Drying solids under reduced

The recently discovered Ugand precursor HOB[OSi(O Bu)3]2 was prepared by the hydrolysis of BuOB[OSi(O Bu)3]2 (in CeHe) with one equiv of H2O [64]. After stirring for 1 h, the solution is frozen and the solvent is removed via lyophiUzation under reduced pressure. Purification can be achieved via subUmation (ca. 50 °C) of the dry powder under reduced pressure to give yields in excess of 85%. Although not stable in solution for extended periods (due to condensation processes), HOB[OSi(O Bu)3]2 is stable indefinitely in the solid state imder an inert atmosphere. 

Figure 1.4 shows that, under oxidizing conditions, iron has +3 oxidation state and form different solid hydroxide species. They transform to oxide hydroxides or oxides under dry conditions. Under reducing conditions, iron(II) can be dominant, for example, in reductive groundwaters. However, when pH > 7, iron(II) forms solid ferrous hydroxide or mixed ferric-ferrous hydroxide. Under dry conditions, it also transforms to oxide. 

Most of the ether is removed on the rotary evaporator and the last traces are removed using the apparatus depicted in Fig. 5 in Chapter 10 for drying a solid under reduced pressure. The residue should weigh more than... 

In a typical process for the preparation of a methylated product, formalin is adjusted to pH 8 and melamine is added to give a melamine to formaldehyde ratio of 1 3.3 molar. The mixture is heated at 70°C for about 15 minutes until the melamine has completely dissolved. The solution is then either spray-dried or allowed to crystallize to give a solid composed essentially of monomeric methylolmelamines. This product is heated with about twice its weight of methanol and oxalic acid (0.5%) at 70°C until a clear solution is obtained. The solution is adjusted to pH 9 and concentrated to 80% solids under reduced pressure. The major component of this solution is the trimethyl ether of trimethy lolmelamine ... 

The dark, air-sensitive filtrate is evaporated under reduced pressure. After all visible liquid has been removed, the residue is dried at 80°C for several hours (e.g., overnight) using a vacuum pump. The resulting solid is washed with pentane (2 X 50 mL) and dried briefly under reduced pressure. This washing step removes any dimerized diene that may have been present and any traces of oil that may be left from the sodium hydride dispersion. Yield 6.8-7.4 g (84—92% based on 7.3 g of C5H5C6F5). 

The best method for removing water (and also solvents of relatively low boiling point) adhering to solids is drying under reduced pressure. A vacuum desiccator is used for this purpose several forms are shown in Fig. II, 38, 1. These are fitted with the exception of ( ) either with... 

Heat a suspension of 22 g. of the diacetate in a mixture of 120 ml. of concentrated hydrochloric acid, 190 ml. of water and 35 ml. of alcohol under reflux for 45 minutes. Cool the mixture to 0°, filter the solid with suction, and wash with water. Purify the crude aldehyde by rapid steam distillation (Fig. II, 41, 3) collect about 1500 ml. of distillate during 15 minutes, cool, filter, and dry in a vacuum desiccator over calcium chloride. The yield of pure o-nitrobenzaldehyde, m.p. 44—45°, is 10 g. The crude solid may also be purified after drying either by distillation under reduced pressure (the distillate of rather wide b.p., e.g., 120-144°/3-6 mm., is quite pure) or by dissolution in toluene (2-2-5 ml. per gram) and precipitation with light petroleum, b.p. 40°-60° (7 ml. per ml. of solution). 

The base may be purified by steam distillation but distillation under reduced pressure is more satisfactory. The oil is dried over 5 g. of solid sodium hydroxide and distilled in vacuo. I he first portion of the distillate may contain -toluidine and must be carefully separated, as it causes rapid discoloration. The 3-bromo-4-aminotoluene is obtained as a colorless liquid of b.p. i20-i22°/30 mm. or 92-94 /3 mm. It solidifies on cooling and melts at 16-18°. The loss on purification is about 15 per cent of the weight of the crude base. 

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