US3699179A

US3699179A - Hydrobromination of alpha-olefins

Info

Publication number: US3699179A
Application number: US856260A
Authority: US
Inventors: John P Boyle; Clarence R Murphy; William L Walsh
Original assignee: Gulf Research and Development Co
Current assignee: Chevron USA Inc
Priority date: 1969-09-09
Filing date: 1969-09-09
Publication date: 1972-10-17
Anticipated expiration: 1989-10-17
Also published as: CA956976A

Abstract

A method is provided for reducing the air-blowing time required to activate a substantially pure alpha-olefin for reaction with anhydrous hydrogen bromide to produce a primary alkyl bromide. The method involves admixing at least four weight percent of a previously activated alpha-olefin with the substantially pure alpha-olefin prior to air-blowing.

Description

United States Patent I 1 1 7 Boyle et al. 1451 Oct. 17, 1972 54] HYDROBROMINATION OF ALPHA- 3,482,000 12/1969 Femald et al.....260/683.l5 1) OLEFINS Primary Examiner-Daniel D. Horwitz [72] Inventors John Boyle Moon Township Attorney-Meyer Neishloss, Deane E. Keith and legheny County; Clarence R.

Murphy, Allison Park; William L. c'caffney Walsh, Glenshaw, all of Pa.

[73] Assignee: Gulf Research 8: Development Company Pittsburgh time required to activate a substantially pure alpha- [22] Filed: Sept. 9, 1969 olefin for reaction with anhydrous hydrogen bromide [211 pp No 260 to produce a primary alkyl bromide. The method in- [5 7] ABSTRACT volves admixing at least four weight percent of a previously activated alpha-olefin with the substantially 52 us. 01.; ..260/663 p p e prior to air-blowing- 511 Int. Cl ..-.C07c 17/08 I [58] Field of Search ..260/663,683.1-5 DY [56] References Cited I y 9 claim,- 2 Drawing Figures UNITED STATES PATENTS 3,422,145 1/1969 Steinmetz ..260/663 RECYCLE l8 A 10 20 pRo ucr ACTIVE 24 RECOVERY O L E FIN 14 v 22 GAS CONTAINING H FREE MOLECULAR A method is provided for reducing the air-blowing PATENTEDnm 11 m2 3. 699 '.1 79

sum 1 m2 FIG. I

' RECYCLE l8 A 2 l6 TO PRODUCT ACTIVE 2o 24 RECOVERY OLEFIN GAS CONTAINING HBr FREE MOLECULAR INVENTORS JOHN P BOYLE BY CLARENCE R. MURPHY WILLIAM L. WALSH minnow 11 m2 3.699.179

SHEEI 2 [IF 2 F IG 2 YINOPERATIVE REGION Y I 55' v A I m I 05 g OPERATIVE I REGION. 7 55 E :3 n- 2:

E5 INOPERATIVE REGION Q0. I 1 I- 60 80 IOO I I 200 TEMPERATURE C INVENTORS JOHN I? BOYLE BY CLARENCE R. MURPHY WILLIAM L. WALSH HYDROBROMINATION OF ALPHA-OLEFINS This invention relates to an improved method for activating an alpha-olefin for reaction with anhydrous hydrogen bromide to produce a primary alkyl bromide.

The addition of HBr to alpha-olefins to produce primary and secondary bromides is known. It is also known that primary alkyl bromides can be made by the addition of I-IBr to alpha-olefins in the simultaneous presence of free radical promoters, such as ultraviolet light (U.S. Pat. No. 2,307,522); extraneously added peroxides, such as organic peroxides (U.S. Pat. No. 2,058,466 and British Pat. No. 843,234); or air (U.S. Pat. No. 3,108,141). Other prior art appears to be contradictory (U.S. Pat. No. 3,336,403) in teaching the use of peroxides is undesirable due to polymerization problems, and further that the use of oxygen or air simultaneously with HBr is slow. Indeed, it has been found thatin some instances the hydrobromination of alpha-olefins proceeded rapidly when air and I-IBr were simultaneously added while in other instances, the reaction was unexplicably slow. It was found, however,

lower temperatures, so as to avoid the necessity for higher pressure equipment to maintain the olefins in the liquid phase. A method has now been discovered which involves recycling a small amount (about 5 percent) of activated olefins which in some manner serves to reduce the time required for activation of the remaining 95 weight percent inactive olefins by abou two-thirds.

In accordance with the invention, the time required to air-blow and activate an alpha-olefin hydrobromination is reduced by a process which comprises adding at least 4 weight percent of a previously activatedalpha-olefin to the substantially pure alphaolefin charge stock to the air-blowing zone. I

The attached FIG. 1 is a simplified flow diagram of the process of this invention. I

to FIG. 1,..a substantially pure alpha-olefin enters reactor 10 through line l2-where'it is contacted under oxygen which enters reactor 10 through line 14 to acthat for a substantially pure olefin, that is, an olefin which contains no detectable amount of oxygen containing materials of any type, the reaction with I-IBr in the simultaneous presence of air was uniformly slow, thus substantiating the general teachings in US. Pat. No. 3,336,403 The simultaneous addition of air and HBr mustoccur at a temperature less than about 50 C., even in the presence of a free radical promoter, if substantial amounts of secondary alkyl bromides are to be avoided. Thus, it was not possible to increase the temperature of the hydrobromination reaction in the simultaneous presence of air in order to speed up the slow reaction since, in so doing, substantial amounts of undesirable secondary bromides would result. It is for this reason that the prior art teaches the use of low temperature olefin activation such as the use of ultraviolet light, the addition of extraneous organic peroxides, such as benzoyl peroxide, or the prior formation of 020- nides.'All of these methods suffer from the difficulty that they are expensive and not easily controlled.

As described in copending Ser. No. 856,374 entitled Activation of Olefins for I-Iydrobromination by Air- Blowing and filed on the same date as this application in the names of Russell G. Hay, Clarence R. Murphy and William R. Walsh and assigned to the same assignee as this application, the above problems were obviated by pre-air-blowing the olefin at a temperature from 60 to 200 C. for a time sufficient to result in activation of the olefin and thereafter reacting the alphaolefin with anhydrous HBr in the absence of an extraneously added catalyst at a temperature less than 50 C. to produce the desired primary alkyl bromide.

It is necessary to activate the olefin by air-blowing in the liquid phase. This creates problems, especially for the lower carbon number olefins, such as the butenes and pentenes, as the air-blowing temperature increases since higher pressure equipment is required to maintain the olefins in the liquid phase. The higher air-blowing temperatures are desired, however, since the timerequired to activate the olefins is inversely proportional to the temperature and the shorter contact times are obviously advantageous.

Methods were therefore sought to decrease the time required for air-blowing the olefins, especially at the tivate the olefin. The activated olefin is removed fromv reactor 10 through line 16 and is sent to hydrobromination reactor 20. A portion of the activated olefin in line 16 is removed through line 18 and is recycled and enters line 12 together with the substantially pure olefin into reactor 10. The amount of activated olefin recycled through line 18 amounts to at least about 4 weight percent of the total charge entering reactor 10. The anhydrous HBr is added to reactor 20 through line 22 and the hydrobrominated product is removed from reactor 20 through line 24 and is sent to a recovery scheme, not shown, for the recovery of the primary alkyl bromide. The alpha-olefin charge stock can be any substantially pure alpha-olefin having from four to 30 carbon atoms per molecule and is preferably an alpha-olefin having from four to 10 carbon atoms per molecule. The alpha-olefin can suitably have the formula:

ilt.

limited to:

butene-l; pentene-l; isobutylene; hexenel; 3-methylbutene-1; 4-ethylhexene-l; octene-l; dodecene-l; decenel; octadecene-l; tetradecenel; Z-methyll -nonadecene; eicosene-l; tetracosene-l;

2-octyl-I-dodecene; and mixtures thereof.

While any of the above alpha-olefins can be used in the process of this invention to insure the production of primary alkyl bromides without the need of an extranefor atoms per molecule, such as. ethylene, under telomerization conditions in the presence of a catalyst such as a Group IIIA metal alkyl such as defined below, for example, aluminum triethyl. Very pure olefins must be used in the telomerization process since the Group IIIA metal alkyls act as scavengers for any oxygen containing materials which might be present and reduce the efficiency of the telomerization reaction. Thus, the telomerization products which are obtained are substantially unreactive in the hydrobromination reaction as defined above. For example, the alpha-olefins freshly produced by the telomerization process result in a'yield of less than 50 mole percent, usually less than 10 mole percent, primary alkyl bromide when reacted with anhydroushydrogen bromide in the absence of an extraneously added catalyst at -10 to C. in a time of about 2 hours. Yet another way to obtain the substantially pure alpha-olefins would be, 'of course, to. distill the alpha-olefins in the contact presence of a Group Me-Ra where Me is any of the Group IIIA metals'defined aboveand wherein at least one and preferably all-of R R and R are alkyl radicals having between one and carbon atoms and wherein any one or two of R R and R, can be selected from the group consisting of hydrogen and halogen radicals. Usually the metal alkyl is an aluminumor boron trialkyl such as triisobutylaluminum or'triisobutylboron.

As noted, the substantially pure alpha-olefin prepared as above was found to be substantially. inactive for the addition of HBr in the absence of an extraneously added free radical promoter. The simultaneous addition of oxygen in the form of air with the I-IBr to the alpha-olefins proved to be a very slow reaction requiring more than 6 hours at 28 C. to produce any appreciable amount of product.

It was found that the olefins could be simply and effectively activated by pretreatment before the HBr addition, the pretreatment consisting of contacting the alpha-olefin charge .stock or the gas containing free molecular oxygen at a temperature from 60 to 200 C. for a time sufficient to activate the alpha-olefins. By an promoter. Minimum times as short as 1 minute or less activated olefin is meant one which results in a yield of at least 85 mole percent primary alkyl bromide when reacted with anhydrous hydrogen bromide in the .absence of an extraneously added catalyst at l 0 to 0 I tive for the subsequent hydrobromination reaction.

are effective at the higher air-blowing temperatures, whereas minimum times on the order of 6 hours are required at the lower air-blowing temperatures of about 60C.

The subject invention relates to air-blowing a substantially pure alpha-olefin as defined above containing at least about 4 weight percent of a previously activated olefin. The purpose of air-blowing in the presence of a small amount of previously activated olefin is to decrease the time required forthe air-blowing-operation. One of the advantages of the subject invention is that a lower air-blowing temperature can be employed to achieve activation in the same time which would be required at a higher temperature. It is thus possible. to employ a wider range of airactivation temperatures than was previously believed economically feasible. Using the methods of this invention, a suitable range of air-blowing temperatures can be from 50 to 200 C., with the preferred activation temperatures being from 60 to 150C. I

FIG. 2 attached is a plot on a semi-log paper of the time required vs. temperature to obtain anolefin in the Operative Region, which is the region where an olefin would be active for the hydrobromination reaction without the need for an extraneously added free radical catalyst. The times shown on FIG. 2, however, are those required without the use of the present invention. Thus, referring to FIG. 2, at C. a minimum of 6 hours would be required to activate the alpha-olefin whereas at 170 C." about 1 minute is required. By operating the air activation step in accordance with the procedure of this invention, namely by air-blowing in the presence of at least about 4 weight percent of previously activated olefin, the total time required to activate the olefin would be reduced. For example, the activation of octene-l by air-blowing at 70 C. would require, referring to FIG. 2, about 6 hours of air-blowing time whereas the octene-l has been found to be ac tivated in a time of only 2 hours at 70 C. by air-blowing a mixture of percent substantially pure octene-l and 5 weight percent previously activated octene-l. Similarly, care must be taken when using the procedure of the present invention not to conduct the air-blowing operation for a time such that the olefin becomes inac- Hence', the minimum activation time is reduced by about'two-thirds when air oxidation. occurs in the presence of about 5'weight percent active olefin, and the maximum time of air-blowing before reaching an inactive state would correspondingly be reduced by about two-thirds.

The minimum amount of activated olefin to'recycle is critical and must be at least about 4 weight percent of the total charge entering the air-blowing reactor. The recycling of active olefins in amounts less than about 4 weight percent is ineffective in reducing the time required for activation in the air-blowing step. Larger amounts of activated olefins can be recycled if desired, but no further beneficial effects are received. Thus, quite unexpectedly, the use of greater amounts than about 4 weight percent of activated olefins does not aid in reducing the air-blowing time still further. 1 As a result, whether 5 or 25 weight percent of the charge stock to the air-blowing reactor is composed of previously activated olefins, the time required for air-blowing is about the same and is considerably reduced over the case where only a substantially pureolefin is airblown. Thus, the amount of recycled activated olefin which can be utilized in the process of this invention can vary from about 4 weight percent to 50 weight percent of the charge stock to the air-blowing step and even greater amounts of recycled olefins can be employed if desired. For economic reasons it is obviously preferable to employ the minimum amount of recycled activated olefins, and for this reason the preferred amount of recycled olefin is from 4to weight percent.

Activated olefin's having a carbon number different than the substantially pure olefin can also suitably be added in the same amounts to decrease the air-blowing time, but these olefins are not preferred due to complications in the recovery procedure.

The activation of the substantially pure alpha-olefins occurs quite simply by passage of a gas containing free molecular oxygen through the liquid alpha-olefin at the desired activation temperature. The terms air-blown or air-blowing in this application refer to blowing with a gas containing free molecular oxygen which may be, but is not necessarily, air. Means should be provided for insuring intimate contacting between the gas containing free molecular oxygen and liquid olefins to be activated. For example, the gas containing free molecularoxygen can be added to the liquid olefin through a sparger which breaks up the gas into very small bubbles. While additional stirring is not required, it can be employed if desired. The gas containing free molecularoxygen can suitably be air, pure oxygen or molecular oxygen diluted with an inert gas such as nitrogen. The gas suitably contains from to 100 mole percent free molecular oxygen-and preferably from 15 to 40 mole percent free molecular oxygen.

Amounts of oxygen in the activating gas less than about or from whence it comes is not critical to the process of the subject invention.

The gaseous hydrogen bromide adds to the activated alpha-olefins in an anti-Markownikoff manner. Markownikoff stated in 1870 that if an unsymmetrical olefin is treated with hydrogen halide the addition will occur at the carbon-carbon double bond and that the hydrogen will attach itself to the carbon atom bearing the greater number of hydrogen atoms and that the halide would attach itself to the carbon atom bearing the least number of hydrogen atoms. Thus, the normal or Markownikoff addition would produce a secondary alkyl bromide whereas the anti-Markownikoff addition produces the more desirable abnormal or anti-Markownikoff primary alkyl bromide.

The hydrogen bromide addition reaction occurs rapidly in any reactor providing for good mass transfer between the gaseous hydrogen bromide phase and the liquid alpha-olefin phase. For example, suitable mass transfer conditions for the addition of the hydrogen bromide to the olefin are obtained by bubbling the hydrogen bromide gas through the liquid activated olefin using, for example, a porous plate gas distributor to insure small gas bubbles resulting in a large interphase area. It is also preferred, of course, to provide vigorous agitation of the liquid phase to aid in the mass transfer and also to insure the maintenance of the desirable low reaction temperatures to be defined below. Under the excellent mass transfer conditions, the reaction is over in a matter of minutes even employing the low reaction temperatures to be defined below.

A suitable range of reaction temperatures is from 30 to 50 C., with the preferred reaction temperatures between 10 and 30 C. The use of increased reaction temperatures is undesirable as the higher temperatures promote the normal or Markownikoff addition with the consequent formation of the less desirable, less stable secondary alkyl bromides. When the reaction is operated in the defined temperature range, rapid completion of the hydrogen bromide addition oc-- curs with the suppression of the formation of secondary alkyl bromides. Thus, suitable reaction times are between 1 and 240 minutes, and in the preferred temperature range the reaction times are usually between 3 and 120 minutes.

The reaction pressure can suitably be between atmospheric and blOO psig or more. An increase in reaction pressure tends to increase the reaction rate. However, since the reaction rate is already quite fast at atmospheric pressure, the use of increased reaction pressures, while technically feasible, is not preferred for obvious economic reasons.

The hydrobromination reaction product which is composed predominantly of primary alkyl bromides and small amounts of secondary alkyl bromides is usually purged of excess hydrogen bromide in any suitable manner. For example, air, nitrogen or helium can be passed or bubbled through the reaction product until it, is free of hydrogen bromide. The resulting hydrogen bromide free alkyl bromide reaction product can then, optionally, be neutralized using any suitable basic solution. For example, a 5 percent aqueous solution of sodium bicarbonate is satisfactory and produces tions, neutralization is not required nor desired. The

upper-organic phase containing the alkyl bromides can then be separated and the alkyl bromide recovered in any suitable manner. 7

The-crude alkyl bromide reaction product can also be recovered by purging with a non-reactive gas as described above and thereafter dissolving the alkyl bromide in about 1 to about 10 times its volume of a nonreactive solvent for the .alkyl bromide, such as chloroform or petroleum ether. The solution of the alkyl bromide in the solvent is then neutralized as before with a weakly basic solution. Alternatively, the unneutralized solution of the alkyl bromide in the nonreactive solvent can be washed with water until neutral, and this procedure is preferred in the case of the more labile alkyl bromides. Whichever method is chosen to neutralize, the neutralized solution is then dried in any conventional manner, such as by drying over magnesium sulfate. The solvent can then be removed by evaporation or distillation under reduced pressure. The pure alkyl bromide reaction product can then be distilled from the dried solvent-free organic phase. The inventionwill be further described with reference to the following experimental work.

Octene-l which was prepared by the telomerization of ethylene, was distilled from tri-n-butylaluminum in a' nitrogen atmosphere to produce a substantially pure octene-l. The peroxide number of the distilled octenel was less than 0.1, the limit of ASTM Test 1832.

A series of runs was made wherein the distilled octene-l was air-blown at varying temperatures and for varying times with and without the addition of weight percent of a previously air-blown and activated octene- The results of this series of runs are shown in Table 1 below.

TABLEI Hydrobromination of Octene-l at --C. to 0C.

Hydrob rumination Referring to Table l, air-blowing the octene-l for 2 hours at 70C. resulted in only a 24 mole percent yield of primary alkyl bromide after a reaction time of 103 minutes. Example 2 shows that 6 hours of air-blowing at 70? C. was sufficient to result in a yield of primary alkyl bromide of over 90 percent in a reasonable reaction time of 6 minutes. In this application, yield means the conversion of the olefin times the efficiency of conversion of the olefin to the desired primary alkyl bromide. Examples 3 and 4 show that when air-blowing occurred in .the presence of 5 percent of a previously air-blown activated octene-l, a time of 2 hours at 70 C. was sufficient to result in a yield of primary alkyl bromide of over 90 percent in a reaction time of-3 to 5 minutes. The 5 percent air-blown activated olefin which was utilized in Examples 3 and 4 above was part of the product of Example 2 in Table 1.

EXAMPLE 5.

140 grams of a mixture of hexene-l (95 weight percent) and activated octene-l (5 weight percent) was air-blown for 2 hours at 60 C. The resulting mixture of olefms was found to give a yield of primary alkyl bromide of 96 mole percent in a hydrobromination reaction time of 5 minutes at-l0 to 0 C.

EXAMPLE 6 140 grams of a mixture of 95 weight percent dodecene-l and 5 weight percent of activated octene-l was air-blown for 2 hours at a temperature of C. Hydrobromination of this air-blown mixture of olefins for 5 minutes at l0 to 0 C. resulting in an v89 mole percent yield of primary alkyl bromides.

EXAMPLE7 EXAMPLE 8 212.6 grams of octene-l were air-blown at a temperature of 70 C. for 2 hours in the presence of 25 weight percent of previously. blown activated octene-l. The resulting mixture of olefins was active for the hydrobromination reaction which is shown by the fact that more than a 90-mole percent yield of primary alkyl bromide was obtained at 12 to 0 C. in a time of less than 10 minutes.

A comparison of Example 8 with Example 6 shows that the presence of 25 weight percent activated olefin in the charge stock achieved about the same results as the presence of 5 weight percent activated olefin in the charge stock. Hence, while it is not detrimental to have larger amounts of activated olefin admixed with the substantially pure olefin, there is no advantage to this process to the presence of the larger quantities of activated olefin which merely serve to reduce the space time yield of products from the air-blowing reactor.

EXAMPLE 9 Example 6 was repeated except the amount of activated olefin in the charge stock to the air-blowing step was 2 weight percent. Six hours were required at 70 C. to activate the mixture.

A comparison of Examples6, 7 and 9 shows that it required as much time with 2 weight percent activated olefin as with a percent substantially pure olefin charge stock (Example 6).

A comparison of all of the above examples shows it is critical to employ an amount of activated olefin in the charge stock of at least about 4 weight percent to obtain the advantages of this invention, i.e., a reduction in the minimum time required for activation of the olefin for hydrobromination.

The above data were obtained in a batch type reactor. In a continuous stirred tank reactor where inactive olefin is continuously added and active olefin is continuously removed, there is considerable backmixing which is equivalent to recycle of active olefin, and this type of recycle operation is, of course, meant to be included in this invention.

Resort may be had to such variations and modifications as fall within the spirit of the invention and the scope of the appended claims.

We claim: a

1. A process for the preparation of a primary alkyl bromide from a substantially pure alpha-olefin having from four to 30 carbon atoms per molecule which comprises:

contacting at least one of said alpha-olefins in an airblowing zone with a gas containing free molecular to equal at least 4 weight percent of the olefins entering said air-blowing zone; and thereafter reacting said activated alpha-olefin with anhydrous HBr in the absence of an extraneously added catalyst at a temperature less than 50 C. to produce the desired primary alkyl bromide.

2. A process according to claim 1 wherein said alphaolefin is one which has been intimately contacted with a Group IllA metal alkyl having at least one carbon to metal bond.

3. A process according to claim 2 wherein the gas containing free molecular oxygen is air.

4. A process according to claim 3 wherein the alphaolefin is octene-l.

5. A process according to claim 1 wherein said previously activated olefin has a different number of carbon atoms than said substantially pure alpha-olefin.

6. A process according to claim 5 wherein the substantially pure alpha olefin is hexenel 7. A process according'to claim 5 wherein the sub stantially pure alpha-olefin is dodecene-l.

8. A method according to claim 1 wherein said alpha-olefins contain from 4 to 50 weight percent of a previously activated olefin.

9. A method according to claim 8 wherein said alpha-olefin is obtained by the telomerization of ethylene under telomerization conditions in the presence of a Group lIlA metal alkyl.

Claims

2. A process according to claim 1 wherein said alphaolefin is one which has been intimately contacted with a Group IIIA metal alkyl having at least one carbon to metal bond.
3. A process according to claim 2 wherein the gas containing free molecular oxygen is air.
4. A process according to claim 3 wherein the alpha-olefin is octene-1.
5. A process according to claim 1 wherein said previously activated olefin has a different number of carbon atoms than said substantially pure alpha-olefin.
6. A process according to claim 5 wherein the substantially pure alpha-olefin is hexene-1.
7. A process according to claim 5 wherein the substantially pure alpha-olefin is dodecene-1.
8. A method according to claim 1 wherein said alpha-olefins contain from 4 to 50 weight percent of a previously activated olefin.
9. A method according to claim 8 wherein said alpha-olefin is obtained by the telomerization of ethylene under telomerization conditions in the presence of a Group IIIA metal alkyl.