Norman Neill Greenwood FRS CChem FRSC was an Australian-British chemist and Emeritus Professor at the University of Leeds. He is best known for the innovative textbook Chemistry of the Elements, co-authored with Alan Earnshaw, first published in 1984. After attending University High School, Greenwood read Chemistry at the University of Melbourne and graduated with a BSc in 1945 and an MSc in 1948. In 1948, he was awarded the Exhibition of 1851 Scholarship to enable him to read for a PhD at Sidney Sussex College, Cambridge under the supervision of Harry Julius Emeléus, he received the PhD in 1951. Greenwood was a senior research fellow at the Atomic Energy Research Establishment from 1951 until 1953 when he was appointed a lecturer at the University of Nottingham, his first PhD student at Nottingham was Kenneth Wade. Professor William Wynne-Jones, the Chairman of the School of Chemistry at Kings College, recruited Greenwood to the first established chair of inorganic chemistry in the country in 1961.
Greenwood was appointed professor and head of the Department of Inorganic and Structural Chemistry at the University of Leeds in 1971, a post which he held until his retirement in 1990 when he was given the title emeritus professor. Greenwood was elected a fellow of the Royal Society in 1987, his wide-ranging researches in inorganic and structural chemistry have made major advances in the chemistry of boron hydrides and other main-group element compounds. He pioneered the application of Mössbauer spectroscopy to problems in chemistry, he was a prolific writer and inspirational lecturer on chemical and educational themes, has held numerous visiting professorships throughout the world. He was appointed by NASA as principal investigator in the study of lunar rocks, he served as chairman of the IUPAC Commission on Atomic Weights from 1970 to 1975 and as president of the IUPAC Inorganic Chemistry Division. Greenwood, N. N.. Principles of Atomic Orbitals – Monograph for Teachers. Royal Society of Chemistry.
P. 48. ISBN 9780854040285. Greenwood, N. N.. Ionic crystals, lattice defects and nonstoichiometry. Butterworths. P. 194. Greenwood, N. N. C.. Mössbauer Spectroscopy. Chapman and Hall. P. 659. Greenwood, Norman N.. Chemistry of the Elements. Butterworth-Heinemann. P. 1340. ISBN 978-0-08-037941-8. Greenwood, N. N.. Recollections of a Scientist Volume 1. Boyhood and Youth in Australia. Xlibris Corporation. P. 288. ISBN 1-4691-7935-0. Greenwood, N. N.. Recollections of a Scientist, Volume 2: Expanding Horizons: England and Europe. Xlibris Corporation. P. 438. ISBN 978-1477151860. Editor: Spectroscopic Properties of Inorganic and Organometallic Compounds, Royal Society of Chemistry, Volume 1 to Volume 9 Norman Greenwood tells his life story at Web of Stories
Organic chemistry is a subdiscipline of chemistry that studies the structure and reactions of organic compounds, which contain carbon in covalent bonding. Study of structure determines their chemical formula. Study of properties includes physical and chemical properties, evaluation of chemical reactivity to understand their behavior; the study of organic reactions includes the chemical synthesis of natural products and polymers, study of individual organic molecules in the laboratory and via theoretical study. The range of chemicals studied in organic chemistry includes hydrocarbons as well as compounds based on carbon, but containing other elements oxygen, sulfur and the halogens. Organometallic chemistry is the study of compounds containing carbon–metal bonds. In addition, contemporary research focuses on organic chemistry involving other organometallics including the lanthanides, but the transition metals zinc, palladium, cobalt and chromium. Organic compounds constitute the majority of known chemicals.
The bonding patterns of carbon, with its valence of four—formal single and triple bonds, plus structures with delocalized electrons—make the array of organic compounds structurally diverse, their range of applications enormous. They form the basis of, or are constituents of, many commercial products including pharmaceuticals; the study of organic chemistry overlaps organometallic chemistry and biochemistry, but with medicinal chemistry, polymer chemistry, materials science. Before the nineteenth century, chemists believed that compounds obtained from living organisms were endowed with a vital force that distinguished them from inorganic compounds. According to the concept of vitalism, organic matter was endowed with a "vital force". During the first half of the nineteenth century, some of the first systematic studies of organic compounds were reported. Around 1816 Michel Chevreul started a study of soaps made from various alkalis, he separated the different acids. Since these were all individual compounds, he demonstrated that it was possible to make a chemical change in various fats, producing new compounds, without "vital force".
In 1828 Friedrich Wöhler produced the organic chemical urea, a constituent of urine, from inorganic starting materials, in what is now called the Wöhler synthesis. Although Wöhler himself was cautious about claiming he had disproved vitalism, this was the first time a substance thought to be organic was synthesized in the laboratory without biological starting materials; the event is now accepted as indeed disproving the doctrine of vitalism. In 1856 William Henry Perkin, while trying to manufacture quinine accidentally produced the organic dye now known as Perkin's mauve, his discovery, made known through its financial success increased interest in organic chemistry. A crucial breakthrough for organic chemistry was the concept of chemical structure, developed independently in 1858 by both Friedrich August Kekulé and Archibald Scott Couper. Both researchers suggested that tetravalent carbon atoms could link to each other to form a carbon lattice, that the detailed patterns of atomic bonding could be discerned by skillful interpretations of appropriate chemical reactions.
The era of the pharmaceutical industry began in the last decade of the 19th century when the manufacturing of acetylsalicylic acid—more referred to as aspirin—in Germany was started by Bayer. By 1910 Paul Ehrlich and his laboratory group began developing arsenic-based arsphenamine, as the first effective medicinal treatment of syphilis, thereby initiated the medical practice of chemotherapy. Ehrlich popularized the concepts of "magic bullet" drugs and of systematically improving drug therapies, his laboratory made decisive contributions to developing antiserum for diphtheria and standardizing therapeutic serums. Early examples of organic reactions and applications were found because of a combination of luck and preparation for unexpected observations; the latter half of the 19th century however witnessed systematic studies of organic compounds. The development of synthetic indigo is illustrative; the production of indigo from plant sources dropped from 19,000 tons in 1897 to 1,000 tons by 1914 thanks to the synthetic methods developed by Adolf von Baeyer.
In 2002, 17,000 tons of synthetic indigo were produced from petrochemicals. In the early part of the 20th century and enzymes were shown to be large organic molecules, petroleum was shown to be of biological origin; the multiple-step synthesis of complex organic compounds is called total synthesis. Total synthesis of complex natural compounds increased in complexity to terpineol. For example, cholesterol-related compounds have opened ways to synthesize complex human hormones and their modified derivatives. Since the start of the 20th century, complexity of total syntheses has been increased to include molecules of high complexity such as lysergic acid and vitamin B12; the discovery of petroleum and the development of the petrochemical industry spurred the development of organic chemistry. Converting individual petroleum compounds into different types of compounds by various chemical processes led to organic reactions enabling a broad range of
Ullmann's Encyclopedia of Industrial Chemistry
Ullmann's Encyclopedia of Industrial Chemistry is a reference work related to industrial chemistry published in English and German. As of 2016 it is in its 7th edition; the first edition was published in German by Fritz Ullmann in 1914. The 4th Edition, published 1972 to 1984 contained 25 volumes; the fifth edition, published 1985 to 1996, was the first version available in English. In 1997, the first online version was available, updated at least every other month; as of 2016, Ullmann's Encyclopedia is in 40 volumes including one index volume. While PDF versions of individual chapters used to be available for purchase from the Wiley Online Library, as of at least 9/2018, it appears that Wiley has restricted access to the online version only to institutional users. Therefore, it is no longer possible to purchase individual chapters through the Wiley Online Library. For individuals or small companies, the only option is to purchase the entire hardcopy 40-volume set for $11,150. Industrial chemistry is the study of chemistry with a higher mathematics and physics education for critical processes engineering and maintenance.
The industrial chemist strengthens the association of new materials investigation and manufacturing development, amid research chemistry and chemical engineering, through innovative intelligence and quality management. Subject areas include "inorganic and organic chemicals, pharmaceuticals and plastics, metals and alloys and biotechnological products, food chemistry, process engineering and unit operations, analytical methods, environmental protection and others"; as of 2016, Barbara Elvers is Editor-in-Chief and the editorial board consists of 17 editors, all but 3 of them from Germany
Vulcanization is a chemical process, invented by Charles Goodyear, used to harden rubber. Vulcanization traditionally referred to the treatment of natural rubber with sulfur and this remains the most common example, however the term has grown to include the hardening of other rubbers via various means. Examples include silicone rubber via room temperature vulcanizing and chloroprene rubber using metal oxides. Vulcanization can therefore be defined as the curing of elastomers, it works by forming cross-links between sections of polymer chain which results in increased rigidity and durability, as well as other changes in the mechanical and electrical properties of the material. Vulcanization, in common with the curing of other thermosetting polymers, is irreversible; the word vulcanization is derived from the Roman god of fire. In contrast with thermoplastic processes, vulcanization, in common with the curing of other thermosetting polymers, is irreversible. Five types of curing systems are in common use: Sulfur systems Peroxides Metallic oxides Acetoxysilane Urethane crosslinkers By far the most common vulcanizing methods depend on sulfur.
Sulfur, by itself, does not vulcanize synthetic polyolefins. Accelerated vulcanization is carried out using various compounds that modify the kinetics of crosslinking, this mixture is referred to as a cure package; the main polymers subjected to sulfur vulcanization are polyisoprene and styrene-butadiene rubber, which are used for most street-vehicle tires. The cure package is adjusted for the substrate and the application; the reactive sites—cure sites—are allylic hydrogen atoms. These C-H bonds are adjacent to carbon-carbon double bonds. During vulcanization, some of these C-H bonds are replaced by chains of sulfur atoms that link with a cure site of another polymer chain; these bridges contain between one and several atoms. The number of sulfur atoms in the crosslink influences the physical properties of the final rubber article. Short crosslinks give the rubber better heat resistance. Crosslinks with higher number of sulfur atoms give the rubber good dynamic properties but less heat resistance.
Dynamic properties are important for flexing movements of the rubber article, e.g. the movement of a side-wall of a running tire. Without good flexing properties these movements form cracks, make the rubber article fail; the vulcanization of neoprene or polychloroprene rubber is carried out using metal oxides rather than sulfur compounds which are presently used with many natural and synthetic rubbers. In addition, because of various processing factors, the choice of accelerator is governed by different rules to other diene rubbers. Most conventionally used accelerators are problematic when CR rubbers are cured and the most important accelerant has been found to be ethylene thiourea, although being an excellent and proven accelerator for polychloroprene, has been classified as reprotoxic; the European rubber industry has started a research project SafeRubber to develop a safer alternative to the use of ETU. Room-temperature vulcanizing silicone is constructed of reactive oil-based polymers combined with strengthening mineral fillers.
There are two types of room-temperature vulcanizing silicone: RTV-1. Acetoxysilane, when exposed to humid conditions, will form acetic acid; the curing process progresses through to its core. The product is either in a fluid or paste form. RTV-1 silicone has good adhesion and durability characteristics; the Shore hardness can be varied between 18 and 60. Elongation at break can range from 150% up to 700%, they have excellent aging resistance due to superior resistance to UV weathering. RTV-2. RTV-2 remains flexible from −80 to 250 °C. Break-down occurs at temperatures above 350 °C, leaving an inert silica deposit, non-flammable and non-combustible, they can be used for electrical insulation due to their dielectric properties. Mechanical properties are satisfactory. RTV-2 is used to make flexible moulds, as well as many technical parts for industry and paramedical applications. Polymer stabilizers Vulcanized fibre
Zinc is a chemical element with symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state, the Zn2+ and Mg2+ ions are of similar size. Zinc has five stable isotopes; the most common zinc ore is sphalerite, a zinc sulfide mineral. The largest workable lodes are in Australia and the United States. Zinc is refined by froth flotation of the ore and final extraction using electricity. Brass, an alloy of copper and zinc in various proportions, was used as early as the third millennium BC in the Aegean, the United Arab Emirates, Kalmykia and Georgia, the second millennium BC in West India, Iran, Syria and Israel/Palestine. Zinc metal was not produced on a large scale until the 12th century in India, though it was known to the ancient Romans and Greeks; the mines of Rajasthan have given definite evidence of zinc production going back to the 6th century BC. To date, the oldest evidence of pure zinc comes from Zawar, in Rajasthan, as early as the 9th century AD when a distillation process was employed to make pure zinc.
Alchemists burned zinc in air to form what they called "philosopher's wool" or "white snow". The element was named by the alchemist Paracelsus after the German word Zinke. German chemist Andreas Sigismund Marggraf is credited with discovering pure metallic zinc in 1746. Work by Luigi Galvani and Alessandro Volta uncovered the electrochemical properties of zinc by 1800. Corrosion-resistant zinc plating of iron is the major application for zinc. Other applications are in electrical batteries, small non-structural castings, alloys such as brass. A variety of zinc compounds are used, such as zinc carbonate and zinc gluconate, zinc chloride, zinc pyrithione, zinc sulfide, dimethylzinc or diethylzinc in the organic laboratory. Zinc is an essential mineral, including to postnatal development. Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children, deficiency causes growth retardation, delayed sexual maturation, infection susceptibility, diarrhea.
Enzymes with a zinc atom in the reactive center are widespread in biochemistry, such as alcohol dehydrogenase in humans. Consumption of excess zinc may cause ataxia and copper deficiency. Zinc is a bluish-white, diamagnetic metal, though most common commercial grades of the metal have a dull finish, it is somewhat less dense than iron and has a hexagonal crystal structure, with a distorted form of hexagonal close packing, in which each atom has six nearest neighbors in its own plane and six others at a greater distance of 290.6 pm. The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C. Above 210 °C, the metal can be pulverized by beating. Zinc is a fair conductor of electricity. For a metal, zinc has low melting and boiling points; the melting point is the lowest of all the d-block metals aside from cadmium. Many alloys contain zinc, including brass. Other metals long known to form binary alloys with zinc are aluminium, bismuth, iron, mercury, tin, cobalt, nickel and sodium.
Although neither zinc nor zirconium are ferromagnetic, their alloy ZrZn2 exhibits ferromagnetism below 35 K. A bar of zinc generates a characteristic sound when bent, similar to tin cry. Zinc makes up about 75 ppm of Earth's crust. Soil contains zinc in 5–770 ppm with an average 64 ppm. Seawater has only 30 ppb and the atmosphere, 0.1–4 µg/m3. The element is found in association with other base metals such as copper and lead in ores. Zinc is a chalcophile, meaning the element is more to be found in minerals together with sulfur and other heavy chalcogens, rather than with the light chalcogen oxygen or with non-chalcogen electronegative elements such as the halogens. Sulfides formed as the crust solidified under the reducing conditions of the early Earth's atmosphere. Sphalerite, a form of zinc sulfide, is the most mined zinc-containing ore because its concentrate contains 60–62% zinc. Other source minerals for zinc include smithsonite, hemimorphite and sometimes hydrozincite. With the exception of wurtzite, all these other minerals were formed by weathering of the primordial zinc sulfides.
Identified world zinc resources total about 1.9–2.8 billion tonnes. Large deposits are in Australia and the United States, with the largest reserves in Iran; the most recent estimate of reserve base for zinc was made in 2009 and calculated to be 480 Mt. Zinc reserves, on the other hand, are geologically identified ore bodies whose suitability for recovery is economically based at the time of determination. Since exploration and mine development is an ongoing process, the amount of zinc reserves is not a fixed number and sustainability of zinc ore supplies cannot be judged by extrapolating the combined mine life of today's zinc mines; this concept is well supported by data from the United States Geol
In chemistry and biology a cross-link is a bond that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural polymers. In polymer chemistry "cross-linking" refers to the use of cross-links to promote a change in the polymers' physical properties; when "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies. Although the term is used to refer to the "linking of polymer chains" for both sciences, the extent of crosslinking and specificities of the crosslinking agents vary greatly; as with all science, there are overlaps, the following delineations are a starting point to understanding the subtleties. Crosslinking is the general term for the process of forming covalent bonds or short sequences of chemical bonds to join two polymer chains together; the term curing refers to the crosslinking of thermosetting resins, such as unsaturated polyester and epoxy resin, the term vulcanization is characteristically used for rubbers.
When polymer chains are crosslinked, the material becomes more rigid. In polymer chemistry, when a synthetic polymer is said to be "cross-linked", it means that the entire bulk of the polymer has been exposed to the cross-linking method; the resulting modification of mechanical properties depends on the cross-link density. Low cross-link densities decrease the viscosities of polymer melts. Intermediate cross-link densities transform gummy polymers into materials that have elastomeric properties and high strengths. High cross-link densities can cause materials to become rigid or glassy, such as phenol-formaldehyde materials. Cross-links can be formed by chemical reactions that are initiated by heat, change in pH, or irradiation. For example, mixing of an unpolymerized or polymerized resin with specific chemicals called crosslinking reagents results in a chemical reaction that forms cross-links. Cross-linking can be induced in materials that are thermoplastic through exposure to a radiation source, such as electron beam exposure, gamma radiation, or UV light.
For example, electron beam processing is used to cross-link the C type of cross-linked polyethylene. Other types of cross-linked polyethylene are made by addition of peroxide during extruding or by addition of a cross-linking agent and a catalyst during extruding and performing a post-extrusion curing; the chemical process of vulcanization is a type of cross-linking that changes rubber to the hard, durable material associated with car and bike tires. This process is called sulfur curing; this is, however, a slower process. A typical car tire is cured for 15 minutes at 150 °C. However, the time can be reduced by the addition of accelerators such as 2-benzothiazolethiol or tetramethylthiuram disulfide. Both of these contain a sulfur atom in the molecule that initiates the reaction of the sulfur chains with the rubber. Accelerators increase the rate of cure by catalysing the addition of sulfur chains to the rubber molecules. Cross-links are the characteristic property of thermosetting plastic materials.
In most cases, cross-linking is irreversible, the resulting thermosetting material will degrade or burn if heated, without melting. In the case of commercially used plastics, once a substance is cross-linked, the product is hard or impossible to recycle. In some cases, though, if the cross-link bonds are sufficiently different, from the bonds forming the polymers, the process can be reversed. Permanent wave solutions, for example, break and re-form occurring cross-links between protein chains in hair. Where chemical cross-links are covalent bonds, physical cross-links are formed by weak interactions. For example, sodium alginate gels upon exposure to calcium ion, which allows it to form ionic bonds that bridge between alginate chains. Polyvinyl alcohol gels upon the addition of borax through hydrogen bonding between boric acid and the polymer's alcohol groups. Other examples of materials which form physically cross-linked gels include gelatin, collagen and agar agar. Chemical covalent cross-links are stable mechanically and thermally, so once formed are difficult to break.
Therefore, cross-linked products like car tires cannot be recycled easily. A class of polymers known as thermoplastic elastomers rely on physical cross-links in their microstructure to achieve stability, are used in non-tire applications, such as snowmobile tracks, catheters for medical use, they offer a much wider range of properties than conventional cross-linked elastomers because the domains that act as cross-links are reversible, so can be reformed by heat. The stabilizing domains may be crystalline as in thermoplastic copolyesters. Note: A rubber which cannot be reformed by heat or chemical treatment is called a thermoset elastomer. On the other hand, a thermoplastic elastomer can be recycled by heat. Many polymers undergo oxidative cross-linking when exposed to atmospheric oxygen. In some cases this is undesirable and thus polymerization reactions may involve the use of an antioxidant to slow the formation of oxidative cross-links. In other cases, when formation of cross-links by oxidation is desirable, an oxidizer such as hydrogen peroxide may be used to speed up the process.
The aforementioned process of applying a permanent wave to hair is one example of oxidative cross-linking. In that process the disulfide bonds
Manganese is a chemical element with symbol Mn and atomic number 25. It is not found as a free element in nature. Manganese is a metal with important industrial metal alloy uses in stainless steels. Manganese is named for pyrolusite and other black minerals from the region of Magnesia in Greece, which gave its name to magnesium and the iron ore magnetite. By the mid-18th century, Swedish-German chemist Carl Wilhelm Scheele had used pyrolusite to produce chlorine. Scheele and others were aware that pyrolusite contained a new element, but they were unable to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, which he did by reducing the dioxide with carbon. Manganese phosphating is used for corrosion prevention on steel. Ionized manganese is used industrially as pigments of various colors, which depend on the oxidation state of the ions; the permanganates of alkali and alkaline earth metals are powerful oxidizers. Manganese dioxide is used as the cathode material in alkaline batteries.
In biology, manganese ions function as cofactors for a large variety of enzymes with many functions. Manganese enzymes are essential in detoxification of superoxide free radicals in organisms that must deal with elemental oxygen. Manganese functions in the oxygen-evolving complex of photosynthetic plants. While the element is a required trace mineral for all known living organisms, it acts as a neurotoxin in larger amounts. Through inhalation, it can cause manganism, a condition in mammals leading to neurological damage, sometimes irreversible. Manganese is a silvery-gray metal, it is hard and brittle, difficult to fuse, but easy to oxidize. Manganese metal and its common ions are paramagnetic. Manganese tarnishes in air and oxidizes like iron in water containing dissolved oxygen. Occurring manganese is composed of one stable isotope, 55Mn. Eighteen radioisotopes have been isolated and described, ranging in atomic weight from 46 u to 65 u; the most stable are 53Mn with a half-life of 3.7 million years, 54Mn with a half-life of 312.3 days, 52Mn with a half-life of 5.591 days.
All of the remaining radioactive isotopes have half-lives of less than three hours, the majority of less than one minute. The primary decay mode before the most abundant stable isotope, 55Mn, is electron capture and the primary mode after is beta decay. Manganese has three meta states. Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before the supernova explosion. 53Mn decays to 53Cr with a half-life of 3.7 million years. Because of its short half-life, 53Mn is rare, produced by cosmic rays impact on iron. Manganese isotopic contents are combined with chromium isotopic contents and have found application in isotope geology and radiometric dating. Mn–Cr isotopic ratios reinforce the evidence from 26Al and 107Pd for the early history of the solar system. Variations in 53Cr/52Cr and Mn/Cr ratios from several meteorites suggest an initial 53Mn/55Mn ratio, which indicates that Mn–Cr isotopic composition must result from in situ decay of 53Mn in differentiated planetary bodies.
Hence, 53Mn provides additional evidence for nucleosynthetic processes before coalescence of the solar system. The most common oxidation states of manganese are +2, +3, +4, +6, +7, though all oxidation states from −3 to +7 have been observed. Mn2+ competes with Mg2+ in biological systems. Manganese compounds where manganese is in oxidation state +7, which are restricted to the unstable oxide Mn2O7, compounds of the intensely purple permanganate anion MnO4−, a few oxyhalides, are powerful oxidizing agents. Compounds with oxidation states +5 and +6 are strong oxidizing agents and are vulnerable to disproportionation; the most stable oxidation state for manganese is +2, which has a pale pink color, many manganese compounds are known, such as manganese sulfate and manganese chloride. This oxidation state is seen in the mineral rhodochrosite. Manganese most exists with a high spin, S = 5/2 ground state because of the high pairing energy for manganese. However, there are a few examples of S = 1/2 manganese.
There are no spin-allowed d–d transitions in manganese, explaining why manganese compounds are pale to colorless. The +3 oxidation state is known in compounds like manganese acetate, but these are quite powerful oxidizing agents and prone to disproportionation in solution, forming manganese and manganese. Solid compounds of manganese are characterized by its strong purple-red color and a preference for distorted octahedral coordination resulting from the Jahn-Teller effect; the oxidation state +5 can be produced by dissolving manganese dioxide in molten sodium nitrite. Manganate salts can be produced by dissolving Mn compounds, such as manganese dioxide, in molten alkali while exposed to air. Permanganate compounds are purple, can give glass a violet color. Potassium permanganate, sodium permanganate, barium permanganate are all potent oxidizers. Potassium permanganate called Condy's crystals, is a used laboratory reagent because of its oxidizing properties. Solutions of potassium permanganate were among the first stains and fixatives to be used in the preparation of biological cells and tissues for electron microscopy