CATALYST STUDY IN THE METHYLATION OF DECABORANE R. J. POLAK AND N. C. GOODSPEED' Olin Mathieson Chemical Carp., New Haven, Conn. In earlier investigations, using aluminum chloride as a catalyst for the methylation of decaborane, conversions were limited to 20 to 30% in order to obtain a product containing 60% of the monomethyldecaborane. In this study, catalysts other than aluminum chloride were investigated to determine whether increased conversions could be obtained without altering product distribution. Metal halides below aluminum in activity, mixed halides, and triethylaluminum failed to catalyze the reaction. Alkylations using alkylaluminum sesquihalides required lower temperatures, proceeded more rapidly, and increased conversions by 5 to 10% with no apparent change in product distribution. Arylaluminum sesquihalides yielded poorer deca borane conversions.
BENLAND
and Newberry ( 2 ) have discussed the methyla-
0 tion of decaborane in relationship to reaction concentra-
tion, temperature, reaction time, and reaction solvents. Another important parameter in the development of a process for a methylated decaborane fuel is the selection of a suitable catalyst. Previous investigations utilized aluminum chloride as the catalyst (2, 4 ) . T o obtain a product containing a minimum of 60% of the monomethyldecaborane, conversions were limited, using aluminum chloride, to a range of 20 to 30% ( 3 ) . Since a low conversion necessitates a costly and timeconsuming recycle for decaborane, it was desirable to find a catalyst which would increase decaborane conversion and still give a high yield of monomethyl product. This led to investigations of other Friedel-Crafts type catalysts (metal halides, mixed halides, and organoaluminum compounds) for the methylation reaction. Experimental
Catalyst Preparation of Organoaluminum Compounds (Sesquihalide Syntheses). These aluminum sesquihalides are known to be of high activity and several were prepared for use as catalysts. The general equation for this preparation is : 3RX
+ 2A1
I2
RzAlX
+ RAlXz
(1)
Using glass Minilab equipment consisting of a lOO-ml., four-necked flask containing a nitrogen inlet, stirrer, condenser, and dropping funnel, several sesquihalides were successfully prepared. After the apparatus had been flushed with nitrogen, aluminum turnings and iodine crystals were added to the flask, a small nitrogen flush was started, and by use of either a n oil or water bath, the temperature was raised to the desired range. T h e halide was then added dropwise with continuous stirring over a 1-hour period. The reaction was continued until complete. The unreacted halide was distilled from the mixture and the liquid product, usually black, was separated from the unreacted aluminum in a dry box. I n the preparation of methylaluminum sesquiiodide the condenser was maintained a t -30" C . The reaction occurred a t the reflux temperature of methyl iodide (42' C.). After a 4-hour reaction period, 62.5 grams of product were isolated from 15 grams of aluminum turnings and 75 grams of methyl iodide. Cold water was circulated through the condenser in the preparation of ethylaluminum sesquiiodide, the reaction
1 Present address, Chemicals Division, Pittsburgh Plate Glass Co., Pittsburgh, Pa.
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l & E C PRODUCT RESEARCH A N D DEVELOPMENT
occurring a t a bath temperature of 50" to 55' C. After a 3hour reaction period, 66 grams of product were isolated from 15 grams of aluminum turnings and 70 grams of ethyl iodide. T h e reaction of ethyl bromide and aluminum occurred a t a water bath temperature of 18' to 20" C . After a 1-hour reaction period, the temperature was raised to 38' to 40' C. (reflux temperature of ethyl bromide). No refluxing was noted, indicating reaction was complete. From 60 grams of ethyl bromide and 15 grams of aluminum turnings, 63.0 grams of product were isolated. To prepare phenylaluminum sesquiiodide, one third of the iodobenzene was added initially and the remainder was added dropwise when the temperature of the oil bath reached 105' to 110" C . A small amount of reactant mixture was heated to the reflux temperature of iodobenzene and then added to the flask to initiate the reaction. After a 30-hour reaction period the mixture was cooled, 50 ml. of dry benzene were added, and the mixture was filtered through a medium-porosity glass sintered funnel. The benzene and unreacted iodobenzene were removed by distillation a t 110" C . and 8 mm. of Hg pressure for 5 hours. The resultant product was viscous a t room temperature, reacted violently with water, but appeared stable in air after a short exposure. From 8.4 grams of aluminum turnings and 86 grams of iodobenzene, 83 grams of product were isolated. The products of these preparations were mixtures of a monoand a dihalide, as shown in the general equation. Although the components could have been separated by distillation, these mixtures (referred to as the sesquihalides) were used as the catalyst. Alkylation Procedure. One mole of decaborane (122 grams) and approximately 2 moles of pentane (144 grams) were placed in a 750-ml. stainless steel reactor equipped with a side arm for a thermocouple insert, a stainless steel condenser, a pressure gage, a vent with rupture disk, and a copper bleedoff tube. The reactor was cooled in a dry ice-acetone bath for 1 hour. One-half mole of methyl chloride (25 grams) was then added, followed by the catalyst to be used. Finally, sufficient cold pentane was added to total 3 moles (216 grams) and the apparatus was assembled. I n experiments where the sesquihalides and triethylaluminum were used, they were premixed with pentane in a dry box and kept a t dry ice temperature until used. The alkylation apparatus was thoroughly flushed with nitrogen before use. Heat was applied to the oil bath and cold methanol (-40' C.) was circulated through the condenser. The reactor temperature was measured with iron-constantan thermocouple wire. T h e temperature was initially raised to 70" to 75" C. If pressure did not rise, the temperature was raised to 85' C . and then to 95" C. if necessary. T h e pressure was never allowed to exceed 100 p.s.i.g., bleeding into a water trap when necessary. When the reaction was complete, the gas was released and the reactor cooled. The contents were transformed to a glass flask and cooled overnight a t dry ice temperatures, separating out most of the unreacted decaborane. The pentane solution was vacuumdistilled (75" C. and 5 to 10 mm. of Hg) to remove pentane.
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1965
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T h e product was weighed and analyzed. Product identification was by mass spectrometry in terms of peak heights representing the different mass levels of the components. Decaborane conversions were obtained by combining the amount of decaborane isolated with that found in the product. Results and Discussion
The results of the alkylations in which aluminum chloride, zinc chloride, titanium chloride, antimony chloride, and mixed halides were used as catalysts are presented in Table I. Table I1 contains the results of the alkylations in which the sesquihalides and triethylaluminum were used as catalysts. Included in Table 11, for comparison, are the results of an aluminum chloride experiment. Reactions using aluminum chloride were conducted to provide a standard by which the results obtained with other catalysts might be compared. The weaker Friedel-Crafts catalysts were of insufficient activity to catalyze this reaction. The mixed catalyst (SbC13AlRr3) also failed to catalyze the reaction. The synthesis of the sesquihalides, utilizing proper precautions, was not difficult. T h e sesquiiodides and bromides were prepared because these aryl and alkyl halides were the most readily available and the preparation did not require pressure equipment. The mixing of the sesquihalides with pentane in a dry box was considered the most effective means of handling these pyrophoric compounds. This mixture could be briefly exposed to air in comparative safety when the transfer to the reactor was made. T h e aryl sesquiiodide, although more difficult to prepare, had the advantage of being nonpyrophoric in air for short periods of time. T h e initial alkylation using 2.5 grams of methyl aluminum sesquiiodide did not occur, probably because of the presence of small amounts of impurities in the decaborane. T h e alkylation proceeded briskly a t 70' to 75' C. when 5- and 10-gram quantities of these catalysts were used. This represents a lower mole per cent of catalyst than necessary for aluminum chloride. When decaborane conversions, using these sesquihalide catalysts, were increased to the 50% range, polymethylation was also increased, lowering the boron content of the product below 50%. KO evidence of the presence of ethyldecaboranes was found when the ethylaluminum sesquihalides were used.
The catalyst activity of phenylaluminum sesquiiodide was considerably less than that of the alkyl sesquihalides. Only an 11 to 13% conversion was realized as compared to the 34 to 38% conversion of alkyl compounds. The use of triethylaluminum as a catalyst was interesting in view of the fact that no reaction occurred. An active compound such as this would be expected to enhance alkylation. The sesquihalides compare in general with aluminum chloride as follows: Slightly higher decaborane conversions ( 5 to 10% over aluminum chloride) can be obtained in the presence of the alkylaluminum sesquihalides without materially affecting product distribution. The alkylation using these sesquihalides proceeded more rapidly and at lower temperatures than the corresponding aluminum chloride reaction. The sesquihalides are, in general, more expensive and more difficult to handle than aluminum chloride. Conclusions
Zinc chloride, antimony chloride, titanium chloride, mixed halides, and triethylaluminum were unsuitable catalysts in the methylation of decaborane under the conditions investigated. The use of alkylaluminum sesquihalides as catalysts does not sufficiently increase decaborane conversions to warrant their replacement of aluminum chloride. Acknowledgment
T h e authors thank John Norman, who furnished all the spectrometry data. literature Cited (1) Grasse, A., Mavitz, J., J. Org. Chem. 5 , 106-21 (1940). (2) Ohenland, C., Newherry, J., Olin Mathieson Chemical
Corp., New Haven, Conn., unpublished paper on methylation of decahorane. ( 3 ) Olin Mathieson Chemical Corp., Niagara Falls, N. Y.,
unpublished work. (4) \Villiams, R. L., Dunstan, I., Blay, N. J., J . Chem. Soc. 1960, pp. 5006-12. RECEIVED for review March 10, 1965 ACCEPTEDJune 1, 1965
STEREOREGULAR POLYMERIZATION OF BUTADIENE WITH ALKYLALUMINUM CHLORIDES AND COBALT OCTOATE M O R R I S G l P P l N
Central Research Laboratories, The Firestone Tire CY Rubber Co., Akron 17, Ohio
earlier publication (70) data were presented which established the unique character of one of the known catalysts for the polymerization of butadiene to a polymer of up to 9870 cis-l,4 content. This catalyst, consisting of diethylaluminum chloride and cobalt chloride, required a modification of a minor proporrion of the diethylaluminum chloride with either water or oxygen in order to activate it. The data reported and discussed at that time included, mainly, the
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effect of water and oxygen on the heterogeneous EtZAlC1CoCl? system and the solvent-soluble EtpAlCI-CoClp.py catalyst. T h e mole ratio variations in the catalyst components, the effects of polymerization temperature and solvent, and some experimental work on polymerization rates were also discussed. The technical importance of configurational uniformity in high polymers is an accepted fact. Among the synthetic polydienes known, only the cobalt-catalyzed polybutadiene
