DE2915736A1 - 1,4-Naphthoquinone cpds. prodn. by oxidn. of 1-naphthol ester cpds. - with cerium IV salts in the presence of water - Google Patents

Abstract

In the prepn. of naphthoquinone derivs. of formula (I), a 1-naphthol derivs. of formula (II) is treated with a cerium IV salt in the presence of water at up to 100 degrees C: In the formulae, R1-4 are H, halogen, 1-4C alkyl, COOM, SO3H, CN or acyl, and R3 and R4 can also be 1-3C alkoxy or NO2; and X is H, 1-4C alkyl, phenyl, OCH3, OC2H5, a group -NR5R6 (in which R5 and R6 are H or 1-4C alkyl and R6 can also be phenyl) or a gp. of formula (III). (I) are useful as intermediates for vitamins and dyestuffs. They are also useful as intermediates for anthraquinones (c.f. Chem. Eng. 1978, 18, 74C). (I) are obtd. smoothly and in high space-time yields.

Description

Process for the production of naphthoquinones

This invention relates to a process for making naphthoquinones from naphthol derivatives.

1,4-Naphthoquinone is produced, for example, by reacting naphthalene produced with oxygen in the gas phase. In this, for example, in DE-OS 24 37 221 processes described always result in significant proportions of other oxidation products, like phthalic acid and carbon dioxide.

It has also been suggested to use naphthalene with chromium or cerium salts to oxidize to naphthoquinone. A good selectivity is achieved with cerium salts (Houben-Weyl, 1975, volume 4/1 b, page 154). If you apply this method to substituted Naphthalenes, e.g. on 1-methyl- or 1-bromonaphthalene, result in mixtures of substances (Synthesis, 1977, pp. 330 to 331). 1,4-naphthoquinones of the formula I are used obtained in only a low space-time yield.

It has now been found that naphthoquinones of the formula do the radicals R1 to R4 hydrogen atoms, halogen atoms, 1 alkyl radicals with 1 to 4 carbon atoms, carboxyl, sulphonic acid, nitrile and acyl groups and the radicals R3 and R4 also mean alkoxy groups with 1 to 3 carbon atoms or Nitro groups can be obtained particularly advantageously if naphthol derivatives of the formula in which the radicals R1 to R4 have the abovementioned meaning and X is a hydrogen atom, an alkyl radical having 1 to 4 carbon atoms, a phenyl radical, a methoxy or ethoxy radical, a radical of the formula or an R6 (R5) N radical in which R5 and R6 are hydrogen atoms or alkyl groups with 1 to 4 carbon atoms and R6 can also stand for a phenyl radical, in the presence of water at temperatures up to 1000C with Cer-IV- Salts treated.

The starting materials of the formula II can easily be prepared, for example, by anodic acyloxylation of the corresponding naphthalene derivatives (DE-AS 24 34 845). Of the starting materials of the formula II, the naphthol derivatives of the formula are in which R7 is a hydrogen atom, a methyl, acyl or carboxyl group, R8 is a hydrogen, chlorine or bromine atom or a sulfonic acid group and Z is a hydrogen atom, a methyl group, a methylamino group or a phenyl radical, of particular technical interest.

For example, the following starting materials may be mentioned: 1-acetoxynaphthalene, 1-acetoxy-2 (3) -methylnaphthalene, 1-naphthyl-N-methylcarbamate, 1-acetoxy-2-carboxynaphthalene, 1-acetoxy-2-acetonaphthalene and 1-naphthyl benzoate.

Cer-IV salts are e.g. cerium-IV-nitrate, cerium-IV-ammonium nitrate and cerium IV sulfate. Ce (NH4) 2 (N03) 6 and Ce (S04) 2.4 H20 are commercially available Products. The cerium salts are useful in the for complete implementation required stoichiometric amount used. There is generally an excess not harmful.

For economic reasons, one becomes that formed in the reaction Cer-III-salt after the reaction in itself be-'kanne into the cerium-IV compound return and insert again. For example, the Cer-III solutions are oxidized in an acidic medium with persulfates (DE-OS 23 01 803).

This reaction proceeds so quickly that, with constant recycling, it becomes catalytic Amounts of cerium salt are sufficient for the implementation according to the invention. You can do the regeneration the cerium III salts can also be carried out in an alkaline solution with hydrogen peroxide. However, it is particularly useful to use electrochemical regeneration (see Baizer "Organic Electrochemistry" 1973, 827) because they do not require additional chemicals gets by.

Ran puts the naphthalene derivatives with the cerium IV salts in the presence of water and expediently in the presence of a mineral acid such as sulfuric acid or nitric acid or perchloric acid. Organic solvents can also be used as solubilizers, such as acetonitrile, glacial acetic acid, benzonitrile, dichloromethane or hexane. The usage of acetonitrile is preferred. To carry out the process according to the invention however, it is not necessary to work in a homogeneous solution. Both the naphthol derivative as well as the cerium salt can be used in suspension or emulsion. Frequently some of the end products crystallize out during the reaction, for example the cerium III sulfate.

The reaction temperature is generally kept between 0 and 80 ° C, preferably between 20 and 600C. But it can also be at the reflux temperature of the appropriate solvent to be worked.

For the space-time yield, it is sometimes advantageous to have an excess to use Cer-IV, in many cases this is not negative for the material yield Influence, since the reaction stops at the naphthoquinone stage. With electrochemical prepared or regenerated Cer-IV solutions, it is also often useful to use a Tolerate residual content of 20 20 # Cer-fII in order to achieve an optimal current yield scored. This cerium III content also has no negative effects.

In the case of chemically regenerated Cer-IV salts, regeneration a residue of oxidizing agent or other chemicals carried into the approach will. The process can often be carried out in such a way that these impurities remain without adverse influence.

The inventive implementation of the naphthol derivatives can also be used with constant electrolytic regeneration of the cerium salts directly in the electrolysis circuit perform, using catalytic amounts of cerium IV salts.

According to a particularly advantageous embodiment of the invention, sets the naphthol derivatives with the cerium IV salts in a reactor and the aqueous phase after separation of the naphthoquinones for electrolytic transfer the cerium III salts into the cerium IV salts in a divided cell. This electrolysis is carried out in a manner known per se, e.g. in an electrolysis cell with anodes made of platinum, Lead / lead oxide, lead dioxide / titanium or graphite and with ion exchange membranes Temperatures from 20 to 600c, currents from 3 to 30 A / dm2 and conversions of 60 to 95.0 through.

According to the new process, the naphthoquinones are smooth and high Space-time yield obtained. Compared to the known oxidation of naphthalenes The particular advantage of the method according to the invention is that the Oxidize O-substituted naphthols of the formula II much more rapidly than naphthalene let (see comparative example b), whereby the space-time yields on economical acceptable values are raised. Because of the given by the stoichiometry Consumption of only 4 instead of 6 oxidation equivalents also increases the cost of reoxidation of cerium III salts decreased by 1/3.

This advantageous result was not to be expected since e.g.

no 1,4-naphthoquinones are obtained if instead of the a-naphthol derivatives of the formula II a-naphthols are used (see comparative example a).

The naphthoquinones produced by the new process are for example as vitamin precursors or as color '' intermediate products of Interest. They have recently become very important as building blocks for anthraquinones (Chem.

Closely. 1978, 18, 74 C).

Example 1 Oxidation of 1-acetoxynaphthalene 5.70 g (0.031 mol) of 1-acetoxynaphthalene in 300 ml of acetonitrile at 40 ° C. with vigorous stirring to 53.5 g (0.132 mol) Ce (SO4) 2.4 H20 in 300 ml of 20% sulfuric acid. When taking a sample after 1 hour the Ce-IV was used up to> 95%. Dilute with water and extract with methylene chloride. The organic phases are dried. The residue is obtained 5.34 g of about 85% 1,4-naphthoquinone; Yield: 93%.

Comparative example a Oxidation of CC-naphthol The procedure is as in Example 1 described, however, instead of 5.7 g of 1-acetoxynaphthalene, 4.77 g (0.033 mol) of ol / naphthol is used, the residue obtained is 2.18 g of a brown one tar-like mass which, according to TLC, IR and NMR analysis, only traces 1,4-naphthoquinone contains.

Example 2 Oxidation of 1-acetoxy-2 (3) -methylnaphthalene 6.00 g (0.030 Mol) 1-acetoxy-2 (3) -methylnaphthalene are oxidized analogously to Example 1. After a Hour is worked up. 4.80 g of 85% 2-methyl-1,4-naphthoquinone are obtained as residue in the form of brownish yellow crystals; Yield: L.

79%. Recrystallization gives 2.9 to 3.9 g of pure 2-methyl-1,4-naphthoquinone; Yield: 56 to 76%.

Example 3 Oxidation of 1-naphthyl-N-methylcarbamate 6.00 g of l-naphthyl-N-methylcarbamate (0.03 mol) are oxidized analogously to Example 1. Work up takes place after an hour.

The residue obtained is 4.58 g of 90% strength 1,4-naphthoquinone in the form yellow crystals; Yield: 87%. Recrystallization from ethanol is obtained 3.5 to 4 g of yellow crystals from Afp. : 124 to 1270C.

Example 4 Oxidation of 1-acetoxy-2 (3) -methylnaphthalene 190 g (0.438 mol) cerium-III-nitrate hexahydrate in 800 ml 5% nitric acid are in a divided cell made of plexiglass with cation exchange membrane and lead cathode at an anode made of lead dioxide-coated expanded titanium metal at a current strength oxidized by 4 A to Cer-IV.

Approx. 400 ml are taken from the anolyte solution, they contain 0.13 Moles of cerium IV. 6.4 g of 1-acetoxy-2 (3) -methylnaphthalene are added to this solution at 40.degree (0.032 mol) in 100 ml acetonitrile. Yellow crystals soon separate out.

After 2 hours it is suctioned off. 2.5 g of 2-methylnaphthoquinone are obtained as residue in the form of yellow needles (yield 45%). From the filtrate are extracted by using Methylene chloride, a further 2.9 g of 2-methylnaphthoquinone (yield 52%) were obtained.

The aqueous phase can be regenerated electrochemically as described above will.

Comparative Example b Comparison of the oxidation of naphthalene and naphthyl acetate To a solution of 40.43 g (0.1 mol) Ce (S04) 2.4H20 in 1.5 liters of 20% sulfuric acid at 200C a) 2.13 g (0.0166 mol) of naphthalene, b) 3.60 g (0.026 mol) of naphthyl acetate each given in 150 ml of acetonitrile.

In both cases, the solution is made with a paddle stirrer at 600 rpm violently stirred. A sample is taken every 3 hours and titrated with Fe-II. The following conversions are determined from the titration: a) 3 h: 45 5t 6 h: 70 % 9h: 85% b) 3h:> 95;

Claims (1)

Fatent claim process for the production of naphthoquinones of the formula in which the radicals R1 to R4 are hydrogen atoms, halogen atoms, alkyl radicals with 1 to 40 atoms, carboxyl, sulfonic acid, nitrile and acyl groups and the radicals R3 and beyond are alkoxy groups with 1 to 3 carbon atoms or nitro groups can, characterized in that naphthol derivatives of the formula in which the radicals R1 to R4 have the abovementioned meaning and X is a hydrogen atom, an alkyl radical having 1 to 40 atoms, a phenyl radical, a methoxy or ethoxy radical, a radical of the formula or an R6 (R5) N radical, in which R5 and R6 mean hydrogen atoms or alkyl groups with 1 to 4 carbon atoms. End R can also stand for a phenyl radical, in the presence of water at temperatures up to 1000C with Cer-IV- Salts treated.