INDUSTRIAL AND ENGINEERING CHEMISTRY
2876
cating the importance of the thermal treatment as compared with variations in the coal composition. ACKYOWLEDGMENT
The authors wish to express their appreciation to G. L. Barthauer and R. J. Friedrich of the analytical group for their development of the infrared analytical techniques applied to cracking of pure compounds, t u R. A. Friedel of the Office of Synthetic Liquid Fuels, Bruceton, Pa., for his assistance in the infrared analyses on phenols of tar origin, to Nrs. Irene Pigman and James Wagner for carrying out the experimental program, and to Everett Gorin for valuable discussions on the cracking mechanism. LITERATURE CITED
(1) Bergtsson, E., U.
1950).
P.Bur. Mines, R e p t . Invest. 4755 (December
Vol. 44, No. 12
( 2 ) Briatom, W.-4., J . Inst. Fuels, 20, 109 (1947). (3) Dietrich, W., H e h . Chim. Acta, 8, 149 (1925). (4) Fisher, C. H., U. 8.Bur. Mines, Bull. 412 (1938). (5) Friedel, R. A , et al., A n a l . Chem., 22, 418 (1950). (6) Hagemann, A., 2. angew. Chem., 42, 355, 503 (1929). ( 7 ) Horrex, C., and Miles, 8. E., Discussions Faraday Soc., 10, 187
(1961). 18) Jager, A., and Katwinkel, G., Brennstof-Chem., 31, 65 (1940). (9) Jones. B. W.. Jones. S. A.. and lieuworth. M. B.. IIUD. ENG CHEX,44,2233 (1952). (10) Kaplan, E. H., U. S. BLIP. Mines, Tech. P a p e r 690 (1946). (11) Kosaka, L., J . SOC.Chem. I n d . ( J a p a n ) , 30,108 (1931). (12) Nakai, R., B u l l . Chem. SOC.J a p a n , 5, 136 (1930). (13) Szwarc, M., J . Chem. Phua., 16, 128 (1948). (14) Wilson, P. J., and Wells, J. H., “Coal, Coke and Coal Chemicals,” p. 374, New York, McGraw-Hill Book Co., 1950. RECEIVED for review May 15, 1952.
ACCEPTED August 13, 1952.
Effect of Associated Salts on the Po~vrnerization of utadiene by Organoium Reagents J
AVERY A. MORTON, FRANK H. BOLTON’, FRANCES W. COLLINS, AND EDWARD F. CLUFF Department of Chemistry, ikfassachusetts Institute of Technology, Cambridge, Mass.
T
HE polymerization of dienes by sodium metal is probably
the oldest known method for producing synthetic rubber. A course for the reaction has been traced by Ziegler and coworkers through the 1,4-disodium-2-butene intermediate and thence as an organosodium reagent through a series of adduct compounds to a rubber which is primarily the result of 1,2- rather than the 1,4-chain growth required to make it relatively similar to Hevea, The same type of polymer is obtained if the first stage with sodium metal is omitted and any active organosodium reagent is substituted as the starting agent. This sodium process gives an unsatisfactory product when used with butadiene and isoprene, but in World War I the Germans applied it to 2,3-dimethylbutadiene to give a moderately suitable polymer. Subsequently the emulsion process was developed and yielded a better type of product in which around 80% of the butadiene was joined end to end, that is, 1,4-. The present synthetic rubber for general use belongs with the emulsion class. All things considered, the rubber made by the emulsion process is distinctly different from that by the sodium method, so much so that an examination of physical properties alone serves easily t o differentiate the t7vo materials, even if their sources are unknown. The purpose of this paper is to point out how the sodium process as practiced with an organosodium reagent as the starting point can be altered so as to produce differences .ivhich are even greater than the significant ones found beti\-een t,he soqium and emulsion types of polymerization. The change is brought about by association of the organosodium compound-a reagent insoluble in the reaction media-with other solid sodium salts of a less reactive type, even of such slight reactivity as found in sodium chloride. In proper kind and proportion, however, the effect of the additional salts can be astonishing, both as to the rate of polymerization and the structure of the polymer. The particular combination rrhich has given the most outstanding result is allylsodium associated with sodium isopropoxide and sodium chloride and is known as an alfin catalyst ( 12 ) . Allylso1 Present address, Research Laboratory, Dow Chemical Co., Midland, Mich.
dium by itself is slowacting and yields a polymer having an intrinsic viscosity less than 1 and having around VOyo external double bonds, the product of 1,2-addition. By the presence of the two associated salts the same quantity of allylsodium achieves polymerization a t enormous speeds to polymers with intrinsic viscosities of 12 or more with 70 to 80% 1,4-structure. Emulsion polymerization can scarcely achieve intrinsic viscosities much above 3. The full scope of these changes, the exact composition of the catalyst, and the degree to which the behavior of an organosodium reagent is controlled by the associated salts were not a t first realized. Indeed, in the beginning, the name alfin was given on the assumption that only two components, the salt of an alcohol and an olefin, were necessary ( 1 7 ) . However, as this paper will show, sodium chloride is as essential as the other tnTo salts. Substitution of sodium chloride by many other related salts is possible. Each single salt of the three ‘component mixture has some influence, but all three are needed to obtain the effects achieved as an alfin catalyst. The cation required for these salts is equally specific, sodium being of prime importance. h limited substitution of sodium by potassium is possible and, in a few cases, may cause a faster rate of polymerization. The lithium ion cannot be used in general without impairment of activity, although in some cases its bad influence can be partly compensated by association with a large anion, such as the iodide in place of chloride. As the organosodium reagent becomes more active and effective, it also becomes more specific. For instance, an ordinary organosodium compound without high specificity will cause styrene to polymerize faster than butadiene, whereas the alfin catalyst xi11 cause butadiene to polymerize much faster than styrene ( 1 6 ) . A given quantity of catalyst \vi11 have a great effect upon butadiene, much less on isoprene, and scarcely any on 2,3-dimethylbutadiene ( 6 ) , the monomer for the old methvl rubber. This high specificity is an important feature of this development where, for the first time, a clear demonstration has been possible in a field where specificity is sorely needed, because it is apparent that if the synthesis of polpdienes of specific struc-
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1952
2877
These features were easily perceived in any good alfin agent. However, some mixtures of salts contained the essential ingredients but showed no Polymeralfin characteristics because the sodium chloride Salts Presenta ization During After Time, Yieldc, Intrinsic Gel, Pptn. Reagent was the commercial granular material and too Viscosity % Testa cleavage cleavageb Min. No. % coarse t o be incorporated properly with the other Low . . Keg. .. 30 Low 1 0.4 3 Neg. 14 480 2 .. salts. Yet even in these cases, a little alfin prod33 Pos. 20.5 30 3 .. 59 uct was detected by a precipitation test (to be 20.5 19 Pos. 30 4 40 .. 1.5 43 Neg. 3 240 5 described later) with iodine monochloride. 51 Pos. 7.9 21 30 NaCi(w) 6 0.3 41 Pos. NaCl(g) 3 7 240 Table I shows the activity of the reagents pre8.9 9 20 .. 240 8 pared by this cleavage. The first two and reagent Low . , Pbs. 150 9 .. Low 2.4 2 23 Pos. 180 10 5 contained sodium isopropoxide or sodium chlo2.0 27 Pos. 240 11 11 49 Pos. 1.6 240 3 12 ride, but not both, and caused no alfin polymeriza22 . . 18 30 9.6 13 tion. The third and fourth contained both salts, 41 .. 17.5 71 30 14 . . the sodium chloride being the finely divided matea R signifies the isopropyl group; the letters w and g in parentheses indicate that the sodium chloride was prepared by a Wurtz reaction or was the granular material obtained ria] from a Wurtz reaction, and showed alfin charfrom commercial sources. b The salt and sodium ieagent were stirred together vigorously in the high-speed stirring acter clearly. Reagent 5, a repeat of reagent 1, apparatus. WaS inactive Until sodium chloride from a Wurtz 0 The yield is the percentage of polybutadiene obtained when 10 ml. of the reagent sots ond30 ml. iodine of butadiene in 200 ml. pentane. on some of the polymers. reaction was stirred into the mixture to make With monochloride; notofattempted reagent 6. A similar attempt with granular sodium chloride gave reagent 7 , which had so little alfin . activity that only the iodine monochloride pretures, such as are found in Hevea or balata, is ever to be achieved cipitation test revealed it. Reagents 8 to 12 also contained commercial sodium chloride and each corresponding polymer in the laboratory or plant, the development of highly specific showed a precipitate with the iodine monochloride reagent even catalysts is essential. The three-component alfin catalyst illusthough the other tests usually gave unsatisfactory characterizatrates unusually well the degree t h a t specific components of the tions. The last two reagents were made with Wurtz sodium reagent contribute t o specific properties of the polymer and shows halides. Their alfin characters were easily discerned. These rethe way to further study of this method of controlling polymerizasults certify the need for the third salt in the alfin catalyst and the tion. PREPARATION OF CATALYST necessity for its thorough incorporation if the reagent is to be good. The alfin catalyst ( l a , 27) has hitherto been prepared by two The use of granular sodium chloride was next improved and different methods. In one ( A ) amylsodium reacts with diisopronumerous commercial halide salts were found to replace sodium pyl ether and in the other (B) amylsodium reacts with propylene chloride. The method was t o prepare the isopropoxide from alcoin the presence of sodium isopropoxide. I n both cases sodium hol and sodium in the presence of the halide and stir the mixture chloride is in the catalyst because it is associated with amylsofor 3 hours before incorporation in the cleavage reaction, all in the dium, having been formed during the reaction of amyl chloride high-speed stirring apparatus (IQ), which grinds as well as mixes. with sodium. An alternative method produces allylsodium free Table I1 lists these tests, except for the last two, in the order of from sodium chloride and sodium isopropoxide by a cleavage (20, 27) (see Equation 1 ) of diallyl ether k i t h an alkali metal. It is designated as method C and was used in the present study. TABLE 11. HALIDE SALTSAS COMPONENTS OF AN ALFIN CATALYST 2Na (CH*=CHCHZ),O + Polymer Bond Cat. Yield CH2=CHCH2Na CH2=CHCH20Na ( 1 )
TABLE I. EFFECTOF SALTSO N THE POLYMERIZATION O F BUTADIENEBY MEANSOF ALLYLSODIUM PREPARED BY CLEAVAGE OF DIALLYL ETHER
.
+
I
+
Prep.
No.
*1
e
Sodium allyloxide was thereby introduced but had no major adverse effect as found by independent tests where the salt was made separately from sodium and allyl alcohol and was then mixed with a n alfin catalyst of known activity and allowed to age over 3 months. However, its presence during a preparation of catalyst by method B decreased the formation of allylsodium because the sodium allyloxide was metalated preferentially and then underwent dimerization or polymerization. The allylsodium prepared by method C was used to polymerize butadiene in the absence and presence of either or both sodium isopropoxide and sodium chloride. When polymerization was of a nonalfin type, the most easily observed features were that the percentage conversion by a given quantity of reagent was low, even though the time was long, and that the intrinsic viscosity of the polymer was low, in these tests less than two. If the alfin type of polymerization prevailed the polymerization was faster, with well over half being completed in a half hour, and the corresponding intrinsic viscosity was higher, usually above four a n d reaching t o ten or more.
1 2 3 4 5 6 6 7 8 9
9 10 10 11 11 12 12 13 13
Salt LiF NaF NaF N.aF LiCl KF KF LiBr LiBr NaCl NaCl NaCl NaCl NaBr NaBr CsF CsF LiI LiI
Dist., A. 2.01 2.31 2.31 e.31 2.57 2.67 2.67 2.75 2.75 2.81 2.81 2.81 2.81 2.98 2.98 3.01 3.01 3.02 3.02
Used,
M1. 25 25 25 25 25 10 20 25 25 10 20 20 10 20 10 25 10 25
Yield,
%
0.5 0.4 0.5 0.7 0.5 0.4 0.9 0.3 0.3 7
10
4 5 13 18 1 3 5 14
per ml.,
%
0.02 0.02 0.02 0.04 0.02 0.04 0.05 0.1 0.1 0.7 0.5 0.4 0.3 1.3 0.9 0.1 0.1 0.5 0.6 0.5 0.5
Intrinsic Viscosity Low 0.6 0.6 0.6 1.0 0.9 0.9 2.4 1.9 8.3 9.2 9.3 9.0 10.7 10.0 4.0 4.7 10.0 9.7 9.4 8.6
Gel,
% ..
30 36 53 40 13 33 24 38 5 5 46 23 4 5 71 81 36 41 8 8
A1fi.n Activity& N
x N
N N N
N
N
N
G G F F VG G P P G G (
a The.letters N, G, F,P, and VG refer,, reapeotively, to none, good, fair, poor, and very good as Judged b y the percentage conversion.
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
2878
Vol. 44, No. 12
oxide, and sodium hydroxide (numbers 6 t o 8) created no alfin TABLE111. IXFLUENCE OF PSEUDOHALIDES, MISCELLASEOUS activity. Therefore, ordinary chemical activity was not reSALTS, ASD OTHER SURFACES ON THE POLYMERIZATIOS -4CTIVITY quired in the t h k d component, Only potassium carbonate of the O F .~LLYLSODIUMTOWARD BUTADIESE miscellaneous salts tested in numbers 9 to 14 bhowed any alfin Polymer activity. Some of the ordinary type of sodium polymerization Yield Cat. may have been present, because the intrinsic viscosity of the Yield, per ml., Intrinsic Gel, Blfin Used, % Activitya 311. Viscosity KO. Salt 5% 5% polymer was comparat,ivelyloa- and \?as much lower a t high con14 10 1.4 9.6 13 VG 1 NaCN version. The common supports for catalysts tested in the last 14 G 8 9.5 0.7 20 four experiments Iist,ed in the table failed t o create activity as 13 10 2 KCN 9.4 18 T’G 1.3 36 1.8 22 TG 9.8 20 did sodium chloride. Specific ions are, therefore, required for nlfin 31 3.1 E 45 3 SaSCN 10 13.8 activity. The geometry of t,he surface seems important. 56 E 2.5 50 20 11.8 Tests on isoprene confirmrd those with butadiene in that 40 4.0 20 E KSCN 10 4 13.9 sodium chloride proved essential for alfin catalysis and sodium 2; 60 50 E 2.4 11.5 thiocyanate could replace the chloride (see Table IV), alt,hough 2 54 15 KCNO 0.2 2.9 10 4 59 N 0.2 20 2.8 in this case not so effectively because it was the coarse granular Low .. N 6 NaH .. Oil material and the chloride was the finely divided Wurtz product. Low S Oil 7 NaOCHa 33 S 8 h-aOH 0.2 0:02 0.5 10 Butadiene was polymerized about seven t,imes faster tlian iso38 S 0.05 1.2 9 YaNOs 10 0.5 prene by the ordinary sodium reagent and about 40 to 70 t,imes Low N 10 hazC03 Oil 25 13 1:3 H i VG 11 &COI 4.0 10 faster by the alfin catalysts. 13 E 25 80 3.2 2.5
P:
12 13 14 15 16 17 18
NazSO4
&so4
CaClr Alumina Carbon5 Sil. “1 Glass
2.5 25
25
25
25 25 25
0.6 Low 0.0 0.1
0.2
0.02
..
1.5 Oil
35
N
0:01 0.01 0.04 0.04
0:3 0.4 0.5 1.0
22. 3
N N N
..
N
EFFECT OF THE C4TION
The sodium cation is essential for alfin catalj-sis and potrtssium The tePts were made by recan reulace sodium only . in part. placing one Or more Of the sodium salts by the correspondillg POa The letters have the same significance as i n Table 11, E llleans exoellent: however the best of the cat,alysts made by this method (C) are intassium one in either method B or C (usually C ) for preparing the ferior t o those made by method B. catalyst. In addition to the criteria already described, several b Merck’s activated carbon. 0 Soft glass was powdered in a mortar with pestle. ot,her features were used as rough guides for alfin catalysis. The viscosity of t h r polymer was independent Of the monomer-catal!-st ratio! nhereas ~ ~A T H I ~A~c rG p I V ~(ALFIX) SALTON P o L Y 1 \ ~ ~ ~ ~ TABLE IV. I s F L U E aoF nonalfin polymerization the usual rule of lower ZATION O F ISOPRENE AKD BUTADIENE B Y ALLYLSODIUM AND SODIUM ISOPROPOXIDE viscosity with inore organosodium reagent held. Yield/ The alfin polymers were only slightly soluble in Hr./B.Il. Third Cat.b, Time, Yield, Cat. Camp; Intrinsic Gel, pentane if a t all under the conditions used, v-hile Diene Salt 1741. Hr. % Used, % Yield Viscosity % the nonalfin polymers obtained under the condiIsoprene None 25 9 1.6 0.007 1 3.1 17 tions of these experiments m r e sticky oils that 0.007 1 .. Sone 25 18 3.2 rl’aCl(w) 10 2 5 5.4 0.22 31 6:3 3 dissolved easily. I n some mses both polymers 2.3 0.4 0.02 3 NitSCN 10 25 5.0 11.8 0.09 13 NaSCN 5:o ii were obtained from the same reaction and could Butadiene None 20 3.0 3.0 0.05 7 1.0 18 be separated by their relative solubilities. The NaCl(v) 10 0.5 46.0 9.2 1310 16.3 30 NaSCN 10 0.5 31.0 6.3 900 13.8 4.5 alfin polymerization was only moderately esotherniic and no appreciable color change n-as oba Actually a fourth salt, sodium allyloxide, was present in all these tests. b Volume of catalyst used on 30 ml. of butadiene in 200 ml. of pentane. served during the reaction, m-hereas the nonalfin C Comparative yield based on the first two as 1. type was noticrably exothermic and the color changed from blue t o pea-green t o brown n- it does when amylsodium is the reagent. By these criteria the sodium cation in the isopropo-de salt or increasing bond distance between the respective ions (the third column) because some physical factor seems important and bond distance can influence surface catalysis. The first 19 preparations are with similar salts, each having the sodium chloride type TABLE 5’. EFFECT O F CllTIOS O S AkLrISCATkLYbIE! of cubic crystal structure. The last two have the cesium chloride Cationb Present with structure. Prep. IsoPolymerization All halide salts of the sodium chloride type with bond distance No. X e t h o d Q Allyl propoxide Chloride &fin Potas. by a t 2.i5 A. and below failed t o produce alfin catalysts, Tvhrreas those at 2.81 A. (the value for sodium chloride) and above did form them. The best were in the range from 2.81 t o 3.29 A., although in uneven gradation, Potassium chloride, sodium bromide, potassium, bromide, and sodium chloride were most effective approximately in order. At 3.53 A., lvhich is the value for potassium iodide, the activity was poor and one of the preparations 13-asvery m T h e letters designate the method of preparing the catalyst as described unsatisfactory. The tn-o cesium salts with cesium chloride struca t the beginning of this paper. b The letters w a n d g i n parentheses refer t o the source of the halide salt a s ture (numbers 20 and 21) were much better than cesium fluoride given in Table I. (reagent 12) which has the sodium chloride cubic structure arid is c Y signifies yes, N means none. The nonalfin type is deaignated a s Potas. in the preferred range for salts of t h a t type. d Observations were made of the following five points on alfin-type The tests were then extended t o other salts and halides. As a polymerization: 1) relative insolubility of the polymer in pentane: (2) high viscosity of the polymer: (3) iodine monochloride precipitation of the class the pseudohalides (see Table 111, numbers 1 to 5) and the polymer; (4) viscosity of polymer largely independent of monomer/catalyst ratio: ( 5 ) moderate exothermic character a n d absence of color change, blue thiocyanates were very good t o fine. The thiocyanates have a t o pea-green t o brown. e Some metallic potassium was present in this reagent. rhombic structure and the potassium salt has a bond distance of 3.33 A. The chemically active sodium hydride, sodium meth0.9
1.0
45 54
S
h-
,
2zg:
December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEVI. EFFECTOF ADDITIONALALKOXIDESOVER NEEDED
TO MAKE THE R A T I O O F
Excess Alkoxidea None iso-NaOCaHi teTt-NaOCsHiI iso-KOCsHi iso-LiOCxHi
?
ALLYLsoDIUM
ISOPROPOXIDE APPROXIMATELY 1: 1 Cat.
C0ncn.b 0 19 0 13 0 13 0.20 0 20
Yieldc,
%
38 63 30d 31 0
Yield per Meq. of Cat., % 40 96 23 31
THAT TO f h D I U M
Intrinsic Viscosity 13.1 15.4 15.9 16.3
Gel,
%
16 13 61 47
0 I n all cases the alkoxide in exoess of that used in the first or control experiment was the same. b This value is given as milliequivalents of allylsodium per milliliter of suspension and the amount is a n average of yields which have been obtained in a number of preparations. C Yield of polymer caused by 5 ml. of,catalyst suspension. d 10 ml. of catalyst used in this experiment.
.
*
TABLE
VII.
EFFECTOFLITHIUMISOPROPOXIDE ON THE ACTIVITY OF AN ALVINCATALYST
Isopropoxide, Polymerization Mole Cat., ml. Yield, 70 0.113 3 54 0.118 10 93 0 0.225 20 Sodium 0.225 3 74 1.125 3 24 1.125 10 100 Excess alkoxide added over that formed by addition of 0.225 mole of 2propanol to standard preparation from 1 gram atom of sodium. Ekoessa Lithium
v,
c
*
2879
by a miscellaneous group of reagents which had all or some of the components of the alfin catalyst. The results arelisted in Table VI11 in the order of increasing percentage of external double bonds. The lowest percentage was 25 where all the components needed for the alfin catalyst were present. The first five reagents have in common the same anions, except that the n-propoxide was substituted for the isopropoxide in number 3. Their average percentage for the external bonds is 34. For numbers 6 t o 11, only two of the salts needed for the alfin catalyst were present. As a class the external double bond percentage is higher; the average is 43. The last tworeagents have only one of the a]fin salts or have a limited quantity of the second salt and the average external double bond is 5201,. The highest is 61%. This last value is near that credited (21) t o the usual type of sodium polymerization. Similar results were found with isoprene where the percentage of external double bonds was lower. The two reagents (Table I X ) which had the three salts that were in alfin catalysts had the lower percentages; the one with only two salts of the alfin system had a higher value. It is clear, therefore, that salts affect the number of external double bonds. The components of the alfin catalyst have so far been responsible for producing polymers with the lowest percentage Of 1,%3trUCtUre,but a h Catalysis iS not essential for a ] O w value, as shown by numbers 3 and 5 of Table VIII. A combination of three salts seems more effective than two. This influence of salts in polymerization may, a t first, seem strange. A salt effect is, however, the rule even in the simplest reactions of organosodium reagents. I n the alkylation of toluene, the yield Of was more than by the presence of certain salts (13). I n the metalation of tert-butylbenzene, the position and amount of metalation is subject t o wide variation by the presence Of which at One time have been SUPposed to be inert (4). Some tertiary alkoxides have pronounced effects in dimetalation Of the hydrocarbon ( I , ' 4 ) . I n the pyrolysis of amylsodium ( 1 5 ) the percentage and manner of decomposition is subject to this type of control. The effect of polymerization by a sodium reagent is, therefore, quite in line with other behavior. BY the choice of Proper salts to accompany allylsodium, with proper care in the quantity of catalyst used and with some attention t o the details of recovery, a polybutadiene can now be obtained which has a weight average molecular weight ( 2 )of around 7,000,000, the highest known value for any synthetic
the halide salt was found to be replaceable separately (Table numbers 1 to5) by potassium but not in both salts simultaneously (number 7 ) . Allylsodium could not be replaced by allylpotassium (number 6) in spite of the fact that ion interchange in the aggregate might and probably does very slowly, earlier experimerits ( 2 0 ) having shown that time often alters the activity of these reagents, The of sodium by potassjum in all three salts produced a fast-acting reagent (see also Table VIII), but the polymer therefrom had a low intrinsic viscosity and was nonalfin by every test. The lithium ion usually destroyed the alfin catalyst when only a moderate amount was present. This fact was shown in Table I1 for the halides and also in two different series where lithium isopropoxide was incorporated in an alfin catalyst which otherwise would have been very active. The activity decreased and disappeared when as many moles of lithium isopropoxide had been added as there were moles of sodium isopropoxide in the catalyst. The same test with TABLE VIII. INFLUENCE OF SALTSON THE POLYMERIZATION OF BUTADIENE AND THE sodium or potassium isoproUNSATURATION OF THE POLYMER Doxide caused no deterioration No. of External in activity (see Tables VI and Alfin Method Total Double Componentsa in Reagent salts of Yield, Intrinsic Gel, Unsat., Bonds, VII). INFLUENCE OF SALTS ON THE POSITION O F THE DOUBLE BONDS IN T H E POLYMERS
The salts associated with t h e o r g a n o s o d i u m reagent affected the number of external double bonds, that is, the side vinyl groups produced by 1,2polymerization, irrespective of Rhether polymerization was of the alfin type or not. Iodine monochloride was used for measuring total unsaturation and perbenzoic acid for the external double bonds, each according to the procedures of Kolthoff and coworkers (y-9). The polymers were prepared
No. 1 2 3 4 6 6 7
8 9
!? 12 13
RM AI-Na A1-Na AI-Wa AI-Na Al-K Am-Na A1-Na A1-Na AI-Na A1-Na A1-Na Al-Nah. Am-Na Am-Na
ROM
Na (iso) Na (ipo) Na (n) Na (180) K (iso) Na (iso) Na (iso) Na (iso) Na iso) Na {iso)
.. .. ..
...
MX NaCl NaCl NaCl NaCl KC1 NaClf LiBr NaCl NaOH
...
NaCl NaCl NaCl
Present 3 3
2 2 2 2 2
Prep. B B B C C B C 33 C C C B
1
B
28
3 3 2 26'
1
...
70
28 65 6 14
95 8 7 14 16 5 4 4
...
45
Viscosity 11.6 12.6 1.2 1.8 1.8 1.0 0.6 0.4 0.8 0.8 0.4 0.6
...
0.7
%
%
7 39 68 11 4 7 4 3
lOOb 98.9C 77 75
70
25 28Czd
2 6
72 73 73 77 73 81 83
32 37 37,41 40 42 44 44 44 47 53
4
83''
61
2
4
...
86
...
a M refers to the metal cation, A1 to allyl, Am to amyl, and R to a propyl radical which is Lo or normal as indicated b This in the value was assumed because the iodine monochloride reagent caused precipitation that made the test unreliable. This value was taken from the literature (6). d This value was confirmed by infrared measurements made by the courtesy of Meyer ( I 1 ) of the United States
Rubber Only two alfin anions were present but the n-propoxide eeemed t o cause about the same effect on 1,4-polymerisation as the isopropoxide did, althodgh without equal effectiveness on the yield and viscosity. 1 This sodium chloride wm the granular variety and was poorly incorporated in the mixture. 0 Actually three alfin anions were r e n t in this reagent but the lithium cation interfered with the influence which the bromide anion might have ad. h This catalyst contained a mixture of allylaodium and amylsodium in the ratio of approximately 2 to I .
INDUSTRIAL AND ENGINEERING CHEMISTRY
2880 TABLE Ix.
I N F L U E N C E O F S.4LTS O S THE P O L Y M E R I X A T I O S O F ISOPREKE BY A4LLYLSODIUN AND ON THE ~ K S A T K R A T I O N08 THE
POLYMERS Allyleodiuni and Sodium Sllyloxide with Na isoprop.-SaCl Na isoprop.-YaSCS hTaisopropoxide
%
Gel,
%
Total Unsat.,
Ext. Bonds,
Viscosity
J
6.3 8 0 3.0
3 21
86 89
11 16
Yield, 12 3
Intrinsic
17
69
so
24
polybutadiene \diich is also soluble. Great possibilities in this method of control of the preparation of diene polymer are thus revealed. IODINE MONOCHLORIDE T E S T FOR A L F I h POLYBUTADIENE
When iodine monochloride was added t o a solution of alfin polybutadiene in carbon disulfide-chloroform (60-40) in the determination for total unsaturation ('i'-9), a precipitate, n-hich aln-ays occurred and made the results unreliable, proved useful instead as a test for these alfin polybutadienes. Under the specified conditions the precipitate formed within 10 minutes, m-hereas114th polybutadienes prepared by sodium reagents several hours were required. I n the presence of ordinary sodium rubber, as little as 0.25% of alfin polybutadiene m a thus detected. This test was applied to those products listed in Tables I, 11, and I11 which had low intrinsic viscosities but had been made by reagents vhose compositions have produced alfin polymers. I n every case a precipitate formed where the proper components in the catalyst had been present and did not form when they were not there. Every mixture which gave a positive test always gave the same test in subsequent experiments. The success of the test is possibly due to the unusual molecular \\-eight of the alfin polybutadiene. The alfin rubber from a benzylsodium-sodium isopropoxide-sodium chloride catalyst gave a precipitate also, although the average intrinsic viscosity of this polymer is lower than from the better catalyst. Actually alfin polybutadienes of log- intrinsic viscosities such as were produced by some of the catalysts tested early in this work (27) may be mixtures of an alfin polymer of very high molecular weight and an ordinary sodium-type polymer of low molecular m-eight, because with catalysts numbers 7 to ll in Table I polymers of very Ion- intrinsic viscosities were formed although the precipitation test was positive, indicative of a small amount of alfin polymer present. In this group the only alfin catalyst that was present was the mixture of allylsodium, sodium isopropoxide, and sodium chloride that regularly produces polymers with intrinsic viscosities of 10 and above. Also, in Table V, the two forms of polymerization took place simultaneously in numbers 3 and 5 and the polymers could be separated by their comparative solubilities in pentane. The test does not apply t o alfin polyisoprene. EXPERIMENTAL PROCEDURES
GENERALPROCEDURES. All preparations of reagents mere carried out in the high-speed stirring apparatus ( 1 9 ) . The speed was a t 5000 r.p.m. except in a few cases designated. Where sodium metal had a tendency to agglomerate, the stirring was much slower and is described as cautious. A11 additions of alcohol or alkyl halide t o alkali metal or alkali metal reagent were dropwise and the mixtures lvere always stirred 30 minutes or longer after addition was completed. The need for care during these steps cannot be overemphasized. No preparation should be attempted unless the apparatus is properly shielded. An attendant should be present a t all times in order to control the reaction and particularly to avoid any chance that vibration would loosen a stopcock or otherwise alter the rate of addition. The making and handling of all reagents, their transfer to storage
Vol. 44, No. 12
bottles, and the removal of samples for test were done under an atmosphere of dry nitrogen. The general techniques for these steps as well as for the tests on polymerization were the same as have already been described (17, 18, 20). Pentane \\*as usually t,he medium for all react,ions. REAGESTS.Most of the reagents used in t,his work have been described in previous publications. The n-amy1 chloride was filtered through calcium chloride, alumina, and calcium sulfate (Drierite) as mentioned in a previous paper (15). Allyl alcohol (Eastman Kodak Co., pure grade) m s distilled (boiling point 96" t o 97" C. uncorrected and ng 1.4140) before use. Diallyl ether of 95% purity \\-as obtained through the courtesy of the General hlills Co. research laborat,ory. I t was dried over calcium chloride and then fract,ionated to remove the binary ieotope which contained 307, allyl alcohol and boiled a t 89.8" C. The fraction which boiled a t 94.8" C. \vas used in the expsriments. Cesium fluoride preparation n-as from anhydrous hydrofluoric acid and cesium bromide, n-hich n-as obtained through t'he kindness of the Don- Chemical Corp. Lithium iodide (1Iallinckrodt's) n as pon-dered by mortar and pestle in a dry box and dried over phosphorous pent,oxide for 4 days. It \vas then recrystallized (3)from anhydrous acetone and finally dried a t 80" C. in a vacuum oven over phosphorous pentoside. Sodium hydride was obt,ained through the courtesy of the Met'al Hydrides Co., Beverly, 1lass. PREPARATION O F R E ~ G E S TTTITH S GRAXLARHALIDES A L T 5 AKD OTHER TECHSICALLY ATAILABLE hhTER1.4L. 2-PrOpanOl
(6.0 grams or 0.1 mole) was added slowly to 0.1 gram atom of sodium sand and 0.4 mole of dried commercial halide salt or other solid suspended in 400 ml. of pentane with stirring a t 8000 r.p.m. Thereafter the mixture was stirred 3 hours before being transferred to a storage bottle. This mixture was added to 0.8 gram atom of sodium sand, the whole diluted with pentane to 500 ml. and stirred cautiously, while 0.2 mole of 2-propanol in a n equal volume of pentane was added a t 10' C. The tendency for the metal to clump was particularly troublesome when potassium fluoride was present. After addition was completed, the temperature a as allowed to rise to 20' C. while the mixture was stirred a t 5000 r.p.m. Diallyl ether (29.4 grams or 0.3 mole) was added over one-half hour while the temperature was maintained a t 20" to 25' C. The stirring was continued for 2 more hours before the brown-colored mixture was transferred to a bottle and diluted with pentane to 600 ml. This procedure x a s the one ordinarily used for the preparation of the reagents used in Tables I1 and 111. I n general the yield of allylsodium, judged by carbonation, was around 60%. TESTS7%ITH SODIUMHYDRIDE, SODIUMHYDROXIDE, AKD SODIUM METHOXIDE.The preparations listed in Table I11 which contained sodium hydride, sodium hydroxide, and sodium methoxide were made ~ i t ah slight alteration of the above technique. 2-Propanol (0.2 mole) was added to 0.7 mole of sodium hydride in pentane, The mixture was stirred for 2 more hours before addition t o the reaction mixture which was to be used for cleavage of diallyl ether. For the reagent that contained sodium hydroxide, a mixture of 0.1 mole of 2-propanol and 0.4 mole of water was added at 10" C. t o 0.5 gram atom of sodium while the mixture was stirred cautiously. After evolution of hydrogen had ceased the suspension was stirred for 2 hours before its introduction into the mixture where cleavage of diallyl ether was to be effected. The same procedure was used for the reagent that contained sodium methoxide except that methanol was used in place of water. EFFECT O F SODIC11 ISOPROPOXIDE AXD SODIUV HALIDES O S THE ACTIVITYOF ALLYLSODIUJI.The reagents for these tests were made in the same way as previously described except that the mixtures of salts were not stirred so thoroughly. The results are listed in Table I. For reagent 1,sodium isopropoxide was made by the addition of 0.1 mole of 2-propanol to 1 gram atom of sodium sand. After 30 minutes more of stirring, 0.15 mole of diallyl ether was added a t 20" C. The temperature was then raised t o
December 1952
I N D U S T R I A L A.ND E N G I N E E R I N G C H E M I S T R Y
50' C. and held there for 4 hours before transfer t o a storage bottle. This material caused no appreciable polymerization of butadiene when 25 ml. were used, whereas 3 t o 10 ml. of an alfin reagent usually show high activity. No better result was obtained 2 weeks later. Carbonation of the remainder produced 6.9 grams of vinylacetic acid (61% yield) and 0.7 gram of crotonic acid, the latter presumably by rearrangement from the former. Similar cleavages of diallyl ether were carried out in the presence of sodium isopropoxide and sodium halides made by Wurtz reactions, sec-butyl chloride being used for sodium chloride, ethyl bromide for sodium bromide, and ethyl iodide for sodium iodide. Each alkyl halide (0.2 mole) was added t o 1gram atom of sodium in 500 ml. of hexane a t -10' C. over 1 hour. After 30 minutes' more stirring, 0.2 mole of 2-propanol was added at 10' C. The temperature was increased t o 35' C. and 0.3 mole of diallyl ether was then added during 30 minutes. After 2 more hours' stirring the mixture was transferred t o a storage bottle. Reagents 3, 12, and 14 were thus prepared. For reagent 2, the Wurtz sodium chloride was made by addition of 0.2 mole of amyl chloride t o 1.0 gram atom of sodium. Thereafter, 0.2 mole of allyl alcohol was added t o destroy the amylsodium and 0.3 mole of diallyl ether was then cleaved. For the tests where sodium halide was added before and after the cleavage reaction (reagents 4, 5, and 6), the mixture of sodium halide and sodium isopropoxide was made by addition of 0.8 mole of amyl chloride a t -10' C. t o 1 gram atom of sodium during 90 minutes. After stirring for 60 minutes more, 0.2 mole of 2-propanol was added a t 10' C. followed by stirring for 90 more minutes. During these reactions the blue color of the amylsodium was replaced by a steel gray. The mixture was transferred t o a storage bottle. Half of this mixture was added t o 1 gram atom of sodium sand t o which was then added 0.2 mole of 2-propanol at 10' C. with cautious stirring. Cleavage of 0.35 mole of diallyl ether was effected a t 35" C. After being stirred 2 more hours, this mixture was transferred t o a storage bottle and used as reagent 4. The other half (300 ml.) was added to a suspension of allylsodium which had been made from 1 gram atom of sodium, 0.2 mole of 2-propanol, and 0.35 mole of diallyl ether and, as reagent 5, had been found inactive. The mixture of three salts was then stirred together for 5 hours a t 5000 r.p.m. before transfer t o a storage bottle and, as reagent 6, proved catalytically active. For reagent 8, the granular sodium chloride, previously ground in the high-speed stirring apparatus, was present during the preparation of the isopropoxide and the subsequent cleavage reaction. The catalyst had a perceptible amount of activity but a second preparation, number 9, was not equally successful. I n reagent 10, the sodium chloride was added prior t o making of the sodium sand. I n reagent 11, the granular sodium chloride was ground for over an hour in decane by high-speed stirring, before addition t o the sodium prior to making sand. I n reagent 12, the sodium chloride was ground separately, as in reagent 8, except that the stirrer shaft was grounded in order t o remove a static charge which caused a troublesome deposit of the finely ground salt on the wall of the glass flask. REAGENTS THAT CONTAINED ALLYLPOTASSIUM AND/OR PoTASSIUM ISOPROPOXIDE. These preparations (for Table V ) were carried out in the same manner as the analogous sodium reagents described for Tables I1 and I11 except for substitution of potassium for sodium during the preparation, as indicated. More care must be taken in preparing these reagents because of the highly exothermic character of the reactions. The cleavage of diallyl ether took place at 10" C. when potassium metal was used. For reagents 3 and 4, the potassium isopropoxide was prepared separately in an amount approximately equal t o the allylsodium t o be produced and added to the suspension of amylsodium before admission of propylene. The polymerizations with the all-potassium reagent were carried out a t room temperature behind a safety glass shield. The reactions were very exothermic. If enough reagent were used the
2881
pressure bottle exploded. I n no case, however, did any high molecular weight rubber form. At -10' and -30' C. no appreciable polymerization took place. EFFECT OF SODIUMALLYLOXIDE ON THE PREPARATION OF A N ALFIN CATALYSTFROM AMYLSODIUM AND PROPYLENE. The preparation of an alfin catalyst from I gram atom of sodium, 0.5 mole of amyl chloride, 0.35 mole of 2-propanol, and propylene was carried out in the usual way (17, 18,20) for method B, except that in a series of preparations the 2-propanol was replaced by mixtures of allyl alcohol and 2-propanol. Each catalyst mixture was then tested for its activity toward butadiene and a portion was also carbonated in order t o determine the content of unsaturated carboxylic acid that was expected t o be vinylacetic acid. For the control catalyst where no alcohol was used, the grams of polymer produced for each milliequivalent of unsaturated acid varied from 3.1 t o 4.0. As allyl alcohol replaced 2-propanol the activity decreased somewhat, and a t a mole ratio of 2.5 isopropyl t o 1 allyl alcohol the yield was 1.5 grams. At a ratio of 1.5 t o 2.0 the yield was only 0.08 gram and a t 1 to 2.5 and higher, no polymer was produced. Qualitative examinations of the unsaturated acids obtained by carbonation indicated that the quantity of vinylacetic acid was small and that sodium allyloxide was being metalated. T o demonstrate the susceptibility of this oxide to attack by amylsodium, allyl alcohol (11.6 grams or 0.2 mole) was added a t 10' C. to a rapidly stirred (4000 r.p.m.) suspension of amylsodium prepared from 1 gram atom of sodium. After being stirred 3 more hours, the mixture was transferred t o a bottle and stored for 2 weeks. Carbonation yielded a water-soluble acid which, unlike caproic acid, was not extracted by petroleum ether but was recovered from the ether extract as a red sirupy liquid (7.1 grams). It was soluble in water, ether, or alcohol and was insoluble in pentane or benzene. It decolorized bromine and permanganate. Attempts t o isolate a product or derivative of a monocarboxylic acid from allyl alcohol were unsuccessful and the material behaved as the carboxylic acid from a dimeric or higher polymer of allyl alcohol. The crude material had a neutralization equivalent of 204 and a molecular weight of 227. Ultimate analysis was correct for C7H1204. Distillation a t pressures below 0.1 mm. in a short path still caused Lhe sirup to harden as if the acid were a,p-unsaturated. A repetition of the experiment with the metalated mixture allowed t o stand for only 2 hours and with decomposition with ethyl bromide instead of carbon dioxide, yielded material from which 3 grams distilled a t 140" C. a t 1 mm. and which had a molecular weight (Rast) of 245, approximately equal t o a trimer. EFFECT OF SODIUMALLYLOXIDE O N A N ALFIN CATALYST.A stock solution of sodium allyloxide was made by addition of the amount of allyl alcohol needed t o react with the amylsodium that had previously been prepared from 3 gram atoms of sodium and was found t o be present in 82% yield as determined by carbonation. The mixture was thoroughly stirred for 1 hour, allowed t o stand overnight, then stirred again for a short period before transfer t o a storage bottle where the suspension was diluted to 1500 ml. An alfin catalyst was made from 3 gram atoms of sodium, 1.5 moles of amyl chloride, 0.35 mole of 2-propanol, and propylene a t 10' C. in the usual manner. Carbonation showed that each 400 ml. of this suspension contained 44.2 meq. of allylsodium and 3.8 meq. of amylsodium, the presence of the latter being caused by the usual failure of the reaction of amylsodium with propylene t o be complete. T o 400-ml. aliquots of the catalyst was added enough of the sodium allyloxide suspension t o give ratios of 0.525, 1.05, 1.48, and 2.00 for the allyloxide t o allylsodium, and the volume of each was diluted with pentane t o 550 ml. These four mixtures were designated as A, B, C, and D, respectively. Each mixture was stirred a t 5000 r.p.m. for 2 hours in a 1-liter flask as was also a control portion of the catalyst without sodium allyloxide but diluted t o 550 ml.
-
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
2882
Duplicate tests for catalytic activity of each suspension were made at stated intervals by bottle polymerization with 5 ml. of the catalyst, 30 i d . of butadiene, and 200 ml. of pentane t h a t had been dried over amylsodium. These tests extended up t o 112 days after the catalysts had been prepared. No important difference could be noted in the effectiveness of the reagentp (Table
X).
T ~ R LX. E COX'.4RATIl E *ACTIVITY O F -4LFIN C4T4LYSTS THE P R E S E ~OF C ESODIUXALLYLOXIDE Cataljst Yielda, ?i 2 days 24 days 47 days 69 days 112 days Intrinsic viscoFity 2 days 24 days 47 days Gel, 7 0 2 days 24 days 47 days
Contiol 88 76 78 29
_I J-
9 9 18. I
16.2 21.9 19.3
?!
113
C
66 85 73 81
70
11.6
21.9 20 9
7.4 16 2 16 9
20 9
58 74 64
46 52 36
24 ' 53
61
33
18.3
B
I
67
41
57
(i 8
?!3 3
13
51
IN
D
Si
80
76 T4 32
77 73
..
15'4
h e l d of polymer after the catalyst had aged for the nunihei of days indicated.
Bfter the 112-day test, the activity of each mixture had deteriorated about equally, probably because repeated opening of each bottle t o remove samples for testing had permitted some contamination with air. The control actually showed more deterioration than did the four with sodium allyloxide. T h e tn-o suspensions with larger amounts of sodium allyloxide thickened appreciably, probably because of a small amount of metalation of the sodium allyloxide by the amylsodium t h a t was present and the consequent dimerization or polymerization of that salt, as described before. This change in the physical condition of the catalyst had no influence on polymerization activity other than t h a t caused by the greater difficulty of removing exactly 5 nil. of the catalyst for the test.
TABLEXI. PRECIPITATIOS O F POLYBUTADIENES BY IODIXE MOSOCHLORIDE
Cat. KO.
1
2 3 4 5 6
7
8
9
10 11 12
Inorganic Saltn Xone NaCl NaCl SaCl NaCl NaCl NaF XalSOA LlCl KCXO LiBr YaClb
Polymer
Yield, % 15 7 2 5
22 2 2
3 2 I)
7 1.5
Intrinsic Tiscoaity 0.8 I 1.3 1.4 3.2 0.8 1.2 1.0
1.8 1.1 3.1 0.6 0.4
Time for Ppt.
To Appear, A h . 420
3
10 5
3
150
150 360 300 360 2
a Allylsodiuin and sodium ijoproposide were the other two com1)onent.s of t h e reagent. b The polymer tested \vas inade by a benzylsodium instead of a n allylsodium reagent and the catalyst \\-ab made by method B instead of C.
EFFECT O F LITHICWISOPROPOXIDE ON THE CATALYST,I n the first series amylsodium was prepared from 3 gram atoms of sodium and 1.5 moles of amyl chloride. For the control experiment 0.66 mole of 2-propanol was added. Propylene was then passed into the mixture in the usual way. If the yield of amylsodium were 82% and the conversion t o propylene quantitative, the quantity of allylsodium would be 0.6 mole. As a rule this yield was reached. The ratio of allylsodium to alkoxide ~ * o u l d then be approximately 1: 1. To obtain the excess alkoxide listed total of 0.9 mole of 2in Table VI. more alcohol was added.
Vol. 44, No. 12
propanol or 0.3 mole of 2-propanol with 0.6 mole of tert-amyl iilc ohoI was used for the second and third reagent of the table. Where the potassium and lithium alkoxides \\*ereadded, the salt was first prepared from 0.6 mole of the metal with 1.08 mole of 2-propanol and the alcohol-alkoxide mixture then added to amylsodium prepared from 2.4 gram atoms of sodium and 1 2 moles of amyl chloride. The concentration of allylsodium vaiied accordingly in these preparations. I n the second series the amylsodium mas prepared from 1 gram atom of sodium and 0.5 mole of amyl chloride. To this mixture v-as added 0.225 mole of 2-propanol with isopropoxide (made hy addition of alcohol to the metal) in the amounts given in Table
VII. REACTIOV OF
THE
POLY~IERS ~ I T I XIODIKE 31ONOCHLORIDE.
The general procedure was the same as described by Kolthoff and coworkers (7-9) for the analysib of the number of double bonds. As used for the detection o€ alfiii polybutadienes (made by pouring a benzene solution into 0.2% methanolic phenyl-p-naphthylamine solution) in this study, 40-mg. samples of the dried prec,ipitate were dissolved in 10 nd. of chloroform and 25 ml. of carbon disulfide in 50-ml. volumetric flasks. Ten nil. of a chloioform solution which contained 0.1% gram of iodine monochloride a-ere added to the polymer solution, the contents of the flask n-ere mixed, and the volume was r ed t o 50 ml. by addition of carbon disulfide. The white flocculent precipitate could be best observed in the deep-red solution by looking through the Aask into a strong light while gently swirling the contents. Some reyults with a variety of catalyst preparations are given in Table XI. ACKNOW LEDGRIEIVT
The authors are greatly indebted t o the Office of Synthetic Rubber, Reconstruction Finance Corp., for financial assistance of this work. A11 experinients except those on the effect of lithium isopropoxide were by F. H. Bolton. Cesium fluoride x-as prepared by D. L. Breck and R.S. Becker. LITERATURE CITED
Claff, C. E., Jr., unpublished experiments. Cleland, R. L., Ibid. Coates, J. E., and Taylor, E. G. G.. J . Chem. Soc.. 1936. 245. Collins, F. W., and Claff, C . E., J r . , unpublished experinknts. Coombs. R. D.. I b i d . D'Ianni,' J. D., kaples, 1:. J,,and Fields, J. E., IND. ENG.& E x , 42, 95 (1950). Kolthoff, I. M., and Lee. T. S.,J . Polgmer Sci., 2, 206 (1947). Kolthoff, I. hf., Lee, T. S.,and >lairs, M.S.,Ibid., 2, 199, 220 11947). Lee, T. 'S., Kolthoff, I. AI., and hfairs, >I. A , Ibid., 3 , 66. 303 (1947). Letsinger, R. L., and Trayiiham, 3.G., J . Am. Chem. Soc., 70, 3342 (1948). Aleyer, A. W., private communiration. Morton, A. il., IND.EKCI. CHCX,42, 1488 (1950). Morton, A. A., and Rrachnian, -4.E., J . Am. Chem. S o c . , 73, 4363 (1951). Morton, 9.A., and Claff, C. E., paper presented a t 119th Meeting, AM. CHEMSOC., Boston, Mass., 1951. Morton, A. L4.,and Cluff, E:. F., J . Am. Chem. Soc., 74, 4056
(1952). Morton, A. A,, and Grovenstein, E., Jr., I b i d . , in press. Morton, A. A., Magat, E. E., and Letsinger, R. L., I h i d . . 69, 950 (1947). Morton, A. A., Marsh, F. D., Coombs, R. D., Lyons, A. I,., Penner, S.E., Ramsdeii, H. E., Baker, V. B., Little, E. I,.,Jr., and Letsinger, R..L., I b i d . , 72, 3785 (1950). Morton, A. A,, and Redman, L. S., IND.ENG.CHEM.,40, 1190 (1948). Morton, A. A , , Kelcher, R. P.. Collins, F. W.,Penner, 9. E., and Coombs, R. D., J . Am. Cl~em.Soc., 71, 451 (1940). Ziegler, K., Grimm, H., and Willar, R., Ann., 542, 90 (1940). RECEIVED for review December 20. 1951. ACCEPrED August 4, 1952. A portion of this work was presented at the Conference on Mechanisms of Organic Reactions, Northwestern University, 1950, and a t the 119th Meeting of t h e ~ ~ E R I O ACHEMICAL N S O C I E T Y , Boston, Mass., 1951.
