Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfonic acids or salts thereof
Reexamination Certificate
2001-07-19
2003-01-21
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfonic acids or salts thereof
C562S125000, C562S604000, C562S605000
Reexamination Certificate
active
06509495
ABSTRACT:
A subject matter of the present invention is the hydrogenolysis of heavy halogen carried by a carbon itself carrying at least one fluorine atom.
A more particular subject matter of the present invention is a process for producing compounds carrying a fluoro atom and a hydrogen atom on a carbon of sp
3
hybridization, said carbon itself carrying an electron-withdrawing functional group. The present invention relates more particularly to a liquid-phase process.
Fluorinated derivatives of aliphatic nature, that is to say fluorinated derivatives in which the fluorine is carried, at least in part, by an sp
3
carbon, are generally obtained by an exchange of fluorine with another halogen atom. This exchange is generally carried out by using hydrofluoric acid or else salts of hydrofluoric acid.
However, one of the problems encountered is that it is often difficult to carry out the exchange between the fluorine and a halogen with a higher atomic number when the halogen to be exchanged is carried by a carbon itself carrying a hydrogen atom.
This is why it is rather difficult to obtain compounds where an aliphatic compound carries both a hydrogen and at least one fluorine. One of the routes provided consists in dehydrohalogenating (that is to say, in removing a molecule of hydrohalic acid to give an ethylenic compound and then hydrogenating this ethylenic compound). This route is not possible for all compounds as a hydrogen is necessarily essential in the &bgr; position to achieve the removal of the hydrogen and the halogen which it is desired to remove.
Provision has been made, in patent GB 1 364 495, to synthesize certain monohydrogenated perfluorinated compounds (Rf-H) from the corresponding iodide (Rf-I) but this use of an iodinated derivative is very expensive and the pressure conditions disclosed in this document are very severe for kinetics which do not appear to be very high.
European patent application EP 0 726 244 discloses the reduction of a very specific cyclopropanic acid structure which, however, does not carry an electron-withdrawing group in in addition to a chlorine and a fluorine (although the acid functional group is certainly an electron-withdrawing group, it is not, however, connected directly to the carbon carrying the fluorine and the halogen).
Gas-route processes have also been provided (in particular EP 0 657 413 A) but, in addition to the disadvantages related to the gas route, it appears difficult to obtain a high selectivity at the same time as a high degree of conversion.
This is why one of the aims of the present invention is to provide a liquid-phase process which makes possible the replacement of a heavy halogen by a hydrogen, this replacement being carried out while a fluorine atom is carried by the same carbon as that which carries the halogen to be replaced by a hydrogen.
Another aim of the present invention is to provide a process of the preceding type which is selective with respect to fluorine.
Another aim of the present invention is to provide a process of the preceding type which is capable of giving good results with a compound which does not exhibit hydrogen &bgr; to the halogen to be made to leave.
Another aim of the present invention is to provide a process of the preceding type which is selective with respect to fluorine without requiring the use of iodide.
These aims, and others which will become apparent subsequently, are achieved by means of a selective hydrodehalogenation process (that is to say, the operation which consists in removing the halogen from a molecule by treating the latter by means of hydrogen to give, on the one hand, hydrohalic acid and, on the other hand, the starting molecule modified by the replacement of a halogen by a hydrogen) which comprises a stage in which a substrate exhibiting a carbon atom of sp
3
hybridization carrying:
at least one electron-withdrawing group (EWG) (that is to say, a group with a positive Hammett constant &sgr;
p
or &sgr;
i
),
at least one fluorine atom,
and at least one halogen atom heavier than fluorine;
is brought into contact with a reactant comprising:
an aqueous phase,
a base,
a metal belonging [lacuna] Group VIII and to the fourth or to the sixth period of the Periodic Table as hydrogenation catalyst,
and hydrogen dissolved in the aqueous phase, at a concentration in equilibrium with a gas phase, the hydrogen partial pressure of which is at least equal to 50 kPa, advantageously between 50 kPa and 2×10
7
Pa.
Of course, the aqueous phase is a liquid phase.
The present invention is targeted more particularly at the case where said atom of sp
3
hybridization carries two fluorine atoms.
The preferred electron-withdrawing functional groups are, on the one hand, optionally substituted aryls and, on the other hand, those for which the Hammett constant &sgr;
p
is at least equal to 0.1 and it is also preferable for the inductive component of &sgr;
p
, &sgr;
i
to be at least equal to 0.1, advantageously to 0.2, preferably to 0.3 (for example, cf. March, “Advanced Organic Chemistry”, 3rd edition, John Wiley and Son, pages 242 to 250 and in particular Tables 4 and 5).
When there is only a single electron-withdrawing group (or functional group) and a single fluorine, it is desirable for one, preferably both, conditions below to be met:
either the electron-withdrawing group exhibits a &sgr;
i
of greater than or equal to 0.15, advantageously at least equal to 2, preferably to 3;
or the halogen which has to be displaced is in the allylic position of a &pgr; bond (double, triple or aromatic bond, including carbonyl and nitrile bonds), it being possible for the &pgr; bond to belong to the electron-withdrawing group.
Mention may be made, among the electron-withdrawing groups (EWG), of:
substituted chalcogen atoms,
aryl groups,
groups exhibiting, as atom carrying the bond connecting it to the remainder of the molecule, a carbon atom connected to at least two fluorine atoms,
chalcogens with an atomic number at least equal to that of perfluorinated sulfur (for example SF
5
);
carboxylic, sulfonic and sulfinic functional groups, that is to say functional groups which derive from carboxylic, sulfonic and sulfinic acids [these functional groups can be the acid functional group proper (in the acid form or advantageously in the salified form) but also amides, imides and esters].
Generally, the process proceeds particularly well when the electron-withdrawing group (EWG) corresponds to a salified acid functional group.
In other words, the electron-withdrawing group (EWG) is then chosen from negatively charged groups.
Preference is given, among the metals from Group VIII, to those of the fourth period, in particular nickel and cobalt, and more particularly nickel. In the present application, reference is made to the Periodic Table of the Elements published in the supplement to the Bulletin de la Societe chimique de France in January 1966).
This is because the metals from the platinum group exhibit a relatively mediocre selectivity with respect to the fluorine to be removed. However, the platinum period is preferable to that of palladium.
The forms which are the most readily used in the process are the solid catalyst forms and more particularly, for nickel and cobalt, the “Raney” forms.
The preferred catalysts are catalysts based on Raney nickel, that is to say the catalysts for which the main active element, preferably the only active element, is Raney nickel.
The substrates generally do not exhibit more than 50 carbon atoms and even do not exhibit more than 25. However, it should be emphasized that the process does not exhibit the same limitations as the gas-phase routes and thus that the molecular mass does not have a critical nature.
To obtain a good yield and a good selectivity, it is highly desirable to carry out the reaction while maintaining the pH at a value sufficient to ionize the possible acid functional group and, more generally, at least equal to 4, advantageously to 7, preferably to 10.
The amount of base to be introduced into the reaction medium is at least equal to th
Cordier Georges
Jacquot Roland
Rhodia Chimie
Siegel Alan
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