Of methylene

One hundred milliliters of an aqueous solution of methylene blue contains 3.0 mg dye per liter and has an optical density (or molar absorbancy) of 0.60 at a certain wavelength. After the solution is equilibrated with 25 mg of a charcoal the supernatant has an optical density of 0.20. Estimate the specific surface area of the charcoal assuming that the molecular area of methylene blue is 197 A. ... 

Dye adsorption from solution may be used to estimate the surface area of a powdered solid. Suppose that if 3.0 g of a bone charcoal is equilibrated with 100 ml of initially 10 Af methylene blue, the final dye concentration is 0.3 x 10 Af, while if 6.0 g of bone charcoal had been used, the final concentration would have been 0.1 x Qr M. Assuming that the dye adsorption obeys the Langmuir equation, calculate the specific surface area of the bone charcoal in square meters per gram. Assume that the molecular area of methylene blue is 197 A. ... 

Selenium dioxide, SeO, is ery poisonous (cf. p. I47), but is valuable particu larly for the oxidation of methylene ( CHs) groups to carbonyl ( CO) groups. 

The p-naphthyl ethers of methylene halides have m.p. 133°, of ethylene halides 217°, and trimethylene halides 148°. 

In a 1-litre three-necked flask, mounted on a steam bath and provided respectively with a separatory funnel, mechanical stirrer and double surface condenser, place 165 g. of bromoform (96 per cent.). Add 10 ml. of a solution of sodium arsenite made by dissolving 77 g. of A.R. arsenious oxide and 148 g. of A.R. sodium hydroxide in 475 ml. of water. Warm the mixture gently to start the reaction, and introduce the remainder of the sodium arsenite solution during 30-45 minutes at such a rate that the mixture refluxes gently. Subsequently heat the flask on the steam bath for 3-4 hours. Steam distil the reaction mixture (Fig. 11, 41, 1) and separate the lower layer of methylene bromide (79 g.). Extract the aqueous layer with about 100 ml. of ether a further 3 g. of methylene bromide is obtained. Dry with 3-4 g. of anhydrous calcium chloride, and distil from a Claisen flask with fractionating side arm. The methylene bromide boils constantly at 96-97° and is almost colourless. 

Sigel and co-workers" investigated the interaction between the aromatic rings of phenyl carboxylates (Ph-(CFl2)n-C02) and 1,10-phenanthroline in ternary copper(II) complexes. Variation of the number of methylene units between the aromatic ring and the carboxylate group (n=0-5) revealed that the arene - arene interaction is most pronounced for n=l. This interaction is more efficient in a 60% 1,4-... 

At first, the dimeric nature of the base isolated from 3-ethyl-2-methyl-4-phenylthiazolium was postulated via a chemical route. Indeed the adduct of ICH, on a similar 2-ethylidene base is a 2-isopropylthiazolium salt in the case of methylene base it is an anilinovinyl compound identified by its absorption spectrum and chemical reactivity (45-47). This dimeric structure of the molecule has been definitively established by its NMR spectrum. It is very similar to the base issued from 2.3-dimethyl-benzo thiazolium (48). It corresponds to 2-(3 -ethyl-4 -phenyl-2 -methylenethiazolinilydene)2-methyl-3-ethyl-4-phenylthiazoline (13). There is only one methyl signal (62 = 2.59), and two series of signals (63= 1.36-3.90, 63= 1.12-3.78) correspond to ethyl groups. Three protons attributed to positions T,5,5 are shifted to a lower field 5.93, 6.58, and 8.36 ppm. The bulk of the ten phenyl protons is at 7.3 ppm (Scheme 22). 

The radical formed m step 3 then adds to a third molecule of ethylene and the process continues forming a long chain of methylene groups... 

Brown and Lin reported a quantitative method for methanol based on its effect on the visible spectrum of methylene blue. In the absence of methanol, the visible spectrum for methylene blue shows two prominent absorption bands centered at approximately 610 nm and 660 nm, corresponding to the monomer and dimer, respectively. In the presence of methanol, the intensity of the dimer s absorption band decreases, and that of the monomer increases. For concentrations of methanol between 0 and 30% v/v, the ratio of the absorbance at 663 nm, Asss, to that at 610 nm, Asio, is a linear function of the amount of methanol. Using the following standardization data, determine the %v/v methanol in a sample for which Agio is 0.75 and Ag63 is 1.07. 

For most samples liquid-solid chromatography does not offer any special advantages over liquid-liquid chromatography (LLC). One exception is for the analysis of isomers, where LLC excels. Figure 12.32 shows a typical LSC separation of two amphetamines on a silica column using an 80 20 mixture of methylene chloride and methanol containing 1% NH4OH as a mobile phase. Nonpolar stationary phases, such as charcoal-based absorbents, also may be used. 

CeUulose triacetate is insoluble in acetone, and other solvent systems are used for dry extmsion, such as chlorinated hydrocarbons (eg, methylene chloride), methyl acetate, acetic acid, dimethylformamide, and dimethyl sulfoxide. Methylene chloride containing 5—15% methanol or ethanol is most often employed. Concerns with the oral toxicity of methylene chloride have led to the recent termination of the only triacetate fiber preparation faciHty in the United States, although manufacture stiH exists elsewhere in the world (49). 

The solvent used to form the dope is evaporated during the extrusion process and must be recovered. This is usually done by adsorption on activated carbon or condensation by refrigeration. For final purification, the solvent is distilled. Approximately 3 kg of acetone, over 99%, is recovered per kg of acetate yam produced. Recovery of solvent from triacetate extmsion is similar, but ca 4 kg of methylene chloride solvent is needed per kg of triacetate yam extmded. 

Most phenohc foams are produced from resoles and acid catalyst suitable water-soluble acid catalysts are mineral acids (such as hydrochloric acid or sulfuric acid) and aromatic sulfonic acids (63). Phenohc foams can be produced from novolacs but with more difficulty than from resoles (59). Novolacs are thermoplastic and require a source of methylene group to permit cure. This is usually suppHed by hexamethylenetetramine (64). 

Formaldehyde is produced and sold as water solutions containing variable amounts of methanol. These solutions are complex equiUbrium mixtures of methylene glycol, CH2(OH)2, poly(oxymethylene glycols), and hemiformals of these glycols. Ultraviolet spectroscopic studies (13—15) iadicate that even ia highly concentrated solutions the content of unhydrated HCHO is <0.04 wt%. 

Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

Methylene chloiide formulas are the most common organic chemical removers. The low molar volume of methylene chloride allows it to rapidly penetrate the finish by entering the microvoids of the finish. When the solvent teaches the substrate, the remover releases the adhesive bond between the finish and the substrate and causes the finish to swell. The result is a bhstering effect and an efficient rapid lifting action. Larger molecule solvents generally cannot... 

Health and Safety. Remover formulas that are nonflammable may be used in any area that provides adequate ventilation. Most manufacturers recommend a use environment of 50—100 parts per million (ppm) time weighted average (TWA). The environment can be monitored with passive detection badges or by active air sampling and charcoal absorption tube analysis. The vapor of methylene chloride produces hydrogen chloride and phosgene gas when burned. Methylene chloride-type removers should not be used in the presence of an open flame or other heat sources such as kerosene heaters (8). 

Table 1. Consumption of Methylene Chloride by Finish Removal Groups ...

There are many colorimetric methods used for trace analysis of peroxides using reagents such as ferrous ion, leuco base of methylene blue, yy -diphenylcarbohydrazide, titanium(IV), iodide ion, and Ai,A7-dimethyl- -phenylenediamine. The latter two are the most commonly used reagents... 

Aqueous Formaldehyde. Water solutions of formaldehyde consist mainly of telomers of methylene glycol having <100 ppm of the formaldehyde as CH2O (5). Alcohols form hemiformals with aqueous formaldehyde according to the following, where n = 1,2,3, etc. 

Zinc acetate catalyst produces essentially 100% o-methylol phenol (8) in the first step. The second step gives an approximately equal quantity of 2,2 -(5, 45%) and 2,4 -diphenyhnethylene (6, 45%) bridges, indicating Htde chelate-directing influence. In addition, a small quantity (10%) of methylene ether units (9) (diben2yl ether) is observed at moderate reaction temperature. 

Alkaline catalysts are also effective in the polymeri2ation—depolymeri2ation of methylene glycol. The mechanism of the formaldehyde addition to the phenolate is still not completely understood. The most likely mechanism involves the contribution of phenol hemiformals (10) (5). 

Table 8. Proton Nmr Chemical Shifts of Methylene Groups in Phenolic Resins...

Table 9. Chemical Shifts of Methylene Carbons in Liquid Resoles...

Methods for isolation of the product polycarbonate remain trade secrets. Feasible methods for polymer isolation include antisolvent precipitation, removal of solvent in boiling water, spray drying, and melt devolatization using a wiped film evaporator. Regardless of the technique, the polymer must be isolated dry, to avoid hydrolysis, and essentially be devoid of methylene chloride. Most polycarbonate is extmded, at which point stabiUzers and colors may be added, and sold as pellets. 

---