J. Org. Chem. 1984,49,3641-3643
of log k / k o for solvolysis of diphenylmethyl chloride in aqueous acetone are lower than those expected from the behavior in other solvents. Return of a free carbocation to reactant is not responsible for these differences, because there is insufficient chloride ion to trap a carbocation. Return of an ion pair is p ~ s s i b l e , ~but J ~ it cannot fully explain the dispersion because ion-pairs derived from tert-butyl or diphenylmethyl chloride can be attacked from the rear, but that from 1-adamantyl chloride cannot. Initial-state interactions could be playing a role, although they are neglected in the formulation of the GrunwaldWinstein and similar equations, despite evidence for their importance in nucleophilic s u b ~ t i t u t i o n . ~Initial-state ~ interactions should be very different for alkyl and arylalkyl substrates. To some extent there will be cancellations of these effects in going from initial states, but they should be least complete in solvolysesof arylalkyl substrates where charge delocalization in the transition state imposes conformational constraints and substrate structure, as well as mechanism, plays a role in kinetic polarity scales. It is therefore probably not feasible to devise generally applicable kinetic solvent scales for SN1reactions.
Experimental Section Materials. The substrates were commercial materials purified by distillation or recrystallization. Solvents were purified by standard m e t h o d ~ ~and * ~mixed ~ J ~ solvents were generally made up by weight. Kinetics. Reactions of diphenylmethyl chloride were generally followed spectrophotometrically at 255 nm, on a Gilford or a Hewlett Packard 8450 spectrophotometer. Some reactions were followed conductimetrically or by monitoring the protonation of methyl orange spectrophotometrically. Most reactions were followed at 25.0 "C except for the faster reactions which were followed at lower temperatures. [Substrate] was 3 X M for reactions followed spectrophotometrically and 5 X M for reactions followed conductimetrically or by use of methyl orange. Reactions in TFE and aqueous MeCN were followed spectrophotometrically and k in 60 w t % MeCN determined conductimetrically and spectrophotometrically agreed. Reactions in aqueous MeOH, EtOH, and MezCO were followed by use of methyl orange. Our choice of temperature was limited by freezing of the solvent or low solubility of the substrate at low temperatures, and we were unable to follow reactions in HFIP or trifluoroacetic acid. The first-order rate constants, k, are in reciprocal seconds.
Acknowledgment. Support by the National Science Foundation (chemical Dynamics) is gratefully acknowledged. Registry No. Diphenylmethyl chloride, 90-99-3. (23) Robertson, R. E. h o g . Phys. Org. Chem. 1967,4,213. Shaskus, J.; Haake, P. J. Org. Chem. 1983, 48, 2036.
Hard Acid and Soft Nucleophile Systems. 8.' Reductive Dehalogenation of o - and p -Halophenols and Their Derivatives Manabu Node, Takeo Kawabata, Keiichiro Ohta, Mayumi Fujimoto, Eiichi Fujita, and Kaoru Fuji*
Institute for Chemical Research, Kyoto University, Uji Kyoto 611, Japan Received August 15, 1983
Combination systems consisting of a hard acid and a soft nucleophile have been effectively applied for cleavage re0022-32631841 1949-3641$01.50/0
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Table I. Reductive Dehalogenation of o-Halophenol Derivatives X.
run X 1 Br 2 Br 3 Br 4 Br 5 1 6 I
AlC13, time, molar equiv h Me H 2.5 1.5 H Me 1.5 0.5 Ac Me 1.5 4.0 H CH2C02Et 1.5 17.0 H H 1.5 0.15 Me COzMe 5.0 6.5
R1
yield,"
R2
tempb rt 0 "C 0 "C 0 "C
rt 0 "C
--
rt rt
%
95 94 89 98 87
rt
95
Isolated yield. rt = room temperature. Table 11. Reductive Dehalogenation of p -Halophenol Derivatives
-
-
"ex - R'o-o EtSH/CHzCI2
AlC13, time, tempd run X R molar equiv min 1 Br H 1.5 15 0 ° C 2 Br Me 2.6 70 rt 1.5 40 0 ° C 3 Br Et 4 5 6
Br Ph 1 H I Me
1.5 1.5 1.5
120
0 "C
10 rt 25
0°C
-
product (yield, %)= R' = H (89)bvc R' = H (86) R' = H (64),bR' = Et (25)b rt R' = Ph (98) R' = H (82) R' = H (72)
Isolated yield. bBy GLC analysis. 10% starting material was recovered. rt = room temperature.
actions of variety of chemical bonds. Chemoselective cleavage can be achieved by proper choice of an acid and a nucleophile. A system involving aluminum chloride and ethanethiol cleaves C-0 bonds in ethers2 and esters: CNO2 bonds: activated C=C bonds,5 and Ar-SR bonds.lP6 Those reactions, except for reductive cleavage of Ar-SR bonds, proceed through a push-pull mechanism associated with hard acids and soft nucleophiles. Intervention of a radical cation has been suggested for the reductive removal of -SR group on polyaromatic ring.6 In our studies on dealkylation of bromoanisoles with the aluminum chloride and ethanethiol system, we encountered the fact that 0- and p-bromoanisoles suffered debromination along with the normal demethylation to afford phenol, while m-bromoanisole was smoothly dealkylated to give m-bromophenol. This paper describes the scope and limitations of this reductive cleavage of the carbonhalogen bond in 0- and p-halophenols and their derivatives with a combination system of aluminum chloride and ethanethiol.' (1) For part 7, see: Node, M.; Nishide, K.; Kawabata, T.; Ohta, K.; Watanabe, K.; Fuji, K.; Fujita, E. Chem. Pharm. Bull. 1983,31, 4306. (2) (a) Node, M.; Hori, H.; Fujita, E. J. Chem. SOC.Perkin Trans. 1 1976, 2237. (b) Fuji, K.; Ichikawa, K.; Node, M.; Fujita, E. J. Org. Chem. 1979,44,1661. (c) Node, M.; Nishide, K.; Sai, M.; Ichikawa, K.; Fuji, K.; Fujita, E. Chem. Lett. 1979, 97. (d) Node, M.; Nishide, K.; Fuji, K.; Fujita, E. J. Org. Chem. 1980,45,4275. (3) (a) Node, M.; Nishide, K.; Sai, M.; Fujita, E. Tetrahedron Lett. 1978,5211. (b) Node, M.; Nishide, K.; Sai, M.; Fuji, K.; Fujita, E. J. Org. Chem. 1981, 46, 1991. (c) Node, M.; Nishide, K.; Ochiai, M.; Fuji, K.; Fujita, E. Ibid. 1981, 46, 5163. (4) Node, M.; Kawabata, T.; Ueda, M.; Fujimoto, M.; Fuji, K.; Fujita, E. Tetrahedron Lett. 1982,23,4047. (5) Fuji, K.; Kawabata, T.; Node, M.; Fujita, E. Tetrahedron Lett. 1981, 22, 875. (6) Node, M.; Nishide, K.; Ohta, M.; Fujita, E. Tetrahedron Lett. 1982, 23, 689. (7) For a preliminary communication, see: Node, M.; Kawabata, T.; Ohta, K.; Watanabe, K.; Fuji, K.; Fujita, E. Chem. Pharm. Bull. 1983,31, 749.
0 1984 American Chemical Society
3642 J. Org. Chem., Vol. 49, No. 19, 1984
Notes fluorophenol (9) were not reactive under the standard reaction conditions. Polyhalophenols require a longer reaction time because of the electron-withdrawing nature of halogen atoms (Table 111). Selective debromination is possible for 12 and 13 to provide p- and o-chlorophenol, respectively. 1-Bromo-2-naphthol (15) was debrominated within 30 min to afforded @naphthol which was further converted to naphthyl sulfide 20 in 96% yield under the reaction
Table 111. Dehalogenation of Polyhalophenols
R3'
substrate 10 11 12 13 14
time,
R'
R2
R3
Br Br Br C1 Br
Br Me C1 Br Br
H Br H H Br
product
h 17 96 48 48 49
yield,"
R'
R6
%
H H H C1 H
H Me C1 H H
84 92 91 61 40b
__
15, R = H
Isolated yield. bThe starting material was recovered (45%).
-_ 16,
R = Ac
Results and Discussion The results of the dehalogenation are summarized in Table I and 11. Bromo- or iodobenzene derivatives with an oxygen function at the ortho or para position were easily dehalogenated in high yields, whereas meta derivatives 1 and 2 were not dehalogenated under the standard condi-
bBP
&I
6 C O O M e
1
2 OH
CH( S E t )
C1
6
!
3, R = Me
5
4, R - H
b' Q OH
21
I I .
CHO
OH
OH
@
c'@Me
8
9
tions. The rate of reaction was considerably retarded when an electron-withdrawing group was attached to the aromatic ring (run 6 in Table I). Thus, methyl 5-bromo-2methoxybenzoate (3) did not afford the corresponding dehalogenated product but gave methyl 5-bromosalicylate (4) under the standard conditions. Notably, with compounds which tends to form a benzylic cation like the aldehyde 5 and the dithioacetal6 the reaction was completely suppressed. A tendency in ethyl (3-bromo-4hydroxypheny1)acetate (run 4 in Table I) to retard the reaction may partly be ascribed to the consumption of aluminum chloride by complexation with oxygen atoms in the ester moiety. Oxygen functions such as hydroxyl, alkoxyl, aryloxyl, and acetoxyl groups on the phenyl ring initiate the dehalogenation. The rate decreases in the order of OH = OR > OAr > OAc, which can be reasonably explained by the magnitude of the mesomeric effect of those oxygen functions. Chlorophenols 7 and 8 and o-
17, R1 = R2 = Br R1 = H, R2 = C1
ig, 19, R1
= R2 = C1
SEt
$1
Br
OH
Rr
22
OMe
__
23
OMe
___ 24
conditions. An acetoxyl group again retards the rate. Thus, the acetate 46 akorded 20 in 87% yield after 23 h but was recovered unchanged after 30 min. Dibromonaphthol 17 provided 21 in 89% yield. Although the chlorine atom in phenol derivatives resisted dehalogenation, it was possible to remove the chlorine in naphthol derivatives. Treatment of 4-chloro1-naphthol (18) under the general conditions at 0 "C for 1 h furnished a-naphthyl sulfide 21, 1-(ethy1thio)-4chloronaphthalene (22), and naphthalene in 59%, 29%, and 9% yield, respectively. Dichloronaphtholl9 afforded 21 and naphthalene in 54% and 11% yield, respectively. Exhaustive defunctionalization of 1-naqhthyl derivatives via 21 has been reported.' The rate of debromination was dramatically lowered when it was carried out in ethanethiol without dichloromethane as a cosolvent. On the other hand, changing the solvent system had little effect upon the rate of demethylation. Thus, p-bromoanisole gave debrominated products (phenol and anisol) in 81% yield and the combined yield of demethylated products (phenol and pbromophenol) was 51% under the standardized conditions (0 "C, 15 min in dichloromethane, run 1 in Table IV), whereas combined yields of dehalogenated products and demethylated products were 6% and 72%, respectively, without dichloromethane (run 2 in Table IV). Another remarkable feature was that debromination was mostly suppressed when diethyl sulfide was used instead of ethanethiol, while demethylation proceeded smoothly (54% combined yield, run 3 in Table IV). A nucleophile, espe-
Table IV. Debromination of p -Bromoanisole under the Various Conditions"
run 1 2 3 4 5
acid, molar equiv nucleophileb AlCl,, 1.5 EtSH EtSH AlCl,, 1.5 AlCl,, 1.5 EtzS AlCl,, 1.5 none AlCl,, 0.4 EtSH
solventc CHzClz EtSH CHZCl2 CH2Clz CHzClz
All reactions were run in around 1-mmol scale.
* 0.4 mL.
reactn time 15 m 15 m 15 m 15 m l h 2 mL.
phenol 45 5 2 0 17
Determined by GLC.
comDounds, % yieldd anisole p-bromophenol p-bromoanisole 36 6 0.3 1 67 23 0.3 52 42 0 0 100 35 2 12
J. Org. Chem. 1984,49, 3643-3646
cially ethanethiol, is necessary for this debromination (run 4 in Table IV). The rate of the reaction may depend on the concentration of aluminum chloride (compare run 1 and 5 in Table IV). These facts may suggest the intervension of a cationic species such as 23 or 24 in the mechanism. Resuls of runs 1and 2 in Table IV indicate that in a push-pull mechanism the function of aluminum chloride as a Lewis acid is comparable between those two reaction conditions because considerable amount of demethylated products were obtained in both cases. A simple push-pull mechanism for this debromination can hardly explain the remarkable retardation of the rate without dichloromethane as a cosolvent. Although there is no direct evidence to distinguish between a simple cationic species 23 and a radical cationic species 24, we prefer the latter to explain all the findings obtained. Almost all of the existing methods for dehalogenation of aromatic compounds involve one- or two-electron transfer from the reagent to the substrate.* Hence, the substitution of electron-withdrawing group(s) on the aromatic ring facilitates the reductive removal of halogen atoms in the reported methods. On the other hand, electron-donating group(s) accelerate the dehalogenation with the present method, since the mechanism involves a cationic species as an intermediate.
Experimental Section IR spectra were recorded with a JASCO A-202 diffraction grating infrared spectrophotometer, and 'H NMR spectra were obtained with a JEOL JNM-FX 100 spectrometer. Chemical shifts are reported relative to internal tetramethylsilane. GLC analyses were performed with a Shimazu Model GC-4CM instrument. Materials. Compounds 1,2,7-15, and 17-19 and those used in runs 1, 2, and 5 in Table I and in all runs in Table I1 are commercially available. The starting halophenol derivatives 3: 5,1° and 16," those listed in runs 3,'2 4,'3 and 614 in Table I, ethyl p-hydr~xyphenylacetate'~ (the product from run 4 in Table I), 5-bromo-2-hydroxybenzoicacid (4),16and naphthyl sulfides 2017 and 2117 are known. Dithioacetal 6. To a stirred solution of aluminum chloride (6.10 g, 46 "01) and ethanethiol (5 mL) in dichloromethane (20 mL) was added 3-iodonanisaldehyde (5) (2.62 g, 10 mmol) in nitrogen under ice-cooling. After being stirred for 3 h at the same temperature, the reaction mixture was poured into water and extracted with dichloromethane. The organic layer was dried (Na2S04),filtered, and evaporated to afford a residue, which was purified by column chromatography over silica gel with elution of dichloromethane-hexane (1:2), giving 6 as a colorless crystal (0.64 g, 18%). Analytically pure sample was obtained by recrystalization from ether-hexane: mp 67-68 "C; IR (KBr) 3100-3400,2970,1590,1495,1405,1260,1205 cm-l; NMR (CDC1,) 6 1.22 (t,J = 7.5 Hz, 6 H), 2.55 (4,J = 7 Hz, 2 H), 2.57 (9,J = 7.5 Hz, 2 H), 4.83 (8, 1 H), 5.39 (s, 1 H), 6.92 (AB d, J = 9 Hz, 1H), 7.35 (ABdd, J = 2,9 Hz,1H), 7.74 (d, J = 2 HZ, 1H). Anal. Calcd for C11H,,01S2: C, 37.29; H, 4.27. Found C, 37.25; H, 4.17. General Procedure for Dehalogenation. A mixture of substrate (1 mmol), ethanethiol (0.4 mL), methanol-free di(8) For an extensive review, see: Pinder, A. R. Synthesis 1980, 425. (9) Thakkar, N.; Haksar, C. N. J. Indian Chem. SOC.1977,54,1111. (10) Fujita, E.; Fuji, K.; Tanaka, T. J. Chem. SOC.C 1971, 205. (11) Hazlet, S. E. J. Am. Chem. SOC.1940, 62, 2156. (12) Tiwari, S. S.; Singh, A. J.Indian Chem. SOC.1961,38,53. [Chem. Abstr. 1961,55, 15395~1. (13) Tolkachev, 0. N.; Prokhorov, A. B.; Voronin, V. G.;Krivko, L. N.; Lyutik, A. I.; Preobrazhenskii, N. A. Zh. Obshch. Khim. 1961,31, 1540 [Chem. Abstr. 1961,55, 24639il. (14) Seidel, J. J. Prakt. Chem. 1899, 59, 106. (15) Narasimhachari, N.; Prakash, U.; Helgeson, E.; Davis, J. M. J. Chromatogr. Sci. 1978, 16, 263. (16) Rainsford, K. D.; Whitehouse, M. W. Agents Actions 1980, 10, 451. (17) Node, M.; Nishide, K.; Ohta, M.; Fuji, K.; Fujita, E.; Hori, H.; Inayama, S. Chem. Pharm. Bull. 1983, 31, 545.
0022-3263/84/1949-3643$01.50/0
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chloromethane (2 mL), and aluminum chloride was stirred in nitrogen under the conditions described in Tables I and 11. The reaction mixture was poured into water and extracted with dichloromethane. The organic layer was washed with brine, dried (Na2S04),filtered, and evaporated to afford a residue which was purified by column chromatography over silica gel or analyzed by GLC. GLC analyses were performed with a 20% SF-96 (3 m x 3 mm) column. Column temperature and internal standards are as follows, respectively, for phenol, anisole, and diethyl disulfide at 100 "C, n-decane; for phenetole at 80 O C , n-nonane; for p-bromophenol, p-bromoanisole, and m-bromoanisole at 150 "C, n-tridecane. l-(Ethylthi0)-4-~hloronaphthalene (22). To a stirred solution 4-chloro-l-naphthol (18) (180 mg, l mmol) in dichloromethane (2 mL) was added ethanethiol(O.4 mL) and aluminum chloride (187 mg, 1.4 mmol). The mixture was stirred for 1h at 0 "C under nitrogen, poured into ice-water, and extracted with dichloromethane. The organic layer was washed with brine, dried, and chromatographed over silica gel with 5% dichloromethanehexane to afford naphthalene (16 mg, 9%), 1-(ethy1thio)-4chloronaphthalene as an oil [(65 mg, 29%); IR (CHC1,) 3060,1580, 1505,1365,990 cm-'; NMR (CDC13)6 1.35 (t,J = 7 Hz, 3 H), 2.95 (4,J = 7 Hz, 2 H), 7.2-7.8 (m, 4 H), 8.1-8.6 (m, 2 H); high-resolution mass spectrum, calcd for ClzHllCIS (M') m/e 222.0269, obsd 222.02611 and 1-(ethy1thio)naphthalene (21,111 mg, 59%). Registry No. 3, 7120-41-4; 4, 4068-76-2; 5, 2314-37-6; 6, 91238-73-2; 7, 106-48-9;8,87-64-9; 9, 367-12-4; 10,615-58-7; 11, 2432-14-6; 12,695-96-5; 13, 3964-56-5; 14, 118-79-6;15, 573-97-7; 16, 91238-72-1; 17, 2050-49-9; 18, 604-44-4; 19, 2050-76-2; 20, 32551-87-4; 21,17539-31-0;22,91238-74-3;@-naphthol,135-19-3; 578-57-4; 2naphthalene, 91-20-3; l-bromo-2-methoxybenzene, bromo-4-methylphenol, 6627-55-0; 2-bromo-4-methylphenyl acetate, 86614-21-3; ethyl 3-bromo-4-hydroxybenzeneacetate, 29121-25-3; 2-iodophenol, 533-58-4; methyl 3-iodo-4-methoxybenzoate, 35387-93-0; phenol, 108-95-2;4-methylphenol, 106-44-5; ethyl 4-hydroxybenzeneacetate,17138-28-2;methyl 4-hydroxybenzoate, 99-76-3; 4-bromophenol, 106-41-2; 1-bromo-4-methoxybenzene, 104-92-7; l-bromo-4-ethoxybenzene,588-96-5; 1bromo-4-phenoxybenzene, 101-55-3; 4-iodophenol, 540-38-5; 1iodo-4-methoxybenzene, 696-62-8; 2-chlorophenol, 95-57-8; methoxybenzene, 100-66-3; ethanethiol, 75-08-1; diethyl sulfide, 352-93-2; aluminum chloride, 7446-70-0.
Direct Condensation of [Hydroxy(tosyloxy)iodo]arenes with Thiophenes. A Convenient, Mild Synthesis of
Aryl(2-thieny1)iodonium Tosylates Anthony J. Margida and Gerald F. Koser* Department of Chemistry, The University of Akron, Akron, Ohio 44325 Received March 15, 1984
Aryl(Zthieny1)iodonium salts are active microbicides and, for that reason, have been the object of considerable attention in the patent literature.' The most common synthetic approach to such iodonium salts entails the condensation of bis(acy1oxy)iodoareneswith thiophenes in the presence of a strong acid (e.g., H2S04,C13CC02H, CF3C02H),a method which may preclude the incorpora(1) For examples, see: (a) Moyle, C. L. Ger. Offen. 2 145 733,March 22, 1973; Chem. Abstr. 1973, 78, P147781z. (b) Jezic, Z., U S . Patent 3712920, Jan 23,1973; Chem. Abstr. 1973, 79, P5254b. (c) Moyle, C. L., Fr. Pat. 2153532, June 8, 1973; Chem. Abstr. 1973, 79, P91987x. (d) Moyle, C. L. U.S. Patent 3763 187, Oct 2, 1973; Chem. Abstr. 1974,80, P14836r. (e) Moyle, C. L. U.S. Patent 3 885 036, May 20, 1975; Chem. Abstr. 1976,83, P152402j. (0 Moyle, C. L. US.Patent 3944 498, March 16, 1976; Chem. Abstr. 1976,84, P181912b. (9) Riley, W. H.; Hendricks, H. J. U S . Patent 4024238, May 17, 1977; Chem. Abstr. 1977, 84, P58525n.
0 1984 American Chemical Society
