HA.LOGENATION OF HYDROCARBONS Flow studies on the chlorination of olefins have revealed that analyses for free halogen in olefin-chlorine mixtures are susceptible to error because of the possibility that extraneous catalyzed reactions may occur in the absorption vessel. Tt has been proved that olefins react bith chlorine only slowly, if at all, in the gas phase at moderate temperatures (below 150’ C.). In the presence of a liquid phase, however, the reactions are exceedingly rapid. Under this condition, the substitution of chlorine into the saturated addition product or into a concurrently present paraffin is inhibited by oxygen, the paraffin reaction being the more strongly influenced. These substitution processes come under Stewart’s classification of induced reactions. The distribution of products from several such chlorination reactions has been determine& Catalytic vapor-phase chlorination of olefins and of olefin-paraffin mixtures occurs at moderate temperature in the absence of liquid. The concurrent substitutive reactions are not inhibited by oxygen and are a consequence of purely thermal and catalytic conditions, rather than induction.
Chlorination of Olefins and Olefin-Paraffin Mixtures at Moderate Temperatures; Induced Substitution
i -
HE halogenation of olefins a t moderate temperatures has been the subject of much study, and a detailed bibliographical review cannot be given in a short paper. However, of special bearing on the material of this report are the recent papers of Stewart and his eo-workers and the patents of Deanesly. I n extension of the earlier work of Stewart and Fowler (16) and Norrish and Jones (11), Stewart and Smith (17, 18) investigated the nonphotochemical chlorination of ethylene in a static system a t room temperature; they found that substitution into the dichloride addition product proceeds concurrently and a t the same rate as the association process and is inhibited by oxygen. (“AssociaB tion” is used here in the kinetic sense of a reaction, A = X.) This substitutive reaction, which does not occur with l12-dichloroethanein the absence of the olefin, is termed “induced” substitution and is correctly attributed to be a consequence of specific molecular transfer of the relatively high heat of formation of the dichloride. Stewart further suggested that this latter reaction itself is also induced.
T
+
1 Present address, Rhenania-Ossag Mineralalwerke A,-G., Hamburg, Germany.
H. P. A. GROLL,‘ G. HEARNE, F. F. RUST, AND W. E. VAUGHAN Shell Development Company, Emeryville, Calif.
Similarly, when ethylene is bubbled into a benzene solution of the halogen, benzene is inductively chlorinated (16) to yield sym-hexachlorocyclohexane. A further series of olefine was studied (IS), and the rates of reaction are in the order 2-pentene > 3-heptene, 2-hexene1 2-heptene >> 1pentene > 1-heptene. I n the case of 2-pentene the percentage of substitution is as high as 50 in contrast to an average value of about 10 for the other compounds. Stewart and Weidenbaum (20)found that in carbon tetrachloride solution, 2-pentene and chlorine react to give 1-chloro-2-pentene as well as the normal addition product. Oxygen had no effect on the “induction factor”-namely, the ratio of moles of chlorine reacting by substitution to moles of chlorine reacting by addition; this lack of effect is rather surprising inasmuch as it seems that one of the qualifying characteristics of induction is its inhibition by oxygen. There seems to be some confusion over this definitive term, and a more precise prescription is needed. For some time work on halogenation processes has been carried on in these laboratories. The studies were initiated by Deanesly, who has contributed extensively to the patent literature on this subject (4-8). He showed (6) that in the chlorination of olefin-paraffi mixtures in the presence of e. liquid phase, saturated monochlorides are produced concurrently with the normal olefin addition product; thus, association giving one molecule of 2,3-dichlorobutane in an n-butane-Pbutene mixture may, under favorable conditions, lead to substitution of chlorine into as many as ten molecules of n-butane. The latter reaction is effectively inhibited by oxygen ( 5 ) ,while the addition proceeds unaltered. This example of the highly specific action of olefins toward promoting substitution into molecules that are usually relatively inert is striking and supports Stewart’s designation of the phenomenon as a particular effect. It appeared worth while to extend the work of Deanesly in order to examine more fully the interesting phenomena associated with halogenation processes, partly in order to eluci1239
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
1240
VOI,. 31, NO. 10
date the mechanisms further and partly to find practical applications, In the course of the several investigations, in addition io some new observations of general interest related to the addition reaction, there have accumulated considerable data which bear on the matter of induced substitution, The present paper is concerned primarily with the chlorination of straight-chain olefins, both in the presence and absence of paraffins, at moderate temperatures. A second paper will deal with the halogenation of isobutene, which is characterized by the formation of large amounts of unsaturated chlorides. The substitution reactions of straight-chain olefins at high temperatures will be discussed in the third paper.
Reactor and Materials The experiments %ere made with flow systems of varied dimensions, and since the amount of reaction was usually of the order of 100 per cent of the chlorine, precise formulation of rate expressions was itnpossible. However, some insight into the general kinetic dependencies has been gained.
CONTROL3 FOE PILOT-P1,Ah-T APPARATUSFOR
.-..... ... ~ ~ ~~. . ~~..
off. the material w&~dist,illedfrom the tank hito a thoiouchlv
CHWRlNATlON OF PROPYLENE
Constant flows were rnaintainod either by high-pressure regulators or tmered needle vdvos. After meterinn. the gases were
passed thrdugh three large wash bottles provided with sintered glass disks in order to bring the bubbles into intimate contact with a 0.4 M chromous sulSate-0.1 M sulfuric acid solution (H), which effectiveiv removes all oxxen: in some exneriments
elcan vacuum system which was all glavs exce t the connettion to the original container; in this manner batefes of 800-900 cc. were frosen~ out in flask . cooled with liauid air. In turn. this .. ... ~ . B~ was surrounded with solid carbon dioxidd, and the chlorine was allowed to melt nhile being agitated and vigorously pumped. At first there was a pronounced evolution of dissolved gas, chiefly carbon dioxide, which was undoubtedly produced in tho electrolytic manufacture of the halogen. This ebullition gradually diminished until it had ceased entirely; then after further pumping and agitation, the chlorine was redistilled i n vacuo into a clean cylinder chilled in solid carbon dioxide. When BS much as 10 grams of the material was absorbed in a large volume it is Dosslbie that a small amount of oxygen had been introduced
ev;: the method p0ss"esses merit, and it may be asserted that the amount of oxygen is quite low. Gas flows from the tank, constant to 1 or 2 cc. per minute for periods of at least 30 minutes, were readily obtained h pssage through.20 em. of 2.5-em. i. d. heavy iron pipe, packelwith 8-mesh calcium chloride to which was attached a long-taper ateel needle valve for delivery; suifurio acid was used in the meter. The ethylene was a commercial roduct (anesthesia grade, Ohio Chemical and Manufacturing Ebmpany); the ethane was also a commercisl product. The athe7 gases were either purified refinery products or were derived by dehydration of alcohols. The analyses (by Podhielniak distillation) are given in the fallon,ing table, in male per cent: Ethylene Ethane
99.5+. CzH'
9G.(2). CXHI; 0.(3),CZHI; U O ) , C a s and CaHs; 0.(5),higher; 2.(0), air Propylene 98.(4). CaHs; 1 . W . butenos (100 olefin) Propane 97.(2), CaHs; 0 . 0 ) . G H s ; 0.0, CIHI; 2.(7), CzHe 90, 1-C4Hs: 9,2-CaHa; 1, lighter than C I 1-Butene %Butene 97.G). 2-C4Hs, mined (98+, total olefin) 99.(4), iso-CaHe Isobutene %(SI, iso-CBta; Butane-butene" 67.(0). n-C+Hm; 2040). 2-C&; 0.0). 1-CaHn; 0.(0). iso- C&; 0.0(5), G H , ; 2.(4). CzHs Refinery product from by sbsorption in mid.
whioh the
isobutene had been removed
.
constant
O
0
I
I
.
I
L
1242
INDUSTRIAL AND ENGINEERING CHEMISTRY
experiments were also made with nitrogen flowing into the delivery tip as a diluent even in those cases (ethylene, propylene, 1-butene) where it was not necessary for proper analysis. The sudden complete removal of chlorine from the reaction zone is undoubtedly the result of a single-phase phenomenon: a minute trace of liquid product appears on the glass surface as a consequence of adsorption and catalytically promoted combination; in this new phase the reaction proceeds a t a much more rapid rate and is autocatalytic, and the halogen is soon eliminated. (That the onset temperature for isobutene falls into line with those of the other olefins may be an indication that the reaction is initiated by the addition process, which in the liquid phase is soon subordinated to the substitution step.) TABLE111. SUBSTITUTION Nz Olefin Dilution No Ethylene NO Propene No I-Butene Yes 2-Butene Yes Isobutene a 100 per cent reaotion of Clz. 200 Nz into tip. b By titration analyses.
AT ONSET
20" c.0
TEMPERATURES AND
AT
Onset 7% SubetitutionbTemp., At onset At O c . temp. 20 a c. 20-23 45 45 54-58 35 33 84-86 43 33 85-88 23 22 65-70 93 86.5 Flow, oa. per min.: 100 olefin, 100 Clz.
Inasmuch as the film can be only slowly evaporated and requires a rise in temperature to near the boiling points of the mixed products in each case to rid the system of it, the reaction once initiated will continue a t temperatures considerably above the onset value. For example, ethylene chlorination initiated at 20" C . will continue at 65" C. without significant change in the percentage of substitution (boiling point of 1,2dichloroethane, 83.5" C.).
Substitution Reactions in the Liquid Phase Table I11 shows the variation of the per cent of chlorine reacting by substitution over several temperature ranges. To check the accuracy of the titration data, samples of chlorination product were collected under strictly comparable conditions in a 1.3 X 45 em. reactor, freed of acid, dried, and distilled. The data given in Table IV show the distribution of products. The trend in the weight percentages of the di-
VOL. 31, NO. 10
chloro addition products of the straight-chain olefins a t the onset temperatures gives support to the suggestion that these hydrocarbons may be classified in regard to their reactivities toward addition according to the degree of alkyl substitution of the double bond. The two experiments with 1-butene a t 83" and 20" C. confirm the difference in the titration analyses for substituted chlorine a t these temperatures. It is significant that, with but one exception, the titration analyses check reasonably well with the distribution of the halogen as calculated from the weight percentages of the products. The agreements are good, in view of the many sources of error and inaccuracy. The exception is the case of the chlorination of the propanepropene mixture, for which there was found 45 per cent substitution by titration analysis and 33 per cent by distillation. The discrepancy is readily explained as a consequence of further reaction of propyl chloride with chlorine; this results in increases in the amounts of acid and 1,2-dichloropropane1and the yield of the latter is in part misinterpreted as product formed by addition. The data on this reaction involving propane bear directly on induction. Neither ethane nor propane alone reacted with chlorine in the dark in the gas phase under the conditions of these experiments (100 cc. of each gaseous constituent per minute, 1.3 X 45 cm. reactor). However, it has been shown that in this temperature range (-10" to +150° C.), the presence of a liquid phase is a requisite for any reaction, both addition and concurrent substitution, and that in the liquid phase the reactions are very rapid. The addition is a highly exothermic process (around 50 kg.-cal. per mole for the formation of 1,2-dichloropropane), and this energy probably effects the propagation of diverse chains in the liquid medium. (Conn, Kistiakowsky, and Smith (3) found AH = -43,653 calories for the gas-phase addition a t 82" C. over catalyst.) The relative velocities of the several processes, dependent on activation energies, collieion frequencies, and other vaguely defined properties in solution, determine the distribution of products. Thus, in the liquid, chiefly ll2-dichloropropane, paraffin and olefin dissolve and are acted upon by chlorine; addition and substitution occur in equal amount. That the reactions are propagated by chains may be inferred from the effect of oxygen. For a propane-propylene mixture (flow ratios as in Table IV, but through a small-diameter reactor, 0.7 X 51 em., a t 22" C.) with total reaction of the halogen, the substitution by titration was found to be 49.2 per cent, either with or without illumination; the admixture of 1 per
OF PRODUCTS OF CHLORINATION OVER PYREX GLASS TABLE IV. COMPOSITION
Hydrooarbon Ethylene
Reaotor Gas Flow Temp. -Monoohlorides--Cc./mnin. C. Wt. % CzHd 100 20 0.0 c12 100
-Diohloridea-
----Triohlorides-
Wt. %
Wt. % 33.4
I,l,Z-CnHsCls
48.6
1,Z-CsHaClr 46.7
1 2 2-CsHsCla 1:1:2-CaHrCIa 1,2,3-C8HsCh
15.2 8.1 16.6-k
1,2-C8HeCln 5 7 . 0
l,Z,Z-CsHsCls 1 2 . 2 l,l,Z-CaHsCla 9.3 1,2,3-CnHsCla 4 . 7
CnHiClt
0.0
--HigherWt. % 1,1,1,2-CnHzCk 1,1,2,2-CnHnCL Bottoms
Cln,Analysis@ Distilla- Titration tion
%
%
7.7 3.8 6.5
42 B 58a
45 s 65a
Bottoms
13.5
37 a 63 a
35 8 65 a
Bottoms
13.6
33 8 67 a
45
Propylene
C ~ I S100 Cla 100
53
Propylenepropane
GnHs 100 Cln 100 CaHa 100
20
I-Butene
C4Ha 100 Cln 100
83
2 4
1,2-C4HsClz 3 8 . 9
1,2,3-CiH~Cls 21.1 Others 8.0
Tetra Bottoms
15.3 14.3
46s 54 a
43 8 57 a
1-Butene
CdHs 100 ClP 100
20
1.5
l,Z-C4HaCln 5 2 . 8
1,2,3-CdH&la Others
22.6 4.6
Bottoms
18.5
35 s 65 a
33 s 67 a
2-Butene
C4Ha 100 Cla 100
75
1.7
2,3-C4HnClr 7 2 . 6
2,Z33-CnH7Cla
9.8
Bott om8
15.7
25 s 75 a
23 s 77 a
Isobutene
C4Hs 100 100 Clz
70
Methallyl chloride 7 4 . 3 Isocrotyl ohloride 4.3
2,3-CdHeCla 4 . 6 (1.1 % unsatd., 3.5% satd.)
Bottoms 16.8 (4.2% unsatd., 12.6% satd.)
88s
93 a
a B
-
substitution: a = addition.
CsHiCl
3.3
+
12a
8
66 a
7 s
cent oxygen reduced the substitution to 27.5 per cent of the chlorine. I n like manner Table V shows the effect of oxygen on the substitution occurring in other instances. Thus it may be said that oxygen is effective as a chain breaker for the substitution steps involving both or either olefin addition product and paraffin, but that the addition is relatively unchanged. TABLE V. EFFECT OF OXYGENON SUBSTITUTION@ Gas Flow Cc./min. 300 CnH4, 300 Clr
Mole Ratio, Hydrooarbon/Clz
Temp., C.
1
-6
2
-6
$6
Oxygen
None 1 None 1 480 C2H4, 120 Clr 4 -6 None 1 400 CaHa, 200 Cln 2 22 None 1 4 22 None 480 CaHs, 120 Cln 1 200 CsHa 200 CaHa, 2 22 None 200 Cd 1 240 CsHs, 240 CsHs, 4 22 None 120 Cln 1 660 C4Hs. 2670 C ~ H I O , 1) 20 None 660 Cla 0.5 1.0 1.5 2.0 5 100 per cent reaotion of chlorine, 0.7 X 51 om. reactor. b Moles 2-butene/mole Cln. 400 CZHI,200 CIS
1243
INDUSTRIAL AND ENGINEERING CHEMISTRY
OCTOBER, 1939
% Ch Reacting by Substitution 29.3 18.7 17.7 12.3 10.1 7.6 18.6 10.1 10.3 8.5 49.2 27.5 11.8 6.7 23.6 15.0 12.4 11.2 10.4
These data are in complete accord with those of Deanesly (6) on the n-butane-2-butene system, despite the fact that his
results were obtained with a different apparatus. Distillation analyses of the product of the butane-butene chlorination showed that the 2 per cent oxygen had caused a reduction from 10.5 to 0.9 per cent in the yield of saturated monochloride. This and other data of Table V prove that substitution into the paraffin is somewhat more strongly inhibited than that into the olefin addition product, a logical result inasmuch as there must be some time lag in the transfer of activating energy from the chain involving addition to the olefin to that of substitution into the paraffin, during which lag the oxygen is enabled to act. No attempt a t a pictorial mechanistic interpretation of the effect of oxygen will be made a t present. Stewart and Smith (17, 18) proposed a general scheme which is satisfactory. No vinyl chloride was detected in the products of the chlorination of ethylene under these experimental conditions, although ethylene shows the greatest tendency to induce substitution into its addition product to form trichloroethane. In the chlorination of butane-butene mixtures a small amount (about 2 mole per cent) of unsaturated monochlorides was formed, but this yield was not decreased by the addition of 2 per cent oxygen to the feed. This is to be contrasted with the effect on the yield of saturated monochlorides. Thus induction can apply only to substitution into saturated compounds (paraffins or saturated chlorides). The reaction of chlorine with isobutene in the liquid phase to form unsaturated monochlorides is not inhibited by oxygen and thus is probably not an induced substitution. The presence or absence of a liquid film of chlorination product on the walls of the reactor is a function of the vapor pressure of the compounds formed a t the prevailing temperature and their partial pressure in the reaction mixture. Therefore, the ratio of hydrocarbon to chlorine in the feed, the boiling points of the products, and the reaction temperature are factors influencing both the onset temperature and the extent to which. substitution occurs. The effect of feed ratio is shown in Table V; the amount of substitution is roughly proportional t o the partial pressure of the chlorine.
Apart from these influencing conditions, a number of others depend on the mode of operation, such as size of the reactor, direction of flow, and inhomogeneity of temperature, (which, in turn, depends upon the efficiency of cooling and the presence or absence of "hot spots" or cold zones), and many others which must be considered for the reproducibility of results and for interpretation of conflicting statements which occur in the literature. Without proper cooling, for instance, the gases may heat considerably above the mixing temperature because of the exothermic nature of the reactions. Under these conditions the liquid phase present in the colder sections of the system may be carried over or back into the region that is above the temperature a t which the liquid film would normally be deposited. Once such a layer has been formed, it is only slowly removable from the surface; this is undoubtedly due to the formation of high-boiling chlorinated products. It is therefore difficult to state exactly the temperature necessary to ensure the absence of a film (or adsorbed layer). The phenomenon described possibly accounts for the "negative temperature coefficient" and other irregularities observed by Williams (22) in the static bromination of ethylene. The conditions become even less clearly defined when the apparatus is so arranged that liquid product may reflux into the reaction chamber ; the recording of temperature becomes relatively meaningless in such cases. Some tests on the chlorination of ethylene catalyzed by calcium chloride, designed to duplicate those of Smyth ( I @ , showed that without cooling, localized hot spots above 200" C. developed. Under such conditions much less acid resulted than when the reactors were thermostatted below 50" C., and a liquid film coated the calcium chloride catalyst. Thus, a 3 to 1 flow of ethylenechlorine over catalyst cooled with ice water resulted in a hot spot of 81" C. and substitution of 31.5 per cent of the halogen; when the reaction was allowed to run wild without cooling, the hot spot reached 337" C. and only 2.1 per cent substitution occurred. Carbon chips had the same effect as calcium chloride. Even when catalysts are present, oxygen strongly inhibits some substitution reactions in the liquid phase. This is demonstrated by the following two sets of data: (a) In a chlorination of ethylene in the presence of liquid film on calcium chloride cooled to about 0' C., 2.0 per cent oxygen reduced the amount of substitution from 31.5 to 20.7 per cent. (b) With flows of 4 to 1 mole ratio of propylene to chlorine over 8-mesh calcium chloride thermostatted at 22 " and 50" C., 7.3 and 8.6 per cent substitution, respectively, were found; 1.0 per cent oxygen reduced these values to 4.7 and TABLEVI. CHLORINATION OF ETHYLENE OVER CALCIUM CHLORIDE" -Flow----CnH4
Cln
C C ~ IBalance at 75' C.-C1? Balance at 125O (2,UnSubstiUnSubstireacted tuted Added reaoted tuted Added Cubic centimeters per minute
50 50 17 0 35 13 0 75 75 . 12.6 0.38 100 100 17 0.22 82.8 11.4 2.95 125 125 6.8 3.60 150 150 0 18.4 13i:6 4.1 10.15 a 44 grams of 8-mesh oatalyst in a 1.3 X 45 om. reactor.
. ..
... ...
...
37 62.0 85.6 114.6 135.8
TABLEVII. CHLORINATION OF ETHYLENE OVER CALCIUM CHLORIDE AT 75' C.a Cln flow 75 100 120 150 N2 flow 75 50 30 0 CL unreaoted 0 0 0.5 0 0.45 1.78 1.98 18.4 Ch substituted Ch added 117.5 131.6 74.5 98.2 a 300 0 0 . per minute total input, ethylene constant at 150 oo. per minute. All values in GO. per minute.
1244
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 31, NO. 10
phenomenon explainable only as a result of hot spots of greater intensity with the faster flows; ( c ) for a given reactor the c. substitution likewise increases with greater input, for the same -Flow--Diluent--. -Chlorine Balancreason as in (5; (d) for a given flow the amount of substitution CzHs Unreaoted Substituted Added ClH4 ClZ N2 markedly decreases with increase in the efficiency of heat disCubic centimeters per m i n u t e 50 50 25 ... 12.2 0 37.8 sipation from the catalyst. ... 25 9.9 0.11 40.0 A further point in the evidence that the vapor-phase sub50 50 50 ... 10.2 0 39.8 ... 50 6.7 0.12 43.2 stitution reactions on calcium chloride are not induced, but 50 50 100 10.4 0 39.6 6.9 0.24 42.9 are purely thermal, is that oxygen has no effect on them. .. i6o 100 100 56 ... 13.1 0.0 3 45 6 : !$' Thus, a t 76" and 150" C., chlorination of propylene a t a mole 50 8.3 100 100. io6 . . . 13.5 0.58 85.9 ratio of 1 to 4 over catalyst in the absence of liquid resulted ... 100 3.87 4.40 91.7 100 100 50 ... 0 5.10 94.9 in 5.1 and 6.5 per cent of the halogen substituting; admix.50 .. 0 8.94 l:;:A ture of 1 per cent oxygen scarcely altered the data (4.4 and 150 150 . 50 .. 6.4 6.8 ... 50 1.7 13.0 135.3 6.1 per cent, respectively); this is quite different from the results obtained when liquid was TABLEIX. CHLORINATION OF ETHYLENE AT 125' C. present. Similarly, the chlorination of the butane-butene mixture a t 80-100" C. in the abClz-CzH, Flow, Cc./Min.: -50-50-~oo-Ioo--. -150-150sence of liquid and over chloride catalyst, givTotal % CL Total % C1n Total % C1z ing 1.8 mole per cent monochlorides, 88.4 2,3% c l n substi- % c l a substi- % c l n substiExperimental Conditions tuted reacted tuted tuted dichlorobutane, and 9.8 trichlorides, was unaf44 g. granular CaCln in 45 om. of 13fected by mixing as much as 50 per cent oxygen 2.95 mm. i. d. tubing 74 0 88.6 97.3 6.8 13 g. granular CaClz in 3 parallel 40into the chlorine; the 14.0 per cent of the chloom. lengths of 5-mm. i. d. tubing 76 0 88.8 1.3 92.8 1.65 rine reacting by substitution remained unaltered. CaCll as a solid film on walls of 3 paralTABLE VIII.
ChoRINATIoN OF I ~ CHLORIDE AT 125'
~ OVER E N CALCIUM E
~
-
7 -
le1 40-om. lengths of 5-mm. i. d. tubing 7 9 . 4
0
88.3
0.24
92.0
0.9
Acknowledgment The authors wish to thank E. C . Williams, vice 5.6 per cent. These results are similar to those of Table V and lead logically to the conclusion that once initiated, the reaction in liquid phase is affected little, if a t all, by the presence of catalyst.
Catalytic Vapor-Phase Chlorination of Olefins The purely vapor-phase chlorination of olefins over catalysts has also been investigated. Table VI gives a typical set of data and shows how markedly the percentage of reaction increases with rate of gas input with concurrent increases in the amount of substitution. These results are undoubtedly ascribable to gross temperature inhomogeneities on the catalyst. Variation in the ratio of olefin to chlorine also produces equally striking results, as Table VI1 shows. At 75" C. nitrogen and ethane are equivalent as diluents, but a t 125" C. where the paraffin does not react with chlorine over the salt, there is a greater amount of substitution (and addition) in the presence of ethane than with nitrogen (Table VIII). Product from a 150 chlorine-150 ethylene50 ethane run was collected and distilled. It showed that 3.0 cc. of ethyl chloride had been formed per minute. Although this may possibly have been produced by the addition of hydrogen chloride to ethylene, we may more reasonably consider it a primary product from the chlorination of ethane. The 3.0 cc. per minute accounts for roughly half of the increase in substitution found when ethane replaced the nitrogen as a diluent; the remainder must be due to other substitution reactions. It is felt that these results from vapor-phase experiments are not a consequence of induced substitution as found in the liquid phase, but rather arise from the presence of localized zones of intense reaction. This is borne out by Table IX, which shows parallel data for three different reactors so designed as to give increasingly efficient thermal contact with the thermostat in order to reduce the accumulation of reaction heat on the glass and granular salt, which are poor conductors. The tabulation shows several points of interest: (a) In the limits of these experiments, for a given flow the amount of reaction is independent of the amount of catalyst which proves the high efficiency of such material; ( b ) for a given reactor the amount of reaction is not proportional to the contact time but, conversely, increases with the input, a
president in charge of research, for his continued interest in and stimulation of the present studies. Likewise, it is a pleasant duty to acknowledge the prior work of R. M. Deanesly, which provided the starting point of the present investigations. To M. L. Adams and D. S. La France are due thanks for competent assistance in the performance of experiments.
Literature Cited Brooks and Humphrey, J. IND. ENG.CHEM.,9 , 750 (1917). Conant and Kistiakowsky, Chem. Rev., 20, 181 (1937). Conn, Kistiakowsky, and Smith, J. Am. Chem. Soc., 60, 2764 (1938). Deanesly, Ibid., 56, 2501 (1934). Deanesly, U. S. Patent 1,952,122 (March 27, 1934). Ibid., 1,991,600 (Feb. 19, 1935). Ibid., 2,010,389 (Aug.6 , 1935). Deanesly and Hearne, Ibid., 2,031,938 (Feb. 25, 1936). Kistiakowsky, private communication. Norrish, J . Chem. Soc., 123, 3006 (1923). Norrish and Jones, Ibid., 126, 55 (1926). Smyth, Gas J., 149, 691 (1920). Stewart, Dod, and Stenmark, J. Am. Chem. Soc., 59, 1765 (1937). Stewart and Edlund, Ibid., 45, 1014 (1923). Stewart and Fowler, Ibid., 48, 1187 (1926). Stewart and Hanson, Ibid., 53, 1121 (1931). Stewart and Smith, Ibid., 51, 3082 (1929). Zbid., 52, 2869 (1930). Stewart and Weidenbaum, Ibid., 57, 2036 (1935). Zbid., 58, 98 (1936). Stone, Ibid., 58, 2591 (1936). Williams, J. Chem. SOC.,1932, 1747, 1758.
PRESENTED before the Division of Organic Chemistry at the 97th Meeting of the American Chemical Society, Baltimore, Md.
