Disulfides from alkyl and acyl halides
1455
color changed from red to faint yellow, the reaction was com-
pleted. The mixture was diluted with 40cm3 diethyl ether, and
the suspension washed three times with water (3ꢂ15cm3).
The organic layer was separated and dried (Na2SO4). The
solvent was removed under reduced pressure to afford the
dialkyl or diacyl disulfides. The pure solid products were ob-
tained by recrystallization of dialkyl disulfides from ethanol
and diacyl disulfides from 1,2-dichloroethane.
ible groups are found to be unreactive under the
reaction conditions. We believe that this method will
present a better and more practical alternative to the
existing methodologies and should find widespread
application in organic synthesis.
Experimental
Dibenzyl disulfide (2a)
1H NMR (90 MHz, CDCl3): ꢀ ¼ 7.23–7.79 (m, 10H, ArH),
Materials were purchased from Fluka and Merck companies.
The reactions were monitored by TLC using silica gel plates.
Products were identified by comparison of their spectra and
physical data with those of authentic samples [20, 23–27]. 1H
NMR spectra were measured at 90 and 500 MHz on a JEOL
spectrometer with tetramethylsilane (Me4Si) as an internal
reference, and CDCl3 as the solvent. IR spectra were recorded
using an Alpha centauri FT-IR spectrophotometer. Elemental
analysis was performed on a LECO 250 instrument; results
agreed favorably with calculated values.
3.60 (s, 4H, CH2S) ppm; IR (KBr): ꢁꢀ¼ 3051, 2964, 2909,
708, 564, 465 cmꢀ1
.
Bis(3-chlorobenzyl)disulfide (2b, C14H12S2Cl2)
Oil; 1H NMR (90 MHz, CDCl3): ꢀ ¼ 7.12–7.27 (m, 8H, ArH),
3.57 (s, 4H, CH2S) ppm; IR (KBr): ꢁꢀ¼ 3050, 2920, 2890,
783, 690, 521 cmꢀ1
.
Bis(4-chlorobenzyl)disulfide (2c) [20b]
1H NMR (90 MHz, CDCl3): ꢀ ¼ 7.36–7.60 (q, 8.5 Hz, 8H,
Preparation of N,N0-dibutyl-N,N,N0,N0-tetramethylethyl-
enediammonium tetrahydroborate (BTMETB) (C14H42B2N2)
and N,N0-dibenzyl-N,N,N0,N0-tetramethylethylene-
ArH), 3.81 (s, 4H, CH2S) ppm; IR (KBr): ꢁꢀ¼ 3080, 2980,
2879, 679, 519, 464 cmꢀ1
.
diammonium tetrahydroborate (BZTMETB) (C20H38B2N2)
An alkaline solution of sodium borohydride was prepared
from 1.53 g NaBH4 (0.04 mol) in 10 cm3 5 M NaOH. Then,
an aqueous solution of N,N0-dibutyl-N,N,N0,N0-tetramethyl-
ethylenediammonium bromide=chloride (5.00 g in 8 cm3 H2O)
or N,N0-dibenzyl-N,N,N0,N0-tetramethylethylenediammonium
bromide=chloride (5.00 g in 15 cm3 H2O) was added drop-
wise to the above solution at room temperature and stirred
for 2 h. The resulting white solid product was filtered
off, washed with ether, and dried in a vacuum desiccator
over CaCl2. The chemical formula of the reagents was es-
tablished by IR andꢀNMR spectra. The content of active
reducing agent BH4 was determined by the titrimetric
method [28].
Bis(4-methoxybenzyl)disulfide (2f) [26]
1H NMR (90 MHz, CDCl3): ꢀ ¼ 7.0–7.3 (m, 8H), 3.78 (2S,
6H, 2OCH3), 3.72 (2s, 4H, 2CH2Ph) ppm.
Diphenacyl disulfide (2g) [24]
1H NMR (90 MHz, CDCl3): ꢀ ¼ 7.38–7.93 (m, 10H, ArH),
4.18 (s, 4H, CH2S) ppm; IR (KBr): ꢁꢀ¼ 3040, 2955, 2893,
1690, 1578, 684, 574, 453 cmꢀ1
.
Bis(1-naphthylmethylene)disulfide (2h, C22H18S2)
1
Mp 147–149ꢁC; H NMR (90 MHz, CDCl3): ꢀ ¼ 7.24–8.04
(m, 14H, ArH), 4.47 (s, 4H, CH2S) ppm; IR (KBr): ꢁꢀ¼ 3080,
2980, 2879, 645, 579, 479 cmꢀ1
.
1
BTMETB: H NMR (500 MHz, D2O): ꢀ ¼ ꢀ0.40–0.10 (m,
J ¼ 80.65 Hz, 8H, BH4ꢀ), 0.92 (t, J ¼ 7.35 Hz, 6H, CH3), 1.35
(m, 4H, CH2), 1.75 (m, 4H, CH2), 3.17 (s, 4CH3), 3.39 (t,
J ¼ 8.5 Hz, 4H, CH2), 3.87 (s, 4H, CH2) ppm; IR (KBr):
ꢁꢀ¼ 2973, 2882, 2296, 2240, 1623, 1497, 1466, 1133, 986,
Bis(cyclohexyl)disulfide (2i) [27]
1H NMR (400 MHz, CDCl3): ꢀ ¼ 1.14–1.34 (m, 10H), 1.55–
1.63 (m, 2H), 1.72–1.80 (m, 4H), 1.97–2.03 (m, 4H), 2.61–
2.69 (m, 2H) ppm; 13C NMR (100MHz, CDCl3): ꢀ ¼ 25.66,
26.05, 32.81, 49.91ppm; IR (KBr): ꢁꢀ¼ 2928, 2852, 1447,
920 cmꢀ1
.
BZTMETB: 1H NMR (500 MHz, D2O): ꢀ ¼ ꢀ0.40–0.10 (m,
J ¼ 80.6Hz, 8H, BH4ꢀ), 3.14 (s, 12H, CH3), 3.97 (s, 4H,
CH2), 4.6 (s, 4H, CH2), 7.52–7.59 (s, 10H, ArH); IR (KBr):
ꢁꢀ¼ 3034, 2988, 2958, 2278, 2227, 1618, 1478, 1421, 1219,
1260, 996 cmꢀ1
.
Dibenzoyl disulfide (2l) [20a]
1H NMR (90 MHz, CDCl3): ꢀ ¼ 7.35–7.70 (m, 10H, ArH)
1006, 880, 789, 733 cmꢀ1
.
ppm; IR (KBr): ꢁꢀ¼ 3047, 1700, 1681, 674, 648, 440 cmꢀ1
Bis(4-chlorobenzoyl)disulfide (2m) [20a]
.
General procedure for preparation of alkyl and acyl disulfides
Sulfur powder (6mmol) and quarternary diammonium tetra-
hydroborates (6mmol) are thoroughly mixed in a two-neck
50cm3 round-bottomed flask bearing a condenser and a drop-
ping funnel containing 10 cm3 methanol. As the methanol is
added to the solid mixture, an exothermic reaction takes place
and the mixture is stirred at room temperature for 10–15min.
Then alkyl or acyl halide (6mmol) was added and the reaction
mixture stirred at room temperature for 3–5 min. When the
1H NMR (90 MHz, CDCl3): ꢀ ¼ 7.44–8.77 (q, J ¼ 8.63,
8H, ArH) ppm; IR (KBr): ꢁꢀ¼ 3118, 1718, 1685, 634,
487 cmꢀ1
.
Bis(3-chlorobenzoyl)disulfide (2n, C14H8O2S2Cl2)
1H NMR (90 MHz, CDCl3): ꢀ ¼ 7.46–8.02 (m, 8H, ArH)
ppm; IR (KBr): ꢁꢀ¼ 3060, 1700, 1688, 720, 690, 507 cmꢀ1
.