Halogen and methylene

In addition to its water solubility poly(vinyl pyrrolidone) is soluble in a very wide range of materials, including aliphatic halogenated hydrocarbons (methylene dichloride, chloroform), many monohydric and polyhdric alcohols (methanol, ethanol, ethylene glycol), some ketones (acetyl acetone) and lactones (a-butyrolactone), lower aliphatic acids (glacial acetic acid) and the nitro-paraffins. The polymer is also compatible with a wide range of other synthetic polymers, with gums and with plasticisers. 

Fig. 16 The experimental geometries of methylenecyclopropane- HC1 and methylene-cyclopropane- -CIF, drawn to scale. The n-electron model for the Lewis base is also shown. The angles C- - H and C- Cl, respectively, where is the centre of the C - C double bond, are both close to 90°, as required by rule 2. The halogen bond again exhibits a smaller non-linearity 6 than the hydrogen bond. See Fig. 1 for key to the colour coding of atoms... 

The present procedure is applicable only to bromomalononitrile various a-halogen active methylene derivatives, (e.g., diethyl chloromalonate, methyl bromoacetoacetate) led predominantly to the formation of ring-contracted styrene derivatives. On the other hand, substituted cycloheptatrienylium salts with bromomalononitrile gave the desired dicyanoheptafulvene derivatives in excellent yields. One notable example is the synthesis of 5- and 7-(dicyanomethylene)-2,3-dihydrocyclohepta-1,4-dithiins.6... 

Fedurco, M., Sartoretti, C.J. and Augustynski, J. (2001) Reductive cleavage of the carbon-halogen bond in simple methyl and methylene halides. Reactions of the methyl radical and carbene at the polarized electrode/aqueous solution interface. Langmuir 17, 2380-2387. 

The third approach is useful when the spiropyran itself (or, more correctly, its intermediates) is easily available, the necessary substituted intermediates are not, and the spiropyran tolerates the chemical transformations involved. Halogenation and nitration of BIPS and spiro(dinaphthopyrans) can be carried out by standard methods bromo substituents replaced by cyano or lithium, nitro substituents reduced to amino, etc. For example, the aldehyde group in 6-formylBIPS can be reduced, oxidized, caused to react with organometallics, condensed with active methylene groups, converted to cyano, and derivatized to give a wide variety of 6-substituted BIPS. These reactions cannot be usefully carried out directly on 5-formylsalicylal-... 

Workers come in contact with a large number of chemical substances in work areas, as does the general public. The commonly found chemical carcinogens are grouped under (1) polycyclic aromatic hydrocarbons (PAHs), (2) nitroso compounds, (3) halogenated hydrocarbons (solvents e.g., carbon tetrachloride, chloroform, trichloroethylene, and methylene chloride), (4) inorganic metals and minerals (beryllium, cadmium, nickel, cobalt, chromium, asbestos and arsenic), and (5) naturally occurring chemical substances (aflatoxins). 

Halogenated hydrocarbons. Several of these compounds are commonly used as solvents. Examples include carbon tetrachloride, chloroform, trichloroethylene, and methylene chloride. 

A blend of hydrocarbon and halogenated hydrocarbons has appeared recently in the patent literature (196). An example is a blend of pentane and methylene chloride in a weight ratio of about 50/50. 

Paints often contain solvents such as toluene, xylene, halogenated aromatic hydrocarbons, and methylene chloride, as well as heavy metals in their pigments including chromium yellow, lemon yellow (barium chromate), vermilion red (cadmium and mercuric sulfides), and flake white (lead). Both acute and chronic exposures to toluene and xylene are associated with neurotoxicity and can also damage the liver and kidneys. 

A solution of 2-phenyl-4,5,6,7-tetrahydroindole (200 mg, 1.02 mmol) and methylene blue (2 mg) in 200 mL methanol was placed in a doughnut-type vessel with a 300 W halogen lamp for 20 min under a stream of oxygen. After evaporation of methanol below 30 °C, the residue was dissolved in benzene/hexane (1 1). Insoluble methylene blue was filtered off. Evaporation of the solvent below 30 °C gave 210 mg (quantitative yield) of 6.2b, mp 126 - 128 °C (dec.). 

The product is soluble in water, but is only sparingly soluble in chloroform and methylene chloride. It can be solubilized in halogenated solvents by the addition of small amounts (ca. 5 % by volume) of MeOH, EtOH, MeCN, or THF. Otherwise, the ancillary ligands are assumed to be H20 or MeOH, depending on the sample s history. These coordinated water/methanol ligands are easily substituted over the course of several hours at room temperature. A variety of pyridyl ligands,10 isocyanides,18 and more complex ligands have been installed.16,17... 

The dried polyarylsulfone (IV) is soluble in halogenated hydrocarbons such as chloroform, chlorobenzene, and methylene chloride. 

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