1.
Polymer
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A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Because of their range of properties, both synthetic and natural polymers play an essential and ubiquitous role in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure, Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. The units composing polymers derive, actually or conceptually, from molecules of low molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, Polymers are studied in the fields of biophysics and macromolecular science, and polymer science. Polyisoprene of latex rubber is an example of a polymer. In biological contexts, essentially all biological macromolecules—i. e, proteins, nucleic acids, and polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e. g. Isoprenylated/lipid-modified glycoproteins, where small molecules and oligosaccharide modifications occur on the polyamide backbone of the protein. The simplest theoretical models for polymers are ideal chains, Polymers are of two types, Natural polymeric materials such as shellac, amber, wool, silk and natural rubber have been used for centuries. A variety of natural polymers exist, such as cellulose. Most commonly, the continuously linked backbone of a used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene, whose repeating unit is based on ethylene monomer, however, other structures do exist, for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen is also present in polymer backbones, such as those of polyethylene glycol, polysaccharides. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network, during the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester, the distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are divided into two categories, step-growth polymerization and chain-growth polymerization. However, some methods such as plasma polymerization do not fit neatly into either category
2.
Bhopal disaster
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The Bhopal disaster, also referred to as the Bhopal gas tragedy, was a gas leak incident in India, considered the worlds worst industrial disaster. It occurred on the night of 2–3 December 1984 at the Union Carbide India Limited pesticide plant in Bhopal, over 500,000 people were exposed to methyl isocyanate gas and other chemicals. The highly toxic substance made its way into and around the shanty towns located near the plant, estimates vary on the death toll. The official immediate death toll was 2,259, the government of Madhya Pradesh confirmed a total of 3,787 deaths related to the gas release. A government affidavit in 2006 stated that the leak caused 558,125 injuries, including 38,478 temporary partial injuries, others estimate that 8,000 died within two weeks, and another 8,000 or more have since died from gas-related diseases. The cause of the remains under debate. Union Carbide Corporation contends water entered the tank through an act of sabotage, the owner of the factory, UCIL, was majority owned by UCC, with Indian Government-controlled banks and the Indian public holding a 49.1 percent stake. In 1989, UCC paid $470m to settle litigation stemming from the disaster, in 1994, UCC sold its stake in UCIL to Eveready Industries India Limited, which subsequently merged with McLeod Russel Ltd. Eveready ended clean-up on the site in 1998, when it terminated its 99-year lease, Dow Chemical Company purchased UCC in 2001, seventeen years after the disaster. Civil and criminal cases were filed in the District Court of Bhopal, India, involving UCC and Warren Anderson, an eighth former employee was also convicted, but died before the judgement was passed. Anderson died on 29 September 2014, the UCIL factory was built in 1969 to produce the pesticide Sevin using methyl isocyanate as an intermediate. A MIC production plant was added in 1979, after the Bhopal plant was built, other manufacturers, including Bayer, produced carbaryl without MIC, though at a greater manufacturing cost. Bayer also used the UCC process at the plant once owned by UCC at Institute, West Virginia. The chemical process employed in the Bhopal plant had methylamine reacting with phosgene to form MIC, in the early 1980s, the demand for pesticides had fallen, but production continued, leading to build-up of stores of unused MIC. In 1976, two trade unions complained of pollution within the plant. In 1981, a worker was accidentally splashed with phosgene as he was carrying out a job of the plants pipes. In a panic, he removed his gas mask and inhaled a large amount of toxic phosgene gas, in January 1982, a phosgene leak exposed 24 workers, all of whom were admitted to a hospital. None of the workers had been ordered to wear protective masks, one month later, in February 1982, a MIC leak affected 18 workers
3.
Occupational exposure limit
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An occupational exposure limit is an upper limit on the acceptable concentration of a hazardous substance in workplace air for a particular material or class of materials. It is typically set by competent national authorities and enforced by legislation to protect occupational safety and it is an important tool in risk assessment and in the management of activities involving handling of dangerous substances. There are many dangerous substances for which there are no formal occupational exposure limits, in these cases, hazard banding or control banding strategies can be used to ensure safe handling. Occupational Exposure Limits have been established for airborne workplace chemicals by multiple regulatory, in the absence of OELs however, there are a variety of tools that can and should be used to assess exposure potential of workers. The Hierarchy of OELs provides a continuum of occupational exposure limit values that allow assessment of the risk of exposure in order to apply adequate controls, personal air sampling is routinely conducted on workers to determine whether exposures are acceptable or unacceptable. These samples are collected and analyzed using validated sampling and analytical methods and these methods are available from OSHA Technical Manual and NIOSH Manual of Analytical Methods Statistical tools are available to assess exposure monitoring data against OELs. The statistical tools are free but do require some previous knowledge with statistical concepts. A popular exposure data statistical tool called IH STAT is available from AIHA, IHSTAT has 14 languages including English and is available for free. Permissible exposure limit, set by the U. S, Occupational Safety and Health Administration Recommended exposure limit, set by the U. S. S. S. & Diwan, P. V. Industrial Guide to Chemical and Drug Safety, topping, M. Occupational Exposure Limits for Chemicals. Health and Safety Executive Research Report No, 172/2003 Occupational exposure limits and their economic costs by J Cherrie. Institute of Occupational Medicine Research Report TM/86/02 The IOM’s position on occupational exposure limits for dust Institute of Occupational Medicine Position Paper
4.
Urea
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Urea, also known as carbamide, is an organic compound with the chemical formula CO2. This amide has two groups joined by a carbonyl functional group. Urea serves an important role in the metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals and it is a colorless, odorless solid, highly soluble in water, and practically non-toxic. Dissolved in water, it is neither acidic nor alkaline, the body uses it in many processes, most notably nitrogen excretion. The liver forms it by combining two molecules with a carbon dioxide molecule in the urea cycle. Urea is widely used in fertilizers as a source of nitrogen and is an important raw material for the chemical industry, Friedrich Wöhlers discovery in 1828 that urea can be produced from inorganic starting materials was an important conceptual milestone in chemistry. More than 90% of world production of urea is destined for use as a nitrogen-release fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use, therefore, it has the lowest transportation costs per unit of nitrogen nutrient. The standard crop-nutrient rating of urea is 46-0-0, many soil bacteria possess the enzyme urease, which catalyzes conversion of urea to ammonia or ammonium ion and bicarbonate ion. Thus urea fertilizers rapidly transform to the form in soils. Ammonium and nitrate are readily absorbed by plants, and are the dominant sources of nitrogen for plant growth, Urea is also used in many multi-component solid fertilizer formulations. Urea is highly soluble in water and is also very suitable for use in fertilizer solutions. For fertilizer use, granules are preferred over prills because of their particle size distribution. The most common impurity of synthetic urea is biuret, which impairs plant growth, Urea is usually spread at rates of between 40 and 300 kg/ha but rates vary. Smaller applications incur lower losses due to leaching, during summer, urea is often spread just before or during rain to minimize losses from volatilization. Because of the nitrogen concentration in urea, it is very important to achieve an even spread. The application equipment must be calibrated and properly used. Drilling must not occur on contact with or close to seed, Urea dissolves in water for application as a spray or through irrigation systems
5.
Methyl isocyanate
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Methyl isocyanate is an organic compound with the molecular formula CH3NCO. Synonyms are isocyanatomethane, methyl carbylamine, and MIC, Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides. It has also used in the production of rubbers and adhesives. As a highly toxic and irritating material, it is hazardous to human health. It was the principal toxicant involved in the Bhopal disaster, which killed nearly 2,259 people initially and officially 3,787 people in total, Methyl isocyanate is a colorless, lachrymatory, flammable liquid. It is soluble in water to 6–10 parts per 100 parts, Methyl isocyanate is usually manufactured by the reaction of monomethylamine and phosgene. For large scale production, it is advantageous to combine these reactants at higher temperature in the gas phase. A mixture of methyl isocyanate and two moles of hydrogen chloride is formed, but N-methylcarbamoyl chloride forms as the mixture is condensed, leaving one mole of hydrogen chloride as a gas. The methyl isocyanate is obtained by treating the MCC with an amine, such as N, N-dimethylaniline. Methyl isocyanate is also manufactured from N-methylformamide and air, in the latter process, it is immediately consumed in a closed-loop process to make methomyl. Other manufacturing methods have been reported, Methyl isocyanate reacts readily with many substances that contain N-H or O-H groups. If MIC is in excess,1,3, 5-trimethylbiuret is formed along with carbon dioxide, alcohols and phenols, which contain an O-H group, react slowly with MIC, but the reaction can be catalyzed by trialkylamines or dialkyltin dicarboxylate. Oximes, hydroxylamines, and enols also react with MIC to form methylcarbamates and these reactions produce the products described below. Ammonia, primary, and secondary amines rapidly react with MIC to form substituted ureas, other N-H compounds, such as amides and ureas, react much more slowly with MIC. It also reacts with itself to form a trimer or higher molecular weight polymers, since the formation of the MIC trimer is exothermic, the reaction can lead to violent boiling of the MIC. The high-molecular-weight polymer hydrolyzes in hot water to form the trimethyl isocyanurate, since catalytic metal salts can be formed from impurities in commercial grade MIC and steel, this product must not be stored in steel drums or tanks. Methyl isocyanate is a chemical in the production of carbamate pesticides. It has also used in the production of rubbers and adhesives
6.
Lossen rearrangement
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Here, 4-toluenesulfonyl chloride is used to form a sulfonyl Ortho-derivative of hydroxamic acid. The isocyanate can be used further to generate ureas in the presence of amines or generate amines in the presence of H2O. The mechanism below begins with an O-acylated hydroxamic acid derivative that is treated with base to form an isocyanate that generates an amine, the hydroxamic acid acid derivative is first converted to its conjugate base by abstraction of a hydrogen by a base. Spontaneous rearrangement kicks off a carboxylate anion to produce the isocyanate intermediate, the isocyanate in the presence H2O hydrolyzes and then decarboxylation via abstraction of a hydrogen by a base generates an amine and CO2 gas. Hydroxamic acids are synthesized from their corresponding esters. Curtius rearrangement Hofmann rearrangement Schmidt reaction Gabapentin Mechanism in Motion, Lossen rearrangement
