US3419603A - Stabilization of water soluble acetohydroxamic acid salts - Google Patents

Description

United States Patent 3,419,603 STABILIZATION OF WATER SOLUBLE ACETOHYDROXAMIC ACID SALTS Stanley A. Lipowski, Livingston, and Charles A. Fetscher,

Short Hills, N.J., assignors to Diamond Shamrock Corporation, a corporation of Delaware No Drawing. Filed Sept. 1, 1964, Ser. No. 393,774

4 Claims. (Cl. 260-5005) ABSTRACT OF THE DISCLOSURE Water soluble alkali metal salts of acetohydroxamic acid are stabilized by treatment with formic and acetic acids. For example, to still liquid potassium acetohydroxamate was added by weight of glacial acetic acid. The stabilized salt was heated to 240 C. without exploding.

The present invention relates to a process for stabilizing water soluble alkali metal salts of acetohydroxamic acid. More particularly, the present invention relates to treatment of water soluble alkali metal salts of acetohydroxamic acid with acid thereby bringing about a new and highly stable form of the aforesaid salts.

Acetohydroxamic acid and its alkali metal salts, because of the hydroxamic acid functional group would make an outstanding chelator for heavy metals such as copper, iron, cobalt, nickel, chromium, manganese, vanadium, uranium, gold, platinum, palladium and rhodium. That is, the low molecular weights of these materials bring about a very high chelating capacity which is about 6.6 meq. per gram for the acetohydroxamic acid and from 4.5 to 5.5 meq. per gram for its alkali metal salts. At tempts to isolate the free acid, we have found, involve cumbersome procedures. The free acid is therefore uneconomical to prepare and hence, has little chance of utility as a chelator. Regarding the preparation of water soluble alkali metal salts of acetohydroxamic acid, these have not been previously isolated. We have isolated alkali metal salts of acetohydroxamic acid, e.g., the potassium salt, which we found exists in the form of a white crystalline mass. It, too, is a chelator for heavy metals including those listed previously. However, we have discovered that upon heating, the salts explode with a violent force. In

view of this unsatisfactory property of the salts, their use as chelators is clearly quite limited.

Accordingly, it is an object of the present invention to prepare water soluble alkali metal salts of acetohydroxamic acid in a highly stable form thereby allowing these salts to be used as chelators. Another object of the present invention is to stabilize water soluble alkali metal salts of acetohydroxamic acid in a novel manner thereby bringing about a new and highly stable form of said salts characterized by enhanced stability, which renders same useful as chelators. A further object is to provide for water soluble alkali metal salts of acetohydroxamic acids which are stable when heated at elevated temperatures. Other objects will become apparent from the detailed description given herein. It is intended, however, that the detailed description and specific examples do not limit the invention, but merely indicate preferred embodiments thereof since various changes and modifications within the scope of the invention will become apparent to those skilled in the art.

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We have discovered that the above and other objects may be achieved by treating water soluble alkali metal salts of acetohydroxamic acid, preferably while in a liquid state, with acid. Upon solidification, a highly stable material is obtained. We have found that especially useful organic acids are formic and acetic acids or their mixtures, preferably glacial acetic acid. In order to achieve stabilization, the salts of acetohydroxamic acid should be treated with at least about 0.1 mol of acid per mol of salt. The maximum quantity of acid is not critical. However, we have found that usually there is no need to treat the salts with more than about 0.6 mol of the acid per mol of salt. For example, when using glacial acetic acid, we can use from about 0.1 to about 0.6 mol of glacial acetic acid per mol of salt, preferably about 0.2 mol of glacial acetic acid per mol of salt. Larger quantities of acid, as indicated above, can be utilized. However, their use will not further enhance the stability of the salts. Although we prefer to add the acid to the salt of acetohydroxamic acid while the latter is in the liquid state, that is, when it is in a molten state, e.g., before it solidifies, stabilization can also be achieved to some degree when the acid is added to and mixed with the solidified salt.

It might appear that the successful stabilization of these salts is due to the fact that the acids when introduced merely neutralize a certain quantity of the salt thereby damping or reducing the violence of the explosion of the remaining salt upon heating, that is, a dilution effect is achieved. However, this is not the case at all because when physical mixtures of salts of acetohydroxamic acid and free acetohydroxamic acid are prepared which correspond stoichiometrically to a partial neutralization based on the same amount of acid used herein, no enhanced stability is obtained. Therefore, it was most unexpected to discover that by treating the salts of acetohydroxamic acid with acid, a highly stable form of the salt was obtained. Thus, it is clear that buffering or partially neutralizing the salts of acetohydroxamic acid brings about thermal stability in an unexpected manner which is not a simple dilution or neutralization effect.

For a fuller understanding of the invention, reference may be had to the following examples which are given merely as further illustrations of the invention and are not to be construed in a limiting sense.

EXAMPLE I.-Preparation of potassium acetohydroxamate 230 grams of potassium hydroxide pellets (85.4% KOH) were dissolved in 1200 cc. of methanol thereby forming a 2.89 normal solution. grams (2 mols) of hydroxylammonium chloride were dissolved in 800 cc. of methanol. Then, 690 cc. of the 2.89 normal potassium hydroxide solution were added with cooling to the hydroxylammonium chloride solution. The resulting mixture was cooled down to 5 C. and the precipitated potassium chloride was filtered off. The pH of the filtrate was 8.0. The filtrate contained hydroxylamine in solution. 132 grams (1.5 mol) of ethyl acetate were then added to the hydroxylamine solution. Thereafter, 345 cc. of the 2.89 normal potassium hydroxide solution were added to the hydroxylamine solution during the course of two hours. During this addition, the pH remained constant at 11.8 and the temperature rose from 22 to 35 C. The reaction mixture was left standing overnight. Then, the methanol solvent and the ethyl alcohol and water which were formed as by-products during the reaction were removed by vacuum distillation .at a pressure of 50 mm. of mercury and at a maximum temperature of 75 C. The residue was a slight yellowish oil of potassium acetohydroxamate which upon slow cooling solidified to a white crystalline mass.

EXAMPLE II Approximately 20 grams of the potassium acetohydroxamate salt which was prepared in accordance with the procedure of Example I were placed in a 150 cc. beaker with a thermometer immersed in the salt. The beaker was heated slowly and carefully on a hot plate. When the temperature reached 100 C., a sudden rise in temperature to 170 C. was observed and the salt exploded violently, shattering the immersed thermometer.

Similarly, when 20 grams of the same salt were placed in a 250 cc. round-bottom flask equipped with a thermometer and stirrer, the salt exploded violently upon heating to 100 C., shattering the flask, stirrer and thermometer.

EXAMPLE IIL-Stabilization of potassium acetohydroxamate To 22.6 grams (0.2 mol) of the still liquid potassium acetohydroxamate prepared in the same manner as Example I were added 2.26 grams (0.037 mol) of glacial acetic acid. Upon cooling, this mixture solidified. The solidified, dry mixture was heated up to 240 C. at which time the mixture started to char slowly. No explosion occurred during this period of heating. The amount of glacial acetic acid utilized in this example was about 0.19 mol of acid per mol of salt, i.e., by weight of the salt. The pH of a 50% solution in water of the mixture was 10.5. This solution was boiled fifteen minutes without any indication of decomposition.

EXAMPLE IV The stabilization procedure of Example III was repeated, however, 4.52 grams of glacial acetic acid were utilized instead. This amounted to about 0.38 mol of glacial acetic acid per mol of salt, i.e., 20% by weight of the salt. The dry mixture was heated to 240 C. without explosion. The pH of a 50% water solution was 9.5.

EXAMPLE V The stabilization procedure of Example III was repeated except that 6.78 grams of glacial acetic acid were utilized. This amounted to about 0.57 mol of acid per mol of salt, i.e., 30% by weight of the salt. When the dry mixture was heated to a temperature of 240 C., no explosion occurred. The pH of a 50% water solution was 7.5.

EXAMPLE VI Attempted Stabilization of Potassium Acetohydroxamate Utilizing a Physical Mixture (A) A mixture was prepared of the materials which would be present if our in-situ stabilization is merely a partial neutralization as shown as follows. In Example III, for instance, the stable composition was made by adding glacial acetic acid to potassium acetohydroxamate in the following ratio:

Mol

Potassium acetohydroxamate 0.2 Glacial acetic acid 0.037

This blend, as observed, was stable up to 240 C., and even at that temperature decomposed slowly without any violence. If this is simply a partial conversion of the explosive salt to the stable acid the system becomes:

Mol Potassium acetohydroxamate 0.163 Free acetohydroxamic acid 0.037 Potassium acetate 0.037

A mixture of these three materials was prepared exactly according to the proportions above. A portion of this mixture exploded violently when warmed to 100 C.

(B) A further portion of the above three component mixture was dissolved in an equal weight of water. The pH of this solution was 10.0, actually somewhat lower than that of a 50% solution of the stable material of Example III. If reduced alkalinity were the whole explanation of stability, this material of Example VI should be slightly more stable than that of Example III.

A part of the aqueous solution of the Example VI mixture was heated to its boiling point, i.e., about C. After a few minutes of boiling, the solution exploded vigorously.

This is evidence that the stability we achieve by the addition of a small amount of acid is not due solely to partial neutralization or to dilution. Some complex and unexplained interaction must take place.

For Example III and Example VI, the molecular and material balance is as follows:

EXAMPLE III M01 Grams Potassium acetohydroxamate 0. 2 22. 6 Acetic acid 0. 037 2. 26

Total 0. 237 24. 86

EXAMPLE VI Mol Grams Potassium acetohydroxamate 0. 163 18. 4 Acetohydroxamic acid 0.037 2. 8 Potassium acetate 0.037 3. 66

Total 0.237 24. 8

Our stabilization procedure is applicable to the sodium and lithium salts of acetohydroxamic acid as well as to the potassium salt set forth above.

The following examples demonstrate the ability of our stabilized salts to chelate metals.

EXAMPLE VII An aluminum oxide catalyst contaminated with 0.1% vanadium oxide (V 0 was purified by washing with a 2% water solution of the potassium acetohydroxamate stabilized as described in Example III above. The solution immediately turned purple in color indicating chelation of the vanadium by potassium acetohydroxamate and the washed catalyst was free from vanadium. Vanadium oxide is otherwise difiicult to remove without damaging the catalyst.

EXAMPLE IX To a 1% cupric sulfate solution was added the stabilized salt of Example III. A copper complex precipitated in form of bright green flocks which was very insoluble in water.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A process for stabilizing water soluble alkali metal salts of acetohydroxamic acid comprising bringing together a wall soluble alkali metal salt of acetohydroxamic acid while in a liquid, solvent free state and from about 0.1 to 0.6 mol of glacial acetic acid per mol of said salt.

2. A process for stabilizing potassium acetohydroxamate which comprises bringing together said salt while in References Cited UNITED STATES PATENTS 2,397,508 4/1946 Rouault et al. 260500 6 OTHER REFERENCES Yale: Chem. Rev., vol. 33, (1943), pp. 228 to 229.

Cambi: Ben, vol. 69 (1936), pp. 2027-33.

LEON ZITVER, Primary Examiner.

J. E. EVANS, Assistant Examiner.

US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,419,603 December 31, 1968 Stanley A. Lipowski et al.

pears in the above identified It is certified that error ap t are hereby corrected as patent and that said Letters Paten shown below:

Column 4, line 31, under column entitled "Grams" the total "24.8 should read 24.86 line 71, "wall" should read water Signed and sealed this 24th day of March 1970.

(SEAL) Attest:

Attesting Officer WILLIAM E. SCHUYLER, JR.