Exposure to air

C10HJ4N2. When pure nicotine is a colourless liquid, b.p. 247 C, but darkens on exposure to air and light. Crude nicotine contains smalt amounts of other alkaloids, but ( —)-nicotine is the principal component. 

Green precipitate, turns brown on exposure to air White precipitate. 

Aniline when freshly distilled is a colourless liquid of b.p. 184° and d, 1025 on exposure to air and light, it develops a deep brown colour. It is an extremely important substance technically, being the starting point of many azo and other dyes. 

Pure phenol is a colourless crystalline substance, having m.p. 43°, and b.p. 182° on exposure to air, it slowly sublimes, and on exposure to light, develops a pink colour. It has a characteristic odour, and a limited solubility in water. Phenol in dilute aqueous solution has strongly antiseptic properties, but the crystalline substance should not be allowed to come in contact with the skin, as it may cause severe blistering. 

Physical properties. Majority are liquids except p toluidine and 1- and 2-naphthylamine. All are colourless when pure, but rapidly darken on exposure to air and light. All are very sparingly soluble in water, but dissolve readily in dilute mineral acids (except the naphthyl-amines, which are only moderately soluble in adds). They form colourless crystalline salts e.g., CjHjNH2,HCl) which are soluble in water these aqueous solutions usually have an add reaction owing to hydrolysis, and give the reactions of both the amine and the acid from which they are derived. Addition of alkali to the acid solution liberates the amine. 

Dioxan develops appreciable quantities of peroxides upon exposure to air or upon keeping. These can be eliminated by refluxing over anhydrous stannous chloride (compare Section VI, 12) or by filtration through a column of activated alumina. 

Triphenylmethane dissolves in about one-third of its weight of warm benzene it crystallises with one molecule of benzene of crystallisation which is lost on exposure to air or heating on a water bath or by recr3 stallisation from alcohol. 

Anthracene and maleic anhydride. In a 50 ml. round-bottomed flask fitted with a reflux condenser, place 2 0 g. of pure anthracene, I 1 g. of maleic anhydride (Section 111,93) and 25 ml. of dry xylene. Boil the mixture under reflux for 20 minutes with frequent shaking during the first 10 minutes. Allow to cool somewhat, add 0 5 g. of decolourising carbon and boil for a further 5 minutes. Filter the hot solution through a small, preheated Buchner funnel. Collect the solid which separates upon coohng by suction filtration, and dry it in a vacuum desiccator containing paraffin wax shavings (to absorb traces of xylene). The yield of adduct (colourless crystals), m.p. 262-263° (decomp.), is 2-2 g. Place the product (9 10-dihydroanthracene-9 10-cndo-ap-succinic anhydride) in a weU-stoppered tube, since exposure to air tends to cause hydration of the anhydride portion of the molecule. 

Scandium is a silver-white metal which develops a slightly yellowish or pinkish cast upon exposure to air. A relatively soft element, scandium resembles yttrium and the rare-earth metals more than it resembles aluminum or titanium. 

Physical Properties. Furfural [98-01-1] (2-furancarboxaldehyde), when freshly distilled, is a colorless Hquid with a pungent, aromatic odor reminiscent of almonds. It darkens appreciably on exposure to air or on extended storage. Furfural is miscible with most of the common organic solvents, but only slightly miscible with saturated aHphatic hydrocarbons. Inorganic compounds, generally, are quite insoluble in furfural. 

Physical Properties. Furfuryl alcohol (2-furanmethanol) [98-00-0] is aHquid, colorless, primary alcohol with a mild odor. On exposure to air, it gradually darkens in color. Furfuryl alcohol is completely miscible with water, alcohol, ether, acetone, and ethyl acetate, and most other organic solvents with the exception of paraffinic hydrocarbons. It is an exceUent, highly polar solvent, and dissolves many resins. 

Furfuryl alcohol, on long storage, becomes progressively darker and less water soluble, a change that is also caused by heat, acidity, and exposure to air. The reactions responsible for this change in water solubiUty may be retarded by the addition in small quantity of an organic or inorganic base. Commercial furfuryl alcohol, however, usually does not contain any additives. 

Furan should be kept from heat and flame because of its low boiling point, low flash point, and high flammabiHty. Unstabilized furan slowly forms an unstable peroxide on exposure to air and, therefore, care should be taken when using furan. When distilling furan, remove peroxides first by chemical... 

Normal precautions for chemicals of mild toxicity are appHcable to the safe handling and storage of commercial tetrahydrofurfuryl alcohol. Discoloration in storage rarely occurs if the proper precautions are observed prevention of exposure to air wiH prevent autoxidation. The Hst price of tetrahydrofurfuryl alcohol (1997) is 1.15/lb. 

Maturation is conducted in closed, full containers to prevent oxidation and aerobic growth of microorganisms. Etee air contact with low alcohol wine soon leads to vinegar. Except for those sherry types already mentioned, wines ate exposed to air minimally and temporarily. During transfers incident to bulk storage and processing, some air exposure is almost inevitable, mote in total the longer the wine is held. In the cases of white and pink table wines, it is ordinarily as neat zero as possible, and stainless steel or other impermeable containers, inert gas headspace, etc ate employed. Red wines withstand and even benefit from small but repeated exposures to air. 

Acetic acid has a sharp odor and the glacial acid has a fiery taste and will penetrate unbroken skin to make bUsters. Prolonged exposure to air containing 5—10 mg/m does not seem to be seriously harmful, but there are pronounced, undesirable effects from constant exposure to as high as 26 mg/m over a 10-day period (8). 

The function of aeration in a wastewater treatment system is to maintain an aerobic condition. Water, upon exposure to air, tends to estabUsh an equihbrium concentration of dissolved oxygen (DO). Oxygen absorption is controlled by gas solubiUty and diffusion at the gas—hquid interface. Mechanical or artificial aeration may be utilised to speed up this process. Agitating the water, creating drops or a thin layer, or bubbling air through water speeds up absorption because each increases the surface area at the interface. 

Immersion electrodes are the most common glass electrodes. These are roughly cylindrical and consist of a barrel or stem of inert glass that is sealed at the lower end to a tip, which is often hemispherical, of special pH-responsive glass. The tip is completely immersed in the solution during measurements. Miniature and microelectrodes are also used widely, particularly in physiological studies. Capillary electrodes permit the use of small samples and provide protection from exposure to air during the measurements, eg, for the determination of blood pH. This type of electrode may be provided with a water jacket for temperature control. 

These nicotinoids are appreciably volatile (nicotine vapor pressure, 5.7 Pa at 25°C) and, although colorless Hquids when pure, rapidly darken upon exposure to air. They are highly basic = 1 x 10 , = 1 x 10 ) and readily form salts with acids and many metals. Nicotine sulfate [65-30-5],... 

Oxidation. Ketones are oxidized with powerful oxidizing agents such as chromic or nitric acid. During oxidation, carbon—carbon bond cleavage occurs to produce carboxyHc acids. Ketone oxidation with hydrogen peroxide, or prolonged exposure to air and heat, can produce peroxides. Concentrated solutions of ketone peroxides (>30%) may explode, but dilute solutions are useful in curing unsaturated polyester resin mixtures (see... 

Manganese Hydroxide. Manganese hydroxide [18933-05-6] is a weaMy amphoteric base having low solubihty in water. Mn(OH)2 crystals are reported to be almost pure white and darken on exposure to air. Manganese dihydroxide occurs in nature as the mineral pyrochroite and can also be prepared synthetically by reaction of manganese chloride and potassium hydroxide that is scmpulously free of oxygen. The entire reaction is conducted under reducing conditions (36). 

Naphthalenol. 1-Naphthol, a-naphthol, or l-hydroxynaphthalene/P(9-/j5 -iJ forms colorless needles, mp 96°C, bp 288°C, which tend to become colored on exposure to air or light. It is almost insoluble in water, but readily soluble in alcohol, ether, and benzene. 1-Naphthol and 2-naphthol are found in coal tar (56). 

Naphthalenol. 2-Naphthol or p-naphthol or 2-hydroxynaphthalene/7i3 -/5 -i7 melts at 122°C and boils at 295°C, and forms colorless crystals of characteristic, phenoHc odor which darken on exposure to air or light. 2-Naphthol [135-19-3] is manufactured by fusion of sodium 2-naphthalenesulfonate with sodium hydroxide at ca 325°C, acidification of the drowned fusion mass which is quenched ia water, isolation and water-washing of the 2-naphthalenol, and vacuum distillation and flaking of the product. A continuous process of this type has been patented (69). The high sulfate content ia the primary effluent from 2-naphthol production is greatiy reduced ia modem production plants by the recovery of sodium sulfate. 

Naphthalenediol. 1,5-Dihydroxynaphthalene or Asurol is a colorless material which darkens on exposure to air. It is manufactured by the fusion of disodium 1,5-naphthalenedisulfonate with sodium hydroxide at ca 320°C in high yield. 1,5-Naphthalenediol is an important coupling component, giving ortho-a2o dyes which form complexes with chromium. The metallised dyes produce fast black shades on wool. 1,5-Naphthalenediol can be aminated with ammonia under pressure to 1,5-naphthalenediamine. 

Chemical Properties. Higher a-olefins are exceedingly reactive because their double bond provides the reactive site for catalytic activation as well as numerous radical and ionic reactions. These olefins also participate in additional reactions, such as oxidations, hydrogenation, double-bond isomerization, complex formation with transition-metal derivatives, polymerization, and copolymerization with other olefins in the presence of Ziegler-Natta, metallocene, and cationic catalysts. All olefins readily form peroxides by exposure to air. 

Upon storage, the amount of ted phosphoms in soHd white or Hquid phosphoms may increase if the material is exposed to light or contains contaminants such as iodine, sulfur, selenium, or sodium that catalyze the conversion from white to ted. Also, because white phosphoms is generally stored under water, some surface oxidation to form viscous white or colored polymeric oxyacids also occurs, especially if the oxygen content of the water can be replenished by exposure to air. 

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