US2735857A

US2735857A - Uranium alkoxy compoundsand method

Info

Publication number: US2735857A
Authority: US
Publication date: 1956-02-21
Anticipated expiration: 1973-02-21

Description

United States Patent Ofi ice 2,735,857 Patented Feb. 21, 1956 URANIUM ALKOXY COMPOUNDS AND METHOD OF PREPARING SAME Application October 17, 1944, Serial No. 559,124

20 Claims. (Cl. 260429.1)

No Drawing.

This invention relates to compounds of uranium and their preparation, particularly to the alkoxy compounds of uranium which have been found to be especially useful.

In order to separate the isotopes of uranium by diffusion methods, uranium compounds are employed. If these compounds are to be useful for their intended purpose it is desirable that they be liquid at ordinary temperatures, that they undergo no substantial thermal de composition nor have corrosive action on conventional construction materials, and that they have an appreciable vapor pressure in the temperature zone of 100 C. to 200 C.

We have discovered that certain of the alkoxides of uranium have the characteristics noted above and that they may therefore be conveniently employed in the separation of uranium isotopes. Those compounds which are considered particularly useful for the above purpose are the tetra-, penta-, and hexa-alkoxides of uranium wherein the alkoxy radical is selected from the group consisting of the methoxy, ethoxy, propoxy, and butoxy radicals. Moreover other alkoxy derivatives of uranium and monovalent alkoxy radicals such as allyloxy methallyloxy derivatives or the corresponding derivatives of other monovalent aliphatic alcohols such as hexyl or lauryl alcohol and similar alcohols were found operative. in general such compounds have the probable structure U(OR) where R is a monovalent aliphatic radical and x is a small whole number from 4 to 6.

It is thus an object of the present invention to provide methods for producing alkoxy compounds of uranium particularly the tetra-, pentaand hexa-alkoxides of uranium wherein the alkoxy radical is selected from the group consisting of the methoxy, ethoxy, propoxy, and butoxy radicals.

Another object of the present invention is the provision of new and useful uranium compounds, such as, uranium tetraalkoxides, uranium penta-alkoxides, uranium. hexaalkoxides and addition, substitution, and interconversion compounds of the uranium penta-alkoxides.

Another and still further object of the present invention is the production of uranium tetraethoxide, uranium pentaethoxide, uranium hexaethoxide and addition, substitution, and interconversion compounds of uranium pentaethoxide.

Other objects and many of the attendant advantages of the present invention will be appreciated as the same becomes better understood by reference to the following description.

We have found that a uranium tetra-alkoxide such as the methoxy, ethoxy, propoxy or butoxy uranium compounds can be converted to a uranium penta-alkoxide of the same radical group by oxidizing the tetra-alkoxide under appropriate conditions.

The first step in the method of producing a uranium penta-alkoxide or a uranium hexa-alkoxide of the abovementioned alkoxy group is the formation of a uranium tetra-alkoxide of said group by the substitution of uranium for the alkali metal of an alkali alkoxide of the t methoxy, ethoxy, propoxy, and butoxy radical group. The uranium tetra-alkoxide so produced is converted to uranium penta-alkoxide in a further step by oxidizing the uranium to a pentavalent state and introducing an additional alkoxy radical into the compound. This may be done by introducing oxygen either as elemental oxygen or by a peroxide such as benzoyl peroxide, or acetyl peroxide into a uranium tetra-alkoxide suspension in an alcohol having the same alkyl radical as that of the uranium tetra-alkoxide, or by introducing bromine followed by an alkali alkoxide having the same alkyl radical as that of the uranium tetra-alkoxide.

The production of a uranium hexa-alkoxide of the above-mentioned alkoxy group from a uranium pentaalkoxide of the same radical group is achieved through the intermediate of a novel addition compound. It is possible to produce this addition complex or compound of a uranium penta-alkoxide by adding the uranium penta-alkoxide to a solution of an alkali alkoxide in alcohol under an inert atmosphere in which the alkali alkoxide has the same alkoxy radical and the alcohol the same alkyl radical as the penta-alkoxide. The addition compound of uranium penta-alkoxide and the alkali metal alcoholate thus formed is then converted to uranium hexa-alkoxide by oxidation.

In practicing the method of the present invention We first prepare a compound of a uranium tetra-alkoxide, such as uranium tetraethoxide, from an alkali alkoxide alcohol solution, such as sodium ethoxide ethanol solution, by addiing a uranium tetrahalide, such as uranium tetrachloride or tetrabromide to the solution while agitating the same. It is to be emphasized that an alkoxide of any of the alkali metals may be employed with other alkoxy radicals such as the methoxy, ethoxy, propoxy, and butoxy radicals. Also other tetrahalides such as the bromides, iodides and fluorides are suitable.

A reaction takes place with evolution of heat producing a uranium tetra-alkoxide, such as uranium tetraethoxide and the corresponding alkali metal halides. If the uranium tetraalkoxide alone is desired the alcohol may first be distilled off in any suitable manner and the residue subjected to fractional distillation at a reduced pressure to remove other substances leaving uranium tetraalkoxide. If it is not desired to isolate the uranium tetraalkoxide, the solution containing the uranium tetraalkoxide is next oxidized by introducing oxygen into the reaction mixture, the oxidation resulting in the attachment of a fifth alkoxy radical to the uranium, thus producing a uranium penta-alkoxide, such as uranium pentaethoxide. The bulk of the alcohol is next distilled off under nitrogen at atmospheric pressure followed by further distillation under vacuum to remove the last traces of alcohol. Finally, the uranium penta-alkoxide is purified by distillation under a high vacuum leaving a residue including an alkali halide.

The sixth alkoxy radical of uranium hexa-alkoxide, as previously noted, is attached to the uranium through the use of a novel intermediate addition compound of a uranium penta-alkoxide, such as uranium pentaethoxide. This addition compound is first formed by reacting the uranium penta-alkoxide with an alkali alkoxide alcohol solution, such as a sodium ethoxide ethanol solution, under an inert atmosphere. A uranium hexa-alkoxide, such as uranium hexaethoxide, is then produced from the addition compound by oxidation with any suitable oxidizing agent, such as acetyl or benzoyl peroxide. The major portion of the alcohol is then distilled off under an inert atmosphere at atmospheric pressure followed by a further distillation under vacuum to remove the last traces of alcohol. The uranium hexa-alkoxide so obtained is finally purified by fractionating at a low pressure leaving a residue including an alkali-benzoate or an alkali acetate.

Solid and liquid compounds'are secured. In general the tetraalkoxy derivatives are solids whicharedifiicultly soluble or insoluble in organicsolvents. On the other hand many of the penta and hexa derivatives, particularly the -alkoxidcs corresponding to the lower aliphatic alcohols are generally liquids.

Example] Aspecific example of the methodof producinga uranium penta-alkoxide, such as uraniumpentaethoxide, in "accordance with the-present invention is as follows: 800

cc. of dry ethanol prepared in anyconvenientmanner is placed in a suitable container equipped with an agitator and a reflux condenser. 46 grams (2 gram atoms) of sodium metal is then. reacted with the alcohol by adding the sodium in small amounts at such a rate that the reaction doesnot get outofcontrol. In order to protect the sodium ethoxide formed by the reaction from undesirable oxidation and moisture when the evolution of hydrogen resulting from the reaction isnot sufficiently rapid, an atmosphere of dry inert gas such as nitrogen is maintained over the contents of the container. When the sodium has completely reacted, the container and contents are cooled, preferably to room temperature.

The cooled sodium ethoxide solution is now stirred rapidly while a total of 190 grams (0.5 mole) of powdered anhydrous UCli, prepared in any suitablemanner, is added in 20-gram portions at intervals'of about minutes in the presence of an atmosphere of dry nitrogen, inasmuch as sodium ethoxide and uranium ethoxide are sensitive to oxygen and moisture. If desired, the reaction may be carried out in an atmosphere ofdry air instead of nitrogen if it is carried out quickly and in a closed vessel. Since the reaction of uranium tetrachloride with an alcoholic solution of sodium ethoxide is exothermic, it may be necessary to cool the reaction vessel during the addition of the uranium tetrachloride if the alcohol boils too vigorously. 'When the heat of the reaction is no longer sufiicient to cause the reaction mixture to reflux, external The reaction above results in the formation of theuranium tetraethoxide in accordance with the following equation:

If desired theuranium tetraethoxide may be recovered by distillation of the excess alcohol. This compound is a light green solid which does not distill at atmospheric pressure. It is insoluble in the common organic solvents such as acetone, or chloroform and is very susceptible to hydrolysis. -Uranium pentaethoxide is generally made from the reaction mixture-secured by the above process without attempting to recover the 'tetraethoxy compound. In such a case, after cooling the reaction mixture, the nitrogen in the container is first evacuated; and 2.5 liters (0.1 mole) of dry oxygen is then slowly admitted to the container, while vigorous stirring is maintained. As the oxygen is absorbed by the reaction mixture, the mixture warms up and changes color from a light green to a dark brown. After all of the oxygen has been passed into the container, nitrogen is readmitted and stirring is continued for another 30 minutes. The foregoing reaction results in the production of uranium pen'taethoxide in accordance with the following equation:

The bulk of the alcohol in the reaction mixture is now distilled off under a streamof nitrogen at atmospheric pressure while suitably stirring the mixture. The heating to effect the distillation is preferably accomplished by immersing the container in an oil bath and gradually raising the temperature of the bath to C. When the dark residue appears to be nearly free of alcohol, the container with its contents is cooled, the nitrogen stream is shut off and the container is evacuated by suitable means.

The distillation is now continued at a, pressure of 15 to 20mm. of Hg by rewarming the oil bath gradually to 150 C. in order to remove more of the alcohol. The pressure in the system is now reduced to 1 to 3 mm. of Hg taking care in doing so to prevent violent boiling of the contents of the container. Heating with the oil bath at a temperature of 150 C. is now continued for an hour to remove the last traces of alcohol. a

In order to separate the uranium pcntaethoxide from the large quantities of sodium chloride and by-products of the reaction mixture, the brown almost solid residue in thecontainer is now heated under a vacuum to distill off the uranium pentaethoxide. To the accomplishment of thisend a clean receiver is attached to the outlet end of 'the container. The system is'evacuated to a pressure of .001.004 mm; of Hg and the temperature of the oil bath is-gradually raised to 200 C., thereby causing distillation of the uraniumpentaethoxide. After the'distillation has started, the temperature-of the oil bath may be lowered to (3., without decreasing the distillation. Toward the end of the reaction, the temperature of the oil bath may be raised to and maintained at 240 C. until the distillation ceases. The distillation of uranium pentaethoxide begins at a bath temperature of about 180 C.

About 151 grams (0.326 mole) of quite pure uranium pentaethoxide is obtained'which represents a yield of 65 per cent based on the amount of UCl4 used. While this product, as stated, is quite pure it may be further fractionated by'redistillation at 0.002 mm. of Hg pressure. The compound obtained is a dark brown liquid which has 'a composition corresponding to the formula U(OC2H5)5 and distills at 122123 C. at a pressure of 0.001 mm. of mercury and has a density d4 1.70. it is soluble in organic solvents such as benzene, acetone and chloroform and is susceptible tohydrolysis. Upon exposure to oxygen -it oxidizes tothe red liquid U(OC2H5)6. Other alkoxy types may be prepared in accordance with this process. For example, the n'-propyl derivative may be prepared by substituting n-propanol for ethyl alcohol. In such a case a similar compound somewhat less stable is secured. In like manner similar compounds may be prepared fromn-butyl or tertiary butyl alcohol.

Example 11 A. specific exampleof the. method of producing a uranium hexa-alkoxide, such as uranium hexaethoxide, in accordance with the present invention is as follows: In a suitable container, designed to enable one to work in an-atmosphere of nitrogen-or other inert gas, is placed 300 milliliters of'dry ethanol and to this is added 1.69 grams (0.0735 gram atom) of sodium. After the sodium has reacted with the ethanol and the solution has been cooled in an atmosphere of. nitrogen, 20 milliliters (34 grams, 0.0735 mole). of uranium pentaethoxide is added. Upon stirring this mixture the dark brown color of pentaethoxide disappears and a clear light green solution of thecompound NaU(OC2H5)s is formed. The foregoing reaction-results in the production of an addition compound in accordance with the following equation:

U OCzHs) 5 NaOCzHs- NaU OCzHs) s Throughout'this.preparation.an atmosphere of dry nitrogen must. bemaintained because uranium hexaethox- .idezis-sensitiveato air a1'1d highly.sensitive'to moisture.

. Tothetforegoing.solution, which is very rapidly stirred, -8z90 grams (0.036? mole) of dry powdered-benzoylperoxide is added. The mixture quickly turns dark red with the liberation of some heat, and a gelatinous precipitate of sodium benzoate appears. The'mixture is rapidly stirred at room temperature under an atmosphere of dry nitrogen for about an hour. The foregoing reaction results in the formation of uranium hexaethoxide in accordance with the following equation:

At the end of the period of stirring the major portion of the ethanol is distilled off with stirring under a stream of nitrogen at atmospheric pressure by heating the container in an oil bath at 110 C. after connecting it to a suitable receiver. The container is now evacuated to a pressure of to mm. of Hg and more of the alcohol removed by gradually raising the temperature of the oil bath surrounding the container to 115 C. The remainder of the alcohol is removed by evacuating to aboutOJS mm. and heating at approximately 100 C. for about 15 minutes.

After cooling and replacing the alcohol receiver with a clean dry receiver, the container is evacuated to a pressure of 0.002 to 0.003 mm. of Hg and the distillation of the uranium hexaethoxide is carried out by heating with an oil bath at a temperature of 140 C. as long as any of the red liquid comes over. While the temperature of 140 C. is preferred because the distillation can be carried out quicker and more completely, the uranium hexaethoxide may alternatively be distilled slowly from the reaction mixture at a temperature of 90 to 100 C.

The yield of crude uranium hexaethoxide is about 20 grams. This material may be further fractionated at a pressure of about 0.001 mm. of Hg in order to separate impurities such as ethyl benzoate and uranium pentaethoxide. The yield is about 16 grams of substantially pure liquid, uranium hexaethoxide, which is' darker red and has a boiling point of 72 to 74 C. at a pressure of 0.001 mm. of Hg. The method gives about 43 per cent yield based on the uranium pentaethoxide used. This compound has density d4 1.55 and is very soluble in all common organic solvents. The corresponding npropyl, n-butyl, isobutyl, isopropyl, tertiary butyl or amyl derivatives may be made in similar manner.

Example III Another example of the method of producing a uranium pentaalkoxide, such as uranium penta-n-propoxide is as follows. In the apparatus used for the preparation of uranium pentaethoxide was placed 150 cc. of dry propanol and 5.75 g. (0.25 g. atom) of finely cut sodium. When all of the sodium was in solution, 23.75 g. (0.0625 mole) of uranium tetrachloride was added in small portions. A green suspension resulted. The mixture was stirred and gently warmed for one hour. After the suspension had cooled to room temperature, a solution of 1.58 cc. (0.0625 g. atom) of bromine in 10 cc. of dry benzene was added dropwise. The reaction mixture became dark brown in color. After five minutes, a solution of 0.0625 mole of sodium propoxide in 75 cc. of anhydrous propanol was added quickly. A lighter gray color resulted and stirring was continued one hour.

The suspension was concentrated into a 200 cc. Claisen fiask and the product was distilled with a mercury ditfusion pump. The uranium penta-n-propoxide obtained distilled at 180l85/0.009 mm., and weighed 16 g. (48.1%). On redistillation there was obtained 13.8 g. (41.5%) distilling at l62-l64/0.00l mm.

Uranium penta-npropoxide was also prepared by the exchange reaction. First, 50 cc. (0.183 mole) of uranium pentaethoxide was treated with 70 cc. (0.937 mole) of propanol. Upon removal of the solvents and distillation with a mercury-diffusion pump, 92.7 g. (94.7%) of ura nium penta-n-propoxide was obtained, and this distilled at 157-159/0.0032 mm.

The corresponding isobutyl compound may be prepared in the same manner. This product is a solid which distilled at 192 C./ 0.007 mm.

Uranium penta-n-butoxide, prepared in accordance with the general procedures given for uranium pentaethoxide and uranium penta-n-propoxide, distils at 208- 210/ 0.012 mm. The compound is a pale brown liquid which is soluble in all common dry, hydroxyl-free organic solvents. The compound is sensitive to moisture which effects rapid hydrolysis.

Although the present invention has been described with reference to specific details of certain embodiments thereof it is not intended that such details shall be regarded as limitations upon the scope of the invention except so far as included in the following claims.

The foregoing description is for purposes of illustration and since the invention may be carried out in a variety of forms other than those specifically described, it is our intention that the invention be only limited by the appended claims or their equivalents.

We claim:

1. As a new composition of matter a compound having the formula U(OR)71 where R represents a monovalent alkyl radical having a maximum of four carbon atoms and n represents one of the integers selected from the group consisting of 4, 5 and 6.

2. As a new composition of matter, uranium tetraalkoxide having a maximum total of sixteen carbon atoms per molecule.

3. As a new composition of matter, uranium pentaalkoxide having a maximum total of twenty carbon atoms per molecule.

4. As a new composition of matter, uranium hexaalkoxide having a maximum total of twenty-four carbons per molecule.

5. A method of preparing a uranium hexa-alkoxide which comprises reacting a uranium penta-alkoxide having the formula U(OR)5, in which the OR represents an alkoxy radical having not more than four carbon atoms, with a corresponding alkali alkoxide in which the alkoxy radical has the same number of carbon atoms as the alkoxy radical in said uranium penta-alkoxide under substantially anhydrous conditions to form an alkali uranium hexa-alkoxide addition compound, and then oxidizing said addition compound under substantially anhydrous conditions.

6. A method of preparing uranium hexaethoxide which comprises reacting uranium pentaethoxide with an alkali ethoxide under substantially anhydrous conditions to form the alkali uranium hexaethoxide addition compound and then oxidizing said addition compound under substantially anhydrous conditions.

7. A step in the method of preparing uranium hexaethoxide comprising reacting uranium pentaethoxide with an alkali ethoxide under substantially anhydrous conditions to form the alkali uranium hexaethoxide addition compound.

8. A method of preparing a uranium penta-alkoxide which comprises reacting a uranium tetrahalide with a solution of an alkali metal in a monohydric alcohol having not more than four carbon atoms and under substantially anhydrous conditions and after the reaction is substantially completed oxidizing the solution under substantially anhydrous conditions.

9. A method of preparing uranium pentaethoxide Whichcomprises reacting a uranium tetrahalide with a solution of an alkali metal in ethanol under substantially anhydrous conditions and after the reaction is substantially completed oxidizing the solution under substantially anhydrous conditions.

10. A method of preparing uranium penta-ethoxide which comprises reacting a uranium tetrahalide with a solution of an alkali metal in ethanol and under substantially anhydrous conditions, oxidizing the resultant mixture under substantially anhydrous conditions, and distil- '37 ling off the ethanol first under an inertatmosphereand subsequently under a vacuum.

11. A method of preparing uranium pentaethoxide which comprises reacting a .uranium tetrahalide=with a -17., As.a..new composition of matteruranium hexafii-hoxide.

,,18.'A..methodof producing uranium. pentaethoxide which comprises oxidizing uranium tetraethoxide under solution of an alkali metalin ethanol under. substantially substantially anhydrous conditions.

anhydrous conditions, oxidizing the resultant mixture under substantially anhydrous conditions, removing the ethanol from the reaction mixture and-subsequently purifying the pentaethoxide by distillation undera vacuum.

12. A method of preparing uranium hexaethoxidelO which comprises reacting uranium pentaethoxide with an alkali ethoxide in ethanol under substantially anhydrous conditions to form an addition compound, oxidizing the addition compound under substantiallyanhydrous conditions, removing the alcohol from the reaction mixture, .15

and subsequently purifying the product by fractionatingat a low pressure.

13. A method of forming uranium hexaethoxide which comprises reacting uranium pentaethoxide with an alkali ethoxide in ethanol under an inert atmosphere to form an alkali uranium hexaethoxide addition compound,

reacting said addition compound with a carboxylic peroxide under substantially anhydrous conditions to remove the alkali metal therefrom, distilling off said ethanol and subsequently purifying the product by fractionating at a v low pressure. p

14. A method of forming uranium hexaethoxide which comprises reacting uranium pentaethoxidev with sodium ethoxide in ethanol under an inert atmosphere to form the sodium uranium hexaethoxide addition compound, reacting said addition compound withbenzoyl peroxide under substantially anhydrous conditions, distilling off said ethanol and subsequently purifying the product by fractionating at a low pressure.

15. As a-new composition of matter uranium tetraethoxide.

16. As a new composition of matter uranium pentaethoxide.

19. A method of producing uranium hexaethoxide which comprises oxidizing an alkali metal uranium hexaethoxide under substantially anhydrous conditions.

20. The method of preparing a uranium hexa-alkoxide, which comprises reacting under substantially anhydrous conditions a uranium tetrahalide with an alkali metal alkoxide-having not, more than four carbonatoms, then subjecting the reaction mixture to oxidation-with a car- .boxylieperoxide under substantially anhydrous conditions whereby a uranium penta-alkoxide is-formed, treating under substantiallyanhydrous conditions said uranium 'penta-alkoxide-with. an alkali metal alkoxide having the same nu mber of, carbon atoms as the alkoxide of the uranium penta-alkoxide to form an alkali metal uranium .hexa-alkoxide addition compound, and then oxidizing said addition compound under substantially anhydrous conditions.

References Cited in the file of this patent UNITED STATES PATENTS 2,125,961 Shoemaker Aug. 9, 1938 OTHER REFERENCES -Friend: Textbook .of Inorganic Chemistry, vol. VII, part III, Chromium and Its Congeners, page 3 (1927), pub. by Charles Grifiin;& Co., Ltd., London.

LiebigsAnnalen, vol. 476 (1929), pages 121, 139, 141, 146, Meerwein etal.

Thiessen et al.: Zeitschrift fiir Anorganische Chemie, vol. 181 (1929), page 292.

Deming: General Chemistry, 3rd ed., page 344 (1930), pub. by John Wiley & Sons, N. Y.

Claims

1. AS A NEW COMPOSITION OF MATTER A COMPOUND HAVING THE FORMULA U(OR)N WHERE R REPRESENTS A MONOVALENT ALKYL RADICAL HAVING A MIXIMUM OF FOUR CARBON ATOMS AND N REPRESENTS ONE OF THE INTEGERS SELECTED FROM THE GROUP CONSISTING OF 4, 5 AND 6.