Preparation method of bicyclobutane

Abstract

The invention provides a preparation method of bicyclobutane, and belongs to the technical field of aerospace fuels. According to the method, the bicyclobutane fuel is efficiently synthesized through nickel-catalyzed bromocyclobutane coupling reaction, and according to the method, nickel chloride serves as a catalyst, a reducing agent manganese powder is added, and the debromination self-coupling reaction of halogenated cyclobutane is promoted. The reduction coupling fuel synthesis strategy shows high efficiency, and the conversion number (TON) of the nickel catalyst can reach 44. The reaction can be carried out in an open system at the temperature of 40 DEG C, a water-free and oxygen-free environment is not needed, the yield of the bicyclobutane fuel is 88%, and the purity of the bicyclobutane fuel is 99% or above. Fuel performance tests show that bicyclobutane has excellent physical and chemical properties, the density is 0.82 g.mL <-1 >, the combustion net heat value is 44.39 MJ.kg <-1 >, and bicyclobutane is a high-energy aerospace fuel with great potential.

Description

Technical Field

[0001] The invention belongs to the technical field of aerospace fuel, and in particular relates to a method for preparing dicyclobutane. Background Art

[0002] Fuel is the power source of aerospace propulsion systems, and its performance directly impacts a vehicle's thrust, specific impulse, payload, endurance, and mission suitability. The rapid development of aerospace has placed higher demands on fuel: high energy density, storage stability, environmental friendliness, and cost-effectiveness.

[0003] Traditional aerospace fuels are primarily liquid hydrocarbon fuels (aerospace kerosene and rocket kerosene) derived from petroleum. Liquid hydrogen, liquid methane, and unsymmetrical dimethylhydrazine are also widely used. However, these fuels still suffer from low energy density, high toxicity, and storage difficulties, necessitating the development of new, green, high-energy fuels. Aerospace kerosene is primarily composed of chain alkanes, while rocket kerosene contains a certain amount of cyclic alkanes, significantly improving its energy density compared to aviation kerosene. Therefore, it is possible to synthesize these high-energy-density hydrocarbon fuels through molecular structural engineering.

[0004] Recent research has led to the development of a variety of high-energy-density fuels, particularly those with strained ring structures containing 3-4 carbon atoms, which exhibit high specific impulse, calorific value, density, and low-temperature viscosity. The strained ring structures possess significant angular and torsional tension, resulting in high tension energy, which can significantly increase the fuel's energy density. Currently, a variety of high-energy-density fuels have been developed, such as Syntin, dicyclopropane, dicyclobutane, dicyclopentane, tetracycloheptane, cubane, and dicyclopropane products of norbornadiene. These fuels possess higher calorific value and energy density than traditional aerospace kerosene, but challenges remain in their economic, stability, and practicality.

[0005] Bicyclobutane, also known as cyclobutylcyclobutane, chemical formula C8H 14 , also known as Bocktan, is a high-energy fuel with excellent performance. In terms of fuel performance, dicyclobutane shows excellent combustion performance, with NHOC data as high as 44.39MJ·kg -1 , higher than RP-4, JP-10 and "Syntin". The theoretical specific impulse of cyclobutane is 370s, which is 7s higher than rocket kerosene. DSC test shows that the freezing point of cyclobutane is -59.4℃ and the boiling point is 160.7℃, indicating that cyclobutane can be used as a propellant in harsh external environments or high-temperature workplaces. In addition, the viscosity test results show that it is 1.50mm at 20℃. 2 ·s -1 , 2.14mm at -10℃ 2 ·s -1, proving the good fluidity of dicyclobutane fuel. Finally, the density of dicyclobutane is 0.82 g·mL -1 , the suitable fuel density proves that dicyclobutane has the potential to be used as a high-energy fuel in the aviation field.

[0006] Currently, there is little research on bicyclobutanes. The literature (1.Chem.Ber., 1966, 99, 2155.2.DOI:10.1002 / 9780470682531.pat0337) reported a strategy for synthesizing bicyclobutanes via silver-catalyzed cyclobutylborane self-coupling. This method involves the reaction of cyclobutene with borane, followed by self-coupling of cyclobutylborane. The route is as follows:

[0007]

[0008] Disadvantages: 1) Borane is toxic; 2) Adding a large amount of AgNO3 is costly; 3) The reaction conditions are harsh and require strict anhydrous and oxygen-free operation; 4) It is a two-step reaction with poor step economy and low yield.

[0009] CN 113336620A discloses a method for preparing bicyclobutane, wherein a Grignard reagent is prepared from bromocyclobutane, and then the Grignard reagent undergoes self-coupling. The method comprises the following steps: step 1, a Grignard reaction is performed in a solvent with 1-halogenated cyclobutane and Mg powder to produce a Grignard reagent of 1-halogenated cyclobutane; step 2, a catalyst and an additive are added to the reaction solution of step 1, and a carbon-carbon self-coupling reaction is carried out under the protection of an inert gas or nitrogen. After the reaction is complete, bicyclobutane is obtained after post-treatment. The catalyst is a copper salt, an iron salt and / or a cobalt salt, and the additive is an oxidant. The route is as follows:

[0010]

[0011] Disadvantages include: 1) the use of a large amount of magnesium; 2) the use of a large amount of NBS oxidant; 3) the high reaction temperature, requiring strict anhydrous and oxygen-free operation; 4) a two-step reaction with poor step economy. Summary of the Invention

[0012] In response to the problems of poor atom economy and step economy in the above two routes, as well as the harsh sensitivity of operating conditions to water and oxygen, the present invention proposes a method for preparing bicyclobutane, which adopts a nickel-catalyzed reductive coupling strategy to achieve a one-step synthesis of bromocyclobutane to bicyclobutane. The conditions are mild and the operation is simple. Experiments have shown that the fuel synthesis does not require a strictly water-free and oxygen-free environment, and can be carried out under air conditions, showing step economy and atom economy.

[0013] In order to solve the above technical problems, the technical solution of the present invention is achieved as follows:

[0014] A method for preparing bicyclobutane, the reaction scheme is as follows:

[0015]

[0016] The method specifically comprises the following steps: dispersing and dissolving 1-halogenated cyclobutane, a catalyst, a ligand and an additive in a solvent to prepare a reaction solution, and then performing a self-coupling reaction to obtain bicyclobutane.

[0017] Furthermore, the 1-halogenated cyclobutane is 1-bromocyclobutane, which has suitable reactivity.

[0018] Furthermore, the catalyst is a nickel salt; the nickel salt is any one or more of NiCl2, NiCl2(glyme), NiBr2 and Ni(cod)2, and has suitable catalytic activity.

[0019] Furthermore, the ligand is any one or more of 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 2,2'-bipyridine, 4,4'-di-tert-butyl-2,2'-bipyridine, 1,10-phenanthroline, 2,2':6',2"-terpyridine, triethylenediamine and triphenylphosphine, and the ligand can coordinate with metallic nickel to form an active catalyst.

[0020] Furthermore, the additive is a reducing substance; the reducing substance is Mn powder, and the molar ratio of the reducing substance to 1-halogenated cyclobutane is 0.5-2: 1. The reducing substance can reduce the high-valent nickel intermediate to low-valent nickel during the reaction.

[0021] Furthermore, the solvent is any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropylene urea, 1,3-dimethyl-2-imidazolidinone, acetonitrile and dimethyl sulfoxide. The use of an amide solvent with greater polarity is conducive to the reaction.

[0022] Furthermore, the molar ratio of the catalyst to 1-halogenated cyclobutane is 0.01-0.03:1; the molar ratio of the additive to 1-halogenated cyclobutane is 0.5-2:1, ensuring that there is enough metal nickel catalyst to participate in the reaction.

[0023] Furthermore, the molar ratio of the ligand to 1-halogenated cyclobutane is 0.01-0.03:1, ensuring that there is sufficient ligand to coordinate with the metal nickel catalyst.

[0024] Furthermore, the concentration of 1-halogenated cyclobutane in the reaction solution is 0.25-2 mol·L -1 , ensuring that the reactant concentrations are within the appropriate range.

[0025] Furthermore, the temperature of the self-coupling reaction is 20-50° C., and the time is 4-24 hours.

[0026] Beneficial effects of the present invention:

[0027] (1) The present invention uses cheap and readily available cyclohalobutane as a raw material, adds a catalyst, a ligand, and an additive under relatively low temperature conditions to realize a C-Br / C-Br coupling reaction from the cyclohalobutane to the dicyclobutane, and obtains the dicyclobutane through post-treatment by reduced pressure distillation.

[0028] (2) The present invention promotes the formation of a free radical intermediate from 1-halogenated cyclobutane through a C-Br / C-Br coupling reaction catalyzed by a metal Ni complex. The free radical intermediate chelates with metal nickel, and an external reducing agent, Mn powder, is added to promote the reduction elimination process to generate a dicyclobutane fuel.

[0029] (3) This reductive coupling fuel synthesis strategy demonstrates high efficiency, with a nickel catalyst turnover number (TON) of up to 44. The reaction can be carried out in an open system at 40°C, without the need for an anhydrous and oxygen-free environment. The yield of bicyclobutane fuel produced is 88%, with a purity exceeding 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 is the H NMR spectrum of the reaction solution in Example 1.

[0032] Figure 2 This is the H NMR spectrum of bicyclobutane.

[0033] Figure 3 This is the carbon NMR spectrum of dicyclobutane.

[0034] Figure 4 This is the infrared spectrum of dicyclobutane.

[0035] Figure 5 This is the GC spectrum of dicyclobutane.

[0036] Figure 6 This is the differential scanning calorimetry (DSC) test spectrum of dicyclobutane. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] A method for preparing bicyclobutane comprises the following steps: adding 0.04 mmol NiCl2, 0.04 mmol 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 2 mmol Mn powder, 2 mmol 1-bromocyclobutane, and 2 mL DMF solvent to a 10 mL Schlenck reaction vessel, reacting at 40°C for 8 hours, cooling to room temperature, adding an internal standard and extracting with an equal volume of dichloromethane, and washing the DMF in the reaction solution with saturated brine three times. The yield can reach 88% ( Figure 1 ), conversion rate>99.

[0040] Example 2

[0041] A method for preparing bicyclobutane comprises the following steps: adding 1.6 mmol of NiCl2, 1.6 mmol of 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 80 mmol of Mn powder, 80 mmol of 1-bromocyclobutane and 80 mL of DMF solvent into a 200 mL Schlenck reaction vessel, sealing the bottle mouth with a rubber stopper, reacting at 40° C. for 24 hours, cooling to room temperature after the reaction is complete, and performing reduced pressure distillation to obtain a pure bicyclobutane fuel product, wherein the product yield is 72% and the purity can reach over 99% as determined by nuclear magnetic resonance.

[0042] Examples 3-5 and Comparative Examples 1-7

[0043] The variable control method was used to change different types of catalysts. The catalyst types are shown in Table 1 to explore their effects on the yield of dicyclobutane. The following reaction steps were used:

[0044]

[0045] A method for preparing bicyclobutane comprises the following steps: adding 0.04 mmol of a catalyst, 0.04 mmol of 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 2 mmol of Mn powder, 2 mmol of 1-bromocyclobutane and 2 mL of DMF solvent into a Schlenck reaction vessel, reacting at 40° C. for 8 hours, cooling to room temperature, adding an internal standard and extracting with an equal volume of dichloromethane, and washing the DMF in the reaction solution with saturated brine three times.

[0046] Table 1. Catalyst screening

[0047]

[0048] Starting from common metals (Fe, Cu, Co, Ni) and using commonly used metal catalysts such as Bi, Mo, and Ce, their chlorides were used as catalysts, 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine was used as a ligand, Mn was used as a reducing agent, and DMF was used as a solvent. The effects of the chlorides on the coupling reaction of bromocyclobutane were investigated at a temperature of 40°C and a reaction time of 8h. The results are shown in Table 1. In this reaction system, the chlorides of Fe, Cu, Co, Bi, Mo, and Ce as catalysts had little effect on the self-coupling of bromocyclobutane, while NiCl2 showed better reaction effects. The conversion rate of bromocyclobutane was >99, the yield reached 88%, and the selectivity reached 88%. Subsequently, we used other Ni compounds as catalysts, all of which showed good catalytic effects.

[0049] Examples 6-11 and Comparative Example 8

[0050] The variable control method was used to change different types of ligands. The types of ligands are shown in Table 2 to explore their effects on the yield of bicyclobutane. The following reaction steps were used:

[0051]

[0052] A method for preparing bicyclobutane comprises the following steps: adding 0.04 mmol of NiCl2, 0.04 mmol of a ligand, 2 mmol of Mn powder, 2 mmol of 1-bromocyclobutane and 2 mL of DMF solvent into a Schlenck reaction vessel, reacting at 40°C for 8 hours, cooling to room temperature, adding an internal standard and extracting with an equal volume of dichloromethane, and washing the DMF in the reaction solution with saturated brine three times.

[0053] Table 2. Ligand screening

[0054]

[0055]

[0056] At a reaction temperature of 40°C for 8 hours, using NiCl₂ as a catalyst, Mn as a reducing agent, and DMF as a solvent, various ligands were used to investigate their effects on the self-coupling of bromocyclobutanes. Table 2 shows that ligands containing pyridine structures are particularly effective in the synthesis of bicyclobutanes. Ligands containing 2,2-bipyridine, 1,10-phenanthroline, and terpyridine achieved 100% conversion of bromocyclobutane with yields and selectivities exceeding 60%. Bipyridines containing two tert-butyl groups and triphenylphosphine also exhibited a moderately promoting effect. In the absence of ligands, no bicyclobutane was produced.

[0057] Examples 12-15

[0058] The variable control method was used to change different types of solvents. The solvent types are shown in Table 3 to explore their effects on the yield of dicyclobutane. The following reaction steps were used:

[0059]

[0060] A method for preparing bicyclobutane comprises the following steps: adding 0.04 mmol of NiCl2, 0.04 mmol of 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 2 mmol of Mn powder, 2 mmol of 1-bromocyclobutane and 2 mL of solvent into a Schlenck reaction vessel, reacting at 40°C for 8 hours, cooling to room temperature, adding an internal standard and extracting with an equal volume of dichloromethane, and washing the highly polar solvent in the reaction solution with saturated brine three times.

[0061] Table 3. Screening of solvents

[0062]

[0063] The effects of solvent on the reaction were investigated at 40°C for 8 hours using NiCl2 as the catalyst, 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine as the ligand, and Mn powder as the reducing agent. Table 3 shows that the reaction performed best in DMF and DMA, followed by DMPU and DMI. The reaction was poor in DMSO, and almost no coupling reaction occurred in acetonitrile.

[0064] Examples 16-18

[0065] The reaction temperature was changed by controlling the variables, as shown in Table 4, to explore its effect on the yield of dicyclobutane.

[0066] The following reaction steps are adopted;

[0067]

[0068] A method for preparing bicyclobutane comprises the following steps: adding 0.04 mmol of NiCl2, 0.04 mmol of 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 2 mmol of Mn powder, 2 mmol of 1-bromocyclobutane and 2 mL of DMF into a Schlenck reaction vessel, reacting at a certain temperature for 8 hours, cooling to room temperature, adding an internal standard and extracting with an equal volume of dichloromethane, and washing the DMF in the reaction solution with saturated brine three times.

[0069] Table 4. Temperature screening

[0070]

[0071] As shown in Table 4, the self-coupling of bromocyclobutane needs to be carried out at an appropriate temperature. The temperature of 20°C is too low and the conversion rate of raw materials is low. When the temperature is raised to 30°C, the yield is 73%. When the temperature is raised to 40°C, the yield is the highest at 88%. When the temperature is further raised to 50°C, the yield decreases to 70%. Therefore, 40°C is selected as the optimal reaction temperature.

[0072] Examples 19-22

[0073] The effect of varying the amount of DMF added on the yield of dicyclobutane was investigated by varying the amount of DMF added, as shown in Table 5. The following reaction steps were used:

[0074]

[0075] A method for preparing bicyclobutane comprises the following steps: adding 0.04 mmol of NiCl2, 0.04 mmol of 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 2 mmol of Mn powder, 2 mmol of 1-bromocyclobutane and a certain volume of DMF into a Schlenck reaction vessel, reacting for 8 hours under certain conditions, cooling to room temperature, adding an internal standard and extracting with an equal volume of dichloromethane, and washing the DMF in the reaction solution with saturated brine three times.

[0076] Table 5. Concentration screening

[0077]

[0078] At a reaction temperature of 40°C and a reaction time of 8 hours, using NiCl2 as the catalyst, 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine as the ligand, and Mn powder as the reducing agent, the effect of bromocyclobutane concentration on the self-coupling reaction was investigated. Table 5 shows that the best reaction was achieved at a bromocyclobutane concentration of 1 mol / L.

[0079] As can be seen from the above examples, when the solvent is DMF, the catalyst is NiCl2, NiCl2 (glyme) and NiBr2, the molar ratio of the catalyst to the 1-halocyclobutane is 0.02, the ligand is 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, the molar ratio of the ligand to the 1-halocyclobutane is 0.02, the molar ratio of the reducing agent to the 1-halocyclobutane is 1, the reaction temperature is 40°C, the reaction time is 8h, and the yield of the dicyclobutane can reach more than 80%; the gram-level preparation of the dicyclobutane fuel (Example 2) is also carried out at 40°C, the reaction is extended to 24h, and after subsequent treatment, a dicyclobutane yield of 72% can be obtained.

[0080] By synthesizing a large amount of dicyclobutane (Example 2), and performing nuclear magnetic resonance and infrared spectroscopy analysis on dicyclobutane, as shown in FIG. Figure 2-4 As shown, the infrared spectrum of dicyclobutane has peaks at 2967, 2933, 2895, 2850, 1464, 1441, 1341, 1287, 1235, 994, 912, 774, and 667 cm -1 , 2800-3000cm -1 The peak position is the stretching vibration characteristic peak of methylene and methine, 1450cm -1 The left and right sides are the characteristic peaks of methylene bending vibration, 774cm -1 The peak position may be the characteristic peak of CC skeleton vibration. 1 HNMR (600MHz, CDCl3) δ2.38-2.27(m,2H),1.98-1.89(m,4H),1.86-1.70(m,4H),1.65-1.55(m,4H). 13 C NMR(151MHz, CDCl3)δ40.8,25.4,18.1ppm.IR(KBr):2967,2933,2895,2850,1464,1441,1341,1287,1235,994,912,774,667cm -1 .

[0081] The density and viscosity of the synthesized dicyclobutane were tested using a density viscosity meter and compared with those of commonly used rocket fuels Syntin, JP-10 and RP-1. Figure 5 As shown in Table 6, at 20°C, the density of dicyclobutane is 0.82 g·mL -1 The viscosity of dicyclobutane is 1.44 mm 2 ·s -1 , mass calorific value is 44.39MJ·kg -1, with high density and low viscosity, good flow performance at low temperature, high effective load and high calorific value, is an ideal high-energy fuel.

[0082] Table 6. Physical and chemical properties of bicyclo-butane

[0083]

[0084]

[0085] a 20℃ viscosity; b -10℃ viscosity; c -20℃ viscosity; d 15℃ viscosity

[0086] The freezing point and boiling point of bicyclo-butane were tested using a differential scanning calorimeter, using a temperature rise rate of -100℃-0℃-195℃, 10℃ / min. As shown in Table 6, the freezing point of bicyclo-butane was measured to be -59.4℃, and the boiling point was measured to be 160.7℃. Figure 6

[0087] Example 23

[0088] A method for preparing bicyclo-butane, comprising the following steps: taking 0.02mmol NiCl2, 0.06mmol 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 4mmol Mn powder, 2mmol 1-bromocyclobutane and 16mL DMF solvent into a 50mL Schlenck reaction container, reacting at 20℃ for 24h, cooling to room temperature, adding an internal standard and an equal volume of dichloromethane for extraction, washing the DMF in the reaction solution with saturated brine, and washing three times.

[0089] Example 24

[0090] A method for preparing bicyclo-butane, comprising the following steps: taking 0.06mmol NiCl2, 0.02mmol 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 1mmol Mn powder, 2mmol 1-bromocyclobutane and 4mL DMF solvent into a 10mL Schlenck reaction container, reacting at 50℃ for 4h, cooling to room temperature, adding an internal standard and an equal volume of dichloromethane for extraction, washing the DMF in the reaction solution with saturated brine, and washing three times.

[0091] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.​

Claims

1. A method for preparing bicyclobutane, characterized in that: The method comprises the following steps: dispersing and dissolving 1-halogenated cyclobutane, a catalyst, a ligand and an additive in a solvent, and then performing a self-coupling reaction to obtain bicyclobutane.

2. The method for preparing bicyclobutane according to claim 1, wherein the method comprises: The 1-halogenated cyclobutane is 1-bromocyclobutane.

3. The method for preparing bicyclobutane according to claim 1, wherein: The catalyst is a nickel salt; the nickel salt is any one or more of NiCl2, NiCl2(glyme), NiBr2 and Ni(cod)2.

4. The method for preparing bicyclobutane according to claim 3, wherein: The ligand is any one or more of 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine, 2,2'-bipyridine, 4,4'-di-tert-butyl-2,2'-bipyridine, 1,10-phenanthroline, 2,2':6',2"-terpyridine, triethylenediamine and triphenylphosphine.

5. The method for preparing bicyclobutane according to claim 4, wherein: The additive is a reducing substance; the reducing substance is Mn powder, and the molar ratio of Mn powder to 1-halogenated cyclobutane is 0.5-2:

1.

6. The method for preparing bicyclobutane according to claim 5, wherein: The solvent is any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropylene urea, 1,3-dimethyl-2-imidazolidinone, acetonitrile and dimethyl sulfoxide.

7. The method for preparing bicyclobutane according to claim 6, wherein: The molar ratio of the catalyst to 1-halogenated cyclobutane is (0.01-0.03):1; the molar ratio of the additive to 1-halogenated cyclobutane is 0.5-2:

1.

8. The method for preparing bicyclobutane according to claim 7, wherein: The molar ratio of the ligand to 1-halogenated cyclobutane is (0.01-0.03):

1.

9. The method for preparing bicyclobutane according to claim 8, wherein: The concentration of 1-halogenated cyclobutane in the reaction solution is 0.25-2 mol·L -1 .

10. The method for preparing bicyclobutane according to any one of claims 1 to 9, characterized in that: The temperature of the self-coupling reaction is 20-50° C., and the time is 4-24 hours.

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