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Acknowledgment Credit should be extended to C. G. Milbourne of this laboratory for his work in connection with the removal of nitric oxide and the revivification of used purification material; to W. E. Stackhouse of The United Gas Improvement Company’s Physical Laboratory for the determinations with the continuous nitric oxide recorder; and to Milbourne, Stackhouse, Bennett, Carwithen, Claffy, Doering, hlcElroy, Skeen, Smoker, and Waring of the two laboratories for work on various aspects of the vapor-phase gum problem which has been included in this series of papers.
Literature Cited (1) Beck and Diekmann, German Patent 544,193 (1928). (2) Belluci, et al., Atti. accad. Lincei, [5] 14, I, 28 (19053; 15, 11, 467 (1906) ; 16,II, 740 (1907) ; 17, I, 424,545 (1908). (3) Bent, U. S. Patent 1,888,547 (1932). (4) Bergfeldt, German Patent 678,326 (1930). (5) Busch, Ber. 42, 1040 (1909). (6) Cambi, Gam. chim. ital., 57, 536 (1927); Atti. accad. Lincei, [6] 6, 448 (1927). (7) Claude, Australian Patent 12,462 (1928); Jean and Matile, U. S. Patent 1,919,842 (1933). (8) Demorest, Fuels and Furnaces, 10, No. 6, 405 (1932). (9) Dunkley and Leitch, Bur. Mines, Tech. Paper 332 (1924). (10) Fulweiler, Am. Gas Assoc. Proc., 1931, 771; 1932, 838; 1933, 829; paper presented before Am. Gas. Assoc. Production Conference, 1934; Am. Gas. J.,140,25 (1934). (11) Gedel, Gasbeleucht., 48, 28,400 (1905). (12) Gehlen, Ber., 66,292 (1933).
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(13) Gluud, Intern. Handbook of the By-product Coking Industry, p. 536, New York, Chemical Catalog Co., 1932. (14) Graire, Compt. rend., 180, 292 (1925). (15) Guyer and Weber, Brennstof-Chm., 14,465 (1933). (16) Jordan, Ward, and Fulweiler, IND.ENG.CHEM..26, 947, 1028, (1934). (17) Linde, German Patent 521,031 (1929); French Patent 701,891 (1930). (18) Manchot, et al., Ann., 459, 47 (1926); Ber., 47, 1601 (1914); 59B, 406, 412, 2445 (1926); 60B, 191, 2318 (1927); 61B, 2398 _ _ -(192%.
\ - - - - I
(19) Morgan, “American Gas Practice,” Vol. I, p. 806, Maplewood, N. J . , J. J. Morgan, 1930. (20) Pavel, Ber., 12,1407, 1949 (1879) ; 15,2660 (1882). (21) Pieters, Brennsfof-Chem., 12, 285 (1931). (22) Porxczinsky, Ann., 107, 120 (1858). (23) Powell, Am. Gas Assoc. Proc., 1932, 851. (24) Reihlen, et al.,Zbid., 457, 71 (1927); 465, 72 (1928). (25) Rosenberg, Acta. Univ. L u n d , 2, 4 (1865); Ber., 3, 312 (1870); 5,793 (1872); 12, 715 (1879). (26) Rosenberg, A r k i v . K e m i . Mineral. Geol., 4, No. 3, 1 (1910). (27) Roussin, Ann. chim. phys., [3] 52, 285 (1858); Bull. soc. chim., [ l ] 1,210 (1864); Compt. rend., 46,224 (1858). (28) Shuftan, “Ton den Kohlen und den Mineralolen,” Vol. I, p. 206, and Vol. 11, p. 31, Berlin, Verlag Chemie, 1928 and 1929; 2. angew Chem., 42, 757 (1929); German Patent 520,793 (1929). (29) Tropsch and Kassler, Brennstof-Chem., 12,345 (1931). (30) Ward and Jordan, U. S. Patent 1,976,704 (1934). ESQ. CHEM.,24, 969, 1238 (31) Ward, Jordan, and Fulweiler, IWD. (1932); 25,1234 (1933).
RECEIVED March 20, 1935. Presented before the Division of Gas and Fuel Chemistry a t the 89th Meeting of the American Chemical Society, N e w York, N. Y., April 22 t o 26, 1935.
Svntheses from Natural Gas J
Hydrocarbons HE great industrial importance of the
OT
chlorination reactions of the simpler paraffins is evident from the fact that they are serving for the commercial production of amyl alcohols, amyl acetates, amyl xanthates, sulfides and mercaptans, tert-amglphenol-formaldehyde resins, caproic acid, and a host of other organic chemicals. Several other important applications of these reactions, for example, the production of the important new anesthetic, cyclopropane, are a t present in the development stage and it is evident that only a start has been made in their util&ation.
Identity of Momochlorides from Chlorination of Simpler Paraffins‘ H. B. HASS, E. T. McBEE,
AND P A U L
WEBER
P u r d u e University, Lafayette, Ind.
Literature Review In spite of the great technical interest in these reactions, the literature concerning them contains many erroneous data. Let us examine, for example, the excellent review by Egloff, Schaad, and Lowry (8)published in 1931. In themonochloride fraction which Schorlemmer (20) obtained in the photochemical chlorination of propane, he reported only 1-chloropropane. A more careful analysis of the product obtained under Schorlemmer’s conditions, with the use of modern rectification equipment, shows a ratio of about 60 per cent 2-chloropropane to 40 per cent 1-chloropropane. More recent work by hlason and Wheeler (16) indicates that both monochlorides 1 T h e first paper of this series appeared in (1931).
IND. ENQ.CHBM.,23, 352
are obtained in the thermal chlorination of propane. In rectifying these chlorides, 2-chloropropane (boiling point, 34.7 O C.) predominates in the first fraction, whereas l-chloropropane (boiling point, 46.6” C.) occurs chiefly in the later one. Mason and Wheeler found that “the first fraction was usually larger than the second, suggesting that more of the normal than of the is0 compound was formed.” Obviously, if we assume reasonably efficient rectification, exactly the reverse is shown by their results. Butlerov (6) reported only tert-butyl chloride and a dichloride boiling a t about 105” C. as products obtained in the photochemical chlorination of isobutane. Apparently there was no primary substitution until after the tertiary hydrogen
OCTOBER, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
FIGURE1.
D I 4 G R A M OF
T Y P I C ~CHLORINATION L
1191
APP4R.4TUS
119.5" C.) ( I ? ) , both of which are actually formed in the atom had reacted. Actually under these conditions one obchlorination of n-butane and/or 2-chlorobutane, would boil tains 38 per cent tert-butyl chloride and 62 per cent isobutyl largely a t 121' to 122" C. and thus account for Mabery chloride. The fraction boiling in the neighborhood of 105" C. and Hudson's observation. Their results are thus expliwas not identified by Butleror but is a mixture of 1,l-dichlorocable only if we postulate no significant amount of carbon 2-methylpropane and 1,2-dichloro-2-meth~~lpropane. skeleton rearrangement. Chlorination of n-blitane yields Mabery and Hudson (16) chlorinated nearly pure Ti-butane only 1-chlorobutane and 2-chlorobutane as monochlurishs. (boiling point, -2" to +2" C.) and reported only one monoT\'hitmore and Fleming (50) reported the production of 6 chloride which boiled a t 68" t o 69" C. This actually was per cent of tert-amyl chloride in the chlorination of neopen2-chlorobutane (boiling point, 68.25" C.) but Mabery and tane (tetramethylmethane) but soon found this conclusion Hudson came to the conclusion that it mas 1-chloro-2-methylto be erroneous and c o r r e c t e d propane (boiling point, 68.25" it ( I O ) . If Whitmore was unC.), To c r e d i t M a b e r y and able to find a carbon skeleton H u d s o n ' s identification, one Most of the articles which have appeared r e a r r a n g e m e n t , it probably must postulate a carbon skeleton in the chemical literature on the chlorinawas not there to be found. It rearrangement, and, since there would also seem that neopention of the paraffins of three to five carbon is a' c o n s i d e r a b l e m a s s o f tane mould be more likely to erroneous evidence for carbon atoms contain serious errors. Very little rearrange than any of' the other skeleton rearrangements, let U' published work in this field can be relied simple paraffins. consider this possibility. upon for correct information as to such The theory of' carbon skeleMabery and Hudson's dichloride fundamental questions as identity of prodton rearrangements receives fraction boiled a t 121" to 122OC. apparent s u p p o r t , how e v e r , ucts and ratios of isomers. The pertinent The three dichlorides derivable from&e work of ilschan ( 1 ) from isobutyl chloride (or isobuliterature abounds in incorrect physical and of Wertyporoch (%), both tane) have the following boiling constants and false identifications. of whom chlorinated n-pentane points: 1,l-dichloro-2-methylUninterrupted research since early in and o b t a i n e d a monochloride propane, 105" to 106" C.; 1, 21929 in this laboratory has yielded results fraction boiling a t about 97" C. dichloro-2-methylpropane, 107 dschan apparently did not comwhich are now reasonably complete and C ,; and 1,3-dichloro-2-methylmit himself as t o the identity propane, 136.0" C.z Thus none mutually consistent. In no case has any of this m a t e r i a l , but Wertyboils a t or near h4abery's figure. evidence appeared of a carbon skeleton reporoch, misled b y e r r o n e o u s A suitable mixture of 1,2-diarrangement during thermal or photoboiling points in the literature chlorobutane ( b o i l i n g p o i n t , chemical chlorination. In every case all of for the chlorides and acetates 124" C.) (17) a n d dl-2,3-dithe theoretically possible isomeric monoderived from the pentanes, rec h l o r o b u t a n e (boiling point, ported the presence of both prichlorides obtainable without such rear2 This compound \\as 6rst reported mary chlorides ci f isope n t a n e rangement have been found. These generby Kleinfeller (IS) 4 s vi11 be shown in in the chlorination products of a later paper, Kleinfeller missed the alizations extend to the polychlorides as n - p e n t a n e . As pointed out boiling point b y 20 5' C , but sinre his far as this work has gone. by Hass a n d W e b e r ( I I A ) , boiling point is t o o hieh, thi? discrepancy does not affect t h e above argument. Wertyporoch's boiling points,
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while somewhat inconclusive, i n d i c a t e s t r.on gl y BOILISGPOIITD i ~ i when interpreted in the light of correct boiling B P of point data for the pure compounds, that no derivaBoiling Point Corresponding Compound o r Range Citation Alcohol Citation tives of isopentane were present in his chlorides obtained from n-pentane. The fact that substanOC tial amounts of chlorides derived from isopentane 2 Chloropropane 34 8 (25) 82 26 46 60 29) 97 18 are not present in the chlorination p r o d u c t s of 51 0 (12 ) 82 86 68 25 ( 2 5 ) 99 53 n - p e n t a n e is evident from two considerations: 68 85 24) 107 89 ( a ) the very much slOMw rate of metathesis with I-Chlorobutane 78 50 123) 117 7 1 (30) 114 (2.21 potassium iodide shown by the secondary chlorides ::"Chh:",f",:~-~~'t~~~~~~~~pane (221 101 8 (221 92 9-93 0' 31) 110 0-111 5 (29 of n-pentane as compared to those of the primary f : ~ ~ i ~ : ~ ~ ~ ~ ~ " , " , y l b u t a n 97 e 1-97 4 TTeber 11.5 40 (31 chlorides of isopentane and ( b ) the fact that the 2-Chloropentane 96 6-96 8 Ueber 119 28 f 3) 99 9 neber 128 0 (I?) mixtures of anilides derived froin the s e c o n d a r y 98 8 TTeher 132 00 (22) chlorides of n - p e n t a n e b y t h e method of Lauer 1-Chloropentane 108 35 211 138 00 (22 Corrected t o 760 mm , value in literature is 91 8-91 9' C a t 736 mm and Stodola (14) have melting points ~xhichcorrespond exactly to the composition calculated from ~__ rule 2 (11B, 11C). The presence of other isomeric anilides would almost certainly have lomered themelting point ton, but reversals are noted in the caie of 2-pentanol and 3and given an incorrect value for the rstio of 2-chloropentane pentanol and in the case of 3-methyl-1-butanol and 2-methylto 3-chloropentane. 1-butanol. Returning to the question of isomeric monochlorides deA fruitful but easily avoided wurce of errors is the forniarivable without carbon skeleton rearrangement, the fact that tion of olefin polymers in converting alcohols to chlorides. These hydrocarbons are easily reniored by refluxing \ T i l t h sulAschan ( 1 ) obtained only two monochloride fractions in the furic acid (18), and thu3 too-high values may be avoided. chlorination of n-pentane, although three isomers are possible, is due to the fact that the boiling point of 2-chloropentane This treatment also removes residual traces of alcohol, whicli (96.7" C.) is so close to that of 3-chloropentane (97.3" C.). form minimum aeeotropic mixtures nith the chloride. aiid thus may cause low results. The boiling points for 2-chloroAnalysis of this mixture by conversion t o the anilides (11B)has pentane and 3-chloropentane given in the International Critishown both secondary isomers to be present. Both Aschan cal Tables (12) are about 7" c. too high, probably because of and Wertyporoch (26) report all four monochlorides derivable the presence of olefin polymers. The writers' data for 2from isopentane but Ayres ( 2 ) and Clark (6) report that 2chloro-3-methylbutane is not present in the Sliarples Solvents chloropentane and 3-chloropentane were obtained h g Yynthesizing the pure alcohol. by the Grignard reaction and Corporation's "mixed amyl chlorides." This product is obtained by thermal chlorination of a mixture of n-pentane and treating these alcohols with C. P. hydrochloric acid at room temperature. It had previously been shown that even niodisopentane. This really means, however, that the corresponding alcohol (3-methyl-2-butanol) has not been isolated from erately elevated temperatures cause rearrangement in synPentasol, since the analyses have been made upon the alcohols thesizing the corresponding bromides from the alcohol^. rather than upon the chlorides from which the alcohols are The substantial absence of such rearrangement under conditions of the present experiinents was demonstrated by reconproduced. It has never been shown that 2-chloro-3-methylbutane yields the corresponding alcohol under the Sharples verting the chlorides to the original alcohols via the Grignard hydrolysis conditions. Recent work by Rhitmore and reagents followed by oxygenation and hydrolysis using the technic of Whitmore and Johnston (3'1) and also by comerJohnston on the rearrangement of the '(positive fragment" CfSHI1of this chloride indicates that a more or less complete sion to the anilides according to the method which Lauer and Stodola (14) used on the corresponding bromides. The conversion to tert-amyl alcohol would be well within the possidata for 1-chloro-2-methylbutane and I-cliloro-3-methylbutane bilities. The writers have found 2-chloro-3-methylbutane t o be present in the products of the chlorination of isopentane a t were similarly obtained except that in this case higher temtemperatures of 200', 330", 400°, 450°, and 475". peratures were necessary for conversion of the pentanol. to chlorides. Chlorination Rule 1 Reagents Carbon skeleton rearrangements do not occur during either The hydrocarbons used in the experiments were all highly photochemical or thermal chlorinations if pyrolysis temperarectified compounds obtained from natural gas gasoline. The tures are avoided ; every possible monochloride derivable propane, most of the isobutane, and some of the n-butane without such rearrangement is always formed. This generaliwere from the Phillips Petroleum Company, Bartlesville, zation extends to the polychlorides so far as this study has Okla. Podbielniak column analyses on these compounds gone. The present paper will be confined to the presentation showed a purity in excess of 99 per cent. Some of the nof evidence for this statement. butane and all of the pentane and isopentane were from Viking Gasoline Corporation, Charleston, W. Va., or from Boiling Point Data Sharples Solvents Corporation, Philadelphia, Pa. Some of the isobutane was from Carbide and Carbon Chemicals CorpoTo aid in the interpretation of the rectification curves, the ration, South Charleston, W.Va. When necessary the prodaccompanying table gives the best boiling points obtainable for ucts were rerectified until satisfactory purity was obtained. the monochlorides of propane, the butanes, and the pentanes, Rectification analyses indicated very high purity in every and for the corresponding alcohols. case in the final products used. The chlorine was ordinary Certain regularities are a t once apparent upon examination liquefied chlorine from Mathieson Alkali Works, Niagara of these data. The normal chlorides boil a little more than S. Y., or from Belle Alkali Company, Belle, W. Va. Falls, I 10' higher than the corresponding secondary isomers. The is0 compounds boil within a degree or so of the secondary norApparatus mal chlorides and always slightly higher. The order of boilA diagram of a typical chlorination apparatus is shown in ing points of the isomeric chlorides is usually the same as that Figure 1; the operation of the apparatus was as follow.: of the correqponding alcohols having the qame carbon skele-
::g;;~;o~;~ane
ii
~~~~~~~~~~~~~~~~~~~~~~~
5
.. OCTOBER, 1935
IADDUSTKIhL l h D EZGINEERIA-ti CHEllISTRl-
Chlorine passed through a differential flowmeter, 2, which contained sulfuric acid. Traps 4 and 5 caught any liquid accidentally expelled from the flownicter. Pressure in the chlorine line was measured by the closed manometer, 6. Glass-to-iron connections were made at 7 by mcans of de Khotinsky cement. .As much of the chlorine line as possible up to the reactor was of steel because of the high pressures employed. The chlorine was preheated in the bath before mixing with the hydrocarbon. The latter passed through flowmeter, 10, trap 11, and the coil of the Pyrex glass reactor, 8, where it was also preheated. The products of the reaction and the excess hydrocarbon passed through condensers 13 and 14, respectively, to t,he continuous rectifying column 17. Stopcock 15 was provided to bypass the material from the reactor until temperatures, ratio of reactants, etc., were regulated as desired for each experiment. The rect,ifying column was filled with small glass Raschig rings. -1liquid reflux of the hydrocarbon was maintained at the top of the column by means of solid carbon dioxide and ethanol cooling in container 19. A pentane thermometer was used in thermometer well 18. The organic chlorides were collected in receiver 16, and the unreacted hydrocarbon and hydrogen chloride were continuously expelled through stopcock 21. The hydrocarbon was scrubbed free from hydrogen chloride in water scrubber 22 and caustic scrubber 26. To test for the presence of free chlorine, the gases were passed through a potassium iodide scrubbcr 29, previous to the caustic scrubber. -411 experiments were conducted so as to avoid free chlorine beyond the reactor. The quantity of hydrogen chloride formed in the reaction could be found from the contents of Erlenmeyer flasks 24, 31, and 28. To test the efficiency of the column in removing organic chlorides from t.he exit gas, the latter was passed through a silica tube, 34, heated to redness by furnace 35. This procedure pyrolyzed any escaping organic chlorides to give hydrogen chloride Tvhich was absorbed by caustic in scrubber 37. The column was operated to prevent these chlorides from escaping with the hydrocarbon.
1193
-60" to +300' C., including reaction. both in Iiquicl m t l 111 vapor phase. d large number of chlorination- have been conducted in the absence of light and of cataly>tsat temperatures ranging from that of the rooin t o above 600"C. Tlie &e of the reaction tube had to be increased a- the temperature wa< lonried 111 order to maintain a rearonable reaction rate. The very J o n est reactions, conducted a t room temperature in the daik. were performed discontinuously by sealing mixtures of liquid hydrocarbon with liquid chlorine in PJ rex glass bonil) tnbeThe tubes were filled only to about 20 per cent of their capacity. Care was taken to avoid approaching exp portions since it is knonn that verx pwerhil expl occur with such mixtures. The lower explosive propane and the butanes in the vapor phase corre-pond to the concentrations where one clilorine atom is present iI ,rea( h carbon atom in the mixture. In the liquid phare the limitare apparently somen hat wider. Immediately after >ealing, the tubes were placed inside cloqed steel pipes and examiiid quickly a t intervals for completeness of reaction. I n the photochemical chlorinations, large flasks or carhoywere used for the vapor-phase reactions, and large test tube. or small flasks immersed in cooling media m r e used for tlie liquid-phaqe work. At the end of the continuou. run. the organic chloride. which had collected a t the bottom of the rectifying (dunin
A diagram of a typical reaction tube used in thernioclieniicia1 chlorinations is shown in Figure 2 : During the course of an experiment the reactor was immersed in a molten tin bath as far up as the exit, H . Therefore, a part of the chlorine line, A , and the hydrocarbon line (coil), B , were immersed in the molten tin. This caused the two gases to be separately preheated to reaction temperature. The chlorine, which was injected at approximately 40 pounds per square inch (2.8 kg. per sq. cm.) pressure, passed t.hrough the jet, D,at a high velocity, causing the hydrocarbon and chlorine to become dispersed in each other quickly. By such a procedure hot hydrocarbon and chlorine can be mixed successfully without burning, provided the hydrocarbon is in sufficient excess. The reaction occurred in the space between the outer tube, F , and the thermocouple well, G. The products passed quickly through H to condenser I . In some cases cold hydrocarbon was passed through J to cause the gases to be cooled more quickly.
Temperature Control Reaction t'ubes have been constructed in such a way as to provide for very close temperature control. If the chlorine is first mixed with hydrocarbon and the mixture is then raised to reaction temperature, chlorination occurs to an unknown extent over a range of temperatures during the heating. By using the procedure of first heat,ing the reactants to the desired temperature and then mixing them very rapidly, the possibility of chlorination occurring at lower t'emperatures is avoided. By using a considerable excess of hydrocarbon, and by confining the reaction zone to the thin annular space between the thermocouple well and the inside of t.he outer tube, the temperature could be maintained within 5" C. of that of the bath in spite of the highly exothermic nature of the chlorination. The temperature was recorded and controlled by means of a Leeds Br Xorthrup pyrometer connected to a thermocouple placed in G (Figure 2). Almost all of the chlorinations were adjusted t o give approximately the shortest exposure time possible with complete utilization of the chlorine. I n this way pyrolysis of the chlorides is minimized. The mole ratio of hydrocarbon to chlorine has been varied from 1: 1 to 20: 1. Photochemical chlorinations have been conducted at temperatures varying from
FIGURE 9 . T I P I C ~RLE ~ C T I OTUBE U
were subjected to batch rectification for analysis. Typical rectification curves obtained with a Davis column (7) on the inonochloride fractions from propane, butane, and isn1iut:ine are included.
Evidence for Identity of Products I n all cases samples of the chlorides have been treated nitli concentrated sulfuric acid with little loss in volunie or tar formation. This eliminates the poqsibility of the presence ot large quantities of olefins or chloroolefins in the samples under discussion, although under certain conditions large quantitiey of these impurities can be produced in the thermal chlorination of paraffins. The rectification data in Figure 3. ~-CHLOROPROPA~E. together with the nature of the starting materials and the density of the product (0.860 at 20" C.) show concluqively that this is 2-cliloropropaiie. I-CHLOROPROPAXE. The boiling point data were supported by conversion to butyric acid through the cyanide u 4 i g the technic of Hass and hlarshall (11). 2-CHLORO-2-METHYLPROP*SE. The rectification data of Figure 4, together with the density (0.840 a t 20" (1.)are conclusive in this case.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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10
certainly, however, it was converted t o the corresponding alcohol via t h e G r i g n a r d reaction followed by 4 oxygenation and hydrolysis. Whitmore and Johnston bb 43 (31) have shown that this procedure yields the alco64 hol corresponding to the chloride used as starting ma42 ijy terial. The secondary isoamyl alcohol thus obtained .u'4/ % boiled a t 110.6" to 111.6" a t 760 mm. pressure, which S @ .E40 is within the reported boiling range of this alcohol $58 39 and differs by nearly 10" C. from the boiling point of .$38 5 56 any other amyl alcohol derived from isopentane. This alcohol gave an a-naphthylurethane (melting point, 4 37 4 54 111.5" C.) after two crystallizations from petroleum 52 3% I j 1 1 I I j ether. The a-naphthylurethane of a known sample f5 30 45 60 7 5 40 /M of methylisopropylcarbinol, kindly furnished by R. T'. 1 5 30 45 69 7 5 92 /05 ml d ~ s l i l l d k McGrew of Pennsylvania State College, had a melting ml distilhfe F I G C R E4 . R E C T I F I C A T I O N point of 111" to 112" C.: mixed melting point, 110" F I G U R E3 . R E C T I F I C . 4 T I O S CURVE FOR MOAOCHLORIDES to 1110 C, CURVE FOR MONOCHLORIDESFROM CHLORIh LTIOS OF ISOBUThe 3,5-dinitrobenzoate was also p r e p a r e d . It Ti>E FROM cHLORIS.4TIOS OF P R O P i N E melted a t 75.0" to 75.5" C. after three crystallizations from dilute methanol. The known sample of 33The rectification data of l-CHLORO-2-METHYLPROPASE dinitrobenzoate of sec-isoamyl alcohol, also supplied by Figure 4 are not conclucive since thie compound boils so close McGrew, had a melting point of 76" C.: mixed melting point to 2-chlorobutane. As pointed out above, these compounds 75.0" to 75.5" C. have been confused in certain previous work. Figure 5 is therefore introduced as confirmatory evidence. It is apEvidence that Carbon Skeleton Rearrangements parent that 2,3-dichlorobutane (boiling point, 119.5" C.) Do Not Occur during Photochemical or Thermal and 1,2-dichlorobutane (boiling point, 124" C.) are not presChlorinations if Pyrolysis Temperatures Are ent in significant amounts although the>- are found in large Avoided quantities in the chlorination productc of 2-chlorobutane. In the case of propane no carbon skeleton rearrangement The identity of the 1-chloro-%methylpropane is, therefore, is possible. established. The 1,3-dichloro-2-n1ethylpropaneobtained by CHLORIDES OF ~-BLJTANE. I n the chlorination products further chlorination of isobutyl chloride obtained by chloof n-butane the absence of tert-butyl chloride is eqtabliqhed rinating isobutane has also been identified by conversion to the by the rectification curve of corresponding glycol, 2-methylpropane-1 ,%diol. F. H. NorFigure 6, since the tertiary chloton and L. F. Hatch identified the conipound in the following 79 manner : 45
\
78
1,3-Dichloroisobutane (boiling a t 136.0' C.), obtained by the chlorination of pure isobutyl chloride made by chlorinating isobutane, was heated at 180" C. for 2 hours in a st,ainless steel bomb with two moles of anhydrous sodium acetat,e in the presence of glacial acetic acid equal to one-half the weight of the sodium acetate. The diacetat'e thus obtained was isolated by rectification. Alcoholysis of the diacetate by refluxing for 30 minutes with a 3 per cent solution of drj- hydrogen chloride in absolute methanol in the ratio of 200,ml. of methanol solution per mole of diacetate, yielded the glycol in 60 per cent yield based on dichloride. The corrected boiling range was 213" to 214' C.; d:o, 1.0290; n?, 1.4445. Faworski (9) gives the boiling range as 214.0"to 214.5' C. at 771 mm. and the specific gravity as 1.0297. This compound has been distinguished ~-CHLOROBUTANE. from 1-chloro-2-methylpropane of approximately the same boiling point by the substantial identity of its pyrolysis rate with that of the synthetic product made from 2-butanol ($8). I-CHLOROBUTAKE. This compound is completely identified by its starting materials and boiling point, but has also been confirmed by conversion to n-valeric acid through the nitrile, using the procedure of Hass and Marshall (11). 2-CHLORO-3-METHYLBUTaSE. Thie is the Only monochloropentane whose formation by chlorination of the corresponding pentane is a t present seriously disputed. It is completely identified by its starting material (pure isopentane) and boiling range (92.9" t o 93.1" C. a t 760 mm.) since no other amyl chloride boils within 4" C. of this isomer. The mixed amyl chlorides were treated with sulfuric acid t o remove any traces of olefins or chloroolefins, and the 2-chloro3-methylbutane was isolated by repeated rectification. The entire purified sample boiled within 0.1" C. of its true boiling point, temperature being taken a t the top of a Weston microrectifying column ($7). To establish ita identity still more
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FIGURE5. RECTIFIC4TIOh FIGURE6. RECTIFICATIOX Cum E FOR DICHLORIDES CURVE FOR MONOCHLOFROM CHLORINATIONOF RIDES FROM CHLORIN4TION 1-cHLORO-2-VETHYLPROP
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OF B U T k U E
ride boils so niuch lower than the other isomers. As pointed out above, the substantial identity of the pyrolysis rates of 2-chlorobutane obtained synthetically from the alcohol and obtained in the chlorination of n-butane demonstrates that not more than traces of the much more difficultly decomposed isobutyl chloride were present. CHLORIDES OF ISOBUTAKE. In the chlorination products of isobutane, the bubstantial absence of 1-chlorobutane is established by the rectification curve of Figure 4. The absence of 2-chlorobutane in the chlorination products of isobutane is established by the rectification curve of Figure 5 for the dichlorides since no detectable amount of 1,2-dichlorobutane or of 2,3-dichlorobutane is present. Theqe compounds
I imatcd off from t,hr orRsnie clrloridrs formed. Thc column used lrsd a length of 110 &.I :&ridinside dir~rnctrrof 1.5 em. It w i i n:t.i:ked with hrriii,ll elass soiral lines nlirnrt 4 nim. ii1 diameter.
ing botwovn 46.0"and 51. I ' to 5 cc. Thereforetheauhstantial absoncc of tho two secorrda chlorides of n-pentane was established. Afbcr complete removal of the two primary isoamyl chloridcs, tin int,errncditite fraction of lcss than 1 cc. waa accompanied by a temperature rise to 70" C., thereby establishing the ilbscncc of I-chloropentane in the mixture of isoamyl ohiorides formed through chlorination of pure isopentane.
~~ekno~lodCnrent
~1
1
A f t a : h u t 90 pcr cent of t,he ~ X D W pentanc: had brcn TLc,uvercd, t h e oil bath temperature was increased to about W o C. ;md all but 5 or 10 cc. of t.lir remaining pentanc was rwovcmd iiitliout x icmperuture risc at the top of the column. Thc cdt m n was then pcrmittod to ~oo1t o room tempemturc, m d conneebad to II vacuum line hcld const,;mt at. 150 mm. ( * 0.1 mm.). .\ liquid air trap was maintained at all times during distillation irirdcr reduced prmsure. With ttie strrpcoeh st the top of the coiunm clo,wl. heat was eradunllv anoiicd to tho oil bath until i t s tcmwrature was xboet'75' C. Ai'the aame time thc column
poi&, nt 150 mm. p&ssure, of 2-ohloropentane); this injicstea .J . Aai. (.'hen. Sot., 50, 26 (19281. (20) Sehoriernmer, Pmc. floii. Sur. (London), 17, 37b-6 (1868); A n n . , 150, ?Ill-14 (lX09); .Inn. chim. ph!,s.. [4] 19, 4RWl (1870). (21) S h m , R i c l i . * c r . h m &lo., 38,4; ~ 7 0 (l'J29). (22) Tiinriierrnans and Ileiiirniilt-Rolao,l, .Inides soc, e q m i i . fia. i,i
