The invention relates to a process for the preparation of substituted quinones and hydro¬ quinones by a new, simple method. The invention relates in particular to a process for the preparation of long-chain, alkyl sulfide substituted quinones and hydroquinones. Substitu¬ ted quinones and hydroquinones prepared by the process according to the invention can be used in the preparation of new liquid crystal polymers.

The starting materials used in the process according to the invention are, in a manner known per se. quinone (Formula I) and a thiol compound (Formula II):

in which formulae R is a long-chain alkyl group containing 8-18 C atoms.

Reactions of quinones with thiol compounds have been described, for example, in Snell, J.M., Weissberger, A., J. Am. Chem. Soc. 60, 2084 (1938), 61, 442 (1939), and 61, (1939), 450. According to the last-mentioned publication, in the reaction between quinone and a thiol compound (cf. reaction (1) according to the publication) there forms substitu- ted hydroquinone which is in equilibrium with quinone, as follows (cf. formula (2) ac¬ cording to the publication):

According to the said publication, the repeating of reactions (1) and (2) produces the formation of disubstituted quinones.

An object of the present invention is, however, to prepare from the starting material according to Formulae (I) and (II) stated above, in a manner deviating from that in th said publication, via monosubstituted quinones according to Formula II, monosubstitute hydroquinones according to Formula (IN).

It is thus an object of the invention to provide a simple process in which commerciall available and economically priced starting materials according to Formulae (I) and (II) ar used and by which process the reaction can be caused to take place almost quantitatively Furthermore, it is an object of the invention to provide for the preparation of compound according to Formula IV a process which will perform also on large scales and i therefore applicable to industrial production.

It has now been observed, surprisingly, that alkyl sulfide substituted hydroquinone according to Formula (IV), in which R is a long -chain alkyl chain containing 8-18 atoms, can be prepared by a process which is characterized in what is stated in th characterizing clause of Claim 1.

The process according to the invention comprises the following reactions (1) and (2):

I

In the process according to the invention, quinone according to Formula (I) and a long- chain thiol according to Formula (II) are thus first allowed to react with each other in a nucleophilic addition reaction in the presence of alcohol in a nitrogen atmosphere to form addition products according to Formula in. The addition products can be produced almost quantitatively by means of a mixing reaction at room temperature, the material amount of quinone being double that of thiol. When alcohol, preferably isopropanol, is used as the solvent, the reaction product, i.e. monosubstituted quinone according to Formula (III), precipitates out directly from the reaction mixture. The obtained product can be recrystal- lized either from isopropanol or from toluene, depending on which thiol is used in the reaction.

The monosubstituted quinone of Formula (III), prepared by the procedure described above, must be further reduced in order that an alkyl sulfide substituted hydroquinone according to Formula (IV) can be formed.

The reduction for the production of the desired end product according to Formula (IV) is now accomplished according to the present invention rapidly and easily by using as the reducing agent sodium dithionite, Na ₂ S ₂ O ₄ . The reducing agent is dissolved in water, preferably up to a saturated solution, and the obtained solution is added to the substituted quinone to be reduced, dissolved in a suitable solvent. The solvent used may be, for example, tetrahydrofuran (THF) or methylene chloride (CH ₂ C1 ₂ ). The reaction mixture is stirred at room temperature until complete reduction occurs. The reduction can be verified, for example, from an organic layer on a thin sheet or from the turning of the orange-yellow quinone solution into a light, yellowish hydroquinone solution. For example, on a scale of approx. twenty millimoles, the reduction takes a few minutes. In this manner an alkyl sulfide substituted hydroquinone according to Formula (IV) is produced, which has OH groups at the p-positions of the benzene ring and an alkyl chain having 8-18 C atoms as a substituent at the 2-position.

The synthesis of substituted quinone and its further selective reduction, carried out by the process according to the present invention, is an economical and simple, as well as rapid, method of preparing the desired 2-alkylmercapto-l,4-benzoquinone according to Formula

(III) and 2-alkyhnercapto-l,4-hydroquinone according to Formula (IV).

The long-chain thiol compound, i.e. long-chain mercaptan, used as the starting material contains, as stated above, an alkyl chain having 8-18 C atoms. Preferably the alkyl chain contains 8, 12 or 18 carbon atoms, in which case the desired reduced end product obtained is respectively 2-octylmercapto-l,4-hydroquinone, 2-dodecylmercapto-l,4- hydroquinone or 2-octadecylmercapto-l,4-hydroquinone.

The monosubstituted hydroquinones according to Formula (IV), prepared by the process according to the present invention, can be used in the preparation of liquid crystal polymers. It has been observed that these compounds improve the compatibility of liquid crystal polymers with cheaper aliphatic polymers, whereupon less expensive liquid crystal polymers are obtained as a result.

The process according to the invention is described in greater detail in the following embodiment examples. Figures 1-12 depict various spectra for alkyl sulfide substituted quinones and hydroquinones prepared by the process according to the invention.

Figures la and lb MS spectrum of 2-octadecylmercapto-l,4-benzoquinone (la) and MS spectrum of 2-octadecylmercapto-l,4-hydroquinone (lb).

Figures 2a and 2b IR spectrum of 2-octadecylmercapto-l,4-benzoquinone (2a) and IR spectrum of 2-octadecylmercapto-l,4-hydroquinone (2b).

Figure 3 400 MHz 'H NMR spectrum of 2-octadecylmercapto-l,4-benzoquinone.

Figure 4 400 MHz 'H NMR spectrum of 2-octadecylmercapto-l,4-hydroquinone.

Figures 5a and 5b MS spectrum of 2-dodecylmercapto-l ,4-benzoquinone (5a) and MS spectrum of 2-dodecylmercaptoJ ,4-hydroquinone (5b).

Figures 6a and 6b IR spectrum of 2-dodecylmercapto-l ,4-benzoquinone (6a) and MS spectrum of 2-dodecylmercapto-l ,4-hydroquinone (6b).

Figure 7 400 MHz *H NMR spectrum of 2-dodecylmercapto-l,4-benzoquinone.

Figure 8 400 MHz Η NMR spectrum of 2-dodecylmercapto-l,4-hydroquinone.

Figures 9a and 9b MS spectrum of 2-octylmercapto-l,4-benzoquinone (9a) and MS spectrum of 2-octylmercapto-l,4-hydroquinone (9b).

Figures 10 a and b IR spectrum of 2-octylmercapto-l,4-benzoquinone (10a) and IR spectrum of 2-octylmercapto-l,4-hydroquinone (10b).

Figure 11 400 MHz ^! H NMR spectrum of 2-octylmercapto-l,4-benzoquinone.

Figure 12 400 MHz 'H NMR spectrum of 2-octylmercapto-l,4-hydroquinone.

The following can be stated regarding the interpretations of the MS, IR and NMR spectra of 1 ,4-benzoquinones and hydroquinones, depicted in Figures 1-12:

According to the mass spectra (MS), the compounds are fragmented so that the entire carbon chain (= R in Formulae I and II) detaches from the ring structure, and what remains is a ring-structured degradation product containing a sulfur atom. The HRMS values indicate the length of the carbon chain.

The following measurement results were obtained for the quinone structures: Figure la; R = C„ m/z 392 (M+), m/z 142 (100 %) HRMS; calculated 392.2749, measured 392.2783 Figure 5a; R = C _I2 m/z 308 (M+), m/z 142 (100 %)

HRMS; calculated 308.1810, measured 308.1810 Figure 9a; R = C ₈ m/z 252 (M+), m/z 142 (100 %)

HRMS; calculated 252.1184, measured 252.1195

The following measurement results were obtained for the hydroquinone structures: Figure lb; R = C ₁₈ m/z 394 (M+), m/z 142 (100 %)

HRMS; calculated 394.2906, measured 394.2939

Figure 5b; R = C ₁₂ m/z 310 (M+), m z 142 (100 %)

HRMS; calculated 310.1967, measured 310.1945 Figure 9b; R = C _g m z 254 (M+), m/z 142 (100 %)

HRMS; calculated 254.1340, measured 254J355

IR spectra: Figures 2, 6 and 10.

In the spectra, s = strong, m = medium, and w = weak; the spectra were produced from

KBr tablets.

In the quinone structures (Figures 2a, 6a and 10a) range 2800-2700 cm ^"1 (s) indicates: C-H extension of carbon chains range 1600 cm ^"1 (s) indicates: C = C conjug. C = O

In the hydroquinone structures (Figures 2b, 6b and 10b) range 3250-3350 cm ^"1 (s) indicates: O-H extension range 2800-2700 cm ^"1 (s) indicates: C-H extension of carbon chains range 1400 cm ^'1 (s) indicates: O-H twist

NMR: U 400 MHz. CDC . Figures 3, 4, 7, 8, 11 and 12. Legend: s = singlet, d = duplet, dd = duplet of duplets, t = triplet, k = quintet, m = multiplet

Tables 1 and 2 show interpretations of the spectra of the quinone and hydroquinone structures. H _a , H _b , and H _c indicate hydrogen atoms at positions 3, 5 and 6 of the benzene ring. H _x and H _y indicate hydrogen atoms in the OH groups at positions 1 and 4 of the hydroquinone structure.

Table 1. Interpretation of the quinone structures, Figures 3, 7 and 11.

chemical transiti¬ multiplexity intensity interpretation on δ/ppm

0,9 t 3 -CH ₃

1,3 - 1,45 m 10, 18, 31 -CH ₂ -groups of the carbon chain

1,7 k 2 -CH _? -CH,

2,2 s impurity (acetone)

2,75 t 2 -S-CH _? -

6,4 d 1 H _a

6,7 dd 1 H _b

6,8 d 1 H _c

7,26 s CDC1 ₃

Table 2. Interpretation of the hydroquinone structures, Figures 4, 8 and 12.

chemical tran¬ multiplexity intensity interpretation sition δ/ppm

0,9 t 3 -CH ₃

1,25 - 1,35 m 10, 18, 31 -CH ₂ -groups of the carbon chain

1,55 k 2 CH,-CH,

2,2 - 2,3 s impurity (acetone)

2,7 t 2 S-CH,-

4,75,4,5,4,4 s 1 -OH, approx. 6,3 s 1 -OH _y

6,75 dd 1 H _a

6,85 d 1 H _b

6,95 d 1 H _c

7,26 s CDC1 ₃

As can be seen from the spectra and their interpretations presented, the products prepared by the process according to the invention are desired alkyl sulfide substituted benzo- quinones and hydroquinones.

Example 1

Preparation of alkyl sulfide substituted quinones.

The reaction was carried out in an N ₂ atmosphere at room temperature. The flask was equipped with a reflux condenser, a magnetic stirrer, and a thermometer. 20 mmol (2J6 g) of 1 ,4-benzoquinone was dissolved in 30 ml of isopropanol (the dissolving could be promoted by heating the reaction mixture). When the quinone had dissolved complete¬ ly, an amount of 10 mmol, i.e. 1.46 g of 1-octanethiol, 2.02 g of 1-dodecanethiol or 2.87 g of solid 1-octadecanethiol dissolved in approx. 20 ml of isopropanol (the dissolving could be promoted by heating), was added to the reaction mixture by injection through the septum.

The product began gradually to precipitate out from the solution, and stirring was continued until all of the starting-material quinone had been spent (monitoring by TLC = thin layer chromatography).

The obtained product was filtered, and more of the product proper could be filtered out from the filtrate after 24 h. The product was recrystallized from isopropanol in the case of 1-octanethiol or 1-dodecanethiol and from toluene in the case of 1-octadecane. The percent yield for all thiols was approx. 90 %.

The products obtained were studied by MS, IR and NMR spectrometry, cf. Figures la, 2a, 3, 5a, 6a, 7, 9a, 10a and 11.

Example 2.

Preparation of alkyl sulfide substituted hydroquinone.

Recrystallized substituted quinones prepared according to Example 1 were reduced in order to obtain the desired hydroquinone compounds. The reduction was carried out by using sodium dithionite Na ₂ S ₂ O ₄ as the reducing agent. The quinone form was dissolved in THF or CH ₂ C1 ₂ , to which Na ₂ S ₂ O ₄ , dissolved in water up to a saturated solution, was added. The solutions were mixed together at room temperature, and complete reduction to hydroquinones was verified from an organic layer on a thin sheet (solvent system: 25 % ethyl acetate/75 % n-hexane). Tables 3 and 4 show the R, values and melting points of the substituted quinone structures and hydroquinone structures. Furthermore, quinone compounds are UV-active and hydroquinone compounds are well colored with iodine. The reduction was also verified visually in a change of the orange-yellow quinone solution into a light yellowish hydroquinone solution. The time taken by the reduction was a few minutes on this scale.

Table 3. R _f values and melting points of alkyl sulfide substimted quinone structures. (R _f value of p-benzoquinone = 0.590)

starting material thiol R _f -value melting point/ °C

1-octanethiol 0,776 94

1-dodecanethiol 0,807 106

1-octadecanethiol 0,823 112

Table 4. R _f values and melting points of alkyl sulfide substimted hydroquinone structures.

starting material thiol R _f -value melting point/ °C

1-octanethiol 0,513 63

1-dodecanethiol 0,554 76

1-octadecanethiol 0,606 90

The obtained products were studied by MS, IT and NMR spectrometry, cf. Figures lb, 2b, 4, 5b, 6b, 8, 9b, 10b and 12.

Example 3

Preparation of octadecylmercapto-l,4-benzoquinone and further octadecylmercapto-1,4- hydroquinones on a larger scale.

The reaction was carried out in an N ₂ atmosphere at room temperature. The flask was equipped with a power stirrer, a reflux condenser, a thermometer, and a drop funnel.

1.0 mol (approx. 108 g) of p-benzoquinone was dissolved in 2.2 liters of isopropanol (the dissolving could be promoted by heating the reaction mixture).

2-octadecylmercapto-l ,4-benzoquinone began gradually to precipitate out from the solution, and the stirring was continued until all of the quinone had been spent (monito- ring by TLC). The product obtained was filtered, and more of the product proper could be filtered out from the filtrate after 24 hours. The product was recrystallized in this case from toluene. The yield was approx. 90 % .

11

In order to obtain 2-octadecylmercaptohydroquinone, the recrystallized quinone structure was reduced. The reduction was carried out by using sodium dithionite. The quinone form was dissolved in THF or CH ₂ C1 ₂ , to which dissolved in water, was added. Complete reduction was verified from an organic layer on a thin sheet.

Example 4, reference example

For reference, a synthesis according to the following scheme, presented in the literature, was carried out (Snell, J.M., Weissberger, A., J. Am. Chem. Soc. 61, 450 (1939)).

Performing of the reaction:

0.05 mol (5.4 g) of 1,4-benzoquinone was dissolved in 100 ml of ethanol (98 %), whereafter 0.025 mol (2.3 g) of thioglycolic acid was added to the solution. The reaction was exothermal, and the mixture gradually turned from yellow to dark red. After 20 minutes of stirring, the ethanol was evaporated out, and the obtained dark, solid substance was recrystallized first from 50 % ethanol and thereafter from water. According to the in¬ struction, the black residue could be removed from the crystals with water; however, this did not materialize in practice. According to the thin sheet, the mixture contained, in addition to the product proper, also 1 ,4-benzoquinone and hydroquinone, which lowered the melting point of the product to approx. 140 °C (in die instruction, m.p. = 157 - 158 °C). The yield from the reaction was approx. 25 % (in the instruction, 32.4 %).

FIGURE 1 la MS spectrum of 2-octadecylmercapto-l,4-benzoquinone lb MS spectrum of 2-octadecylmercapto-l,4-hydroquinone

FIGURE 2 2a IR spectrum of 2-octadecylmercapto-l,4-benzoquinone 2b IR spectrum of 2-octadecylmercapto-l,4-hydroquinone

FIGURE 3 400 MHz Η NMR spectrum of 2-octadecylmercapto-l,4- benzoquinone

FIGURE 4 400 MHZ ^l H NMR spectrum of 2-octadecylmercapto-l,4-hydroquinone

FIGURE 5 5a MS spectrum of 2-dodecylmercapto-l,4-benzoquinone 5b MS spectrum of 2-dodecylmercapto-l, -hydroquinone

FIGURE 6 6a IR spectrum of 2-dodecylmercapto-l,4-benzoquinone (top)

6b IR spectrum of 2-dodecylmercapto-l,4-hydroquinone (bottom)

FIGURE 7 400 MHz Η NMR spectrum of 2-dodecylmercapto-l,4-benzoquinone

FIGURE 8 400 MHz Η NMR spectrum of 2-dodecylmercapto-l,4-hydroquinone

FIGURE 9 9a MS spectrum of 2-octylmercapto-l,4-benzoguinone 9b MS spectrum of 2-octylmercapto-l, -hydroquinone

FIGURE 10 10a IR spectrum of 2-octylmercapto-l,4-benzoquinone

10b IR spectrum of 2-octylmercapto-l,4-hydroquinone

FIGURE 11 400 MHz Η NMR spectrum of 2-octyl ercapto-l,4-benzoquinone

FIGURE 12 400 MHz Η NMR spectrum of 2-octylmercapto-l,4-hydroquinone