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Synlett 2008(8): 1219-1221  
DOI: 10.1055/s-2008-1072731
LETTER
© Georg Thieme Verlag Stuttgart · New York

Short Synthesis of a Specifically Perdeuterated Hexaethylene Glycol Terminated Alkanethiol

Rajamalleswaramma Jogireddy, Izabella Zawisza, Gunther Wittstock, Jens Christoffers*
Center of Interface Science (CIS) and Institut für Reine und Angewandte Chemie, Universität Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26111 Oldenburg, Germany
Fax: +49(441)7983873; e-Mail: jens.christoffers@uni-oldenburg.de;
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Publikationsverlauf

Received 28 January 2008
Publikationsdatum:
16. April 2008 (online)

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Abstract

An oligo(ethylene glycol) terminated alkanethiol being an important building block for self-assembled monolayers was synthesized in three steps with high efficiency and without use of protective groups. The same sequence was utilized to prepare a specifically deuterated congener from an isotope-labeled starting material.

Keywords

oligo(ethylene glycol) - alkanethiol - self-assembled monolayer - mercaptane - thiourea

1

New address: Universite Louis Pasteur, Institut de Science et Ingenierie Supramoleculaires, Organic and Bioorganic Laboratory, ISIS-ULP-CNRS (UMR 7006), 8, Allee Gaspard Monge, 67083 Strasbourg Cedex, Fance

7

We actually presume a Br,O-acetal formation by a radical mechanism followed by hydrolysis.

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Hexaethylene glycol (12-bromododecyl) ether (3a) NaH (145 mg, 3.63 mmol, 60% dispersion in mineral oil) was added portionwise to a solution of 1 (6.00 g, 21.3 mmol) in abs. DMF (60 mL) at 23 °C. After the reaction mixture was stirred for 1 h, 2a (1.20 g, 3.66 mmol) was added and the resulting mixture stirred for 17 h at the same temperature. Then it was diluted with Et2O (100 mL) and washed with H2O (50 mL). After the separation of the organic layer, the aqueous layer was extracted with Et2O (2 × 25 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated. The crude product was purified by column chromatography [SiO2, CH2Cl2-MeOH (15:1), R f = 0.37] to obtain compound 3a (800 mg, 42%) as a colorless liquid. IR (ATR): 3440 (m), 2926 (s), 2856 (s), 1675 (vs), 1460 (m), 1387 (m), 1256 (m), 1094 (vs), 946 (w), 733 (w), 660 (m) cm-1. 1H NMR (500 MHz, CDCl3): δ = 1.22-1.29 (m, 14 H), 1.36 (quint, J = 7.1 Hz, 2 H), 1.52 (quint, J = 6.8 Hz, 2 H), 1.80 (quint, J = 7.2 Hz, 2 H), 2.79 (s, 1 H), 3.35 (t, J = 6.9 Hz, 2 H), 3.39 (t, J = 6.8 Hz, 2 H), 3.51-3.56 (m, 4 H), 3.58-3.61 (m, 18 H), 3.66-3.68 (m, 2 H). 13C{1H} NMR (125 MHz, CDCl3): δ = 25.93 (CH2), 28.02 (CH2), 28.60 (CH2), 29.27 (CH2), 29.32 (CH2), 29.35 (CH2), 29.38 (CH2), 29.41 (CH2), 29.48 (CH2), 32.68 (CH2), 38.86 (CH2), 61.54 (CH2), 69.90 (CH2), 70.20 (CH2), 70.40-70.47 (8 CH2), 71.36 (CH2), 72.40 (CH2). HRMS (CI, isobutane): m/z calcd for C24H50BrO7 [M+ + H]: 529.2740; found: 529.2740.
Hexaethylene glycol (12-bromododecyl- d 24 ) ether (3b) IR (ATR): 3440 (m), 2926 (s), 2867 (s), 2197 (m), 2095 (m), 1456 (m), 1349 (m), 1256 (w), 1105 (vs), 946 (w), 731 (m) cm-1. 1H NMR (500 MHz, CDCl3): δ = 2.96 (s, 1 H), 3.46-3.48 (m, 2 H), 3.49-3.51 (m, 2 H), 3.53-3.58 (m, 18 H), 3.61 (t, J = 4.6 Hz, 2 H). 13C{1H} NMR (125 MHz, CDCl3): δ = 27.52-28.54 (m, 10 CD2), 61.33 (CH2), 69.68 (CH2), 70.04 (CH2), 70.25 (CH2), 70.26-70.28 (5 CH2), 70.32 (CH2), 70.33 (CH2), 72.32 (CH2); signals for OCD2 and CD2Br are not observed. HRMS (CI, isobutane): m/z calcd for C24H26D24BrO7 [M+ + H]: 553.4246; found: 553.4245.

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Hexaethylene glycol (12-bromododecyl) methyl ether (4a) A solution of MeI (2.60 g, 18.3 mmol) in abs. DMF (12 mL) was added to a cooled solution of NaH (55 mg, 1.38 mmol, 60% dispersion in mineral oil) in abs. DMF (12 mL) at -5 °C. After 15 min, a solution of alcohol 3a (487 mg, 0.920 mmol) in abs. DMF (12 mL) was added dropwise at -5 °C and the mixture was stirred for 3.5 h at the same temperature. Few drops of MeOH were added and the resulting mixture was poured into a mixture of ice-cold H2O (5 mL) and Et2O (10 mL). After layers were separated, the aqueous layer was extracted with Et2O (2 × 10 mL) and the combined organic layers were dried over MgSO4, filtered, and concentrated in vacuo. The crude product was purified by column chroma-
tography [SiO2, CH2Cl2-MeOH (24:1), R f = 0.50] to obtain compound 4a (430 mg, 86%) as a colorless liquid. IR (ATR): 2925 (s), 2860 (s), 1659 (m), 1460 (m), 1352 (m), 1251 (m), 1106 (vs), 948 (w), 853 (w), 723 (m) cm-1. 1H NMR (500 MHz, CDCl3): δ = 1.21-1.29 (m, 14 H), 1.31-1.39 (m, 2 H), 1.51 (quint, J = 6.9 Hz, 2 H), 1.79 (quint, J = 7.2 Hz, 2 H), 3.32 (s, 3 H), 3.34 (t, J = 6.9 Hz, 2 H), 3.38 (t, J = 6.8 Hz, 2 H), 3.48-3.52 (m, 4 H), 3.57-3.60 (m, 20 H). 13C{1H} NMR (125 MHz, CDCl3): δ = 25.91 (CH2), 27.99 (CH2), 28.58 (CH2), 29.24 (CH2), 29.29 (CH2), 29.32 (CH2), 29.35 (CH2), 29.38 (CH2), 29.46 (CH2), 32.65 (CH2), 33.78 (CH2), 58.83 (CH3), 69.89 (CH2), 70.34 (CH2), 70.40-70.45 (9 CH2), 71.32 (CH2), 71.77 (CH2). HRMS (CI, isobutane): m/z calcd for C25H52BrO7 [M+ + H]: 543.2897; found: 543.2898.
Hexaethylene glycol (12-bromododecyl- d 24 ) methyl ether (4b) IR (ATR): 2926 (s), 2866 (s), 2197 (m), 2095 (m), 1456 (m), 1350 (m), 1296 (w), 1106 (vs), 989 (m), 949 (w), 852 (m) cm-1. 1H NMR (500 MHz, CDCl3): δ = 3.32 (s, 3 H), 3.48-3.51 (m, 4 H), 3.56-3.60 (m, 20 H). 13C{1H} NMR (125 MHz, CDCl3): δ = 27.56-28.52 (m, 10 CD2), 58.82 (CH3), 69.81 (CH2), 70.33 (CH2), 70.40-70.42 (7 CH2), 70.44 (CH2), 70.47 (CH2), 71.76 (CH2); signals for OCD2 and CD2Br are not observed. HRMS (CI, isobutane): m/z calcd for C25H28D24BrO7 [M+ + H]: 567.4403; found: 567.4403.

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Hexaethylene glycol (12-thiododecyl) methyl ether (5a) A solution of bromide 4a (418 mg, 0.768 mmol) and thiourea (65 mg, 0.853 mmol) in EtOH (0.2 mL) was degassed (freeze, pump, thaw) and refluxed under N2 for 6 h. After cooling to 23 °C, NaOH (0.5 mL, c = 5 mol L-1, aqueous solution) was added. The solution was again degassed (freeze, pump, thaw) and slowly heated to reflux. After refluxing for 2 h under N2 atmosphere, it was cooled to 23 °C, acidified with HCl (1 mL, c = 2 mol L-1) and diluted with CH2Cl2 (1 mL). The layers were separated and the aqueous layer was extracted with CH2Cl2 (3 × 1 mL). The combined organic layers were washed with sat. aq NaHCO3 solution (1 mL), dried over MgSO4, filtered, and evaporated in vacuo. The crude product was purified by column chromatography [SiO2, CH2Cl2-MeOH (24:1), R f = 0.45] to obtain compound 5a (280 mg, 73%) as a colorless liquid. IR (ATR): 2923 (s), 2854 (s), 1458 (m), 1350 (m), 1248 (w), 1104 (vs), 1040 (w), 945 (m), 852 (m), 722 (m) cm-1. 1H NMR (500 MHz, CDCl3): δ = 1.21-1.34 (m, 15 H), 1.47-1.60 (m, 4 H), 2.46 (q, J = 7.4 Hz, 2 H), 3.32 (s, 3 H), 3.40 (t, J = 6.8 Hz, 2 H), 3.48-3.53 (m, 4 H), 3.57-3.60 (m, 22 H). 13C{1H} NMR (125 MHz, CDCl3): δ = 24.51 (CH2), 25.97 (CH2), 28.25 (CH2), 28.94 (CH2), 29.36-29.52 (7 CH2), 33.92 (CH2), 58.89 (CH3), 69.93 (CH2), 70.40-70.47 (9 CH2), 71.39 (CH2), 71.82 (CH2). HRMS (CI, isobutane):
m/z calcd for C25H53O7S [M+ + H]: 497.3512; found: 497.3512.
Hexaethylene glycol (12-thiododecyl- d 24 ) methyl ether (5b)
IR (ATR): 2925 (s), 2866 (s), 2197 (m), 2095 (m), 1456 (m), 1350 (m), 1297 (w), 1246 (m), 1106 (vs), 947 (m), 852 (m) cm-1. 1H NMR (500 MHz, CDCl3): δ = 1.23 (s, 1 H, SH), 3.32 (s, 3 H), 3.48-3.51 (m, 4 H), 3.56-3.60 (m, 20 H). 13C{1H} NMR (125 MHz, CDCl3): δ = 27.55-28.56 (m, 10 CD2), 58.83 (CH3), 69.79 (CH2), 70.33 (CH2), 70.40-70.42 (7 CH2), 70.46 (CH2), 70.47 (CH2), 71.75 (CH2); signals for OCD2 and CD2SH are not observed. HRMS (CI, isobutane): m/z calcd for C25H29D24O7S [M+ + H]: 521.5018; found: 521.5018.