Majority impurity

Although acetic acid and water are not beheved to form an azeotrope, acetic acid is hard to separate from aqueous mixtures. Because a number of common hydrocarbons such as heptane or isooctane form azeotropes with formic acid, one of these hydrocarbons can be added to the reactor oxidate permitting separation of formic acid. Water is decanted in a separator from the condensate. Much greater quantities of formic acid are produced from naphtha than from butane, hence formic acid recovery is more extensive in such plants. Through judicious recycling of the less desirable oxygenates, nearly all major impurities can be oxidized to acetic acid. Final acetic acid purification follows much the same treatments as are used in acetaldehyde oxidation. Acid quahty equivalent to the best analytical grade can be produced in tank car quantities without difficulties. 

The 4,4 -MDA is sold commercially with a diamine assay of 98 —99%. The major impurity is the 2,4 -MDA isomer, which can be present in amounts up to 3%. PMDA products are normally defined by hydrogen equivalent weight and viscosity. Typical products exhibit a 50 hydrogen equivalent weight and a viscosity of 80 140 mPa-s(=cP) at 70°C. PMDA products normally contain, in addition to the isomers and oligomers of MDA, small amounts of aniline, water, chlorides, and various alkylated amines. AH MDA products should be stored in sealed containers in a cool dry area. 

Performance information for the purification of p-xylene indicates that nearly 100 percent of the ciystals in the feed stream are removed as produc t. This suggests that the liquid which is refluxed from the melting section is effectively refrozen oy the countercurrent stream of subcooled crystals. A high-meltingproduct of 99.0 to 99.8 weight percent p-xylene has been obtained from a 65 weight percent p-xyfene feed. The major impurity was m-xylene. Figure 22-12 illustrates the column-cross-section-area-capacity relationship for various product purities. 

The submitters purified the product by distillation in a Kugelrohr apparatus with an oven temperature of 85-88 C (20 mm) and obtained 3.80-3.85 g (88-89%). The purity of the product was 93-96% according to GLC analysis. The major impurity (2-6%) was 1-acetyl-2-methy1cyclohexene. 

Bistrifluoroacetamide [407-24-9] M 209.1, m 85 , b 135-136 /744mm, 141 /760mm. Major impurity is trifluoroacetamide. Add trifluoroacetic anhydride, reflux for 2h and fractionate using a Vigreux column at atmospheric pressure. [J Chromatogr 7S 273 1973.]... 

Rhodamine B chloride [3,5-his-(diethylamino)-9-(2-carboxyphenyl)xanthylium chloride] [81-88-9] M 479.0, m 210-211"(dec), Cl 45170, A,max 543nm, Free base [509-34-2] Cl 749, pK 5.53. Major impurities are partially dealkylated compounds not removed by crystn. Purified by chromatography, using ethyl acetate/isopropanol/ammonia (conc)(9 7 4, Rp 0.75 on Kieselgel G). Also crystd from cone soln in MeOH by slow addition of dry diethyl ether or from EtOH containing a drop of cone HCl by slow addition of ten volumes of dry diethyl ether. The solid was washed with ether and air dried. The dried material has also been extracted with benzene to remove oil-soluble material prior to recrystn. Store in the dark. 

Carbonyl bromide/595-95-iy M 187.8, b 64.5°/760mm. Purified by distn from Hg and from powdered Sb to remove free bromine, then vacuum distd to remove volatile SO2 (the major impurity) [Carpenter et al. y Chem Soc. Faraday Trans 2 384 1977]. TOXIC... 

Sodium chlorite [7758-19-2] M 90.4, m 180°(dec). Crystd from hot water and stored in a cool place. Has also been crystd from MeOH by counter-current extraction with liquid ammonia [Curti and Locchi Anal Chem 29 534 1957]. Major impurity is chloride ion can be recrystallised from O.OOIM NaOH. 

The distilled product was determined by the checkers to be 85-90% pure (gas chromatographic analysis), the major impurity being... 

Conversion of 2-chloro-2-difluoromethoxy-l,lJ trifluoroethane to 2-difluo-romethoxy-l,l,l,2-tetrafluoroethane (98% purity) is accomplished with bromine trifluoride. The starting material is the major impurity [7] (equation 4)... 

Step 5. HPLC on a gel filtration column (Zorbax GF250, Du Pont Instruments) at 20°C, using 10 mM sodium phosphate, pH 6.5, containing 2mM EDTA and 0.1 M Na2SC>4. A major impurity is eluted immediately before the photoprotein peak. The purified photoprotein is stored at -75° C. 

The purity of the product is greater than 99% as determined by gas chromatographic analysis using a 6-m. column of 30% Carbowax 20M on 60-80 Chromosorb W. The major impurity (<1%) was shown to be 3-heptanol by comparison of gas chromatographic retention times and mass spectral fragmentation patterns with those of an authentic sample. 

Ultra-high-purity Mg has been prepared by either zone refining or vacuum distillation. Zone refining " is a difficult process because of the high volatility and reactivity of the metal. Nevertheless, the process can be carried out in SOj atmospheres where protective films of MgS04 and MgO are formed " ", or in ultra-pure Ar atmospheres "". Zone refining removes a number of major impurities, includ-... 

The relatively impure crude Ca obtained from both thermal reduction and electrolytic sources (97-98%) is distilled to give a 99% pure product. Volatile impurities such as the alkali metals are removed in a predistillation mode at 800°C subsequent distillation of the bulk metal at 825-850°C under vacuum removes most of the involatile impurities, such as Al, Cl, Fe and Si. The N content is often not reduced because of atmospheric contamination after distillation. Unfortunately, these commercial methods have no effect on Mg, which is the major impurity (up to 1 wt%). Typical analytical data for Ca samples prepared by electrolysis, thermal reduction (using Al) and distillation are collated in Table 1. 

Commercial Sr and Ba are quite impure, typical assays being 98.5 and 98.0%, respectively, with the major impurities being the other alkaline-earth metals (with the exception of Be) and the nonmetals H, C, N and O. The former are obtained from the ores and the latter from reaction with the constituents of the atmosphere. 

In discussing the enviromnental fate of technical DDT, the main issue is the persistence of p,p -DDT and its stable metabolites, although it should be bom in mind that certain other compounds— notably, o,p -DDT and p,p -DDD—also occur in the technical material and are released into the environment when it is used. The o,p isomer of DDT is neither very persistent nor very acutely toxic it does, however, have estrogenic properties (see Section 5.2.4). A factor favoring more rapid metabolism of the o,p isomer compared to the p,p isomer is the presence, on one of the benzene rings, of an unchlorinated para position, which is available for oxidative attack. p,p -DDD, the other major impurity of technical DDT, is the main component of technical DDD, which has been used as an insecticide in its own right (rhothane). p,p -DDD is also generated in the environment as a metabolite of p,p -DDT. In practice, the most abundant and widespread residues of DDT found in the environment have been p,p -DDE, p,p -DDT, and p,p -DDD. 

The major raw materials used at present for the production of alumina are bauxites, which are found in the following mineral forms gibbsite (Al(OH)3), boehmite (AlO OH), and diaspore (AlO OH). The major impurities are the oxides of iron, silicon, and titanium, and organic compounds, all of which must be removed before alumina is suitable for aluminum production. The process objectives are, therefore, separation of impurities and compound production in the present case. Bauxite is first dried to facilitate grinding, destroy organic matter, and oxidize the associated ferrous minerals to the ferric state. The temperature of drying is not allowed to exceed 150 °C, because at higher temperature a part of the combined water is expelled and the solubility is affected adversely. 

The quality of the refined metal, and the current efficiency strongly depend on the soluble vanadium in the bath and the quality of the anode feed. As the amount of vanadium in the anode decreases, the current efficiency and the purity of the refined product also decrease. A laboratory preparation of the metal with a purity of better than 99.5%, containing low levels of nitrogen (30-50 ppm) and of oxygen (400-1000 ppm) has been possible. The purity obtainable with potassium chloride-lithium chloride-vanadium dichloride and with sodium chloride-calcium chloride-vanadium dichloride mixtures is better than that obtainable with other molten salt mixtures. The major impurities are iron and chromium. Aluminum also gets dissolved in the melt due to chemical and electrochemical reactions but its concentrations in the electrolyte and in the final product have been found to be quite low. The average current efficiency of the process is about 70%, with a metal recovery of 80 to 85%. 

The well documented synthetic method for 37 is chlorination of cyclopropyl-methylketone followed by base treatment [29]. However, this method did not provide a suitable impurity profile. The most convenient and suitable method we found was the one-step synthesis from 5-chloro-l-pentyne (49) by addition of 2equiv of base, as shown in Scheme 1.18 [21, 30]. Two major impurities, starting material 49 and reduced pentyne, had to be controlled below 0.2% each in the final bulk of 37, to ensure the final purity of Efavirenz . Acetylene 37 was isolated by distillation after standard work-up procedure. 

Since the amine by-product formation was essentially derived from the reaction of an enamine or a ketone with iodoaniline, the direct use of a ketone as the substrate instead of an amine, would also be expected to yield the indole (Scheme 4.21). Indeed, we were gratified to find that direct condensation of o-iodoaniline 24 (77, R, = H) with cyclohexanone (in the presence of 5mol% Pd(OAc)2 and 3 equiv DAB CO as a base at 0.3 M and 105 °C afforded the tetrahydrocarbazole 81a in 77% yield with no other major impurities (Figure 4.4) [5], The use of DMF as a solvent is crucial to the success of this reaction other solvents such as acetonitrile and toluene were ineffective. 

Generally water is used, in a nickel sulfate plant for process reaction, cooling of reactor, crystallization, plant washdown of spills, pump leaks and general cleanup. The water used in the process reaction is for preliminary preparation of the spent plating solution. In other units, especially where impure nickel raw material is used, the wastewater is often recycled. Wastewaters from this plant contain contact and noncontact water, which predominantly contain nickel as a major impurity. 

The pH of the reaction stream was adjusted to neutral and the dark stream was washed with methyl-t-butyl ether to remove neutral organic impurities. The major impurity observed in the MTBE wash is phenyl oxazole formed by de-iodination of the starting iodoxazole. Phase separation of this wash is a difficult one due to the dark color of the reaction stream. 

For purification of the product, tubes A and B are cleaned, dried, and reassembled with a dry glass-wool insert in B. Tube C, containing the initially formed product, is attached to tube B as shown in Fig. 2. The system is evacuated and this time left open to the vacuum. The two furnaces are separated by ca. 1.5 cm. Furnace I is heated to 80° and furnace II to 130 to 140°. Sublimation is allowed to continue until all the titanium(IV) iodide has left tube C (12 to 16 hours). The purified product crystallizes in tube B at the separation of the two furnaces. The major impurity, iodine, crystallizes in tube A and in the liquid-nitrogen trap. A fluffy tan residue of negligible weight (0.04 to 0.06 g.) remains in tube C. If desired, further purification can be accomplished by moving tube B farther into furnace II, which results in a second sublimation of the product. 

---