Method for electrochemical synthesis of 3, 4-dihydroisoquinoline-1 (2H)-ketone compound

Abstract

The invention discloses a method for electrochemical synthesis of a 3, 4-dihydroisoquinoline-1 (2H)-ketone compound, and the method comprises the following steps: dissolving a 1, 2, 3-benzotriazinone compound, a benzyne compound and an electrolyte salt in a solvent to obtain a reaction solution, placing an anode and a cathode in the reaction solution, introducing a direct current, and carrying out electrochemical reaction to obtain the 3, 4-dihydroisoquinoline-1 (2H)-ketone compound. And after the reaction is finished, carrying out post-treatment to obtain the 3, 4-dihydroisoquinoline-1 (2H)-ketone compound. The method has the characteristics that synthesis is performed through an electrochemical method, a transition metal catalyst is not needed, the use of a chemical oxidation reducing agent is avoided, and the method is green, environment-friendly, high in safety, simple to operate, mild in reaction condition, easy to control and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and specifically relates to a method for electrochemically synthesizing 3,4-dihydroisoquinoline-1(2H)-one compounds. Background Art

[0002] 3,4-Dihydroisoquinolin-1(2H)-one compounds are an important and valuable class of skeletons that are widely present in many drugs, natural products, and synthetic drugs due to their unique biological activities. Although such compounds can be synthesized by reducing isoquinolin-1(2H)-one compounds, it requires precious metal catalysts and uses pressurized hydrogen as a hydrogen donor, which poses safety issues.

[0003] Recent research focuses on the [4+2] cyclization reaction of 1,2,3-benzotriazinone compounds with alkynes or allenes catalyzed by transition metals (such as Pd, Ni, Ir, etc.) or visible light to construct 3,4-dihydroisoquinolin-1(2H)-one compounds, such as ([1] Hari Balakrishnan, M.; Mannathan, S., Palladium / Copper-Catalyzed Denitrogenative Alkylidenation and ortho-Alkynylation Reaction of 1,2,3-Benzotriazin-4(3H)-ones. Organic Letters 2020, 22, 542-546. [2] Wang, N.; Zheng, S.-C.; Zhang, L.-L.; Guo, Z.; Liu, X.-Y., Nickel (0)-Catalyzed Denitrogenative Transannulation of Benzotriazinones with Alkynes: Mechanistic Insights of Chemical Reactivity and Regio-and Enantioselectivity from Density Functional Theory and Experiment. ACS Catalysis 2016, 6, 3496-3505. [3] Wang, H.; Yu, S., Synthesis of Isoquinolones Using Visible-Light-Promoted Denitrogenative Alkyne Insertion of 1,2,3-Benzotriazinones. Organic Letters 2015, 17, 4272-4275.). However, for most of the reported synthesis methods, it is usually necessary to use air-sensitive transition metal catalysts and equivalent redox reagents, which are costly, have harsh reaction conditions, are environmentally unfriendly, and do not conform to the concept of green chemical synthesis.

[0004] Therefore, it is highly desirable to develop new environmentally friendly, safe, and sustainable strategies to construct 3,4-dihydroisoquinolin-1(2H)-ones from readily available starting materials. Summary of the invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a method for electrochemically synthesizing 3,4-dihydroisoquinoline-1(2H)-one compounds. The method does not require the use of transition metal catalysts and equivalent redox reagents, is environmentally friendly, low in cost, safe, and easy to operate.

[0006] The technical solution adopted by the present invention to solve the technical problem is: dissolving a 1,2,3-benzotriazine ketone compound, a benzyne compound and an electrolyte salt in a solvent to obtain a reaction solution, placing an anode and a cathode in the reaction solution, passing a direct current, and performing an electrochemical reaction. After the reaction is completed, a 3,4-dihydroisoquinoline-1(2H)-one compound is obtained through post-treatment. The specific reaction formula is as follows:

[0007]

[0008] Among them, R 1 , R 2 , R 3 H, C1~C 10 Aliphatic hydrocarbon group, halogen substituent, C1~C 10 Alkyl, C1~C 10 Alkyl or C1~C 10 of alkane groups.

[0009] Compared with traditional redox methods, electrochemical synthesis exhibits unique advantages: on the one hand, electrochemical synthesis effectively replaces traditional redox agents through electron transfer, and is green, environmentally friendly, and sustainable; on the other hand, stable metals can be reduced in situ to highly active low-valent metals through electrochemistry, which can effectively avoid the risk of explosion of metal powders.

[0010] As a preferred solution,

[0011] Preferably, the electrolyte salt is n Bu4NPF6, n Bu4NClO4, n Bu4NHSO4, n Bu4NOAc, n Bu4NBF4, n One of Et4NBF4 and KPF6, the electrolyte salt has a significant effect on the product yield, preferably n Bu4NBF4.

[0012] Preferably, the concentration of the electrolyte salt in the reaction solution is 0.1 to 0.6 mol / L, preferably 0.3 mol / L.

[0013] Preferably, the anode is one of gold, iron, platinum or nickel electrodes, preferably a platinum electrode; the cathode is one of gold, iron, platinum or graphite felt electrodes, preferably a graphite felt electrode.

[0014] Preferably, the solvent is one of DMSO, MeCN, 1,4-dioxane or a mixed solvent thereof with H2O. The choice of solvent has a significant effect on the product yield, and a mixed solvent of DMSO and H2O is preferred.

[0015] Preferably, the electrochemical reaction conditions are: the reaction is carried out in an air atmosphere, the direct current is 3-40mA, the reaction temperature is 5-60°C, and the reaction time is 1-12 hours. Preferably, the reaction is carried out in an air atmosphere, the direct current is 8mA, the reaction is carried out at room temperature, and the reaction time is 3.5 hours. The electrolysis is carried out in a constant current mode, and the current is controlled by a power supply device. The current should not be too large or too small. The reaction can be carried out at room temperature without heating.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0017] 1) The technical solution of the present invention is to synthesize 3,4-dihydroisoquinoline-1(2H)-one compounds by an electrochemical method, effectively replace the traditional chemical redox agent through electron transfer, avoid the use of redox agents, and has the characteristics of being green, environmentally friendly, highly safe, and sustainable.

[0018] 2) The technical solution of the present invention does not require the use of transition metal catalysts, thus avoiding the use of expensive noble metals and improving the economic efficiency of the method.

[0019] 3) The technical solution of the present invention is simple to operate, has mild reaction conditions, low energy consumption, is easy to control, the reaction can be stopped by power off, and has little safety hazard. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the H NMR spectrum of 2,3-diphenyl-3,4-dihydroisoquinolin-1(2H)-one synthesized in Example 1;

[0021] Figure 2 This is the carbon NMR spectrum of 2,3-diphenyl-3,4-dihydroisoquinolin-1(2H)-one synthesized in Example 1. DETAILED DESCRIPTION

[0022] The following is a further description of the method for electrochemically synthesizing 3,4-dihydroisoquinolin-1(2H)-one compounds of the present invention in conjunction with the examples, but the present invention is not limited thereto.

[0023] Embodiment 1:

[0024] 0.2 mmol 3-phenylbenzo[d][1,2,3]triazine-4(3H)-one, 0.6 mmol phenylacetylene, 1.62 mmol n Bu4NPF6 was added to the electrolytic cell, and then DMSO (5.0mL) and H2O (0.4mL) were added to dissolve it. A gold sheet (20mm×10mm×0.1mm) was used as the anode, and a graphite felt (20mm×10mm×5mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50mL of ethyl acetate, the organic layer was dried over sodium sulfate, filtered, and the organic reagent was dried under reduced pressure. The target product was purified by silica gel column chromatography to obtain a yield of 61%, namely 2,3-diphenyl-3,4-dihydroisoquinoline-1(2H)-one, with the structural formula:

[0025]

[0026] The characterization data of the compound are as follows: 1 H NMR (400MHz, CDCl3) δ8.29 (dd, J = 6.8, 2.2Hz, 1H), 7.50-7.42 (m, 2H), 7.42-7.22 (m, 10H), 7.15-7. 10(m,1H),5.30(dd,J=6.4,2.7Hz,1H),3.96(dd,J=15.7,6.3Hz,1H),3.22(dd,J=15.8,2.7Hz,1H), 13 C NMR (100MHz, CDCl3) δ164.3,142.6,140.6,135.3,132.3,129.8,128.8,128.6,128.3,127.6,127.5,127.3,126.5,126.4,126.1,63.3,36.7.

[0027] Embodiment 2:

[0028] 0.2 mmol 3-(4-methoxyphenyl)benzo[d][1,2,3]triazine-4(3H)-one, 0.6 mmol phenylacetylene, 1.62 mmol nBu4NClO4 was added to the electrolytic cell, and then MeCN (5.4 mL) was added to dissolve, and an iron sheet (20 mm × 10 mm × 0.1 mm) was used as the anode, and a graphite felt (20 mm × 10 mm × 5 mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8 mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50 mL of ethyl acetate, and the organic layer was dried over sodium sulfate, filtered, and the organic reagent was dried under reduced pressure. Purification by silica gel column chromatography gave the target product with a yield of 40%, namely 2-(4-methoxyphenyl)-3-phenyl-3,4-dihydroisoquinolin-1(2H)-one, with the structural formula:

[0029]

[0030] The characterization data of the compound are as follows: 1 H NMR (400MHz, CDCl3) δ8.20 (dd, J=7.2, 2.0Hz, 1H), 7.43-7.31 (m, 2H), 7.25-7.12 (m, 7H), 7.07-7.02 (m, 1H), 6 .88-6.79(m,2H),5.16(dd,J=6.4,2.7Hz,1H),3.95-3.83(m,1H),3.77(s,3H),3.13(dd,J=15.8,2.7Hz,1H), 13 C NMR (100MHz, CDCl3) δ164.5,157.9,140.6,135.5,135.3,132.2,129.8,128.5,128.3,127.6,127.5,127.2,126.5,114.1,63.6,55.4,36.6.

[0031] Embodiment 3:

[0032] 0.2 mmol 3-phenylbenzo[d][1,2,3]triazine-4(3H)-one, 0.6 mmol 4-methoxyphenylacetylene, 1.62 mmol n Bu4NHSO4 was added to the electrolytic cell, and then DMSO (5.4 mL) was added to dissolve, and a platinum sheet (20 mm × 10 mm × 0.1 mm) was used as the anode, and a platinum sheet (20 mm × 10 mm × 5 mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8 mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50 mL of ethyl acetate, the organic layer was dried over sodium sulfate, filtered, and the organic reagent was dried under reduced pressure. Purification was performed by silica gel column chromatography to obtain the target product with a yield of 40%, namely 3-(4-methoxyphenyl)-2-phenyl-3,4-dihydroisoquinolin-1(2H)-one, with the structural formula:

[0033]

[0034] The characterization data of the compound are as follows: 1 H NMR(400MHz, CDCl3)δ8.20(dd,J=7.3,1.8Hz,1H),7.44-7.24(m,6H),7.23-7.17(m,1H),7.09-7.03(m,3H),6.77- 6.71(m,2H),5.17(dd,J=6.1,2.6Hz,1H),3.85(dd,J=15.7,6.2Hz,1H),3.72(s,3H),3.11(dd,J=15.7,2.6Hz,1H), 13 C NMR (100MHz, CDCl3) δ164.3,158.9,142.6,135.5,132.5,132.3,129.8,128.8,128.3,127.7,127.6,127.2,126.5,126.2,113.9,62.8,55.1,36.8.

[0035] Embodiment 4:

[0036] 0.2 mmol 3-phenylbenzo[d][1,2,3]triazine-4(3H)-one, 0.6 mmol methyl 4-ethynylbenzoate, 1.62 mmol n Bu4NOAc was added to the electrolytic cell, and then 1,4-dioxane (5.0 mL) and H2O (0.4 mL) were added to dissolve, and a nickel sheet (20 mm × 10 mm × 0.1 mm) was used as the anode, and a graphite felt (20 mm × 10 mm × 5 mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8 mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50 mL of ethyl acetate, the organic layer was dried over sodium sulfate, filtered, and the organic reagent was dried under reduced pressure. Purification by silica gel column chromatography gave the target product with a yield of 42%, namely 4-(1-oxo-2-phenyl-1,2,3,4-tetrahydroisoquinolin-3-yl)benzoic acid methyl ester, the structural formula of which is:

[0037]

[0038] The characterization data of the compound are as follows: 1H NMR (400MHz, CDCl3) δ7.89-7.74(m,3H),7.70-7.59(m,2H),7.59-7.38(m,4H),7.32-7.25(m,1H),7.15(dd,J=7.3,1.1Hz,1 H),6.92-6.85(m,2H),5.52(dd,J=7.5,3.6Hz,1H),3.88(s,3H),3.40(dd,J=13.8,3.6Hz,1H),3.03(dd,J=13.8,7.5Hz,1H), 13 C NMR (100MHz, CDCl3) δ166.8,143.5,140.5,137.0,132.3,131.7,130.2,129. 7,129.4,129.3,128.9,128.7,125.5,124.3,123.2,122.7,60.8,52.1,37.9.

[0039] Embodiment 5:

[0040] 0.2 mmol 3-phenylbenzo[d][1,2,3]triazine-4(3H)-one, 0.6 mmol 3-fluorophenylacetylene, 1.62 mmol n Et4NBF4 was added to the electrolytic cell, and then DMSO (5.0 mL) and H2O (0.4 mL) were added to dissolve, and a platinum sheet (20 mm × 10 mm × 0.1 mm) was used as the anode, and a gold sheet (20 mm × 10 mm × 5 mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8 mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50 mL of ethyl acetate, the organic layer was dried over sodium sulfate, filtered, and the organic reagent was dried under reduced pressure. The target product was purified by silica gel column chromatography with a yield of 46%, namely 3-(3-fluorophenyl)-2-phenyl-3,4-dihydroisoquinolin-1(2H)-one.

[0041]

[0042] The characterization data of the compound are as follows: 1H NMR (400MHz, CDCl3) δ8.20(dd,J=7.2,1.8Hz,1H),7.45-7.25(m,6H),7.25-7.15(m,1H),7.07(d,J=7.1Hz,1H),6.96(d,J =7.8Hz,1H),6.92-6.83(m,2H),5.22(dd,J=6.5,2.5Hz,1H),3.89(dd,J=15.8,6.4Hz,1H),3.13(dd,J=15.8,2.6Hz,1H), 13 C NMR (100MHz, CDCl3) δ164.2, 162.83 (d, J = 247.0Hz), 143.3 (d, J = 6.5Hz), 142.4, 135.0, 132.5, 130.2 (d, J = 8.4Hz), 129. 6,129.0,128.4,127.6,127.5,126.7,126.1,122.1(d,J=2.8Hz),114.6(d,J=21.1Hz),113.6(d,J=22.1Hz),62.9,36.5.

[0043] Embodiment 6:

[0044] 0.2 mmol 8-methyl-3-phenylbenzo[d][1,2,3]triazine-4(3H)-one, 0.6 mmol phenylacetylene, 1.62 mmol n Bu4NBF4 was added to the electrolytic cell, and then DMSO (5.0 mL) and H2O (0.4 mL) were added to dissolve, and a platinum sheet (20 mm × 10 mm × 0.1 mm) was used as the anode, and a graphite felt (20 mm × 10 mm × 5 mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8 mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50 mL of ethyl acetate, the organic layer was dried over sodium sulfate, filtered, and the organic reagent was dried under reduced pressure. Purification by silica gel column chromatography gave the target product with a yield of 65%, namely 5-methyl-2,3-diphenyl-3,4-dihydroisoquinoline-1(2H)-one, with the structural formula:

[0045]

[0046] The characterization data of the compound are as follows: 1H NMR (400MHz, CDCl3) δ8.15-7.97(m,1H),7.35-7.13(m,12H),5.25(dd,J=6.3,2.9 Hz,1H),3.65(dd,J=16.1,6.3Hz,1H),3.26(dd,J=16.1,3.0Hz,1H),2.19(s,3H), 13 C NMR (100MHz, CDCl3) δ164.6,142.6,140.9,135.0,133.9,133.8,129.8,128.7,128.6,127.4,126.7,126.4,126.3,126.2,126.0,62.7,33.5,19.0.

[0047] Embodiment 7:

[0048] 0.2mmol 3-phenylbenzo[d][1,2,3]triazine-4(3H)-one, 0.6mmol 2-methoxyphenylacetylene, and 1.62mmol KPF6 were added to the electrolytic cell, and 1,4-dioxane (5.4mL) was added to dissolve, and a platinum sheet (20mm×10mm×0.1mm) was used as the anode, and a graphite felt (20mm×10mm×5mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50mL of ethyl acetate, the organic layer was dried over sodium sulfate, filtered, and the organic reagent was dried under reduced pressure. The target product was purified by silica gel column chromatography to obtain a yield of 46%, namely 3-(2-methoxyphenyl)-2-phenyl-3,4-dihydroisoquinolin-1(2H)-one, with the structural formula:

[0049]

[0050] The characterization data of the compound are as follows: 1 H NMR (400MHz, CDCl3) δ8.21(dd,J=6.9,2.2Hz,1H),7.38-7.32(m,2H),7.32-7.28(m,4H),7.23-7.09(m,3H),7.05-6.98(m,1H),6.83(d,J =8.2Hz,1H),6.76(t,J=7.5Hz,1H),5.59(dd,J=6.6,2.2Hz,1H),3.84(s,3H),3.77(dd,J=15.9,6.5Hz,1H),3.20(dd,J=16.0,2.2Hz,1H), 13C NMR (100MHz, CDCl3) δ164.9,155.8,142.8,136.1,132.2,129.7,128.8,128.5,1 28.2,127.9,127.8,127.4,127.0,126.3,126.0,120.3,110.4,58.0,55.3,34.2.

[0051] Embodiment 8:

[0052] 0.2mmol 3-(m-tolyl)benzo[d][1,2,3]triazine-4(3H)-one, 0.6mmol phenylacetylene, 1.62mmol KPF6 were added to the electrolytic cell, and then DMSO (5.0mL) and H2O (0.4mL) were added to dissolve, and a platinum sheet (20mm×10mm×0.1mm) was used as the anode, and an iron sheet (20mm×10mm×5mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50mL of ethyl acetate, the organic layer was dried over sodium sulfate, filtered, the organic reagent was dried under reduced pressure, and purified by silica gel column chromatography to obtain the target product with a yield of 49%, namely 3-phenyl-2-(m-tolyl)-3,4-dihydroisoquinolin-1(2H)-one, with the structural formula:

[0053]

[0054] The characterization data of the compound are as follows: 1 H NMR (400MHz, CDCl3) δ8.25-8.15(m,1H),7.42-7.31(m,2H),7.25-7.11(m,7H),7.07-6.98(m,3H),5 .20(dd,J=6.4,2.6Hz,1H),3.88(dd,J=15.7,6.3Hz,1H),3.14(dd,J=15.8,2.6Hz,1H),2.30(s,3H), 13 C NMR (100MHz, CDCl3) δ164.4,142.5,140.6,138.7,135.3,132.3,129.8,128.7,1 28.5,128.3,127.6,127.5,127.4,127.3,127.1,126.5,123.0,63.3,36.7,21.4.

[0055] Embodiment 9:

[0056] 0.2mmol 3-phenylbenzo[d][1,2,3]triazine-4(3H)-one, 0.6mmol 3.4-dimethoxyphenylacetylene, 1.62mmol KPF6 were added to the electrolytic cell, and MeCN (5.0mL) and H2O (0.4mL) were added to dissolve, and a nickel sheet (20mm×10mm×0.1mm) was used as the anode, and a graphite felt (20mm×10mm×5mm) was used as the cathode. The mixture was stirred at room temperature for 3.5 hours at a constant current of 8mA. The reaction was monitored by thin layer chromatography. After the reaction was completed, the reaction mixture was extracted three times with 50mL ethyl acetate, the organic layer was dried over sodium sulfate, filtered, the organic reagent was dried under reduced pressure, and purified by silica gel column chromatography to obtain the target product with a yield of 45%, namely 3-(3,4-dimethoxyphenyl)-2-phenyl-3,4-dihydroisoquinolin-1(2H)-one, with the structural formula:

[0057]

[0058] The characterization data of the compound are as follows: 1 H NMR(400MHz, CDCl3)δ8.20(dd,J=7.5,1.7Hz,1H),7.44-7.25(m,6H),7.24-7.17(m,1H),7.08(d,J=7.1Hz,1H),6.72-6.67(m,2H) ,6.61(s,1H),5.14(dd,J=6.2,2.7Hz,1H),3.86(dd,J=15.7,6.2Hz,1H),3.79(s,3H),3.67(s,3H),3.12(dd,J=15.7,2.8Hz,1H), 13 C NMR (100MHz, CDCl3) δ164.3,148.8,148.3,142.6,135.6,133.0,132.3,129.8,128. 8,128.1,127.7,127.3,126.6,126.2,118.8,111.0,109.6,63.1,55.7,55.7,36.8.

[0059] Those skilled in the art should understand that the above are only some specific embodiments of the present invention, rather than all embodiments. It should be noted that for those of ordinary skill in the art, many modifications and improvements can be made, and all modifications or improvements that do not exceed the scope of protection of the present invention should be regarded as the scope of protection of the present invention.

Claims

1. A method for electrochemically synthesizing 3,4-dihydroisoquinolin-1(2H)-one compounds, characterized in that: A 1,2,3-benzotriazine ketone compound, a benzylene compound and an electrolyte salt are dissolved in a solvent to obtain a reaction solution, an anode and a cathode are placed in the reaction solution, a direct current is passed through, and an electrochemical reaction is performed. After the reaction is completed, a post-treatment is performed to obtain a 3,4-dihydroisoquinoline-1(2H)-one compound.

2. The method for electrochemically synthesizing 3,4-dihydroisoquinolin-1(2H)-one compounds according to claim 1, characterized in that: The electrolyte salt is n Bu4NPF6, n Bu4NClO4, n Bu4NHSO4, n Bu4NOAc, n Bu4NBF4, n One of Et4NBF4 and KPF6.

3. The method for electrochemically synthesizing 3,4-dihydroisoquinolin-1(2H)-one compounds according to claim 1, characterized in that: The electrolyte salt concentration in the reaction solution is 0.1-0.6 mol / L.

4. The method for electrochemically synthesizing 3,4-dihydroisoquinolin-1(2H)-one compounds according to claim 1, characterized in that: The anode is one of gold, iron, platinum or nickel electrodes, and the cathode is one of gold, iron, platinum or graphite felt electrodes.

5. The method for electrochemically synthesizing 3,4-dihydroisoquinolin-1(2H)-one compounds according to claim 1, characterized in that: The solvent is one of DMSO, MeCN, 1,4-dioxane or a mixed solvent thereof with H2O.

6. The method for electrochemically synthesizing 3,4-dihydroisoquinolin-1(2H)-one compounds according to claim 1, characterized in that: Electrochemical reaction conditions: The reaction is carried out in an air atmosphere, with a direct current of 3 to 40 mA, a reaction temperature of 5 to 60° C., and a reaction time of 1 to 12 hours.

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