under carbon dioxide in the dark.
115
was given off and some foaming occurred. When a high vacuum had been attained, the only distillation which took place between room temperature and 160" C. was in exactly the ranges in which the pure unpolymerized esters distilled-namely, between 100" and 115' C. The amounts of distillate and residue were determined by weighing the still when empty, when filled, and after distillation. The data obtained on the polymerized mixtures, the distillates, and the residues are summarized in Table I1 and presented graphically in Figure 2. In order to ascertain how much the development of free fatty acid in the polymerized mixture was affecting the refractive index, the 12-hour ethyl eleostearate polymer was washed with alkali according to the method of Jamieson (6). The removal of the free fatty acid by this treatment resulted in a drop of the refractive index from 1.4945 to 1.4922.
Ultramicroscopic Examination
Ten per cent solutions of both pure ethyl eleostearate and its 10-minute polymer in absolute alcohol were examined in the Cardioid ultramicroscope. X o moving particles could For orientation z)urposes samples of commercial tung oil be detected, although the low viscosity of the solutions and the and a dehydrated'castor oil were large difference in refractive index heated in open Pyrex test tubes between solute and solvent provided at 300" C. The refractive index the most favorable conditions posof the tung oil dropped, and gelasible for the detection of any partion occurred in 8 to 9 minutes; ticles of colloidal dimensions which A comparison has been made the refractive index of the dehymight have been present in the of the polymerization of ethyl drated castor oil increased, and solutions. esters of eleostearic acid from gelation developed in approximately tung oil and the mixed 9,1190 minutes. 9,11- and 9,12-Ethyl LinoTwo cubic centimeter samples and 9,12- linoleic acids which leates of each of the esters in sealed Pyrex occur in dehydrated castor flasks evacuated to 0.5 mm. of The fact that polymerized monooils. The purified esters were mercury were heated in a nitratehydric alcohol esters of unsaturated polymerized at 300" C. for vanitrite bath a t 300" * 5" C. for fatty acids remain liquid, regardrious lengths of time up to 20 periods of 10 minutes to 20 hours. less of the time of polymerization, Ethyl oleate, obtained by alcohours, after which the monomakes it possible to study the holysis of olive oil, was included in changes which take place at their mer was separated from the the series as a control. The ethyl double bonds for polymerization polymer by high-vacuum dissleostearate turned deep yellow times corresponding to and greater tillation. within 10 minutes a t 300" C.; than that necessary for gelation of In both cases after polythe mixed ethyl linoleates became the triglycerides. yellow only after 12 hours of heatmerization the monomer was Thermal polymerization of the mixed 9,11- and 9,12-ethyl linolenot identical with the original $g, Ethyl oleate did not change m appearance. The constants deates is accompanied by a gradual ester, which indicated that termined after the different times increase in refractive index (Table some isomerization occurred are summarized in Table I and I and Figure 1A). I n this respect as well as polymerization. graphically presented in Figure 1. it closely resembles the polymeriMolecular weights were determined Molecular weight determinazation of pure 9,12-ethyl linoleate by the Itast camphor method acwhich was studied by Steger and tions in camphor indicate that cording to the procedure outlined van Loon (17). For example, they the polymers were dimers. by Kamm (7). Approximately 20 found that 9,12-ethyl linoleate In both cases an apparent mg. of the material and ten to fifwhich had been polymerized a t equilibrium between monoteen times its weight of resublimed 300" C. for 14 hours had a refracgum camphor were used. Determer and polymer was reached tive index (n") of 1.4747. Figure minations on the pure ester and IA shows that after 14-hour polyafter about three-fourths of duplicates indicated that the results merization a t 300" C., mixed 9,11 the weight of original ester are accurate to within * 10 units. and 9,12 esters have a refractive had polymerized. The time The polymerization of larger index of 1.4737. This is a striking required to reach this equilibamounts of the esters was repeated agreement which indicates that under the same conditions as the rium was considerably greater both the 9,11- and the 9,12-linoleabove, and the unpolymerized maates probably polymerize to the than that required for the terial then separated from the polysame product. This may be accorresponding triglycerides to mer by high-vacuum distillation. counted for by the assumption ge€ at the same temperature. As the pressure was reduced in that the first step in the polythe still a t room temperature, a merization of 9,12-ethyl linoleate is small amount of volatile matter an isomerization to the 9,11 isomer,
Polymerization Experiments
INDUSTRIAL AND ENGINEERING CHEMISTRY
116
VOL. 31, NO. 1
, TABLE11. POLYMERIZATION AT 300' C. Heating Time
Fraction
Per Cent
Mol.
wt.
n %o
d;"
Acid Value
Wijs Iodine Value (4 Hr.)*
Diene Value
Appearance
Mixed 9.11- and 9,lP-Ethyl Linoleates 0
1 hr.
12 hr.
20 br.
Original ester
100
308
1,4663
0 8796
1
28
105
Thin, colorless oil
Distillate Residue
74 26
380 340 600
1.4672 1.4646 1.4765
.... ....
..
..
...
...
Colorless oil Same as original Viscous, faint yellow
D'istiiiate Residue
26 74
315 680
...
1.4730 1.4610 1.4794
...
Colorless Same as original, turned yellow on standing Pale yellow, viscous
riistiiiate Residue
26 74
..
520 315 580
Pure ester
100
..
.....
..
....
....
..
0.870 0.936
15 30
1.4740 1.4610 1.4800
....
.. ..
306
1.5052
0,8936
490
.... ....
..
0.950
..
.... ....
..
....
..
2 2
.
...
I
1
0.3
120 75
..
...
..
.......
..
... ...
66
152
Thin, colorless oil
..
, . .
'3
103
...
Yellow Same as original Yellow
77; 63
Deep yellow Same as original Viscous, yellow
Same as original, turned amber on standing Viscous, yellow
Ethyl Eleostearate 0 10 min.
1 hr.
12 hr.
20 hr.
rii$tiiiate Residue
40 60
... ...
1.4890 1.4885 1.4905
D'isliiiat e Residue
28 72
510 310 570
1.4868 1.4795 1.4915
30 70
500 340 610
1 ,4880 1.4805 1.4945
....
25 75
465 280 540
1.4892 1.4804 1,4954
0,925 0,977
.....
Distillate Residue
.....
Distillate Residue
0,913
.... ....
....
1
..
2 2
31
... ... ... ... ...
, .
..
..
15 30
..
.. ..0
*.
..
37
56
...
Yellow Same as original, turned yellow on standing Viscous, yellow Yellow Same as original, turned amber on standing Viscous, yellow
a Theoretical iodine values for ethyl esters of 18-carbon unsaturated fatty acids are: 1 double bond 82, 2 double bonds 165, 3 double bonds 249.
and that in both cases the polymer of 9,ll-ethyl linoleate is finally formed. Such a theory of isomerization of isolated double bonds to conjugated positions preceding polymerization is not new (IS). It is well known that compounds containing conjugated double bonds polymerize more readily than isomeric compounds in which the double bonds are isolated. Consequently the 9,ll-ethyl linoleate would be expected to polymerize more readily in the mixture, so that the unreacted monomer should be chiefly 9,12-ethyl linoleate. This was found to be the case, as shown by the constants in Table I1 of the monomeric distillate from polymerized 9 , l l - and 9,12-ethyl linoleates. The distillate had practically the same refractive index as pure 9,12-ethyl linoleate (~8: 1.4608) and, as shown by its negligible diene value, no longer contained conjugated double bonds. The residual polymer of the mixed ethyl linoleates was chiefly a dimer. The higher molecular weight found for the 12-hour polymer may have been due to copolymerization of some decomposition products with the ester polymer. In agreement with this possibility is the observation of Steger and van Loon (17) that the mean molecular weight of the polymer building unit, which they determined from saponification values, is 340 after 14-hour polymerization a t 300" C. The lower molecular weight of the polymer after 20-hour polymerization is difficult to reconcile with this hypothesis, however, unless the decomposition products of lower molecular weight are split off from the polymer molecules upon continued heating a t 300" C. The three possible types of dimer of 9,ll-ethyl linoleate which could result from intermolecular attachment a t the double bonds contain four-, six-, and eight-membered rings, respectively. A study of these possible structures by means of Mack's molecular models (11) showed that the six-membered ring is the only one which is likely to be formed; that is, dimerization of 9,ll-ethyl linoleate probably occurs by a modified Diels-Alder type of reaction (8) I
Ethyl Eleos tearate The rapid change in the constants of the monomeric distillates from the constants of pure ethyl eleostearate (Table 11) indicates that some isomerization takes place simultaneously with polymerization, and that both occur rapidly a t 300" C. The type of isomerization which occurs is uncertain, although it undoubtedly involves the three conjugated double bonds in ethyl eleostearate. The changes in refractive index, density, and iodine value which had occurred after 1 hour a t 300' C. are in accord with those which would be expected to take place if isomerization to the ester of 5butyl-1,3-cyclohexadiene-6-caprylic acid occurred as Rossman suggested (12)- However, the diene values are not in Refractive Index- Time of Polymerization /.4800
.........................................................
4
8
..............................................
/2
/6
20
H o u r s o f H e a t i n g a i 30OoC.
FIGURE2. EFFECTOF POLYMERIZATION ON REFRACTIVE INDEX OF POLYMERS, MIXTURES, AND MONOMERS agreement with this hypothesis. For the cyclic isomer postulated still contains conjugated double bonds and should have the same diene value as the original ethyl eleostearate, assuming that maleic anhydride reacts with a substituted 1,3-
JANUARY, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
cyclohexadiene as readily as with conjugated double bonds in a straight chain. Even if this assumption is not justified, the problem of explaining the continued decrease in the diene value to zero still remains. Apparently some unknown change takes place in the unpolymerized monomer upon continued heating which does not appreciably change the refractive index and does not cause the double bonds completely to disappear, but which does destroy the conjugation of the double bonds or prevent their reaction with maleic anhydride. Molecular weight determinations showed that the residual polymer of ethyl eleostearate was, a t most, dimeric regardless of the time of polymerization. The small increase in refractive index of this dimer with time is paralleled by an increase in acid value. The drop in refractive index of the dimer which resulted after an alkaline wash shows that the gradual change in constants of the polymers upon prolonged heating is a t least in part due to the formation of free acid by pyrolysis of the ester linkage. Consequently the constants of the 10-minute polymerization residue should probably be taken as most characteristic of the ethyl eleostearate dimer. Since ethyl eleostearate contains three conjugated double bonds, the possible types of dimers which could be formed by intermolecular attachment a t the double bonds contain four-, six-, eight-, ten-, and twelve-membered rings. Construction of all these possible forms with Mack's molecular models (11) and consideration of ease and probability with which the rings could be formed show that in this case also only the six-membered ring is likely to be formed without excessive strain due to deformation of bond angles or steric interference of peripheral hydrogen atoms. This dimeric structure containing a six-membered ring would be formed in the manner of a modified Diels-Alder reaction as first suggested by Kappelmeier (8): CHs (CHa)aCH=CH-CH-CH-CH=CH-(CH&COOC2Hs
I
CHa(CHn)aCH=CH-bH
\
\ d6H(CH2)iCOOC~Hj
CH= H
The theoretical molecular refraction for this formula is 186.2; that calculated for the 10-minute dimer is 186.4. If the dimer contained a twelve-membered ring as suggested by Rossman, its molecular refraction should be 185.6, according to his calculations. However, the other observed data on the ethyl eleostearate dimer and the evidence from the construction of molecular models shows that Rossman's hypothesis of dimerization is untenable. Eisenlohr's values for atomic refractions (3) were used in the Lorenz-Lorentz formula for calculating the molecular refraction; no increment was assumed for the cyclohexene ring structure. Rossman also used Eisenlohr's values with the additional assumptions that the two pairs of conjugated double bonds in the ring would show no exaltation, and that the twelve-membered ring structure would have an increment of -0.6. The data in Table I1 show that in polymerization of both 9,11- and 9,la-ethyl linoleates and ethyl eleostearate, the ratio of monomer to dimer becomes constant when approximately 25 per cent monomer and 75 per cent dimer are present. This corresponds to a molar ratio of 2 monomer to 3 dimer. This apparent equilibrium is not reached until after almost 1 hour of heating a t 300" C. in the case of ethyl eleostearate and about 5 or 6 hours in the case of the ethyl linoleates. In both cases the time required for equilibrium between ' monomer and dimer to be attained is much longer than the time required for gelation of the corresponding triglycerides. If the percentage of polymer in the polymerized mixture is plotted against time of polymerization, a t the time corre-
117
sponding to gelation of tung oil (8-9 minutes) approximately 50 per cent of the ethyl eleostearate has polymerized. Similarly, approximately 50 per cent of the mixed ethyl linoleates had polymerized in the time (1.5 hours) required for gelation of the dehydrated castor oil. This is in agreement with the results of Steger and van Loon (16); they found that, by conversion of both gelled tung oil and gelled linseed oil to their ethyl esters and subsequent separation of monomer from polymer, approximately 50 per cent of the acid chains in the glyceride molecules had polymerized through intermolecular attachment a t the double bonds. Fifty per cent polymer corresponds to two monomeric acid chains to each dimeric acid chain. In other words, gelation of polymerized drying oils occurs when approximately half of the acid chains have united to form dibasic acids by intermolecular attachments a t the double bonds, or before the maximum possible number of intermolecular attachments have occurred. Not all the glyceride molecules need be united in one complex threedimensional structure a t gelation; there may be considerable amounts of unpolymerized or low polymers of glyceride molecules which are completely enmeshed by the larger threedimensional polymers in a brush-heap manner, so that the gel structure as a whole is semirigid. The fact that no particles could be detected upon ultramicroscopic examination of ethyl eleostearate polymer in alcohol solution showed that no high polymers or colloidal aggregates of ethyl eleostearate had been formed. This is in agreement with the molecular weight evidence that only dimers were formed. These results are consistent with the modern theory of polymerization of the esters of unsaturated fatty acids as recently outlined by Bradley (2). The entire unsaturated systems of drying-oil fatty acids offer only one potential point of intermolecular attachment or, in other words, have a polymeric functionality of only one. Consequently monohydric alcohol esters can result in the formation of only dimers (dihydric alcohol esters in linear polymers), whereas only tri- and polyhydric alcohol esters (e. g., drying oils) can form the complex three-dimensional polymers necessary for film formation.
Conclusions
1. Polymerization of mixed 9,ll- and 9,12-ethyl linoleates yields a product which is chiefly a dimer, although some higher polymers may also be formed. An apparent equilibrium between monomer and polymer is reached after about 5 hours of polymerization a t 300" C.; the equilibrium proportions of 26 per cent monomer and 74 per cent polymer correspond to a ratio of two molecules of monomer to three molecules of dimer. The unchanged monomer a t equilibrium is composed chiefly of 9,12-ethyl linoleate, the proportion of the conjugated ester present being much less than in the original mixture. Polymerization of 9,12-ethyl linoleate probably first involves isomerization to 9,ll-ethyl linoleate which then polymerizes to a dimer. 2. The polymer of ethyl eleostearate is exclusively dimeric and probably contains a six-membered hydroaromatic ring. Equilibrium between the monomer and dimer of ethyl eleostearate is reached in slightly less than an hour a t 300" C.; the equilibrium proportions are 27 per cent monomer and 73 per cent dimer, which correspond approximately to the ratio of two molecules of monomer to three molecules of dimer. During polymerization, some isomerization of ethyl eleostearate occurs also, probably to a cyclic form. At equilibrium the unchanged monomer consists chiefly of the isomeric form of ethyl eleostearate. Although equilibrium is reached in the amount of monomer present in the polymerized mixture, some change in this monomer continues to take place
118
INDUSTRIAL AND ENGINEERING CHEMISTRY
upon continued heating until no more conjugated double bonds are present. 3. Gelation occurs in the triglycerides of the higher unsaturated fatty acids before the maximum possible number of dibasic acids have been formed by intermolecular attachment a t the double bonds. 4. Ultramicroscopic examination of polymerized ethyl eleostearate in alcohol solution shows that no aggregates of the dimers or higher polymers of colloidal dimensions are formed.
(2) (3) (4) (5) (6) (7)
(8) (9) (10) (11) (12) (13)
Acknowledgment The authors express their appreciation to the Procter and Gamble Company, whose grant of the Procter and Gamble Fellowship for 1936-37 to John S. Brod greatly facilitated this investigation.
(14) (15) (16)
Literature Cited
(17)
(1) Boeseken, J., and Hoevers, R., Rec. trav. chim., 49, 1161, 1165 (1930).
VOL. 31, NO. 1
Bradley, T. F., IND.ENG.CHEM.,29, 440, 579, 1270 (1937). Brooks, “Nonbenzenoid Hydrocarbons,” p. 551 (1922). Ellis, B. A., and Jones, R. A., Analyst, 61, 812 (1936). Hickman, K., and Sanford, C. R., J . Phys. Chem., 34, 637 (1930). Jamieson, G. S., “Vegetable Fats and Oils,” p. 401 (1932). Kamm, “Qualitative Organic Analysis,” 2nd ed., pp. 131-2 (1 936). Kappeimeier, C. P. A., Farben-Ztg., 37, 1018, 1077 (1933). Kino, K., Szi. Papers I n s t . Phys. Chem. Research (Tokyo), 20, 103-8 (1933); 26, 91-7 (1935). Kurz, H., Fdtte u. Seifen, 43, 184 (1936). Mack, E., S.Am. Chem. Soc., 56, 2757 (1934). Rossman, E., Fettchem. Umschau, 40, 96, 117 (1933). Scheiber, J., Farbe u. Lack, 1929, 586, 1936, 315, 329, 341, 351, 361; Fette u. Seifen, 43, 103 (1936). Steger, A,, and van Loon, J., Rec. trav. chim., 51, 648, 996 (1932). Ibid., 53, 769, 860 (1934); 54, 428, 750 (1935); Fettchem. Umschau, 42, 217 (1935), 43, 17 (1936). Steger, A,, snd van Loon, J., Rec. trav. chim., 53, 769, 860 (1934). Ibid., 54, 756 (1935).
RECEIVED May 26, 1938.
Action of Mineral Acids on Primary
Convenient and economical procedures have been developed for the preparation of acetic, propionic, butyric, and isobutyric acids in good yields from the corresponding primary nitroparaffins by refluxing them with 85 per cent sulfuric acid. Hydroxylamine acid sulfate is a by-product of the reaction. Propionohydroxamic acid has been prepared from 1-nitropropane and concentrated sulfuric acid in fair yield.
J
Nitroparaffins’ S. B. LIPPINCOTT2AND H. B. HASS Purdue University and Purdue Research Foundation, Lafayette, Ind.
R
ECENT researches a t Purdue University (6)have made available the nitro derivatives of methane, ethane, propane, butanes, pentanes, and other hydrocarbons. An interesting reaction common to the primary nitroparaffins is their conversion to fatty acids and hydroxylamine salts by the action of mineral acids and water. The action of a number of acids on primary nitroparaffins has been studied. Sulfuric, hydrochloric, and orthophosphoric acids were tried, and conversions to fatty acids obtained in each case. If the mineral acid is volatile, such as hydrochloric, the mixture must be heated under pressure. If the acid is a strong oxidizing or reducing agent, it causes the destruction of the hydroxylamine. Sulfuric acid was found to be the best of those studied. It gives rapid reaction rates and good yields of both the fatty acid and of hydroxylamine. It is convenient to use and is cheap, Only the experiments with sulfuric acid will be described, and the examples will be limited to those giving approximately optimum results. Previous t o this investigation the reaction of primary nitroparaffins with mineral acids had been studied by several This article is the eighth in a series on the subject of syntheses from natuAND ENQINEERral gas hydrocarbons. The others appeared in INDUSTRIAL INQ CHEMISTRY, 23, 352 (1931); 27, 1190 (1936); 28, 333, 339, 1178 (1936); 29, 1835 (1937); 30, 67 (1938). 2 Preaent addreas, Commeroial Solvents Corporation, Terre Haute, Ind. 1
4
investigators. Meyer and associates (9, 10, 11) studied the action of sulfuric acid on nitroethane and obtained acetic acid and hydroxylamine sulfate. Preibisch (IS) showed that sulfuric acid converts nitromethane to carbon monoxide and hydroxylamine sulfate. Donath (2) and Mel’nikov (8) also studied this reaction; the latter found that carbon dioxide and ammonium salts are formed simultaneously. Worstall (17) investigated the action of sulfuric acid on 1-nitroheptane, obtaining the expected heptanoic acid. The action of hydrochloric acid upon primary nitro compounds was studied by Meyer and Locher (IO),who prepared formic, acetic, and propionic acids; by Werner (16),who prepared acetic acid; by Zublin (18), who prepared butyric acid; by Henry ( 6 ) , who prepared succinic acid from wnitrobutyronitrile; by Gabriel and Koppe (S), who prepared benzoic acid from phenylnitromethane; and by Worstall (16), who prepared caproic, heptanoic, octanoic, and nonanoic acids from the corresponding primary nitroparaffins. Geuther (4) reported that phosphorous acid converts nitroethane to acetic acid and ammonium phosphate. Bamberger and Rust ( I ) showed that hydroxamic acids, RCH(0H) :NOH, are formed as intermediate products in the conversion of primary nitroparaffins to fatty acids. They obtained yields of hydroxamic acid of only about 2 per cent.
