The coupling reaction of aryl bromide and aryl boronic acid in water/DMF as solvent was studied using a palladium-complex as a catalyst in the presence of ultrasound at room temperature. The effect on the reaction of a base and a solvent was also studied with and without ultrasound and was found to increase the speed of the reaction. In this regard, we propose reaction mechanisms that could explain the results obtained.
Due to the urgent need for solutions to the increasing environmental problem of pollution, awareness has recently grown to limit all its sources as much as possible. Hence, chemists have sought to change the conventional methods of organic synthesis so as to make them more efficient and environmentally friendly. This lies within the framework of a new vision of chemistry known as “green chemistry”. To do so, new synthesis strategies and activation methods are established to adhere to regulations around the world. Among the eco-compatible activation methods we can mention temperature, light, pressure, ultrasound and microwave as physical activation methods, phase transfer catalysis as a chemical activation method, and enzymatic catalysis as a biochemical activation method. These new unconventional methodologies involve green chemistry, which is a developing discipline involving selective high-yield catalysis, solvent-free syntheses that are economical in terms of energy and raw material, clean processes and biodegradable materials.
This research work is interested in studying bi-activation through ultrasonic bias [
All compounds were characterized by IR, 1H NMR spectra, 13C NMR spectra and mass spectra. The IR spectra were recorded in KBr with a JASCO FT-IR-420 spectrometer, with a precision of ±2 cm−1 in the 400 - 4000 cm−1 range. The 1H NMR spectra (400 MHz) and 13C NMR spectra (100 MHz) were obtained on a Bruker AC300 spectrometer using CDCl3 as solvent and TMS as an internal standard. Chemical shift is given in ppm.
The coupling products were analyzed by GC-MS (Hewlett-Packard computerized system consisting of a 5890 gas chromatograph coupled with a 5971A mass spectrometer) using fused-silica-capillary columns with a polar stationary phase: Supelcowax 10 (60 m × 0.2 mm × 0.20 Ø film thickness). GC-MS analyses were obtained using the following conditions: carrier gas He; flow rate 1 ml/min; split 1:20; injection volume 0.1 ll; injection temperature 250˚C; oven temperature programmed from 60 to 220˚C at 4˚C/min and holding at 220˚C for 30 min; ionization mode used was electronic impact at 70 eV.
PL spectra were measured on a C6PbI4 thin film using a double monochromator U1000 equipped with a photomultiplier. The excitation wavelength was the 325 nm (3.815 eV) line of a Spectra-Physics beamlock 2085 Argon laser.
Melting points were taken on a Reichert-Heizbank apparatus.
In the present research work, the study of some Suzuki and Hiyama coupling reactions using arylboronic acids (2a), trimethoxy(Aryl)silane (4a-4b) and aryl bromides (1a) [
As was found in [
As can be seen in
The aim of studying the impact of the base nature on the evolution of the Suzuki reaction between 2a and 1a in
Entry | Solvent | ԑ à 25˚C | Yield (%)a* | Yield (%)b* |
---|---|---|---|---|
1 | MeOH | 33 | 47 | 88 |
2 | EtOH | 32.6 | 43 | 81 |
3 | iPrOH | 18 | 40 | 79 |
4 | THF | 7.58 | 22 | 50 |
5 | Toluene | 2.38 | 8 | 40 |
6 | Acetonitrile | 37.5 | 35 | 72 |
7 | DMF | 36.70 | 27 | 40 |
8 | Water | 87 | 34 | 77 |
9 | Water/Acetonitrile (v/v = 1:1) | - | 15 | 20 |
10 | Water/EtOH (v/v = 1:1) | - | 55 | 90 |
11 | Water/DMF (v/v = 1:1) | - | 58 | 95 |
12 | Water/MeOH (v/v = 1:1) | - | 33 | 52 |
13 | Water/MeOH (v/v = 2:1) | - | 54 | 90 |
14 | Water/EtOH (v/v = 2:1) | - | 59 | 94 |
15 | Water/i-PrOH (v/v = 2:1) | - | 48 | 85 |
16 | Water/Dioxane (v/v = 2:1) | - | 48 | 89 |
17 | Water/THF (v/v = 2:1) | - | 49 | 73 |
18 | Water DMF (v/v = 2:1) | - | 52 | 89 |
aReaction conditions: PdCl2(MeCN)2 (0.02 mmol), 1a (1.0 mmol), 2a (1.5 mmol), K2CO3 (2 mmol), PPh3 (0.6 mmol) and solvent (3 mL) at 100˚C for 8h; bPdCl2(MeCN)2 (0.02 mmol), 1a (1.0 mmol), 2a (1.5 mmol), K2CO3 (2 mmol), PPh3 (0.6 mmol) and solvent (3 mL), Ultrasonic irradiation for 5 min; *Determined by means of GC, based on the 1a, yields in parenthesis are those of purified products.
water/DMF is to provide some additional elements to the process. That’s why several trials involving various types of basic catalysts were made.
The analysis of the results in
As a result, in the presence of these bases, the free carbonate anion in the environment is insufficiently activated, which leads to the weakening of the base cation-anion attraction force [
Entry | Base | Reticular energy Kj.mol-1 | Yield (%)a* |
---|---|---|---|
1 | - | - | 0 |
2 | Et3N | - | 40 |
3 | KOH | - | 50 |
4 | NaOH | 824 | 55 |
5 | Na2CO3 | 2301 | 37 |
6 | KOtBu | - | 14 |
7 | Cs2CO3 | 1921 | 58 |
8 | K2CO3 | 2084 | 53 |
9 | K3PO4 | - | 48 |
aReaction conditions: PdCl2(MeCN)2 (0.02 mmol), 1a (1.0 mmol), 2a (1.5 mmol), base (2 mmol), PPh3 (0.6 mmol), water, (1.5 mL), DMF (1.5 mL), 100˚C, 8 h; *Determined by means of GC, based on the 1a, yields in parenthesis are those of purified products.
alter their efficiency. Indeed, the use of cesium or potassium carbonate provides good conversions with a slight advantage to Cs2CO3. The opposite-ion, however, does not seem to affect the selectivity for it was found to be perfect and identical in both cases.
The present research work undertakes the study of the effect brought by the ultrasounds on the yield of Suzuki reactions involving 1a-1h and 2a-2p in a water /dimethylformamide mixture and using Cs2CO3 as a base.
The results reported in
These bubbles constitute chemical microreactors in which very high temperature and pressure values in the final stage of their implosion are reached causing the high release of energy. This allows for the stirring of the reaction environment, an activation of the catalytic system and the nearing of reactants by increasing their specific surface area and mixing the liquid layers located near them. This leads to an increase in the contact between the reactants promoting the formation of the product for a very short period of time and with very high yields.
In order to examine the effect of the solvent type on the course of the Hiyama reaction [
Arl Br | R1 | Reagent | Product | Yield (%)a* | Yield (%)b* |
---|---|---|---|---|---|
H | 2a | 3a | 32 | 87 | |
H | 2b | 3b | 36 | 82 | |
H | 2c | 3c | 39 | 86 | |
4-CH3 | 2d | 3d | 35 | 84 | |
H | 2e | 3e | 34 | 81 | |
H | 2f | 3f | 32 | 93 | |
H | 2g | 3g | 31 | 77 | |
4-CH3O | 2h | 3h | 41 | 93 | |
4-Cl | 2i | 3i | 40 | 91 | |
4-CH3O | 2j | 3j | 37 | 89 | |
H | 2k | 3k | 39 | 92 | |
4-CH3O | 2l | 3l | 37 | 88 | |
4-Cl | 2m | 3m | 37 | 91 | |
4-CH3 | 2n | 3n | 33 | 80 |
4-CN | 2o | 3o | 35 | 90 | |
---|---|---|---|---|---|
4-Cl | 2p | 3p | 43 | 91 |
aReaction conditions: PdCl2(MeCN)2 (0.02 mmol), 1a-1h (1.0 mmol), 2a-2p (1.5 mmol), Cs2CO3 (2 mmol), PPh3 (0,6 mmol) , water (1.5 mL) in DMF (1.5 mL) at 100˚C for 8 h; bPdCl2(MeCN)2 (0.02 mmol), 1a-1h (1.0mmol), 2a-2p (1.5mmol), Cs2CO3 (2mmol), PPh3 (0.6 mmol), water (1.5 mL) in DMF (1.5 mL), Ultrasonic irradiation 5 min, 25˚C; *Determined by means of GC, based on the 1a-1h; yields in parenthesis are those of purified products.
Entry | Solvent | Yield (%)a* | Yield (%)b* |
---|---|---|---|
1 | EtOH | 24 | 51 |
2 | CH3CN | 31 | 63 |
3 | Water | 23 | 45 |
4 | DMSO | 15 | 30 |
5 | DMF | 25 | 45 |
6 | THF | 32 | 50 |
7 | toluene | trace | trace |
8 | Water/THF (v/v = 1:1) | 9 | 39 |
9 | Water/EtOH (v/v = 1:1) | 29 | 56 |
10 | Water/DMSO (v/v = 1:1) | 40 | 70 |
11 | Water/DMF (v/v = 2:1) | 45 | 88 |
12 | Water/DMF (v/v = 1:1) | 62 | 96 |
13 | Water/Acetonitrile (v/v = 1:1) | 46 | 76 |
THF: tetrahydrofurane, EtOH: ethanol, DMSO: dimethylesulfoxyde, DMF: N, N-dimethylformamide; aReaction conditions: PdCl2(MeCN)2 (0.02 mmol), 1a (1.0 mmol), 2a (1.5 mmol), base (2 mmol), PPh3 (0.6 mmol), water (1.5 mL) in DMF (1.5 mL), 100˚C, 8 h bultrasounds for 5 min; *Deter- mined by means of GC, based on the 1a, yields in parenthesis are those of purified products.
The impact of the organic co-solvent on the organic solvent system/H2O (1:1) and the relationship with the solvent mixture DMF/H2O was studied (
In the light of these results, the assessment of the 5a coupling was studied using the DMF/H2O solvent system (1:1).
To illustrate the effect of ultrasound and phase transfer catalysts on the Suzuki reaction trials (
When working under standard conditions the yield was found to be relatively low. However, in the presence of ultrasound and/or with Aliquat-336 the reaction was almost complete. The acceleration of the reaction under ultrasound is probably due to the chemical effects of cavitation which consists in the formation of bubbles in the liquid and which undergo an implosion after their growth. These bubbles constitute chemical microreactors in which very high temperatures and pressures are reached in the final stage of their implosion are reached causing a high release of energy. This allows for the stirring of the reaction environment, the activation of the catalytic system and the nearing of reagents by increasing their specific surface area and mixing the liquid layers located near them. The increase in the contact between the reactants can therefore be induced, which promotes the formation of the product in a very short time and with very high yields. The set of phenomena, stirring, pressure, temperature, ionization, etc., generated by ultrasounds leads to the disruption of the classical reaction mechanisms. Hence, very high yields have been observed under ultrasounds in the water-DMF environments and in the presence of phase transfer catalysts.
However, the anionic and sonochemical bi-activation also produces purer products with higher yields, which significantly increase if ultrasound is used with a remarkable decrease in reaction time (8 hours to 5 minutes). This can be explained by the fact that ultrasounds improve the contact of heterogeneous liquid-solid environments through the effects of microemulsion also providing energy to the reaction. Nonetheless, there is not much difference between the yields obtained when using ultrasound and those using both the ultrasound and Aliquat-336. Indeed, given that the reaction is almost complete in the presence of ultrasounds, the phase-transfer catalyst no longer has a big role to play.
The yield of these reactions significantly improved, reaching 80%, in the simultaneous presence of ultrasound and Aliquat-336 in a record time of 5 minutes. Indeed, as shown in Scheme 1 that displays the reaction mechanism, the ion exchange reaction between Cs2CO3 and Aliquat-336 induces the formation of an ammonium hydroxide ion which becomes lipophilic, and thus soluble in the organic phase. Furthermore, the
To further evidence these results, we propose the most likely reaction mechanism for this Hiyama coupling reaction in the two-phase water/dimethylformamide environment in the presence of TCP (Scheme 1).
Scheme 2 illustrates the photoluminescence spectrum of Pd Aliquat-336. The PL spectra of the prepared samples are obtained as a result of the competition among electron-hole separations, electron-phonon scattering and electron-hole recombination. Two emissions are observed in the PL spectra, the first one is a weak blue emission located at about 420 nm and is attributed to the carbon chain, which is due to trap the state emission based on the large Stokes shift from the band gap energy. The second emission at 470 nm may be due to the recombination between the shallow donor level (S vacancy) and the t2 level of the Pd2+ ion.
The 1a (1.0 mmol), 2a (1.5 mmol), Cs2CO3 (2 mmol) and the catalyst PdCl2(MeCN)2) (0.02 mmol), PPh3 (0.6 mmol) were placed in a Schlenk tube. Vacuum was applied for 30 minutes, and then argon was admitted. Water (1.5 mL) and N, N-dimethylformamide (1.5 mL) were added. The reaction was carried out at 100˚C for 8 h. After reaction, the mixture was cooled and the organic phase was extracted (three times) with diethyl ether. The
Ar-2Br (R2-C6H4-Br) | Ar3-siloxane | Product | Yield (%)c* |
---|---|---|---|
3a | 94 | ||
4a | 3c | 90 | |
4a | 3b | 99 | |
4a | 3q | 98 | |
4a | 3r | 96 | |
4a | 3s | 98 | |
4a | 3t | 99 | |
3u | 80 | ||
4b | 3d | 84 | |
4b | 3v | 86 | |
4b | 3w | 82 | |
4b | 3h | 99 |
Aliquat-336: N-Methyl-N, N, N-trioctylammonium chloride; cReaction conditions: PdCl2(MeCN)2 (0.02 mmol), 1a-1d, 1f, 1h, 1i-1k (1.0 mmol), 4a, 4b (1.5 mmol), Aliquat-336 (1.25 mmol), Cs2CO3 (2mmol), PPh3 (0.6 mmol), DMF(1,5 mL) and water (1.5 mL), Ultrasonic irradiation at 25˚C for 5 min. *determined after purification by chromatography.
latter was dried on MgSO4 and the solvent removed under vacuum. The coupling product was finally isolated by silica gel chromatography.
Ultrasonic IrradiationThe ultrasonic probe was immersed directly in the reactor. An ultrasonic generator (sonics VC 505 300 W)
Scheme 1. Proposed mechanism for the Hiyama coupling in the water/DMF biphasic system in the presence of Aliquat-336.
Scheme 2. PL emission spectrum of Pd Aliquat-336 prepared in a mixture of water and DMF.
emits the sound vibration into the reaction mixture. Sonification was achieved at low frequencies of 20 kHz (amplitude of 50%) at room temperature for 5 min. The 1a (1.0 mmol), Aliquat-336 (1.25 mmol), 2a (1.5 mmol), Cs2CO3, PPh3 (0.6 mmol) and the catalyst PdCl2(MeCN)2) (0.02 mmol) are placed in a reactor. Water (1.5 mL) and N,N-dimethylformamide (1.5 mL) are added. After reaction, the mixture is extracted (three times) with diethyl ether. The latter is dried on MgSO4 and the solvent removed under vaccum. The coupling product is finally isolated by silica gel chromatography.
The yields of the reactions were determined by gas chromatography on a Shimadzu 2014-GC apparatus. The capillary column was DB-5 and the carrier gas was helium.
PdCl2(MeCN)2 (0.02 mmol) was added to a solution of 1a (1.0 mmol), 4a-4b (1.5 mmol), Aliquat-336 (1.25 mmol), PPh3 (0.6 mmol) in a mixture of dimethylformamide (1.5 mL) and water (1.5 mL). The reaction mixture was heated to reflux for 8 h. After the reaction, the mixture was cooled and the organic phase was extracted (three times) with water/hexane (1:1). The latter was dried on MgSO4 and the solvent removed under vacuum. The coupling product was finally isolated by silica gel chromatography.
Biphenyl (3a, C12H10)
White solid; m.p.: 66˚C - 68˚C; 1H NMR (CDCl3): δ = 7.63 - 7.62 (m, 4H), 7.50 - 7.45 (m, 4H), 7.4 - 7.35 (m, 2H) ppm; 13C NMR (CDCl3): δ = 127.23, 127.31, 128.81, 141.32 ppm; IR (KBr): ῡ = 3032, 1946, 1568, 1475, 1427, 902, 729, 694 cm−1; MS: m/z (%) = 154 (M+, 100), 153 (42), 149 (74), 85 (40), 71 (50).
4-Methylbiphenyl (3b, C13H12)
m.p.: 47˚C - 48˚C; 1H NMR (CDCl3): δ = 7.51 (d, 2H, J = 8 Hz), 7.44 (t, 2H, J = 7 Hz), 7.34 (t, 1H, J = 7 Hz), 7.26 (d, 2H, J = 8 Hz), 7.57 (d, 2H, J = 7 Hz) 2.44 (s, 3H, CH3) ppm; 13C NMR (CDCl3): δ = 21.1, 126.8; 127.1, 128.6, 129.4, 137.1, 138.3, 141.1 ppm.
4-Methoxybiphenyl (3c; C13H12O)
Colorless solid; m.p.: 85˚C - 86˚C; 1H NMR (CDCl3): δ = 3.85 (s, 3H), 6.97 (d, 2H, J = 9 Hz), 7.28 - 7.35 (m, 1H), 7.41 - 7.46 (m, 2H), 7.52 - 7.58 (m, 4H) ppm; 13C NMR (CDCl3): δ = 159.4, 141.5, 134.1, 129.0, 128.3, 127.0, 126.7, 114.4, 55.6 ppm; MS: m/z (%) = 184 (M+, 92.5), 169 (77.5), 150 (45.0), 141 (70), 139 (40), 131 (30), 115 (55), 99 (32.5), 91 (52.5), 76 (100), 63 (55.0), 50 (42.5).
4-Nitrobiphenyl (3d, C12H9NO2)
Pale yellow powder; m.p.: 115˚C - 116˚C; 1H NMR (CDCl3): δ = 7.45 - 7.53 (m, 3H), 7.63 - 7.66 (m, 2H), 7.77 (d, 2H, J = 6.9 Hz), 8.33 (d, 2H, J = 6.9 Hz) ppm; 13C NMR (CDCl3): δ = 145.8, 139.4, 132.7, 129.3, 128.7, 128.0, 127.5, 119.1; 111.1 ppm; MS: m/z (%) = 199 (M+, 35.6), 169 (28.9), 153 (19.3), 152 (100), 127 (20.7), 102 (13.3), 76 (49.6), 50 (40).
4-Biphenylcarbaldehyde (3e, C13H10O)
mp.: 58˚C - 60˚C; 1H NMR (CDCl3): δ = 10.05 (s, 1H), 7.98 - 7.96 (m, 2H), 7.78 - 7.75 (m, 2H), 7.68 - 7.64 (m, 2H), 7.52 - 7.49 (m, 2H), 7.47 - 7.44 (tt, 1H, J = 7.2, J = 1.2 Hz) ppm; 13C NMR (CDCl3): δ = 192.1, 147.4, 140.0, 135.5, 130.5, 129.2, 128.7, 127.9, 127.6 ppm; IR (KBr): ῡ = 3059, 3032, 2924, 2828, 2735, 1700, 1604, 1565, 1515, 1485, 1450, 1412, 1384, 1308, 1281, 1214, 1170, 1076, 1007, 917, 838, 762, 729, 697, 646, 629, 547 cm−1; MS: m/z (%) = 183 (M+, 18), 182 (M+, 59), 181 (65), 180 (53), 153 (51), 152 (100), 150 (26), 77 (13), 76 (36).
4-Acetylbiphenyl (3f, C14H12O)
Colorless crystals; m.p.: 117˚C - 119˚C; 1H NMR (CDCl3): δ = 8.03 (d, 2H, J = 8.4 Hz), 7.74 (d, 2H J = 8.4 Hz), 7.62 - 7.64 (m, 2H), 7.34 - 7.49 (m, 3H), 2.64 (s, 3H) ppm; 13C NMR (CDCl3): δ = 197.8, 146.0, 140.4, 136.4, 129.2, 129.1, 128.5, 127.3, 127.3, 26.8 ppm; MS: m/z (%) = 196 (M+), 181, 152, 76, 43.
4-Acetoxybiphenyl (3g, C14H12O2)
Pale yellow solid; m.p.: 114˚C - 116˚C; 1H NMR (CDCl3): δ = 8.07 - 8.03 (dt, J = 8.4, J = 2 Hz, 2H), 7.72 - 7.69 (dt, J = 8.4, J = 1.6 Hz, 2H), 7.67 - 7.63 (m, 2H), 7.51 - 7.48 (m, 2H), 7.45 - 7.41 (tt, J = 7.6, J = 1.2 Hz, 1H), 2.67 (s, 3H) ppm; IR (KBr): ῡ = 2925, 2855, 1679, 1602, 1484, 1361, 1265, 1181, 1083, 960, 838, 765, 722, 680 cm−1; MS: m/z (%) = 196 (M+, 8), 184 (10), 167 (36), 149 (100), 83 (82), 77 (20).
4-Acetyl-4'-methoxybiphenyl (3h, C15H14O)
White crystals; m.p.: 153˚C - 154˚C; 1H NMR (CDCl3): δ = 7.64 (d, J = 8.4 Hz, 2H), 7.54 (d, J = 8.7 Hz, 2H), 7.02 (d, J = 8.7 Hz, 2H), 8.01 (d, J = 8.4 Hz, 2H), 3.89 (s, 3H), 2.62 (s, 3H) ppm; MS: m/z (%) = 226 (M+, 44), 211 (100), 183 (30.5), 168 (28), 152 (33.5), 139 (65.5), 89 (21.6), 77 (20), 63 (40.9), 55 (27.2).
4-Chloro-4'-methoxybiphenyl (3i, C13H11ClO)
White crystals; m.p.: 112˚C - 114˚C; 1H NMR (CDCl3): δ = 7.47 - 7.51 (m, 4H), 7.37 (d, J = 8.4 Hz, 2H), 6.97 (d, J = 8.7 Hz, 2H), 3.86 (s, 3H) ppm; 13C NMR (CDCl3): δ = 159.3, 139.2, 132.5, 128.8, 128, 127.9, 125.9, 114.3, 55.3 ppm; MS: m/z (%) = 220 (M++2, 37.7), 218 (M+, 88.7), 203 (66), 175 (62.3), 152 (47.2), 139 (56.6), 111 (24.5), 101 (30.2), 87 (49.1), 75 (67.9), 63 (79.2), 57 (100).
4-Methoxy-4'-nitrobiphenyl (3j, C7H11NO3)
Yellow powder; m.p.: 105˚C - 106˚C; 1H NMR (CDCl3): δ = 8.27 (d, J = 8.7 Hz, 2H), 7.70 (d, J = 8.7 Hz, 2H), 7.58 (d, J = 8.7 Hz, 2H), 7.04 (d, J = 8.7 Hz, 2H), 3.89 (s, 3H) ppm; 13C NMR (CDCl3): δ = 160.4, 147.2, 131.1, 128.5, 127.0, 124.1, 114.6, 55.4 ppm; MS: m/z (%) = 229 (M+, 100), 199 (25.4), 183 (13.9), 168 (23), 139 (49.8), 63 (23.2).
4-Acetylbiphenyl (3k, C14H12O).
1H NMR (CDCl3): δ = 8.01 - 8.05 (m, 2H), 7.70 - 7.60 (m, 4H,), 7.50 - 7.38 (m, 3H), 2.63 (s, 3H); 13C NMR (CDCl3): δ = 197.9, 146.0, 140.1, 136.1, 129.2, 129.1, 128.5, 127.5, 127.4, 26.8; MS: 196 (M+), 181, 152, 76, 43.
4,4′-Dimethoxybiphenyl (3l, C14H14O2)
Colorless crystals; m.p.: 175˚C - 176˚C; 1H NMR (CDCl3): δ = 7.51 (d, J = 8.7 Hz, 4H), 6.98 (d, J = 8.7 Hz, 4H), 3.88 (s, 6H) ppm; 13C NMR (CDCl3): δ = 158.8 133.8, 127.6, 114.5, 55.7 ppm; MS: m/z (%) = 214 (M+, 93.4), 199 (100), 171 (36.8), 156 (25), 128 (48.7), 115 (17.1), 102 (28.9), 91 (39.5), 74 (32.9), 63 (47.4), 51 (38.2).
4,4’-Dichlorobiphenyl (3m, C12H8Cl2)
white solid; m.p.: 150˚C; 1H NMR (CDCl3): δ = 7.46 (d, J = 8 Hz, 4H), 7.39 (d, J = 7.6 Hz, 4H) ppm; 13C NMR (CDCl3): δ = 127.2, 128.0, 132.7, 137.4 ppm.
4, 4’-Dimethylbiphenyl (3n, C14H14)
White solid; m.p.: 124˚C - 125˚C; 1H NMR (CDCl3): δ = 7.51 (d, J = 8.1 Hz, 4H), 7.26 (d, J = 8.1 Hz, 4H), 2.42 (s, 6H) ppm; 13C NMR (CDCl3): δ = 136.8, 129.7, 138.5, 127.0, 21.3 ppm.
4,4’-Dicyanobiphenyl (3o, C14H8N2 )
white solid; m.p.: 234˚C; 1H NMR (CDCl3): δ = 7.75 - 7.82 (m, 4 H), 7.68 - 7.74 (m, 4 H) ppm; 13C NMR (CDCl3): δ = 112.4, 118.4, 127.9, 132.8, 143.5 ppm.
4-Chlorobiphenyl (3p, C12H9Cl) Viscous liquid; m.p.:77˚C - 78˚C: 1H NMR (CDCl3): δ = 7.55 (m, 4H), 7.41 (m, 5H) ppm; 13C NMR (CDCl3): δ = 140.0 135.6, 133.3, 128.9, 128.8, 128.4, 126.9, 127.6 ppm; IR (KBr): ῡ = 1420, 1114, 1061, 892, 803 cm−1.
The present research work has undertaken the study of the bi-activation of some coupling reactions by phase transfer catalysis (PTC) coupled with ultrasounds. The effect of phase transfer catalysis associated with ultrasound waves on the reactivity of certain organic reactions such as Suzuki and Hiyama was therefore also examined. The obtained results have demonstrated that Suzuki reactions are significantly favored in the presence of ultrasound in an aqueous environment. The use of Aliquat-336 plays an important role in the reduction of Pd(II) as well as in the stabilisation and solubilisation of Pd(0).
We greatly acknowledge financial support of the Ministry of Higher Education and Scientific Research of Tunisia.
Khemais Said,Ridha Ben Salem, (2016) Ultrasonic Activation of Suzuki and Hiyama Cross-Coupling Reactions Catalyzed by Palladium. Advances in Chemical Engineering and Science,06,111-123. doi: 10.4236/aces.2016.62013