US2785196A - Method of preparing sulfamic acids from organic isocyanates - Google Patents

Description

ldETHOD OF PREPARING SULFAMIC ACIDS FROMORGANIC ISOCYANAIES Theodore I. Bieber, Kew Gardens, N. Y.

No Drawing. Application August 12, 19 53,

SerialNo'. 373,890

9 Claims. (Cl. 260-500) The present invention relates to a method of preparing sulfamic acids from organic isocyan ates and, more particularly, it relates to a method or" preparing sulfamic acids 'by reacting organic isocy anates with sulfuric acid or oleum.

I have found that if organic isocyanates cf the general formula (R)NCO or ON(.R")NCO, where R is any alkyl radical and R is any bivalent aliphatic hydrocarbon radical that are not readily sulfon'ated, sulfated or oxidized under the reaction conditions, are treated with sulfuric acid or oleum, the corresponding sulfamic and di-sulfamic acids will be produced in very satisfactory yield.

Accordingly, it is an object of the present invention to provide a method of preparing monoand di-sulfa nic acids from corresponding organic monoand di-isocyanates.

Another object of the present invention is to provide a novel di-sulfarnic acid of a type never pr'oduced heretofore.

Other objects and advantages of the present invention will become more apparent as it is described in detail below.

The novel process that I have discovered for forming the mono and di-sulfamic acids may be generally represented by the following reaction where W is R when is equal to l and Wis R" when 1 is equal to 2, and where R and R" are alkyl and bivalent aliphatic hydrocarbon radicals, respectively, that are not readily sulfonated, sulfated, or oxidized under the reaction conditions.

With respect to the process for forming the monosulfamic acids, it may be represented by the following equation where R is any alkyl radical that is not readily sulfon'ated, sulfated or oxidized under the conditions of the reaction.

The process for forming the di-sulfamic acid may be represented by the equation where R" is any bivalent aliphatic hydrocarbon radical that is not readily sulfonated, sulfated or oxidized under the conditions of the process.

I have discovered that any sul-fonation, sulfation or oxidation of the alkyl or bivalent aliphatic hydrocarbon groups that may occur may be completely eliminated or at least reduced to a minimum amount, if the process is carried out at the lowest temperature at which the evolution of carbon dioxide occurs. To effect this, the process may be performed in an ice cooled vessel. However, higher temperatures may be employed where the alkyl or bivalent aliphatic hydrocarbon groups are particularly in sensitive to sulfonation, sulfation or oxidation.

Although the above reactions may be carried out with 100% sulfuric acid, I prefer to employ oleum for the sake firm P ten 0..

q 2,785,196 .Eatpntss Me 2 of convenience. Additionally, I prefer an oleum with a low sulfur trioxide content rather than one with a high sulfur trioxide content because the sulfonating, sulfating and oxidizing ability of oleum increases with an increase in sulfur trioxide content. Thus the possibility of undesired attack on the alkylor bivalent aliphatic hydrocarbon group is reduced ;by using an oleum oflow sulfur trioxide content.

Concentrated sulfuric acid may also be employed for the above reactions out it is noted that amine bisulfates are formed along with the sulfaniic acids. This is due to hydrolysis of the organic isocyanates by the water contained in the concentrated sulfuric acid. Thus, it is preferable to use sulfuric acid or oleum if 'sulfamic acids are to be obtained in high yields.

In order to isolate the sulfamic acids produced by my process, I dilute the reaction mixture with a liquid in which the sulfamic'acid is insoluble and in which the excess sulfuric acid or oleum is readily soluble. Ether is such a liquid which I have found useful for this purpose. I then filter the ether mixture to obtain the crystalline sulfamic acid.

Although the above ether filtration technique leaves the sulfami-c acid in a pure form, it may be necessary in some cases to recrystallize the sulfamic acids formed fro'm :a suitable solvent or solvent mixture. If this recrystallization still does not suflice to obtain the sulfamic acids in pure form, I employ the use of lead oxide to purify the product.

Thelea-d oxide method comprises the steps of adding lead oxide to an aqueous solution of the sulfamic acid to be purified. Lead hydroxide and lead sulfate are filtered out of the solution. The filtered solution containing the Water soluble lead salt of the sulfamic acid is treated with hydrogen sulfidefto precipitate lead sulfide. The lead sulfide is then removed by filtration. 'Next, the filtrateis preferably evaporated at reduced pressure and temperature (less than 100 C.) to avoid hydrolysis of the sulfamic acid. The remaining material will be pure crystals of the .sulfamic "acid.

' Below are several examples which illustrate my invention but do not in any way limit it thereto.

Example 1 To prepare ethyl sulfamic acid, 6.0 g. of ethyl isocyanate were added dropwise to 70 g. of ice cooled and mechanically stirred 20% oleum. The reaction proceeded with the evolution of carbon dioxide. A white solid, which dis solved with bubbling, was noticed during the reaction. When one half of the isocyanate had been added, the ice bath was removed and the reaction continued. After all the isocyanate was added, the reaction mixture was slightly lukewarm.

The chilled reaction mixture was poured slowly into 450 ml. of chilled anhydrous ether, which mixture was ice cooled and shaken during the mixing. The precipitated ethyl sulfamic acid was collected on a sintered-gl-ass tunnel and washed with ether. The ethyl sulfamic acid weighed 8.8 g. which represented an 83% yield. Also, it gave only a very faint test for sulfate ion.

To purify the product, it was dissolved in methanol and reprecipitated by the addition of -a relatively large quantity of ether.

Example II The ethyl sulfamic acid formed in Example I was dissolved in water. More than an equivalent amount of lead monoxide was added to the solution. Excess lead hydroxide and lead sulfate were removed by filtration. The filtrate, which contained lead ethylsulfamate, was treated with hydrogen sulfide to precipitate lead sulfide. After filtration to remove the lead sulfide, the filtrate was distilledat--reduced-pressure. The distilling bath did-not exceed-55 Q. The residual solid was dissolved in methanol and, on slow evaporation of the solvent, large crystals of ethyl sulfamic acid were obtained. These crystals had a melting point of 170-171 C. a

This example of the lead oxide purification method need only be employed when there is heavy sulfate contamination of the sulfamic acid produced in accord with my invention. In the case of the sulfamic acid produced in Example I, it was not actually necessary. However, this example is given as an illustration of the lead oxide method.

Exampie III In order to form hexamethylenedisulfamic acid, 5.3 g. of hexamethylene di-isocyanate were slowly added, to 22.4 g. of ice cooled and mechanically stirred oleum. It was noted that a white solid formed and carbon dioxide was evolved. After all the isocyanate was added to the reaction mixture, gas evolution continued sluggishly in the cold. In order to carry the reaction to completion, the mixture was gradually heated to 95 C., at which time no more gas was given ofi. it is possible that the second isocyanate group requires a higher reaction temperature because of the low solubility of the substance formed in the intermediate stage.

The reaction mixture, which contained a finely divided solid, was chilled to 0 C. whereupon considerably more solid material was precipitated. The chilled mixture was added to 300 ml. of ice cooled ether and filtered by suction. The filtered hexamethylenedisulfamic acid was washed with ether. It was found to weigh 8.6 g., which was 98.9% of theoretical yield.

Complete removal of sulfate ion was not achieved even though the product was dissolved in methanol and re precipitated by ether. Accordingly, the lead oxide puriiication method described in Example II was employed to obtain sulfate free hexamethylenedisulfamic acid.

While the invention has been described in detail and prises mixing an alkyl isocyanate with a sulfonating agent which is at least about H2804, and maintaining a temperature at which evolution of carbon dioxide occurs, whereby alkyl sulfamic acid is formed.

2. A method of forming sulfamic acids which comprises mixing an alkyl isocyanate wih a sulfonating agent which is at least about'100% H2804, and maintaining a temperature at which evolution of carbon dioxide occurs, whereby alkyl sulfamic acid is formed, then diluting the reaction mixture with a liquid in which said sulfamic acid is insoluble and said sulfuric acid is soluble and recovering said sulfamic acid.

3. A method of forming sulfamic acids which comprises introducing with stirring small amounts of an alkyl isocyanate into a body of a sulfonating agent which is at least about 100% H2804, and maintaining a temperature at which evolution of carbon dioxide occurs, whereby alkyl sulfamic acid is formed.

4. A method of forming sulfamic acids which comprises inmixing an alkyl isocyanate with a sulfonating agent which is at least about 100% H2804, and maintaining a temperature at which evolution of carbon dioxide occurs by cooling the reaction mixture below room temperature, whereby alkyl sulfamic acid is formed.

5. A method of forming sulfamie acids which comprises mixing an alkyl isocyanate with a sulfonating agent which is sulfuric acid containing excess S03, and maintaining a temperature at which evolution of carbon dioxide occurs, whereby alkyl sulfamic acid is formed.

6. A method according to claim 1 in which the isocyanate is a monoalkyl isocyanate.

7. A method according to claim 1 in which the isocyanate is an aliphatic di-isocyanate.

8. A method according to claim 1 in which the isocyanate is ethyl isocyanate.

9. A method according to claim 1 in which the isocyanate is hexamethylene di-isocyanate.

References Cited in the file of this patent Traube et al.: Berichte, vol. 53, PP. 1493-1501 (1920).

Linhardz. Justus Liebigs Annalen der Chemie, vol. 535, pp. 267-284 (1938).

Audrieth et al.: Chemical Reviews, vol. 26 (19 39), p. 58.

Noller: Chemistry of Organic Compounds, p. 302 (1954), reprint, Copyright 1951.

Claims (1)

1. 2. A METHOD OF FORMING SULFAMIC ACIDS WHICH COMPRISES MIXING AN ALKYL ISOCYANATE WITH A SULFONATING AGENT WHICH IS AT LEAST ABOUT 100% H2SO4, AND MAINTAINING A TEMPERATURE AT WHICH EVOLUTION OF CARBON DIOXIDE OCCURS, WHEREBY ALKYL SULFAMIC ACID IS FORMED, THEN DILUTING THE REACTION MIXTURE WITH A LIQUID IN WHICH SAID SULFAMIC ACID IS INSOLUBLE AND SAID SULFAMC ACID IS SOLUBLE AND RECOVERING SAID SULFAMIC ACID.