Carbon dioxide atomic crystal
What is the total number of compounds?
A New Method of Synthetic Ammonia —— Electrosynthesis
Explosive high-energy N5+ cation appeared.
New progress in direct synthesis of hydrogen peroxide
Methane in rice fields
Theoretical Calculation of a New Hydrogen Bond —— Double Hydrogen Bond (A-H…H-B)
Resveratrol is widely found in food and is an anticancer substance.
Yes/this is the chemistry portal website run by China Academy of Sciences.
Recently, V. Lota, C. S. Yoo and H. Cynn of Lawrence Livermore National Laboratory (LLNL) in the United States have successfully transformed CO2 into atomic crystals similar to SiO2 under high pressure.
It has been found in the past that there are four kinds of crystals of CO2, all of which are molecular crystals. They found that liquid CO2 was put into a diamond anvil with a temperature of -40℃ and heated to 1800K by a Nd: YbLiF4 laser. Under the high pressure of 40GPa, CO2 forms SiO2 _ 2-like atomic crystals on micron-sized ruby chips or platinum films (Science,1999,283,65433). The sample shows a new phase on the micrograph above 1800K K, and it can exist stably at room temperature as long as the pressure is higher than 1GPa. Comparing the Raman spectra before and after heating, it is found that the vibration spectrum of Si-O-Si bond in the form of molecular crystal CO2 orthogonally transformed into silica coesite crystal (coesite, the high-pressure phase of silica, exists in meteorites and is synthesized under high pressure in the laboratory) has the same characteristics. The second resonance frequency of Nd:YLF laser strongly emitted by the crystal; This property has aroused great interest in the application of this crystal in optoelectronics.
By the end of 1998, the total number of registered compounds in American Chemical Abstracts, the largest chemical abstract in the world, was18.8 million, and 1998 was the third consecutive year that the number of registered compounds exceeded1600,000.
It can be predicted that this growth rate and momentum will not last, and 1999 should also be the fourth year of registration of more than1100,000 registered compounds. By the end of the year, the total number of known compounds-isolated from nature and synthesized by human beings-will definitely exceed 20 million. Therefore, when entering 2000, teachers can stay in the classroom with confidence and boldness.
Recently, two Greek chemists, George Marnellos and Michael Stoukides of Aristotle University in Thessaloniki, invented a new method for synthesizing ammonia (Science, 2 Oct. 1998, p98).
Under normal pressure, hydrogen and nitrogen diluted with helium were introduced into the electrolytic cell with SrCe Yttrium Perovskite Porous Ceramics (SCY) as the solid electrolyte, heated to 570℃, and converted into ammonia through the porous palladium polycrystalline membrane covering the inner and outer surfaces of the solid electrolyte, with a conversion rate of 78%. Comparison: Harper's conversion rate of synthetic ammonia process in the past century is usually 10- 15%!
Exploration of experimental conditions: they use online gas chromatography to detect the gas entering and leaving the electrolytic cell, and estimate the output of ammonia gas through the change of pH value caused by HCl absorption of ammonia gas, which proves that increasing the partial pressure of nitrogen gas is ineffective in improving the conversion rate; Although increasing current and temperature improves the proton transfer speed in SCY, the conductivity of SCY is limited by temperature, and increasing temperature will accelerate the decomposition of ammonia.
Karl O. Christe, a chemist who studies energetic materials in the Air Force Laboratory of Edward Air Force Base in California, announced at the Winter Fluorine Conference of the American Chemical Society that he and his colleague W. W. Wilson had synthesized and characterized a salt containing N5+ ions. This cation can be regarded as the third separable total nitrogen species in 100 years. N2 was isolated for the first time in 1772 and synthesized for the second time in 1890. Although other nitrogen-containing substances in gas have been reported, they have not been separated. Professor S. H. Strauss of Colorado State University called the synthesis of N5+ a truly incredible discovery.
The synthetic method of Christe is that N2F+ASF6-reacts with HN3 in anhydrous hydrogen fluoride at -78℃. The reaction product is white powder, and the stability limit temperature is 22℃. He obtained mass spectrometry data at this temperature, but in the low-temperature laser spectrometer, only a few micrograms of samples exploded, destroying the sample cells.
Professor DesMarteau of Clemson University commented that it is not surprising that this compound is highly explosive, but it is surprising that this compound can exist.
Professor J. Schrobilgen of McMaster University in Canada pointed out that only a few laboratories can do this kind of work.
Crystal pointed out that N5+ cation is a much stronger oxidant than O2+, and it will explode when it reacts with water and organic matter. The synthesis amount can reach half a gram. After calculation, the enthalpy of formation of the compound is as high as+1460kJ/mol, so it is really surprising that the compound can still exist stably. The vibration spectrum and theoretical calculation show that the ion has a V-shaped configuration. The researchers predict that other salts containing N5+ ions can also be synthesized. For example, maybe N5+sb F6-- is a more stable salt, and they even plan to synthesize a new species composed of nitrogen -N5+N3-.
It has long been known that hydrogen peroxide can be directly synthesized under the catalysis of Group VIII metals such as palladium and gold. However, because this reaction is at the explosive limit of hydrogen and oxygen, there are obvious safety problems and conversion problems.
Recently, J-P Pirard et al. applied for a patent (U.S. Pat. No.5,500,202,1Mar. 9 1996) to solve these problems: they used a trickle bed reactor, and the mixed gas of hydrogen and oxygen diluted with nitrogen and acidified water vapor flowed in the same direction with the palladium-supported catalyst. The inventor used 100 ml tubular Hastelloy C reactor (1 cm inner diameter × 120 cm) and 40 g carbon catalyst containing 2% by weight of palladium (150-0). M particle size), the water phase composition is 0. 1 M H2SO4 and 0.00 1M NaBr (to prevent decomposition of hydrogen peroxide), the liquid phase velocity is 0.8 L/h, the gas phase velocity is 25L/min(STP), and the gas phase composition is 59% O2, 5.5% H2 and 35.5% N2. The pressure is 60 bar. When O2/N2 enters the front space of the reactor, hydrogen is introduced into the liquid phase. As a result, the concentration of hydrogen peroxide in water vapor reached 5% by mass, which is equivalent to 80 mol% selectivity and 30 mol% conversion (based on introduced hydrogen). The gas mixture in the system exceeds the explosion limit of hydrogen and oxygen. It is estimated that the investment cost of this method will be lower than the traditional indirect method.
According to the reports of C & AMPEN1October 7 1996 and p 10, the scientist Landing of the Philippine International Rice Research Institute (IRRI) pointed out that methane is a greenhouse gas with greater influence than carbon dioxide, and the annual release to the atmosphere is 500 million tons, of which 20% comes from rice fields. About 90% of methane produced by anaerobic decomposition of organic matter in rice fields is released into the atmosphere through the roots, stems and leaves of rice. The rest is oxidized to carbon dioxide by oxygen diffused from the roots of rice. The concentration of methane in the atmosphere is much less than that of carbon dioxide, but its warming effect is 30 times greater than that of carbon dioxide. Methane also stays in the atmosphere for a long time. It affects the levels of ozone, hydroxyl and carbon monoxide in the atmosphere and troposphere. Therefore, the research institute believes that efforts should be made to cultivate rice varieties or cultivation techniques that release less methane into the atmosphere.
A letter from Ralph Cicero of the University of California was published in the journal 10/0 on October 28th. The author first points out that the life of methane in the atmosphere is shorter than that of carbon dioxide. The author also pointed out that according to the latest data, according to the statistics of Japanese soil chemist Yagi Miho, the amount of methane released into the atmosphere by rice fields all over the world is only half of the data given by Lanting. Moreover, field experiments tell us that the amount of methane released from rice fields is restricted by many factors, such as organic matter added to soil, water management during rice growth period, soil type, methane transport mechanism of rice and so on.
Note: It has also been reported in the early literature that termites or African grassland ant colonies will also release a large amount of methane into the atmosphere.
By the way, similar to the methane problem, there is also the problem of nitrogen oxides released from rice fields. The rice research institute is studying how to make rice have nitrogen fixation ability and reduce the use of nitrogen fertilizer. In fact, all crops are inevitably polluted by nitrogen compounds because of excessive application of nitrogen fertilizer. Nitrogen oxides released into the atmosphere are also an important reason for changing the atmospheric temperature.
Crabtree et al reported 26 kinds of intermolecular double hydrogen bonds B-H…H-A, DHH.
The calculation shows that the reaction product NH4++CH4 = [NH4CH4] (J.AM. Chemistry. SOC。 , 1972,94,5188,6305) reported in1972 should contain double hydrogen bonds, and the calculated bond energy is 14. The systems involved in the calculation are BH4-…HCN, BH4-…CH4, LIH … NH4+,LIH……HCN, LIH……HCCH, BEH2 … NH4+,be H2……HCN, CH4……NH4+ and so on. Among them, the length of double hydrogen bond calculated by BH4-…HCN is 1.709 angstrom, which is the smallest and the bond energy reaches 75.44 kJ/mol, which is the highest.
A joint research group of the University of Illinois in the United States and the University of Madrid in Spain recently reported that resveratrol, a trihydroxy derivative of stilbene, exists widely in many foods, such as mulberry, peanuts, especially grapes, and may have anticancer properties [Science 275, 1997: 2 18]. They found that plant extracts containing this compound can inhibit cyclooxygenase. In another in vivo experiment, the compound can inhibit the generation of free radicals in leukemia cells treated with phorbol ester, inhibit the variation of other cells, and activate quinone reductase which can reduce the toxicity of carcinogens.
The skin test of mice showed that resveratrol not only reduced the number of skin cancer in mice, but also reduced the number of mice with cancer. The researchers pointed out that resveratrol is a ubiquitous substance in human diet and a potential chemical anticancer agent worthy of in-depth study.