Iodination process

Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing

Reexamination Certificate

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Reexamination Certificate

active

06573410

ABSTRACT:

The present invention relates to a process for the iodination of perfluoropolyether acylhalides having the formula:
XCO—CF
2
O[(CF
2
O)
n
(CF
2
CF
2
O)
m
]
p
CF
2
—Q  (II)
wherein X, Q and the indexes have the values defined hereunder to obtain perfluoropolyethers having iodinated —CF
2
I end groups with high yields.
The iodinated perfluoropolyethers are usable as oleohydro-repellent compounds, or as components for preparing fluororesins, fluoroelastomers; or used as precursor of fluorinated surfactants.
Methods to iodinate perfluoropolyether acylhalides are known in the prior art, but having repeating units different from those of formula (II).
The iodination is for example carried out by reacting an acylfluoride with iodine in the presence of a perhalogenated solvent and of an alkaline or alkaline-earth metal carbonate, as described for example in EP 348,948. As an example of perhalogenated solvent hexachloro-1-3-butadiene is mentioned. The drawback of this process is that hexachloro-1-3-butadiene is not a solvent usable from an industrial point of view since it is an irritating compound.
Another process for preparing iododerivatives of perfluoropolyethers having a structure different from that shown in (II) is reported in EP 520,821 which describes the reaction of an acylfluoride with a metal iodide, wherein the metal is for example Li, Na, Mg, Ca, Al, to form perfluoropolyethers having —COI end groups. According to this patent the reaction takes place at temperatures between 0° C. and 100° C., and in a subsequent step the irradiation of the obtained compound is carried out by UV rays at room temperature, obtaining the perfluoropolyether with iodinated end groups. The drawback of said process is to comprise two distinct steps and to use a UV ray source, which as well known requires rather complex plants to be industrially operated.
The need was felt to have available a process for preparing perfluoropolyethers having one or both the end groups with an iodine atom starting from linear perfluoropolyether monoacyl- or diacyl-halides, having structure (II), which allowed to obtain products having high yields, without substantially modifying the number average molecular weight M
n
, of the starting product of structure (II), said average molecular weight being considered without the two —COX end groups.
An object of the present invention is a process for preparing perfluoropolyether iodides, by reaction with LiI of monoacyl- or diacyl-halides of perfluoropolyethers, having a number average molecular weight from 200 to 3,000, preferably from 500 to 3,000, still more preferably from 1,000 to 3,000, and having the following structure:
XCO—CF
2
O[(CF
2
O)
n
(CF
2
CF
2
O)
m
]
p
CF
2
—Q  (II)
wherein:
m
=0.5-10; p=0-20;
X=Cl, F;
Q=H, CF
3
, X as above defined or COX′, wherein X′ is Cl, F with the proviso that X′=X;
said process being characterized in that the iodination reaction is carried out in a reactor, at a temperature from 180° C. to 260° C., preferably from 185° C. to 220° C.
The process of the present invention can operate both in the presence and in absence of solvents.
As solvents, those which solubilize the perfluoropolyethers of formula (II) are used. Acetonitrile, perfluorooctane, etc. can for example be mentioned.
Preferably in the process of the invention in formula (II) X=X′=F.
The ratio by moles between LiI and —OCF
2
COX end groups ranges from 1.1 to 2.
The reaction time is that necessary to reach the total conversion of the perfluoropolyether halide in the corresponding iodide at the selected reaction temperature. Generally the reaction is considered over when in the reactor a pressure value is reached which remains constant at the selected reaction temperature. Generally reaction times of 4-6 hours are sufficient to end the reaction.
In the sealed reactor used in the process according to the present invention, before starting the reaction, the gases are removed by reducing the internal pressure.
The iodinated perfluoropolyether compounds obtained with the process of the invention have the following formula:
I—CF
2
O[(CF
2
O)
n
(CF
2
CF
2
O)
m
]
p
CF
2
—T  (I)
wherein T=I, F, CF
3
, H, Cl; m
=0.5-10, p=0-20 and having average number molecular weight from 200 to 3,000.
The results of the present invention are particularly surprising and unexpected since in the prior art the preparation of iodinated compounds of perfluoropolyethers having structure (I) has never been described. Indeed in the starting compounds of structure (II), —OCF
2
O—units (Cl unit) in position &bgr; with respect to the —COX end group are present in the structure. When the structure of the fluorinated acylhalide compound comprises the aforesaid groups, contemporaneously with the iodination the secondary reaction of &bgr;-scission takes place. This causes the decrease of Cl units in the perfluoropolyether structure, with formation of carbonyl fluoride COF
2
. Therefore the &bgr;-scission reaction causes a mass loss of the final product. It has been found by the Applicant that the effect of this secondary reaction is particularly evident when an iodinating agent different from LiI is used.
By operating with the process of the invention it has been unexpectedly found that the &bgr;-scission reaction can be remarkably reduced or substantially eliminated.
The following Examples illustrate the invention but they do not limit the scope thereof.


REFERENCES:
patent: 5117055 (1992-05-01), Abe et al.
patent: 0 348 948 (1990-01-01), None
patent: 0 520 821 (1992-12-01), None

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