Ladies and gentlemen!
Let me proudly present you a small research.
Look what i've found on Espacenet
GB994506 (the temperatures look funny sometimes, but you can make them out):
Aromatic mercapto compounds are made by reacting a phenol or a phenol ether, which contains at least one hydrogen atom in ortho or para position to the -OH group or ether group, with a sulphur chloride and hydrogen sulphide at a temperature in the range of from -50 DEG C. and + 200 DEG C., recovering the poly-sulphide formed and reducing the polysulphide to the mercaptan. The phenols used are mono or polyhydroxy phenols of mono- or poly-nuclear aromatic systems in which the hydroxy groups may be etherified partly or entirely with aliphatic or aromatic radicals. They can be substituted by alkyl or aryl radicals or by halogen, mercapto- and alkyl(aryl)-mercapto groups. Suitable examples are given. The process may be effected with or without solvents. A Lewis acid or proton acid may be used as a catalyst, particularly FeCl3,AlCl3, ZnCl2, SnCl3, BF3, H2SO4 and H3PO4. The polysulphide may be reduced to the mercaptan by reaction with nascent or catalytically activated hydrogen, with hydrogen sulphide and its alkali metal salts, with grape sugar and with alkali metals or alkali metal amalgams.
Cool, huh? Considering that sulfur chloride can be
easily made from sulfur/chlorine (pass dry Cl2 over S at 120 C, distill off S2Cl2 at 136 C) and H2S - from iron turnings and sulfur, it's funny to say that, but it
is a completely OTC procedure! Not for a beginner chemist, though:
108 parts by weight of anisole and 150 parts by volume of methylene chloride and 103 parts by weight of sulphur chloride in 200 parts by volume of methylene chloride were introduced dropwise into 200 parts by volume of methylene chloride in the presence of 7 parts by weight of aluminium chloride at 380C., 22400 parts by volume (=34 parts by weight) of hydrogen sulphide being introduced.
The total reaction time was 4 hours, the mixture was then stirred into 2000 parts by volume of water and filtered off from 9 parts by weight of sulphur. The aqueous phase was extracted with methylene chloride. After hydrogenation of the combined organic phases (3 hours at 1500 C. and 100 atmospheres of hydrogen using 30 parts by weight of cobalt trisulphide as catalyst), the products were worked up as in Example 1 and 58 parts by weight of 4-mercapto-anisole (B.p. 88--900C. at 5 mm Hg. 54% of theoretical, calculated on the amount of conversion) were obtained.
They also say benzene may be used instead of DCM, 1,5 times as much is needed.
Well, as far as the reduction step goes, of course, hi-psi hydrogenation sucks, fortunately,
The reduction of polysulphide to mercaptans could also be carried out with the aid of Na2S. In this case, the polysulphide solution was stirred with excess Na2S dissolved in water. Owing to the alkalinity of Na2S, the polysulphide went into the aqueous phase as a phenolate. When the reduction was complete, the solution is neutralised and the mercapto compound was obtained from the organic layer as above.
Now, note that in this patent the need for H2S introduction was explained as follows:
...The reason for this is that the action of sulphur monochioride on phenols and naphthols does not lead to the formation of di-(hydroxyaryl)-disulphides, as would be expected from the reactants, but results in disproportionation reactions and deposition of sulphur to form mixtures of mono- and polysulphides in which the monosulphide content predominates.
(H2S introduction interferes w/disproportionation)
OK, ladies and gentlemen now that you've read that far, comes the time for the final trick:
EP0640590
The present invention relates to a process for the synthesis of the intermediates 4-hydroxy-thiophenol, 2,6-dimethyl-4-mercaptophenol,<et cetera - phenols only, no ethers>,which comprises reacting sulfur chloride and the corresponding phenol or naphthalenol in methanol, then reducing the products in mineral acid, such as hydrochloric acid, in the presence of zinc metal.
The reason that phenolic comp'ds don't disproportionate in this case is found in the previous patent:
...It is also possible to use solvents which themselves react with sulphur chlorides, e.g. alcohols or ethers, provided that these reactions are considerably slower than the reaction of the process according to the invention and provided the sulphur chloride is added to the dissolved hydroxyl-containing components which are present in excess.
In contrast w/the 1st patent, everything here is very simple:
General Procedure: Step 1 - Preparation of 2,3-Dimethyl-4-mercaptophenol
To a solution of 2,3-dimethylphenol (10g, 81.9mmoles) in anhydrous reagent grade methanol (200mL) at room temperature was added dropwise sulfur monochloride (4mL, d=1.688 8/mL, 135.03g/mol, 50.0mmoles). The reaction was mildly exothermic and the color became somewhat darker. The mixture was stirred at room temperature for about one hour and was examined by analytical thin layer chromatography eluted with 20% ethyl acetate in hexanes (v/v). TLC showed no starting material and the formation of two other spots was evident. The crude mixture was evaporated to one half of the original volume and was diluted with 200ml of diethylether and 100ml of distilled water. The heterogeneous mixture was subjected to the next reduction step without further purification.
The heterogeneous sulfuration mixture was treated with granular zinc metal (20g, excess) and 100ml of conc. hydrochloric acid at room temperature for about 16 hours. When the reduction was complete (monitored by TLC), the organic layer was separated, washed with water to remove as much zinc residue as possible. The organic layers were combined, concentrated and the crude product was preabsorbed on 40g of fine silica gel (type-H). The desired product was purified by silica gel column chromatography eluted with 5% ethyl acetate in hexanes (v/v), 5.5g of the title compound was isolated (36mmoles, 44%). The product could be further purified by crystallization from ethyl acetate and hexanes.m.p. = 98-99 DEG C;
On the downside here, we want a mercaptane of an ether (you know which one
), not a phenol (BTW, dihydroxy compds can't be used in this rxn). On the up-side, dimethoxybenzene nucleus is much more activated than anisole's, and then let me quote the #1 one more time:
Although the free hydroxy compounds generally react even without a catalyst, a catalyst is usually advisable for the reaction of the ethers.
Catalytically active compounds which can be used for the first stage of the process according to the invention are such Friedel-Crafts catalysts as proton acids and Lewis acids. Particular examples to be mentioned are iron-(III)-chloride, aluminium chloride, cinz chloride, tin chloride, boron fluoride and anhydrous sulphuric and phosphoric acids. Solid catalysts may be used in the form of a fine powder or in solution
Well, L&D, i want to ask you only one question: will any Lewis acid bee of use here (like will ZnCl2 react w/methanol and will it interfere w/its activity) If so, than it seems that 2,5-dimethoxyphenylmercaptan can be made by reacting 2,5-dimethoxybenzene with S2Cl2 and ZnCl2 in MeOH and then reduced w/aq. Na2S. That could bee IMHO a breakthrough in 2C-T's chemistry!
Someone i Have Known And Loved has recently made about 60 g of S2Cl2 from sulfur (from the gardening section of his local market), conc. HCl and pool shock and says even a baby can do it (having blown it up the 1st time he did it
)
OK, that's finally it.
Antoncho