Process for the preparation of substituted dibenzoylmethane...

Details Process for the preparation of substituted dibenzoylmethane... Process for the preparation of substituted dibenzoylmethane...

1999-10-13

2001-08-21

Padmanabhan, Sreeni (Department: 1621)

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

Organic compounds

Oxygen containing

C568S313000, C568S327000, C568S331000, C549S512000

Reexamination Certificate

active

06278025

ABSTRACT:

The invention relates to a process for the preparation of substituted dibenzoylmethane compounds.
Sunlight which reaches the earth's surface contains UV-B radiation (280 to 320 nm) and UV-A radiation (>320 nm), which directly border the visible light region. The effect on human skin is noticeable, particularly in the case of UV-B radiation, from sunburn. Accordingly, the industry offers a relatively large number of substances which absorb UV-B radiation and thus prevent sunburn.
Dermatological investigations have shown that UV-A radiation is also perfectly capable of causing skin damage and triggering allergies by, for example, damaging the keratin or elastin. As a result, the skin's elasticity and its ability to store water are reduced, i.e. the skin becomes less supple and tends toward wrinkle formation. The remarkably high incidence of skin cancer in regions where solar irradiation is high indicates that damage to the genetic information in cells is also evidently caused by sunlight, specifically by UV-A radiation. For these reasons, the development of more efficient filter substances for the UV-A and UV-B region would therefore appear necessary.
Substances which have a dibenzoylmethane group as a structural element
are notable for very high absorption properties in the UV-A region. Customary light protection filter substances from this class of compound are, for example, Eusolex® 8020 (INCI name: Isopropyldibenzoylmethane, Merck) and Parsol® 1789 (INCI name: Butylmethoxydibenzoylmethane, Givaudan).
DE-A-2945125 describes a process for the preparation of Parsol® 1789 by ester condensation of methyl 4-tert-butylbenzoate with 4-acetylanisole.
Because of the continually increasing demand for light protection agents which have a dibenzoylmethane group as structural element, the object was to provide a process for the preparation of substituted dibenzoylmethane compounds which is easy to carry out and affords economic advantages as a result of high yields.
This object has been achieved by a process for the preparation of substituted dibenzoylmethane compounds of the formula I,
where the substituents R
1
and R
2
independently of one another are defined as follows:
R
1
is C
3
-C
12
-alkyl;
R
2
is hydrogen, C
3
-C
12
-alkyl, C
1
-C
12
-alkoxy,
which comprises
a
1
) condensing benzaldehydes of the formula II with acetophenones of the formula III to give the chalcones of the formula IV, in which the exocyclic double bond is in the E- or Z-configuration or a mixture thereof, and the substituents R
1
and R
2
are as defined above,
 or
a
2
) condensing benzaldehydes of the formula V with acetophenones of the formula VI to give the chalcones of the formula VII, in which the exocvclic double bond is in the E- or Z-configuration or a mixture thereof, and the substituents R
1
and R
2
are as defined above, and
b) converting the chalcones of the formulae IV or VII into the dibenzoylmethane compounds of the formula I.
Examples of alkyl radicals R
1
and R
2
are branched or unbranched C
3
-C
12
alkyl chains, preferably n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl-, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-ethylhexyl, n-octyl, n-nonyl, n-decyl, n-undecyl and n-dodecyl.
Particularly preferred alkyl radicals R
1
and R
2
from the abovementioned group are the C
3
-C
6
-alkyl chains, very particularly preferably the C
3
-C
4
-alkyl chains, such as n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl and 1,1-dimethylethyl.
Suitable alkoxy radicals R
2
are those having from 1 to 12 carbon atoms, preferably from 1 to 8 carbon atoms.
Examples thereof are:
methoxy
ethoxy
isopropoxy
n-propoxy
1-methylpropoxy
n-butoxy
n-pentoxy
2-methylpropoxy
3-methylbutoxy
1,1-dimethylpropoxy
2,2-dimethylpropoxy
hexoxy
1-methyl-1-ethylpropoxy
heptoxy
octoxy
2-ethylhexoxy
Particularly preferred alkoxy radicals R
2
are those having from 1 to 6 carbon atoms, very particularly preferably those having from 1 to 4 carbon atoms, such as methoxy, ethoxy, isopropoxy, n-propoxy, 1-methylpropoxy and n-butoxy.
The reaction of the benzaldehydes II or V with the acetophenone derivatives III or VI respectively in process steps a
1
) or a
2
) is carried out in accordance with aldol condensations known from the literature (see in this connection: Organikum [Organic Chemistry], VEB Deutscher Verlag der Wissenschaften, Berlin 1981, pages 563-571; Indian J. Chem. Sec. B, 33, 1994, 455-459).
The condensation can either be base- or acid-catalysed. Suitable catalysts are:
basic alkali metal and alkaline earth metal salts, preferably those which are soluble neither in the starting materials nor in the products and which can be readily removed after the reaction has finished, particularly preferably: sodium, potassium or calcium carbonate or sodium bicarbonate;
alkali metal hydroxides, preferably sodium or potassium hydroxide;
alkaline earth metal oxides, preferably calcium or magnesium oxide;
basic zeolites;
alkali metal alkoxides, for example sodium methoxide, sodium ethoxide, butyllithium;
tertiary amines, for example pyridine, morpholine, triethylamine, triethanolamine;
NH
3
, NaNH
2
, NH
4
OAc;
basic aluminum oxide, basic ion exchanger;
acid catalysts, for example HCl, H
2
SO
4
, HNO
3
, phosphoric acid, glacial acetic acid;
acid ion exchanger, for example Lewatit® S100 (Bayer).
The amount of catalysts is generally from 1 to 80 mol %, preferably from 5 to 50 mol %, based on the amount of aldehyde used.
The process is preferably carried out at temperatures from 10 to 150° C., particularly from 20 to 100° C., particularly preferably from 25 to 60° C. Specific conditions as regards the pressure are not necessary; the reaction is generally carried out at atmospheric pressure.
Solvents which can be used are alcohols, for example methanol, ethanol, propanol, isopropanol, n-butanol or isobutanol; aromatics, for example toluene or xylene; hydrocarbons, for example heptane or hexane; chlorinated hydrocarbons, for example chloroform or dichloromethane; miglyol or tetrahydrofuran. The reaction can, however, also be carried out without solvent.
The reaction can either be carried out batchwise or continuously. A continuous procedure preferably involves passing the reactant over a solid bed of an insoluble base, for example basic zeolites.
The further reaction of the chalcones IV or VII to give the dibenzoylmethane compound of the formula I in process step b) comprises
b
1
) converting the chalcones IV or VII into the compounds of the formulae VIII or IX by addition of halogens or hypohalites,
where R
1
and R
2
are as defined above, and X is halogen and OH, and Y is a halogen, and
b
2
) preparing the dibenzoylmethane compounds of the formula I from the compounds VIII and IX by elimination of HY and with or without subsequent hydrolysis.
The halogens used for the addition to the exocyclic double bond of the chalcones IV and VII are preferably bromine or chlorine, very particularly preferably chlorine. The reaction is carried out in a simple manner by mixing the two starting materials in an inert solvent. The reaction products formed are dihalogen compounds of the formulae VIII or IX in which the substituents X and Y are both bromine or chlorine, preferably chlorine.
Suitable solvents include: aliphatic and aromatic hydrocarbons, such as cyclohexane, benzene, toluene or xylene; halogenated aliphatic and aromatic hydrocarbons, such as tetrachloromethane, dichloromethane or chlorobenzene. It is, however, also possible to carry out the halogen addition in alcohols such as, for example, ethanol or propanol.
The reaction temperatures are in the range from &minus

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