Process for obtaining mixtures of phosphoric mono- and diesters

Details Process for obtaining mixtures of phosphoric mono- and diesters Process for obtaining mixtures of phosphoric mono- and diesters

2002-01-18

2003-11-25

McKane, Joseph K. (Department: 1626)

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

Organic compounds

Phosphorus esters

Reexamination Certificate

active

06653495

ABSTRACT:

The present invention relates to a process for obtaining in high yield phosphoric esters having a perfluoro-polyoxyalkylene structure useful to give hydro- and oil-repellence in the treatment of various natural and artificial substrata, such as for example, ceramic, wood.
Specifically, the present invention relates to a process which allows to obtain phosphoric esters having a perfluoropolyoxyalkylene structure with high conversions and yields. Besides, the process of the invention allows to obtain, startting from the same precursor alcohol, phosphoric esters having a perfluoropolyoxyalkylene structure with a complete absence of triester groups and to modulate in a predetermined way the molar ratio between monoester and diester groups. Phosphoric esters are therefore obtained having a variable and controllable monoester/diester molar ratio starting from the same precursor alcohol.
It is known that the phosphoric esters of perfluoropolyethers are used to give hydro- and oil-repellence or easy stain removal to a wide range of natural and artificial substrata.
For the above mentioned applications, depending on the type of substratum, mixtures are required having a different content of phosphoric mono- and di-ester to obtain optimal results in connection with the desired effect. Therefore, from the industrial point of view, it would be desirable to have available a process which allows to modulate in a predetermined way the mono/diester composition of the phosphoric esters obtained from the phosphatization reaction.
Phosphoric esters deriving from monofunctional (per)fluoroalkyl alcohols are known in the prior art. These compounds must be phosphoric diesters to confer suitable hydro- and oil-repellence properties. However, the synthesis of diester phosphates in high yield is difficult and it unavoidably leads to a mixture containing significant amounts of triester as by-product. This is undesirable since the phosphoric triester shows adhesion problems to the substratum to which it is desired to confer hydro- and oil-repellence.
Alcoholic precursors have been synthesized having a perfluoroalkyl structure containing two monofunctional perfluorinated chains linked to a hydrogenated alkyl radical having an alcoholic function (di-R
f
-alcohols wherein R
f
is a perfluoroalkyl group) or two alcohol functions (di-R
f
-diols) as described in U.S. Pat. Nos. 3,935,277 and 4,946,992. Said patents describe the synthesis of di-R
f
-alcohols and of di-Rf-diols by reaction of R
f
-ethylenthiols with halogenated alcohols and dials. Phosphoric esters of di-Rf-diols are described in U.S. Pat. Nos. 5,091,550 and 5,132,445. However the synthesis of the precursor alcohols requires many steps and expensive intermediates. The phosphoric esters obtained from said precursors are not easily available on the market.
To impart hydra- and oil-repellence properties to natural and artificial substrata, it is also known, as described in U.S. Pat. No. 3,492,374, the use of phosphates deriving from monofunctional alcohols having a perfluoropolyoxyalkylene structure, of general formula:
[XCF
2
CF
2
O(CFXCF
2
O)
x
CFXCH
2
O]
2
PO(OM)
wherein:
X is F or CF
3
; x is an integer in the range 1-8; M is a cation such as for example H
+
, a cation of alkaline metals or an optionally alkyl substituted ammonium ion.
In this patent it is suggested the use of said phosphoric diesters to give oil-repellent properties to various materials for example textile fibres, skin, paper, plastic material, wood, ceramic. However these compounds are not very stable to hydrolysis. Besides, the synthesis reaction is carried out by using POCl
3
as phosphating agent: there are no high yields and phosphoric triesters with the above drawbacks are obtained.
The most used method in the prior art for preparing fluorinated phosphoric esters consists in the partial esterification of the phosphor oxychloride POCl
3
, with an alcohol and subsequent hydrolysis of the reaction intermediates. However this process leads to the formation of phosphoric triesters which give the above drawbacks. Besides, the esterification reaction of alcohols with POCl
3
takes place in highly exothermic conditions and with development of hydrochloric acid wherefore severe control measures are required, as regards both the process safety and the material used in the plant construction.
Another phosphatization reaction known in the prior art is is the reaction between an alcohol and the phosphoric anhydride P
2
O
5
. However this reaction leads to the formation of mixtures of monoesters and diesters in a fixed and not variable ratio, once the starting alcohol has been defined. Therefore this process does not allow to control in a predetermined way the mono/diester composition of the phosphoric esters obtained from the reaction, starting from the same precursor alcohol. From the industrial point of view this is a drawback since mono- and diester mixtures cannot be obtained in a variable ratio starting from the same precursor alcohol.
The need was therefore felt to have available a process for obtaining phosphoric esters having a perfluoropolyoxyalkylene structure (PFPE), which allows to obtain a complete absence of triester groups and to modulate in a predetermined way the molar ratio between the monoester groups —P(O)(OH)
2
, and the diester groups >PO(OH) present in the final product obtained by the reaction.
The Applicant has surprisingly found a process characterized by high yields and conversions to obtain phosphoric esters having a PFPE structure with the above properties.
An object of the present invention is therefore a process to obtain phosphoric mono- and diesters mixtures having the formula:
[R
f
—CF
2
—(CH
2
)
q
—Z]
w
—P(O)(OH)
3−w
  (I)
HO—[OH(O)P—Z—(CH
2
)
q
CF
2
—O—R
f
CF
2
—(CH
2
)
q
—Z]
v
—P(O)(OH)
2
  (II)
wherein:
w=1-2
v=1-6, preferably 1-4;
q=is an integer from 1 to 20, preferably 1-5;
Z=O(C
2
H
4
O)
p
—, O(CH
2
)
n
—O—, O(C
3
H
6
O)
p
—, S(C
2
H
4
O)
p
—, S(C
3
H
6
O)
p
—;
n=is an integer from 1 to 20, preferably 1-10;
p=is an integer from 1 to 5, preferably 1-3;
R
f
represents a (per)fluoropolyether chain;
R
f
in formula (I) is a monofunctional perfluoropolyether chain wherein the chain end group is selected from: CF
3
O—, C
2
F
5
O—, C
3
—F
7
O—, Cl(C
3
F
6
O)—, H(C
3
F
6
O)—;
said process comprising the following steps:
a) a monofunctional alcohol having a perfluoropolyoxyalkylene structure of formula:
R
f
—CF
2
—(CH
2
)
q
—ZH  (IA)
 or
a &agr;,&ohgr;-diol having a perfluoropolyoxyalkylene structure of formula:
HZ—(CH
2
)
q
—CF
2
—O—R
f
—CF
2
—(CH
2
)
q
—ZH  (IIA)
wherein R
f
, Z and q have the above meanings, is added with an amount of water in the range 1-60% by moles, preferably 5%-40% by moles, with respect to the alcohol equivalents;
b) the reaction product obtained in step a) is reacted with phosphoric anhydride P
2
O
5
added in a single portion or in more portions with a ratio between the alcohol equivalents and the moles of phosphoric anhydride in the range 1.5:1-4:1, preferably 2:1-3:1;
c) the compound obtained in step b) is hydrolysed by water or by a diluted solution of hydrochloric acid;
d) optionally the organic phase is separated by a solvent immiscible in water;
e) the product is recovered from the organic phase.
Generally, Rf has a number average molecular weight in the range 300-8,000, preferably 500 and 3,000 and comprises repeating units having at least one of the following structures, statistically placed along the chain:
(CFXO), (CF
2
CF
2
O), (CF
2
CF
2
CF
2
O), (CF
2
CF
2
CF
2
CF
2
O), (CR
4
R
5
CF
2
CF
2
O), (CF(CF
3
)CF
2
O), (CF
2
CF(CF
3
)O),
wherein
X=F, CF
3
;
R
4
and R
5
, equal to or different from each other, are selected from H, Cl, or perfluoroalkyl having from 1 to 4 carbon atoms.
In particular, the perfluoropolyether chain R
f
is selected from the following structures:
—(CF
2
O)
a
—(CF
2
CF
2
O)
b
—  1)
with b/a in the range 0.3-10, extremes included;
—(C
3
F
6
O)

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