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Description  |
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This invention is concerned with novel organosilicon compounds which are
effective in absorbing ultra violet radiation and is also concerned with a
process of preparing such compounds.
A number of organic compounds, generally organic acids and derivatives
thereof, are known to be chromophores having U.V.-absorbing properties and
are employed on a commercial scale as ingredients in sunscreen
preparations or as plastic additives. Although such materials function
adequately they are easily removed from the substrate to which they have
been applied. For example, cosmetic sunscreen preparations can be removed
during bathing thus requiring repeated applications if protection is to be
maintained. It is also desirable that the active ingredient remain on the
surface of the skin rather than penetrate into or through the skin.
Compounds which overcome this problem to a certain extent are disclosed for
example in European Patent Specification 305 059, which provides
organosilicon compounds having at least one unit of the general formula
##STR3##
any other units present in the said siloxanes being those represented by
the general formula
##EQU1##
wherein R represents a C.sub.1-18 alkyl group, R' is a divalent alkylene
or oxyalkylene group having from 2 to about 20 carbon atoms, or a divalent
alkenylene or oxyalkenylene group having from 2 to 20 carbon atoms,
wherein the carbon-carbon double bond is adjacent to the silicon atom, R"
is a halogen atom, an alkyl, aryl, alkoxy or alkoxyalkoxy group having
less than 9 carbon atoms, Q represents a hydrogen atom, a monovalent
C.sub.1-18 hydrocarbon or halogenated hydrocarbon group, Z is an alkyl or
an alkoxy group having from 1 to 8 carbon atoms or a hydroxyl group, a and
b each have a value of 0, 1, 2 or 3 and c is 0 or 1, provided that at
least one of Z and R' is linked to the multivalent aryl group via an ether
linkage.
It was found, however, that although the materials described above were, in
comparison with the prior art, less susceptible to hydrolysis at the ester
linkage, for example by enzymatic hydrolysis on the skin when these
materials were used as cosmetic sunscreen agents, they were not
sufficiently photostable when exposed to UV irradiation.
EP publication 392 882 discloses the use of diorganopolysiloxanes with a
benzalmalonate functionality in cosmetic applications. The
diorgano-polysiloxanes which are useful in said application have the
average general formula
B--Si(R).sub.2 --O[Si(R).sub.2 --O].sub.r --[Si(R)(A)--O].sub.s
--Si(R).sub.2 --B, or
##STR4##
wherein R is C.sub.1-10 alkyl, phenyl or trifluoropropyl, B is R or A, r
is from 0 to 200, s is from 0 to 50, u is from 1 to 20, t is from 0 to 20,
t+u is at least 3, there being at least one group A per molecule and A
denotes a structure of the general formula
##STR5##
wherein R.sup.1 is H, OH, trimethylsiloxy, C.sub.1-6 alkoxy or a divalent
group --(O).sub.n --(CH.sub.2).sub.p --CH(R")--CH.sub.2 --, n is 0 or 1, p
is 1 to 10, R" is H or C.sub.1-4 alkyl, R.sup.2 is H, C.sub.1-6 alkyl or
C.sub.1-6 alkoxy, R.sup.3 is C.sub.1-8 alkyl, at least one of the R.sup.1
groups being the divalent group.
We have found that although the materials described in both above
identified references perform well in many applications, and although
there is a reduction in the amount of chromophore which penetrates through
the skin when applied thereto in comparison with the amount of chromophore
which penetrates when it has been applied as a pure compound (i.e. not
linked to an organosilicon compound), there is still a need to further
reduce the amount of penetration through the skin.
We have now found that if certain novel chromophores are used in the
preparation of organosilicon compounds, improved cosmetic preparations,
effective in absorbing ultra violet radiation can be obtained.
According to a first aspect of the invention there is provided an
organosiloxane compound having at least one unit of the general formula
##STR6##
any other units present in the said siloxanes being those represented by
the general formula
##EQU2##
wherein R represents a C.sub.1-8 alkyl or an aryl group, R.sup.1 is a
hydrogen atom or a C.sub.1-5 alkyl group, R.sup.2 is a hydrogen atom, a
C.sub.1-5 alkyl group or a group OR.sup.1, R.sup.3 is a C.sub.1-5 alkyl
group, R" represents a hydrogen atom, a monovalent C.sub.1-8 hydrocarbon
or halogenated hydrocarbon group, a has a value of 0, 1 or 2, b has a
value of 0, 1, 2 or 3 add n has a value of from 1 to 6, provided that the
--C(R.sup.1).dbd.CH--(CR.sub.2.sup.1).sub.n --O--
group and the two R.sup.2 groups are linked to the aromatic ring at the
para and both meta positions in relation to the group
--CH.dbd.C[C(O)OR.sup.3 ].sub.2.
In the general formula of the organosilicon compounds of the invention R
may be for example methyl, ethyl, butyl or phenyl. R" is hydrogen or a
monovalent hydrocarbon or halogenated hydrocarbon group having less than 8
carbon atoms, for example alkyl, alkenyl, aryl, alkaryl, aralkyl and
halogen substituted alkyl, alkenyl, aryl, alkaryl and aralkyl groups.
Examples include methyl, ethyl, vinyl, phenyl and 3,3,3-trifluoropropyl.
R.sup.3 denotes alkyl groups having up to 5 carbon atoms for example
methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, isobutyl, pentyl
and neopentyl. R.sup.1 is either a group R.sup.3 or a hydrogen atom and
R.sup.2 is a group R.sup.1 or a group OR.sup.1. It is preferred that at
least 80% of all R and R" groups are methyl groups, most preferably
substantially all R and R" groups are methyl groups. It is also preferred
that R.sup.1 is either hydrogen, methyl or ethyl, most preferably
hydrogen. Preferably each R.sup.2 group is H or one R.sup.2 group is a
hydrogen, while the other one is an alkoxy group, preferably methoxy or
ethoxy. R.sup.3 is preferably methyl or ethyl. a is preferably 1 while b
is preferably 2, making the organosilicon compound a substantially linear
or cyclic diorgano-siloxane polymer. However, if the diorganosiloxane is a
substantially linear polymer at least two endblocking units must be
present, thus requiring the presence of 2 units in which a has a value of
2, two units in which the value of b is 3 or one unit wherein a is 2 and
one unit in which b is 3. n is preferably 1, 2 or 3. Suitable preferred
polymers have therefore either the general formula
##STR7##
wherein R and R" are as defined above, X denotes a group Y or a group R"
and Y denotes a group of the formula
--C(R.sup.1).dbd.CH--(CR.sup.1)--O--C.sub.6 R.sub.2.sup.2 H.sub.2
--CH.dbd.C--[C(O)OR.sup.3 ].sub.2
r has a value of from 0 to 100, s has a value of from 0 to 20, whereby at
least one X denotes Y in the case that s=0, t has a value of from 0 to 10,
v has a value of from 1 to 10 and v+t has a value of at least 3.
In the substituent Y of the organosilicon compounds according to the
invention, the group
--C(R.sup.1).dbd.CH--(CR.sub.2.sup.1).sub.n --O--
may occupy the meta-position or the para-position of the aromatic ring in
relation to the group --CH.dbd.C[C(O)OR.sup.3 ].sub.2. Preferably the
para-position is thus occupied. The groups R.sup.2 occupy the remaining
two positions out of the para- and meta-positions in relation to the group
--CH.dbd.C[C(O)OR.sup.3 ].sub.2. Examples of preferred substituents Y thus
include
##STR8##
The organosilicon compounds of the present invention have at least one unit
falling within the general formula (i), preferably at least 2. Suitable
organosilicon compounds are polymeric materials which may be homopolymers
consisting only of such units (i), or they may be copolymers containing
both units (i) and units having the general formula (ii). The
organosilicon compounds may vary from freely flowing liquids to highly
viscous gum-like materials or resinous solids. Preferred, at least for
cosmetic applications, are the liquid substantially linear organosiloxane
homopolymers and copolymers, for example those having a viscosity of from
100 to 20000 m.sup.2 /s, more prefer- ably 500 to 5000 mm.sup.2 /s as
these are more easily mixed with other ingredients to make cosmetic
compositions and as they will spread more easily onto the skin.
Organosilicon compounds of the invention which are especially preferred are
those wherein the number of units (i) is limited to a maximum of 20% of
the total number of siloxane units in the molecule. For maximum efficiency
in its U.V. absorbing property it is preferred that the number of units
(i) be limited to 10% or less of the total. The units of formula (i) may
be distributed randomly in an organosiloxane polymer, they may be
end-blocking units of the polymer or they may be located at the end of the
poly-mer and pending in chain of the polymer at the same time. Units of
the general formula (i) are preferably situated at the end of the
organosiloxane polymer forming one or more endblocking units of the
polymer. In the most preferred organosilicon compounds which are
substantially linear polyorganosiloxane polymers, both endblocking units
have a structure represented by the general formula (i), while all other
units are according to the general formula (ii). The most preferred
organosilicon compounds have two units of the formula (i) and a larger
number of units according to the general formula (ii), e.g. 8 to 90,
especially 8 to 40.
The organosilicon compounds according to the invention are effective in
absorbing ultra violet radiation in the erythemic region (290-320 nm)
which makes them particul-arly suitable for use in cosmetic sunscreen
preparations where absorption in the UV-B region is particularly
desirable. Most preferred for this application are those that have a
maximum absorbance at 300-320 nm.
The organosilicon compounds of the present invention can, quite generally,
be prepared by the reaction of an organosilicon compound in which each
unit (i) is replaced with a unit having the general formula
##STR9##
with a chromophore of the general formula
C(R.sup.1).tbd.C--(CR.sup.1.sub.2).sub.n --O--C.sub.6 R.sup.2.sub.2 H.sub.2
--CH.dbd.C--[C(O)OR.sup.3 ].sub.2 (iii)
These chromophores are in themselves novel compounds and the invention
therefore includes in one of its aspects a compound of the formula
C(R.sup.1).tbd.C--(CR.sup.1.sub.2).sub.n --O--C.sub.6 R.sup.2.sub.2 H.sub.2
--CH.dbd.C--[C(O)OR.sup.2 ].sub.2 (iii)
wherein R.sup.1 is a hydrogen atom or a C.sub.1-5 alkyl group, the group
C.sub.6 R.sup.2.sub.2 H.sub.2 represents an aromatic ring, wherein R.sup.2
is a hydrogen atom, a C.sub.1-5 alkyl group or a group OR.sup.1, R.sup.3
is a C.sub.1-5 alkyl group and n has a value of from 1 to 6, provided that
the group containing the unsaturated carbon-carbon triple bond and the two
R.sup.2 groups are linked to the two meta-positions and to the
para-position of the aromatic ring in relation to the ester containing
group.
Compounds of the general formula (iii) may be prepared e.g. by reacting a
hydroxy or dihydroxy benzaldehyde with halogenopropyne, followed by a
further reaction with a diester of malonic acid. The first reaction is
preferably carried out in the presence of a suitable solvent, e.g.
acetone, preferably at reflux temperatures. The presence of a catalyst is
also preferred. The second reaction is also preferably carried out in the
presence of a solvent, e.g. toluene at reflux temperatures. The final
product of formula (iii) is a light brown crystal.
The invention also includes a process for the preparation of organosilicon
compounds of the kind specified herein, which comprises reacting together
(A) a compound of the general formula
C(R.sup.1).tbd.C--(CR.sup.1.sub.2).sub.n --O--C.sub.6 R.sup.2.sub.2 H.sub.2
--CH.dbd.C--[C(O)OR.sup.2 ].sub.2 (iii)
wherein R.sup.1 is a hydrogen atom or a C.sub.1-5 alkyl group, the group
C.sub.6 R.sup.2.sub.2 H.sub.2 represents an aromatic ring, wherein R.sup.2
is a hydrogen atom, a C.sub.1-5 alkyl group or a group OR.sup.1, R.sup.3
is a C.sub.1-5 alkyl group and n has a value of from 1 to 6, provided that
the group containing the unsaturated triple bond and the two R.sup.2
groups are linked to the two meta-positions and to the para-position of
the aromatic ring in relation to the group
--CH.dbd.C--[C(O)OR.sup.3 ].sub.2
and
(B) an organosilicon compound having at least one unit of the general
formula
##EQU3##
any other units present in the organosilicon compound being those
represented by the general formula
##EQU4##
wherein R, R", a and b are as hereinabove defined.
The reaction is preferably carried out employing stoichiometric proportions
of (A) and (B) or a slight stoichiometric excess of (A). However, a
stoichiometric deficiency of (A) can be employed if residual
silicon-bonded hydrogen is desired in the product.
Alternatively polymeric organosilicon compounds of the invention can also
be obtained by first preparing the corresponding hydrolysable silane,
employing in place of the organosilicon compound (B) the corresponding SiH
containing silane (C) which has the general formula
Z.sub.3-x Si(R.sub.x)--H (v)
wherein R is as defined above, Z is a hydrolysable group, preferably alkoxy
having 1 to 8 carbon atoms and x has a value of 0, 1 or 2.
The silane (D) resulting from this reaction may be submitted thereafter to
cohydrolysis with a further hydrolysable silane or equilibration with (E)
cyclic or (F) linear polyorganosiloxanes consisting essentially of units
of the formula (ii). Silanes (D) which can be used in this method are
novel in themselves and are included in the scope of the present
invention. Silanes (D) have the general formula
Z.sub.3-x Si(R.sub.x)--C(R.sup.1).dbd.CH--(CR.sub.2.sup.1).sub.n
--O--C.sub.6 R.sub.2.sup.2 H.sub.2 --CH.dbd.C--[C(O)OR.sup.3 ](vi)
wherein R, R.sup.1, R.sup.2, R.sup.3, Z, x and n are as defined above.
Thus, in more detail, the process comprises
I) the preparation of a hydrolysable silane by reacting a silane of the
general formula
Z.sub.3-x Si(R.sub.x)--H (v)
wherein R represents a C.sub.1-8 alkyl or aryl group, Z is a hydrolysable
group and x has a value of 0, 1 or 2, with a compound of the general
formula
C(R.sup.1).tbd.C--(CR.sup.1.sub.2).sub.n --O--C.sub.6 R.sup.2.sub.2 H.sub.2
--CH.dbd.C--[C(O)OR.sup.3 ].sub.2 (iii)
wherein R.sup.1 is a hydrogen atom or a C.sub.1-5 alkyl group, the group
C.sub.6 R.sup.2.sub.2 H.sub.2 represents an aromatic ring, wherein R.sup.2
is a hydrogen atom, a C.sub.1-5 alkyl group or a group OR.sup.1, R.sup.3
is a C.sub.1-5 alkyl group and n has a value of from 1 to 6, provided that
the group containing the unsaturated triple bond and the two R.sup.2
groups are linked to the two meta-positions and to the para-position of
the aromatic ring in relation to the group --CH.dbd.C--[C(O)OR.sup.3
].sub.2, and
II) submitting the hydrolysable silane to cohydrolysis or equilibration
with cyclic or linear polydiorganosiloxanes consisting essentially of
units of the formula
##EQU5##
wherein R" represents a hydrogen atom a monovalent C.sub.1-8 hydrocarbon
or halogenated hydrocarbon, and b has a value of 0, 1, 2 or 3.
Z is preferably an alkoxy group having from 1 to 8 carbon atoms.
As concerns the cohydrolysis, such reaction will conveniently be in
conjunction with other hydrolysable silanes (e.g. diorgano-dihalosilanes,
or diorgano-alkoxysilanols, etc.) or with siloxanes having hydrolysable
endgroups (e.g. .alpha.,w dihydroxy polydimethylsiloxanes).
As concerns the equilibrium aspect on the linear or cyclic
polydiorganosiloxanes, cyclic siloxanes will conveniently have the general
formula [R.sup.2 SiO].sub.n, wherein n has a value of from 3 to 9, and
linear polydiorganosiloxanes are usually used as end-blocking units, and
will be short chain triorganosiloxane end-blocked polydiorgano-siloxanes
(in the shortest form hexaorganodisiloxane [R.sub.3 Si--O--SiR.sup.3 ]).
This alternative process involves thus technique which is known per se.
In order to obtain the particularly preferred polymeric organosilicon
compounds of the invention the reaction is carried out in such a way that
in the reaction product at least one siloxane unit and no more than 20% of
the total number of siloxane units has a structure according to formula
(i). This may be achieved by reacting polymeric organosilicon compounds
(B) which have a maximum of 20 mole % silicon-bonded hydrogen atoms, with
stoichiometric amounts of compound (A). Excess amounts of (A) may also be
used in this case. If residual Sill groups are desired in the
organosilicon compound product less than stoichiometric amounts of
compound (A) may be employed. The particularly preferred polymeric
organosilicon compounds of the invention may also be obtained by reacting
polymeric organosilicon compounds (B) having more than 20 mole %
silicon-bonded hydrogen atom, with less than stoichiometric amounts of
compound (A). Most preferably, however, organosilicon compounds (B) are
employed which are polydiorganosiloxanes endblocked with
diorganohydrosiloxane units provided the siloxane has a minimum chain
length of 10 silicon atoms.
The reaction between (A) and (B) may be carried out employing known
procedures for the addition of silicon-bonded hydrogen atoms to groups
containing aliphatic unsaturation. Thus, such reactions are generally
catalysed by a platinum group metal or a compound or complex of such a
metal. Examples of catalysts which may be employed in the reaction between
(A) and (B) are platinum on carbon, chloroplatinic acid, platinum acetyl
acetonate, complexes of platinum compounds with unsaturated compounds e.g.
olefins and vinyl siloxanes, complexes of rhodium and palladium compounds
and complexes of platinum compounds supported on inorganic substrates. The
addition reaction may be performed at reduced, atmospheric or increased
pressure. It is generally preferred to employ a solvent e.g. toluene or
xylene in the reaction mixture although the presence of a solvent is not
essential. It is also preferred to carry the reaction out at elevated
reaction temperatures e.g. from about 50.degree. C. up to the reflux
temperature of the reaction mixture.
The organosilicon compounds of this invention have similar UV absorbance
characteristics to those disclosed in the prior art. They are useful as
agents for preventing sunburn and are thus useful in skin care and hair
care applications. They may be applied per se to the skin or hair but are
more preferably formulated into cosmetic compositions with, for example,
inert carriers e.g. solvents such as water, ethanol, isopropanol,
glycerine and mineral oil and cream base materials such as stearic acid,
propylene glycol, beeswax and cetyl alcohol. Other conventional
ingredients e.g. perfumes and known U.V. absorbing substances may also be
included in the formulated compositions. The organosilicon compounds of
the present invention are also useful in the coating of substrates e.g.
wood, plastics or metal, to which they may be applied either per se or as
additives to coating compositions or they may be incor- porated as
addit-ives in plastics materials.
The following examples, in which parts and percentages are expressed by
weight illustrate the invention.
EXAMPLE 1
Preparation of propanedioic {[4-(2-propynyloxy)phenyl]methylene}-diethyl
ester (the most preferred compound).
To a stirred suspension of 4-hydroxybenzaldehyde (425.8 g) and K.sub.2
CO.sub.3 (807.6 g) in acetone (2,960 ml) at reflux temper-ature of about
60.degree. C. under a nitrogen atmosphere, was added dropwise
3-bromo-propyne (502.4 g) over a period of 2 hours. The reaction was
heated at reflux for 3 more hours. After cooling to room temperature the
reaction mixture was filtered and the excess of K.sub.2 CO.sub.3 removed
and washed several times with acetone. The filtrate was washed with
saturated aqueous solution of NaHCO.sub.2 and NaCl. The aqueous phase was
extracted with diethyl ether. The combined organic extracts were dried
over Na.sub.2 SO.sub.4, filtered and concentrated to a volume of 1 liter.
The solution was kept in the refrigerator overnight. The crystals were
filtered out and washed with cold diethyl ether. The filtrate was kept in
the refrigerator and some more crystals were formed and removed. This
procedure was repeated 3 times resulting in 1,385.26 g of
4-(2-propynyloxy) benzaldehyde in 83% yield. The material was analysed by
gas chromatography, and shown to be 99.9% pure. Infrared and mass
spectroscopic analysis confirmed the structure.
The resulting compound (449.2 g) was added in small amounts to a stirred
solution of diethyl malonate (448.5 g), piperidine (23.84 g), toluene
(1,400 ml) and acetic acid (59 g) at about 50.degree. C. The acetic acid
had been added in three equal portions after 1, 1.5 and 2 hours
respectively. The reaction mixture was heated to reflux. After four hours
the mixture was allowed to cool to room temperature and washed with
saturated aqueous solution of NaHCO.sub.3 and NaCl, dried with Na.sub.2
SO.sub.4, filtered and concentrated, giving 853.4g of a dark brown oily
product. Diethyl ether (458 ml) and n-hexane (358 ml) were added and the
solution kept in a refrigerator overnight. The solution was filtered,
giving 564.8 g of light brown crystals (67% yield) having a melt-ing point
of 45.5.degree. to 48.degree. C. Recrystallisation in ethanol and n-hexane
yielded 543 g of the title compound as light brown crystals. Analysis
revealed a melting point of 48.5.degree. to 49.5.degree. C. and a purity
by capillary gas chromatography of 99.9%.
EXAMPLE 2
Preparation of propanedioic {[4-(2-propynyloxy)phenyl]methylene}-dimethyl
ester
The procedure of the above method was repeated except that dimethyl
malonate was used instead of diethyl malonate.
EXAMPLE 3
5 g of {[4-(2-propynyloxy)phenyl]methylene}-diethyl ester were dissolved in
20 g of toluene and heated under nitrogen to about 80.degree. C. 13.2 g of
a hydrosiloxane having a degree of polymerisation of 20 and 10 mpc SiH
groups (3.62% SiH) were then added dropwise after a platinum complex was
also added, giving 10.sup.-4 mole of Pt per mole of SiH of the
hydro-siloxane. The mixture was heated to reflux and maintained until all
SiH had disappeared of the infrared spectroscopic analysis. It was then
allowed to cool to room temperature. The toluene was then evaporated to
leave afar washing 16.5 g of a slightly brown polymer having the average
structure R--[(CH.sub.3).sub.2 SiO].sub.2) --R, wherein R has the formula
##STR10##
Only 1.6% by weight of the total reaction product of unreacted
{[4-(2-propynyloxy)phenyl]methylene}-diethyl ester was present in the
endproduct.
EXAMPLE 4
10 g of {[4-(2-propynyloxy)phenyl]methylene}-diethyl ester were dissolved
in 10 g of toluene and heated under nitrogen to about 80.degree. C. 13.2 g
of a hydrosiloxane having a degree of polyme- risation of 100 and 20 mpc
SiH groups (8.43% SiH) were then added dropwise after a platinum complex
was also added, giving 10.4 mole of Pt per mole of SiH of the
hydro-siloxane. The mixture was heated to reflux and maintained until all
SiH had disappeared of the infrared spectroscopic analysis. It was then
allowed to cool to room temperature. The toluene was then evaporated to
leave after washing 21.2 g of a hazy, very viscous polymer having the
average structure
(CH.sub.3).sub.3 SiO--[(CH.sub.3).sub.2 SiO].sub.79
--[(CH.sub.3)RSiO].sub.20 --Si(CH.sub.3).sub.3
wherein R has the formula
##STR11##
EXAMPLES 5 AND 6
Similar procedures as described for Examples 3 and 4 were used to make
polymers with the average formulae (5) R--[(CH.sub.3).sub.2 SiO].sub.2 --R
wherein R has the formula
##STR12##
(6) (CH.sub.3).sub.3 SiO--[(CH.sub.3).sub.2 SiO].sub.6
--[(CH.sub.3)RSiO].sub.2 --Si(CH.sub.3).sub.3
wherein R has the formula
##STR13##
COMPARATIVE EXAMPLE 1
A similar procedure as described for Examples 3 and 4 was used to make a
polymer with the average formula
Q--[(CH.sub.3).sub.2 SiO].sub.20 --Q
wherein Q has the formula
##STR14##
3.3% by weight of the total reaction product of unreacted
{[4-(2-allyloxy)phenyl]methylene}-diethyl ester was present in the
endproduct.
COMPARATIVE EXAMPLE 2
A similar procedure as described for Examples 3 and 4 was used to make a
polymer with the average formula
(CH.sub.3).sub.3 SiO--Si(CH.sub.3)Z--OSi(CH.sub.3).sub.3,
wherein Z has the formula
##STR15##
COMPARATIVE EXAMPLE 3
Commercially available Parsol MCX was used which has the formula
CH.sub.3 --O--C.sub.6 H.sub.4 --CH.dbd.CH--C(O)OC.sub.8 H.sub.17.
UV Absorption Tests
Comparative Example 1 and Example 1 were both tested for their absorption
at 300 nm (E 1%,cm). To this effect the samples were dissolved in
tetrahydrofuran. Example 1 showed an absorption of 211 while Comparative
Example 1 only gave a value of 83. This shows that the organosilicon
compounds according to the invention are better than the prior art.
Stability and Water Resistance
Each sample was tested and found satisfactory in view of the stability to
UV radiation and its resistance to washing off with water.
Skin Penetration Tests
Invitro penetration tests were carried out on rat skin. The samples were
dissolved in tetrahydrofuran at a concen-tration of 10%, and this was
applied to the sun at a dosage of 30 .mu.l per 5 cm.sup.2 and penetration
was checked after 16 hours. After the test the penetration level was
inspected by measuring the amount of material on the skin surface, in the
horny layer, in the upper part of the skin, in the lower part of the skin
and in the chamber (vitro). This was tested by wiping the surface to
remove all non-penetrated material and placing it in a glass vial,
followed by stripping the cleaned skin several times with adhesive tape to
remove the horny layer and placing the tapes in a second glass vial. The
stripped skin was then divided in an upper and lower part. The upper part
was homogenised in 10 ml of tetrahydrofuran and placed in a third vial,
while the lower part was treated separately in the same way and placed in
a fourth vial. The chamber liquid was then placed in a fifth vial, the
chamber rinsed with tetrahydrofuran which was also added to the vial.
The content of each of the vials was then extracted with tetrahydrofuran
and analysed by high performance liquid chromatography. The most preferred
materials are those where the amount of penetration in the lower skin is
minimal. The results, based on an average from 2 experiments each, are
shown in Table I.
TABLE I
______________________________________
Skin penetration values in %
Skin Horny Upper Lower Chamber
Example surface layer skin skin liquid
______________________________________
3 90.7 1.6 7.5 0.2 <0.1
4 73.7 24.0 2.1 0.2 <0.1
5 89.4 6.7 3.5 0.4 <0.1
6 98.5 3.2 0.9 0.4 <0.1
Comp. 1 88.9 6.1 3.3 1.7 <0.1
Comp. 2 52.2 6.8 7.8 3.2 <0.1
Comp. 3 46.3 3.0 8.5 2.8 9.4
______________________________________
It is dear that materials according to the invention have less penetration
through the skid than prior art materials.
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