US1916327A - Process for preparing organic fluorine compounds - Google Patents

Description

' composition. In t is process,

Patented July 4, 1933 UNITED STATES PATENT, orslca FREDERICK IADIBON BEIGE, OF WILMINGTON, DELAWARE, ASBIGNOB TO I. I. DO PON'I.

DE NEHOUBS & COMPANY, OF WILMINGTON, DELAWARE, A ,QQBPOBATION OF DELAWARE PROCESS FOR PREPARING ORGANIC FLUORINE COKP OUNDS Io Drawing.

This invention relates to a process for the reparation of organic compounds conta1nmg fluorine, and more particularly 1t relates to a process for the preparat on of organic compounds containing fluorme atoms attached directly to the carbon atoms of aromatic nuceli. o

Among the various methods d1 sclosed 1n the prior art for preparing organic fluorme compounds there may be mentioned the proc ess of Le Fevre and Turner (J. Chem. Soc., 1930, 1158) wherein an aryldiazonium chloride is converted, by means of sodlum borofluoride, to the 'aryldiazonium borofluoride which yields the a l fluoride b thermal deowever, and in other processes of which I am aware, the precipitation of the aryldiazonlum borofluoride has been conducted in the presence of a large excess of acid which has resulted in yields considerably lower than obtained through the practice of-the present invention.

This invention has as an object the preparation of organic fluorine com ounds in which the fluorine atom (or atoms is attached d1 rectly to the carbon atoms of aromatic nucel A further object is an improvement in the yield of the intermediate aryldlazonlum borofluorides. A still further object is the simplification of the preparation of these compounds so that the process becomes both industrially applicable and economically feasible.

lhese objects are accomplished by the use of a medium of low hydrogen-ion concentration during the conversion of the diazotized amine into the aryldiazonium borofluoride.

The following equations, in which an organic radical is represented generally by the phenyl group, indicate the diazotizatlon of the amine salt, the formation of the aryldiazonium borofluoride, and the thermal decomposition oi the latter:

50 vent a coupling of the diazonium salt with a lication filed 1m 15,

the amine salt, that the acid be present in ex cess of the amount theoretically required by the equation. While the presence of only'a slight excess ofacid is necessary, it is the general practice to addthe acid to substantial excess inasmuch as there is usually no purpose or need for adding the calculated quanobtained when the reaction indicated by 10 Equation (2) is carried out in a medium of low hydrogen-ion concentration.

A hydrogen-ion concentration sufiiciently low for the precipitation of the diazonium borofluoride in the higher yields which characterize the present invention may be ob- 'tained by forming the diazonium salt with substantially the minimum amount of acid which will prevent the coupling of the amine and diazonium salt, or by adding alkali after formation of the orgamc diazonium salt to give a neutral or alkaline solution when the diazotization has been carried out with excess acid, and then using as a precipitant a borofluoride compound, as sodium borofluoride, which does not raise the hydrogen-ion content of the solution beyond the desired value. In case the diazotization reaction of Equation (1) has been carried out in the presence of excess acid the alkali mentioned above may also be added after the sodium borofluoride to keep the hydrogen-ion concentration in the reaction of Equation (2) below the desired value and drive the reaction of Equation (2) to the right because, although a precipitate has formed the precipitation of aryldiazonium borofluoride is not complete in solutions of high hydrogenion concentration.

One of the most convenient methods for 100 maintaining low hydrogen-ion. concentration during the prcci itation of the diazonium borofiuorides is t e use. of sodium borofluoride as a precipitant. When borofiuoric acid is used as the precipitant free acid is formed by double decomposition and the hydrogenion concentration is built up during the reaction. An important feature of the present of the solution of organic diazonium salt during preci itation of the organic diazonium borofluoride should not be allowed to rise above 1 mole per liter. I prefer to keep the hydrogen-ion concentration below 0.3

moles per liter inasmuch as the yields obtained are markedly higher than were obtained by prior methods. The hydrogen-ion concentration ma vary from the values given to the minlmum possible value represented by the slight excess of acid necessary for the formation of the organic diazonium salt. Or, if the hydrogen-ion content is reduced to the proper value by neutralizing the excess acid after the formation of the organic diazonium salt, the lower limit of hydrogen-ion content includes neutral and alkaline solutions. Inasmuch as it is practically impossible to determine the exact-ion concentrations due to the difficulty of making measurements in solutions of easily oxidizable or reducible substances, the values given herein represent only the total available hydrogen-ion concentration in moles per liter (assuming complete ionization) after the precipitate of the aryldiazonium borofluoride has been formed. While the true hydrogen-ion concentration may difler considerably from these values it is pointed out that the true hydrogen-ion concentration cannot exceed the values given.

The following examples are illustrative of the methods that may be used in carrying out the invention:

Example I 9.3 grams of aniline dissolved in 18.3 cc. of concentrated hydrochloric acid and 10 cc. of water is diazotized with a solution of 7 grams of sodium nitrite dissolved in 20 cc. of water. The temperature is maintained below 10 C. 30 grams of a 40% solution of sodium borofluoride is added to the clear phenyl diazonium solution. The precipitated phenyl-diazonium borofluoride is collected on filter paper and dried in vacuo under reduced pressure. The yield of phenyl diazonium borofluoride is 16.2 grams or 84.8% of theory on the basis of aniline. Quantitative decomposition of the borofluoride to fluorobenzene is accomplished by heating the salt to 110 C. The boron trifiuoride which is evolved is recovered by solution in a suspension of sodium fluoride in water. As the boron trifiuoride is absorbed the suspension gradually becomes a clear solution of sodium borofluoride. v

The hydrogen-ion concentration after the precipitate of borofluoride had been formed was 0.25 moles per liter.

Example I I A solution of 46 grams of benzidine in 500 cc. of water and 40 cc. of concentrated hydrochlorio acid is added to a solution of nitrous acid prepared by the addition of 52 cc. of concentrated hydrochloric acid to 35 grams of sodium nitrite dissolved in 400 cc. of water and ice. A few grams of butyl alcohol is added to prevent foaming. The temperature of the diazotization mixture is kept below 10 C. 50 grams of 40% solution of sodium borofluoride is added to precipitate the diphenyl tetrazonium borofluoride. The salt is brought on a filter and dried under reduced pressure. The yield or pure salt is 82 grams or 86. 4% on the basis of benzidine. Quantitative conversion to difluorodiphenyl is accomplished by heating the dry salt. The boron trifiuoride evolved is absorbed in 40% sodium hydroxide. On addition of an equivalent amount of hydrofluoric acid this solution is converted to a solution of sodium borofluoride.

The hydrogen-ion concentration after the precipitate of borofluoride had been formed was 0.08 moles per liter.

Ewample III A solution of 72 grams of beta-naphthylamine in 250 cc. of water and 200 cc. of concentrated hydrochloric acid is treated with a solution of 35 grams of sodium nitrite in cc. of water. The temperature of the reaction mixture is kept below10 C. 165 grams of a 40% solution of sodium borofluoride is added to the clear solution of diazonium salt. A solution containing 50 grams of sodium hydroxide is added to reduce the hydrogenion concentration and complete the precipitation of the diazonium borofluoride. The precipitate is collected on a filter and dried under reduced pressure. The yield of betanaphthyldiazonium borofluoride is 97.4% of theory on the basis of the amine. Thermal decomposition of the diazoniun. borofluoride to beta-fiuoronaphthalene is almost quantitative. The boron trifiuoride which is evolved may be absorbed in solution of anaryldiazonium fluoride, with the precipitation of the corresponding aryldiazonium borofluoride.

the aryldiazonium fluoride from solutions of low hydrogen-ion concentration by means of sodium borofluoride, the objects of the invention may be attained by followin several different modes of rocedure. For mstance, the aryldiazonium rofluoride may be precipitated. from either an acid or neutral solution of the dia-zonium salt with borofluoric acid and sodium hydroxide added to remove hydrogen-ions formed by substituting this precipitant for sodium borofluoride in Equation (2), together with hydrogen-ions that may have been originally. present in the solution of the diazonium salt, and thereby reduce the hydrogen-ion concentration to shift the equilibrium of the reaction in the direction favoring a high yield of the aryldiazonium borofluoride and consequently of the arylfluoride of Equation (3). If desired the sodium hydroxide may be added, in certain cases, to the solution of diazonium salt before precipitating with the borofluoric acid, the alkali being present in such amount as will reduce the hydrogen-ion concentration of the reaction mixture to the proper value. I These methods in which the precipitation is with borofluoric acid accompanied with the use of sodium hydroxide are'less economical and convenient than using the equivalent amount of the sodium borofluoride as a precipitant. Sodium borofluoride is also desirable because of its high solubility as compared with other borofluorides.

Ezcample IV This example illustrates the use of a mixture of a borofluoride and borofluoric acid as a precipitant.

A solution in 50 cc. of water containing 0.1

' mole of phenyldiazonium chloride and less than 0.02 mole of hydrochloric acid is treated with a solution containing 0.11 mole of a mixture consisting of 50% sodium borofluoride and 50% borofiuoric acid. The yield of the diazonium borofluoride is 14.0 grams or 78.1% of theory. If, however, 0.055 mole of sodium hydroxide in solution is added before the precipitate is brought on a filter, the yi .d is increased to 84% of theory as in Example I.

The hydrogen-ion concentration was 1.13 moles per liter before the addition of alkali and 0.28 moles per liter after the addition of alkali.

The mixture of sodium borofluoride and borofluoric acid referred to above is prepared by the treatment of borax with the calculated amount of hydrofluoric acid to convert all the boron to the borofluoride complex.

Another means of obtaining low hydrogenion concentration during formation of the intermediate diazonium borofluoride is through the use of hydrofluoric acid in the diazotization solution and the subsequent addition of gaseous borontrifluoride for the formation of borofluoride ion and precipitation of the diazonium borofluoride. The

equations are:

o.H.N;F+BF.- o,H.N,BF.+2H,o

The following example is illustrative of this method of carrying out the invention:

Ewample 7 A solution of 9.3 grams of aniline dissolved in 9.2 cc. of concentrated hydrochloric acid, 5 cc. of concentrated hydrofluoric acid, and 10 cc. of water is treated with a solution of 7 ams of sodium nitrite in water. The resu ting clear. solution of phenyldiazonium chloride is treated with gaseous boron trifluoride prepared by any of the methods known in the art, or obtained during decomposition of an aryldiazonium borofluoride, until the recipitation of phenyldiazonium borofluori e is complete. The salt is brought in a filter, dried, and decomposed as above.

The hydrogen-ion concentration after the precipitate of borofluoride had been formed was 0.92 moles per liter.

The diazotization with hydrofluoric acid may be followed by the addition of borax instead of the borontrifluoride for the precipitation of the aryldiazonium borofluoride. a suflicient excess of hydrofluoric acid being allowed for conversion of the boron to the borofluoride complex.

Another method of procedure is to conduct the diazotization reaction in the presence of sodium borofluoride while maintaining the hydrogen-ion concentration within the desired limits as indicated in the following example:

Ewwmple V1 9.3 grams of aniline dissolved in a solution containing 0.22 mole of available hydrogen-ion and 0.11 mole of available borofluoride ion (for instance 18.3 cc. of concentrated hydrochloric acid and 12 grams of soduim borofluoride) is diazotized with a solution of 7 grams of sodium nitrite in water. During diazotization the temperature of the mixture is maintained below 30 C. Phenyl-diazonium borofluoride precipitates out as the diazotization progresses and is frozen out at the completion of the reaction. The salt is dried and decomposed in the usual manner.

The hydrogen-ion concentration after the precipitate of borofluoride had been formed was 0.41 mole per liter.

scribed in the examples and many others will suggest themselves to those skilled in the art. Among these may be mentioned the use of any soluble salt of borofluoric acid as a preci itant. In the diazotization' reaction, sulfuric and other known diazotizing acids may be used.

The efl'ect of the hydrogen-ion concentration on the yield of the diazonium borofluoride is clearly shown by the following results which vwere obtained under similar conditions except for the concentration of the hydrogen-ion during precipitation. In each case, the solution of phenyldiazonium chloride was prepared by treatment of a solution of 9.3 grams of aniline in 18.3 cc. of concentrated hydrochloric acid and 10 cc. of water with a solution of 7 grams of sodium nitrite dissolved in 20 cc. of water. This is equivalent to 0.1 mole of aniline and 0.22 mole of acid, an excess of 0.02 mole of acid.

Inasmuch as certain compounds will give higher yields than others, comparisons of the effect of lowered hydrogen-ion concentration must be made with identical compounds. However, lowering the hydrogen-ion concentration in a given preparation increases the yield of that compound over that obtainable under conditions of higher hydrogenion concentration. Another illustration of the high yields possible through the practice of the present invention may be had by comparing the 44.2% yield from benzidine obtained in the LeFevre'and Turner citation mentioned with a hydrogen-ion concentration of 1.09 and the yield obtained in Example II herein which was 86.4% with a hydrogen-ion concentration of 0.08.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the following claims.

I claim:

1. A process of making organic fluorine compounds which comprises precipitating an organic diazonium borofluoride from. solutionshaving a hydrogen-ion concentration not eater than one mole per liter, and convertlng' the organic diazonium borofluoride into organic fluoride.

2. A process of making aromatic fluorine compounds which comprises precipitating an ar ldiazonium borofluoride from solutions aving a hydrogen-ion concentration not greater than one mole per liter, and convertlng the. aryldiazonium borofluoride into aryl fluoride.

3. A process of making aromatic fluorine compoundswhich comprises precipitating an aryldiazonium borofluoride from solutions having a hydrogen-ion concentration not greater than 0.3 mole per liter, and converting the aryldiazonium borofluoride into aryl fluoride. j

4. A process of making aromatic fluorine compounds which comprises precipitating with sodium borofluoride an aryldiazonium borofluoride from solutions having a hydrogen-ion concentration not greater than one mole per liter, and converting the aryldiazonium borofluoride into aryl fluoride.

5. A process of making aromatic fluorine compounds which comprises precipitating with sodium borofluoride an aryldiazonium borofluoride from solutions having a hydrogen-ion concentration not greater than 0.3 mole per liter, and converting the aryldiazonium borofluoride into aryl fluoride.

6. A process of making aromatic fluorine compounds which comprises preparing a solution of aryldiazonium salt, adding a boroflu0- ride preclpitant. maintaining the hydrogenion concentration of the solution during precipitation below one mole per liter with alkali, and converting the precipitated aryldiazonium borofluoride formed into aryl fluoride.

7. A process of making aromatic fluorine compoundswhich comprises diazotizing an aryl amine hydrochloride with sodium nitrite and hydrochloric acid to form a solution of aryldiazonium chloride, precipitating aryldiazonium borofluoridewith sodium borofluoride, the hydrogen-ion concentration of said solution during precipitation being not greater than one mole per liter, and forming aryl fluoride from the aryldiazonium borofluoride by thermal decomposition.

8. A process of making aromatic fluorine compounds which comprises diazotizing an aryl amine salt in the presence of the minimum quantity of acid which will prevent coupling of the diazonium salt formed with the amine salt, precipitating aryldiazonium borofluoride with sodium borofluoride, and converting the aryldiazonium borofluoride into aryl fluoride.

9. A process of making aromatic fluorine compounds which comprises preparing a solution of diazonium salt having an available hydrogen ion concentration of less than one III tration of the solution below one mole per liter, precipitating aryldiazonium borofluorige and converting the latter into aryl fluor- 1 e.

12. A process of making aromatic fluorine compounds which comprises diazotizing an aryl amine in the presence of hydrofluoric acid, maintaining the hydrogen ion concentration of the solution below one mole per liter, precipitating aryldiazonium borofluoride with boron trifluoride and converting the latter into aryl fluoride.

In testimony whereof, I aifix my signature.

FREDERICK MADISON MEIGS.