US3375265A - Production of trialkoxyboroxine - Google Patents

Description

United States Patent 3,375,265 PRODUCTION OF TRIALKOXYBOROXINE Lloyd C. Fetterly and George W. Conklin, Oakland, Kenneth F. Koetitz, Pleasant Hill, Friedrich G. .Heliferich,

Berkeley, Peter W. Gilderson, Oakland, and Stanley F.

Newman, San Francisco, Calif., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Sept. 7, 1965, Ser. No. 485,564

2 Claims. (Cl. 260-462) This invention relates to the production of alcohols by the controlled oxidation of paraflins. More particularly, this invention is concerned with the production of secondary alcohols by the controlled reaction of paraflins with an oxygen-containing gas in the presence of certain oxyboron compounds.

Oxidation of organic compounds with the aid of a variety of oxyboron compounds has been accomplished. The oxidation of aliphatic hydrocarbons to secondary alkyl borate esters with oxygen in the presence of boric oxide or boric acid is known (see, for example, T. Hellthaler et al., German Patent 552,886, Apr. 19, 1934). The borate esters can be hydrolyzed to yield corresponding secondary alcohols. Saturated hydrocarbons can also be converted to alcohols by reaction with oxygen and borate esters or esters of boronic and borinic acids (see, for example, Netherlands application 649,l81, Feb. 22, 1965). Similarly oxidation in the presence of metaboric acid is known (see, for example, S. N. Fox et al., US. 3,109,864, Nov. 5., 1963). These processes suffer from disadvantages which make the oxidation process inefficient and economically undesirable. Certain of the aforementioned oxyboron compounds are solids, thereby creating handling and solubility problems, particularly in multistage continuous processing; some yield gla'ssing at high temperatures. In the prior art processes the protective reaction of the oxyboron compound for achieving alcohol production is slow. Therefore, the oxidation reaction rate must be kept low in order to attain highest selectivity to the production of alcohol over other oxidation products, thereby diminishing the commercial feasibility and utility of the prior art processes.

It is, therefore, a principal object of the present invention to provide a rapid, efficient, and improved process for the controlled and continuous oxidation of parafiins. A further object of the invention is to provide an improvide process for the production of predominantly secondary alcohols by carrying out the controlled oxidation of paraffins in the presence of certain boron compounds.

These objects Will be better understood and others will be apparent from the description of the invention as given hereinafter.

Now, in accordance with this invention, it has been found that aliphatic secondary alcohols are prepared, preferentially over ketones, by contacting a paraflin in liquid phase at a temperature within the range of about 100 to about 300 C. with an oxygen-containing gas and carrying out the controlled oxidation of said parafiin in the presence of trialkoxyboroxine containing alkoxy of 4 or more carbon atoms to form from said parafiin secondary alcohols and their boron esters, followed by recovery of the secondary alcohols with means which provide for hydrolysis of the corresponding secondary alkyl borate ester.

The parafiins useful in the process of this invention are saturated aliphatic hydrocarbons of from 6 to 40 carbon atoms which can be normal or branched but preferably acyclic and essentially free of aromatics. Satisfactory results are obtained especially with parafiin designated RH Where R is an aliphatic hydrocarbyl of 8 to 30 carbons and preferably of 10 to carbons, especially alkyl of 10'to 20 carbons. Representative examples of suitable hydrocarbons include n-hexane, n-octane, 2- ethylhexane, .n nonane, n dodecane, n tetradecane, eicosane, hexacosane, tr'iacontane, and the like, including their mixtures.

The paraffin is oxidized in liquid phase with molecular oxygen, the controlled oxidation being carried out in the presence of trialkoxyboroxine and in the optional presence of a polyvalen't heavy metal catalyst.

The source of molecular oxygen is any oxygen-containing gas as, for example, air or oxygen diluted to any desired extent with an inert gas such as nitrogen, methane, carbon dioxide, and the like.

The trialkoxyboroxines useful in the process are those containing alkoxy of 4 or more carbon atoms. Especially preferred are those containing from 4 to 10 carbon atoms in each alkoxy, wherein the alkoxy contains at least 2 less carbons than the parafiin to be oxidized, with the proviso that the alkoxy contains at least 4 less carbons than the parafiin to be oxidized when the paraffin is of at least 10 carbon atoms. They maybe represented as oo-ia B-OQ or (QOBO) where Q is appropriate alkyl.

The trialkoxyboroxines are particularly advantageous in that their selectivity to the production of desired secondary alcohol is high, accompanied by a low selectivity to production of ketone, as compared to the poorer selectivity to alcohol, accompanied by high selectivity to ketone, obtained with the aforementioned prior art oxyboron compounds. In continuous operation, for example,

the alkyl ortho borates of the prior art yield higher ketone and lower alcohol selectivity for the same reaction rate. A further advantage of trialkoxyboroxines is that only one Q radical per boron atom is exposed to oxidative attack during the process as compared to three Q radicals per boron atom for the alkyl ortho borates. The net result is that oxidative losses of Q are much lower in the process of the invention. Another advantage in the use of trialkoxyboroxines is their wide range of solubility in parafiin. Representative useful trialkoxyboroxines include tri(n-butoxyyboroxine, tri(isobutoxy)- boroxine, tri(sec butoxy)boroxine, tri(n heptoxy)- boroxine, tri(2 ethylhexoxy)boroxine, tri(n non0xy)- boroxine, tri(decoxy)boroxine, and the like. The preparation of trialkoxyboroxines are Well summarized in H. Steinberg, Organoboron Chemistry, vol. 1, 445-454, Interscience Publisher s (Wiley), New York, 1964.

For each molecule of secondary alcohol (ROI-I) produced by the oxidation reaction, a molecule of the lower boiling alkanol (QOH) is liberated from the trialkoxyboroxine.

By selecting a trialkoxyboroxine of alkoxy at least 2 to 4 less carbons than the paraffin to be oxidized as described herein-above, it is comparatively easy to conduct the oxidation under conditions of temperature and pressure at which the liberated lower alkanol (QOH) is rapidly stripped into the reactor off-gas. This rapid removal of the lower boiling alkanol assures that it will not remain in solution in the reactor and be subjected to degradation by oxidation. Conversely, the trialkoxyboroxine must have alkoxy of long enough carbon chain, i.e., at least 4, so that the trialkoxyboroxine is sufficiently high boiling to remain in the reaction system and not be stripped therefrom during reaction. Hence, a lower limit of 4 carbons for the alkoxy of the trialkoxyboroxine is essential. The alkoxy carbon content will preferably be as low as possible consistent with the aforesaid requirements so that there will be the fewest carbon atoms per boron atom exposed to oxidative attack, thereby lowering the oxidative losses of Q.

In general, it is desirable to provide at least one gram atom of boron in the form of trialkoxyboroxine for each mol of paraffin being oxidized. However, greater or lesser amounts may be utilized if desired. A suitable range may include, for example, the use of about 0.1 to about 1.5 mols of trialkoxyboroxine per mol of paraffin being oxidized. A preferred range includes the use of about 0.2

to about 0.7 mol of trialkoxyboroxine per mol of parafiin being oxidized.

A polyvalent heavy metal compound catalyst which is soluble in the reaction mixture may optionally be employed in a catalytically effective amount. Thus, for ex ample, soluble salts of cobalt, manganese, lead, iron, and the like, may be used in the form of acetate, octoate, stearate, and the like. Preferred compounds include those such as cobalt octoate, cobalt stearate, and the like. The amount of such additional reagent may be such that the reaction mixture contains from about 0.001 to 0.2% by weight (based on total weight of paratfin to be oxidized) of solu'bilized polyvalent heavy metal.

The controlled oxidation and concomitant esterification are conducted at a temperature Within the range of about 100 to about 300 C. at a pressure sufiicient to prevent excessive loss of paraffin with the exit gas. Pressures within the range of about 15 to about 1000 p.s.i.g. can be'employed. A preferred temperature range is from about 150 to about 190 C.

At the completion of the controlled oxidation, unconverted paraffin and ketone by-product are removed from the mixture by any suitable means, for example, by vacuum flashing. The remaining product is a boron ester complex of the alkoxyboroxine and a secondary alcohol, from which the desired secondary alcohol is recovered by subsequent hydrolysis. Although any suitable hydrolyzing agent well known to the art may be used, the preferred agent is water. The hydrolysis is accomplished conveniently by adding water to the ester complex at a temperature sufiicient to maintain a liquid medium. The complex is substantially hydrolyzed thereby to produce secondary alcohol, lower alkanol derived from the alkoxy of trialkoxyboroxine, and aqueous boric acid. These products may then be resolved by any suitable method, for example, distillation, phase separation, fractional crystallization, or a combination thereof, in order to recover the desired secondary alcohol. A preferred mode of operation encompasses separating the boric acid in aqueous phase and vacuum distilling the nonaqueous phase to obtain secondary alcohol free of lower alkanols, i.e. the light ends, and diol impurities arising in the oxidation, i.e. the heavy ends. The secondary alcohol may be hydrogenated to reduce any carbonyl and unsaturation content.

In order to improve the over-all efliciency of the process, the separated mixture of unconverted parafiin and ketone by-product may be hydrogenated to convert the ketone to paraffin or alcohol and the resulting material recycled to the oxidation reactor. Alternatively, the ke- Itone may be removed by adsorption, for example, on alumina.

The aqueous boric acid from the hydrolysis of the boron ester complex is reconverted to trialkoxyboroxine for reuse in the process. Continuous operation can be achieved therein by a novel regeneration method. In this method, hot aqueous boric acid from the hydrolysis is mixed with normally liquid, water-insoluble alkanol of at least 4 carbon atoms such that the alkanol to boron mole ratio is about 4 and the resulting mixture is fed to :a continuous esterification column which yields trialkyl ortho borate plus a slight excess of alkanol as bottoms and an alkanol-water azeotrope as overhead. From an overhead phase-splitter, alkanol is returned to the column while water, saturated with alkanol, goes back to the hydrolyzer of the initial systempossibly after alkanol recovery. 'Irialkyl ortho borate from the column is partially hydrolyzed to trialkoxyboroxine:

where Q is alkyl or 4 or more carbon atoms. This partial hydrolysis is smoothly achieved, contrary to the teachings in the prior art (see, for example, M. F. Lappert, J. Chem. Soc. 1958, 2790), at elevated temperatures, at about to about 225 C. and preferably at about -160 C., under a partial pressure of water vapor no higher than 250 mm. Hg. These conditions are conveniently achieved, for example, by passing either watercontaining nitrogen or steam under reduced pressure through the liquid trialkyl ortho borate. Overheaded alkanol is recycled to the esterification column. Too low a temperature or too high a partial pressure of water at this step in the method leads to the highly undesirable precipitation of boric acid. There is no real lower limit for the partial pressure of water. From a practical standpoint though, the lower the partial pressure the slower the regeneration of tria'lkoxyboroxine. Hence, a preferred range of partial pressure of water vapor is from about 150 to about 200 mm. Hg. It is possible to use the oxidation react-or od-gas, if necessary admixed with steam, to carry out this partial hydrolysis step.

The partial hydrolysis to the alk-oxyboroxine may be carried out after addition of par-affin to the trialkyl ortho borate in continuous production. The parafiin is preferably that which is to be oxidized, thereby providing a paraffin solution of the alkoxyboroxine which can be fed directly to the oxidation zone. The partial hydrolysis is preferably carried to about 90% conversion rather than to completion because overshooting may result in formation of excessively viscous, gel-like, highly condensed polyborates, which are undesirable for the process of this invention. Preferred trialkoxyboroxines to be used in such a continuous regeneration cycle are tri(n-butoxy) boroxine, tri(iso-butoxy)-b-oroxine, or tri(sec-butoxy) boroxine because of the relative volatilities of the various components of the system. Additionally, these butyl oxyboron compounds yield a more favorable alkanol/water azeot-r-ope, i.e. butanol/ water.

As an alternative to the production of trialkoxyboroxine for recycle by the partial hydrolysis of trialkyl ortho borate, trialkoxyboroxine can be prepared in one step by feeding alkanol and boric acid in a ratio of from 1:1 to 12:1 to the esterification column and operating with alkanol reflux high enough to prevent crystallization of boric acid in the column.

The following specific examples of the invention will serve to illustrate more clearly the application of the invention, but the details thereof are not to be construed as limiting the invention.

Example I n-Dodeoane is contacted with 20% oleum at ambient temperature to remove aromatic components. Following the acid treatment, the n-dodecane is charged to a stainless-steel oxidation reactor vessel containing the trialkoxyboroxine indicated in Table 1 below. To the wellagitated reactor vessel, equipped with a reflux condenser, is passed a N /O mixture containing 10% by vol. of oxygen. The mixture is heated to temperature indicated below for 4 hours. The heat of reaction is removed by boiling water in internal coils. Unreacted n-dodecane and by-product ketone are removed from the resulting boron esters of secondary C alcohol by flashing at about 171 C., in two stages, one at 25 Hg and the other at 8 mm. Hg. The boron esters of secondary alcohol are then hydrolyzed with water at 121 C. A rotating disk contactor (see G. T. Rem-an, US. 2,601,674, June 24, 1952) is used to provide the necessary staging for essentially complete hydrolysis. Hydrolyzer products are crude secondary alcohols, lower alkanols corresponding to the alkoxy of trialkoxyboroxine, and approximately 20% by wt. aqueous boric acid. The aqueous and nonaqueous phases are separated. The nonaqueous phase containing the secondary alcohol and lower alkanols is treated with KOH for ester removal and then distilled to remove the lower alkanols and heavy ends. The heavy ends are mainly diols. The results are shown in Table l.

TABLE 1 Dodecane Charge, g- 120 560 Temperature, 0.... 182 182 Trlalkoxyboroxine Amount of Trialkoxyboroxine, g. 12 56 Dodecane Conversion, percent 16. 1 14. 2 Selectivity, percent:

C Alcohol 91 84 C12 Ketone 6 4 Example II In a manner similar to Example I, n-dodecane was oxidized in the presence of tributoxyboroxine and cobalt octoate. The results are summarized in Table 2.

Example III In a manner similar to Example I, n-dodecane was oxidized in a glass oxidation reactor vessel in the presence of tri(isobutyl) ortho borate and tri(isobutoxy)boroxine, respectively, to approximately the same dodecane conversion level. The comparative results are summarized in Table 3.

TABLE 3 Dodecane Conversion, percent 11 13 Temperature, C 165 165 Oxyboron Compound (B). Amount B, percent wt. of boron (based on wt. of dodecane) 1.1 1.1 Wt. Ratio of C11 Alcohol/Cir Ketone 3. 7 12.0

Tri(isobutyl) ortho borate.

These results demonstrate that the trialkoxyboroxine of the invention yields the desired high selectivity to alcohol and low selectivity to ketone compared to the alkyl ortho borate of the prior art, which yields poorer selectivity to alcohol and higher selectivity to ketone.

Example IV n-Dodecane is passed through a continuous reaction cycle and oxidized in the presence of tri(n-butoxy) boroxine to yield dodecyl alcohols in the following manner:

n-Dodecane containing by weight of tri(n-butoxy) boroxine is pumped at a rate of 500 ml. per hour through a continuous oxidation reactor consisting of four wellstirred stages, each of 500 ml. of volume, arranged in series with respect to liquid flow and in parallel with respect to gas flow. As oxidizing gas, nitrogen containing 10% by volume of oxygen, is sparged into each stage at a rate of 220 ml. per minute (STP). The reactor-temperature is maintained at 170 C. and the pressure, atmospheric. Of the n-dodecane passed through the reactor, 19.5% is oxidized, and 74.5% of the oxidation products b Tri(isobutoxy)boroxine.

are dodecyl alcohols, in the form of their borate esters. The exit gas from the reactor is cooled to condense water and n-butanol, which are charged to the esterification column described below. n-Butanol recovery by this condensation is 650 g. per 1000 g. of tri(n-butoxy) boroxine charged to the reactor. The dodecyl alcohols are recovered as their crude borate esters after unreacted dodecane and by-product ketone have been overheaded in a continuous cyclone flasher. Ketone is removed from the dodecane by adsorption on alumina and the purified dodecane is returned to the reactor.

The flasher bottoms are hydrolyzed by a countercurrent stream of water under pressure at C., giving quantitative yield of crude free dodecyl alcohols together with some n-butanol and an aqueous solution of boric acid. Subsequent purification results in 730' g. of dodecyl alcohols per 1000 g. of dodecane reacted. The aqueous boric acid solution, the condensate from the reactor exit gas, and sufficient n-butanol to supply a molar ratio of butanol to boric acid of 4:1 are fed to the 20th plate of a 25-plate Oldershaw (esterification) column. The thermosyphon reboiler at the base of the column has previously been charged with n-butanol and tri(n-butyl) ortho borate in a 1:1 ratio to furnish synthetic bottoms and is heated to about C. Reaction on the plates of the column forms tri(n-butyl) ortho borate, which is then bled from the thermosyphon reboiler; water/butanol being azeotroped overhead, and the butanol returned as reflux after phase separation from the water. The water from the phase separator, being saturated with n-butanol, is returned to the hydrolyzer. A 95.1% yield of tri(nbutyl) ortho borate is obtained by this step.

Tri(n-butoxy)boroxine is produced from the above tri (n-butyl) ortho borate by controlled and partial hydrolysis with nitrogen, at atmospheric pressure, containing water vapor at 150 mm. Hg. The tri(n-butyl) ortho borate is fed into a hydrolyzer, heated to C., and sparged with the wet nitrogen passed at the rate of ml. per min. per 100 g. of tri(n-butyl) ortho borate. This step results in 89% conversion to tri(n-butoxy)boroxine in about 5 hours, and a comparable amount of n-butanol is overheaded. Thi butanol is used as feed for the above esterification column. The losses of n-butanol per pass through the reactor, replaced by make-up in the feed to the esterification column, average 8% of the butanol r charged as butoxy in tri(n-butoxy) boroxine. The tri(nbutoxy)boroxine produced in this partial hydrolysis is recycled to the oxidation reactor for utilization to complete the reaction cycle.

We claim as our invention:

1. The process of producing trialkoxyboroxine containing alkoxy radicals of at least 4 carbon atoms by partially hydrolyzing trialkyl ortho bor-ate ester, wherein the alkyl is of at least 4 carbon atoms, in liquid phase at about 130 to about 225 C. in the presence of water vapor at a partial pressure no gerater than 250 mm. Hg.

2. The process of producing a par-aflin solution of trialkoxyboroxine by partially hydrolyzing trialkyl ortho borate ester in paraflin solution, wherein the alkyl is of at least 4 carbon atoms and the parafiin is of from 6 to 40 carbon atoms, at about 130 to about 225 C. in the presence of water vapor at a partial pressure no greater than 250 mm. Hg.

References Cited UNITED STATES PATENTS 3,232,704 3/1962 Heldbig et al. 23-149 FOREIGN PATENTS 939,534 10/1963 Great Britain. 1,025,443 4/ 1966 Great Britain. 1,035,624 7/1966 Great Britain.

CHARLES B. PARKER, Primary Examiner.

L. C. MARUZO, Assistant Examiner.

Claims (1)

1. THE PROCESS OF PRODUCING TRIALKOXYBOROXINE CONTAINING ALKOXY RADICALS OF AT LEAST 4 CARBON ATOMS BY PARTIALLY HYDROLYZING TRIALKYL JORTHO BORATE ESTER, WHEREIN THE ALKYL IS OF AT LEAST 4 CARBON ATOMS, IN LIQUID PHASE AT ABOUT 130 TO ABOUT 225*C. IN THE PRESENCE OF WATER VAPOR AT A PARTIAL PRESSURE NO GREATER THAN 250 MM. HG.