BACKGROUND OF INVENTION : From technical as well as from patent literature, numerous examples are known to effect the dialkylation of phenols and especially polyhydric phenols such as -hydroquinone with reagents forming carbocation species in the presence of catalysts.

The art of such conversions can be found in literature, which dates back as far as 1892 (Koenig, Ber. 1892,25, 2649). Specifically, dialkylation of hydroquinone and iso- amylene is carried out in very large amounts of concentrated sulphuric acid, which also acts as solvent. Similar examples with relatively concentrated sulphuric acid in large amounts are given in patent literature, e. g. US 2469101 or US 2832808.

Another old method is described in US 2439421: The conversion of specific alkyl halides with hydroquinone, resorcinol or catechol in presence of very large amounts of zinc chloride is carried out in an alcohol.

More recent art describes usage of various kinds of acid-based catalysts both in molar as well in catalytic amounts. All of these are referred to as being useful for generating a carbocation species from a suitable precursor to react with phenolic and polyhydric phenols, respectively, e. g. GB 831828 discusses alkylation of phenolic compounds with olefins in presence of such catalysts as boron trifluoride, phosphoric acid, hydrogen halides, hydrocarbon sulfonic acids or acid activated clay in presence of triisobutylen as solvent.

Comparable examples can also be found in US 4847429 (Eastman Kodak), US 5208390 (Chevron), US 6049015 (Rhodia Chimie) or in WO 02/055461 (Eastman).

Acid catalysed processes under predominantly heterogenous conditions, which are based on strongly acidic resins, are described in DD 263752 (VEB Filmfabrik <BR> <BR> Wolfen), JP 4103550 & JP 4103549 (Konica Corp. ), as well as JP 6157384 & JP 6157383 (Fuji Photo Film Co.) Due to the variety of existing methods for the production of alkyl substituted phenols and polyhydric phenols, one skilled in the art of synthesising such materials would not expect to meet with problems in the conversion of benzene diols with a carbocation forming compound, especially hydroquinone with isoamylene. Indeed, for our purposes we have found practical ways related to those disclosed in the literature for-- synthesising 2,5-diisoamylhydroquinone. Moreover, the method we focussed on features only catalytic amounts of an acid, thus avoiding large amounts of waste material derived from neutralisation of the acid which gives rise to environmental problems and consequently high costs.

To our surprise, however, the material which has been synthesised previously tends to be prone to discolouration, especially if introduced into aqueous dispersion.

Instead of being white or colourless, the material turns at least slightly pink or even dark brown. We have found that these effects are due to the oxidation of hydroquinone to the corresponding quinone species. This discolouration represents a big disadvantage in terms of quality, e. g. if the material is introduced into a process for production of high quality polymer materials. Such polymer materials could be white or transparent plastics, where non-staining properties are essential.

Staining phenomena like those described above very often are based on impurities that are either introduced or formed during the reaction within known processes and with known catalysts and that obviously have not been removed efficiently in the course of the work-up procedure of the crude product. It is known that hydroquinone and derivatives are comparably easily transformed into the dehydrogenated form, i. e. the quinone derivative. This is due to oxidation reactions. According to Nernst redox reactions can be efficiently influenced by the pH value of the environment, which in our case the dihydroxy benzene compound is exposed to. In specific cases, even slight deviations in the proton concentration, i. e. the pH-value, within said environment might cause non-stable conditions that in turn favour formation of the quinone form. As a matter of fact, those slight deviations might even be caused by traces of impurities. This is especially true with regard to colour.

A closer look into the technical and patent literature concerning the production of substituted dihydroxy benzenes reveals very similar work-up procedures. For example, in US 2469101 the inventors describe a simple washing of the organic solution containing the alkylated dihydroxy benzene with sodium bicarbonate solution in order to neutralise the acid.

In another case (US 2832808) solid product is--washed with water followed by potash solution and again with sufficient water in order to achieve the same goal.

Alternatively, slurrying of the product in water and treating with a wetting agent followed by the aforementioned washings is described. Accordingly, the inventors-of GB 831828 specify neutralisation of the reaction mixture with alkali, especially if sulphuric acid is used as catalyst, followed by washing of the organic layer with water. Similar simple work-up procedures are found in US 4847429 (washing with water, only), US 5208390 (washing with aqueous isopropanol), US 6049015 (washing with water only, optionally in presence of a reducing agent) or WO 02/055461 (washing with water at elevated temperature).

According to the present invention, there is provided a process for the production of a disubstituted hydroquinone which comprises alkylating hydroquinone in the presence of a sulphonic acid condensation catalyst with an olefin or a substance which under the reaction conditions acts as a source of the olefin characterised in that the reaction product is worked-up under complete dissolution of the product by washing with an aqueous medium which combines pH buffering capability and reducing activity.

The present invention relates to the production of essentially non-staining hydroquinones, especially 2,5-dialkylhydroquinones, of high quality, which can be used as an additive or even introduced into aqueous dispersion without showing any discoloration. The novel process is based on an efficient acid catalysed conversion of an aromatic dihydroxy compound with a carbocation forming compound under homogenous conditions. The invention requires the reaction mixture to be worked-up under complete dissolution of the product by washing with an aqueous medium which combines pH-buffering capability and reducing activity. The combination of the latter two properties, which is not disclosed in the prior art, guarantees stability in terms of colour of the final product as well as in an aqueous dispersion form.

The process of the invention provides an antioxidant additives with relatively good non-staining behaviour.

The process of invention comprises reaction of a benzenediol with an olefin or tertiary alcohol in the presence of an acid, most preferably sulfonic acid, and especially work- up of the reaction mixture with a pH-buffering solution. Particularly, the invention focusses on production-of-2, 5-dialkylhydroquinones featuring excellent quality-in respect of specific applications. This quality is reflected by non-staining properties, which can be achieved only, if impurities, especially acid residues, are efficiently eliminated by the special work-up method of the invention.

Regarding the synthesis, the benzenediol, preferably hydroquinone is reacted with a carbocation source, i. e. a tertiary olefin or a suitable alcohol which under specific reaction conditions acts as a source thereof.

The olefin suitably is a linear, branched or cyclic hydrocarbon having 3 to 12 carbon atoms.

Representative examples are, but are in no way limited to, olefins selected from 2- methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, 2-methyl-1, 3 pentadiene, 3- methyl-1,3 pentadiene, 4-methyl-1, 3 pentadiene, 2-ethyl-1, 3 butadiene, 2-methyl-1, 3 butadiene, 2, 3-dimethyl-1, 3 butadiene, 3-methyl-1, 4-pentadiene, l-methyl cyclopentene, 1-methyl-cyclohexene and isobutylene.

Most preferably, the olefin is 2-methyl-2-butene either alone or in admixture with isomers thereof.

Suitably, also, the alcohol, which dehydrates or in some way eliminates or rearranges under the reaction conditions to form a reactive carbocation, is selected from tertiary- butyl, amyl or hexyl alcohols.

The process of the invention is conveniently conducted and especially suitable under homogenous catalytic conditions.

Preferably, only catalytic amounts of catalyst are present in the alkylation reaction.

Further preferably, the catalyst is present in an amount of 0.01 to 10% by weight of the reactants.

The catalyst may be an alkyl, aryl or arylalkyl sulphonic acid.

The catalyst may have the formula R-S03H wherein R is Cl-to C3 alkyl ; Cl to C3 perfluoroalkyl, phenyl, tolyl or cresyl.

Preferably, the catalyst is methanesulphonic acid.

The process conveniently is conducted in the presence of an aromatic or aliphatic solvent.

The aromatic solvent may be benzene, toluene or xylene or mixtures thereof.

The aliphatic solvent may be hexane, cyclohexane, methyl cyclohexane, heptane or mixtures thereof, triisobutylene or petroleum ether.

The alkylation reaction suitably is conducted at a temperature of 35 to 130°C, preferably 55 to 75°C.

Most important the reaction product is worked-up under complete dissolution by washing with an aqueous medium, which combines pH-buffering capability and optionally, reducing activity. Naturally, the pH buffering has to take place within the basic domain. The desired compound has to be completely dissolved in order to effectively neutralise the acid that can be encapsulated within the solid product. Only in this way the deteriorating properties are eliminated thus giving non-staining material. Accurate dosage of base is crucial for successful neutralisation without provoking undesired side reactions. Therefore, simple alkaline reagents alone are not necessary efficient, since they might push the pH to much higher values than necessary thereby causing discoloration. Precisely, such extreme alkaline conditions could favour deprotonation of the aromatic hydroxyl group thereby enabling an easy oxidation of the electron rich moiety. Thus mildly basic reagents, such as Na2HP04, are suitable. Most desirable is the fact that a solution of this compound exhibits pH- buffering properties (Na2HP04 + H-'- NaH2P04 + Na+), which inhibit formation of extreme pH-values. For example, a 4% aqueous solution of Na2HP04 gives mildly basic pH values of approx. 9. As reducing agent, Na2SO3 or the like can be used in order to destroy oxidising impurities and transform back oxidised species into the hydroquinone counterpart, respectively.

The process of the invention is especially suitable for the production of 2,5-di-tert- amylhydroquinone for critical applications, where non-staining properties are essential.

The following examples illustrate the nature of the invention and the manner in which it may be performed.

Example 1 110. 1g (1.000 mol) of hydroquinone (HQ) are placed into an autoclave together with 132.0 g of toluene. After purging with N2,3. 30g (0.0343 mol) of methane sulfonic acid are added and the mixture is heated to 60°C. Starting at 55°C, 158. 5g (2. 260mol) of iso-amylene are added within 3.5 h. The secondary reaction takes place for 3.5 h at 65-70°C followed by dilution of the reaction mixture with 397.6 g toluene. Then 25.7g (8%, 0.0245 mol) NaHCO3-solution are added at 70°C within 7 min. for neutralization of approx. 70% of free acid. In order to effectively neutralize acid residues, harboured within the solidified product and to eliminate intermediary formed quinone species, 74. 1g of an aqueous solution (I), consisting of 4% Na2HP04 as well as 1% Na2S03, are added within 23 min. under stirring. Simultaneously the reaction mixture is heated to 90°C in order to guarantee complete dissolution of the <BR> <BR> product. After a stirring period of 25 min. , the heavy, aqueous phase is drained off at a. m. temperature. Thereafter, 196.3g of the above used buffer solution (II) are added for another washing under identical conditions. The pH of the drained aqueous phase was 7,6. For removal of salt impurities, 171.3 g deionised water are added and stirred for 60 min. and then the aqueous phase is drained off. The organic solution is gradually cooled to 0°C to allow for precipitation. After filtering at this temperature and washing with 200g of cold toluene the product is dried at max. 70°C at 10 mbar using a rotatory evaporator. Yield: 92% (rel. hydroquinone (HQ)). Analytics Value Colour (5g + 95 g aceton) 4 [Apha] Melting point [°C]-180, 6 pH (aqueous suspension) 7,8 Volatiles (2g/2h/80°C) [%] 0, 17 Ash (5g/800°C) [%] 0, 05 Purity (GC) [%] * 98, 0 Dispersion** Slightly beige * In case of a different sample of product the structure/identity has also been confirmed by'H-NMR-spectroscopy.

* * For testing, this material has been worked into dispersion form based on water and additives giving a pH value of 9,9.

Example 2 30. 85 kg (280 mol) HQ (photo grade) are placed in a 3001 glasslined reactor followed by purging with N2. Then 43.2 kg toluene are added and the resulting suspension is heated to approx. 70°C while stirred. During the heating phase, 0.93 kg methane sulfonic acid (min. 98%) [MSA] are slowly added. Once the desired temperature is reached, 44.4 kg (630 mol) isoamylene (mixture of isomers) [IA] are added within a period of 3.5 h. To complete the reaction, stirring for another 3.5 h at 70°C after the IA-dosing is continued. The reaction mixture is then further diluted with approx. 100 kg toluene. An aqueous solution of Na2HP04 (4%) and Na2SO3 (1%) is used as neutralization/washing medium.

First the reaction mixture is mixed with 68 kg of the neutralization solution and stirred for 20 min. at 80-90°C. After stopping the stirrer to allow for phase-separation, (15 min. ) the heavy aqueous phase is drained off. The amount of the solution is measured so that an approx. 1: 1 buffer system hydrogen-/dihydrogenphosphate is formed.

Following is another washing with approx. 40 kg of the same solution at a corresponding temperature.

After that washing under conditions, a hot water wash with approx. 50 kg of decalcified water follows. It is important that all of the raw material produced is completely dissolved at all times during the described treatment! While stirring, the washed organic product solution is cooled down to-0-5°C. At this temperature the product crystallises efficiently. The so produced suspension is centrifuged and the crystalline product is washed with cold toluene. The subsequent drying takes place in a vacuum tray drier at 55°C/100 mbar yielding 90% of product (rel HQ). Analytics: Value Colour (5g + 95 g aceton) 11 [Apha] Melting point [°C] 181,2 pH (aqueous suspension) 7,5 Volatiles (2g/2h/80°C) [%] 0, 07 Ash (5g/800°C) [%] <0, 01 Purity (GC) [%] 97, 4 Dispersion* Beige * For testing, this material has been worked into dispersion form based on water and additives giving a pH value of 10.

Example 2. 1-Comparative procedure without application of pH-buffering solution and complete dissolution of material In a 300 L stirring vessel are placed 60.0 kg HQ, 5.65 kg p-toluene sulfonic acid- monohydrate (p-TSA) and 58.1 kg toluene under a blanket of nitrogen and heated to 85°C. Then 86. 25 kg of IA are dosed within 3. 5h to this mixture and the temperature is risen to 100°C at the same time. The reaction occurs at atmospheric pressure and water (from p-TSS) is removed by azeotropic distillation. To complete the reaction, the reaction mixture is stirred for an additional lh, while the temperature is risen to 110°C in the closed reactor. After this, the reaction mixture is cooled below 100°C and neutralised with conc. NaHC03-soln. (8%) under open system conditions- (pH = 7.0).

7, 50g of toluene are added to the suspension and then cooled to 20°C for crystallization. After centrifugation and washing with a) toluene (<25°C) and b) decalcified water (<30°C) the wet product (66.0 kg) is dried in a rotating drum drier @ 55°C/60 mbar, till the water content is <0. 05% yielding 61.7 kg of 2, 5-di-isoamyl- hydroquinone. The material appears to be slightly beige. Analytics: Value Colour (5g + 95 g acetone) 33 [Apha] Melting point [°C] 180,2 pH (aqueous suspension) 6,8 Volatiles (2g/2h/80°C) [%] 0, 10 Ash (5g/800°C) [%] 0, 02 Purity (GC) [%] 95, 2 Dispersion* pink * For testing, this material has been worked into dispersion form based on water and additives giving a pH value of 10. The dispersion is beige but tends to strong pinking within a couple of days! Example 2.2-Comparative procedure without application of pH-buffering solution and complete dissolution of material In a 300 L stirring vessel are mixed 59.3 kg HQ, 5.55 kg of p-TSA, 0.75 kg sodium sulfite and 56.3 kg toluene under a blanket of nitrogen followed by heating to 85°C.

Then 84.0 kg of IA are dosed within 4. 5h to this mixture and the temperature held @ 85-90°C while stirring. The reaction occurs at atmospheric pressure and water (from p-TSA) is removed by aceotropic distillation. To complete the reaction, stirring for further 3h is continued while the temperature is-risen to 105°C in the closed reactor system.

After this, the reaction mixture is cooled below 100°C and neutralized with conc.

NaHCO3-soln. (8%) within 35 minutes in an open system @ 80°C. T-he-pH-at-this stage was 8. The suspension of 2, 5-di-isoamyl-hydroquinone is adjusted to a pH of 4 by adding 555 g of formic acid and crystallisation occurred on lowering the temperature down to 18°C, while stirring.

After centrifugation and washing with a) toluene (25°C) and decalcified water with formic acid as reducing agent the wet product was found to be slightly pink.

After drying in a tray drier at 95°C/80 mbar (abs.) for 15h. the product is rust brown and shows the following analytic results: Analytics Value Colour (5g + 95 g acetone) 81 [Apha] Melting point [°C] 180 pH (aqueous suspension) 6.4 Volatiles (2g/2h/80°C) [%] 0, 1 Ash (5g/800°C) [%] 0, 3 Purity (GC) [%] 95 % Dispersion' Deep red-brown The product is not suitable for use as antioxidant in polymers.

* For testing, this material has been worked into dispersion form based on water and additives giving a pH value of 10.

Example 3 Procedure as described in Example 2 except for work-up. To minimize wastewater volumes and to reduce their phosphate load, it is also possible to neutralize most of the MSA used with an aqueous NaHCO3 (approx. 8%) in a first step followed by application of a. m. neutralization solution. This-would result in the following-values- for the above batch: 1. washing: 7.2 kg NaHCO3 solution (8%) + 21 kg neutralization solution 2. washing: 55 kg neutralization solution 3. washing: 50 kg water Crystallisation and drying yields 90% of product (rel HQ). Analytics Value Colour (5g + 95 g acetone) 7 [Apha] Melting point [°C] 181, 3 PH (aqueous suspension) 7,2 Volatiles (2g/2h/80°C) [%] 0, 04 Ash (5g/800°C) [%] <0, 01 Purity (GC) [%] 96,6 Dispersion* Beige * For testing, this material has been worked into dispersion form based on water and additives giving a pH value of 10.

Example 4 110. 1g (1. OOOmol) of hydroquinone, 330g of toluene and 3.30g (0. 0343mol) of methane sulfonic acid are placed into a doubly walled glass reactor equipped with an thermostat, mechanical stirrer and reflux condenser. After purging with N2, the mixture is heated to 110°C under stirring. Then 211.6g (2. 400mol) of tertiary-amyl alcohol is added slowly within 6. 5h. Water formed in course of the addition is removed from the reaction by azeotropic distillation at 88-102°C. The secondary reaction takes place for 2 h at 88-98°C followed by dilution of the reaction mixture with 500g toluene at 90°C.

Then 25.7g (8%, 0. 0245mol) NaHCO3-solution and 74. 1g of a buffer solution (I), consisting of 4% NaHP04 as well as 1% Na2SO3, are added under stirring at the same temperature for neutralization. After stirring for an appropriate period of time, the heavy, aqueous phase is drained off at a. m. temperature. Thereafter, 196.3g of the above used buffer solution (II) are added for another washing. For removal of salt impurities, 171.3g deionised water are added at 80°C and stirring is-continued-for some time. Then the aqueous phase is drained off. After an initial slow cooling to ambient temperature, the mixture is cooled to 5°C. Filtering and washing with 100g of cold toluene followed by drying at max. 70°C at 1 mbar yields 207.7g of product (83% rel. hydroquinone). Analytics Value Colour (5g + 95 g acetone) [Apha] 5 Melting point [°C] 181. 8 pH (aqueous suspension) 6.8 Volatiles (2g/2h/80°C) [%] 0. 02 Ash (5g/800°C) [%] <0.01 Purity (GC) [%] 98. 5 Dispersion* beige * For testing, this material has been worked into dispersion form based on water and additives giving a pH value of 10.2 Example 5 110. 1g (1. OOOmol) of hydroquinone and 330g of toluene are placed into an autoclave.

After purging with N2,3. 30g (0. 0343mol) of methane sulfonic acid are added. Then the reaction vessel is slowly flooded with iso-buten causing a slight rise of reaction temperature. Altogether 127.6g (2. 274mol) of the alkene is added during 3h at 22- 35°C giving a pressure of 1. 6bar. Stirring is continued overnight at 22-31°C causing the pressure decrease to 1.2 bar. Heating to 70°C increases the pressure to 2.8bar followed by gradual decrease to 1. 5bar after 4. 5h.

After ventilation, 25.7g (8%, 0. 0245mol) NaHCO3-solution along with 74. 1g of the buffer solution (I) are added under stirring. Simultaneously the reaction mixture was heated until it became clear. At 106°C-the heavy, aqueous phase is drained off.

Thereafter, the organic phase is treated with 196.3g of the above used buffer solution (II) at 106-115°C. For removal of salt impurities, the reaction mixture is washed with 171.3g deionised water at elevated temperature. After an initial cooling to-30°C within 2h, the temperature is further decreased to 0°C. Filtering, washing with 100g of cold toluene and drying at max. 90°C at 3 mbar yields 113.2g (50.9% rel hydroquine) of 2,5-di-tertiary-butyl hydroquinone. Analytics Value Colour (5g + 95 g acetone) [Apha] 3 Melting point [°C] 217 pH (aqueous suspension) 7.3 Volatiles (2g/2h/80°C) [%] 0. 02 Ash (5g/800°C) [%] 0. 01 Purity (GC) [%] * 98. 1 * The structure/identity has also been confirmed by'H-NMR-spectroscopy.

As can be seen from the above examples, the process according to the present invention employs a novel catalyst which excellently fits the need to make the synthesis work quickly and efficiently under homogenous catalyst conditions in presence of an organic solvent. An important advantage of the process of the invention is that it requires only catalytic amounts of catalyst (0.01 to 10% by weight). A further advantageous and crucial feature in terms of providing a non-staining product of the present invention is the work-up process. The work-up process comprises washings with an aqueous medium under complete dissolution of the crude product. The remarkable thing about this aqueous medium is its pH-buffering capability combined with reducing activity. This procedure guarantees especially that acid residues and salty impurities enclosed within the crystalline reaction product become neutralized and removed, respectively. Hydroquinones, e. g. 2,5-di-tert- amylhydroquinone, are known to be sensitive towards oxidative degradation. This is especially also true for"worked-up'-'materials if impurities are present, which e. g. locally cause significant differences in pH that in turn give rise to accelerated oxidation of the hydroquinone to the corresponding quinone (Nernst equation). These disadvantages can be solved by application of the above mentioned aqueous-medium.

Additionally, due to the application of a recyclable organic solvent instead of a corrosive liquid medium in huge quantities that consequently needs to be neutralized and disposed after usage, a significant reduction of waste streams can be achieved.

The process of invention yields a product in high yield and very good quality for special non-staining applications. The high quality is reflected both in solid form as well as in aqueous dispersions featuring an increased pH.