US 3853735 A
Electrolytic apparatus for preparing organometallic compounds is disclosed. The apparatus includes anode and cathode members in the form of shot material, separated by a tubular perforate member comprising an open mesh haircurler member sandwiched between fine mesh screen, with the electrodes connected to a source of low frequency alternating current potential.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Shepard, Jr. et a1.
I ELECTROLYTIC APPARATUS FOR PREPARATION OF ORGANOMETALLIC COMPOUNDS  Inventors: John C. Shepard, Jr., Lake Jackson; Edward E. Johnson, Sweeny; Robert W. Bearman, Lake Jackson, all of Tex.
 Assignee: Nalco Chemical Company, Chicago,
 Filed: Feb. 16, 1973  Appl. No.: 333,041
Related U.S. Application Data  Division of Ser. No. 185,005, Septv 30, 1971,
 U.S. Cl 20 1/260, 204/59 QM, 204/59 L, 204/283  Int. Cl B01k 3/10  Field of Search 204/59 L, 59 OM, 260, 272, 204/275, 283, 284
[ 1 Dec. 10, 1974  References Cited UNITED STATES PATENTS 3,287,248 1 1/1966 Braithwaite 204/260 3,630,858 12/1971 Ganci et a1 204/59 L FOREIGN PATENTS OR APPLICATIONS 1,194,181 6/1970 Great Britain 204/260 Primary Examiner-John H. Mack Assistant Examiner--W. I. Solomon Attorney, Agent, or Firm--Lockwood, Dewey, Zickert & Alex 5 7] ABSTRACT Electrolytic apparatus for preparing organometallic compounds is disclosed, The apparatus includes anode and cathode members in the form of shot material, separated by a tubular perforate member comprising an open mesh haircurler member sandwiched between fine mesh screen, with the electrodes connected to a source of low frequency alternating current potential.
3 Claims, 3 Drawing Figures PATENTE'U SE8 1 (H974 FEED DRUM
sum 2 or 2 FIG-L3 I HEAT (CHANGER SURGE DRUM INITIAL CELL T EXCHANGER SURGE DRUM FINAL CELL APPARATUS FOR ELECTROLYTIC PREPARATION OF ORGANOMETALLIC COMPOUNDS This is a division of application Ser. No. 185,005, filed Sept. 30, 1971, and now abandoned.
It is now well known that organometallic compounds may be produced by the electrolysis of Grignard reagents using sacrificial metal anodes. This process is particularly suitable for the production of organolead compounds particularly tetramethyllead and tetraethyllead. The details of this well known electrolytic process is set forth in the teachings of U.S. Pat. No. 3,007,858. The invention as described in this patent is summarized by the patentee as follows:
In accordance with the invention it has been found that organo metallic compounds can be produced by electrolyzing a substantially anhydrous solution of a Grignard reagent in an organic solvent for the Grignard reagent using a sacrificial anode and adding an organic halide to the electrolyte, the organic radical of which corresponds to the organic radical of the Grignard reagent being used. As the electrolyzing action proceeds. magnesium normally tends to deposit at the cathode and this normally causes serious problems, such as bridging between the anode and the cathode, but the added organic halide reacts with this magnesium and reconverts it to a Grignard reagent thereby avoiding the deposit of magnesium at the cathode. The term organic halide as used herein is intended to include organic chlorides. bromides and iodides. The halogen portion of the added organic halide does not have to be the same as the halogen portion of the Grignard reagent. The free hydrocarbon radicals derived from the Grignard reagent during electrolysis combine with the anode material to form the corresponding organo metallic compound which can be separated from the electrolyte in any suitable manner.
cathode may be composed of the same material as the anode. Thus, in producing tetraethyl lead both the cathode and the anode can be composed of lead. It is preferable, however, that the anode be composed of lead and the cathode of stainless steel.
The invention is particularly valuable in the preparation of tetraethyl lead and this preparation will be used to illustrate the practice of the invention. In carrying out this process a lead anode and preferably a stainless steel cathode are placed in a solution of ethyl magnesium chloride dissolved in a suitable organic solvent. A suitable organic solvent preferably employed for this purpose is the dibutyl-ether of diethylene glycol. An electrolyzing current is passed into the ethyl magnesium chloride solution (Grignard solution) in sufficient amount to cause the lead anode to be dissolved. Ethyl chloride is passed into the ethyl magnesium chloride solution either intermittently or continuously in sufficient amount to react with the magnesium liberated at the cathode to reconvert it to ethyl magnesium chloride. The free ethyl radicals react at the anode with the lead to form tetraethyl lead. Magnesium chloride is a byproduct of this process. The tetraethyl lead is removed in any suitable manner from the organic solvent solution. Where a high boiling solvent is used such as dibutyl ether of diethylene glycol, the tetraethyl lead, is treated to remove the magnesium chloride. This can be done by adding a substance which forms an insoluble compound with the magnesium chloride, for example, dioxane, and filtering the insoluble precipitate. The solvent solution from which the magnesium chloride has been removed is then recirculated to the cell in which the electrolyzing action is carried out or to a suitable container where it is used as a solvent for additional quantities of Grignard reagent. The removal of a partially electrolyzed solution from the electrolyzing cell is preferably agitated with suitable mechanical stirring or other agitating means.
Over the ensuing years numerous improvements have been made in the process whereby it is possible to produce organo lead compounds efficiently and on a large scale commercial basis. Typical of such improvements are the various techniques and procedures described in the following U.S. Pat. Nos: 3,234,1 12; 3,312,605; 3,372,098; 3,391,066; 3,391,067; 3,393,137; 3,409,518; and 3,497,428. The disclosures of all of these patents are incorporated herein by reference.
In preparing organo metallic compounds by the direct current electrolysis of Grignard reagent using sacrificial anodes several operating parameters must be observed if the process is to operate efficiently. It is always necessary that some Grignard reagent be present during all of the electrolysis procedure since experience has shown that when the Grignard reagent is depleted electrical shorting occurs which on large scale equipment can produce costly shutdowns. The requirement that Grignard reagent be present at the end of electrolysis run means that the reaction may never go to completion. Another problem that is encountered in the large scale direct current electrolysis of Grignard reagents to produce organo metallic compounds resides in the expense involved in the rectification of alternating current to direct current. Since most electrical current produced in the world is alternating current, it must be converted by means of suitable rectifying devices, such as silicone diodes, to convert it to usable directcurrent. If alternating current is not rectified, then specially designed direct current generators must be manufactured to provide the quantity of direct current needed to operate large scale plants.
If it were possible to electrolyze Grignard reagents to produce organo metallic compounds whereby excess Grignard reagent need not be present to prevent electrical shorts from occurring and alternating current could be substituted for direct current, a valuable contribution to the electrochemical arts would be afforded.
THE INVENTION In accordance with the invention it has been found that organometallic compounds of the type having a carbon atom of a non-polar organic radical linked to a metal may be prepared by electrolyzing with low frequency alternating current a substantially anhydrous solution of a Grignard reagent which is in contact with a sacrificial metal electrode. Upon completion of the electrolysis the organometallic compound is recovered by known processing techniques. The organometallic compounds that may be produced using the process of this invention include a large number of well known organometallic chemicals. Thus, organo compounds of the metals lead, zinc, tin, copper, mercury, and the like may be synthesized. The non-polar organic radicals attached to the metals may be selected from any organic radical that is capable of existing in the form of a Grignard reagent. Exemplary are such organic radicals as methyl, ethyl, butyl, isobutyl, phenyl and substituted phenacyl radicals, such as benzyl. These hydrocarbon radicals may contain substituents thereon such as halo radicals, e.g., trifluoroethyl. It is preferred that the organic radicals be an aliphatic hydrocarbon radical and preferably any organic radical used should not contain more than six carbon atoms.
The process employs a Grignard reagent dissolved in a substantially anhydrous solvent which is chemically inert to the conditions of the reaction and which is capable of allowing a Grignard reagent to be formed therein. This solvent is further characterized as being electrically conductive when the Grignard reagent is present therein. Solvents of this type include, most preferably, the well-known organic ethers which have been used for the preparation of Grignard reagents for many years. To maximize the electrical conductivity of the anhydrous Grignard reagent solutions, certain blends of ethers are extremely desirable. For instance, certain blends of aliphatic ethers either alone or in combination with cyclic ethers such as tetrahydrofuran are desirably employed in the practice of the invention. An excellent blend of ethers in which the starting Grignard reagent may be prepared are the aliphatic glycol diethers blended with tetrahydrofuran with the latter being present in the range of 65 75 percent by weight which are described in US. Pat. No. 3,312,605, the disclosure of which is incorporated herein by reference.
CONDITIONS OF THE ELECT ROLYSIS The alternating current electrolysis of the Grignard reagent may be conducted under a wide variety of conditions. The alternating current should be of low frequency and may be either one, two, or three phase. One phase alternating current is preferred. By the term low frequency alternating current is meant that the frequency of such current in terms of cycles per second should not exceed 60 cycles. Excellent results are obtained when the frequency of the alternating current is within the range of to 60 cycles and most preferably within the range of 5 30 cycles. While the voltage may vary between 1 60, good results are obtained when the voltage is within the range of volts. The amperage will of course vary depending upon the size of the particular cell used.
The electrolysis is conveniently conducted at temperatures within the range of 50- 60 C. when organolead compounds are produced. The temperature may be increased or decreased with the controlling factor being the boiling points of the organic liquids used in the electrolysis process.
THE ELECTRODES The electrodes may be of any of the metals previously described, e.g., those capable of being converted by Grignard electrolysis into organometallic compounds. The electrodes may be in any size, shape, or configuration just as long as when they are immersed in the Grignard solution, they are electrically insulated from each other. While a preferred form of the invention dictates that the electrodes be of the metal corresponding to the organometallic compound sought to be produced it will be understood that only one electrode need be of such metal. In this case the other electrode should not be sacrificial in nature and hence would be composed of an inert conducting substance such as platinum or carbon.
To illustrate a typical cell design for producing organometallic lead compounds such as tetraethyllead or tetramethyllead reference may be had to the drawings.
DRAWINGS FIG. 1 is a vertical cross-sectional view of a typical cell that may be used to electrolytically produce organic lead compounds from Grignard reagents.
FIG. 2 is a top view taken across the lines 22 of FIG. 1.
FIG. 3 is a schematic view of two series connected cells of the type shown in FIG. I and FIG. 2 that may be employed for the continuous production of organolead and other organometallic compounds by the practice of this invention.
With particular reference to the drawings, there is shown in FIGS. 1 and 2 a substantially cylindrical vessel having side walls 12, a bottom 14, and top 16. Positioned in the bottom 14 is an inlet 18 which is adapted to allow Grignard solution to enter the cell along with other ingredients that will be more fully described.
Fitted inside of the cell near the bottom is a screened support 20 upon which rests a Teflon plug 22. Fitted about the Teflon plug and in sealing relationship there with are a series of overlayed cylindrical insulating materials. The first such layer 24 is a fine mesh nylon screen which is impressed upon the inner surface of a polypropylene haircurler 25 which is a large open mesh semi-rigid lattice work of polypropylene which supports the nylon screen 24. Wrapped around the outside of the haircurler 25 is another nylon screen 26 which is substantially the same thickness as the inner nylon screen M. Good results are achieved when the nylon screens are from 60 mesh. Positioned within the opening 28 defined by the nylon screens is an electrical contact strip 30.
Within the space 28 as well as the area outside of the space and enclosed by the cell wall 12 there are placed into the cell lead electrodes 31 which are in the form of beebees or shot. The outside wall 12 is fitted with an electrical contact strip or buss bar 32.
The top of the cell 16 is fitted with a liquid opening 34 and is preferably sealed to the remainder of the cell by means of a Teflon gasketed flange 36.
In operation the electrical contacts 30 and 32 are connected to a source of alternating current (not shown) and the Grignard reagent dissolved in an appropriate solvent is added to the cell through inlet 18. As the cell fills the fluid leaves the cell through outlet 34 where it is recirculated back into the cell by means of an appropriate recycle line and pump (not shown).
When it is desired to produce organometallic compounds, particularly tetramethyllead, continuously an arrangement of the type illustrated by FIG. 3 may be used. With particular reference to FIG. 3, there is shown a feed drum which contains a Grignard reagent such as methyl magnesium chloride dissolved in an ether solvent which preferably is a blend of 60 parts by weight of tetrahydrofuran and 40 parts by weight of the diethyl ether of tetraethylene glycol. A preferred amount of Grignard reagent in this solvent system is 1.5 moles per liter.
The Grignard reagent solution is removed from feed drum 110 through line 112 and circulated by pump 114 through lines 115 and 116 back to the feed drum 110. When it is desired to begin, the reaction valve 118 which is Td to line 115 is opened and the Grignard solution flows through line 120 into surge drum 122. Upon filling of surge drum 122 the Grignard solution is removed therefrom to line 124 by means of circulating pump 126 where it moves to line 128 through line 130 into electrolysis cell 132. The cell is constructed in accordance with FIGS. 1 and 2 previously discussed.
6 EXAMPLE 1 The cell used in this series of experiments was a /2 liter cell in corresponding construction to the cell shown in FIG. 1. Alternating current was supplied by a potentiostat supplied with l 10 volts 60 cycle current. Appropriate 1.5 molar solutions of methyl, ethyl, butyl, and phenyl Grignards were prepared in a tetrahydrofuran-diethyl ether of tetraethylene glycol in proportions previously specified. Throughout the run the appropriate methyl, ethyl, butyl, or phenyl halides were added to the cell to provide about 1.0 percent by weight of the total cell content. The runs were monitored by analyzing the alkyl halide concentration and the concentration of the active Grignard. The results of these tests Effluent from the cell is discharged therefrom through are presented below in TABLE I.
TABLE I Run Frequency Average Average Avera e Initial Final Current No. cycles/sec. Volts Amps. Temp (OH )mm/gm (OH )mm/gm Efficiency TML l 60 24 I0 80 L06 0.23 137 2 60 25 I0 78 l 39 0.ll I54 3 60 25 I0 76 0. 17 l 13 TEL 4 60 26 6 75 1.00 0.77 58 5 60 3O 9 75 1.38 0.92 6l 6 60 I0 77 0.92 0.50 62 7 60 9 70 L 0.20 56 TBL 8 e0 37 9 77 1.44 t8 0.29 32 25 I0 77 L32 0.45 28 line 134 into heat exchanger 136 where it is cooled and discharged through line 140 and returned to the surge drum 122.
As can be seen from the drawing line 128 is fitted with a control valve 142 which allows feed from surge drum 122 to be transported into surge drum 144. Surge drum 144 is fitted with a discharge line 146, a circulating pump 148 and a discharge line 150 therefrom which feeds into a second cell 152. The effluent therefrom which passes through line 154 into heat exchanger 156 and vents to line 158 into surge drum 144. Line 154 is Td into product discharge line 160 which is fitted with a valve 162 which allows discharge of the final cell electrolysis product.
When arrangement shown in FIG. 3 is used there is provided in the system a source of extraneous alkyl halide which is contained in storage tank 164 which is discharged through line 166 into surge drum 122. The use of the alkyl halides is an important additive since it prevents the build-up of magnesium etherates, salts and the like in cell 132 which would require the intermittent cleaning thereof were it not for the excess alkyl halides.
While the use of extraneous halides are required in conventional direct current Grignard electrolysis processes, it is not required when the present invention is used as a batch process. It may be employed in both the continuous or batch process to insure efficient operation of the cell. As will be shown by the examples hereinafter presented, organometallic compounds can be produced with all of the Grignard reagents being utilized without cell shorts or substantial current efficiency impairment occurring.
To illustrate the invention the following are presented by way of examples:
In the above Table the initial and final (OI-I)mm/ gm indicates the initial and final molarity of the Grignard reagent in the cell. The current efficiency is the ratio of current used to produce lead in relation to the total current put through the cell. Two hundred is ideal. In the above experiments the average temperature was maintained between 50 60 C. and the average batch time was 10 hours. It will be noted from the above Table that the current efficiencies were less when tetraethyllead and tetrabutyllead were produced. In similar experiments, not shown, poor current efficiencies were obtained with tetraphenyllead. Improvements in these runs are obtainable when the frequency of the alternating current is reduced to between 5 10 cycles.
EXAMPLE 2 In this series of experiments two cells of the type shown in FIG. 1 were arranged as shown in FIG. 3. To averaged the overall procedure a partially direct current electrolyzed Grignard ether solution was used as the feed in the first surge drum. The Grignard concentration in the feed was 0.35 moles of methyl magnesium chloride. To this was added 1.5 percent of methyl chloride based on the weight of the Grignard. The first cell was operated for 2 hours under the conditions specified and the effluent therefrom which contained 0.1 1 active Grignard and 0.4 percent methyl chloride was fed to the final cell. This cell was operating in the effluent averated 0.02 moles of methyl magnesium chloride and 0.2 percent methyl chloride. The cells which are connected electrically in series were constantly monitored with respect to voltage drop and amperage. The following operational parameters were established:
Average Range Temperature 133 F. l25-l40 F. Net Flow Rate 7.1 gm/min 4.0-13.) grams/min Current 10 amps 9.5l().5 amps Voltage 52 volts 50-59 volts Active Grignard* 0.02 0.0l0.04 moles/gm MeCl 0.15 nil-0.02
of final cell After this series of experiments was completed, the final cell was dismantled and examined. The lead shot in the center bed was clean and fluid, and no solids were indicated. However, the outer lead bed was cemented into a solid mass by magnesium salts and etherates. During the cell runs, it was noted that both temperature and voltage increased. This apparently was due to solids coating the outer lead bed and reducing the circulation through the cell. No gas make was observed and the lead yield based on OH was high so the Wurtz losses were insignificant.
The following results were obtained from the runs:
Total Time 80.23 hours Total Weight of Effluent 34,262 grams Lead Yield (OH) 105 Current Efficicncy 77 (200 max) Magnesium Balance 101 Total Mass Balance 98 EXAMPLE 3 Using the experimental techniques shown in EXAM- PLE l, tetraethyltin and tetramethyltin were prepared.
CONCLUSIONS compounds. Thus if one were to electrolyze methyl magnesium chloride and ethyl chloride using lead elec trodes a mixture of methyl-ethyl lead compounds would be produced.
By using the invention, it is possible to electrolyze with inexpensive and available alternating current a solution of Grignard reagents and metal electrodes to produce organometallic compounds. The efficiency of the reaction is surprising in that at the end of an electrolysis run little or no Grignard reagent remains.
1. An electrolytic cell for producing organometallic compounds comprising a substantially upstanding cylindrical metal vessel having side, top and bottom walls, a perforate support within the vessel extending thereacross and spaced above the bottom wall, a plug of insulating material supported centrally of said perforate support, a tubular perforate member of insulating material vertically extending upwardly from the plug and defining with the plug a first chamber within the member and a second chamber with the perforate support and the vessel side walls, said tubular perforate member including a semi-rigid open large mesh haircurler member, inner and outer layers of fine mesh nylon screen along the inner and outer sides of said haircurler member and supported thereby, the mesh of the screen layers being substantially finer than the mesh of the haircurler member and such as to prevent the movement therethrough of the shot, a first lead electrode in the form of shot within said first chamber, a second lead electrode in the form of shot within said second chamber, means connecting said first and second lead electrodes to a source of low frequency alternating current potential, an opening in the bottom wall, and an opening in the top wall for permitting a Grignard reagent solution to flow through the vessel to be electro lysed, whereby said perforate member provides a flow path through the cell for the solution.
2. The electrolytic cell as defined in claim 1, wherein said nylon screens are about -80 mesh. and said haircurler member is of polypropylene.
3. The electrolytic cell as defined in claim 2, wherein said means connecting said electrodes to a source of alternating current potential includes a contact mounted on the vessel for said second electrode and a contact extending into said first electrode.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 853 735 Dated December 10 1974 John C. Shepard, Jr., Inventor(s) Edward E. Johnson and Robert W. Bearman It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Col. 6, Table I, second to last line, delete "t8" before "0.29"; line 54, change "averaged" to -simplify--; line 64, change "averated" to -averaged--; line 65, change "are" to -were--; Col. 7, line 5, change "4.0-l3.)" to --4.0l3.l--.
Signed and sealed this 15th day of April 1975.
(BELT- n-) Attest C. E-QIRfiiALL DANE RUTH C. Elfin-S 321 Commissioner of Patents rttestin; Ufficer and Trademarks F ORM PO-I 050 (10-69) USCOMM-DC 603764 59 U.S. GOVERNMENT PRINTING OFFICE II' O-Jll-Sll,