LOW-EXTRACTABLETHIOXANTHONES
Technical field
The present invention relates to substituted derivatives of thioxanthone which can
be used as photoinitiators and sensitizers, to photopolymerizable compositions
comprising said derivatives and to a method for coating a substrate applying said
compositions .
Description of t e invention.
Photopolymerizable systems contain photoinitiators that possess in the molecule a
functional group which, by exposure to light radiation of appropriate wavelength,
generate radicals able to initiate the polymerization.
It is well known that photoinitiators must meet strict requirements of low toxicity,
low volatility, low extractability (low migration) and low odor, and must be highly
compatible with the photopolymerizable system. These properties are essential in
the food-packaging sector, in particular for the inks used for package printing.
Contamination from the photoinitiator can modify the organoleptic characteristics
of food and is forbidden by the current legislative regulations.
Moreover, in the photopolymerizable systems, it is essential to reduce the
migration of compounds that can cause undesired effects, such as loss of
adhesion to the substrate.
It is known that isopropyl thioxanthone (ITX) and its derivatives are very good
photoinitiators and sensitizers for pigmented systems; however ITX is not suitable
for the food packaging, since it has the tendency to migrate from the
photopolymerized coating, in particular from the printing inks into the packaged
food product, as a consequence of indirect contact.
Generally, the structural modifications aimed at avoiding migration of the
derivatives of thioxanthone are based on the introduction of unsaturated
copolymerizable groups, as described for example in US 4,348,530, or on the
synthesis of oligomeric derivatives of thioxanthone, such as OMNIPOL TX® (IGM
Resins) or the products described in CN 660837.
Unfortunately, the chemical reactivity of the these derivatives of thioxanthone
turn out to be always inferior than ITX. In particular, the oligomeric derivatives are
definitely less reactive than ITX.
It is known from the literature (Journal of Photochemistry, 35 ( 986), 353-356) that
some high molecular weight derivatives of thioxanthone, opportunely substituted,
can have a reactivity comparable to the reactivity of ITX. In particular, the presence
of a electron-attractive group in position 1 or 3 of thioxanthone produces a
bathochromic shift in the absorption of light which causes an increase of reactivity.
Such increase of reactivity compensates the increase of molecular weight that,
using the same amount by weight of photoiniziators, would reduce the applicative
performance of the photopolymerizable composition.
US 4,505,794 describes the preparation of several esters and amides of
thioxanthone substituted in positions 1and 3 in order to improve their solubility in
formulates in comparison with ITX. In particular, the methyl ester and the Nisopropyl
amide of thioxanthone in position 1 are indicated as the products with
high activity, while only the ethyl and n-butyl esters, but no amide, are described
as substituents in position 3.
We have now observed that the introduction of an ester or an amide in position 1
or 3 is not equivalent from the point of view of their reactivity and that, in
particular, the derivatives substituted in position 3 are sensibly more active.
Surprisingly, moreover, the overall performance (i.e. reactivity, solubility and
compatibility with photopolymerizable systems and low extractability) of the esters,
thioesters and amides in 3 of thioxanthone is strongly dependent from the length
of the al y l chain bonded to the oxygen or nitrogen. These chains, when
appropriately selected, reduce or eliminate the extractability of the derivatives of
thioxanthone in formulates, thus maintaining superior compatibility and reactivity.
The object of the present invention are therefore specific esters and amides of
thioxanthone, which bear alkyl chains of appropriate length and can be used as
photoinitiators or sensitizers in photopolymerizable systems, in particular for the
preparation of coatings compatible with the food use.
By sensitizer w e mean a compound that, through a process of energy transfer,
activates the photoinitiator at a wavelength where the photoinitiator alone would
not be reactive.
Description of the invention
It is an object of the present invention a photopolymerizable composition
comprising from 70 to 99.9 % by weight, preferably from 70 to 98.9% by weight,
of at least one photopolymerizable compound and from 0. to 20 % by weight,
preferably from 0.2 to 7% by weight, of at least one derivative of thioxanthone of
formula I
where
R is OR,, SR , or NR2R3;
R' is hydrogen or a linear or branched alky/ chain C -C ;
R is a linear or branched alkyl chain C8-C ;
R2 and R3 can be equal or different and are a linear or branched chain C4-Cs or can
be combined in order to form a ring, optionally substituted, with 5 or 6 members
and containing up to two further heteroatoms.
It is a further object of the present invention a derivative of thioxanthone of
formula I
wherein R is OR and R is a C 2 linear alkyl chain, or R is NR2R3 and R2 and R3 are
isobutyl, and R' is hydrogen or R' is in the position 7 and is methyl.
Another object of the invention is the use of the above described
photopolymerizable compositions in the preparation of food packaging, in
particular as photocrosslinkable pigmented inks.
A further embodiment of the present invention is a method for coating a substrate
comprising the following steps:
I . applying onto said substrate the above photopolymerizable composition
according to the invention in such an amount to obtain, after
polymerization, a coating with a thickness comprised between 0.2 and 100
microns;
II. photopolymerizing the composition with a light source having emission
bands in the UV-Visible region.
It is finally an object of the invention the use of the substrates coated according to
the method described above in the preparation of food packaging.
Detailed description of the invention
For the preparation of the photopolymerizable composition, the derivatives of
thioxanthone of formula I in which R is O or 2 3 are preferred.
Preferably R' is hydrogen or R' is in position 7 and is methyl.
The derivatives in which R is a linear C 2 chain and R2 and R3 are both a isobutyl
group are particularly preferred.
The derivatives of thioxanthone of formula I according to the invention can be
prepared according conventional methods known to the experts in the art.
In articular they can be prepared cyclizing compounds of formula II or 
in which R' it has the same meaning of formula I, according the scheme
eq. I
The cyclization of compounds can be obtained in the presence of protic acids or
Lewis' acids at temperatures comprised between -50 °C and 0 °C and preferably
between - 0 °C and 50 C° for a period of time adequate to complete the reaction,
which is normally comprised between min and 2 hours.
Examples of suitable protic acids are concentrated sulfuric acid, chlorosulfonic acid,
methanesulfonic acid and polyphosphoric acid. Examples of Lewis' acid are
aluminum trichloride, aluminum tribromide, boron trifluoride, zinc chloride and
iron trichloride.
The compounds of formula II can be prepared by reacting a compound of formula
III or IV, or one of their derivatives, with a compound of formula V
In the compounds III and IV R' has same meaning of formula I, Y can be OMe, OEt,
CI, Br or OY' where Y' can be hydrogen, an alkaline or alkaline-earth metal, and Z
can be a thiol group, one of its salts with an alkaline or alkaline-earth metal, or one
of its chlorinated derivatives.
In the compound of formula V the group X is a good leaving group, for example
an atom of CI, Br, and Yassumes the same meaning as described before.
The reaction is carried out at a temperature comprised between 0 and 300 °C, but
preferably between 50 and 200 °C in the presence of an organic solvent,
preferably aprotic solvents such as dimethyl sulfoxide, ,-dimethyl formamide,
N,N dimethyl acetamide, N-methyl pyrrolidone, and in the presence of copper
powder and anhydrous potassium carbonate, as described in US 3,904,647,
according to the reaction scheme:
Examples of compound III that can be used are thiosalicylic acid and its derivatives,
while examples of compound IV are dithiosalicylic acid and its derivatives.
The compounds of formula can be obtained, as described in US 4,505,794,
reacting a compound of formula VI, or a its derivative, with a formula compound
VII,
in which R', X, Y and Z have the meaning as previously described, according to the
scheme:
The formation of the diphenyl thioether may be obtained by reacting a salt of a
thiol group with an alkaline-earth metal with a nitro-benzene substituted in a highboiling
polar organic solvent, such as those indicated before, or a mixture thereof.
The mixture is maintained at a temperature preferably comprised between 50 °C
and 0 °Cfor a period of time sufficient to complete the reaction, usually between
2 and 7 hours.
The preparation of the ester or the thioester of formula I can be carried out by
reacting the carboxylic acid obtained in Eq. I or one of its derivatives, as an
example its acyl chloride, with an alcohol or a thiol, optionally in organic solvent
such as toluene or methylene chloride, but the reaction is preferably carried out
using a n excess of the alcohol or thiol a t the reflux temperature of the reaction
mass. The use of carboxylic acid requires the presence of a dehydrating agent such
as gaseous HCI or concentrated sulphuric acid, while the use of a n acyl chloride
requires the presence of an organic base such as triethyl amine o r pyridine.
The secondary amides of formula I are obtained by reacting the carboxylic acids
obtained in eq. I or one of its derivatives with the corresponding secondary amine
in a suitable inert solvent like methylene chloride, toluene, dioxane, optionally in
the presence of a n excess of the amine at a temperature comprised between 20
and OCTC.
The conversion of the acid obtained in eq. I in one of its derivatives, in particular in
an acyl chloride, can be obtained using chlorination agents such as thionyl
chloride, oxalyl chloride, phosphorus pentachloride, optionally in the presence of
an inert solvent, employing a n excess of the chlorination agent.
The photopolymerizable compositions of the invention can also conveniently
include a coinitiator, which is a molecule that acts as hydrogen donor that
increases the polymerization rate. The coinitiators are known in the art and are
typically alcohols, thiols, amines or ethers that have a n available hydrogen,
bonded to a carbon adjacent to the heteroatom. Such coinitiators are generally
present in a n amount comprised between 0.2 and % by weight, preferably from
0.2 to 8% by weight. Suitable coinitiators include, but are not limited to, aliphatic,
cycloaliphatic, aromatic, aryl-aliphatic, heterocyclic, oligomeric o r polymeric
amines. They can be primary, secondary or tertiary amines, for example butyl
amine, dibutyl amine, tributyl amine, ciclohexyl amine, benzyldimethyl amine, dicyclohexyl
amine, triethyl amine, phenyl-diethanol amine, pyperidine, pyperazine,
morpholine, pyridine, quinoline, esters of dimethylamino benzoic acid, Michler's
ketone (4,4'-bis-dimethyl aminobenzophenone). For food packaging, it is advisable
to use non-extractable coinitiators, for example Esacure A 98 (bis-N,N-[4-
dimethylaminobenzoyl) oxyethylen- -yl]-methylamine) from Lamberti S.p.A., IT.
The photopolymerizable composition of the invention can also conveniently
include other photoinitiators. Examples of photoinitiators which can be used in
combination with the derivatives of thioxanthone of formula I are benzophenones,
ketosulfones, -aminoketones, benzoin and benzoin ethers, benzil ketals, -
hydroxyketones.
Preferred photoinitiators, suitable for food packaging, belong to the classes of a -
hydroxyketones, ketosulfones and bi-functional photoinitiators, for example
Esacure 100 and Esacure ONE (commercialized by Lamberti S.p.A., IT).
Additional photoinitiators can be added to the photopolymerizable composition
of the invention in an amount comprised between 0.5 and 10% by weight,
preferably between 1and 5% by weight.
In a particularly preferred embodiment of the invention the derivatives of
thioxanthone of formula I are used as sentitizers of sensitizable photoinitiators in
photopolymerizable compositions.
In this case, the photopolymerizable composition comprises from 70 to 98.9 % by
weight of at least one photopolymerizable compound, from 0. to 5% by weight
of at least one thioxanthone derivative of formula I, from 1 to a 10% by weight at
least one sensitizable photoinitiator, for example a ketosulfone or an a -
aminoketone and, possibly, a coinitiator
The preferred sensitizable photoinitiator is l-[4-[(4-benzoyl-phenyl)-thio]-phenyl],2-
methyl,2-[(4-methyl-phenyl)-sulfonyl]-propan- 1-one (Esacure 00 ).
In the above particularly preferred compositions, the coinitiator is generally present
in an amount comprised between 0.2 and % by weight, preferably from 0.2 to
8% by weight.
By photopolymerizable compounds we mean a monomer, oligomer, prepolymer,
typically ethylenically unsaturated compounds or mixtures thereof, capable of
undergoing radical polymerization. Also monomer combinations, oligomers and
prepolymers with different degrees of functionality can be used.
The monomers and oligomers of the photopolymerizable composition of the
present invention can be chosen between vinyl ethers; N-vinyl pyrrolidone; monoand
poly-functional allyl ethers such as trimethylol propane diallyl ether; styrenes
and alpha-methyl styrenes; esters of (meth)acrylic acid with aliphatic alcohol,
glycols, polyhydroxylated compounds such as pentaerythritol or trimethylol
propane; ester of vinyl alcohol with acrylic or aliphatic acids, derivatives of fumaric
and maleic acids.
Suitable oligomers or prepolymers for the present invention comprise, for example,
polyesters, polyacrylates, polyurethanes, epoxy resins, polyethers with acrylic,
maleic or fumaric functionalities.
Besides the above-mentioned compounds, other components normally used in
the field and known to the experts in the art can be added to the
photopolymerizable composition of the invention. For example, thermal stabilizers,
photo-oxidation stabilizers, anti-oxidants, fillers, dispersants, pigments, coloring
and/or opacifying substances and other additives of general use. Others
components of the photopolymerizable composition of the invention can be nonphotopolymerizable
polymers present as chemically inert substances, as an
example nitrocellulose, polyacrylic esters, polyolefins etc. Preferred components are
those with reactivity and toxicity characteristics suitable for food packaging.
The derivatives of the thioxanthone of formula I work both in transparent
photopolymerizable compositions and in non-transparent or pigmented
compositions and are useful for example also for the preparation of
photocrosslinkable inks.
Thioxantone derivatives of formula I wherein R is R is O R and R is a C 2 linear alkyl
chain, or R is R2R3 and R2 and R3 are isobutyl, and R' is hydrogen or R' is in the
position 7 and is methyl are particularly suitable for the preparation of pigmented
photocrosslinkable inks, especially for food packages.
The compositions claimed in the present invention are useful in the treatment of
metallic, wood, paper and plastic surfaces.
Examples of suitable light source for photopolymerizing the compositions of the
invention are mercury or super actinic lamps; metal-halogen, i.e. iron iodide, or
excimers lamps; LED with emission bands in the UV-Visible region and in particular
between 180 and 450 nm or laser emitting at an adequate wavelength (for
example 405 nm) and with a good power. Among the suitable light sources, solar
light and other sources which emit electromagnetic radiation with wavelength
from 180 nm to the IR zone can be also included.
The photopolymerizable composition of the present invention is in general
particularly suitable for the preparation of coatings compatible with the food
contact use and in particular for the preparation of photopolymerizable inks used
in food packaging.
Examples of preparation of derivatives of thioxanthone of formula I and
photopolymerizable compositions according to the invention, only for illustrative
purpose and not limitative, are reported in the following paragraphs.
Examples
Preparation of 7-methyl-9-oxo-9H-thioxanthene-3-carboxylicacid
10 g (80.65 mmoles) of 4-methylbenzenethiol are added to a three-neck flask
equipped with a thermometer and a condenser and dissolved in 50 cc of dimethyl
formamide. 3.39 g (84.75 mmoles) of finely ground sodium hydroxide are added
and the solution is left to rest at room temperature under constant stirring for half
hour. Then, 18.89 g (79.04 mmoles) of dimethyl 2-nitrobenzene-l,4-dicarboxylate
are added maintaining the temperature at 75 °C for 1.5 hours. Once the reaction is
terminated, the mixture is cooled down and 100 ml of water are added . The
precipitate formed is filtered and stirred for 1 hour under refluxing with a solution
of 9.33 g ( 6.67 mmoles) of potassium hydroxide in 20 ml of methanol.
The mixture is cooled and poured in water containing activated carbon for
decoloration, after one hour of stirring the mixture is filtered on celite. The organic
solvent is distilled on a rotary evaporator and the residue is washed with
methylene chloride (twice ) . The aqueous phase is then acidified with hydrochloric
acid 37%. The precipitate obtained is filtered on a buckner, washed with water
and dried in a vacuum oven to a final yield of 2 .72 g (yield : 95%) of 2-(ptolylthio)
benzene- 1,4-dicarboxylic acid as a white solid
The 2-(p-tolylthio) benzene- 1,4-dicarboxylic acid is transferred slowly to a flask,
containing 100 ml of chlorosulfonic acid. The temperature is maintained between
the 5 and 0 °C with an ice-bath. At the end of the addition, the solution is left to
rest for maturation and after 1 hour is poured in water and ice. The precipitate is
filtered, washed with water and dried in a vacuum oven obtaining 9.69 g (yield :
96.7%) of 7-methyl-9-oxo-thioxanthene-3-carboxylic acid as a yellow solid.
Melting point>250°C
Preparation of 7-methyl-9-oxo-thioxanthene-3-carbonyl chloride
8 g of 7-methyl-9-oxo-thioxanthene-3-carboxylic acid are suspended in 00 ml of
toluene containing 7 drops of DMF and 7.2 g of thionyl chloride. The temperature
is kept at 75-80 °C and the solution is stirred for approximately 1 hour. The
reaction is completed by adding a further 2 g of SOCI2 and stirring for another ½
hour.
The solvent is distilled in a rotary evaporator and the residue is dissolved in CH2CI2,
obtaining a yellow solution used as such in the following reactions.
Example . Synthesis of dodecyl-7-methyl-9-oxo-9H-thioxanthene-3-carboxylate
1.5 g (8.06 mmoles) of dodecan- l-ol and 1.0 g (9.90 mmoles) of triethyl amine are
added to a CH2C 2 solution containing 2.26 g (7.4 mmoles) of 7-methyl 9-oxothioxanthene-
3-carbonyl chloride. After approximately 1 hour at room
temperature under stirring, the mixture is poured in water, the organic phase is
separated and washed again with water. The organic phase is then separated,
dehydrated and after purification on a flash column (Si0 2 - eluent : CH2CI2: AcOEt
8:2) it is dried, obtaining 1.62 g (49.8%) of a yellow solid with the following
spectral properties:
Ή -NMR (CDCI3): (ppm): 8.65 (d, 1H); 8.4 (s, 1H); 8.2 (s, H); 8.0 (d, H); 7.45 (m,
2H); 4.35 (t, 2H); 2.45 (s, 3H); .8 (m, 2H); 1.5-1 . (bm, 8H); 0.85 (t, 3H).
Example 2 (Comparative). Synthesis of pentyl 7-methyl- 9-oxo-9H-thioxanthene-3-
carboxylate
1.0 g ( 11.36 mmoles) of pentan-l-ol (containing also -pentan-2-ol) and 1.0 g (9.90
mmoles) of triethyl amine chloride are added to the CH2C 2 solution containing
2.26 g (7.4 1 mmoles) of 7-methyl-9-oxo-thioxanthene-3-carbonyl chloride. After
approximately 1 hour at room temperature under stirring, the mixture is poured in
water, the organic phase is separated and washed again with water. The organic
phase is then separated, dehydrated and after purification on a flash column (Si0 2
- eluent: CH2CI2:AcOEt 8:2) it is dried, obtaining .74 g (7 .6%) of a yellow solid
with the following spectral properties :
Ή -NMR (CDCI3): (ppm): 8.65 (d, 1H); 8.4 (s, 1H); 8.2 (s, 1H); 8.0 (d, H); 7.45 (m,
2H); 4.35 (t, 2H); 2.45 (s, 3H); .8 (t, 2H); .4 (m, 4H); 0.95 (t, 3H).
Example 3 (Comparative). Synthesis of methyl 7-methyl-9-oxo-9H-thioxanthene-3-
carboxylate
1.0 g (3 .3 mmoles) of methanol and 1.0 g (9.90 mmoles) of triethyl amine are
added to the CH2CI2 solution containing 2.26 g (7.4 mmoles) of 7-methyl 9-oxothioxanthene-
3-carbonyl chloride. After approximately 1 hour at room
temperature under stirring, the mixture is poured in water, the organic phase is
separated and washed again with water. The organic phase is then separated,
dehydrated and after purification on a flash column (Si0 2 - eluent : CH2CI2:AcOEt
8:2) it is dried, obtaining .22 g (58%) of a yellow solid with the following spectral
properties:
Ή -NMR (CDCI3): (ppm): 8.65 (d, 1H2H); 8.4 (s, H); 8.25 (s, H); 8.0 (s, 1H); 7.45
(m, 2H); 4.0 (s, 3H); 2.5 (s, 3H).
Example 4 (Comparative). Synthesis of a y 7-methyl-9-oxo-9H-thioxanthene-3-
carboxylate
1. 13 g ( 9.4 mmoles) of prop-2-en-l-ol and 2.06 g (20.4 mmoles) of triethyl amine
are added to the CH2CI2 solution containing 5.34 g ( 18.5 mmoles) of 7-methyl-9-
oxo-thioxanthene-3-carbonyl chloride. After approximately 1 hour at room
temperature under stirring, the mixture is poured in water, the organic phase is
separated and washed again with water. The organic phase is then separated,
dehydrated and dried after purification on a flash column (Si0 2 - eluent: CH2CI2) .
3.02 g (52.6%) of a yellow solid with the following spectral properties are
obtained:
Ή -NMR (CDCI3): (ppm): 8.65 (d, H); 8.35 (s, H); 8.2 (s, H); 8.0 (d, H); 7.45 (m,
2H); 6.05 (m, H); 5.5-5.3 (dd, 2H); 4.85 (d, 2H); 2.45 (s, 3H).
Example 5. S nthesis of ,-disobutyl 7-methyl-9-oxo-9H-thioxanthene-3-
carboxamide
A solution of 5.0 g (38.8 mmoles) of diisobutyl amine and 5.0 g (49.5 mmoles) of
triethyl amine in 40 cc of CH2CI2 is poured drop by drop in the CH2CI2 solution
containing 7.47 g (25.9 mmoles) of 7-methyl 9-oxo-thioxanthene-3-carbonyl
chloride. After approximately 1 hour at room temperature under stirring, the
mixture is poured in water, the organic phase is separated and washed again with
water. The organic phase is then separated, dehydrated and dried after
purification on a flash column (SiO - eluent CH2CI2:AcOEt 9: ) . 5.4 g (54.7%) of a
yellow solid with the following spectral properties are obtained:
Ή -NMR (CDCI3): (ppm): 8.65 (d, 1H); 8.4 (s, H); 7.5 (s, 1H); 7.45 (d, 2H); 7.35 (d,
H); 3.35 (d, 2H); 3.05 (d, 2H); 2.45 (s, 3H); 2. (m, H); 1.85 (m, H); 1.0 (d, 3H);
0.75 ( , 3H).
Example 6. Synthesis of the 4-methyl-piperazinyl 7-methyl-9-oxo-9H-thioxanthene-
3-carboxamide
A solution of 3.0 g (3 mmoles) of 4-methyl piperazine and 3. 1 g (3 mmoles) of
triethyl amine in 40 cc of CH2CI2 is poured drop by drop in the CH2CI2 solution
containing 7.47 g (25.9 mmoles) of 7-methyl-9-oxo-thioxanthene-3-carbonyl
chloride. After approximately 1 hour at room temperature under stirring, the
mixture is poured in water, the organic phase is separated and washed again with
water. The organic phase is then separated, dehydrated and dried after
purification on a flash column (Si0 2 - eluent: CH2CI2:AcOEt 9. ) obtaining 4.63 g
(50.8%) of a yellow solid, with the following spectral properties:
Ή -NMR (CDCI3) : (ppm): 8.65 (d, H); 8.4 (s, H); 7.6 (s, H); 7.5-7.4 (m, 3H); 3.85
(bs, 2H); 3.45 (bs, 2H); 2.55 (bs, 2H); 2.45 (s, 3H); 2.4 (bs, 2H); 2.3 (s, 3H).
Preparation of 7-methyl-9-oxo-9H-thioxanthene-1-carboxylicacid
28.Og (0.23 moles) of 4-methylbenzenethiol are dissolved in 80 cc of dimethyl
formamide. 14.8 g (0.26 moles) of finely ground potassium hydroxide are added
and the solution is stirred at room temperature for half hour.
Then, 48.8 g (0.20 moles) of dimethyl-3-nitrophthalate are added at 75 °C . After 3
hours the reaction is complete. After cooling 400 ml of water are added. The
organic phase is extracted with diethyl ether, dried and the solvent distilled on a
rotary evaporator, then purified by flash chromatography (Si0 2 - eluent:
toluene. AcOEt 8:2) obtaining .66 g of a yellow oil. .60 g of the yellow oil was
dissolved in 20 ml of methanol in presence of 5 g (75.8 mmoles) of potassium
hydroxide and stirred under reflux for 1hour in.
The mixture is cooled and poured in diluted chloridric acid; the organic phase is
extracted with diethyl ether. The organic solvent is distilled off obtaining .32 g
(4.88 mmoles) (90.4%) of 3-(p-tolylthio) benzene- 1,2-dicarboxylic acid as a white
solid.
The 3-(p-tolylthio) benzene- 1,2-dicarboxylic acid is slowly added to 18 g of
chlorosulfonic acid cooling at 5 and 0 °C with an ice-bath. After 1 hour the
mixture is poured in iced water . The precipitate is filtered, washed with water and
dried obtaining 1.20 g (87.7%) of 7-methyl-9-oxo-9H-thioxanthene - l-carboxylic
acid as a yellow solid.
Ή -NMR (DMSO): (ppm): 8.4 (d, 1H); 7.85 (d, 1H); 7.35 (t, 1H);7. (s, 1H); 7.5-7.4
(m, 2H); 2.45 (s, 3H).
Preparation of 7-methyl-9-oxo-9H-thioxanthene- 1-carbonyl chloride
0.2 1 g (0.78 mmoles) of 7-methyl-9-oxo-9H-thioxanthene - l-carboxylic acid are
suspended in 30 ml of toluene containing 2 drops of DMF and 0.35 g of thionyl
chloride. After stirring for 1 hour at 80°C the mass is cooled to room
temperature obtaining a yellow solution of 7-methyl-9-oxo-9H-thioxanthene -lcarbonyl
chloride.
Example 7. Synthesis of N,N-diisobutyl-7-methyl-9-oxo-9H-thioxanthene -lcarboxamide
(Comparative)
1.0 g (7.75 mmoles) of diisobutyl amine is dropped into a toluene solution of 7-
methyl-9-oxo-9H-thioxanthene-l-carbonyl chloride (0.22g, 0.78 mmoles).
After 2 hours at room temperature under stirring, the mixture is poured in water,
the organic phase is separated and washed with water. A crude oil is obtained
after evaporation of the solvent. 11.5 mg of a yellow solid are isolated by flash
chromatography of the crude oil (Si02 - eluent: CH2CI2:MeOH 96:4).
Ή -NMR (CDCI3): (ppm): 8.40 (d, 1H); 7.55 (d, 2H); 7.35 (s, 1H);7.25 (m, 3H); 3.5
(d, 2H); 3.0 (m, 2H);2.5 (s, 3H); 2.45-2.3 (m, 1H); 2.0- 1.75 (m, 1H); 1.1 (m, 6H); 0.75
(m, 6H).
Example 8. Synthesis of dodecyl 7-methyl-9-oxo-9H-thioxanthene- -carboxylate
(Comparative)
0.43 g (2.3 mmoles) of -dodecyl alcohol are added to a toluene solution
containing 0.22 g (0.76 mmoles) of 7-methyl-9-oxo-9H-thioxanthene- l-carbonyl
chloride. After stirring 1 hour at room temperature , the mixture is poured in water,
the organic phase is separated and washed with water. After avaporati on of the
solvent the oil is purified by flash chromatography (Si02 - eluent : Petroleum
Ether: AcOEt 8:2) obtaining 50 mg of a yellow solid.
Ή -NMR (CDCI3) : (ppm): 8.40 (d, H); 7.6 (d, 2H); 7.40 -7.30 (m, 2H); 4.45 (t, 2H);
2.45 (s, 3H); .8- .7 (m, 2H); 1.5- 1. (bm, 8H); 0.85 (t, 3H).
Applicative tests.
Evaluation of formulability through solubility in methylene chloride.
10 g of the thioxanthone derivatives under investigation are weighed and
suspended in the same amount of solvent; the mixture is maintained under
stirring at room temperature.
After 2 m the clearness of the solution is evaluated: if the sample is not dissolved
further aliquots of solvent are added, keeping the mixture under stirring for two
min after each addition until complete solubilization. The results are shown in
Table 1.
Table 1
* Comparative
The derivatives of the thioxanthone of the invention turn out to be sufficiently
soluble for application as photoinitiators.
Evaluation of the derivatives of thioxanthone in a pigmented photopolymerizable
composition by means ofFT-IR.
Pigmented photopolymerizable compositions are prepared by mixing 3% by
weight of both the photoinitiators of formula I (Examples 1-6) and the coinitiator
Esacure A 98 (bis-N,N-[4-dimethyl aminobenzoyl)oxyethylen- l-yl]-methylamine),
commercialized by Lamberti S.pA and up to 00% by weight of a cyan ink for o ff
set inking.
Isopropyl thioxanthone (ITX) is chosen as reference photoinitiator.
The photopolymerizable compositions are milled with a three cylinders mill
(laboratory scale) in order to homogenize the mix and applied with a thickness of
3 [Mm on a soft polyethylene substrate by means of a film coater (RK Print Coater
Instrument Ltd).
The sample, placed in the sample lodgment of a FT-IR (FT-IR 430-Jasco), is exposed
to a Mercury/Xenon Vapors light source at high pressure to 20 W/cm (L8868
Light-cure, Hamamatsu) set at a distance of 8 cm from the sample and at an angle
of 30°.
R spectra are acquired at constant time intervals during the photopolymerization
and the reduction over time of the peak area at 408 cm assigned to the acrylic
double bond was determined by IR software (Perkin Elmer, Spectrum ONE v. 2.0).
This allows to quantify the degree of polymerization over the time and therefore
the efficiency of the photoinitiator.
The results as % degree of polymerization over the time are reported in Table 2.
Table 2
* Comparative
The derivatives of thioxanthone of Examples 1, 5 and 6 have similar or greater
effectiveness in comparison with ITX.
The compounds described in the examples were evaluated also as sensitizer in a
pigmented composition as described below.
Pigmented photopolymerizable compositions are prepared by mixing 3% by
weight of both Esacure 100 and coinitiator Esacure A 98 (both commercialized
by Lamberti S.p.A.), 0,5% by weight of derivatives of thioxanthone of the Examples
listed in Table 1and up to 100% by weight of a cyan ink for off-set inking.
ITX is used as reference sensitizer.
The photopolymerizable compositions are milled with a three cylinders mill
(laboratory scale) in order to homogenize the mix and applied with a thickness of
3 [Jim o n a soft polyethylene substrate by means of film coater (RK Print Coater
Instrument Ltd).
The sample, placed in the sample lodgment of a FT-IR (FT-IR 430-Jasco), is exposed
to a Mercury/Xenon Vapors light source at high pressure to 20 W/cm (L8868
Light-cure, Hamamatsu) set at a distance of 8 cm from the sample with an angle of
30°.
IR spectra were acquired at constant time during the photopolymerization and the
reduction over the time of the area of the peak at 1408 cm assigned to the acrylic
double bond is determined with the help of a IR software (Perkin Elmer, Spectrum
ONE v. 2.0).
This allows to quantify the degree of polymerization over time and therefore the
efficiency of the photoinitiator.
The results as %degree of polymerization over time are reported in Table 3.
The effectiveness as sensitizer of the derivatives of thioxanthone according to the
invention is higher or only slightly lower than the effectiveness of ITX.
Evaluation of "through-cure"
The "through cure" test evaluates the degree of cross-linking of the deeper layers
of the formulate (film) spread on the substrate. The film is considered completely
crosslinked when it is not detached from the substrate or damaged by the "thumb
twist test". The test is carried out at various speeds of exposure to UV source. The
higher the speed the higher the reactivity of the system.
Table 3
* Comparative
The products described in the examples were tested both as photoinitiators and
sensitizers. For the evaluation as photoinitiator the following formulation is
employed (by weight): 3% of derivative of thioxanthone of formula I, 3% of
Esacure A 98, up to 100% with cyan ink for off-set printing. For the evaluation as
sensitizers the formulation is composed as follows (by weight): 0,5% of derivative
of thioxanthone of formula I, 3% of Esacure A 98, 3% of Esacure 00 , up to 00%
with cyan ink for off-set printing.
The resulting mixtures are milled with a three cylinders mill (laboratory scale) and
applied on a coated cardboard with a thickness of 3 m by means of film coater
(RK Print Coater Instrument Ltd), then exposed at different speed to a mercury
vapors lamp at high pressure 20 W/cm.
ITX, in the same amounts, is chosen as reference.
The result are reported in Table 4.
Table 4
* Comparative
The derivatives of the thioxanthone of the invention have an activity comparable
to ITX, both as photoinitiators and as sensitizers.
Evaluation of the extractability in off-setprinting.
The same formulations prepared for the "through cures" (photoinitiator) were
applied on coated cardboard with thickness 3 m (3 g/m 2; printed area 7 .4 cm2)
by means of a film coater (RK Print Coater Instrument Ltd) and exposed to a
mercury vapor lamp at high pressure with a power of 60 W/cm at a speed of 30
m/min. After photopolymerization the coated surface is put in contact with
another coated cardboard and submitted to a pressure of 20 kg for 0 days at
room temperature. At the end of this period the off-set printed cardboard is
dipped in 200 ml_ of a mixture ethanol/water 0/90 or 95/5 and stored for 0 days
at the temperature of 40 °C.
The amount of derivatives of thioxanthone extracted from the contact solution is
determined by means of HPLC (HPLC Method: Column Water Novapak C 8,
mobile phase in min from 30%/70% Acetonitrile/ 0.08 M Phosphoric Ac. to
90%/ 0% Acetonitrile/ 0.08 M Phosphoric Ac, 3 0 nm). Every test was executed
in triplicate and the results (mean values) are reported in Table 5.
Table 5
* Comparative
The compounds described in examples 1, 5 and 6 do not show migration in the
contact solution contrary to both ITX and the compound with a reactive double
bond described in Example 4.
Compa son of the reactivity of the 1and 3 derivatives of thioxanthone by means
of Photo DSC
The compound of Example 1 (dodecyl 7-methyl-9-oxo-9H-thioxanthene-3-
carboxylate) and the compound of Example 8 (dodecyl 7-methyl-9-oxo-9Hthioxanthene-
l-carboxylate, comparative) were formulated and evaluated by
PhotoDSC.
The compound of Example 5 (N,N-diisobutyl-7-methyl-9-oxo-9H-thioxanthene-3-
carboxamide) and the compound of Example 7 (N,N-diisobutyl-7-methyl-9-oxo-9Hthioxanthene-
l-carboxamide, comparative) were also formulated and compared
by PhotoDSC.
The formulations were prepared dissolving in tripropylene glycol diacrylate the
compounds described in the Examples 1, 8, 5 and 7 at a concentration of 0. 1%
w/w and EDB (Ethyl 4-dimethylamino-benzoate) at a concentration of 0. % w/w.
Photo DSC test.
About mg of formulation (exactly weighted) was kept into a DSC aluminum
panel and analyzed by a Mettler DSC 1calorimeter equipped with a 400nm LED
with a power of 450 mW. The LED was set in order to irradiate the formulation
with an intensity of 24.3 mW/cm
Results
During the exposition to LED at 400nm the heat developed from the
polymerization of formulations prepared with the compounds described in the
Examples 1, 8, 5 and 7 was recorded as peak height and peak area () . The peak
height is proportional to the rate of polymerization: higher is the peak - faster is
the polymerization.
The results are reported in Table 6.
The comparison of the two formulations obtained with the esters isomers 3
(Example 1) and the ester isomer 1 (Example 8) demonstrate that the isomer 3 is
about 1,5 times more reactive than the isomer 1, and the of the polymerization
of isomer 3 is 1.2 higher than the of the polymerization of isomer .
The same effect was observed comparing the two formulations obtained with the
amide isomer 3 (Example 5) and amide isomer 1 (Example 7). The amide isomer 3
was 3.5 times more reactive than the amide isomer 1and the of amide isomer
3 was about 2 times higher than the of isomer .
Tab. 6.
Compound Peak height (peak
from (W/g) area) (J/g)
Example
1 58,9 266,4
8 38,4 208,5
5 39,0 224,8
7 11, 1 111,4
CLAIMS
1. Photopolymerizable composition comprising from 70 to 99.9 % by weight
at least one photopolymerizable compound and from 0. to 20 % by weight
of at least one derivative of thioxanthone of formula I
where
Ris OR,, SR, or NR2R3;
R' is hydrogen or a linear or branched alky/ chain Ci-C ;
R is a linear or branched alkyl chain C8-C 6;
R2 and R3 can be equal or different and are a linear or branched chain C -C8
or can be combined in order to form a ring, optionally substituted, with 5 or
6 members and containing up to two further heteroatoms.
2. The photopolymerizable composition according to Claim 1in which the
derivatives of thioxanthone are compounds of formula 1wherein Ris OR
or NR2R3.
3. The photopolymerizable composition according to Claim 2 in which the
derivatives of thioxanthone are compounds of formula 1wherein R' is
hydrogen or R' is in the position 7 and is methyl.
4. The photopolymerizable composition according to Claim 2 or 3 in which
the derivatives of thioxanthone are compounds of formula 1wherein Ris
OR and R is a C 2 linear alkyl chain.
5. The photopolymerizable composition according to Claim 2 or 3 in which
the derivatives of thioxanthone are compounds of formula 1wherein Ris
R2R3 and R2 and R3 are isobutyl.
6. The photopolymerizable composition according to Claim 1or 4 or 5 further
comprising at least one coinitiator.
7. The photopolymerizable composition according to Claim 6 wherein the
coinitiator is (bis-N,N -[4-dimethylaminobenzoyl) oxyethylen- -yl]-
methylamine).
8. The photopolymerizable composition according to Claim 1or 4 or 5
comprising from 70 to 98.9% by weight of at least one photopolymerizable
compound, from 0. to 5% by weight of at least one thioxanthone
derivative of formula I and from 1to 0% by weight at least one sensitizable
photoinitiator.
9. The photopolymerizable composition according to Claim 8 wherein the
sensitizable photoinitiator is l-[4-[(4-benzoyl-phenyl)-thio]-phenyl], 2-methyl,
2-[(4-methyl-phenyl)-sulfonyl]-propan- -one.
10. Derivative of thioxanthone of formula I
wherein R is R is O R and R is a C 2 linear a y chain, and R' is hydrogen or
R' is in the position 7 and is methyl.
11. Derivative of thioxanthone of formula I
wherein R is NR2R3 and R2 and R3 are isobutyl, and R' is hydrogen or R' is in
the position 7 and is methyl.
12. Use of the photopolymerizable compositions of any of the claims from 1to
9 in the preparation of food packaging.