Silanes with hydrophilic groups, their synthesis and use as...

Details Silanes with hydrophilic groups, their synthesis and use as... Silanes with hydrophilic groups, their synthesis and use as...

1994-09-06

2001-07-03

Shaver, Paul F. (Department: 1621)

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

Organic compounds

Silicon containing

C556S418000, C556S420000, C556S423000, C556S425000, C556S428000

Reexamination Certificate

active

06255511

ABSTRACT:

FIELD OF INVENTION
The invention relates to novel silanes with hydrophilic groups, their synthesis and surfactants in aqueous media comprising the novel silanes. More particularly, it relates to silane surfactants, which are resistant to hydrolysis in acidic and alkaline media and significantly lower the surface tension of aqueous media. The concept of “aqueous” media is understood to include also those media which consist predominantly of water and additionally can contain water-soluble or water-miscible organic solvents.
BACKGROUND INFORMATION AND PRIOR ART
It is known from the state of the art that organo-modified siloxanes, such as polyether siloxanes or polysiloxanes, which have substituents with anionic, cationic or amphoteric groups, an appropriate structure and a balanced ratio of hydrophilic and hydrophobic groups, can lower the surface tension of aqueous solutions to a pronounced extent.
Surfactants with at least silicon atoms are disclosed in the German patent 41 41 046. They correspond to the general formula
wherein
R
1
is a methyl or phenyl group, with the proviso that at least 90% of the R
1
groups are methyl groups,
R
2
is R
1
or —(CH
2
)
6
—OSO
3
31
.M
+
, wherein
M
+
is an alkali, ½alkaline earth or optionally an alkyl-substituted ammonium ion,
R
3
is R
1
or R
2
,
with the proviso that in the average molecule, at least one R
2
or R
3
group is a —(CH
2
)
6
—OSO
3
−
.M
+
,
a is 0 to 5, and
b is 0 to 5.
The selected siloxane hexyl sulfates, which are trisiloxane hexyl sulfates in the event that three silicon atoms are present, bring about a pronounced lowering in the interfacial tension of neutral aqueous media to values of about 21 mN/m. However, they are unstable in acidic or alkaline solutions and, due to the hydrolysis of the Si—O—Si bonds and renewed condensation of the hydrolysis products to higher molecular weight oligomers, very rapidly lose their effectiveness and partly become insoluble in aqueous media.
Surfactants with a low content of silicon atoms are furthermore described in the European publication 0 367 381 (A2) and the British patent 1,520,421.
The European publication 0 367 381 (A2) relates to organosilicon compounds of the general formula
wherein the R groups, independently of one another, represent an alkyl, aryl, halogenated alkyl or halogenated aryl group with up to 18 carbon atoms, each R′ groups represents an alkylene group, which separates adjacent silicon atoms by up to 6 carbon atoms from one another, and the R″ groups independently of one another represent R or, when a=0, the R
3
SiR′ group. Z is a hydrophilic substituent, which contains sulfur, nitrogen or phosphorus, a carboxy-functional group or the salt of such a group, while a has a value of 0, 1 or 2.
It follows from this that, by definition, the organosilicon group contains at least two silicon atoms. The synthesis of these carbosilanes is relatively expensive and is carried out, for example, by a reaction similar to a Grignard reaction. After that, carbosilane surfactants with a quaternary, sulfonate or betaine structure are synthesized by means of the hydrosilylation of, for example, allyl glycidyl ether or allylamine. The substances, so obtained, lower the surface tension of a 1% solution in distilled water to 23 to 25 mN/m.
Carbosilanes surfactants and their synthesis are disclosed in the British patent 1,520,421. They have the general formula
wherein R is a methyl, ethyl, propyl or trifluoropropyl group, with the proviso that at least 50% of the R groups are methyl groups, R′ is an alkyl group with 1 to 6 carbon atoms and R″ is a divalent aliphatic hydrocarbon group with 2 to 6 carbon atoms, which connects Q and the adjacent silicon atom by a bridge of at least 2 carbon atoms. Q is an —O(C
2
H
4
O)
c
X, wherein c has a value of 3 to 12 and X is a hydrogen group, R′″ group,
in which R′″ is an alkyl group with 1 to 5 carbon atoms, a has a value or 1 or 2 and b a value of 2 or 3.
By definition, at least two silicon atoms must be present here also. In application tests, these compounds show remarkable foaming properties.
In this connection, it was known to those skilled in the art that, within groups of these known carbosilanes with comparable structure, the surfactant properties of the compounds deteriorate as the number of silicon atoms decreases, particularly from 4 to 3 or 2. This observation is reflected in the theory of Neumann (A. W. Neumann, D. Renzow, Zeitschrift f. Phys. Chem., New Issue 68, 11, (1969)), which states that the permethylated surface of the siloxane backbone is responsible for lowering the surface tension of aqueous solutions to below 30 to 40 mN/m.
Furthermore, reference is made to the Japanese publications of H. Maki et al. in YUKAGAGU 19, No. 4, page 51 ff. and YUKAGAGU 19, No. 11, page 23 ff., both from the year 1970, in which defined compounds of the formulas
(CH
3
)
3
Si(CH
2
)
3
(C
2
H
4
O)
n
H
and
((CH
2
)
4
)
3
Si(CH
2
)
3
(C
2
H
4
O)
m
H
are described, wherein n=4.0 or 7.7 and m=10 or 17. However, these compounds lower the interfacial tension of a 0.1% by weight solution only to values of not less than 26.5 mN/m.
Likewise, quaternary nitrogen compounds having the formula
Bu
3
M(CH
2
)
3
N
+
(CH
3
)
3
Cl
−
(Bu=Butyl, M=Sn, Si),
which, admittedly, are bacteriostatic but not very surface active, are described in these Japanese publications. The best representatives of these quaternary compounds lower the surface tension of a 1% aqueous solution to 32 mN/m.
The present invention is based on the surprising finding that, in contrast to general theoretical or factual knowledge, as expressed, for example, in the Neumann theory, selected silanes, that is, compounds with only a single silicon atom, but in which the ratio of hydrophilic to hydrophobic parts of the molecule is balanced, lower the surface tension of water exceeding effectively and, in contrast to the siloxane surfactants, are resistant to hydrolysis for days and weeks even in acidic and alkaline media. A further and not foreseeable advantage of the inventive silanes is their complete biodegradability, which makes them particularly suitable for use as surfactants. Such a profile of properties could not be derived from the state of the art and contradicts the previously customary assumptions concerning structural requirements, which organosilicon compounds should fulfill in order to show interfacial tension-lowering properties in aqueous systems.
OBJECT OF THE INVENTION
An object of the present invention is a novel silane. Another object of the invention is the synthesis of novel silanes. Yet another object of the invention is a surfactant in aqueous media comprising the novel silanes.
The silanes have the general formula
wherein
R
1
, R
2
and R
3
in the molecule are the same or different and represent aliphatic or aromatic hydrocarbon groups,
R
4
is a divalent hydrocarbon group with 4 to 12 carbon atoms and a lateral hydroxyl group, wherein the hydrocarbon group can be interrupted by an ether oxygen, and
R
5
is a hydrophilic, ionic group.
Examples of preferred R
1
, R
2
and R
3
groups are methyl, ethyl, propyl, butyl or phenyl groups. However, preferably only one of the R
1
, R
2
and R
3
groups is a phenyl group. Preferably, at least 90% of the R
1
, R
2
and R
3
groups are methyl groups.
The R
4
group is a divalent hydrocarbon group with 4 to 12 carbon atoms and a lateral hydroxyl group. This group is derived from an epoxide, which has an olefinic double bond, which can be hydrosilylated, and the epoxide ring of which has been opened. Diagrammatically, this can be shown by the following example:
The group in the box corresponds to the R
4
group.
Preferred examples of the R
4
group are:
R
5
is an ionic group having the formula
In the above, R
6
, R
7
and R
8
are alkyl groups with 1 to 6 carbon atoms, which can be the same or different in the molecule. Examples of such groups are methyl, ethyl, propyl, butyl and the isobutyl group.
X

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