Field of the Invention

This invention relates to a process for the preparation of 4-hydroxy-diphenyl ether (hereinafter 4-HDPE) in high yields and purities, under convenient reaction conditions, by the hydrolysis of 4-bromodiphenyl ether (hereinafter 4-BDPE).

Background of the Invention

4-HDPE is used as a bactericide, an insecticide, antioxidant, lubricant or a resin, as an intermediate for agrochemicals, and in the pharmaceutical industry. Several processes for its preparation have been described in the art. Its preparation by means of the Ullmann condensation of 4- bromophenol with excess phenol is described, for instance, in J. Am. Chem. Soc, 54, 298-305 (1932). Other known processes comprise the dehydration of hydroquinones or the reaction of hydroquinone with phenols; see JP 59- 206326 (1984) to Mitsui Petrochemical Industries. The catalytic hydrolysis of 4-iododiphenyl ether is described in JP 63-99029 and JP 63-104935 (1988) to Asahi Chemical Industry Co., Ltd..

4-BDPE is a convenient starting material for the preparation of 4-HDPE. Various processes are known in the art for the preparation of the starting material, 4-BDPE. For instance, 4-BDPE has been prepared by the Ullmann ether condensation of 1,4-dibromobenzene with phenol in the presence of KOH and Cu (Krause et al., Aromatic tin compounds of high molecular weight, Chem. Ber. 62, 2235, 1929; L.D. Karyakina, Synthesis and spectra of diphenyl ethers, Tr. Voronezh. Tekhnol. Inst. 19 (2) 34-7, 1971). Preparation of 4-BDPE by the bromination of diphenyl ether (DPE)

has been known since the beginning of the century, and is usually carried out in CS ₂ or CCl,, as solvent, in the presence of I ₂ (Bergmann et al., Dipole moments of some aromatic oxygen and sulfur compounds, Z. Phys. Chem. <B> 17, 107-112, 1932; Mailhe, Murat, CR. Hebd, Seances Acad. Sci., 154, 603, 1912, Bull. Soc. Chim. Fr., <4> 11, 331, 1912). Regioselective para- brominating agents such as benzeneseleninyl chloride with AlBr ₃ (N. Kamigata et al., Regioselective para halogenation of substituted benzenes with benzeneseleninyl chloride and aluminum halide, Bull. Chem. Soc. Jpn, 61(6), 2226-8, 1988) and halodimethylsulfonium bromide (G. Olah et al., Synthetic methods and reactions. 127. Regioselective para halogenation of phenols, phenol ethers, and anilines with halodimethylsulfonium halides (Synthesis, 10, 868-70, 1986) have been used to brominate DPE with good selectivities. The bromination of DPE without a solvent or catalyst has been mentioned, giving 56-59 mole % DPE, 36-40 mole % 4-BDPE and 3-6 mole % DBDPE (4,4'-Dibromodiphenyl ether) [O.V. Bakhvalov et al., Isomerisation of monobromodiphenyl ethers in the presence of aluminum halides, Zh. Org. Khim., 5(2) 331-6, 1969].

German Patent 609080 describes the preparation of 4-HDPE by the hydrolysis of 4-BDPE at 200°C in a solution of an alkali hydroxide in 50-50

(by volume) water-alcohol medium, under (unspecified) pressure, with copper powder as a catalyst. After 10 hours reaction followed by work-up, a 65% yield of a product having m.p. 84-85°C, is obtained. D. Janssen et al, J.

Org. Chem. 20, 1326-9 1955, describe the preparation of 4-HDPE by the hydrolysis of 4-BDPE with potassium hydroxide and copper powder catalyst, in an autoclave, at 245-250°C, for 16 hours. After work-up, the yield was 81.6% of a product having m.p. 81-82°C.

However, none of the processes known in the art for the preparation of 4- HDPE are fully satisfactory, from the viewpoint of the process conditions (for example, they require long reaction times) or from the viewpoint of the yield with which the final product is obtained.

It is a purpose of this invention to provide a process for the preparation of 4- HDPE by a more efficient process than those known in the art.

It is another object of the invention to provide such a process which yields 4- HDPE in high yields and with high purity.

It is a further purpose of this invention to provide such a process by which 4- HDPE is prepared by the hydrolysis of 4-BDPE under mild reaction conditions and with a shortened reaction duration.

It is yet another purpose of this invention to provide such a process which includes a simple work-up procedure.

Other purposes and advantages of the invention will appear as the description proceeds.

Summary of the Invention

The process according to the invention comprises contacting 4-BDPE with an aqueous alkali hydroxide solution, a copper compound catalyst, and an autocatalytic amount of 4-HDPE in pure form or in the form of its sodium salt, e.g. in the form of a crude reaction mixture from a previous reaction,

and heating the reagents to temperatures above 180°C, under pressure, for a time sufficient substantially to hydrolyze the 4-BDPE. Any amount of 4- HDPE that appreciably accelerates the reaction should be considered as being an autocatalytic amount in the sense in which this expression is used herein. However, preferably, the amount of 4-HDPE that should be present before the reaction begins is comprised between 1% and 50%, and preferably between 3% and 20%. The heating to the reaction temperature may be carried out before, after or during the addition of the autocatalyst, and said addition may be carried out in several steps.

The autocatalysis due to the presence of the reaction product 4-HDPE at the beginning of the reaction considerably shortens the duration of the reaction at any particular temperature, from several hours down to 1-2 hours at a lower temperature, and to even a few minutes at a higher temperature. It further affords higher yields and purity of the final product. Delaying the addition of the autocatalyst will tend to decrease the benefits deriving from it, but may not nullify them, if said delay is not such that the reaction is already under way.

The catalytic amount of 4-HDPE can be added in any suitable way. In batch operation, 4-HDPE may be introduced as a pure product or through the introduction of the crude reaction mixture of a previous reaction. Conveniently, the process may be carried out continuously by passing the 4- BDPE, together with the alkaline solution and the copper compound catalyst, into an appropriate stirred reactor operating at the steady state conditions, the space velocity of the reagents through the reactor being such that the reagents will remain therein for the required time for completion of

the reaction at the respective temperature. In this case, the reaction mixture itself acts as the autocatalyst and no recirculation of the reaction mixture is necessary. The issuing reaction mixture is subjected to work-up. In the batch mode the aqueous NaOH, copper compound catalyst and autocatalyst may be introduced into the reactor together with the 4-BDPE, or the 4-BDPE can be fed into a mixture of the other reagents (aq. NaOH, copper catalyst and autocatalyst) in a semi-continuous mode. The latter method is preferred, as it initially provides a higher molar ratio of NaOH to the 4-BDPE.

The copper compound catalyst is preferably Cu ₂ O, CuO, CuSO ₄ , CuCl or CuCl _2> . Metallic copper is also a possible catalyst and should be considered as included in the expression "copper compound", as used herein. The catalyst is present in an amount of from 0.01% w/w to 10% w/w, and preferably from 0.5% w/w to 2.5% w/w.

The reaction temperatures are above 180°C, preferably from about 200 to 260°C, and more preferably, about 220-240°C. The pressure is autogenous. At the lower temperatures (~200°C) the reaction is relatively slow and may take a few hours, e.g. about 5 hours, while at the higher temperatures it is very fast and is completed in a few minutes: e.g. at 260°C it is completed in about 5 minutes. High temperatures are preferred for a continuous process where short reaction times are desirable, but batch reactions are preferably carried out at lower temperatures in order to maintain control of the temperature.

The alkali hydroxide solution is preferably an aqueous solution of sodium or potassium hydroxide. The concentration of the solution is from 10 to 50%, preferably from 20 to 40%. The amount of alkali solution used per mole of the reaction substrate, viz. the 4-BDPE, is from 2 to 20 moles, and preferably from 2 to 5 moles.

The conversion of the 4-BDPE is as high as 99.9%. The work-up of the crude reaction mixture consists of transferring -95% of the contents of the hydrolysis reactor (~5% of the crude reaction mixture is left in the hydrolysis reactor to act as autocatalyst for the next batch) to a neutralization vessel (optionally with filtration), acidifying to pH 4-7 with any suitable acid, such as, for example, concentrated HCl, and separating the phases at ~90°C. The aqueous phase is transferred to waste treatment.

The organic phase, containing the crude HDPE, is subjected to fractional distillation. According to the analyses, the crude HDPE is obtained in a yield of 92 ± 2%. The crude 4-HDPE may be purified, e.g., by fractional distillation (after adjustment of the pH to ~7), at a vacuum of 15-40 mm Hg. 4-HDPE is obtained in an overall yield of 88% and a purity of >99%.

Detailed Description of Preferred Embodiments

The following examples illustrate embodiments of the process for the preparation of 4-HDPE by the hydrolysis of 4-BDPE, according to the invention. Example 1 illustrates a reaction carried out at a higher temperature than recommended, without addition of autocatalyst. The reaction product of this reaction was used in subsequent reactions. Examples 2-6 show the effects of addition of different amounts of autocatalyst. Examples 7-11 illustrate the effects of temperature on the

time required for reaction. Examples 12-20 show the effect of different concentrations of NaOH and different NaOH/4-BDPE molar ratios on the reaction. Examples 16, 21 and 22 demonstrate the effect of catalyst concentration, and Examples 23-27 illustrate the effect of the identity of the catalyst. Examples 1, 8, 11 and 28 are comparative reactions with and without the addition of autocatalyst. Example 29 illustrates the use of KOH as the base. Example 30 demonstrates a semi-continuous process. Example 31 demonstrates all the features of the invention when applied in a batch process, including scale-up, work-up and fractional distillation.

Example 1

Into a one liter autoclave was placed a mixture of 4-BDPE (400 g, 1.61 moles), aqueous 30% NaOH (540 g, 4 moles) and Cu ₂ O (4 g, 28 mmol). The autoclave was sealed and heated to 250°C. For the first hour, the reaction was very slow, but as soon as a small amount of 4-HDPE had been formed, it acted as an autocatalyst and a runaway reaction occurred. The temperature rose to 280 ^C C in 8 minutes. The autoclave was cooled to room temperature and opened. The reaction mixture was analyzed for Br" and it was determined that full conversion of the 4-BDPE had been achieved.

The reaction mixture obtained was used as an autocatalysis additive in subsequent reactions.

Example 2

Into a half-liter autoclave was placed a mixture of 4-BDPE (200 g, 0.8 moles), aqueous 30% NaOH (270 g, 2 moles), reaction mixture from Example 1 (84 g), and Cu ₂ O (1 g, 7 mmol). The autoclave was sealed and heated to

210°C. After 1 hour, the autoclave was cooled to room temperature and opened.

The reaction mixture was analyzed for Br- and the 4-BDPE conversion was determined. The results are presented in Table I.

Examples 3 - 6

Example 2 was repeated at 210°C for a period of 1 hour, with the addition of varying quantities of the reaction mixture from Example 1. The results are presented in Table I.

Table I

Expt. No. Amount of crude reaction Conversion mixture from Ex. 1 added %, by Br- g % of feed

2 84 18 38

3 56 12 30

4 28 6 18

5 14 3 6

6 0 0 <1

It can be seen that the rate of the reaction is dependent on the amount of autocatalyst added.

Example 7 Into a half-liter autoclave was placed a mixture of 4-BDPE (200 g, 0.8 moles), aqueous 30% NaOH (270 g, 2 moles), reaction mixture from Example 1 (56 g) and Cu ₂ O (1 g, 7 mmol). The autoclave was sealed and heated to 210°C. After 150 minutes, the autoclave was cooled to room temperature and opened. The reaction mixture was analyzed for Br" and the 4-BDPE conversion was determined. The results are presented in Table II.

Examples 8 - 11 Examples presented in Table II were performed as described for Example 7 at temperatures and for reaction times required to achieve complete conversion.

Table II

Examples 12 - 20

Into a half-liter autoclave was placed a mixture of 4-BDPE (200 g, 0.8 moles), aqueous 30% NaOH (270 g, 2 moles), reaction mixture from Example 7 (28 g), and Cu ₂ O (1 g, 7 mmol). The autoclave was sealed and heated to 220°C. After 1.5 hours, the autoclave was cooled to room temperature and opened. The reaction mixture was analyzed by GC and for Br" to determine the 4-BDPE conversion.

The reaction mixture was placed into a four-necked flask equipped with a stirrer, a condenser, a dropping funnel and a thermometer and acidified to pH 4-7 with 32% HCl (145 g) at 85-95°C. The phases were separated and the crude 4-HDPE (organic phase) analyzed by GC.

Table III shows the effect of the aqueous NaOH concentration and the NaOH/4-BDPE molar ratio on the product composition.

Table III

Example aq. NaOH Molar ratio Composition*, GC, Area % No. % w/w NaOH/4-BDPE

DPE 4-HDPE DPDPE

12 20 3.0 1.4 96.9 1.4

13 20 2.5 1.3 97.0 1.6

14 20 2.2 1.3 96.0 2.4

15 30 3.0 2.0 94.7 2.5

16 30 2.5 1.9 95.7 2.4

17 30 2.2 1.8 93.4 4.7

18 40 3.0 2.5 92.7 3.4

19 40 2.5 2.0 93.4 4.5

20 40 2.2 2.8 89.9 7.6

*DPE - Diphenyl ether 4-HDPE - 4-Hydroxydiphenyl ether DPDPE - 4,4'-Diphenoxydiphenyl ether

Examples 16. 21 - 22

Further experiments were carried out under the same conditions as in Example 16 (described above) with varying amounts of Cu ₂ O catalyst (0.5 (Ex. 16), 1.0 (Ex. 22) and 5.0 (Ex. 23) w/w% relative to 4-BDPE ). The analyses showed that the quantity of catalyst had no significant effect on the rate and selectivity of the reaction, within the range tested.

Examples 23 - 27

Comparative tests with different catalysts (Cu, Cu ₂ O, CuCl, CuO, CuSO ₄ .5H ₂ O) were carried out at 220°C for 1.5 h under the same conditions as in Example 16. All the reactions went to completion, except for when metallic Cu was used. The conversion of 4-BDPE in the presence of Cu was >99% after two hours reaction time.

Comparison of Examples 1. 8. 11. and 28

These Examples were carried out according to Example 7, under the conditions specified in Table IV.

Table IV

At 250°C, a reaction occurs even without additive, but the rate of reaction is initially slow, after which there is a runaway reaction. At 220°C, no reaction occurs without additive, even after 6 hours reaction time.

Example 29

Into a half-liter autoclave was placed a mixture of 4-BDPE (124.5 g, 0.5 mol), aqueous 30% KOH (235 g, 1.26 mol), reaction mixture from Example 7 (28 g), and Cu ₂ O (1 g, 7 mmol). The autoclave was sealed and heated to 220 °C. After 1.5 hours the autoclave was cooled to room temperature and opened. The reaction mixture was analyzed by GC and for Br". The analyses showed that there was no significant effect on the rate and selectivity of the reaction by the use of KOH instead of NaOH.

Example 30

Into a 9-liter autoclave was placed a mixture of aqueous 30% NaOH (5.0 kg, 37.5 mol), reaction mixture from a previous reaction (260 g, ~3% of feed) and Cu ₂ O (21.5 g, 0.15 mol). The autoclave was sealed and heated to 220°C. 4-

-12-

BDPE (3.75 kg, 15 mol) was then fed into the autoclave by means of a pressure pump. When all the 4-BDPE had been introduced (about 1 hour), the autoclave was maintained at 220°C for one hour, then cooled and opened. The reaction mixture was analyzed for Br" to determine the 4- BDPE conversion. It was found that full conversion had been achieved.

The reaction mixture was placed into a reactor equipped with a stirrer, a condenser and a thermocouple and acidified to pH 4-7 with 32% HCl (2.6 kg) at 85-95°C. The phases were separated and the organic phase (2.9 kg) was analysed by titration and GC. The assay, by titration, was 92% and the composition, by GC, was 3.2 % DPE, 93.5% 4-HDPE and 2.4% DPDPE. The yield of crude 4-HDPE was 93%.

Example 31

Into an 9-liter autoclave was placed a mixture of 4-BDPE (3.75 kg, 15 moles), aqueous 30% NaOH (5.0 kg, 37.5 moles), reaction mixture from a previous reaction (260 g, -3% of feed) and Cu ₂ O (21.5 g, 0.15 moles). The autoclave was sealed and heated to 220°C. After 2.0 hours, the autoclave was cooled to room temperature and opened. The reaction mixture was analyzed by GC and for Br" to determine the 4-BDPE conversion.

The reaction mixture was placed into a reactor equipped with a stirrer, a condenser, a pump and a thermocouple and acidified to pH 4-7 with 32% HCl (2.7 kg) at 85-95°C. The phases were separated and the organic phase, containing the crude 4-HDPE, treated to fractional distillation.

Fractional distillation was carried out on the crude 4-HDPE at 20 mm Hg. 2.58 kg pure 4-HDPE was obtained at 187-189°C in a yield of 89.8% and a purity of >99.5%.

While a number of embodiments have been described by way of illustration, it will be apparent that the invention may be carried out with many variations, modifications and adaptations, by persons skilled in the art, without departing from its spirit or exceeding the scope of the claims.