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Pyrithione
Pyrithione is the common name of an organosulfur compound with molecular formula , chosen as an abbreviation of pyridinethione, and found in the Persian shallot. It exists as a pair of tautomers, the major form being the thione 1-hydroxy-2(1''H'')-pyridinethione and the minor form being the thiol 2-mercaptopyridine ''N''-oxide; it crystallises in the thione form. It is usually prepared from either 2-bromopyridine, 2-chloropyridine, or 2-chloropyridine ''N''-oxide, and is commercially available as both the neutral compound and its sodium salt. It is used to prepare zinc pyrithione, which is used primarily to treat dandruff and seborrhoeic dermatitis in medicated shampoos, though is also an anti-fouling agent in paints. Preparation The preparation of pyrithione was first reported in 1950 by Shaw and was prepared by reaction of 2-chloropyridine ''N''-oxide with sodium hydrosulfide followed by acidification, or more recently with sodium sulfide. 2-chloropyridine ''N''-ox ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zinc Pyrithione
Zinc pyrithione (or pyrithione zinc) is a coordination complex of zinc. It has fungistatic (inhibiting the division of fungal cells) and bacteriostatic (inhibiting bacterial cell division) properties and is used in the treatment of seborrhoeic dermatitis and dandruff. Structure of the compound The pyrithione ligands, which are formally monoanions, are chelated to Zn2+ via oxygen and sulfur centers. In the crystalline state, zinc pyrithione exists as a centrosymmetric dimer (see figure), where each zinc is bonded to two sulfur and three oxygen centers. In solution, however, the dimers dissociate via scission of one Zn-O bond. This compound was first described in the 1930s. Pyrithione is the conjugate base derived from 2-mercaptopyridine-''N''-oxide (CAS# 1121-31-9), a derivative of pyridine-''N''-oxide. Uses Medicine Zinc pyrithione can be used to treat dandruff and seborrhoeic dermatitis. It also has antibacterial properties and is effective against many pathogens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allium Stipitatum
''Allium stipitatum'', Persian shallot, is an Asian species of Allium, onion native to central and southwestern Asia. Some sources regard ''Allium stipitatum'' and ''Allium hirtifolium, A. hirtifolium'' as the same species, while others treat ''A. stipitatum'' and ''A. hirtifolium'' as distinct., p. 101f. and p. 137f. ''Allium stipitatum'' in the more inclusive sense occurs in Turkey, Iraq, Iran, Pakistan, Afghanistan, Turkmenistan, Tajikistan, Uzbekistan, Kyrgyzstan, and Kazakhstan. The epithet ''stipitatum'' means 'with a little stalk' referring to the ovary. Description ''Allium stipitatum'' grows from bulbs, 3 to 6 cm in diameter, which have blackish, paper-like tunics. The 4–6 basal leaves are broad, green to greyish green in colour, and variably hairy. The leaves are normally withered by the time the bulb flowers. Flowers are borne on stems which are tall and arranged in an umbel (a structure where the individual flowers are attached to a central point). The umbe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dandruff Shampoo
Shampoo () is a hair care product, typically in the form of a viscous liquid, that is used for cleaning hair. Less commonly, shampoo is available in solid bar format. Shampoo is used by applying it to wet hair, massaging the product into the scalp, and then rinsing it out. Some users may follow a shampooing with the use of hair conditioner. Shampoo is typically used to remove the unwanted build-up of sebum in the hair without stripping out so much as to make hair unmanageable. Shampoo is generally made by combining a surfactant, most often sodium lauryl sulfate or sodium laureth sulfate, with a co-surfactant, most often cocamidopropyl betaine in water. The sulfate ingredient acts as a surfactant, trapping oils and other contaminants, similarly to soap. Specialty shampoos are marketed to people with dandruff, color-treated hair, gluten or wheat allergies, an interest in using an organic product, infants and young children ("baby shampoo" is less irritating). There are also sham ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dandruff
Dandruff is a skin condition that mainly affects the scalp. Symptoms include flaking and sometimes mild itchiness. It can result in social or self-esteem problems. A more severe form of the condition, which includes inflammation of the skin, is known as seborrhoeic dermatitis. Dandruff in the hair is caused by a fungus called “ Malassezia Globosa” which eats the oil present on the head and when the oil breaks down produce a new substance, “oleic acid”. And many people are allergic to “oleic acid”. And it causes a lot of damage to the skin of the scalp, due to which the skin of the scalp starts falling off a lot. In this, as the layers of damaged skin are continually replaced, the cells are pushed outwards where they die and fall off. The cause is unclear, but believed to involve a number of genetic and environmental factors; the condition may worsen in the winter. It is not due to poor hygiene, and the underlying mechanism involves the excessive growth of skin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is a natural constituent of petroleum and is one of the elementary petrochemicals. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma of gasoline. It is used primarily as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. Although benzene is a major industrial chemical, it finds limited use in consumer items because of its toxicity. History Discovery The word "''benzene''" derives from "''gum benzoin''" ( ben ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thiourea
Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), except that the oxygen atom is replaced by a sulfur atom (as implied by the ''thio-'' prefix); however, the properties of urea and thiourea differ significantly. Thiourea is a reagent in organic synthesis. " Thioureas" refer to a broad class of compounds with the general structure . Thioureas are related to thioamides, e.g. , where R is methyl, ethyl, etc. Structure and bonding Thiourea is a planar molecule. The C=S bond distance is 1.71 Å. The C-N distances average 1.33 Å. The weakening of the C-S bond by C-N pi-bonding is indicated by the short C=S bond in thiobenzophenone, which is 1.63 Å. Thiourea occurs in two tautomeric forms, of which the thione form predominates in aqueous solutions. The equilibrium constant has been calculated as ''K''eq is . The thiol form, which is also known as an isothiourea, can be encountered in substituted compounds such a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
William Andrew (publisher)
William Andrew is a technical publishing house and an imprint of Elsevier Elsevier () is a Dutch academic publishing company specializing in scientific, technical, and medical content. Its products include journals such as '' The Lancet'', ''Cell'', the ScienceDirect collection of electronic journals, '' Trends'', .... The publisher was founded as an independent publisher in 1990, providing technical databooks to the plastics industry. They are based in Norwich, NY. In 1999, they purchased Noyes Publications. After an 18-month shared distribution agreement, Elsevier purchased William Andrew in January, 2009. References External links * * Elsevier imprints Book publishing companies based in New York (state) {{publishing stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peracetic Acid
Peracetic acid (also known as peroxyacetic acid, or PAA) is an organic compound with the chemical formula, formula CH3CO3H. This peroxy acid is a colorless liquid with a characteristic acrid odor reminiscent of acetic acid. It can be highly corrosive. Peracetic acid is a weaker acid than the parent acetic acid, with a Acid dissociation constant, p''K''a of 8.2. Production Peracetic acid is produced industrially by the autoxidation of acetaldehyde: :O2 + CH3CHO → CH3CO3H It forms upon treatment of acetic acid with hydrogen peroxide with a strong acid catalyst: :H2O2 + CH3CO2H CH3CO3H + H2O As an alternative, acetyl chloride and acetic anhydride can be used to generate a solution of the acid with lower water content. Peracetic acid is generated ''in situ'' by some laundry detergents. This is achieved by the action of bleach activators, such as tetraacetylethylenediamine and sodium nonanoyloxybenzenesulfonate, upon hydrogen peroxide formed from sodium percarbonate in water. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Sulfide
Sodium sulfide is a chemical compound with the formula Na2 S, or more commonly its hydrate Na2S·9 H2O. Both the anhydrous and the hydrated salts in pure crystalline form are colorless solids, although technical grades of sodium sulfide are generally yellow to brick red owing to the presence of polysulfides and commonly supplied as a crystalline mass, in flake form, or as a fused solid. They are water-soluble, giving strongly alkaline solutions. When exposed to moist air, Na2S and its hydrates emit hydrogen sulfide, an extremely toxic, flammable and corrosive gas which smells like rotten eggs. Some commercial samples are specified as Na2S·''x''H2O, where a weight percentage of Na2S is specified. Commonly available grades have around 60% Na2S by weight, which means that ''x'' is around 3. These grades of sodium sulfide are often marketed as 'sodium sulfide flakes'. Structure Na2S adopts the antifluorite structure, which means that the Na+ centers occupy sites of the fluoride ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Hydrosulfide
Sodium hydrosulfide is the chemical compound with the formula NaHS. This compound is the product of the half-neutralization of hydrogen sulfide () with sodium hydroxide (NaOH). NaSH and sodium sulfide are used industrially, often for similar purposes. Solid NaSH is colorless. The solid has an odor of owing to hydrolysis by atmospheric moisture. In contrast with sodium sulfide (), which is insoluble in organic solvents, NaSH, being a 1:1 electrolyte, is more soluble. Structure and properties Crystalline NaHS undergoes two phase transitions. At temperatures above 360 K, NaSH adopts the NaCl structure, which implies that the behaves as a spherical anion owing to its rapid rotation, leading to equal occupancy of eight equivalent positions. Below 360 K, a rhombohedral structure forms, and the sweeps out a discoidal shape. Below 114 K, the structure becomes monoclinic. The analogous rubidium and potassium compounds behave similarly. NaSH has a relatively low melting poi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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