Synthesis of fluorocarbon compounds

Details Synthesis of fluorocarbon compounds Synthesis of fluorocarbon compounds

2001-09-25

2004-08-03

McKane, Joseph K. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

C562S125000, C568S027000, C568S029000, C568S056000, C568S065000, C568S074000, C568S677000, C568S681000, C568S683000, C568S684000

Reexamination Certificate

active

06770776

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to the synthesis of hydrocarbon compounds which are fluorinated on a carbon atom of an “alkyl” moiety thereof via exchange between a halogen atom having an atomic number greater than fluorine, employing a fluorine-containing reactant which is at least partially in the form of a complex salt.
This invention more especially relates to a process for the preparation of fluorocompounds that are fluorinated on a carbon atom bearing substituent groups which are electron-withdrawing (or attracting) by means of an inductive effect.
2. Description of the Prior Art
Fluorocompounds are characteristically difficult to prepare. The reactivity of fluorine is such that it is difficult, or even impossible, to directly prepare fluoro derivatives.
One of the most commonly used techniques for preparing fluoro derivatives entails reacting a halogen compound, generally a chloro derivative, and exchanging the halogen with an inorganic fluorocompound, generally an alkali metal fluoride, typically of high atomic weight.
In general, the fluoride employed is potassium fluoride, which provides a satisfactory economic compromise.
Under these conditions, many processes such as, for example, those described in French Certificate of Addition No. 2,353,516 and in the article
Chem. Ind.,
56 (1978), have been carried out industrially to produce aryl fluorides, onto the aryl moieties of which electron-withdrawing groups are grafted.
Except in the instances where the substrate is particularly suitable for this type of synthesis, this technique presents drawbacks, the principal ones of which are those analyzed below.
The subject reaction requires reactants such as alkali metal fluorides, for example potassium fluoride, which are relatively expensive vis-a-vis the technical specifications they must satisfy in order to be suitable for this type of synthesis; they must be very pure, dry and in a suitable physical state.
In addition, this reaction is not operative for an entire class of compounds, in particular those bearing substituents on the halophoric carbon atom (namely, on the carbon atom bearing the halogen or halogens destined to be exchanged with fluorine).
Reactants such as hydrofluoric acid in liquid form, or diluted with dipolar aprotic solvents, are also used. However, hydrofluoric acid is too powerful or harsh a reactant and often results in unwanted polymerization reactions or in tars.
In this event, and especially in the case where it is desired to obtain derivatives fluorinated on a carbon atom of an alkyl radical (including aralkyl) rendered electron-deficient by the presence of electron-withdrawing groups, this art is faced with an alternative which is not encouraging; either very harsh conditions are selected, and tars are especially obtained, or mild reaction conditions are adopted and, in the best of scenarios, the substrate is unchanged. Lastly, the literature describes exchanges carried out utilizing hydrofluoric acid salt reactants in the presence of heavy elements in oxide or fluoride form. Among the elements thus used, antimony and heavy metals such as silver and quicksilver (mercury) are exemplary.
Another disadvantage is the selectivity of the reaction: when there are more than one halogen to be exchanged on the same carbon atom, it is often difficult to exchange less than all of same.
SUMMARY OF THE INVENTION
Accordingly, a major object of the present invention is the provision of an improved exchange reaction between, on the one hand, heavy halogen atoms such as chlorine and, on the other, fluorine, while significantly enhancing the specificity of the reaction.
Another object of the present invention is the provision of an improved exchange reaction between the heavy halogens such as chlorine and fluorine, carried out under particularly mild reaction conditions.
Yet another object of this invention is the provision of an improved such process which permits utilizing a source of fluoride whose morphology is less critical.
Still another object of this invention is the provision of an improved such process which permits exchange of only one out of two or three possible halogen atoms.
And yet another object of the present invention is the provision of an improved such process which permits exchange of only two out of three possible halogen atoms.
Another object of this invention is the provision of an improved such process which permits exchange of molecules or atoms to obtain carbon atoms which bear only one fluorine atom simultaneously with one or two other halogen atoms different from fluorine.
Yet another object of the present invention is the provision of an improved such process which permits exchange of molecules or atoms to obtain carbon atoms which bear only two fluorine atoms simultaneously with one other halogen atom which is different from fluorine.
Yet another object of this invention is the provision of an improved such process which avoids the use of a large amount of metals considered to be expensive or toxic, such as mercury and/or silver.
Still another object of this invention is the provision of an improved such process which permits reducing the amounts of metals considered to be expensive or toxic, such as mercury and/or silver, such that the molar ratio between the metal and the substrate whose halogen atoms are to be exchanged is at a value at most equal to 0.5, advantageously at most 0.2, preferably at most 0.1.
And another object of the present invention is the provision of an improved such process which permits avoiding entirely the use of metals considered to be expensive or toxic, such as mercury and/or silver, such as not to add to the reaction mixture any of the elements indicated above; in other words, such that the concentrations of each of said metals do not exceed values of 10
−3
M, advantageously 10
−4
M, preferably 10
−5
M.
Briefly, the present invention features a process for the synthesis of fluorocarbon compounds, comprising reacting a substrate containing at least one sp
3
-hybridized halophoric carbon atom bearing at least two halogen atom substituents, at least one of which is a halogen atom having an atomic number greater than that of fluorine, said at least one halophoric carbon atom being bonded to at least one chalcogen, with at least one reactant which comprises the combination of a Bronstedt base with a defined amount n of hydrofluoric acid, n being at least equal to 3 and at most equal to 20, preferably at most 10.
DETAILED DESCRIPTION OF BEST MODE AND PREFERRED EMBODIMENTS OF THE INVENTION
More particularly according to the present invention, it has now been determined that certain carbon atoms bearing groups which are electron-withdrawing by an inductive effect are capable of reacting with a reactant of the above type, on condition that at least one of the electron-withdrawing groups is a chalcogen.
The reaction temperature ranges from the melting point of the reaction mixture to its decomposition or boiling point, generally from 0° C. to 150° C., advantageously from 20° to 100° C.
The subject process is advantageously carried out at atmospheric pressure, but it can be conducted at pressures of up to 20 10
5
pascals
Exemplary preferred bases include those which are trivalent hydrocarbon derivatives of elements of column VB, advantageously from a period ranking at least equal to the second and generally less than the sixth, of the Periodic Table of the Elements (supplement to the
Bulletin de la Société Chimique de France,
No. 1, January 1966). Other than those described below, exemplary such compounds are trivalent derivatives, which, when they are trisubstituted, are in fact pnictines, these pnictines being more fully described below.
Among said hydrocarbon derivatives of the elements of column V, preferred are those which are derived from hydrogen pnictides by total or partial substitution of the hydrogen with hydrocarbon residues, which may be bonded to the atom from column VB via a double bond (as in the imines), or a t

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