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Para-dichlorobenzene
1,4-Dichlorobenzene (1,4-DCB, ''p''-DCB, or ''para''-dichlorobenzene, sometimes abbreviated as PDCB or para) is an aryl chloride and isomer of dichlorobenzene with the formula C6H4Cl2. This colorless solid has a strong odor. The molecule consists of a benzene ring with two chlorine atoms (replacing hydrogen atoms) on opposing sites of the ring. It is used as a disinfectant, pesticide, and deodorant, most familiarly in mothballs in which it is a replacement for the more traditional naphthalene because of naphthalene's greater flammability (though both chemicals have the same NFPA 704 rating). It is also used as a precursor in the production of the chemically and thermally resistant polymer poly(''p''-phenylene sulfide). Production ''p''-DCB is produced by chlorination of benzene using ferric chloride as a catalyst: :C6H6 + 2 Cl2 → C6H4Cl2 + 2 HCl The chief impurity is the 1,2 isomer. The compound can be purified by fractional crystallization, taking advantage of its re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Urinal Cake
Urinal deodorizer blocks (commonly known as urinal cakes, urinal cookies, urinal biscuits (or jocularly piscuits), urinal donuts, toilet lollies, trough lollies, urinal pucks, toilet pucks, or urinal peons (alternately urinal pee-ons)) are small disinfectant blocks or tablets that are added to urinals. As these products originally contained para-dichlorobenzene (pDCB) they may also be called para blocks. Besides disinfecting, the purpose of these materials is to deodorize restroom urinals. They are placed above the urinal drain, often in the confines of a small plastic device called a ''urinal screen'' that prevents loss down the drain when they dissolve down to a small size. Chemistry The chemicals composing the block vary. The original formulations were based upon naphthalene and then later para-dichlorobenzene, both now known to be hazardous to health by inhalation. In some areas, the use of para-dichlorobenzene-based blocks has been banned; in other areas para-dichlorobenze ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mothball
Mothballs are small balls of chemical pesticide and deodorant, sometimes used when storing clothing and other materials susceptible to damage from silverfish, Mold (fungus), mold or moth larvae (especially clothes moths like ''Tineola bisselliella''). Composition Older mothballs consisted primarily of naphthalene, but due to naphthalene's flammability, many modern mothball formulations instead use 1,4-dichlorobenzene. The latter formulation may be somewhat less flammable, although both chemicals have the same NFPA 704 rating for flammability. The latter chemical is also variously labeled as 1,4-Dichlorobenzene, para-dichlorobenzene, p-dichlorobenzene, P-DCB, pDCB, or PDB (Palm OS), PDB, making it harder to identify unless all these names and initialisms are known to a potential purchaser. Both of these formulations have the strong, pungent, sickly-sweet odor often associated with mothballs. Both naphthalene and 1,4-dichlorobenzene undergo Sublimation (phase transition), subli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dichloromethane
Dichloromethane (DCM, methylene chloride, or methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odor is widely used as a solvent. Although it is not miscible with water, it is slightly polar, and miscible with many organic solvents.Rossberg, M. ''et al.'' (2006) "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. . Occurrence Natural sources of dichloromethane include oceanic sources, macroalgae, wetlands, and volcanoes. However, the majority of dichloromethane in the environment is the result of industrial emissions. Production DCM is produced by treating either chloromethane or methane with chlorine gas at 400–500 °C. At these temperatures, both methane and chloromethane undergo a series of reactions producing progressively more chlorinated products. In this way, an estimated 400,000 tons were produced in the US, Europe, and Japan in 199 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Precursor Chemical
In chemistry, a precursor is a compound that participates in a chemical reaction that produces another compound. In biochemistry, the term "precursor" often refers more specifically to a chemical compound preceding another in a metabolic pathway, such as a protein precursor. Illicit drug precursors In 1988, the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances introduced detailed provisions and requirements relating the control of precursors used to produce drugs of abuse. In Europe the Regulation (EC) No. 273/2004 of the European Parliament and of the Council on drug precursors was adopted on 11 February 2004. (European law on drug precursors) Illicit explosives precursors On January 15, 2013, the Regulation (EU) No. 98/2013 of the European Parliament and of the Council on the marketing and use of explosives precursors was adopted. The Regulation harmonises rules across Europe on the making available, introduction, possession and u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mildew
Mildew is a form of fungus. It is distinguished from its closely related counterpart, mold, largely by its colour: molds appear in shades of black, blue, red, and green, whereas mildew is white. It appears as a thin, superficial growth consisting of minute hyphae (fungal filaments) produced especially on living plants or organic matter such as wood, paper or leather. Both mold and mildew produce distinct offensive odours, and both have been identified as the cause of certain human ailments. In horticulture, mildews are species of fungus in the order Erysiphales, or fungus-like organisms in the family '' Peronosporaceae''. It is also used more generally to mean mold growth. In Old English, mildew meant honeydew (a substance secreted by aphids on leaves, formerly thought to distill from the air like dew), and later came to mean mold or fungus. Household varieties The term mildew is often used generically to refer to mold growth, usually with a flat growth habit. Molds can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mold (fungus)
A mold () or mould () is one of the structures that certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not all fungi form molds. Some fungi form mushrooms; others grow as single cells and are called microfungi (for example yeasts). A large and taxonomically diverse number of fungal species form molds. The growth of hyphae results in discoloration and a fuzzy appearance, especially on food. The network of these tubular branching hyphae, called a mycelium, is considered a single organism. The hyphae are generally transparent, so the mycelium appears like very fine, fluffy white threads over the surface. Cross-walls (septa) may delimit connected compartments along the hyphae, each containing one or multiple, genetically identical nuclei. The dusty texture of many molds is caused by profuse production of asexual spores (conidia) form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Moth
Moths are a group of insects that includes all members of the order Lepidoptera that are not Butterfly, butterflies. They were previously classified as suborder Heterocera, but the group is Paraphyly, paraphyletic with respect to butterflies (suborder Rhopalocera) and neither subordinate taxon is used in modern classifications. Moths make up the vast majority of the order. There are approximately 160,000 species of moth, many of which have yet to be described. Most species of moth are nocturnal, although there are also crepuscular and Diurnal animal, diurnal species. Differences between butterflies and moths While the Butterfly, butterflies form a monophyly, monophyletic group, the moths, comprising the rest of the Lepidoptera, do not. Many attempts have been made to group the superfamilies of the Lepidoptera into natural groups, most of which fail because one of the two groups is not monophyletic: Microlepidoptera and Macrolepidoptera, Heterocera and Rhopalocera, Jugatae a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chlorobenzene
Chlorobenzene (abbreviated PhCl) is an aryl chloride and the simplest of the chlorobenzenes, consisting of a benzene ring substituted with one chlorine atom. Its chemical formula is C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals. Uses The major use of chlorobenzene is as a precursor for further intermediates such as nitrophenols, nitroanisole, chloroaniline, and phenylenediamines, which are used in the production of herbicides, dyestuffs, chemicals for rubber, and pharmaceuticals. It is also used as a high-boiling solvent in industrial and laboratory applications, for materials such as oils, waxes, resins, and rubber. Chlorobenzene is nitrated on a large scale to give a mixture of 2-nitrochlorobenzene and 4-nitrochlorobenzene, which are separated and used as intermediates in production of other chemicals. These mononitrochlorobenzenes are converted to related 2-nitrophenol, 2-nitroanis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Melting Point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilibrium, equilibrium. The melting point of a substance depends on pressure and is usually specified at a Standard temperature and pressure, standard pressure such as 1 Atmosphere (unit), atmosphere or 100 Pascal (unit), kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Because of the ability of substances to Supercooling, supercool, the freezing point can easily appear to be below its actual value. When the "characteristic freezing point" of a substance is determined, in fact, the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice, that is, the #Melting point measurements, melting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fractional Crystallization (chemistry)
{{crystallization In chemistry, fractional crystallization is a stage-wise separation technique that relies on the liquid–solid phase change. This technique fractionates via differences in crystallization temperature and enables the purification of multi-component mixtures, as long as none of the constituents can act as solvents to the others. Due to the high selectivity of the solid–liquid equilibrium, very high purities can be achieved for the selected component. Principle of separation The crystallization process starts with the partial freezing of the initial liquid mixture by slowly decreasing its temperature. The frozen solid phase subsequently has a different composition than the remaining liquid. This is the fundamental physical principle behind the melt fractionating process and quite comparable to distillation, which operates between a liquid and the gas phase. The crystals will grow on a cooled surface or alternatively as a suspension in the liquid. The heat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibility of isomers. Isomers do not necessarily share similar chemical property, chemical or physical property, physical properties. Two main forms of isomerism are structural isomerism, structural (or constitutional) isomerism, in which ''chemical bond, bonds'' between the atoms differ; and stereoisomerism (or spatial isomerism), in which the bonds are the same but the ''relative positions'' of the atoms differ. Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different Isotopologue, isotopologues. The depth of analy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
