A method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds, their application.

Abstract

This invention provides a method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds, their preparation, and their applications, belonging to the fields of organic synthesis and liquid propellant technology. 1,3-Propanediamine is dispersed in a suitable amount of chlorinated hydrocarbon solvent, and the corresponding aldehyde or ketone, a suitable amount of trifluoromethane sulfonate, and diisopropylethylamine are added sequentially. After half an hour, N-chlorosuccinimide is slowly added, and the reaction continues for 6-48 hours. The reaction is quenched with a suitable amount of water, and the mixture is extracted with dichloromethane. After concentrating the filtrate, column chromatography is used to obtain the corresponding 1,5-diazabicyclo[3.1.0]hexane compounds. Experiments have confirmed that 1,5-diazabicyclo[3.1.0]hexane compounds can rapidly and spontaneously ignite with fuming nitric acid and dinitrogen tetroxide, showing promising application prospects as a green fuel to replace methylhydrazine in the field of bicomponent liquid propellants.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis and liquid propellant technology, specifically, it relates to a method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds, its preparation method, and its application. Background Technology

[0002] Self-igniting liquid propellants achieve spontaneous ignition through direct contact between fuel and oxidizer, eliminating the need for external auxiliary facilities such as ignition devices and catalysts. This significantly reduces the weight and size of the propulsion system, offering advantages such as high specific impulse, long lifespan, multiple restarts, and precisely adjustable thrust. They are widely used in the main propulsion and attitude control systems of launch vehicles, satellites, spacecraft, and equipment. Traditional self-igniting liquid propellants primarily use hydrazine compounds such as methylhydrazine and unsymmetrical dimethylhydrazine, which are highly toxic, carcinogenic, flammable, and explosive, increasing safety risks and operating costs during fuel storage and refueling. Therefore, developing green, self-igniting fuels has become a hot research topic in the field of advanced aerospace propulsion.

[0003] The Scheneider team at the U.S. Air Force Research Laboratory first reported that dicyandiamide-based ionic liquids can undergo a spontaneous combustion reaction with fuming nitric acid, pioneering research on ionic liquids as spontaneous combustion propellants and green fuels (Energy & Fuels, 2008, 22, 2871-2872). Subsequently, more than ten institutions or teams, including Professor Shreve, a senior advisor to the U.S. Department of Defense (Chemical Reviews, 2014, 114, 10527-10574; Journal of Materials Chemistry, 2012, 22, 11022-11024), Professor Rogers, winner of the U.S. Presidential Challenge Award for Green Chemistry (Inorganic Chemistry, 2014, 53, 4770-4776), Professor Zhang Yanqiang of the Institute of Process Engineering, Chinese Academy of Sciences (Angewandte Chemie International Edition, 2011, 50, 9554-9562), the China Academy of Engineering Physics, and Beijing Institute of Technology, quickly followed up, designing and synthesizing a large number of self-igniting ionic liquid fuels, and carrying out physicochemical characterization and combustion performance research. Patent CN201811608166.6 reports a self-igniting N-alkyltriazole dicyanoborane complex and its preparation method: first, 1,2,4-triazole and a haloalkanes are reacted via N-alkylation, followed by N-hydrohydration coordination with sodium cyanoborohydride to form the target product; it exhibits a short ignition delay time with fuming nitric acid. Patent CN202210035348.9 relates to a method for preparing a self-igniting ionic liquid containing bis(1,2,3-triazole)borohydride anion, using 1,2,3-triazole as a raw material, reacting it with a borohydride metal salt to prepare the bis(1,2,3-triazole)borohydride metal salt, and then performing an exchange reaction with the ionic liquid to obtain the target product; its ignition delay time with fuming nitric acid is 25-130 ms. Patent CN201811608166.6 relates to a type of rocket kerosene containing polysubstituted azazine compounds or such substances, which can spontaneously combust upon contact with oxidizers such as nitrogen tetroxide and nitric acid, thus enabling its use as a green, spontaneously combusting fuel for bicomponent liquid propellants. These fuels are primarily boron- and azole-containing ionic liquids, with very few molecular fuels involved.

[0004] 1,5-Diazabicyclo[3.1.0]hexane molecules possess a highly strained ring structure, attracting widespread attention in the research of energetic materials and high-energy fuels; however, publicly reported synthetic methods are extremely limited. Punniyamurthy, Guha, Trushkov, et al. reported a method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds using tert-butyl hypochlorite as a chlorinating agent (Chemical Communications 2024, 60, 3441-3444; Journal of Organic Chemistry 2023, 88, 9447-9458; European Journal of Organic Chemistry 2019, 5475-5485). Tert-butyl hypochlorite is a strong oxidizing agent, readily decomposes and explodes, and is difficult to transport (stored at -20°C); whether for laboratory research or as an industrial raw material, it is mostly produced and used in-house. These factors greatly limit the synthesis and application of 1,5-diazabicyclo[3.1.0]hexane compounds. The Beijing Aerospace Testing Technology Research Institute uses a saturated sodium hypochlorite solution method to prepare 1,5-diazabicyclo[3.1.0]hexane compounds. This method generates a large amount of sodium chloride inorganic salt byproducts, resulting in cumbersome and complex post-processing and a low overall yield, which does not conform to the principles of green chemistry (Industrial & Engineering Chemistry Research, 2017, 56, 2883-2888; Propellants, Explosives, Pyrotechnics, 2017, 42, 477-483). Therefore, developing new methods for the efficient synthesis of 1,5-diazabicyclo[3.1.0]hexane compounds and their applications is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds and their applications. This invention is simple and practical to operate, uses readily available raw materials, has a high yield, and can avoid the use of hazardous materials such as tert-butyl hypochlorite and sodium hypochlorite, making it safe, reliable, and environmentally friendly.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds, comprising the following steps:

[0008] The first step involves dispersing 1,3-propanediamine in an appropriate amount of chlorinated hydrocarbon solvent. At a temperature of -20 to 50°C, the corresponding aldehyde or ketone, an appropriate amount of trifluoromethane sulfonate, and diisopropylethylamine are added sequentially. After stirring for half an hour, a mixed solution is obtained.

[0009] In the second step, N-chlorosuccinimide is slowly added to the mixed solution obtained in the first step, and the reaction is continued for 6-48 hours. Then, post-processing is performed to obtain the product.

[0010] Furthermore, the post-processing of the second step is as follows: after the reaction, an appropriate amount of water is added to quench the reaction, dichloromethane is used for extraction, the filtrate is concentrated, and column chromatography is used to obtain the corresponding 1,5-diazabicyclo[3.1.0]hexane compounds;

[0011] Furthermore, the molar ratio of 1,3-propanediamine, aldehyde or ketone, diisopropylethylamine to N-chlorosuccinimide is 1:1-3:1-2.5:1-3; the molar ratio of trifluoromethane sulfonate to 1,3-propanediamine is 1:20-1:200.

[0012] Furthermore, the trifluoromethane sulfonate is one of copper trifluoromethane sulfonate (II), copper trifluoromethane sulfonate (I), zinc trifluoromethane sulfonate, silver trifluoromethane sulfonate, magnesium trifluoromethane sulfonate, scandium trifluoromethane sulfonate, lithium trifluoromethane sulfonate, and iron trifluoromethane sulfonate (III), preferably silver trifluoromethane sulfonate.

[0013] Furthermore, the chlorinated hydrocarbon solvent is dichloromethane, chloroform, 1,2-dichloroethane, or carbon tetrachloride, preferably dichloromethane.

[0014] Furthermore, in the first step, the molar concentration of 1,3-propanediamine in the chlorinated hydrocarbon solvent is 0.2-0.4 mol / L.

[0015] Furthermore, in the second step, the reaction temperature is preferably 0°C; the reaction time is preferably 24 hours.

[0016] A synthetic method for 1,5-diazabicyclo[3.1.0]hexane compounds was prepared using the method described above. The structural formula of the 1,5-diazabicyclo[3.1.0]hexane compound is as follows: Among them, R 1 It is a hydrogen, alkyl, cyclopropyl, allyl, or phenyl group containing 1-4 carbon atoms; R 2 It is a hydrogen, alkyl, cyclopropyl, allyl, or phenyl group containing 1-4 carbon atoms.

[0017] An application of synthesized 1,5-diazabicyclo[3.1.0]hexane compounds is disclosed, providing their application in bicomponent liquid propellants. Specifically, 1,5-diazabicyclo[3.1.0]hexane compounds can serve as a green and non-toxic fuel to replace currently used toxic methylhydrazine and unsymmetrical dimethylhydrazine fuels. When applied to bicomponent liquid propellants, they exhibit rapid spontaneous ignition upon contact with fuming nitric acid and dinitrogen tetroxide, with an ignition delay time between 8-95 ms, meeting the design requirements of rocket engines and demonstrating promising application prospects.

[0018] The beneficial effects of this invention are as follows:

[0019] (1) This invention introduces N-chlorosuccinimide as a chlorinating agent into the synthesis of 1,5-diazabicyclo[3.1.0]hexane compounds for the first time, avoiding the use of explosive tert-butyl hypochlorite, sodium hypochlorite and other dangerous materials. The whole process is safe and reliable, and the operation is simple and practical.

[0020] (2) This invention provides a new method for the synthesis of 1,5-diazabicyclo[3.1.0]hexane compounds catalyzed by silver trifluoromethanesulfonate, which provides ideas and guidance for the design and synthesis of novel nitrogen-containing strained ring substances. Attached Figure Description

[0021] Figure 1 The 1H NMR spectrum of the synthesized 1,5-diazabicyclo[3.1.0]hexane liquid;

[0022] Figure 2 The image shows the liquid carbon NMR spectrum of the synthesized 1,5-diazabicyclo[3.1.0]hexane;

[0023] Figure 3 High-speed photographs of the spontaneous combustion of synthesized 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane with nitrogen tetroxide are shown. Among them, (a) is a diagram of the free dripping process of 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane; (b) is a diagram of the first contact between the 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane droplet and nitrogen tetroxide; (c) is a diagram of the initial spontaneous ignition of 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane with nitrogen tetroxide; and (d) is a diagram of the stable combustion of 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane with nitrogen tetroxide. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example 1: Optimization of reaction conditions for the synthesis of 6-phenyl-1,5-diazabicyclo[3.1.0]hexane

[0026]

[0027] Table 1 Optimization of reaction conditions a

[0028] Serial Number catalyst solvent Temperature (°C) Time (h) <![CDATA[Yield (%) b > 1 <![CDATA[Cu(OTf)2]]> dichloromethane 0 8 48 2 Cu(OTf) dichloromethane 0 8 15 3 <![CDATA[Zn(OTf)2]]> dichloromethane 0 8 25 4 AgOTf dichloromethane 0 8 72 5 <![CDATA[Mg(OTf)2]]> dichloromethane 0 8 26 6 <![CDATA[Sc(OTf)3]]> dichloromethane 0 6 0 7 <![CDATA[Fe(OTf)3]]> dichloromethane 0 6 0 8 AgOAc dichloromethane 0 8 35 9 AgCl dichloromethane 0 6 0 10 AgOTf methanol 0 8 55 11 AgOTf dichloroethane 0 8 71 12 AgOTf Chloroform 0 8 66 13 AgOTf Toluene 0 8 12 14 AgOTf dichloromethane 50 8 50 15 AgOTf dichloromethane -20 8 12 16 AgOTf dichloromethane 0 24 92 <![CDATA[17 c ]]> AgOTf dichloromethane 0 48 92 18 none dichloromethane 0 8 6

[0029] a Reaction conditions: benzaldehyde A1 (1 mmol), 1,3-propanediamine (1.1 mmol), solvent 5 mL, catalyst amount (1 mol%), N-chlorosuccinimide (1.1 mmol). b Separation yield. c 0.5 mol% AgOTf

[0030] To achieve efficient preparation of 1,5-diazabicyclo[3.1.0]hexane compounds, benzaldehyde A1 and 1,3-propanediamine were selected as model substrates to optimize the synthetic reaction conditions. Metal salt screening results showed that silver trifluoromethanesulfonate exhibited the best reactivity, with a yield of 72% (Table 1, No. 4). Copper, zinc, magnesium, scandium, and iron salts showed relatively low activity (Table 1, Nos. 1-7). Counterion screening results for silver salts showed that silver chloride had no catalytic activity, with a silver acetate yield of only 35% (Table 1, Nos. 8-9). Polar solvents were favorable for the reaction, while non-polar solvents such as toluene significantly reduced the yield (Table 1, Nos. 10-13). Reaction temperature studies showed that temperatures above or below 0°C led to a decrease in yield (Table 1, Nos. 14-15). Extending the reaction time to 24 hours increased the yield to 92% (Table 1, No. 16); reducing the catalyst dosage to 0.5 mol% did not affect the reaction yield (Table 1, No. 17). Without the catalyst, the reaction hardly occurred (Table 1, No. 18), possibly because N-chlorosuccinimide is significantly less active as a chlorinating agent than tert-butyl hypochlorite and sodium hypochlorite. Therefore, the optimal reaction conditions for the synthesis of 1,5-diazabicyclo[3.1.0]hexane compounds from aldehydes or ketones via chlorination / condensation / cyclization are: aldehyde or ketone (1 mmol), 1,3-propanediamine (1.1 mmol), dichloromethane 5 mL, silver trifluoromethanesulfonate (0.5 mol%), N-chlorosuccinimide (1.1 mmol), diisopropylethylamine (1.1 mmol), reaction temperature 0 °C, and reaction time 24 h.

[0031] Example 2: Synthesis of 1,5-diazabicyclo[3.1.0]hexane derivatives catalyzed by silver trifluoromethanesulfonate

[0032] The specific steps are as follows: 1,3-propanediamine and dichloromethane are added to a reaction flask. Under 0°C conditions, the corresponding aldehyde or ketone, 0.5 mol% AgOTf, and diisopropylethylamine are added sequentially. After half an hour, N-chlorosuccinimide is slowly added, and the reaction is continued for 24 hours. The reaction is quenched with an appropriate amount of water, and the mixture is extracted with dichloromethane. After concentration of the filtrate, column chromatography is used to obtain the corresponding 1,5-diazabicyclo[3.1.0]hexane compounds. The experimental results show that under standard reaction conditions, most aldehyde substrates (alkyl, cyclopropyl, or phenyl substituted) can be obtained in high yields (80-92%) (Table 2, serial numbers 1-7). The yield of ketone substrates (alkyl, cyclopropyl, or phenyl substituted) was reduced to some extent, mainly due to their large steric hindrance, especially for dicyclopropyl ketone. After 48 hours of reaction, the product 6,6-dicyclopropyl-1,5-diazabicyclo[3.1.0]hexane B14 was only 50% in yield (Table 2, No. 14).

[0033] Table 2. Synthesized 1,5-diazabicyclo[3.1.0]hexane compounds

[0034]

[0035]

[0036]

[0037] The liquid nuclear magnetic resonance spectroscopy characterization data of some products are shown below.

[0038] The liquid nuclear magnetic resonance (NMR) spectroscopy characterization data of 6-phenyl-1,5-diazabicyclo[3.1.0]hexane B1 are as follows: 1 HNMR (400MHz, CDCl3) δ7.31-7.21(m,5H), 3.52-3.46(m,2H), 3.11-3.07(m,3H), 1.90-1.78(m,2H).

[0039] The liquid nuclear magnetic resonance (NMR) spectral characterization data of 1,5-diazabicyclo[3.1.0]hexane B2 are as follows: 1 H NMR (400MHz, CDCl3) δ3.35 (dd, J=12.0, 8.0Hz, 2H), 2.99 (td, J=12.0, 8.0Hz, 2H), 2 .57(d,J=4.0Hz,1H),2.22(d,J=4.0Hz,1H),1.87–1.77(m,1H),1.77-1.64(m,1H). 13 C NMR (101MHz, CDCl3) δ51.17, 46.74, 20.18.

[0040] The liquid nuclear magnetic resonance (NMR) spectroscopy characterization data of 6-methyl-1,5-diazabicyclo[3.1.0]hexane B3 are as follows: 1 HNMR (400MHz, CDCl3) δ3.27-3.32(dt,2H),2.85-2.93(dt,2H),2.26-2.30(q,1H),1.58-1.77(m,2H),1.12-1.13(d,3H); 13 C NMR (101MHz, CDCl3) δ52.4, 51.0, 22.0, 17.7.

[0041] The liquid nuclear magnetic resonance (NMR) spectroscopy characterization data of 6-ethyl-1,5-diazabicyclo[3.1.0]hexane B4 are as follows: 1 HNMR (400MHz, CDCl3) δ3.30-3.20(m,2H),2.92-2.87(m,2H),2.15(t,1H),1.78-1.61(m,2H),1.42-1.36(m,2H),0.89(t,3H).

[0042] The liquid nuclear magnetic resonance (NMR) spectroscopy characterization data of 6,6-dimethyl-1,5-diazabicyclo[3.1.0]hexane B9 are as follows: 1 H NMR (400MHz, CDCl3) δ3.20-3.24(dt,2H),2.80-2.91(dt,2H),2.22-2.25(q,1H),1.51-1.67(m,2H),1.02-1.08(d,3H); 13 C NMR (101MHz, CDCl3) δ52.4, 51.0, 22.0, 17.7, 17.2.

[0043] The liquid nuclear magnetic resonance (NMR) spectroscopy characterization data of 6-methyl-6-ethyl-1,5-diazabicyclo[3.1.0]hexane B10 are as follows: 1 H NMR (400MHz, CDCl3) δ3.22-3.12(m,2H),2.80-2.71(m,2H),2.25-2.11(m,1H),1.94-1.81(m,1H),1.34(q,2H),1.02(s,3H),0.84(t,3H).

[0044] The liquid nuclear magnetic resonance (NMR) spectroscopy characterization data of 6,6-diethyl-1,5-diazabicyclo[3.1.0]hexane B16 are as follows: 1H NMR (400MHz, CDCl3) δ3.28-3.10(m,2H),2.84-2.70(m,2H),2.46-2.28(m,1 H),2.18-2.00(m,1H),1.44(q,2H),1.38(q,2H),1.04(t,3H),0.85(t,3H).

[0045] Table 3. Toxicity of synthesized 1,5-diazabicyclo[3.1.0]hexane compounds and their auto-ignition properties with oxidants.

[0046]

[0047] This invention uses the TEST (Toxicity Estimation Software Tool) toxicity calculation software developed by the U.S. Environmental Protection Agency (USEPA) to analyze the LD50 of the 1,5-diazabicyclo[3.1.0]hexane compounds prepared in Example 2. 50 Toxicity (LD50 in mice) (Table 3). 50 The smaller the LD value, the greater the toxicity of the compound. Calculations show that the LD values ​​for 1,5-diazabicyclo[3.1.0]hexane-like substances are... 50 Between 738.2 and 5719.2 mg / kg (methylhydrazine LD50) 50 The concentration is 32.5 mg / kg, and its toxicity is 1 / 23 to 1 / 176 that of methylhydrazine. Both are low-toxicity compounds and can be used as green and non-toxic fuels for bicomponent liquid propellants.

[0048] Example 3: Spontaneous combustion test of 1,5-diazabicyclo[3.1.0]hexane compounds with oxidants

[0049] The ignition delay time of the fuel and oxidizer is one of the key indicators for the application of bicomponent liquid propellants. A long ignition delay time may cause propellant accumulation in the engine during startup, resulting in pressure spikes or even explosions. Therefore, the ignition delay time of the fuel and oxidizer should be as short as possible. The specific implementation steps of the spontaneous combustion test are as follows: approximately 50 μL of the 1,5-diazabicyclo[3.1.0]hexane compound synthesized in Example 2 is added dropwise using a syringe to a flask containing 10 mL of fuming nitric acid or dinitrogen tetroxide. The time interval from the initial contact of the compound droplet with the fuming nitric acid or dinitrogen tetroxide to the appearance of a visible flame is recorded using a high-speed camera at a shooting speed of 1000 frames per second. This is repeated three times, and the average value is taken. The results of the spontaneous combustion test are listed in Table 3.

[0050] The results in Table 3 show that the prepared 1,5-diazabicyclo[3.1.0]hexane compounds can spontaneously ignite upon contact with fuming nitric acid and dinitrogen tetroxide. The ignition delay time with fuming nitric acid ranges from 8 to 42 ms, with 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane exhibiting an ignition delay time of 8 ms, comparable to methylhydrazine (Table 3, No. 7), demonstrating promising application prospects. The ignition delay time with dinitrogen tetroxide is slightly longer than that with nitric acid, but still less than 100 ms, with 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane having the shortest ignition delay time of 13 ms (Table 3, No. 7). The ignition delay times of the 16 1,5-diazabicyclo[3.1.0]hexane compounds prepared in this invention, together with fuming nitric acid and dinitrogen tetroxide, are between 8 and 95 ms, which initially meet the design requirements of bicomponent rocket engines and demonstrate their application prospects as green and non-toxic bicomponent liquid propellants.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the design concept of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds, characterized in that, Includes the following steps: The first step involves dispersing 1,3-propanediamine in a chlorinated hydrocarbon solvent, wherein the molar concentration of 1,3-propanediamine in the chlorinated hydrocarbon solvent is 0.2-0.4 mol / L. At a temperature of -20-50℃, an aldehyde or ketone, an appropriate amount of trifluoromethane sulfonate and diisopropylethylamine are added sequentially. After stirring for half an hour, a mixed solution is obtained. The trifluoromethane sulfonate is one of copper trifluoromethane sulfonate, cuprous trifluoromethane sulfonate, zinc trifluoromethane sulfonate, silver trifluoromethane sulfonate, and magnesium trifluoromethane sulfonate. In the second step, N-chlorosuccinimide was slowly added to the mixed solution obtained in the first step, and the reaction was continued for 6-48 hours. After post-treatment, the product 1,5-diazabicyclo[3.1.0]hexane compounds were obtained. The structural formula of the 1,5-diazabicyclo[3.1.0]hexane compounds is as follows: The reaction formula for the 1,5-diazabicyclo[3.1.0]hexane compounds is as follows: Among them, R 1 It is hydrogen, cyclopropyl, allyl, or phenyl; R 2 It can be hydrogen, cyclopropyl, allyl, or phenyl.

2. The method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds according to claim 1, characterized in that, The molar ratio of 1,3-propanediamine, aldehyde or ketone, diisopropylethylamine and N-chlorosuccinimide is 1:1-3:1-2.5:1-3; The molar ratio of the trifluoromethane sulfonate to 1,3-propanediamine is 1:20 to 1:

200.

3. The method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds according to claim 1, characterized in that, The trifluoromethane sulfonate is silver trifluoromethane sulfonate; the chlorinated hydrocarbon solvent is dichloromethane, chloroform, 1,2-dichloroethane, or carbon tetrachloride.

4. The method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds according to claim 1, characterized in that, In the second step, the reaction temperature is 0℃ and the reaction time is 24h.

5. The method for synthesizing 1,5-diazabicyclo[3.1.0]hexane compounds according to claim 1, characterized in that, The second step of the post-processing is as follows: after the reaction, water is added to quench the reaction, dichloromethane is used for extraction, the filtrate is concentrated, and column chromatography is used to obtain the corresponding 1,5-diazabicyclo[3.1.0]hexane compounds.

Images