Salt vacuum purified

These substances contain the -C=NH group and, because they are strong, unstable bases, they are kept as their more stable salts, such as the hydrochlorides. (The free base usually hydrolyses to the corresponding oxo compound and ammonia.) Like amine hydrochlorides, the salts are purified by solution in alcohol containing a few drops of hydrochloric acid. After treatment with charcoal, and filtering, dry diethyl ether (or petroleum ether if ethanol is used) is added until crystallisation sets in. The salts are dried and kept in a vacuum desiccator. 

Water-soluble salts are best purified by preparing a eoncentrated aqueous solution to which, after decolourising with charcoal and filtering, ethanol or acetone is added so that the salts crystallise. They are collected, washed with aqueous ethanol or aqueous acetone, and dried. In some cases, water-soluble salts can be recrystallised satisfactorily from alcohols. With very water-soluble salts, pure crystals are best obtained by dissolving them in water and allowing the solution to evaporate slowly in a desiccator over a suitable desiccant in a cold room. When crystals are formed they are removed, e.g. by centrifugation, washed with a little ice-cold water and dried in a vacuum. Water-insoluble salts are purified by Soxhlet extraction, first with organic solvents and then with water, to remove soluble contaminants. The pmified salt is recovered from the thimble. 

The necessary functional group equivalence required for the poly condensation is achieved by first producing the salt from molar equivalents of the diamine and dicarboxylic acid. For example, adipic acid and hexamethylene diamine form what is known as the AH salt. The purified salt is directly used in the melt polycondensation. The amidation equilibrium is so favorable that the polycondensation can take place in the presence of water, which is therefore used as a heat sink. A typical industrial synthesis is, for example, the polycondensation of the AH salt a 60%-80% sludge of the salt is precondensed with a little acetic acid as regulator (see also Section 28.2.3.2) at 275-280° C for 1-2 hr at 13-17 bar, that is, at the vapor pressure of the steam produced. After a yield of 80%-90% has been reached, further condensation takes place above the melting temperature of 264° C under vacuum. 

The data presented in this section should be considered indicative only and not used in design. The brine used in their generation was prepared from vacuum-purified salt. Brine prepared from other grades of salt may have different characteristics. 

A. Vacuum Purified Salt. Brine is produced from crude salt by standard techniques and then treated chemically to remove hardness and sulfate. When this is... 

IB. Recrystallized Salt. Section 7.1.5.3 on salt refining also mentioned the salt recrystallization process. The product is an alternative to vacuum-purified or vacuum-pan salt. To the chlor-alkali producer, the differences among all these evaporated/crystallized products come down to a value analysis of material cost vs in-plant processing cost. 

Problems with aluminum and silica sometimes occur when vacuum purified salt is used without primary chemical treatment That part of the process often removes most of these secondary impurities by co-precipitation. Contamination by filter media is usually avoided by proper selection of materials (Section 7.5.4). 

Salt. The basic raw material for the mercury cell and membrane cell processes is usually solid salt. This may be obtained from three sources rock salt, solar salt, or vacuum-evaporated salt from purifying and evaporating solution-mined brine. 

The crude o-phenylenediamine may be converted into the dihydrocliloride and the salt purified in the following manner. Dissolve it in 60 ml. of concentrated hydrochloric acid and 40 ml. of water containing 2 g. of stannous chloride, and treat the hot solution with 2-3 g. of decolourising carbon. Filter, add 100 ml. of concentrated hydrochloric acid to the hot colourless filtrate, and cool in a freezing mixture of ice and salt. Collect the colourless crystals of the dihydrochloride on a Buchner or sintered glass funnel, wash with a small volume of concentrated hydrochloric acid, and dry in a vacuum desiccator over sodium hydroxide. The yield is 61 g. 

No attempt should be made to purify perchlorates, except for ammonium, alkali metal and alkaline earth salts which, in water or aqueous alcoholic solutions are insensitive to heat or shock. Note that perchlorates react relatively slowly in aqueous organic solvents, but as the water is removed there is an increased possibility of an explosion. Perchlorates, often used in non-aqueous solvents, are explosive in the presence of even small amounts of organic compounds when heated. Hence stringent care should be taken when purifying perchlorates, and direct flame and infrared lamps should be avoided. Tetra-alkylammonium perchlorates should be dried below 50° under vacuum (and protection). Only very small amounts of such materials should be prepared, and stored, at any one time. 

Acids that are solids can be purified in this way, except that distillation is replaced by repeated crystallisation (preferable from at least two different solvents such as water, alcohol or aqueous alcohol, toluene, toluene/petroleum ether or acetic acid.) Water-insoluble acids can be partially purified by dissolution in N sodium hydroxide solution and precipitation with dilute mineral acid. If the acid is required to be free from sodium ions, then it is better to dissolve the acid in hot N ammonia, heat to ca 80°, adding slightly more than an equal volume of N formic acid and allowing to cool slowly for crystallisation. Any ammonia, formic acid or ammonium formate that adhere to the acid are removed when the acid is dried in a vacuum — they are volatile. The separation and purification of naturally occurring fatty acids, based on distillation, salt solubility and low temperature crystallisation, are described by K.S.Markley (Ed.), Fatty Acids, 2nd Edn, part 3, Chap. 20, Interscience, New York, 1964. 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

Benzoxazolinone [59-49-4] M 135.1, m 137-139 , 142-143 (corrected), b 121-213 /17mm, 335-337 /760mni. It can be purified by recrystn from aqueous Me2CO then by distn at atm pressure then in a vacuum. The methyl mercury salt recryst from aq EtOH has m 156-158°. [J Am Chem Soc 67 905 1945.]... 

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