Methylene chloride, replacement

Most cellulose acetate is manufactured by a solution process, ie, the cellulose acetate dissolves as it is produced. The cellulose is acetylated with acetic anhydride acetic acid is the solvent and sulfuric acid the catalyst. The latter can be present at 10—15 wt % based on cellulose (high catalyst process) or at ca 7 wt % (low catalyst process). In the second most common process, the solvent process, methylene chloride replaces the acetic acid as solvent, and perchloric acid is frequentiy the catalyst. There is also a seldom used heterogeneous process that employs an organic solvent as the medium, and the cellulose acetate produced never dissolves. More detailed information on these processes can be found in Reference 28. 

Various solvents were evaluated as methylene chloride replacements. Toluene was selected as best meeting all the needs. Thus, the R-amine was sufficiently soluble, water phases were readily separable at 25°C, and toluene contamination was of no consequence since the reaction of R-amine and 5-bromoacetylsalicylamide was already conducted in the presence of traces of toluene. 

A soln. of N,N-diethylbenzamide and 1 equivalent Iriethyloxonium fluoroborate in dry methylene chloride stirred 20 hrs. at 25, methylene chloride replaced by abs. ethanol, excess NaBH4 added portionwise at 0° with stirring, which is then continued 18 hrs. at 25° N,N-diethylbenzylamine. Y 75%. F. e., also reduction of lactams, s. R. F. Borch, Tetrah. Let. 1968, 61. 

Trichloroethylene use has declined as a result of environmental concerns. However, trichloroethylene may replace some 1,1,1-trichloroethane appHcations. Perchloroethylene used in small businesses for dry cleaning will be regulated for emissions under the same guidelines as those that govern the large chemical producers. This will cause replacement of perchloroethylene for those appHcations where recovery is uneconomical. Methylene chloride has been classified as a suspected carcinogen and its use will decline in aerosol and paint stripping appHcations because of health concerns. 

The reaction vessel is cooled to 30° and the reflux condenser replaced with a distillation head and condenser. The methylene chloride is removed by distillation, b.p. 35-55°. The residue is then transferred to a 500-ml. round-bottomed flask and distilled through a 30-cm. Vigreux column. The yield of a-chloroanisole is 266-271 g. (93-95%), b.p. 74-77° (13 mm.), w23d 1.5342 (Notes 5, 6, 7). 

One solution is to replace the column, but a less expensive approach is to attempt to clean the column. Baking is one approach that removes some forms of contamination, but also shortens the column life because it removes some of the stationary phase. A solvent rinse is the most effective means of cleaning a bonded or cross-linked phase column. Solvent rinse kits are available with instructions from most column manufacturers. The procedure involves forcing solvents through the GC column, usually in the following order—water, methanol, methylene chloride, and hexane—using 10-15 psi back pressure. 

Most thiirene dioxides (and oxides) have been prepared through a modified Ramberg-Backlund reaction as the last crucial cyclization step, as illustrated in equation 40 for the benzylic series . Synthesis of thiirene dioxides requires two major modifications of the originally employed reaction first, the inorganic base has to be replaced by the less basic and less nucleophilic triethylamine - and second, the aqueous media has to be substituted by an aprotic organic solvent (e.g. methylene chloride). Under these mild reaction conditions the isolation of aryl-substituted thiirene dioxides (and oxides) is feasible . In fact, this is the most convenient way for the preparation of the aryl-disubstituted three-membered ring sulfones and sulfoxides. ... 

Note Benzene and chloroform are suspected carcinogens. Perhaps they could be replaced by toluene and methylene chloride, respectively, with some modification of the proportions used. 

Solvent-assisted decaffeination of coffee can result in residues of solvent reaching the consumer.208 The use of chlorinated hydrocarbon solvents such as chloroform,209 methylene chloride, trichloroethylene,208 and difluoromonochloromethane (Freon),210 will probably be replaced by compounds already found in roasted coffee. The use of an ethyl acetate and 2-butanone mixture leaves a 26-ppm residue in green coffee, but zero residue in roasted coffee.211 Other solvent compounds used or suggested for coffee improvement or decaffeination include propane, butane,212 carbon dioxide,213 214 acetone215 dimethyl succinate,2161,1-dimethoxymethane, and 1,1-dimethoxyethane.217 Of all these, supercritical carbon dioxide, ethyl acetate, and methylene chloride are the solvents most used currently in decaffeination processes. 

The disulfide fragment separating phosphorus and boron atoms was not replaced in 181 by chloral even after refluxing in benzene, evidence for high betaine stability. In methylene chloride, 175 reacts with 1,2-naphthoquinone, yielding phosphorane 182 [Eq. (135)]. This result is surprising, as one could have expected the formation of a betaine structure. 

The three examples related to solvent replacement cover the generation and evaluation of solvent alternatives for Ethyl Glycol Acetate, Ethyl Glycol and Methylene Chloride. Where feasible, the selected solvent alternatives have been tested under conditions of industrial application and/or laboratoiy scale experiments with very encouraging results. 

The above solution procedure has been applied to find replacement solvents for the following solvents Ethyl Glycol Acetate, Ethyl Glycol and Methylene Chloride. These three solvents are extensively used in the paints and ink industry, although, recent studies have shown that they carry an appreciable environmental burden in addition to being found harmful for the health of the people exposed to them (for example, employees in the manufacturing plants and/or consumers). 

Replacement of Methylene Chloride Step 1 Pre-specified Properties... 

Similar to the previous examples, the pre-selected target properties for the replacement of methylene chloride as a solvent, are listed in Table 3. 

The remaining solvent candidate, i.e., Propanone was tested as a replacement of Methylene Chloride under laboratory conditions and the results were found to be promising (Constantinou 2005). Eventhough it was not applied under actual industrial conditions, Propanone appears to be a likely replacement for Methylene Chloride. 

Much of the current interest in using analytical-scale SFE systems comes from the need to replace conventional liquid solvent extraction methods with sample preparation methods that are faster, more efficient, have better potential for automation, and also reduce the need for large volumes of potentially hazardous liquid solvents. The need for alternative extraction methods is emphasized by current efforts to reduce the use of methylene chloride as an extraction fluid for environmental sample preparation [158]. The potential for applying SFE to a wide variety of environmental and biological samples for both qualitative and quantitative analyses is widely described in reviews [159-161] and the references therein. Analytical-scale SFE is most often applied to relatively small samples (e.g., several grams or less). 

Small firm uses methylene chloride to strip coatings off small aircraft Firm identified and tested low mediylene chloride-content strippers to replace use of only methylene chloride. 

---