GB1605469A - Improvements in the production of fluoro-nitrogen compounds - Google Patents

Description

We, ALLIED CHEMICAL CORPORATION, a corporation organised and existing under the laws of the State of New York, United States of America, of 61 . Broadway, New York 6, New York, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly' described in and by the following statement:-

THI S INVENTION relates to the production of fluoro-nitrogen compounds, more particularly perfluoro-nitrogen compounds such as nitrogen trifluoride, NF., b.p, - 129°C.; difluorodiazine, N,F2, b.p. -106° to - 1 1 1 °C.: and tetrafluorohydrazine, N2F4. b.p. -73°C.

The invention provides a process whereby a relatively large class of compounds containing nitrogen-hydrogen bonds can be converted into such perfluoro-nitrogen compounds by direct fluorination. Previous attempts to fluorinate compounds containing nitrogen-hydrogen bonds have been characterised by low yields, notably incomplete fluorination, and irregular and erratic reactions often leading to more or less explosive condition.

More particularly the invention makes it possible to catalyse or promote the reaction between starting material containing nitrogen-hydrogen bonds and elemental fluorine so as to make it proceed smoothly with the formation of perfluoro-nitrogen compounds.

According to the invention perfluoro-nitrogen compounds are made by effecting reaction between fluorine and a substituted ammonia compound which is an alkali metal amide, urea, biuret, sulpham ide. formamide, hydrazine, ethylene.diamine or melam ine at a temperature of 0°-300°C. But not above the phase change temperature of the substituted -ammonia compound, in the presence as catalyst of ammonia fluoride or a fluoride of a metal which forms an acid salt with hydrogen fluoride.

In carrying out the invention the substituted ammonia compound and the catalyst are preferably intimately mixed together in comminuted or granular form, (or as a paste or slush when the substituted ammonia compound is liquid) and the mixture is then subjected to the action of elemental fluorine at the temperatures indicated. A gaseous product is obtained which contains the perfluorinated nitrogen compounds. The preferred starting materials include the alkali metal amides, especially lithium and sodium amides but also including the amides of potassium, rubidium and caesium, and also urea and biuret.

Metals whose fluorides may be employed as catalysts include the alkali metals, the alkaline earth metals including magnesium, aluminium, silver, mercury, thallium, zirconium, tin, bismuth, cobalt, nickel, copper and lead. Typical metal fluorides are NaF, LiF, KF, MgF,. ALF,, AgF. AgF2, AgF_, CaF,. BaF BeF,, CoF., NiF, NiF2and PbF4, and bifluorides and higher fluorides of the same metals. (When the context permits the term “fluoride'’ is intended to include the normal fluorides, such as NaF; the bifluorides, such as NaHF,: and other fluorides such as NaF.,HF).

Most advantageously, the catalysts as charged into the reaction zone are the normal fluorides and bifluorides of the alkali metals and ammonium, bifluorides, particularly those of lithium, sodium and potassium, being preferred. It has been found that in general the bifluorides initiate the reaction more quickly, while giving rise to the production of substantially the same nitrogen-fluorine products, as the normal fluorides. For example, when using NaF as catalyst, about an hour may elapse before any substantial formation of product takes place, whereas when the catalyst initially charged is NaHF2, the same degree of product formation may be effected in fifteen minutes.

The ratios of the amounts of substituted ammonia compound to catalyst may vary widely. At the outset of an operation, the catalyst may be present in amount 10-600%. more usually 10-400%, by weight based on the substituted ammonia compound; more preferably the proportion is at least 100% and especially 100-400%. When the substituted ammonia compound is liquid, the amount of catalyst may be such as to form a damp, relatively solid mash.

The reactions occurring are mildly exothermic. It has been found that reaction temperatures should be substantially in the range of 0°-300°C., preferably 0°-200°C.. provided, in all cases, that they are below, normally at least a few degrees below, the phase change temperature of the particular substituted ammonia compound employed, e.g. below' the boiling point of the normally liquid hydrazine, and below' the decomposition temperature of the normally solid sulphamide. Particularly good results have been obtained when the external reactor temperature is maintained substantially in the range 0°100°C., and especially 50°-100°C.

The rate of feed of the elemental fluorine is dependent to a large extent upon variables such as the scale of operation and method of contacting the gas and solid or semi-solid composition in the reactor, and on whether the material in the reactor is a mixture of dry granular solids or a pasty mass or slush formed from liquid starting material and solid catalyst. In a reactor in which the contents are packed to avoid substantial channelling, incoming gas is fed to the reactor preferably at. a rate such that substantially all the fluorine is consumed, the optimum rate being readily determinable by a trial run. Usually the fluorine is diluted with at least half its volume of an inert gas such as nitrogen; preferably the ratio by volume is roughly 1 : 1 , though it may be higher, e.g. up to about 5:1. The principal reaction products are nitrogen trifluoride, trans-difluorodiazine, and tetrafluorohydrazine, the first usually predominating. However the nature and proportions of the products obtained may vary as illustrated in the Examples, depending upon the starting material employed. For example lithium amide may produce nitrogen trifluoride and difluorodiazine and substantially no tetrafluorohydrazine. while sodium amide may produce nitrogen trifluoride and tetrafluorohydrazine and substantially no diflurodiazine. These products are readily recoverable from the reactor gases by conventional low temperature condensation and fractional distillation. The residue in the reactor is generally a mixture of various fluorides. Nitrogen trifluoride is of known utility, for example as an intermediate for reaction witha metal to make tetrafluorohydrazine, which is in commercial production. Difluorodiazine is useful as a catalyst for the polymerisation of unsaturated monomers such as methyl methacrylate, styrene and cyclopentadiene.

The principles of the invention may also be used to advantage to fluorinate cyanoguanidine, H,N.C(:NH).NH.C:N, giving a high yield production of perfluoromethylamine (CF,NF„ m.p. - 122°C.), a known compound which is a gas under normal conditions, in this modification, the reaction temperature should be substantially i the range 0°-200°C., preferably 0°- 150°C. Apart from this all of the above operational techniques and procedural factors such as catalyst composition, proportions of the cyanoguanidine and catalyst, the rate of feed of fluorine and its degree of dilution, and recovery of the product apply in the practice of this modification of the invention.

The following Example illustrate the invention. All determinations of the products were made by infra-red absorption spectrometry.

EXAMPLE 1

About 1 g. of lithium amide was mixed with about 0.65g. of lithium fluoride, both as reagent grade powders. The mixture was placed in a 1 inch I.D. nickel Swartz type U-tube, of wall thickness about 1/8 inch, which was immersed in a dry ice-acetone cold bath. Gaseous fluorine was purified by passing it through a hydrogen fluoride scrubber containing sodium fluoride at a flow rate of 20 to 30 cc./min.. and was then diluted with about its own volume of nitrogen and passed through the lithium fluoride-lithium amide mixture. The gases leaving the U-tube were passed directly into and through an infra-red cell which was equipped with barium fluoride windows and had been placed in an infrared spectrophotometer. The tube was held at about -78°C. for about two hours during which time, aside from fluorine and nitrogen, the only compound leaving the reactor was carbon tetrafluoride. believed to be an impurity in the incoming fluroine. The reactor was removed from the cold bath and permitted to warm up. When the temperature reached about 0°C., infra-red analysis of the material in the cell showed that the reactor off-gas contained about 2 mm.Hg of nitrogen trifluoride. In about 15 minutes the reactor warmed up to about room temperature, and difluorodiazine was formed and discharged into the cell. The same fluorine-nitrogen mixture was then passed through the tube at the same rate fro about half an hour at between room temperature and a few degrees higher. After this time, it was found that the reactor off-gas contained approximately 24 mm.Hg of nitrogen trifluoride and about 8 mm.Hg of difluorodiazine. The fluorine flow was then terminated, and the reactor was flushed with nitrogen for one hour. The tube was cooled to about 0°C. and passage of the 1 : 1 nitrogen-fluorine mixture was resumed with the reactor held at this temperature. Nitrogen trifluoride was observed immediately, and after about 30 minutes, difluorodiazine was again formed and discharged from the reactor. After about 60 minutes the fluorine flow was stopped, and the tube was flushed with nitrogen and allowed to warm to room temperature. The passage of the same fluorine-nitrogen ixture was then resumed at a flow rate increased to 40 to 50 cc./min. for about another 60 minutes, during which the intensity of the infra-red spectrum of diflurodiazine slowly increased to 15 mm.Hg, while that of the nitrogen trifluoride increased rapidly to about 60 mm.Hg.

EXAMPLE 2 About 1 g. of reagent grade urea was mixed with about its own weight of sodium fluoride, and the resulting mixture was charged into the U-tube of Example 1. Incoming fluorine gas was scrubbed as in Example 1. The fluorine flow' was adjusted to 20 to 30 cc./min, and after about 1 :1 dilution with nitrogen, the mixture was fed into the tube. The temperature was held at about 25°C. Nitrogen trifluoride was formed in about 60 minutes. Reaction was continued for another hour, during which the reactor off-gas contained about 330 mm.Hg of nitrogen trifluoride and about 100 mm.Hg of tetrafluorohydrazine. The residue in the tube at the end of the run was a white solid containing red and yellow discolourations. EXAMPLE 3

About 2 g. of 95% anhydrous hydrazine was mixed with about its own weight of sodium fluoride, forming a think slush. The U-tube was passivated with fluorine and nitrogen, and the hydrazine-sodium fluoride mixture was charged into the tube. Scrubbed fluorine gas at a flow rate of 20 to 30 cc./min. was diluted with its own volume of nitrogen and passed through the tube, which w'as initially at room temperature. After about an hour, about 3 m.Hg of nitrogen trifluoride and a trace of difluorodiazine were formed. The tube and its contents were warmed up to about 50°C., and the intensity of the infra-red spectra began to decrease. The tube was then immersed in a bath at 0°C. About 15-30 minutes later, the intensities of the infra-red spectra of nitrogen trifluoride and difluorodiazine greatly increased, and it was found that approximately 18 mm.Hg of difluorodiazine and about 15 mm.Hg of nitrogen tri fluoride were present in the gas leaving the reactor.

EXAMPLE 4 the resulting mixture was placed in the nickel U-tube. Scrubbed fluorine gas at a flow' rate of approximately 40 cc./min was diluted with its own volume of nitrogen, and passed through the tube which was cooled to 0°C. About half an hour after the beginning of the fluorine feed, nitrogen trifluoride was being formed. About five minutes later, sulphuryl fluride and tetrafiuorogydrazine appeared, the reactor off-gas containing about 4 mm.Hg of tetrafluorogydrazine and about 30 mm.Hg of nitrogen trifluoride. When the tube w'as allowed to warm up to 25°C., the composition of the reaction off-gas did not change appreciably.

EXAMPLE 5

Approximately 0,6 g. of lithium amide was placed in the nickel this example is given to show the effect of omitting the fluorine catalyse U-tube and flushed with nitrogen for over one hour. The tube was immersed in a bath at -78°C., and fluorine gas at a flowrate of 20 cc./min., diluted 1 : 1 with nitrogen, was passed through the tube. The effluent gases were passed through an infra-red cell inserted in an infra-red spectrophotometer as in the above Examples. After one hour, only silicon tetrafluoride and carbon tetrafluoride (an impurity in the fluorine gas) were observed. The fluorine flow was terminated, and the tube flushed with nitrogen and permitted to warm up to room temperature. The passage of gaseous fluorine over the lithium amide was then resumed. During about 1 1⁄2 hours of fluorine gas feed, only silicon and carbon tetrafluorides were observed in the effluent gas stream.

EXAMPLE 6

About 1 g. of biuret was ground with its own weight of lithium fluoride. The resulting mixture was charged into a Monel (registered Trade Mark) cylinder about 6 inches high, 2 inches I.D., and wall thickness about 1/4 inch, provided with a gas inlet about 2 inches from the top, consisting of a dip-tube extending down to within an inch from the bottom. The gas outlet about 2 inches from the top of the cylinder communicated with an infra-red cell inserted in an infra-red spectrophotometer as in the above Examples, The scrubbed fluorine gas flow rate was adjusted to the 15 cc./min. and it was diluted with about its own volume of nitrogen. Throughout this run the reaction temperature was held at about 25°C. in about 30 minutes nitrogen trifluoride appeared in the reactor effluent gas in amount about 30 mm.Hg. with about 8 mm.Hg of tetrafluorohydrazine, and smaller amounts of carbon dioxide, carbonyl fluoride, and carbon tetrafluoride. In a similar supplemental run. about 0.1 -0.2 g. of biuret was ground with its own weight of lithium fluoride, the resulting mixture was introduced into the “Monel” reactor, immersed in a bath at -4°C.. and fluorine gas, diluted 1 : 1 with nitrogen, was passed over the mixture at a rate of 10 to 15 cc./ in. After 20-30 minutes nitrogen trifluoride and tetrafluorohydrazine were present in the gas, with small amounts of carbon dioxide and carbonyl fluoride. However, the yields of nitrogen trifluoride and tetrafluorohydrazine were less than those previously obtained at 25°C. The cold bath was removed, and when the temperature rose to about 10°C., the yield of nitrogen trifluoride and tetrafluorohydrazine increased rapidly. Heat was applied to the reactor, and when the outside temperature of the reactor reached 75 00°C,, yields of about 45 mm.Hg of nitrogen trifluoride and about 20 mm.Hg tetraflurohydrazine were obtained.

EXAMPLE 7

About 1 g. each of lithium amide and sodium bifluoride were mixed and charged into the reactor of Example 6. The scrubbed fluorine gas flow rate was adjusted to about 20 cc./mi . and after nitrogen dilution of about 1 : 1. the fluorine-nitrogen mixture was passed into the reactor. Throughout the run the reactor temperature was maintained at about 25°C. Nitrogen trifluride formed immediately on the introduction of fluorine into the reactor, and within about 30 minutes the yield of nitrogen trifluoride was about 5 mm.Hg. After about two hours the reactor off gas contained about 53 mm.Hg of nitrogen trifluoride and 20 mm.Hg of difluorodiazine. The gaseous impurities included small amounts of nitrous oxide, nitrosyl fluoride and nitrogen dioxide.

EXAMPLE 8

About 1 g. each of biuret and sodium bifluoride were mixed and charged into the reactor of Example 6. The scrubbed fluorine gas flow rate was ad justed to about 20 cc./ min., and after nitrogen dilution of about 1 : 1 , the fluorine-nitrogen mixture was passed into the reactor. Throughout the run, the reactor temperature was maintained at about 25°C. Within half an hour after the first introduction of fluorine, nitrogen trifluoride and difluorodiazine were formed, and thereafter, for a period of about 60 minutes the yields thereof increased rapidly. Then tetrafluorohydrazine was observed and masked the infra-red bands of difluorodiazine. About 105 minutes after start-up the infra-red bands of tetrafluorohydrazine became so strong that the absorbance became infinite. Infrared analysis of the product gas diluted to about 50% with nitrogen showed the presence of about 20 mm.Hg of nitrogen trifluoride and 40 mm.Hg of tetrafluorohydrazine. In a supplemental and substantially identical run, after about an hour<'>s operation at about 25°C., the external temperature of the reactor was raised to 75°-100°C. as in Example 6, and shortly thereafter about 360 mm.Hg of nitrogen trifluoride and about 200 mm.Hg of tetrafluorohydrazine were found in the gas.

EXAMPLE 9

About 1 g. each of urea and sodium bifluoride were mixed, and the mixture was introduced into the reactor of the previous Example. The scrubbed fluorine gas flow rate was adjusted to about 20 cc./min, and after nitrogen dilution of about 1 : 1, the fluorinenitrogen mixture was charged into the reactor. Throughout the run the reactor temperature was maintained at about 25 °C. Immediately on the introduction of fluorine into the reactor some nitrogen trifluoride was formed; during the next 30 minutes larger yields of nitrogen trifluoride were obtained; after about one hour the gas contained about 4 mm.Hg of tetrafiuorohydrazine and 40 mm.Hg of nitrogen trifluoride: after two hours more than 75 mm.Hg of nitrogen trifluoride and more than 25 mm.Hg of tetrafiuorohydrazine. along with small amounts of impurities such as carbonyl fluoride, carbon monoxide, nitrous oxide and nitrosyl fluoride, were present.

EXAMPLE 10

About 1 g. each of cyanoguanidine and sodium bifluoride were mixed and charged into the‘‘Monel'<5>reactor of Example 6. The scrubbed fluorine gas flow rate was adjusted to about 20 cc./min.. and after nitrogen dilution of about 1 : 1 , the fluorine-nitrogen mixture was charged into the reactor. Throughout the run. the external temperature of the reactor was maintained at about 25°C.. the internal temperature being several degrees higher. The reactor exit gas contained perf!uoromethyl amine in amount about 50 mm.Hg.

EXAMPLE 1 1

About 5 g. each of cyanoguanidine and sodium bifluoride were mixed and charged into the "Monel<">reactor of Example 6. The scrubbed fluorine gas flow rate was adjusted to 20-30 cc./min, and after nitrogen dilution of about 1 : 1 , the fluorine-nitrogen mixture was charged into the reactor. Throughout the run, the external temperature of the reactor was maintained at about 25°C. , the internal temperature being several degrees higher. For about the first half hour the reactor off-gas contained some carbon tetrafluoride. For about the next three hours, it contained a large yield of perfluoromethulamine, the amount being about 100 mm.Hg. After the initial half hour forerun in which some carbon tetrafluoride was present, the only fluorine compound present in the reactor exit gas in any significant proportion was perfluoromethylamine.

In the foregoing Examples, the notation "mm.Hg<5>' indicates the partial pressure of each of the constituent gases observed in the infra-red cell.

Claims (14)

1. WHAT WE CLAIM 1S 1. Process for the production of perfluro-nitrogen compounds, which comprises effecting reaction between fluorine and a substituted ammonia compound which is an alkali metal amide, urea, biuret, sulphamide, formamide, hydrazine, ethylene diamine or melamine at a temperature of 0°-300°C. but not above the phase change temperature of the substituted ammonia compound, in the presence as catalyst of ammonia fluoride or a fluoride of a metal which forms an acid salt with hydrogen fluoride.
2. 2. Process according to claim 1 , in which the temperature is 0°-200°C.
3. 3. A modification of the process of claim 1 , in which the substituted ammonia compound is cyanoguanidine and the temperature is maintained at 0°-200°C,
4. 4. Process according to claim 3, in which the temperature is 0°- 150°C.
5. 5. Process according to any one of the preceding claims, in which the catalyst is an alkali metal or ammonia fluoride.
6. 6. Process according to claim 5, in which the catalyst is a sodium or lithium fluoride.
7. 7. Process according to any one of the preceding claims, in which the catalyst is a bifluoride.
8. 8. Process according to any one of the preceding claims, in which 10-600% of the catalyst, based on the weight of the substituted ammonia compound, is employed,
9. 9. Process according to claim 8, in which 100-400% of the catalyst is employed,
10. 10. Process according to any one of the preceding claims, in which the fluorine as charged is diluted with at least half its volume of an inert gas.
11. 1 1. Process according to any one of the preceding claims, in which the substituted ammonia compound is lithium or sodium amide.
12. 12. Process for the production of perfluoro-nitrogen compounds according to claim 1 substantially as hereinbefore described.
13. 13.PerfIuoro-nitrogen compounds obtained by a process claimed in any one of claims 1 -12.
14. 14. Nitrogen trifluoride, diflurodiazine, and tetrafluorohydrazine obtained by a process claimed in any one of claims 1 -12. 1605469: Improvements in the production of fluoro-nitrogen compounds Allied Chemical Corporation 17 June 1964 25165/64 Heading C1A (ALSO IN DIVISION C2) Perfluoro-nitrogen compounds are made by reaction between fluorine and a substituted ammonia compound at 0°-300°C in the presence of a catalyst consisting of ammonia fluoride or a fluoride of a metal which form an acid salt with hydrogen fluoride. The substituted ammonia compound may be an alkali metal amide, urea, biuret, sulphamide. formamide, hydrazine, ethylene diamine or melamine. Compounds formed are NF,, N,F„ and N^F . The preferred catalyst is lithium, sodium or potassium bifluoride, but several other metal fluorides are specified. The substituted ammonia compound and the catalyst are mixed together in dry granular form or as a pasty mass or slush and treated with fluoride diluted with an inert gas e.g. nitrogen. The products may be separated by low temperature condensation and fractional distillation. For example, flurorine is reacted with lithium amide, biuret, urea, hydrazine, and sulphamide, in the presence of sodium and lithium normal fluorides and sodium bifluoride. Perfluoro-methylamine CF.-NF. is made by reaction between orsanomagnesium and fluorine of 0°-200°C in the presence of a catalyst consisting of ammonia fluoride or a fluoride of a metal which forms an acid salt with hydrogen fluoride. The preferred catalyst in lithium, sodium, or potassium bifluoride, but several other metal fluorides are specified. For example, a mixture of organomagnesium and sodium bifluoride is treated with a fluorine-nitrogen mixture at about 25°C. 1605469: Improvements in the production of fluoro-nitrogen compounds Allied Chemical Corporation 17 June 1964 25165/64 Heading C2C (ALSO IN DIVISION C1) Perfluoro-nitrogen compounds are made by reaction between fluorine and a substituted ammonia compound at 0°-300°C in the presence of a catalyst consisting of ammonia fluoride or a fluoride of a metal which form an acid salt with hydrogen fluoride. The substituted ammonia compound may be an alkali metal amide, urea, biuret, sulphamide. formamide, hydrazine, ethylene diamine or melamine. Compounds formed are NF., N,F„ and N,F . The preferred catalyst is lithium, sodium or potassium bifluoride, but several other metal fluorides are specified. The substituted ammonia compound and the catalyst are mixed together in dry granular form or as a pasty mass or slush and treated with fluoride diluted with an inert gas e.g. nitrogen. The products may be separated by lo temperature condensation and fractional distillation. For example, flurorine is reacted with lithium amide, biuret, urea, hydrazine, and sulphamide, in the presence of sodium and lithium normal fluorides and sodium bifluoride. Perfluoro-methyiamine CF.-NF. is made by reaction between organo agnesium and fluorine of 0°-200°C in the presence of a catalyst consisting of ammonia fluoride or a fluoride of a metal which forms an acid salt with hydrogen fluoride. The preferred catalyst in lithium, sodium, or potassium bifluoride, but several other metal fluorides are specified. For example, a mixture of organomagnesium and sodium bifluoride is treated with a fluorine-nitrogen mixture at about 25°C.