Compounds of the formula ##STR1## wherein R.sub.1 is hydrogen, chlorine, phenyl, dialkylamino of 2-4 carbon atoms or alkyl or alkoxy each of up to 18 carbon atoms; R.sub.2 is hydrogen, chlorine, bromine or alkyl or alkoxy each of up to 4 carbon atoms; R.sub.3 and R.sub.4, which can be the same or different, each is hydrogen or alkyl of up to 6 carbon atoms; R.sub.5 is hydrogen or alkyl or alkanoyl each of up to 4 carbon atoms; and R.sub.6 is hydrogen or methyl, with the proviso that not all of R.sub.1 to R.sub.6 simultaneously are hydrogen, are effective photosensitizers, especially for photopolymerization of unsaturated compounds and for hardening of printing dyes.

BACKGROUND OF THE INVENTION 
Many reactions in organic chemistry are accelerated or in some instances 
even made possible by irradiation with visible or ultra-violet (UV) 
radiation. Such reactions include, for example, fission reactions, e.g., 
in the vitamin D series, rearrangement reactions, e.g., 
cis-transisomerizations, and addition reaction, e.g., of maleic acid to 
benzene. However, the technically most important addition reactions of 
this kind are the photochemically initiated polymerization reactions. 
For all of these reactions, it is necessary that at least a portion of the 
reaction mixture be capable of absorbing irradiated visible or UV 
radiation. When this portion is one of the reaction components, the 
reactions can be carried out without further additives simply by 
appropriate irradiation of the reaction mixture. However, frequently the 
reaction components are not able to absorb a sufficient amount of the 
photochemically effective irradiation. In such cases, substances called 
photosensitizers are frequently added. These do not participate in the 
reaction but are able to absorb the visible UV irradiation and to transfer 
the absorbed energy to one of the reaction components. Important criteria 
for the choice of such sensitizers are, inter alia, the nature of the 
reaction to be carried out, the relationship of the absorption spectrum of 
the sensitizer to the spectral energy distribution of the available source 
of radiation, the solubility of the sensitizer in the reaction mixture and 
the influence on the end product of residues of the sensitizer and/or the 
products resulting therefrom during the photochemical reaction. 
As sensitizers for the photopolymerization of unsaturated compounds, 
previously there have principally been used benzophenone derivatives, 
benzoin ethers, benzil monoacetals and .alpha.-haloacetophenone 
derivatives. However, these substances possess various disadvantages which 
distinctly limit their industrial usefulness. Such disadvantages include, 
in particular, the tendency of monomers of prepolymers to polymerize when 
mixed with photosensitizers of these groups prior to irradiation, i.e., in 
the dark. Consequently, many reaction mixtures containing such sensitizers 
possess only a low stability in the dark. Other compounds from these 
classes possess only a low chemical stability; thus, for example, some 
benzil monoacetals are split even by very small amounts of water, e.g., by 
atmospheric humidity, into benzil and alcohol. Furthermore, others of 
these known sensitizers cause a yellowing of the resultant 
photopolymerized polymers, which, especially in the case of normally 
colorless synthetic resins or in particular in the case of UV-hardened 
printing dyes, is highly undesirable. For this last-mentioned field of 
use, the generally low solubility of the known sensitizers in the monomers 
of prepolymers often plays an important role. Since, as a rule, printing 
dyes contain considerable amounts of colored pigments which absorb a large 
part of the irradiated energy, which is thus unavailable for photochemical 
reactions, a comparatively large amount of sensitizer must be added. 
Frequently, as a result, amounts up to 5 to 10 weight percent of the 
reaction mixture, i.e., the printing dye, must be employed whereas 
otherwise in the synthetic resin industry, in the absence of coloring 
additives, only 1 to 2 weight percent are often completely sufficient. 
Usually even this relatively low concentration can barely be achieved with 
the sparingly soluble known sensitizers. In the case of the much higher 
concentrations necessary in printing dyes, the known sensitizers 
frequently partially crystallize out. In addition to the fact that the 
proportions which have crystallized out no longer act sensitizingly, after 
some time, the resultant crystallites also damage the printing plates 
consisting of relatively soft materials. 
Acetophenone and derivatives thereof have also been suggested and used as 
photosensitizers, especially for photochemical cyclo-additions, [e.g., K. 
GOLLNICK "Type II Photooxidation Reactions" in Advances in Photochemistry, 
Vol. 6, pages 1-122 (Interscience Publishers, New York 1966, Editors: A. 
N. Noyes, G. S. Hammond and J. N. Pitts)]. The results obtained with 
compounds of this class, especially the quantum yields of the 
photochemical reactions sensitized therewith, are mostly markedly poorer 
than, for example, the results obtained with benzophenone. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide photosensitizers, 
especially for the photopolymerization of unsaturated compounds, which, in 
admixture with the other reaction components, are storage stable in the 
dark, which themselves and due to products derived from them do not cause 
yellowing of the reaction products and which possess a solubility which is 
as high as possible in the monomers or prepolymers normally subjected to a 
photopolymerization. 
It is another object of this invention to provide such photosensitizers 
which possess the greatest possible photosensitizing effectiveness in the 
wavelength range of 250 to 500 nm, preferably between 300 and 400 nm. 
Upon further study of the specification and appended, claims, further 
objects and advantages of this invention will become apparent to those 
skilled in the art. 
These objects has been attained by providing, in a method aspect, a method 
of photosensitizing which comprises using compounds of formula (I), 
##STR2## 
wherein R.sub.1 is hydrogen, chlorine, phenyl, dialkylamino of 2-4 carbon 
atoms or alkly or alkoxy of, in each case, up to 18 carbon atoms; R.sub.2 
is hydrogen, chlorine, bromine or alkyl or alkoxy of, in each case, up to 
4 carbon atoms; R.sub.3 and R.sub.4, which can be the same or different, 
each is hydrogen of alkyl of up to 6 carbon atoms; R.sub.5 is hydrogen or 
alkyl or alkanoyl of, in each case, up to 4 carbon atoms and R.sub.6 is 
hydrogen or methyl; wherein, however, all residues R.sub.1 to R.sub.6 are 
not simultaneously hydrogen atoms; 
as photosensitizers, especially for photopolymerization of unsaturated 
compounds, as well as for the UV hardening of photohardenable printing 
dyes. 
In a composition aspect, this invention relates to new compounds of formula 
(II), 
##STR3## 
wherein R.sub.1 is hydrogen, phenyl, dialkylamino of 2-4 carbon atoms or 
alkyl or alkoxy of, in each case, up to 18 carbon atoms; R.sub.2 is 
hydrogen, chlorine, bromine or alkyl or alkoxy of, in each case, up to 4 
carbon atoms; R.sub.3 and R.sub.4 are the same or different and each is 
alkyl of up to 6 carbon atoms or one of R.sub.3 and R.sub.4 is hydrogen; 
and R.sub.5 is hydrogen or alkyl or alkanoyl of, in each case, up to 4 
carbon atoms; with the proviso (a) that R.sub.1 and R.sub.2 are not 
simultaneously hydrogen atoms; (b) that R.sub.1 is not methyl, methoxy or 
phenyl when (i) R.sub.2 is hydrogen and (ii) R.sub.3 and R.sub.4 are both 
methyl or one is hydrogen and the other is methyl; and (c) that R.sub.2 is 
not methyl when (i) R.sub.1 is hydrogen and (ii) R.sub.3 and R.sub.4 are 
both methyl or one is hydrogen and the other is methyl. 
DETAILED DISCUSSION 
In view of the common structural characteristics of conventional 
photosensitizers which, as a rule, contain two possibly substituted phenyl 
nuclei, the aromatic systems of which are cross-conjugated via one or two 
carbon atoms, it is surprising that the hydroxyalkyl ketones to be used 
according to this invention, having only one aromatic ring possess such a 
good photosensitizing action especially in view of the relatively poor 
results previously obtained with acetophenone derivatives as discussed 
above. 
It has now been found that the compounds of formula (I) possess a good 
photosensitizing effectiveness for irradiation in the wavelength region of 
250-500 nm and are clearly more soluble in the monomers or prepolymers 
generally employed for photopolymerizations, e.g., based upon unsaturated 
esters, such as acrylic acid esters, methacrylic acid esters or maleic 
acid esters, or styrene, than are most of the sensitizers previously 
employed. Furthermore, the solutions of the photosensitizers of the 
formula (I) in these monomers and prepolymers generally possess a better 
storage stability in the dark than, for example, analogous solutions of 
benzoin ethers. Finally, in photopolymerizations using the sensitizers of 
formula (I), yellowing of the polymers is not observed or is found to only 
a substantially smaller degree than for the conventional sensitizers. 
In formula (I), R.sub.1 is preferably alkyl or alkoxy of up to 18 carbon 
atoms, preferably 1-12 carbon atoms, a chlorine atom, dialkylamino of 2-4 
carbon atoms or phenyl. Especially preferred as R.sub.1 are alkyl groups 
of up to 12 carbon atoms of the dimethylamino group. R.sub.2 is most 
preferably hydrogen. For the other embodiments R.sub.2 is preferred in the 
3-position. It can also preferably be a chlorine or bromine atom or a 
methyl or methoxy group in the 2- or 3-position, preferably in the 
3-position, of the phenyl nucleus. 
For R.sub.3 and R.sub.4, preferably not more than one is a hydrogen atom. 
Especially preferred are compounds in which both residues R.sub.3 and 
R.sub.4 are alkyl groups which together contain 2 to 10, preferably 2 to 8 
carbon atoms. 
R.sub.5 is preferably hydrogen. When it is alkyl or alkanoyl, of these 
methyl, ethyl and acetyl are preferred. 
Finally, R.sub.6 is preferably hydrogen. It is preferably only a methyl 
group when R.sub.1 is hydrogen and R.sub.2 is 2-methyl. 
Consequently, according to this invention, there are especially employed as 
photosensitizers those compounds of formula (I) in which at least one of 
R.sub.1 to R.sub.6 has one of the above-mentioned preferred meanings. Some 
groups of compounds to be used preferably according to the invention can 
be expressed by the following partial formulae (Ia) to (Ip) which 
correspond to formula (I) and wherein the residues not more precisely 
defined are defined as for the formula (I) but wherein 
in (Ia) R.sub.1 is alkyl of 1-12 carbon atoms; 
in (Ib) R.sub.1 is alkyl of 3-12 carbon atoms; 
in (Ic) R.sub.1 is dimethylamino; 
in (Id) R.sub.2 is hydrogen; 
in (Ie) R.sub.2 is 3-chloro-, 3-bromo, 3-methyl or 3-methoxy; 
in (If) R.sub.1 is alkyl of 1-4 carbon atoms and R.sub.2 is as defined in 
(Ie); 
in (Ig) R.sub.3 and R.sub.4 are both methyl; 
in (Ih) R.sub.3 is ethyl and R.sub.4 is n-butyl; 
in (Ii) R.sub.3 is methyl and R.sub.4 is ethyl; 
in (Ij) R.sub.5 is hydrogen; 
in (Ik) R.sub.5 is methyl, ethyl or acetyl; 
in (Il) R.sub.1 is alkyl of 3-12 carbon atoms and R.sub.2 and R.sub.5 both 
are hydrogen; 
in (Im) R.sub.1 is alkyl of 3-12 carbon atoms, R.sub.2 is hydrogen and 
R.sub.3 and R.sub.4 both are methyl; 
in (In) R.sub.1 is alkyl of 1-12 carbon atoms, R.sub.2 is hydrogen, R.sub.3 
is ethyl and R.sub.4 is n-butyl; 
in (Io) R.sub.6 is hydrogen; 
in (Ip) R.sub.1 is hydrogen, R.sub.2 is 2-methyl and R.sub.6 is methyl. 
The foregoing discussion of the entities R.sub.1 -R.sub.6 also applies to 
formula II where applicable. 
The preparation of some of the compounds of formula (I) to be used 
according to this invention is known from Bull. Soc. Chim. France 1967, 
1047-1052; J. Amer. Chem. Soc. 75 (1953), 5975-5978; and Zh. Obshch. Khim. 
34 (1964), 24-28, all of which are incorporated by reference herein. 
However, their outstanding photosensitizing effectiveness is not disclosed 
in these literature references not rendered obvious thereby. The new 
compounds of formula (I) can be prepared analogously to the standard 
processes of organic chemistry described in the mentioned literature 
references. 
In a preferred preparation process, a benzene derivative of formula (III) 
##STR4## 
wherein R.sub.1, R.sub.2 and R.sub.6 are as defined above, is reacted in 
the presence of a Lewis acid, for example, aluminum chloride, with an 
.alpha.-halocarboxylic acid chloride of formula (IV) 
##STR5## 
wherein R.sub.3 and R.sub.4 are as defined above and Hal is a halogen 
atom, preferably chlorine or bromine, and the so obtained 
.alpha.-haloketone of formula (V) 
##STR6## 
wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.6 and Hal are as defined 
above is conventionally saponified to the hydroxyalkylphenone of the 
formula (I) (R.sub.5 =H). When R.sub.3 and R.sub.4 are alkyl, this 
saponification is conducted by simple heating of the .alpha.-haloketone 
(V) with a concentrated solution of an alkali metal hydroxide in a solvent 
miscible with water, such as, for example, methanol, ethanol, isopropanol, 
acetone or dimethyl sulphoxide. If one or both of the residues R.sub.3 and 
R.sub.4 are hydrogen, then, as a rule, it is expedient first to convert 
the .alpha.-haloketone (V), by reaction with a carboxylic acid salt, for 
example, sodium acetate, in an anhydrous organic solvent, into an 
alkanoyloxyalkylphenone of the formula (I) (R.sub.5 =alkanoyl). If 
desired, this is converted by hydrolysis in the presence of a weakly basic 
compound, for example, sodium hydrogen carbonate, into the 
hydroxyalkylphenone (I, R.sub.5 =H). 
Alkanoyloxyalkylphenones of formula (I) (R.sub.5 =alkanoyl) can also be 
prepared by acylation of the hydroxyalkylphenones (I, R.sub.5 =H) with 
suitable carboxylic acid derivatives, for example, carboxylic acid 
anhydrides or halides. 
The alkoxyalkylphenones of formula (I) (R.sub.5 =alkyl) can be prepared, 
for example, by reaction of the .alpha.-haloketones (V) with an 
alcoholate, for example, sodium ethylate, in an anhydrous organic solvent, 
such as, for example, ethanol. 
In addition to the Friedel-Crafts reaction of (III) with (IV), the 
.alpha.-haloketones (V) can also be conventionally prepared by 
halogenation, preferably chlorination or bromination, of a phenone of 
formula (VI) 
##STR7## 
wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.6 are as defined 
above. This process is then preferably employed when the phenone (VI) is 
readily obtainable and no side reactions occur in the halogenation, e.g., 
halogenation of benzyl carbon atoms in R.sub.1, R.sub.2 and/or R.sub.6. 
Furthermore, the hydroxyalkylphenones of formula (I) can be prepared by 
reacting a Grignard compound of formula (VII) 
##STR8## 
wherein R.sub.1, R.sub.2, R.sub.6 and Hal are as defined above, with a 
cyanohydrin compound having a protected oxygen atom of formula (III) 
##STR9## 
wherein Sch--O-- is an hydroxyl group protected against Grignard 
compounds, for example, a tetrahydropyranyl ether group, and R.sub.3 and 
R.sub.4 are as defined above, and subsequently conventionally hydrolyzing 
the reaction mixture in the presence of an acid. This preparation process 
is preferred for the synthesis of compounds of formula (I) in which 
R.sub.1 is a dialkylamino group. 
The photosensitizers according to this invention are employed in the 
customary fashion for such projects, e.g., by analogy to the use of any of 
the conventional photosensitizers mentioned herein. For example, for the 
photopolymerization of unsaturated compounds, 0.05-15 wt. %, preferable 
0.1 to 12 wt. %, of one or more compounds of formula (I), optionally 
together with other conventional photosensitizers is dissolved in the 
unsaturated monomer, its prepolymer or its precopolymer. These solutions 
are then irradiated with visible or UV radiation in the wavelength range 
of 250 to 500 nm, preferably of 300 to 400 nm. Suitable unsaturated 
compounds which can be photopolymerized using the sensitizers of this 
invention include all those having C.dbd.C double bonds which are 
activated by, for example, halogen atoms; carbonyl, cyano, carboxy, ester, 
amide, ether or aryl groups; or by other conjugated double or triple 
bonds. Examples of such compounds include vinyl chloride, vinylidene 
chloride, acrylic acid methyl ester, acrylonitrile, hydroxyethyl acrylate, 
cyclohexyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, 
benzyl acrylate. 2-ethylhexyl acrylate, phenyloxyethyl acrylate, lower 
alkoxyethyl acrylate, tetrahydrofurfuryl acrylate, N-vinylpyrrolidone, 
N-vinylcarbazole, vinyl acetate, styrene, divinylbenzene and substituted 
styrenes. Polyunsaturated compounds, such as trimethylolpropane 
diacrylate, propoxylated bisphenyl-A diacrylate and dimethacrylate and 
1,6-hexanediol diacrylate and pentaerythritol triacrylate can also be 
photopolymerized using the sensitizers of this invention. Suitable 
prepolymers and and prepolymers include, for example, unsaturated 
polyesters, acrylic materials, epoxy materials, urethanes, silicones, 
amine polyamide resins and, in particular, acrylated resins, such as 
acrylated silicone oil, acrylated polyesters, acrylated urethanes, 
acrylated polyamides, acrylated soya bean oil, acrylated epoxy resin and 
acrylated acrylic resin. 
The photopolymerizable compounds or mixtures of this invention can be 
stabilized by the addition of known inhibitors, e.g., hydroquinone, in the 
conventional amounts, without the sensitizer action of the 
photosensitizers according to this invention being notably impaired. 
Furthermore, they can contain pigments or dyestuffs, such as are 
conventional in the photochemical hardening of printing dyes. In this 
case, the amount of sensitizer is chosen to be higher, for example, 6-12 
wt. %, whereas for colorless photopolymerizable products, 0.1-3 wt. % is, 
in most cases, completely sufficient. 
Suitable photosensitizers which are known and can optionally be used 
together with the sensitizers according to this invention include, for 
example, Michler's ketone, (4,4'-bis-[dimethylamino]-benzophenone), 
4,4'-bis-(diethylamino)-benzophenone, p-dimethylaminobenzaldehyde, 
4,4'-bis-(dimethylamino)-benzil, p-dimethylaminobenzophenone, 
p-dimethylaminobenzoin p-dimethylaminobenzil, N-substituted 9-acridanones, 
the amino- (or phenyl-) carbonyl compounds described in U.S. Pat. No. 
3,661,588, the p-aminophenylcarbonyl compounds described in U.S. Pat. No. 
3,552,973, acetophenone, propiophenone, xanthone, benzaldehyde, 
benzophenone, p-chlorobenzophenone, biacetyl, benzil, fluorenone, 
3-nitro-4-chlorobenzophenone-2-carboxylic acid, phenanthrenequinone, 
benzoin and alkyl ethers of benzoin, 2-chlorothioxanthone, 
10-thioxanthenone, 1-phenyl-1,2-propanedione oxime and the esters and 
ethers thereof, isatin, anthrone, hydroxypropyl benzoate, benzoyl benzoate 
acrylate, 2,4-dimethylbenzophenone, benzoyl-biphenyl, acenaphthenoquinone 
and dibenzosuberone. 
Suitable sources of irradiation for effecting the photopolymerization, 
include sunlight or artificial radiation. However, there are 
advantageously also used mercury vapor high or low pressure lamps, xenon 
and tungsten lamps. Laser light sources can also be employed.

Without further elaboration, it is believed that one skilled in the art 
can, using the preceding description, utilize the present invention to its 
fullest extent. The following preferred specific embodiments are, 
therefore, to be construed as merely illustrative, and not limitative of 
the remainder of the disclosure in any way whatsoever. In the following 
examples, all temperatures are set forth uncorrected in degrees Celsius; 
unless otherwise indicated, all parts and percentages are by weight. 
Examples 1 to 6 concern the preparation of compounds of formula (I) to b 
used according to the invention: 
EXAMPLE 1 
Into a suspension of 665 g of aluminum chloride in 2000 ml of 
1,2-dichloroethane are introduced at 0.degree., 740 g of 
.alpha.-chloroisobutyryl chloride (prepared by chlorination of isobutyryl 
chloride in the presence of catalytic amounts of chlorosulphonic acid and 
chloroanil). To this mixture are added dropwise, with vigorous stirring, 
at 0.degree. to 5.degree., 1230 g of commercially available technical 
dodecylbenzene (Marlican.RTM. of Chemische Werke Huels AG, Marl). After 
completion of the dropwise addition, the reaction mixture is stirred at 
this temperature for a further 45 minutes and subsequently stirred into a 
mixture of 1000 g of ice and 400 ml of concentrated hydrochloric acid. The 
organic layer is separated off, washed twice with 300 ml amounts of dilute 
hydrochloric acid, dried over calcium chloride and evaporated. The 
1-(4'-dodecylphenyl)-2-chloro-2-methyl-propanone-(1) remaining behind is 
dissolved in 2000 ml of isopropyl alcohol with stirring and gentle 
heating. This solution is heated to the boil for 11/2 hours, with 
stirring, with 550 ml of 32% aqueous hydroxide solution and subsequently 
poured into 2000 ml of water. The aqueous reaction mixture is extracted 
with 1000 ml of toluene, the extract washed with 1000 ml of 10% aqueous 
sodium chloride solution, dried over sodium sulphate and evaporated. The 
1-(4'-dodecylphenyl)-2-hydroxy-2-methyl-propanone-(1) remaining behind is 
distilled under reduced pressure; b.p..sub.0.01 180.degree.-183.degree.. 
There are prepared analogously: 
1-(4'-hexylphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-octylphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-nonylphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-hexadecylphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-octadecylphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-hexyloxyphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-octyloxyphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-dodecylphenyl)-2-hydroxy-2-ethyl-hexanone-(1), 
1-(4'-dodecylphenyl)-2-hydroxy-2-methyl-butanone-(1), 
1-(4'-chlorophenyl)-2-hydroxy-2-methyl-propanone-(1), b.p..sub.0.1 
117.degree.-118.degree. and 
1-phenyl-2-hydroxy-2-methyl-propanone-(1), b.p..sub.0.3 
86.degree.-88.degree.. 
EXAMPLE 2 
Analogously to Example 1, with 133 g of aluminum chloride in 500 ml of 
dichloroethane, there are prepared from 141 g of .alpha.-chlorosiobutyryl 
chloride and 92 g of toluene, 
1-(4'-methylphenyl)-2-chloro-2-methyl-propanone-(1) and the crude product 
dissolved in 500 ml of anhydrous methanol. A solution of 54 g of sodium 
methylate in 1500 ml of methanol is added dropwise, with stirring, the 
reaction mixture warmed to 60.degree. and then left to stand for 16 hours. 
Subsequently, the precipitated sodium chloride is filtered off and the 
filtrate evaporated. The 1-(4'-methylphenyl)-2-methoxy-2-methylpropanone 
remaining behind is distilled under reduced pressure; there are obtained 
98.4 g with b.p..sub.0.03 75.degree.-77.degree.. 
There are prepared analogously: 
1-(4'-methylphenyl)-2-ethoxy-2-methyl-propanone-(1), 
1-(4'-methylphenyl)-2-butoxy-2-methyl-propanone-(1), 
1-(4'-isopropylphenyl)-2-ethoxy-2-methyl-propanone-(1), 
1-(4'-pentylphenyl)-2-methoxy-2-methyl-propanone-(1), 
1-(4'-methylphenyl)-2-methoxy-2-ethyl-hexanone-(1) and 
1-(4'-dodecylphenyl)-2-ethoxy-2-methyl-propanone-(1). 
EXAMPLE 3 
Analogously to Example 1, with 335 g of aluminum chloride in 1000 ml of 
dichloroethane, from 300 g of toluene and 455 g of .alpha.-chloropropionyl 
chloride there are prepared 550 g of 
1-(4'-methylphenyl)-2-chloropropanone-(1). The crude material is dissolved 
in 3000 ml of ethanol and heated to the boil for 15 hours with 392 g of 
anhydrous potassium acetate. Subsequently, the reaction mixture is 
evaporated under reduced pressure, the residue taken up in 2500 ml of 
diethyl ether and filtered. The filtrate is evaporated and the 
1-(4'-methylphenyl)-2-acetoxy-propanone-(1) remaining behind distilled 
under reduced pressure; yield: 364 g, b.p..sub.0.3 
115.degree.-122.degree.. 
There are prepared analogously: 
4-tert-butyl-.alpha.-acetoxy-acetophenone; b.p..sub.0.3 
140.degree.-143.degree.; and 
1-(4'-tert-butylphenyl)-2-acetoxy-2-methyl-propanone-(1), b.p..sub.0.3 
144.degree.-148.degree.. 
EXAMPLE 4 
A solution of 371 g of 1-(4'-methylphenyl)-2-acetoxypropanone-(1) in 3000 
ml of isopropyl alcohol is mixed with a solution of 151 g of sodium 
hydrogen carbonate in 1200 ml of water and the mixture heated to the boil 
for 15 hours, while stirring. Subsequently, the solvent is distiled off 
under reduced pressure, the residue taken up in 500 ml of water and 
extracted three times with 300 ml amounts of diethyl ether. The combined 
ether extracts are dried over sodium sulphate and evaporated. The 
1-(4'-methylphenyl)-2-hydroxypropanone-(1) remaining behind is distilled 
under reduced pressure; yield: 224 g, b.p..sub.0.3 85.degree.-90.degree.. 
There are prepared analogously: 
1-(3',4'-dimethylphenyl)-2-hydroxy-2-methyl-propanone-(1), b.p..sub.0.6 
88.degree.-90.degree.; 
1-(4'-methoxyphenyl)-2-hydroxy-2-methyl-propanone-(1), b.p..sub.0.1 
125.degree.-129.degree.; 
1-(4'-biphenylyl)-2-hydroxy-2-methyl-propanone-(1), m.p. 85.degree.; 
1-(4'-isopropylphenyl)-2-hydroxy-butanone-(1), 
1-(4'-isopropylphenyl)-2-hydroxy-propanone-(1), 
1-(4'-tert-butylphenyl)-2-hydroxy-propanone-(1) and 
1-(4'-nonylphenyl)-2-hydroxy-hexanone-(1). 
EXAMPLE 5 
To a solution of 0.1 mol of acetone cyanohydrin tetrahydropyranyl ether in 
50 ml of anhydrous tetrahydrofuran is added dropwise, in the course of 40 
minutes, with stirring, a solution of 0.075 mol of 4-dimethylaminophenyl 
magnesium bromide in 100 ml of anhydrous tetrahydrofuran and the reaction 
mixture heated to the boil for a further 1.5 hours. Subsequently, 100 ml 
of 10% aqueous sulphuric acid are added thereto, the mixture again briefly 
heated to the boil and then adjusted to a pH value of about 10 with 10% 
aqueous sodium hydroxide solution. The weakly alkaline reaction mixture is 
shaken out three times with 150 ml amounts of diethyl ether, the combined 
ether extracts are washed out with 100 ml of water, filtered and dried 
over sodium sulphae. After distilling off the ether, there remain 12 g of 
1-(4'-dimethylaminophenyl)-2-hydroxy-2-methyl-propanone-(1), which are 
recrystallized from ethanol, m.p. 115.degree.. 
There are prepared analogously: 
1-(4'-diethylaminophenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-ethoxyphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-butyloxyphenyl)-2-hydroxy-2-methyl-propanone-(1), 
1-(4'-dimethylaminophenyl)-2-hydroxy-2-methyl-butanone-(1), and 
1-(4'-dimethylaminophenyl)-2-hydroxy-2-ethyl-butanone-(1). 
EXAMPLE 6 
(a) To a suspension of 1038 g of anhydrous aluminum chloride in 3000 ml of 
dichloroethane there are first added dropwise at 6.degree.-10.degree., 
with ice cooling, 750 g of isobutyryl chloride and thereafter 900 g of 
tert-butylbenzene. The reaction mixture is left to stand for a further 1 
hour at 6.degree. and then for 15 hours at room temperature. Subsequently, 
it is slowly stirred into a solution of 600 ml of concentrated 
hydrochloric acid in 2400 ml of ice water, the organic phase separafted 
off and the aqueous solution washed out once with 600 ml of 
dichloroethane. The combined organic phases are washed once each with 500 
ml of 5% hydrochloric acid and water, dried over calcium chloride and 
evaporated. The 1(4'-tert-butylphenyl)-2-methyl-propanone-(1) remaining 
behind is distilled under reduced pressure; yield: 1085 g, b.p..sub.0.1 
98.degree.-102.degree.. 
(b) In the course of 1.5 hours, 550 g of chlorine are passed into a 
solution of 1007 g of 1-(4'-tert-butylphenyl-2-methyl-propanone-(1) in 
3000 ml of methanol in the presence of 2 ml of concentrated hydrochloric 
acid and 2 g of iodine at 50.degree., with stirring. Subsequently, the 
reaction mixture is further stirred for 30 minutes at 50.degree. and the 
solvent then distilled off. The residue is taken up in 1000 ml of toluene 
and washed neutral and chlorine-free with aqueous sodium hydrogen 
carbonate solution and aqueous sodium thiosulphate solution. Subsequently, 
the toluene is distilled off and the crude 
1-(4'-tert-butylphenyl)-2-chloro-2-methyl-propanone-(1) remaining behind 
dissolved in 2000 ml of isopropyl alcohol. To this solution are added 420 
ml of 32% aqueous sodium hydroxide solution and the reaction mixture 
heated to the boil for 1.5 hours. After cooling, the reaction mixture is 
shaken out with 1000 ml of toluene, the toluene extract washed with 1000 
ml of 10% aqueous sodium chloride solution, dried over calcium chloride 
and evaporated. The 1-(4'-butylphenyl)-2-hydroxy-2-methyl-propanone-(1) 
remaining behind is distilled under reduced pressure; yield: 839 g, 
b.p..sub.0.1 132.degree.-135.degree.. 
There are prepared analogously: 
1-(4'-methyphenyl)-2-hydroxy-2-methyl-propanone-(1), b.p..sub.0.5 
120.degree.-122.degree.; 
1-(4'-ethylphenyl)-2-hydroxy-2-methyl-propanone-(1), b.p..sub.0.3 
104.degree.-109.degree.; 
1-(4'-isopropylphenyl)-2-hydroxy-2-methyl-propanone-(1), b.p..sub.0.4 
108.degree.-109.degree.; 
1-(3'-chloro-4'-methoxyphenyl)-2-hydroxy-2-methyl-propanone-(1), m.p. 
92.degree.-93.degree.; 
1-(3'-bromo-4'-methoxyphenyl)-2-hydroxy-2-methyl-propanone-(1), m.p. 
104.degree.-106.degree.; 
1-(3'-chloro-4'-methylphenyl)-2-hydroxy-2-methyl-propanone-(1), 
b.p..sub.0.7 130.degree.-135.degree.; 
1-(2',5'-dimethylphenyl)-2-hydroxy-2-methyl-propanone-(1); 
1-(2',4'-dimethylphenyl)-2-hydroxy-2-methyl-propanone-(1); 
1-(4'-methylphenyl)- 2-hydroxy-2-ethyl-hexanone-(1), b.p..sub.0.3 
155.degree.-158.degree.; 
1-(4'-tert-butylphenyl)-2-hydroxy-2-ethyl-hexanone-(1), b.p..sub.0.2 
162.degree.-166.degree.; 
1-(4'-isopentylphenyl)-2-hydroxy-2-methyl-propanone-(1); 
1-(4'-methylphenyl)-2-hydroxy-2-methyl-butanone-(1); 
1-(4'-isopropylphenyl)-2-hydroxy-2-methyl-butanone-(1); 
1-(4'-tert-butylphenyl)-2-hydroxy-2-methyl-butanone-(1) and 
1-(3',4'-dimethylphenyl)-2-hydroxy-2-methyl-butanone-(1). 
The following Examples 7-14 concern the use of the photosensitizers 
according to this invention in the photopolymerization of unsaturated 
compounds. 
EXAMPLE 7 
20 g amounts of a commercially available casting resin based on partly 
polymerized methyl methacrylate and allyl methacrylate (Plexit.RTM. MU 51 
of the firm Rohm GmbH, Darmstadt) are each mixed with 0.4 g of a 
sensitizer according to this invention or of a commercially available 
product. After complete dissolving of the sensitizer and uniform mixing, 
the samples are stored in the dark at 60.degree. in closed glass vessels. 
The samples are tested at regular intervals of time for the commencement 
of gelling. The results summarized in the following Table are a measure of 
the dark storage stability of photopolymerizable mixtures with the use of 
various sensitizers. 
TABLE B 7 
______________________________________ 
Experiment Dark Storage 
No. Sensitizer Stability (Days) 
______________________________________ 
1 1,2-diphenyl-2,2-dimethoxy- 
4 
(prior art) 
ethanone-(1) 
2 Benzoin butyl ether 
0.5 
(prior art) 
3 1-(4'-dodecylphenyl)-2- 
5 
hydroxy-2-methyl-propanone- 
(1) 
______________________________________ 
The results show that photopolymerizable mixtures with the sensitizer 
according to the invention (experiment 3) possess a markedly better dark 
storage stability than the mixtures with the known sensitizers 
(experiments 1 and 2). 
EXAMPLE 8 
Analogously to Example 7, there is determined the dark storage stability of 
photopolymerizable mixtures each of 20 g of a commercially available 
casting resing based on unsaturated polyesters and styrene (Palatel.RTM. p 
70 of the firm BASF AG, Ludwigshafen) and 0.4 g each of a sensitizer 
according to the invention and two known sensitizers. The results are 
summarized in Table B 8 
TABLE B 8 
______________________________________ 
Experiment Dark Storage 
No. Sensitizer Stability (Days) 
______________________________________ 
1 1,2-diphenyl-2,2-dimethoxy- 
7 
(Prior art) 
ethanone-(1) 
2 Benzoin butyl ether 8 
(Prior art) 
3 1-(4'-dodecylphenyl)-2- 
12 
hydroxy-2-methyl-propane-(1) 
______________________________________ 
The results also show the superior properties of the 15 sensitizers 
according to the invention. 
EXAMPLE 9 
50 g amounts of a commercially available casting resin based on partly 
polymerized methyl methacrylate and allyl methacrylate (Plexit.RTM. MU 51 
of the firm Rohm GmbH, Darmstadt) are each mixed with 1.25 g of 
1-(4'-tert-butyl-phenyl)-2-hydroxy-2-methyl-propanone-(1) or benzoin butyl 
ether as sensitizer and coated onto glass plates in 250 .mu.m thicknesses. 
Immediately after the coating, the layers are irradiated for 30 seconds 
with a mercury vapor lamp at a distance of 11 cm. From both materials 
there is formed a hard layer having a non-sticky surface which, for the 
sensitizer according to this invention is colorless and clear, whereas for 
the known benzoin ether possesses a markedly yellowish coloration. 
EXAMPLE 10 
A solution of 0.2 g of 1-(4'-methylphenyl)-2-hydroxy-2-methyl-propanone-(1) 
in 10 g of trimethylolpropane triacrylate is coated onto a glass plate in 
a 50 .mu.m thick layer and irradiated as in Example 9. A hard, colorless, 
glass-clear and highly glossly coating is obtained. 
EXAMPLE 11 
A solution of 0.1 g of 
1-(2',5'-dimethylphenyl)-2-methoxy-2-methylpropanone-(1) and 0.1 g of 
benzoin butyl ether in 10 g of trimethylol-propane triacrylate is applied 
with a rubber roller in about 100 .mu.m thickness to white drawing paper. 
After irradiation as in Example 9, there results a colorless, glossy 
coating. 
EXAMPLE 12 
In a solution of 8.0 g of 
1-(4'-tert-butylphenyl)-2-hydroxy-2-methylpropanone-(1) and 0.8 g of 
1-(4'-isopropylphenyl)-2-hydroxy-2-methylpropanone-(1) in 16.4 g of 
pentaerythritol triacrylate are dispersed 2.0 g of blue copper 
phthalocyanin pigment. A rastered stereotype plate is colored with this 
dispersion and white paper printed therewith. The print surface, which is 
sticky after the printing process, is subsequently irradiated for 20 
seconds at a distance of 11 cm with a mercury vapor lamp. A non-sticky, 
wipe-proof print is obtained. 
EXAMPLE 13 
A solution of 0.2 g of 1-phenyl-2-hydroxy-2-methyl-propanone-(1) in 10 g of 
trimethylol-propane triacrylate is applied with a 25 .mu.m spiral doctor 
to white glazed paper, and the coating is irradiated as in Example 9. A 
glossy, colorless non-sticky coating is obtained. 
EXAMPLE 14 
A solution of 0.75 g of 
1-(4'-chlorophenyl)-2-hydroxy-2-methyl-propanone-(1) in a mixture of 20 g 
of trimethylol-propane triacrylate and 10 g of butanediol diacrylate is 
applied with a 25 .mu.m spiral doctor to white glazed paper, and the 
coating is irradiated as in Example 9. A colorless, highly glossy coating 
is obtained. 
The preceding examples can be repeated with similar success by substituting 
the generically or specifically described reactants and/or operating 
conditions of this invention for those used in the preceding examples. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics of this invention, and without departing 
from the spirit and scope thereof, can make various changes and 
modifications of the invention to adapt it to various usages and 
conditions.