APRIL, 1936
'
INDUSTRIAL AKD ENGINEERING CHEMISTRY
tively small. Apricot leaves kept in darkness showed no injury from oils containing less than 0.40 per cent of these acids, irrespective of the percentage of unsaturated hydrocarbons present in the oils. With 0.70 per cent, injury became noticeable. The toxic threshold value for apricot leaves is therefore approximately 0.50 per cent acids. Although this value may differ for other kinds of foliage, the indications are that it is always small. The results, obtained in the oxidation tests carried out under the light and moisture conditions somewhat comparable to those found in leaves, indicate that the formation of asphaltogenic acids is roughly proportional to the percentage of unsaturated hydrocarbons present in an oil. We would not expect, however, that all oils with the same unsulfonated residue (i, e., the same amount of unsaturates) would neces-
464
sarily be equally resistant to oxidation in the presence of light. For this reason a test whereby petroleum oils intended for foliage spraying could be examined as to their relative resistance to oxidation in light appears of value.
Literature Cited (1) Gray, G. P., and de Ong, E. R., IXD.ENQ.CHEM.,18, 175-80
(1926).
(2) (3) (4) (5) (6)
Haslam, R. T., and Frolich, P. K., Ibid., 19, 292-6 (1927). Knight, Hugh, Plant Physiol., 4, 299-321 (1929). Rohrbaugh, P. W., Ibid., 9, 699-730 (1934). Staeger, H . C., IND.EXG.CHEM.,17, 1272-5 (1925). Young, Paul, Am. J. Botany, 22, 1-8 (1935).
RECBIVED September 24, 1935. Presented before the Division of Petroleum. Chemistry at the 90th Meeting of the American Chemical Society, Sss Francisco, Calif., August 19 t o 23. 1935.
Action of Aluminum Chloride on Paraffins Autodestructive Alkylation v. N. IPATIEFF A N D A. V. GROSSE Universal Oil Products Company, Riverside: Ill.
F
OR the understanding and correct interpretation of the reaction of paraffins with olefins in the presence of aluminum chloride (S),a knowledge of its behavior towards paraffins alone was necessary. A number of investigations on the action of aluminum chloride on hydrocarbons have been carried out in the past; the most interesting are recent papers by Grignard and Stratford ( 1 ) and Kenitzescu with his co-workers (6). However, in these investigations no explanation seems to be given of the reactions taking place with paraffins. The present writers believe that they have found a n explanation after their discovery of the reaction of paraffins with olefins which takes place under very mild conditions ( 2 ) . In this paper data on the action of aluminum chloride on n-butane, n-hexane, n-heptane, and 2,2,4-trimethylpentane will be given and discussed. Theoretical Discussion
It was found that aluminum chloride acts on all these paraffins. However, the presence of hydrogen chloride is necessary for the reaction, and it can be added either directly or indirectly-for instance, through the addition of water. If every trace of hydrogen chloride and water is eliminated, aluminum chloride does not react to any material extent with the hydrocarbons unless the temperature is raised sufficiently high (about 150" to 200" C . ) to cause the formation of
Aluminum chloride converts paraffins, into a complex mixture of paraffins of. lower and higher molecular weight according to a type of reaction which has been termed 'autodestructive alkylation." The conversion and reactivity of an individual paraffin is dependent on its structure; in general it increases with (a)its molecular weight and ( b )its degree of branching.
hydrogen chloride, owing to a reaction between the aluminum chloride and the paraffin itself. The reaction products consist in all four cases of a waterwhite upper layer and a much smaller red-brown viscous lower layer containing the aluminum chloride, combined with highly unsaturated hydrocarbons; in the case of n-butane the upper layer consists of liquefied gas, stable only undep pressure. n-Butane showed no appreciable change below 100" C.. At 175" during 3 or 4 hours it was converted to a large extent into propane, ethane, and methane and partly isomerized' into isobutane; a t this high temperature the other three. paraffins are completely broken down. The n-hexane was converted in 3 hours a t its boiling point, (69" C.) into higher and lower boiling paraffins to the extent. of 20-25 per cent. With n-heptane a marked reaction took place a t its boiling point (98" C,), and about 35 to 40 per cent is changed in 3 hours. In the case of 2,2,4-trimethylpentane the reaction with. aluminum chloride took place even a t room temperature a n d a t 25" to 50" C. in 3 or 4 hours about 90 per cent of the octane. was converted into lower and higher boiling paraffin hydro-. carbons. From these examples it can be concluded that the reactivityof paraffins under comparable conditions increases both with (a) their molecular weight and (b) their degree of branching. The nature of the reaction becomes clearer if we look a t the products formed. The distillation curve (Figure 1) representing a high-temperature Podbielniak distillation analysis of the upper layer obtained in the case of 2,2,4-trimethylpen--
INDUSTRIAL AND ENGINEEKIKG CHEMISTRY
462
VOL. 28, NO. 4
hydrogen disproportionation, produces a paraffin of lower molecular weight and an olefin; the olefin immediately combines with another octane molecule, forming a paraffin of higher molecular weight. Since both the so-formed lower and higher paraffins can undergo the same reaction while splitting a t different places in the carbon chain, the final product will represent a complex mixture of paraffins of a wide boiling range. The different single steps or reactions taking place may be further differentiated under the following terms : CATALYTIC CRACKING OR BONDSPLITTIXG.This means a rupture of a carbon-carbon bond in the presence of aluminum chloride and hydrogen chloride, and the formation of a paraffin and olefin, either directly or through free radicals and hydrogen disproportionation. (The olefin may be stabilized through the addition of hydrogen chloride.) The final reaction is given by the following equation, the original paraffin being CnHzn+ 2 : CnHL + z
+C,
-zj
+2
lower mol. weight paraffin
f C,Hz,
(1)
olefin
ALKYLATION. This reaction consists in the direct addition of an olefin to a paraffin and is the reverse of the preceding reaction. It is expressed by the following equation, the original paraffin again being C,H2, + 2 : paraffin
ISOMERIZATION. The isomerization can be mainly accounted for by a splitting of a paraffin according to Equation 1 and by consequent alkylation according to Equation 2, leading to an isomeric paraffin. For instance, CH~.CH~.CHZ.CH~.CH~.CH~ n-hexane CH3.CHz.CHz.CHs n-butane H H
~
/
I 31 /o
50d)
I
I
80
l
I
30
CC.O
I
I
40
II
50
lI
60
l
l
\
\
H n-butane
70
CH2 AH8
f D/ST/LLAT€
FIGURE1. HIGH-TEMPERATURE PODBIELNIAK DISTILLATION O F PRODUCT FROM 2,2,4-TRIMETHYLPENTA“BI tane is the most instructive example. The properties of the fractions are given in Table IV. The chemical analysis, molecular weight determinations, chemical tests [stability to ( a ) nitrating mixture (absence of aromatics) and (b) potassium permanganate solution (absence of the olefins)], and index of refraction all consistently confirm the view that the upper layer consists of practically only paraffins with a boiling range of -10” C. (isobutane) up to about 350° C. The lower layer corresponds to about 10 per cent by weight of the original octane and represents (besides unreacted aluminum chloride) addition compounds of aluminum chloride with unsaturated cyclic hydrocarbons; these complexes can be decomposed by water with a large evolution of heat, giving an aluminum chloride solution and a hydrocarbon oil similar to the lower layer from ethylene polymerization (4). The nature of the products from n-heptane and n-hexane is similar although, as stated, the amounts differ widely (discussed later in the experimental section). In the case of the three liquid paraffins the paraffin of lowest molecular weight obtained was isobutane. The products of the upper layer are best accounted for if we assume that aluminum chloride plus hydrogen chloride splits a carbon-carbon bond in an octane molecule and, after
+ CH2:CH1 ethylene
isohexane
Furthermore, a fourth reaction, polyPOLYMERIZATION. merization, can take place. The olefin formed according to Equation 1 can polymerize-i. e., 2CnH2, +C*,H&,, to another olefin-but this latter will again alkylate a paraffin and lead to a paraffin of higher molecular weight, according to Equation 2, since no free olefins are ever observed in the reaction product. An exception happens only if the olefin combines with the aluminum chloride and undergoes different reactions of condensation, leading to the lower layer compounds (4). The general reaction can be thus embraced by the following equation,
+
CnHzn + z +a Cm1Hz,,+ 2 b CaZHzzz +Z where 2.n = as1 bxg cs3 .. z
+
+
+ .
+ c Cs,H,m + + . . (3) z
It is proposed to call this general reaction “autodestructive alkylation” of paraffins. For the notion of “destructive alkylation,” see citation 1.
Experimental Procedure APPARATUS. An all-glass apparatus with interchangeable ground-glass joints (Figure 2) was used in all experiments except those using butane. A train of absorbers cooled with dry-ice and a gas holder were inserted behind the manometer, For the study of n-butane a rotating autoclave with a glass liner was used.
,
APRIL, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY *
ALUMINUM CHLORIDE.Pure commercial aluminum chloride was mixed with powdered aluminum and melted under pressure in a glass liner placed in a pressure bomb. Absolutely pure, clear white crystals were obtained in this way; in some cases they were further purified by sublimation in a vacuum. PARAFFINS.The n-butane was taken from a cylinder containing a 99 per cent pure compressed gas and scrubbed with concentrated sulfuric acid to free from any possible traces of butylenes. A pure commercial preparation of ;-hexane was purified and checked like the octane and n-heptane; n2,0 of all fractions = 1.3755; boiling range at 760 mm. = 69.0" to 69.0' C. (uncorrected). A pure commercial preparation of n-heptane was purified and checked in the same way as the isooctane, the first and last fractions being discarded; ng of all fractions = 1.3855; ng = 1.3860; boiling range a t 760 mm. = 98.0"to 98.0" C.; d i 5 = 0.6808; d i 0 =
463
TO
MOTOR DRIV€
1
0.6839.
The commercial standard 2,2,4-trimethylpentane (from Rohm and Haas Company) was fractionated in a high-temperature Podbielniak apparatus; all fractions had the same density and index of refraction, within 1 unit of the fourth decimal; n2,0 = 1.3922; d i a = 0.6895; d i = 0.7068; boiling range at 760mm. = 99.3O t o 99.3" c. All these paraffins were absolutely stable toward nitrating mixture and alcoholic potassium permanganate solution. HYDROGEN CHLORIDE AND NITROGEN.The hydrogen chloride was taken from a cylinder containin%the pure dry compressed gas. Nitrogen was obtained from a omb containin the compressed gas stored over sodium hydrosulfite solution @or oxygen absorption) and dried over phosphorus pentoxide.
D G A S aURNER
FIGURE 2.
DIAGRAM OF APPARATUS
Experiment with n-Butane The experiment was carried out in a rotating autoclave of 800-cc. capacity; the aluminum chloride was placed in a glass liner1 and then n-butane was condensed in it by cooling in dry-ice. Below 100" C. no appreciable reaction took place. At 175" C. during 4 hours at a maximum pressure of 35 atm., the following quantities of reagents were converted : 1
T o be described separately.
,
1 -
4-
130.9 grams = 198 cc.; all distilled fractions were water-white and absolutely stable to nitrating mixture) Boiling Fraction Range at NO. 760 Mm. Volume Weight ny O
c.
cc. el000 4.8 13.0 56.0 78.6 30.1 2.8
1.8
6.34 0.4 0.4 s 7
n-Butane AlCli HC1
30.0 .-LO
Total
95
E3.3
60.0
:
1
1 35k6 1.3730 1.3754 1.3758 1.3756 1.3859 1,3924
1.4044 1.4365
....
Total 198 130.9 a Analysis: C 84.05%, H 16.98%; mol. weight 108. Theory for CsHla: C 84.11%, H 15.89%, mol. weight 114.
6 g n-butane 8 g. isobutane Propane Ethane
]
14.0 25 2 46
No.
1 2 3 4 5 6 7 Bottoms Losses Total
(Fractions 2, 3, and 4 of Table I = 141 cc.) Boiling Test for UnsatuRange rates and Areat matics (Nitrat760 Mm. Volume ng ing Mixture) O c. cc 27.0-55.0 0.75 1.3569 1.3687 1.00 55.0-60.0 5.70 1.3729 60,O-65.0 36.10 1.3746 65.0-67.0 54.0 1.3749 67.0-67.5 Absolutely stable 29.3 1'. 3747 67.5-68.0 9.4 1.3749 68.0-68.0 3.0 1.3781 >68.0 . . , 52.0 ...~
.
. . .
141
46.5 12 35 1.5 95
Grams
Methane Hydrogen Total
2 7 0 04 -
46 5
S o paraffins boiling above n-butane were formed. The lower layer on decomposition with water gave a very heavy brown oil soluble in ether.
Experiment with n-Hexane The hexane was heated to boiling temperature (69' to 72" C.) for 3 hours with continuous stirring and with the addition of hydrogen chloride gas; condensable gas was evolved and gradually a sticky red-brown lower layer, containing large amounts of unreacted aluminum chloride, formed; the upper layer was water-white and had a refractive index, n2,, of 1.3744. The balance sheet (in grams) is as follows: -Before Reaotionn-Hexane 163.60 AlClj 16.35 HC1 2.0
TABLE11. HIGH-TEMPERATURE PODBIELNIAK DISTILLATION OF FRACTIONS CONTAINING HEXANES
Fraction
Grams
Upper layer and gas Lower la er (hydrocarbon portion) AlCla a n a HC1 Losses Total
The upper layer and gas analyzed by low-temperature Podbielniak distillation showed only paraffins 9.5 follows :
Grams
3.14 8.59 36.86 51.46 19.41
After Reaction
J
Grams
\
=
0 Gas (isobutane) 1 21.0-46.7 2 46.7-61,8 3 61.8-67.O 4 67.0-71.4 5 71.4-75.4 6 75.4-100 70 100-125 8a 125-150 8b 150-175 Bottoms >175 Losses (including gas)
Reaction-
Grams
PODBIELNIAK DISTILLATION OF TABLEI. HIGH-TEMPERATURE UPPERLAYER FROM HEXANE (Charge
-Before
Total
182
After Reaction Uncondensable gas (HCl, traces of lower para5ns) Condensable gas = 4900 c c . a t 17.3O C.: Isobutane 90% Pentanes '9% Hexanes '1% , Upper lay& Lower layer Losses Total
2.0 11.1 1.2 0.1 134.4 25.0 8.0
182
The results of a high-temperature Podbielniak distillation of the upper layer are given in Table I. The fractions containing hexanes (2, 3, and 4) were again subjected to a high-temperature Podbielniak distillation. The results are given in Table 11. The properties of fractions 2 to 7 (boiling range, quantities, index of refraction) indicate that other hexanes besides nhexane are p r e s e n t t h a t isomerization has taken place. Besides isomerization about 20 to 25 per cent of the original
IKDUSTRIAL AND ENGXNEERING CHEMISTRY
464
n-hexane has changed into lower and higher paraffins with a boiling range of -10" (isobutane) to about 200' C. The lower layer on decomposition yielded, as in the case of n-heptane and isooctane, a n unsaturated oil.
Experiment with n -Heptane
After Reaction Condensable gas. Upper water-white layer Lower layer Incondensable gas (HCI, traces of lower paraffins) Losses
221.5
Total
38.5 147.0 30.5 4.0 1.5
91
221.5
(Charge = 210 cc.; all distilled fractions were water-white and absolutely stable to nitrating mixture) Boilina Ran& Fraction a t 760 n %5 NO. Mm. Volume O
12 Bottoms a
cc .
c.
Gas
s
1
0
8 1
91
TABLE IV. HIQH-TEMPERATURE PODBIELNIAK DISTILLATION OF UPPER LAYERFROM 2,2,4-TRIMETHYLPENTANE (Charge
=
74 cc.
Fraction No.
= 51 grams: all distilled fractions were water-white and absolutely stable t o nitrating mixtures) Boiline Range a t 760 Mm. Volume Weight n %o O
c.
PODBIELNIAK DISTILLATION OF TABLE 111. HIGH-TEMPERATURE UPPERLAYERFROM HEPTANE
9
Total
18 1 53 18
The condensable gas was fractionated by means of a lowtemperature Podbielniak column and identified as isobutane (92 per cent) with small amounts of pentanes. The upper water-white layer after washing and drying was distilled on the high-temperature Podbielniak apparatus with results shown in Table IV and Figure 1. The upper layer was stable towards nitrating mixture and potassium permanganate solution, indicating the absence of aromatics and olefins.
-
The condensable gas distilled in a low-temperature Podbielniak apparatus consisted of the following (in per cent by weight) : Propane, 2; isobutane, 81; butanes-hexanes, 4 ; n-heptane, 13 (total, 100). The upper layer distilled in a high-temperature Podbielniak apparatus gave results RS shown in Table 111.
10 11
After ReactionCondensable gas: Isobutane Pentanes Upper water-white layer Lower layer
7
,-
-Before Reaction199.02 n-Heptane AlCla 20 48 2.00 H20
6
--
Before Reaction2,2,4-Trimethylpentane 79 95 41Cla 9 49 HC1 About 2 0
Total
In this experiment water instead of hydrogen chloride was added. At 20" to 25' C. with continuous stirring for 12 hours no noticeable reaction occurred, and the index of refraction of the heptane remained unchanged. On heating for 3.0 hours to 97-99" C., a lower layer formed, and condensable gas was evolved; the amount of uncondensable gas (besides hydrogen chloride) was very small. The balance sheet (in grams) is as follows:
Total
--
VOI,. 28, NO. 4
32-67 67-94 94-98 98-98 98-99 99-100 100-100 100-110 110-130 130-1 50 150-170 170-200
> 200
Total %-Heptane = 82% of charge.
0.7 (liquid) 13.7 7.5 16.5 54.0 27.0 3.2 2.0
1.7 1.9 1.9 1.5
-
.... 1.3607
1.3797 1,3853 1.3857 1.3852 1.3860 1,3853 1.3954 1.3993 1.4088 1,4180 1,4272 1.4472
2 10
The autoalkylation of n-heptane took place only to a very limited extent compared to isooctane; 60 per cent by weight of the original heptane, containing small quantities of isoheptanes, was recovered in fractions 3 to 7. On decomposing the lower layer with ice, about 10 grams of a n unsaturated hydrocarbon oil were recovered.
Experiment with 2,2,4-Trirnethylpentane At first the isooctane and aluminum chloride were stirred alone in a n atmosphere of nitrogen a t 20' C. under which circumstances no reaction took place. However, a reaction began immediately on the addition of hydrogen chloride gas; it manifested itself in the formation of a red-brown lower layer and the evolution of a gas condensable a t -70" C. The reaction was allowed to proceed a t 20' to 25" C. for 2 hours and then for 2 hours a t 50' C.; a t this time the amount of reaction products did not appreciably increase, and therefore the reaction was stopped and the glass flask was cooled and flushed out with nitrogen. No uncondensable gas was formed. The balance sheet (in grams) is as follows:
cc.
Grams
~ 6 . 0 7.0 10.4 9.8 10.0 8.0 10.6 1.63 1.50 2.25 0.75 1.10 0.75
33.6 4.74 7.17 6.77 6.92 5.55 7.79 6.29
- -
....
1.3800 1.3918 1.3930 1.3962 1.4028 1.4165 1.4328 1.4349 1.4388 1.4453 1.4488 1.4617
Total 69.9 48.8 Losses e4.1 2.4 a Chemical analysis: C 83.78% H 16.31%. mol. weight i n benzene 102. Theory for paraffins of same mol. ;eight: C 83'.89%, H.16.11%. b Chemical analysis: C 83.92%, H 15 82 mol weight 139. Theory for paraffins of same mol. weight: C 84.275 H%.73% 0 Chemical analysis: C 85.14%. H 15.b2%; mol.'weight 240. Theory for paraffins of same mol. weight: C 84.9056 , H 15.10%.
.
7d
Out of the whole upper layer, a t a maximum only about 15 cc. of 2,2,4-trimethylpentane were recoverable (in fractions 2 , 3, and 4), corresponding to 12 per cent of the initial amount. The lower layer was decomposed by ice water and gave about 9 grams of a n oil of unsaturated hydrocarbons described'in another publication (4).
Production of Isobutane from Paraffins The production of fairly large quantities of isobutane from the paraffins mentioned requires special attention and and will be discussed in detail in a separate article. This fact was also observed by Grignard and Stratford ( I ) ; the only difference was that the latter writers said n-butane was the isomer produced. This statement however is erroneous. I n fairness to Grignard and Stratford it must be said that their fractionating equipment was very poor compared to the Podbielniak apparatus used in this laboratory and therefore it would be naturally difficult for them to distinguish between the two isomers.
Literature Cited (1) Grignard, V.,and Stratford, R., Compt. rend., 178, 2149 (1924); Bull. SOC. chim., [4]35,931 (1924). (2) Grosse, A. V., and Ipatieff, V. N., J . An. Chem. Soc., 57, 2415 (1935). (3) Ipatieff, V. N., and Grosse, A. V., J. A m . Chem. Soc., 57, 1616 (1936). (4) Ipatieff, V. N.,and Grosse, A. V., to be published. (5) Nenitresou, a, D., and Dragen, A.,Ber., 66, 1892 (1933); also other papers in Ber., 1932, 1933, and 1934.
RECEIVED August 26, 1935.
