METHYLTHIOPHENETHYLAMINE

SYNTHESIS: A short foreword to the synthetic portion is needed. First, although the required thioanisole, 2,3-dimethoxythioanisole, is now commercially available, it is of the utmost importance that it be free of the impurity, veratrole. I know that the material presently available from Aldrich Chemical Company is satisfactory, as I have had a hand in making it. But, if veratrole is present, there are very difficult separations encountered during these preparations. And secondly, the synthesis of 2-TIM and 4-TIM requires a separation of isomers. The first intermediates are common to both. They will be presented here, under this recipe for 2-TIM.

A solution of 150 mL of 1.6 M butyllithium in hexane under N2 was vigorously stirred and diluted with 150 mL petroleum ether (30-60 deg C) and then cooled with an external ice bath to 0 deg C. The addition of 26.7 g of veratrole produced a flocculant white precipitate. Next, there was added a solution of 23.2 g of N,N,N',N'-tetramethylethylenediamine in 100 mL anhydrous Et2O and the stirred reaction mixture was allowed to come to room temperature. The subsequent addition of 20.7 g of dimethyl disulfide over the course of several min produced an exothermic response, and this was allowed to stir for an additional 30 min. There was then added 10 mL EtOH followed by 250 mL of 5% NaOH. The organic phase was washed first with 150 mL 5% NaOH, followed by 2x100 mL portions of 5% dilute HCl. The removal of solvent and bulb-to-bulb distillation of the residue provided 2,3-dimethoxythioanisole boiling at 72-80 deg C at 0.4 mm/Hg as a white oil. This product contained some 20% unreacted veratrole as a contaminant and the isolation of subsequent products from this impure material was extraordinarily difficult. The effort needed for careful purification at this point was completely justified. The product could be obtained in a pure state by distillation at 0.1 mm/Hg through a 6 cm Vigreaux column with collection of several fractions. Those that distilled at 84-87 deg C were pure 2,3-dimethoxythioanisole. An analytical sample can be obtained by cooling a concentrated MeOH solution in dry ice, filtering the generated crystals, and washing with cold MeOH. This product melts at 36.5-37 deg C. Anal. (C9H12O2S) C,H,S. The picrate can be formed by treatment with a saturated EtOH solution of picric acid. It formed orange crystals with a mp of 73-78 deg C. Anal. (C15H15N3O9S) N.

To 18 mL of POCl3 there was added 25 mL N-methylformanilide and the solution allowed to stand at room temperature for 0.5 h, until the color had developed to a rich claret. There was then added 25.0 g of 2,3-dimethoxythioanisole and the mixture heated on the steam bath for 2.5 h. This was added to 500 mL H2O and stirred at ambient temperature for 2 h. The product was extracted with 4x150 mL CH2Cl2, the extracts combined, and the solvent removed under vacuum. The residue was distilled through a Vigreaux column under vacuum (0.1 mm/Hg) with the fraction boiling at 125-135 deg C being richest in aldehydes, as determined by GC analysis. If the starting 2,3-dimethoxythioanisole contains appreciable veratrole as a contaminant, then this aldehyde fraction contains three components. There is present both 2,3-dimethoxy-4-(methylthio)benzaldehyde and 3,4-dimethoxy-2-(methylthio)benzaldehyde (the two desired precursors to 4-TIM and 2-TIM, respectively), but also present is 3,4-dimethoxybenzaldehyde from the veratrole contamination. The weight of this fraction was 11.9 g and was a white oil free of starting thioether.

Although efforts to separate this mixture were not effective, one of the aldehydes could be isolated in small yield by derivative formation. This was too wasteful to be of preparative value, but it did allow the generation of seed that was of great value in the later separation of the mixed nitrostyrenes that were prepared. If a 1 g portion of this mixture was fused with 0.6 g p-anisidiine over an open flame and then cooled, the melt set up as a solid. Triturating under MeOH gave a yellow solid (0.45 g, mp 77-80 deg C) which on recrystallization from hexane appeared to be a single one of the three possible Schiff's bases that could theoretically be prepared. It had a mp of 80-81 deg C. Anal. (C17H19NO3S) C,H. Hydrolysis with hot 3 N HCl freed the benzaldehyde which was isolated by quenching in H2O and extraction with CH2Cl2. The extracts were stripped of solvent under vacuum and the residue distilled bulb-to-bulb under vacuum to give white crystals of 3,4-dimethoxy-2-(methylthio)benzaldehyde (the 2-TIM aldehyde) with a mp of 23-24 deg C. A micro-scale conversion of this to the corresponding nitrostyrene provided the seed that was effectively used in the large scale preparation described below.

A solution of 9.0 g of a mixture of 3,4-dimethoxy-2-(methylthio)benzaldehyde and 2,3-dimethoxy-4-(methylthio)benzaldehyde in 50 mL of nitromethane was treated with 1.5 g anhydrous ammonium acetate and held at reflux for 5 h. The excess nitromethane was removed under vacuum to yield 10.4 g of a dark orange oil which, upon dissolving in 40 mL hot MeOH and being allowed to cool and slowly evaporate at ambient temperatures, provided dark colored crystals. Filtration (save the mother liquors!) and recrystallization from 40 mL MeOH provided 6.3 g of a yellow crystalline solid. A second recrystallization from 50 mL MeOH gave 5.0 g of lemon yellow plates 3,4-dimethoxy-2-methylthio-beta-nitrostyrene with a mp of 102-103.5 deg C. An analytical sample, from IPA, had a mp of 103-104 deg C and a single spot on TLC with CHCl3, with an Rf of 0.54. Anal. (C11H13NO4S) C,H. When there had been veratrole left as a contaminant in the original 2,3-dimethoxythioanisole, the nitrostyrene that was isolated by this method had, after recrystallization, a mp of 93-95 deg C. This substance acted as a single compound through a number of recrystallization trials, but on TLC analysis always gave two components (silica gel, chloroform) with Rf's of 0.54 and 0.47. It proved to be a mixture of 3,4-dimethoxy-2-methylthio-beta-nitrostyrene and 3,4-dimethoxy-beta-nitro-styrene in an exact molecular ratio of 2:1. This latter nitrostyrene is the precursor to DMPEA, q.v. Anal. (C32H37N3O12S2) C,H. The mother liquor above is the source of the 4-TIM nitrostyrene, and its isolation is described in the recipe for 4-TIM.

A solution of 4.2 g LAH in 70 mL anhydrous THF was cooled to 0 deg C under He and with stirring. There was added, dropwise, 2.8 mL of 100% H2SO4, followed by 4.4 g of 3,4-dimethoxy-2-(methylthio)-beta-nitrostyrene dissolved in 25 mL THF. Stirring was continued for a few min as the reaction returned to room temperature, and then it was heated to a reflux for 10 min on the steam bath. The reaction was cooled again, and 25% NaOH was added dropwise until a white granular precipitate was obtained. This was removed by filtration, and the filter cake was washed with 2x50 mL Et2O. The filtrate was extracted into 100 mL dilute H2SO4 which was, in turn, made basic again and extracted with 2x100 mL CH2Cl2. The extracts were pooled, and the solvent removed under vacuum to give a residue of crude product. This was distilled from 100-115 deg C at 0.3 mm/Hg yielding 3.2 g of a clear white oil. This was dissolved in 25 mL IPA, neutralized with 23 drops of concentrated HCl, and diluted with 75 mL anhydrous Et2O. There was a deposition of beautiful white platelets of 3,4-dimethoxy-2-methylthiophenethylamine hydrochloride (2-TIM) which were removed by filtration, washed with ether, and air dried. This hydrochloride salt contained a quarter mole of H2O of crystallization. The mp was 183-184 deg C. Anal. (C11H18ClNO2Sa1/4 H2O) C,H,N.

DOSAGE: greater than 240 mg.

DURATION: unknown.

QUALITATIVE COMMENTS: (with 160 mg) There was perhaps some awareness in an hour or so, but in another hour there was absolutely nothing. A small amount of wine in the evening was quite intoxicating.

(with 240 mg) No effects of any kind.

EXTENSIONS AND COMMENTARY: The problems that might be associated with the making of the three amphetamines that correspond to 2-TIM, 3-TIM and 4-TIM might very well prove quite exciting. These would be the three thio analogues of TMA-3; vis, 3,4-dimethoxy-2-methylthioamphetamine, 2,4-dimethoxy-3-methylthioamphetamine, and 2,3-dimethoxy-4-thioamphetamine. The first challenge would be to name them. Using the 2C-3C convention, they would be the 3C analogs of trivially named 2-carbon compounds, namely 3C-2-TIM, 3C-3-TIM and 3C-4-TIM. Using the thio convention (the number before the T is the position of the sulfur atom), they would be 2-T-TMA-3, 3-T-TMA-3 and 4-T-TMA-3. The second challenge would be their actual synthesis. The information gained from the separation of the 2-carbon nitrostyrenes and that most remarkable mixed-nitrostyrene thing that acted as a single pure material, would not be usable. But it is intriguing to speculate if there might be some parallel problems in the 3-carbon world. It seems almost certain that none of the compounds would be pharmacologically active, so the incentive would be the challenge of the chemistry. Some day, maybe.

Date: 2016-04-22; view: 805